# Patent

## Title
Methods and devices for obtaining a broadcast-like streaming content

## Abstract

Obtaining a broadcast-like streaming content by an assembling device from a distributed storage. The assembling device obtains erasure-coded fragments associated with sequential segments of streaming content from fractional-storage servers, approximately at the same rate that the fragments are being stored on the servers and shortly after the fragments are stored. And wherein the streaming content is segmented, encoded into the fragments, and stored on the servers progressively as the streaming content is made available.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Patent Application No. 61/105,683, filed Oct. 15, 2008.


BACKGROUND
There are wide varieties of Internet broadcasting systems, also known as web broadcasting, net broadcasting, or webcasting, all of which have different capabilities. Some Internet broadcasting techniques include edge caching and/or packet duplication by routers, which require servers at many Internet edge locations, or control over routers. Some Internet broadcasting involves a streaming medium that presents its recipients with a continuous stream of media over which they may have no control, much like traditional broadcast media. Some commonly used broadcasting CDNs are not scalable and reliable to the degree that allows large-scale broadcasting operation. Some of the solutions require large amounts of storage to cache content, or expensive dedicated communication lines to connect content aggregation centers to locations near end users.
BRIEF SUMMARY
In one embodiment, a method comprising: obtaining by an assembling device an indication of one or more segments of streaming content for which erasure-coded fragments were recently distributed to fractional-storage servers; and retrieving at least some of the recently distributed erasure-coded fragments using a fragment pull protocol.
In one embodiment, an apparatus comprising: an assembling device configured to obtain erasure-coded fragments associated with sequential segments of streaming content from fractional-storage servers, approximately at the same rate that the fragments are being stored on the servers and shortly after the fragments are stored; wherein the streaming content is segmented, encoded into the fragments, and stored on the servers progressively as the streaming content is made available.
In one embodiment, an apparatus comprising: an assembling device configured to receive an indication that it is allowed to access a first segment, and obtain erasure-coded fragments associated with the first segment from fractional-storage servers; the assembling device is further configured to obtain fragments associated with subsequent segments as the access to the segments is progressively allowed; wherein the first segment and the subsequent segments belong to streaming content, and their associated fragments are pre-stored on the servers.
Implementations of the disclosed embodiments involve performing or completing selected tasks or steps manually, semi-automatically, fully automatically, and/or a combination thereof. Moreover, depending upon actual instrumentation and/or equipment used for implementing the disclosed embodiments, several embodiments could be achieved by hardware, by software, by firmware, or a combination thereof. In particular, with hardware, embodiments of the invention could exist by variations in the physical structure. Additionally, or alternatively, with software, selected functions of the invention could be performed by a data processor, such as a computing platform, executing software instructions or protocols using any suitable computer operating system. Moreover, features of the embodiments may be combined.



BRIEF DESCRIPTION OF THE DRAWINGS
The embodiments are herein described, by way of example only, with reference to the accompanying drawings. No attempt is made to show structural details of the embodiments in more detail than is necessary for a fundamental understanding of the embodiments. In the drawings:
FIG. 1 illustrates an assembling device obtaining erasure-coded fragments from fractional-storage servers.
FIG. 2 illustrates real-time content segmentation, encoding, and distribution.
FIG. 3 illustrates real time fragment retrieval, segment reconstruction, and content presentation.
FIG. 4 is a flow diagram of one method in accordance with one embodiment.
FIG. 5 illustrates one embodiment of segmenting content, encoding the segments into erasure-coded fragments, distributing the fragments to fractional-storage servers, and obtaining the fragments by assembling devices and assembling servers.
FIG. 6 illustrates a broadcast-like effect.
FIG. 7 illustrates fractional-storage servers located on the Internet backbone.
FIG. 8 illustrates an assembling server located at a network juncture.
FIG. 9 illustrates distribution and storage of erasure-coded fragments on fractional-storage servers.
FIG. 10 illustrates three examples of changes made to redundancy factors according to changes in demand.
FIG. 11 illustrates fractional-storage servers having the same bandwidth capability.
FIG. 12 illustrates fractional-storage servers having different bandwidth capabilities.
FIG. 13 and FIG. 14 illustrate a case where a fractional-storage server has failed.
FIG. 15 illustrates retrieving fragments according to locality.
FIG. 16 illustrates a broadcast-like layered cluster.
FIG. 17 to FIG. 19 illustrate a broadcast-like layered cluster.
FIG. 20 to FIG. 22 illustrate changes in content consumption.
FIG. 23 illustrates utilization of the entire aggregated bandwidth of fractional-storage servers for multiple content delivery.
FIG. 24 illustrates fast real time fragment retrieval.
FIG. 25 to FIG. 28 illustrate various embodiments of fragment pull protocols.
FIG. 29 illustrates a server array managing a pool of bandwidth amplification devices.
FIG. 30 and FIG. 31 illustrate generation of a larger quantity of erasure-coded fragments near fast start points.
FIG. 32 and FIG. 33 illustrate different embodiments of content segmentation.
FIG. 34 to FIG. 36 illustrate different embodiments of content segmentation according to components and/or properties.
FIG. 37 illustrates operation of hybrid pull and push protocols.
FIG. 38 illustrates geographically distributed fractional-storage servers.
FIG. 39 illustrates peak-to-average traffic ratios generated by assembling devices distributed over different time zones.
FIG. 40 illustrates US-based fractional-storage servers delivering erasure-coded fragments to assembling devices spread over the globe.
FIG. 41 illustrates different loads at different times for different time zones.
FIG. 42 illustrates data centers communicating via shared links.
FIG. 43 illustrates fractional-storage servers communicating via shared networks.
FIG. 44 illustrates fractional-storage servers placed at different locations.



DETAILED DESCRIPTION
FIG. 1 illustrates one embodiment of a server array including fractional-storage servers 399a to 399(N) storing erasure-coded fragments 390a to 390(N) associated with content. In order for assembling device 661 to reconstruct a segment 101a of the content, it has to retrieve at least K erasure-coded fragments. In one example, k=4 and the assembling device 661 chooses approximately randomly from which servers to retrieve the 4 different erasure-coded fragments. It chooses to retrieve fragments 390a, 390c, 390(N−1) and 390(N), which are noted as group 573, and reconstruct the segment 101a. Consequent segments of the content are reconstructed in a similar fashion, and the content may eventually be fully retrieved by combining all relevant segments. If the assembling device 661 cannot reconstruct the segment 101a, it retrieves one or more additional unique erasure-coded fragments, and tries again.
In one embodiment, the content being distributed supports stream presentation, and segment 101a is of small size, to enable content presentation by assembling device 661 shortly after beginning the reception of the segment (or any other segment of the content). For example, segment 101a is 96 KByte, allowing a 5 Mbps download speed receiver to obtain the entire segment (by requesting enough erasure-coded fragments to enable the reconstruction of the segment, and such that the total size received of all requested erasure-coded fragments is slightly larger than the segment) after approximately 0.2 seconds from request, and beginning the presentation shortly or right after the successful decoding and reconstruction of segment 101a. 
FIG. 2 illustrates one embodiment of processing a content source 700 for real time presentation. Content examples include, but are not limited to, a live video broadcast event, a pre-recorded show, or any real time conditioned source. The content 700 is available at time T1=0. The content 700 is segmented in real time into multiple segments, such that the first segment 710a is available at T3. T3 is determined by the size of the segment and the selected compression scheme. For example, if an H.264 compression is used to generate an average stream of 1 Mbps, and the size of the segment is 96 Kbytes, then T3 minus T2 equals 96 KByte×8(Bits/Byte)/1 Mbps=0.77 seconds on average, where T2 is the process delay. If T2 is about 0.2 second, then the first segment 710a can be ready for the next step after about 1 second from the time that content 700 is first made available. Subsequent segments 710b to 710J are made available sequentially in time.
Next, at T4, erasure-coded fragments 720a to 720(N) are being encoded from segment 710a. At T6, the encoding process is performed for segment 710a, and all the erasure-coded fragments 720a to 720(N) are made available. In one example, the time between T4 and T6 is equal to or less than the average segment creation time, in order to allow the process to maintain real time performance, such that at any point in time during the on-going availability of segments, the encoding process generates all erasure-coded fragments without picking up any delay above T6 minus T3 (which is the latency between segment availability and erasure-coded fragment availability). T6 minus T1 may be typically 2-3 seconds if T3 minus T2 is 0.77 seconds. T4 minus T3 may be typically a fraction of a second. Similarly, erasure-coded fragments 730a to 730(N) are being encoded from segment 710b, and are made available at time T9. The process of fragment encoding is repeated in real time up to the last segment 710J of content 700.
Next, at T5 (which can potentially occur before T6, but also after T6) the erasure-coded fragments 720a to 720(N) are distributed 740a to a server array. The distribution process 740a ends at T8. In one example, T8 minus T5 is equal to or less than the average segment creation time, in order not to have delays. The process of distributing the erasure-coded fragment is repeated 740b for erasure-coded fragments 730a to 730(N), and for all subsequent erasure-coded fragments associated with the next segments.
Optionally, at T7, the erasure-coded fragments 720a to 720(N) are distributed 750a from the servers to groups of bandwidth amplification devices. In one example, the distribution ends at T10, such that T10 minus T7 is equal to or less than the average segment creation time, in order not to have delays. Subsequent erasure-coded fragments associated with the next segment are distributed 750b, and the process continues until the erasure-coded fragments associated with the last segment 710J are distributed.
FIG. 3 illustrates one embodiment of real time streaming content retrieval from fractional-storage servers. An assembling device begins a process of obtaining streaming content 700 for presentation. Starting at T1, the assembling device requests erasure-coded fragments 720a to 720(K). By T2, all K erasure-coded fragments are obtained, and at time T2b until T4, erasure-coded fragments 720a to 720(K) are decoded into segment 710a. The retrieval time of the erasure-coded fragments and the segment decoding time should be equal to or faster than the corresponding presentation time, in order to enable a continuous presentation, once presentation begins at T5. T2b minus T2 is a short delay, and can be fractions of a second. Subsequent erasure-coded fragments 730a to 730(K) are retrieved between T2 and T3, and are decoded into subsequent segment 710b between T4 and T6.
In one example, the streaming content 700 is encoded at 1 Mbps, and the segment size is 96 Kbytes. The presentation of each segment takes about 0.77 seconds. Retrieving fragments 720a to 720(K) takes no more than 0.77 seconds, meaning that the assembling device's connection bandwidth must be 1 Mbps or higher. Decoding segment 710a takes no more than 0.77 seconds. If a small delay of 0.2 seconds is assumed for both T2b minus T2 and T5 minus T4, then T5 can start at 0.77+0.2+0.77+0.2=1.94 seconds after T1, meaning that presentation can begin about 2 seconds following request of the first erasure-coded fragment. In another example, the retrieval process and the decoding process are performed faster than the real time presentation bounds, therefore enabling a shorter time to play and a download rate that exceeds the presentation rate.
In one embodiment, the erasure-coded fragments 720a to 720(K) are retrieved in approximately random order, or any other order, as long as at least the K erasure-coded fragments needed for decoding the segment 710a are available until time T2.
The term “approximately random” as used herein refers to, but is not limited to, random, pseudo random, and/or based on a long list of numbers featuring very low autocorrelation and very low correlation with other similar lists of numbers.
FIG. 4 is a flow diagram illustrating one method, comprising the following steps: In step 7310, obtaining by an assembling device an indication of one or more segments of streaming content for which erasure-coded fragments were recently distributed to fractional-storage servers. In step 7311, retrieving at least some of the recently distributed erasure-coded fragments using a fragment pull protocol. In optional step 7312, the fragment pull protocol is a fragment pull protocol for high latency, the fractional-storage servers are fractional-storage CDN servers, and further comprising governing the rate of erasure-coded fragments retrieval via the fragment pull protocol. And in optional step 7313, reconstructing the segments from the retrieved erasure-coded fragments at an average rate approximately equals the average rate of making the segments available on the servers through distributing the fragments. Optionally, the fragment pull protocol is a fragment pull protocol for high latency, and further comprising reconstructing the segments from the retrieved erasure-coded fragments at a rate that approximately maintains a fixed distance in segments between the recently reconstructed segment and the segment whose fragments were recently distributed to the servers. Optionally, the fragment pull protocol is a fragment pull protocol for high latency, and retrieving the fragments comprises retrieving the fragments at a rate approximately equal the corresponding rate at which the streaming content is played. Optionally, the method further comprising reconstructing, by the assembling device, at least a portion of the streaming content, and forwarding the portion, or a transcoded version of the portion, to its client. Optionally, the erasure-coding is rateless-coding potentially resulting in fragments having a limitless redundancy factor.
In one embodiment, the fragments associated with sequential segments of streaming content are delivered to an assembling device as a plurality of sub-transmissions. In this case, each fractional-storage server participating in the delivery of the fragments to the assembling device sends a transmission to the assembling device comprising a sequence of erasure-coded fragments. This transmission is referred to as a sub-transmission. In one example, each sub-transmission contains at least one fragment per each sequential segment of the streaming content. In one example, the sub-transmission starts at a segment indicated by the assembling device, and continues from that point onwards, approximately according to the sequential order of segments, until the assembling device instructs the server to stop, or until reaching the last segment of the content. Each sub-transmission carries only a fraction of the fragments (per segment) needed to reconstruct the segments of the streaming content, such that the combination of at least two sub-transmissions received by the assembling device from the servers allows the assembling device to obtain enough fragments needed to reconstruct each segment.
In one embodiment, each sub-transmission is delivered to the assembling device via a streaming session, such as an RTP session, wherein the RTP packets transport the fragment sequence approximately according to the order of the sequential segments. In one embodiment, each sub-transmission is delivered to the assembling device via an HTTP connection, or other closed-loop data transfer mechanisms over TCP/IP. In one embodiment, the assembling device may change one or more transmitting servers on the fly, by instructing the server(s) to stop sending an already active sub-transmission—as may be needed in a case of an RTP session, and initiating new sub-transmissions from other servers instead. Replacement of transmitting servers on the fly may be needed in a case of a server failure, network failure, or high load or latency conditions.
In some embodiments, a push protocol is used to obtain fragments. A push protocol may be implemented using one transmission carrying fragments from a source server to a destination receiver, or may be implemented using a plurality of sub-transmissions. When using sub-transmissions, each sub-transmission transports a fraction of the fragments needed for segment reconstruction. Segments may be reconstructed from fragments received via sub-transmissions after obtaining decodable sets of erasure-coded fragments; optionally one set per segment. A sub-transmission may be transported using an IP stream such as RTP, an HTTPS session, or any other protocol suitable for transporting a sequence of fragments between a source server and a destination assembling device.
FIG. 1 illustrates one embodiment, in which content is segmented and erasure-coded. Fragments 390a to 390(N), belonging to a first segment, are distributed to servers 399a to 399(N) respectively. Other fragments belonging to subsequent segments are similarly distributed to servers 399a to 399(N). The servers may use a push protocol to transport the fragments to an assembling device. A push protocol sub-transmission may comprise a sequence of fragments associated with multiple segments. In one example, the fragments are ordered according to the sequential order of the segments in a streaming content. Server 399a sends a first sub-transmission to a destination assembling-device. Optionally, the first sub-transmission comprises a sequence of fragments starting with fragment 390a, associated with the first segment, and continuing with fragments belonging to subsequent segments. Server 399c sends a second sub-transmission to the destination assembling-device, optionally starting with fragment 390c, associated with the first segment, and continuing with fragments belonging to subsequent segments. In a similar fashion, servers 399(N−1) and 399(N) send additional sub-transmissions to the destination assembling-device, each comprising a unique fragment sequence.
When using a push transmission, the assembling device does not explicitly ask for each fragment, but instead instructs each of the different servers to start sending it a fragment sequence using a sub-transmission. The destination assembling-device receives the sub-transmissions sent by servers 399a, 399c, 399(N−1) and 399(N). It gathers 573 the first fragment from each sub-transmission to reconstruct the first segment 101a. In a similar fashion, additional fragments belonging to subsequent segments are obtained from the sub-transmissions, and used to reconstruct the segments. It is noted that any combination of sub-transmissions may be used, as long as a decodable set of fragments is obtained per each segment. It is also noted that FIG. 1 illustrates a non-limiting embodiment and a sub-transmission may include two or more unique erasure-coded fragments per segment.
In one embodiment, the push sub-transmissions is synchronous (all servers sending the fragments of each segment at approximately the same time). In another embodiment, the push sub-transmission is asynchronous and the arrival of different fragments associated with a specific segment at the assembling device side may be spread over a long period. This may occur, as an example, when some push servers are faster than others. In one embodiment using asynchronous sub-transmissions, the assembling device aggregates whatever fragments it can before presentation time of each segment, and then optionally supplements fragments using a pull retrieval process. A server that does not send fragments fast enough, and therefore usually causes supplemental requests, may be ordered to stop the sub-transmission. Another server may be requested, optionally by the assembling device, to replace the slow server by initiating a new sub-transmission.
In one embodiment, the push-transmissions carry more erasure-coded fragments than needed for segment reconstruction. In one embodiment, the push transmissions carry fewer erasure-coded fragments than needed for segment reconstruction, and the remaining fragments are pulled by the assembling device.
The term “erasure coding” as used herein denotes a process in which a sequence of erasure-coded fragments can be generated from a segment such that the segment can be reconstructed from any or almost any subset of the erasure-coded fragments of size equal to or somewhat larger than the size of the segment (sometimes may be referred to as “enough erasure-coded fragments” or “sufficient subset of fragments”). Examples of erasure codes include, but are not limited to, rateless codes, Reed-Solomon codes, Tornado codes, Viterbi codes, Turbo codes, any Block codes, any Convolutional codes, and any other codes that are usually used for forward error correction (FEC).
The term “rateless coding” as used herein denotes a type of erasure coding in which a very long, potentially limitless, sequence of rateless-coded fragments can be generated from a segment such that the segment can be reconstructed from any or almost any subset of the rateless-coded fragments of size equal to or somewhat larger than the size of the segment (sometimes may be referred to as “enough rateless-coded fragments”). Examples of rateless codes include, but are not limited to, Raptor codes, LT codes, online codes, any Fountain codes, and any other Rateless codes.
The term “erasure-coded fragment” denotes a fragment comprising data encoded with an erasure code (which may also be a rateless code in some embodiments). The term “rateless-coded fragment” denotes a fragment comprising data encoded with a rateless code.
The term “assembling device” as used herein denotes a computing device that retrieves erasure-coded fragments from servers over a network. The assembling device may perform one or more of the following: (i) Decode the retrieved erasure-coded fragments into segments. (ii) Present the content reconstructed from the retrieved erasure-coded fragments. (iii) Act as a bandwidth amplification device, by receiving, storing, and forwarding erasure-coded fragments. In some embodiments, the assembling device may be any device located at the user premises, like an STB, PC, gaming console, DVD player, PVR device, or any other device able to retrieve erasure-coded fragments from a communication network. In some embodiments, the assembling device may be an assembling server. In some embodiments, the assembling device may be any computational device with access to a communication network, located at a central office, data center, BRAS location, ISP premises, or any other place with direct network connectivity. In one embodiment, the assembling device is coupled to a display device used for content presentation.
The abbreviation CDN denotes “Content Delivery Network”. The term “CDN server” as used herein denotes a server having one or more of the following characteristics: (i) A bandwidth (CDN_BW) that is much greater than the average bandwidth consumed by a user premises device (User_BW) receiving video streaming content. In some examples, the CDN_BW is at least 10 times, 100 times, 1,000 times, or 10,000 times greater than the User_BW. (ii) The server is located outside the last mile communication infrastructure of the end users, such that the CDN server and the end users are located in different networks. For example, the CDN server is not located under a BRAS, while the end users are located under a BRAS. Moreover, in some embodiments, the CDN servers are deployed over a wide area across the Internet and optionally located close to or on the Internet backbone. In some embodiments, the CDN server does not usually retrieve and play streaming content. In some embodiments, the CDN server has a much greater storage space than the storage space of an average player of streaming content.
The term “fractional-storage server” in the context of erasure-coded fragments (also applicable to “fractional-storage CDN server”), as used herein denotes a server that (i) stores less than the minimum quantity of erasure-coded fragments required to decode the erasure-coded fragments, and (ii) where at least a meaningful quantity of the stored erasure-coded fragments is not stored in order to be consumed by the fractional-storage server.
The term “streaming content” as used herein denotes any type of content that can begin playing as it is being delivered. Streaming content may be delivered using a streaming protocol, a progressive download protocol, or any other protocol enabling a client to begin playing the content as it is being delivered. Moreover, the term “streaming protocol” includes “progressive download protocol”. In addition, the verb “streaming” refers to using a streaming protocol, using a progressive download protocol, or using any other protocol enabling the receiver to begin playing the content as it is being delivered.
In some embodiments, expressions like “approximately sequential segments” may denote one or more of the following non-limiting options: segments that are sequential (in time or according to a file's order), segments that are approximately sequential (such as segments with some interlace, or segments without a great amount of non-sequential data), segments generated sequentially and/or approximately sequentially from different components of content (such as storing the i-frames and p-frames of a compressed content in different segments), and/or other sequential or approximately sequential segmentation after classification or separation into different components and/or elements.
FIG. 5 illustrates one embodiment of a fractional-storage system storing erasure-coded fragments. Content 100, which may optionally be streaming content, is segmented into content segments 101a, 101b to 101j (for brevity referred to as segments). Each of the segments is encoded into erasure-coded fragments. For example, segment 101a is encoded into erasure-coded fragments 390a to 390(N). The erasure-coded fragments are distributed to the fractional-storage servers 399a to 399(N) and/or to the bandwidth amplification devices 610aa. The erasure-coded fragments are then obtained by assembling devices like 661 or proxy servers like proxy server 661s from the fractional-storage servers 399a to 399(N) and/or the bandwidth amplification devices 610aa. The obtained erasure-coded fragments are decoded to reconstruct the segments. The proxy server 661s may broadcast/multicast and/or re-stream the reconstructed content, optionally using standard streaming technique, to its client(s) 661o, optionally over network 300n. In some embodiments, the content distribution is performed in real time. In some embodiments, the content assembly is performed in real time and the presentation starts a short time after the content request.
Similarly to content 100, additional contents are segmented, encoded into erasure-coded fragments, and distributed to the fractional-storage servers and/or to the bandwidth amplification devices. Each segment may be reconstructed independently of other segments by obtaining and decoding enough erasure-coded fragments generated from that segment.
In some embodiments, the encoding scheme is erasure codes and/or rateless codes. In some embodiments, the fractional-storage servers 399a to 399(N) are Content Delivery Network (CDN) servers, optionally accessed over the public Internet. In some embodiments, the control, management, content reception, content segmentation, segment encoding, erasure-coded fragment distribution, allocation of bandwidth amplification devices, and/or other kind of central supervision and operation may be performed by managing server(s) 393, which may be a part of the CDN network. It is noted that the term “fractional-storage server” is not limited to a large server and, according to the context, may include a fractional-storage bandwidth amplification device, a fractional-storage peer server, or other types of fractional-storage servers.
In some embodiments, a broadcast-like effect is achieved by distributing to and retrieving from fractional-storage servers a broadcast channel/live content in real time, using a combination of real time distribution and real time retrieval techniques. In a broadcast-like effect, a given channel or content for broadcasting is distributed to at least one assembling device, optionally by means of pushing relevant fragments to the assembling device, or by pulling the relevant fragments by the assembling device, and potentially to many assembling devices at approximately the same time, which creates a similar effect to traditional broadcasting.
FIG. 6 illustrates one example of creating a broadcast-like effect (i.e. retrieving the content while it is distributed). Streaming content 700a, which may be ready in advance or received on-the-fly, is to be received and presented by multiple assembling devices at approximately the same time. Content 700a is segmented into segments on-the-fly, such that the first segment 710a is ready shortly after the data is available, and subsequent segment 710b is ready right after that. Segments 710a and 710b are sequentially encoded into erasure-coded fragments 782a and 782b correspondingly, such that the average rate of encoding segments into erasure-coded fragments does not fall below the average rate of introducing new segments (as content 700a is being received for broadcast).
As the erasure-coded fragments 782a are ready, they are distributed 783a to the fractional-storage servers. Subsequent erasure-coded fragments 782b are similarly distributed 783b to the servers, such that the average rate of distributing the erasure-coded fragments associated with each segment does not fall below the rate of introducing new segments (or in other words, such that there is approximately no piling-up of undistributed segments). Optionally, the erasure-coded fragments 782a are also distributed 784a by the servers to bandwidth amplification devices at an average distribution rate per segment that does not fall below the average rate of introducing new segments.
The assembling devices obtain erasure-coded fragments 785a associated with segment 710a from the fractional-storage servers, and optionally also from the bandwidth amplification devices. Subsequent erasure-coded fragments, such as 785b associated with segment 710b, are obtained at an average rate that does not fall below the average rate of introducing the new segments. The segment 710a is then reconstructed from the obtained erasure-coded fragments 785a. The subsequent segment 710b is reconstructed from the obtained erasure-coded fragments 785b, such that reconstructing each segment is performed at an average rate that does not fall below the average rate of introducing the new segments.
Then, the reconstructed segments are presented, optionally on-the-fly, as reconstructed content 700b. In one embodiment, the entire process end-to-end is performed in real time, such that the presentation of 700b starts at T2 minus T1 after the availability of content 700a, and such that the delay of T2 minus T1 (between the availability of new segments and their subsequent presentation by the assembling device) is kept approximately constant throughout the entire presentation of the streaming content 700b, once begun.
In one example, the content 700a is a 4 Mbps video stream, and the segment size is 96 Kbytes, meaning that new segments 710a, 710b are made available at a rate of one every 0.19 seconds. Assuming that each process as described takes 0.19 seconds, and that all processes are performed sequentially (with no overlapping in time, which may be possible for some of the processes), then the accumulated process time, which includes 710a, 782a, 783a, 784a, 785a and 710a, takes about 6×0.19=1.14 seconds. This means that an assembling device may begin with content presentation 1.14 seconds after the content is first made available to the system.
Still referring to FIG. 6, in one embodiment, the fragments are obtained from the servers using multiple sub-transmissions, such that each transmitting server sends a fraction of the needed fragments to the assembling device, according to the sequential order of segments. Each sub-transmission transmits the fragments approximately at a rate at which the fragments are being created on-the-fly from segments of the content to be received by the assembling device. According to another embodiment, the fragments are obtained from the servers using fragment requests made by the assembling device using a fragment pull protocol.
The Audio/Video compression utilized in creating content 700a is not necessarily a fixed rate compression, meaning that the various resulting segments do not necessarily contain the same amount of presentation time.
In one embodiment, once starting to retrieve a broadcast-like stream, the assembling device may use one of the following methods to synchronize the retrieval of the stream's segments with the ongoing availability of new segments of the stream: (i) The assembling device retrieves additional segments such that the average rate of obtaining new frames approximately equals the average rate of presenting frames. (ii) The assembling device retrieves additional segments such that it does not try to retrieve segments that are not yet indicated as being available. And (iii) The assembling device retrieves additional segments so as to approximately maintain a constant distance (in segments) between the most currently available segment and the segment currently being retrieved.
In one embodiment, the assembling device presents the broadcast-like stream at approximately the same frame rate as the rate of producing new frames for the broadcast-like stream. In one example, the frame rate is constant throughout the stream, such as the case of fixed 24, 25, 50, or 60 frames per second.
In one embodiment, the assembling device obtains an indication regarding the most newly available segment (per specific broadcast-like stream) for retrieval. The assembling device then starts to retrieve from the most newly available segment. In one example, the most newly available segment is the last segment that was distributed to the fractional-storage servers. In another example, the most newly available segment is a segment that was recently distributed to the fractional-storage servers, but wherein there are newer distributed segments, which are not yet indicated as being available.
In one embodiment, the broadcast-like stream is of a pre-recorded content, such that it is possible to distribute the entire content to the fractional-storage servers, and after any period of time allow the real time consumption of the content by any number of assembling devices. In such a case, an indication is made to the assembling devices regarding the real time allowance to retrieve the related segments. The allowance can start at a certain point in time (which corresponds to the beginning of the broadcast-like “transmission”) for the first segment, and then the allowance may continue for subsequent segments, at a rate that approximately corresponds to sustaining the frame rate of the broadcast-like stream.
In one embodiment, the system amplification factor (Bout/Bin) may approach the ratio (Tout/(R*Bstream)), where Bout is the total average output bandwidth at which the fragments are obtained by the assembling devices, Bin is the total average bandwidth needed to deliver the fragments for storage on the servers, Tout is the total aggregated outgoing bandwidth of all servers, R is the redundancy factor, and Bstream is the average bandwidth of the streaming content.
The term “redundancy factor” as used herein denotes the following ratio: (total size of the unique erasure-coded fragments generated from a segment and actually stored on the servers)/(size of the segment).
Assuming all segments have approximately the same size and all fragments generated from the segments have approximately the same size (without limiting any of the embodiments), the term “storage gain” as used herein denotes the following ratio: (size of a segment)/(size of an erasure-coded fragment). If the server stores more than one erasure-coded fragment per segment, the storage gain denotes the following ratio: (size of segment)/((size of erasure-coded fragment)*(number of stored erasure-coded fragments per segment)).
Referring again to FIG. 5 with device 661o as a non-assembling CPE, such as a STB, PC or gaming console, capable of performing standard request, reception, and decoding of video over IP network. In one embodiment, server 661s—also referred to as proxy server, assembling server, and in some cases assembling device—performs three primary functions: (i) receipt of content requests from non-assembling client device 661o; (ii) assembly of content, as requested by client 661o, from the fractional-storage servers and optionally from the bandwidth amplification devices; (iii) optionally, conversion of the assembled content into a streaming format; and (iv) transmission of the streaming content to the requesting client 661o. Client 661o can then store the content, or present it. In one embodiment, the assembled content is a general web content, including HTML, FLASH or any other data format that can be found in a web-based site.
In one embodiment, although server 661s is illustrated as being connected to network 300 on one side and to network 300n on the other, server 661s may also be connected to another network element, such as a router, which makes the topological connection between networks 300 and 300n. In that case, server 661s communicates with both networks 300 and 300n via the other network element.
In one embodiment, a CDN is created by the aggregated bandwidth and storage capacity of the participating erasure-coded fractional-storage servers. In one example, a large scale CDN includes several hundreds or thousands of fractional-storage servers connected to the Internet. These servers send erasure-coded fragments to a large number, potentially millions, of assembling devices. In order to keep costs low for sending a large number of fragments from fractional-storage servers to assembling devices, the servers are located on the Internet backbone, or close to it.
The current Internet backbone primarily comprises different Tier one ISP (or other) networks that interconnect at various Internet Exchange Points (IX or IXP), using peering agreements. Tier one ISPs, or other backbone-forming network entities, can reach any portion of the Internet via other Tier one ISPs or other backbone-forming networks, without paying any Internet transit fee, and solely by utilizing mutual peering agreements. In order to gain access to large amounts of inexpensive bandwidth, the fractional-storage servers are typically located on the Internet backbone. This means that the servers are either co-located (and connected) with a core switching router that interconnects the Internet backbone networks at an IXP, or, alternatively, co-located (and connected) with a router which is part of the backbone network, typically located at a data center or co-location center. Fractional-storage servers can also be located close to the Internet backbone, which means that they are co-located (and connected) with a router which is part of a Tier two ISP network, which has a high bandwidth connection with at least one Tier one operator, to which it pays transit fees in order to potentially reach all portions of the Internet. FIG. 7 illustrates one example of a fractional-storage server 3001, which is one of a plurality of servers forming a large-scale CDN, located on the Internet backbone by being connected to the Internet backbone via IXP 3091. In a second example, fractional-storage server 3002 is located on the Internet backbone by being connected to a Tier one backbone network 3080. In a third example, fractional-storage server 3011 is located close to the Internet backbone by being connected to a Tier two ISP network 3070, which is connected to the backbone via Tier one ISP network 3081. In one embodiment, a typical fractional-storage server is located on the backbone or close to the backbone by being attached to a switching router via a high bandwidth port, such as a 1 Gbps, 10 Gbps, or a higher bandwidth port, such as high-speed Ethernet port, usually carried over a fiber, or suitable short-distance copper lines. In one embodiment, in a typical deployment using high bandwidth connections (in 2009 terms), each of about 1,000 fractional-storage servers is located on the backbone or close to the backbone and is connected to the backbone via a dedicated (guaranteed bandwidth) 1 Gbps Ethernet port, resulting in an aggregated throughput of 1,000 Gbps, which can serve about one million subscribers of standard definition streaming video, such as client device 3020, simultaneously. Such aggregated bandwidths would have required a substantially larger number of fractional-storage servers, had they been connected to other locations in the Internet, such as at edges of the Internet (close to last mile networks), Tier 3 ISPs, or at the user premises. Moreover, in some embodiments, the cost of streaming the mentioned 1,000 Gbps when the fractional-storage servers are located on the Internet backbone, or close to the Internet backbone, is expected to be significantly lower than what is expected when the servers are located elsewhere as mentioned before.
FIG. 8 illustrates one example where an assembling server 4020 is located at the juncture 4010 between two networks: the first network is an ISP transit network 4014 that connects the juncture to the Internet and provides Internet transit via a switching router 4015, and the second is a last mile network 4041 that connects end users 4051 to the Internet via a switch 4031 (located, for example, inside a Central Office, a Head-End, or a street-level cabinet). In one embodiment, the juncture 4010 is a network operated by a local ISP that pays transit fees for Internet traffic passing through the transit network 4014, and last mile fees for traffic passing through the last mile network 4041. A unique property of the juncture 4010 is that it is possible for an assembling server 4020 located at the juncture to receive erasure-coded fragments sent by fractional-storage servers, such as 4001 and 4002, to assemble content, and to stream the content to a client 4051 via the last mile network 4041, without incurring any additional costs in comparison to other scenarios, such as where Internet packets flow from the Internet backbone to a Tier two ISP network to the Internet backbone and to the last mile network. In other words, since the assembling server 4020 is located at the juncture, it does not create any extra traffic via networks 4014 and 4041. The assembling server can also be located at or close to an edge of the Internet, which may include the juncture, or a point above server 4015, such as at the transit network 4014 connecting the juncture to the Internet. When located at or close to an edge of the Internet, the assembling server has the potential not to incur additional transit fees as a result of the relaying operation, since approximately the same traffic would have to pass via the same transit network in a normal scenario. Another beneficial location for the assembling server is at the home premises, since, clearly, a relaying operation performed there does not add any significant traffic to higher levels of the network. In contrast to the above-suggested locations, in some cases an assembling server may be located at an arbitrary point on the backbone, or at other high-level points of the Internet, where it incurs additional transit fees, as fragments assembled by the server flow once over an Internet transit network going from a fractional-storage server to the assembling server, and then a second time when streamed by the assembling server to a destination client over an Internet transit network.
FIG. 9 (without the fragments marked with dashed lines) illustrates one example of distributing the erasure-coded fragments to ‘M’ CDN servers 399a to 399(M), connected to a network 300. Encoded fragments 310a to 310(M) of a first segment are sent for storage in servers 399a to 399(M) respectively. Similarly, erasure-coded fragments 320a to 320(M) of a second segment are sent for storage in servers 399a to 399(M) respectively. In addition, other erasure-coded fragments associated with other segments of other contents, illustrated as erasure-coded fragments 390a to 390(M), are sent for storage in servers 399a to 399(M) respectively. The number of unique erasure-coded fragments from each segment that are stored on the servers (399a to 399(M)) is equal to M in this example, where M may be smaller than the maximum number of unique erasure-coded fragments, meaning that only a subset of the potential erasure-coded fragments are actually stored. It is also possible to store the maximum number of unique erasure-coded fragments, or store more than one unique erasure-coded fragment per segment per server. The network 300 may be the Internet for example, or any other data network connecting multiple nodes, such as a private IP network, or a Wide Area Network (“WAN”). In one embodiment, the fragments marked with dashed lines illustrate one example where (N−M) additional servers are added to the array, and (N−M) new unique erasure-coded fragments per segment per content (310(M+1) to 310(N), 320(M+1) to 320(N), and 390(M+1) to 390(N)) are generated and added to the array. In one embodiment, only M out of the maximum possible erasure-coded fragments (L) are actually generated for storage in the first place. In one embodiment, when the additional N−M erasure-coded fragments are needed for storage (e.g., when additional servers are made available), the remainder of the N−M erasure-coded fragments are actually generated. Any time that additional unique erasure-coded fragments are needed, this process of calculating the additional erasure-coded fragments is repeated, up to the point that all L possible erasure-coded fragments are used.
In one embodiment, and especially when using rateless coding, L may be chosen as a sufficiently large number to account for any realistic future growth of the server array. For example, a segment of 96 Kbytes is expanded using a rateless code with a ratio of 1 to 2^16 original symbols to encoded data, into an encoding symbol of potential size 6.29 GBytes. Assuming a 1500 Bytes erasure-coded fragment size, then potentially 4.19 million unique erasure-coded fragments can be generated. Now, it is safe to assume that for all practical uses, the server array will not grow to more than 4.19 million nodes, and may contain several thousands of servers, meaning that the encoded data can be used in all cases where additional unique erasure-coded fragments are needed, by generating new erasure-coded fragments out of the segment. Optionally, a server may store erasure-coded fragments for only some of the segments.
In one example of redundancy factor and storage gain (without the fragments marked with dashed lines), server 399a stores only erasure-coded fragment 310a from a first segment, erasure-coded fragment 320a from a second segment, and erasure-coded fragment 390a from a third segment. Assuming that: (i) the segment size is 1024 Kbytes; (ii) the segment is encoded using erasure code into a 4096 KByte encoded segment; (iii) the encoded segment is segmented into 256 erasure-coded fragments of size 4096/256=16 KByte; and (iv) the erasure-coded fragments are stored on 256 servers (M=256); it turns out that each server stores only a 1/64 portion of the original size of the segment. This means that each server can manage with only 1/64 of the storage requirements in comparison to a situation where it had to store the entire segment. In addition, there are 256 erasure-coded fragments altogether from each encoded segment, meaning that an assembling device that is assembling the erasure-coded fragments from the servers need only select slightly more than 64 erasure-coded fragments in order to completely reconstruct the segment, and it can select whichever slightly more than 64 erasure-coded fragments it desires out of the 256 possibly available. The redundancy factor in this example is approximately 256/64=4. All contents in this example enjoy a factor of 64 in storage gains, meaning that server 399a, for example, stores only 1/64 of the information associated with the first segments and any additional segments belonging to other contents. In one example, each server supports high volume storage of between about 500 GByte and 500 TBytes, optionally utilizing hard drive, Solid State Drive, or any other high volume storage device(s). In these cases, each server may store many millions of erasure-coded fragments, associated with millions of segments, belonging to hundreds of thousands of different contents, and possibly more.
In one embodiment, new content initially encoded with a low redundancy factor is distributed to an initial number of fractional-storage servers. As the content is distributed to more servers, additional unique fragments are encoded and therefore the redundancy factor increases. Optionally, as the content's popularity increases, and/or as the load on the fractional-storage servers increases, the redundancy factor is increased, and vice versa.
In one embodiment, multiple unique erasure-coded fragments per segment of a new content are distributed to an initial number of fractional-storage servers with a low storage gain (i.e. each server stores multiple unique erasure-coded fragments per encoded segment). As the content is distributed to more fractional-storage servers, some of the erasure-coded fragments stored on the initial number of fractional-storage servers are removed and thereby the storage gain is increased. Optionally, as the demand for the content increases, the storage gain is decreased, and vice versa.
In one embodiment, the size of the segments and the size of the erasure-coded fragments are selected to optimize the following two requirements: (i) small segments to minimize the time to play, and (ii) medium or higher storage gains to balance the loads.
In some embodiments, the erasure-coded fragments are small, but not too small, since this will reduce IP transmission efficiencies. In one example, the nominal client side download rate is 1.5 Mbps and the nominal allowed delay in content presentation is about 1 second. The size of the segment is therefore about 1.5 Mbps×1 Sec=1.5 Mb=187 Kbytes. Assuming that the erasure-coded fragment size is kept at 1500 bytes, this results in a storage gain of 187K/1500=about 120. In other examples, the nominal client side download rate is 5 Mbps, or 1.5 Mbps, and the nominal allowed delay in content presentation is about 1 second, or 0.5 second. The sizes of the segments are therefore about 5 Mbps×1 Sec=5 Mb=625 Kbytes, or 1.5 Mbps×0.5 Sec=750 Kb=about 93 Kbytes, correspondingly. And, assuming that the erasure-coded fragment size is kept at about 1500 bytes, or about 300 bytes, this results in a storage gain of 625K/1500=about 420, or 93K/300=about 300, correspondingly.
In another example, 1,000 servers, each having 10 TBytes of storage encoded with a redundancy factor of 4 and a storage gain of 250, store 1,000/4×10 T=2,500 TBytes of contents (equals, for example, to approximately 2.5 Million full length Standard Definition H.264 compressed motion pictures, or approximately 200 Million YouTube clips).
FIG. 10 illustrates three examples (each depicted by one of the columns A-C) of changing the redundancy factor according to the demand. Column A illustrates one simplified example of a storage array including 16 servers (1001 to 1016). Each server stores up to 2 different erasure-coded fragments, and can service an erasure-coded fragment transmission bandwidth of up to B. Assuming three contents (#1, #2, and #3) processed to segments and erasure-coded fragments with a storage gain of 4.
Assuming content #1 is the most popular, and requires a peak bandwidth of 11×B. Since each server can service up to bandwidth B, at least 11 servers are needed to service content #1 bandwidth requirements. Content #1 is therefore encoded into 11 unique erasure-coded fragments per segment, illustrated as group 1100 of erasure-coded fragments stored on servers 1001 to 1011. Out of these 11 erasure-coded fragments, it is sufficient to obtain slightly more than 4 erasure-coded fragments in order to reconstruct a segment of content #1. Therefore, the resulting redundancy factor of the stored fragments associated with content #1 is approximately 11/4=2.75. Content #2 requires less bandwidth, and manages with a peak of 7×B. It is therefore encoded into 7 unique erasure-coded fragments per segment, illustrated as group 1101 of erasure-coded fragments on servers 1010 to 1016. Therefore, the redundancy factor of the stored fragments associated with content #2 is 7/4=1.75. Content #3 requires a peak bandwidth of 5×B, but for some reason (for example, being a more critical content), it is encoded into 14 erasure-coded fragments per segment, illustrated as group 1102 of erasure-coded fragments on servers 1001 to 1009 and 1012 to 1016. Therefore, the redundancy factor of the stored fragments associated with content #3 is 14/4=3.5. This concludes the storage availability of the servers in this example, as every server stores two erasure-coded fragments.
Column B illustrates an example where content #2 becomes more popular than content #1, and therefore requires more bandwidth and hence more of a redundancy factor. This is achieved by eliminating 5 erasure-coded fragments associated with content #1 that were previously stored on servers 1001 to 1005, and replacing them with 5 new unique erasure-coded fragments 1103 associated with content #2. This brings the total number of erasure-coded fragments per segments of content #1 and #2 to 6 and 12 respectively. In column C, new content #4 is stored on servers 1001 to 1003 and 1014 to 1016 (illustrated as 1104), by eliminating 3 erasure-coded fragments of content #1 and 3 erasure-coded fragments of content #2.
Throughout the examples of FIG. 10, a record of “what erasure-coded fragments are stored where” may be: (i) kept in each of the servers 1001 to 1016. In this case, when an assembling device is assembling content #2, it will send a query to servers 1001 to 1016, asking which one is storing erasure-coded fragments of content #2; (ii) kept in a control server. In this case, an assembling device will ask the control server to send back a list of all servers storing erasure-coded fragments of its required content.
With reference to FIG. 10, the following embodiments discuss various alternative ways to distribute the erasure-coded fragments among the various servers.
In one embodiment, the erasure-coded fragments associated with a first segment of a first content are stored on exactly the same servers as the erasure-coded fragments associated with a second segment of the first content. In one embodiment, the erasure-coded fragments associated with the first and the second segments of the first content are stored on different servers.
In one embodiment, different servers have different maximal bandwidths. The process that assigns erasure-coded fragments to servers takes that into account, and selects the different servers and the number of erasure-coded fragments per segment such that the integration of bandwidth over all selected servers yields the desired content's peak bandwidth.
In one embodiment, different servers have different bandwidth quota per content. The process that assigns erasure-coded fragments of a new content to servers takes that into account, and selects the different servers and the number of erasure-coded fragments per segment such that the integration of bandwidth quotas over all selected servers yields the desired content's peak bandwidth.
In some embodiments, each server stores a different number of erasure-coded fragments, and has a different bandwidth quota per content. The following examples describe possible processes for assigning erasure-coded fragments of a new content to servers. A first example including: (i) Identifying all servers with enough storage space to accommodate the new erasure-coded fragments. (ii) Sorting the identified servers by bandwidth quota (optionally, highest to lowest). (iii) Integrating the bandwidth quotas from the sorted list, up to the point where the resulting integrated bandwidth equals the content's desired bandwidth. All of the servers in the list up to the equality point are then selected as hosts for the new erasure-coded fragments. A second example including: (i) Identifying all servers with enough storage space to accommodate the new erasure-coded fragments. (ii) Approximately randomly selecting servers out of the identified list, up to the point where the resulting integrated bandwidth equals the desired bandwidth for the content. All of the chosen servers are then selected as hosts for the new erasure-coded fragments. A third example including: (i) Identifying all servers with available bandwidth quota for the new erasure-coded fragments. (ii) Sorting the identified servers by available storage space (available to unavailable). (iii) Integrating the bandwidth quotas from the list sorted by storage, up to the point where the resulting integrated bandwidth equals the desired bandwidth for the content. All of the servers in the list up to the equality point are then selected as hosts for the new fragments.
In one embodiment, a method for distributing content to a fractional-storage CDN comprising the following steps: storing on a first set of fractional-storage CDN servers erasure-coded fragments encoded with a low redundancy factor from content. And increasing the redundancy factor of the stored content by storing on a second set of fractional-storage CDN servers additional unique erasure-coded fragments encoded from the content. Wherein the redundancy factor of fragments stored on the first set of servers is increased without updating the fragments stored thereon. Optionally, the method further comprising the step of increasing the redundancy factor when the content's demand increases, without updating the already stored erasure-coded fragments.
In one embodiment, a method for load balancing a plurality of fractional-storage servers storing rateless-coded fragments in medium or higher storage gain comprising the following steps: registering the load on the fractional-storage servers. And increasing the redundancy factor when the load exceeds a first threshold. Wherein the redundancy factor is increased without updating the already stored rateless-coded fragments. Optionally, the method further comprising the step of decreasing the redundancy factor after the load falls below a second threshold.
In one embodiment, a method for distributing content to fractional-storage CDN servers comprising the following steps: storing multiple unique erasure-coded fragments per segment per content on a first set of fractional-storage CDN servers, to achieve a low storage gain. And increasing the storage gain by storing additional unique erasure-coded fragments on a second set of fractional-storage CDN servers and diluting the number of the unique erasure-coded fragments stored on the first set of fractional-storage CDN servers. Whereby the storage gain is increased without updating the remaining erasure-coded fragments stored on the first set of fractional-storage CDN servers. Optionally, when the content's demand increases, further comprising the step of decreasing the storage gain, without updating the already stored erasure-coded fragments.
FIG. 11 illustrates one example of a fractional-storage system comprising servers 699a to 699(N) having a bandwidth capability 681. In other words, no server can send data at a rate higher than 681. Assembling device 661 can select from which servers to obtain erasure-coded fragments for reconstruction of a segment. In one example, each server stores one relevant, unique, erasure-coded fragment. Therefore, from the N servers storing N possible unique fragments, the assembling device needs only K erasure-coded fragments for complete reconstruction of the segment (K<N). Since it is not important which K fragments from the N are retrieved, the assembling device may retrieve from the least loaded servers, so as to keep the load between the different servers balanced. When many assembling devices assemble contents in parallel, and since all assembling devices can select the least loaded servers, the end effect is that the load on the servers is balanced, with the potential for most servers to approach their maximal bandwidth capabilities. Optionally, that load balancing is achieved without significant coordination between the servers.
In the example of FIG. 11, assuming that K=3, the assembling device 661 may select servers 699b, 699(N−1), and 699a for fragment retrieval, as they have the lowest load of all N servers. Servers 699c and 699(N), as an example, will not be chosen, as they have relatively higher loads.
The assembling device may select the least loaded servers using any appropriate method, such as, but not limited to (i) accessing a central control server having data about the load conditions on the various servers, or (ii) periodically querying the various servers on their load conditions.
In one embodiment, instead of, or in addition to, selecting the least loaded servers, the assembling device 661 tries a random set of K servers from the N, and retrieves erasure-coded fragments from all servers reporting a load below a threshold, while higher loaded servers will be replaced by least loaded servers from the possible N servers. The end result is that the server array is balanced because the K erasure-coded fragments are retrieved from servers loaded below the threshold.
In one embodiment, the assembling device does not know which of the servers store erasure-coded fragments related to the content to be retrieved, but the assembling device knows over how many servers (from the total number) the erasure-coded fragments are distributed. Therefore, the assembling device compensates for the infertile requests by enlarging the number of requests for erasure-coded fragments. Optionally, the requested servers are selected based on approximately random algorithm.
FIG. 12 illustrates one embodiment of different servers 698a to 698(N) having different bandwidth capabilities of 683a to 683(N) correspondingly. Assembling device 661 selects from which K servers, out of the possible N, to retrieve the fragments for segment reconstruction, wherein each server may have different unutilized bandwidth and different bandwidth capability. When many assembling devices assemble contents in parallel, while rejecting servers with a high load, the end effect is that the server array is approximately balanced and most servers can approach their maximal bandwidth capabilities. In one embodiment, the server array is balanced by enabling many assembling devices to select the least loaded servers.
Still referring to FIG. 12, in the example, and assuming that K=3, servers 698a, 698(N−1) and 698(N) will be selected, as they have the highest unutilized bandwidth. In another example, the servers having the highest percentage of unutilized bandwidth will be selected.
In one embodiment, servers 698a to 698(N) represent completely different types of server hardware, operating systems and capabilities, all put together in an array, and achieving load balance without the need for significant inter-server coordination. In one example, the fragments are distributed to at least two different classes of servers; the first class comprises high bandwidth CDN servers directly connected to the Internet backbone, and the second class comprises lower bandwidth CDN servers not directly connected to the Internet backbone.
In one embodiment, the servers are selected for fragment retrieval according to their unutilized fragment delivery bandwidth. For example, the servers report their unutilized bandwidth, and the assembling devices, or a control server, obtain the report and decide which servers to use for fragment delivery based on the unutilized bandwidth of each server.
In one embodiment, the servers are selected for fragment retrieval according to their ability to support additional fragment delivery load. For example, the servers report their ability to support additional fragment delivery loads. And the assembling devices, or a control server, obtain the report, and select the servers that report an ability to support additional fragment delivery loads.
In one embodiment, the assembling device, or a control server, looks for a pool of servers that may be used as replacements for servers that are loaded to a degree that does not allow continuation of fragment delivery. For example, the assembling device looks for potential unloaded servers, while retrieving fragments from other servers. The assembling device may sample relevant servers approximately randomly, and/or according to indications from a control server. The sampling process may comprise querying the potential server for load information, or measuring the latency or latency variance to the servers in order to estimate the current load on the server.
In one embodiment, it is desired to replace one or more servers by other servers for the delivery of erasure-coded fragments, wherein the replacement servers are selected using a second criterion from a pool of servers identified using a first criterion. For example, the first criterion for identifying the pool of replacement servers comprises looking for servers capable of increasing their fragment delivery throughputs, and the second criterion for selecting the replacement servers from the pool comprises selecting the best latency response server from the pool. In one example, the first criterion is a latency criterion, and the second criterion is a load criterion. In another example, the first criterion is a latency criterion, and the second criterion is a latency variance criterion. In another example, the second criterion is an approximately random selection. In one embodiment, a server selected using the second criterion is compared to the server to be replaced based on the second criterion. For example, the second criterion is latency, and the replacing server, selected from the pool, has a smaller latency than the server it replaces.
In one embodiment, the server to be replaced is identified by comparing the actual performance level of the server with a threshold performance level. For example, when the compared performance is latency, a server having response latency above a certain threshold is replaced. In another example, the compared performance is the load on the server, which may be measured in terms of the amount of the unutilized fragment delivery bandwidth, or in terms of the percent of the server's unutilized fragment delivery bandwidth, or measured by any other appropriate technique.
In some embodiments, the assembling devices use a fragment pull protocol to retrieve the fragments and approach the servicing servers. In some embodiments, the assembling devices use a push protocol to obtain the fragments and approach the servicing servers, possibly by obtaining multiple sub-transmissions comprising fragment sequences.
FIG. 13 illustrates one embodiment of a fractional-storage system. Assembling device group 661g obtain erasure-coded fragments from the servers, such that the resulting outgoing bandwidth utilizations of each server in the array is 682a to 682(N) correspondingly. FIG. 14 illustrates a case where server 698b has failed, its bandwidth capability 682b1 is zero, and is therefore unable to provide erasure-coded fragments. The assembling devices from group 661g, which previously obtained fragments from server 698b, may attempt to access it again for additional fragments, but are now unable to get a response. These assembling devices therefore obtain fragments from alternative servers. The end effect is that bandwidth 682b is now loaded on the still available servers, such that the total bandwidth 682a1 to 682(N)1 approximately increases by a total amount equal to 682b, optionally with no inter-server coordination, and simply by the fact that each assembling device selects alternative available servers for obtaining fragment on-the-fly. In one example, instead of obtaining from server 682b1, the assembling devices obtain from the least loaded available servers. In one embodiment, a control server selects the alternative server/s for the assembling devices. In one embodiment, the assembling devices use a fragment pull protocol to obtain the fragments, and approach the alternative servers. In one embodiment, the assembling devices use a push protocol to obtain the fragments, and approach alternative servers, possibly by obtaining multiple sub-transmissions comprising fragment sequences. In this case, the sub-transmissions of the faulty server are discontinued and compensated for by other sub-transmissions from the alternative servers.
FIG. 15 illustrates a few examples of retrieving fragments according to locality. In one example, the fractional-storage servers are connected to a data network or networks comprising the routers 201 to 209. Assembling devices 235, 237, and 238 are connected to the same data network or networks, and K=3, meaning that any assembling device needs to obtain 3 erasure-coded fragments per segment from optionally 3 different servers out of the 10 in order to successfully reconstruct the segment.
Each assembling device tries to obtain erasure-coded fragments from fractional-storage servers that are closest to it topologically. In one embodiment, the topological distance is a function of the number of separating routers. Assembling device 238 can select three servers from groups 242, 248 or 249. According to the minimal path criterion, it retrieves the erasure-coded fragments from servers 399h to 399i of group 248, since they are only one router 208 away. Groups 242 and 249 are three (208, 202, 203) and five (208, 202, 203, 201, 209) routers away, and are therefore not selected for retrieval. Similarly, device 237 selects three servers out of group 242, and device 235 can select any three servers from groups 242 and 249, since both are located four routers away.
In one embodiment, if topologically close servers do not respond to the assembling device, or report a bandwidth limitation, the assembling device will attempt to obtain an erasure-coded fragment from the next topologically closest server.
In one embodiment, an assembling device attempts to obtain erasure-coded fragments from servers featuring the lowest latency. Upon no response, for whatever reason, the assembling device will attempt to retrieve from the next lowest latency server. In one embodiment, the assembling device obtains information regarding the unutilized fragment delivery bandwidths of servers, and then attempts to retrieve from the lowest latency servers out of the servers having enough unutilized bandwidth. In one embodiment, the assembling device obtains information regarding the unutilized fragment delivery bandwidths of the servers, and then attempts to retrieve from the topologically closest servers out of the servers having enough unutilized bandwidth.
Still referring to FIG. 15, in one embodiment the assembling devices select servers according to a latency criterion, such as selecting servers with the shortest time between fragment request and fragment delivery, or selecting servers having latency below a dynamic or static threshold. Assembling device 237 assembles content from servers 399c, 399f, 399g, and assembling device 235 assembles content from servers 399b, 399c, 399g (both use a mixture of servers from groups 242 and 249). At a certain point in time, router 209 becomes congested or blocked, and prevents the erasure-coded fragments from servers 399b and 399c from arriving at assembling devices 235 and 237, or causes the fragments to arrive with an increased delay. Therefore, assembling device 235 switches to three servers of group 242, and assembling device 237 switches from server 399c to server 399e. 
In one embodiment, the assembling device selects fractional-storage servers according to the following criterion: first, servers with adequate unutilized fragment delivery bandwidth are considered, then out of these, those with latency below a threshold are considered, and out of these, the servers with minimal topological routing path are selected.
In some embodiments, the assembling devices use a fragment pull protocol to retrieve the fragments, and approach servers having low latency or low hop count as compared to other servers. In some embodiments, the assembling devices use a push protocol to retrieve the fragments, and approach servers having low latency or low hop count as compared to other servers, optionally by obtaining multiple sub-transmissions comprising fragment sequences.
In one embodiment, a plurality of unsynchronized retrieving assembling devices, which optionally use fragment pull protocol, choose the least loaded servers from which to retrieve the erasure-coded fragments. Optionally, the servers have almost no inter-communication between them and the load balancing calculation is performed by the retrieving assembling devices. Because the assembling devices can select the least loaded servers, the assembling devices manage the load balancing. When the erasure-coded fragments stored by the servers are unique erasure-coded fragments, the retrieving assembling device may retrieve erasure-coded fragments from any relevant server. Therefore, it may be enough for the retrieving assembling device to have indication of the load on its targeted servers, and retrieve enough erasure-coded fragments from the least loaded servers.
In one embodiment, a server signals the retrieving assembling device that it is close to its bandwidth limit and the assembling device searches for an alternative server. Optionally, the assembling device selects the server according to one or more of the following parameters: locality, cost, latency, or reliability. In one embodiment, the servers register their loads on a central server, and the assembling device selects the server to retrieve from, from the registered servers. In one embodiment, a central server, holding the loads of the various servers, determines for the assembling devices from which server to retrieve the erasure-coded fragments.
In one embodiment, assembling devices measure the latency of the different servers in responding to fragment requests, and then use the latency information to estimate the loads on the servers. In one example, a high latency may indicate a high load on the server.
In one embodiment, the topological router hop count between an assembling device and fragment delivering servers is used to estimate the latency of the servers in responding to fragment requests.
In one embodiment, the latency of fragment delivering servers in responding to fragment requests by an assembling device is used to estimate the topological router hop count between an assembling device and the servers.
In one embodiment, the assembling devices perform several latency measurements for the different servers in responding to fragment requests, and then use the latency variance information to estimate the loads on the servers. In one example, a high latency variance may suggest a high load on server.
In one embodiment, fractional-storage servers, from which the fragments are obtained for reconstructing a segment, are selected based on an approximately random selection algorithm from all of the servers storing the relevant fragments. In one example, an approximately random selection algorithm weighted according to the unutilized bandwidth of the servers is used for the approximately random selection of servers. The weighted random selection algorithm assigns servers with selection probabilities proportional to the amount of unutilized bandwidth for fragment delivery in each of the servers, such that the probability to select a server having a larger amount of unutilized bandwidth is higher than the probability to select a server having a lower amount of unutilized bandwidth.
The following embodiments describe processes for on-the-fly selection and re-selection of fractional-storage servers from which to obtain erasure-coded fragments.
In one embodiment, a method for selecting enough new servers from which to obtain fragments, based on the unutilized bandwidth of the servers, includes the following steps: (i) accessing data regarding servers storing relevant fragments (referred to as the relevant servers); (ii) accessing data regarding the unutilized bandwidth of the relevant servers. Optionally, the data is received by the assembling device from the relevant servers; and (iii) obtaining fragments from enough of the relevant servers having approximately the highest unutilized bandwidth; or obtaining fragments from enough of the relevant servers selected randomly and having unutilized bandwidth above a certain threshold.
In one embodiment, a method for selecting enough new servers from which to obtain fragments, based on latency, includes the following steps: (i) accessing data regarding the relevant servers; (ii) accessing data regarding the latencies from the relevant servers to the assembling device; and (iii) obtaining fragments from enough of the relevant servers having the lowest latencies; or obtaining fragments from enough of the relevant servers selected randomly and having latencies below a certain threshold.
In one embodiment, a method for selecting enough new servers from which to obtain fragments, based on bandwidth and latency, includes the following steps: (i) accessing data regarding the relevant servers; (ii) accessing data regarding the unutilized bandwidth of the relevant servers; (iii) identifying more than enough relevant servers having the most unutilized bandwidth; or randomly identifying more than enough relevant servers having unutilized bandwidth above a certain threshold; (iv) accessing data regarding the latencies from the identified servers to the assembling device; and (v) obtaining fragments from enough of the identified servers having the lowest latencies; or obtaining fragments from enough of the relevant servers selected randomly and having latencies below a certain threshold.
In one embodiment, a method for selecting enough new servers from which to obtain fragments, based on latency and bandwidth, includes the following steps: (i) accessing data regarding the relevant servers; (ii) identifying more than enough relevant servers having latencies to the assembling device below a certain threshold; or randomly identifying more than enough relevant servers having latencies to the assembling device below a certain threshold; (iii) accessing data regarding the unutilized bandwidth of the identified servers; and (iv) obtaining fragments from enough of the identified servers having the highest unutilized bandwidth; or obtaining fragments from enough of the relevant servers selected randomly and having the highest unutilized bandwidth.
In one embodiment, a method for selecting enough new servers from which to obtain fragments, based on locality, includes the following steps: (i) accessing data regarding the relevant servers; (ii) accessing data regarding the network topology distance (locality) from the relevant servers to the assembling device; and (iii) obtaining fragments from enough of the topologically closest relevant servers; or obtaining fragments from enough of the relevant servers that are located in the same sub-network as the assembling device, or located in the closest sub-networks.
In one embodiment, a method for selecting enough new servers from which to obtain fragments, based on bandwidth and locality, includes the following steps: (i) accessing data regarding the relevant servers; (ii) accessing data regarding the unutilized bandwidth of the relevant servers; (iii) identifying more than enough relevant servers having the most unutilized bandwidth; or randomly identifying more than enough relevant servers having unutilized bandwidth above a certain threshold; (iv) accessing data regarding the network topology distance from the relevant servers to the assembling device; and (v) obtaining fragments from enough of the topologically closest relevant servers; or obtaining fragments from enough of the relevant servers that are located in the same sub-network as the assembling device, or located in the closest sub-networks.
In one embodiment, a method for selecting enough new servers from which to obtain fragments, based on latency and locality, includes the following steps: (i) accessing data regarding the relevant servers; (ii) identifying more than enough relevant servers having latencies to the assembling device below a certain threshold; or randomly identifying more than enough relevant servers having latencies to the assembling device below a certain threshold; (iii) accessing data regarding the network topology distance from the relevant servers to the assembling device; and (iv) obtaining fragments from enough of the topologically closest relevant servers; or obtaining fragments from enough of the relevant servers that are located in the same sub-network as the assembling device, or located in the closest sub-networks.
In one embodiment, a method for selecting enough new servers from which to obtain fragments is based on bandwidth, latency, locality, and, optionally, one or more additional relevant parameters. The method may weigh the different parameters in various ways, all of them are intended to be covered by the embodiments. For example, the method may include the following steps: (i) accessing data regarding the relevant servers; (ii) receiving data regarding the unutilized bandwidth latencies to the assembling device, and topology distances to the assembling device; (iii) weighting the received data and identifying a quantity of the most proper relevant servers, which can provide enough fragments to reconstruct content; and (iv) obtaining the fragments from the identified servers. In another example, the method may include the following steps: (i) accessing data regarding the relevant servers; (ii) identifying a set of more than enough relevant servers having the most unutilized bandwidth; or randomly identifying a set of more than enough relevant servers having unutilized bandwidth above a certain threshold; (iii) from the set, identifying a sub-set of more than enough relevant servers having latencies to the assembling device below a certain threshold; or randomly identifying more than enough relevant servers having latencies to the assembling device below a certain threshold; and (iv) obtaining fragments from enough of the topologically closest relevant servers out of the sub-set; or obtaining fragments from enough of the relevant servers out of the sub-sets, which are located in the same sub-network as the assembling device, or located in the closest sub-networks.
In one embodiment, a server may be loaded to a point that it is approximately unable to transmit additional fragments as a response to new fragment requests or new sub-transmission requests. The server may also be too loaded to continue transmitting fragments to its currently served assembling devices. In one example, these cases result from one or more of the following conditions: (i) server hardware limitation, such as CPU power or memory bus constraints, which prevents it from delivering fragments beyond a certain throughput, (ii) outgoing communication link limitation, such as a fixed-bandwidth line, which prevents the server from transmitting fragments beyond a rate that can be supported by the line, (iii) sharing of an outgoing communication line with other servers, and the other servers utilizing the shared line to a point that lowers the bandwidth available for fragment transmission, and (iv) sharing the fragment storage and transmission software together with other applications on one physical server, and the other applications consuming CPU, memory, or communication resources to a point that affects the ability of the fragment storage and transmission software to respond to fragment or sub-transmission requests.
In some embodiments, approximately random selection of fractional-storage servers is utilized for dealing with changes in network conditions, such as packets loss and/or server failure, without affecting the user experience, and optionally without prior knowledge of the type of the change in network condition. Optionally, new erasure-coded fragments are requested from the randomly selected servers instead of failed requests. Optionally, failed servers are replaced with other servers. Optionally, the combination and/or the number of fractional-storage servers from which the fragments are obtained changes over time. Optionally, the number of redundant fragment requests changes over time.
In one embodiment, different servers receive different weights proportional to their bandwidth. For example, the higher the bandwidth capability of the server, the higher the server coefficient; the higher the server coefficient, the higher the probability of selecting the server by an assembling device. In one embodiment, selecting the servers approximately randomly enables the fractional-storage system to operate well when the assembling devices do not know the load on at least some of the servers.
In one embodiment, the approximately random selection of servers produces a set of source servers from which erasure-coded fragments are retrieved using a fragment pull protocol. In another embodiment, the approximately random selection of servers produces a set of source servers from which erasure-coded fragments are retrieved using a push-protocol. In this case, multiple sub-transmissions may be used to transport the fragments from multiple servers to an assembling device. When new server sources are randomly selected instead of others, the assembling device may end the sub-transmissions associated with the replaced servers, and initiate new sub-transmissions from the replacing servers, optionally from the point that the terminated sub-transmissions were interrupted.
In one embodiment, the approximately random server selections are made from the servers not currently servicing the assembling device. In one embodiment, the approximately random server selections are made from all servers storing relevant fragments, including the server(s) that serviced the assembling device before being identified as problematic.
In one embodiment, approximately random reselections of servers are performed occasionally, even if all currently servicing servers are functioning correctly. In this case, the assembling device may select a few servers from the current set, to be randomly replaced. In one embodiment, functioning servers are kept throughout several segment retrieval cycles, and potentially for the entire delivery cycle of a segmented content.
In one embodiment, the assembling device does not know which of the servers store erasure-coded fragments related to the content to be retrieved, but the assembling device does know over how many servers (from the total number) the erasure-coded fragments are distributed. Therefore, the assembling device compensates for the infertile requests by increasing the number of requests for erasure-coded fragments. Optionally, the requested servers are selected based on approximately random algorithm.
In one embodiment, a method for reselecting one or more fractional-storage CDN servers on-the-fly, comprising: pulling erasure-coded fragments from the servers; estimating the servers' load, latency, network congestion, and packet loss; and operating a fuzzy algorithm on the estimations in order to replace at least one of the servers with at least one other fractional-storage server. Optionally, the method further comprising operating the fuzzy algorithm based on measurements of many assembling devices and recommendations received from a central server. Optionally, the method further comprising replacing the servers quickly after missing a fragment. And optionally, the fuzzy algorithm weighs many possible solutions and converges to a sufficient one.
In some embodiments, the fragments are small enough to be contained in one packet. In one embodiment, each fragment is about 1400 bytes, and can fit into one UDP or RTP packet transmitted over Ethernet. The stateless nature of UDP and RTP allows the servers to send one packet with one fragment very quickly, without the need for any acknowledgement or hand shaking. In some embodiments, the fragment pull protocol requests use one stateless packet, like UDP or RTP. In one embodiment, the assembling device requests about 100 fragments approximately in parallel, using 100 separate requests or one or few aggregated requests. About 100 servers respond by sending about 100 fragments, each encapsulated in one stateless packet, after a short delay, and the assembling device receives the fragments within a fraction of a second. Assuming an Internet round trip delay of 100 ms, and server processing latency of 100 ms, then after 200 ms the assembling device starts receiving all 100 fragments. With a modem of 5 Mbps, and assuming 1400 bytes per fragment, all 100 fragments are received 1400×100×8/5 Mbps=224 ms after the initial delay, meaning that content can be presented 200+224=424 ms after request (decoding and other process time has been ignored in this example).
The following embodiments describe processes for on-the-fly erasure-coded fragment retrieval from fractional-storage servers.
In one embodiment, a method for obtaining erasure-coded fragments from fractional-storage servers to reconstruct a segment includes the following steps: (i) identifying the next segment to be obtained; optionally, the segments are approximately sequential segments of streaming content obtained according to their sequential order; (ii) optionally, determining the minimum number of fragments needed to reconstruct the segment; (iii) are enough identified relevant servers (i.e. servers storing the required fragments) available from the process of obtaining prior segment/s? (iv) if no, identifying enough relevant servers; (v) if yes, requesting enough fragments from the identified relevant servers; if less than enough fragments are obtained from the identified relevant servers, go back to step iv and identify additional relevant server/s; (vi) reconstruct the segment from the obtained fragments; and (vii) optionally, go back to step i to obtain the next segment.
In one embodiment, a method for obtaining erasure-coded fragments from fractional-storage servers to reconstruct multiple segments includes the following steps: (i) identifying multiple segments to be obtained, optionally according to their sequential order; (ii) optionally, determining the minimum number of fragments needed to reconstruct the segment; (iii) optionally, determining the number of fragments to be obtained approximately in parallel; (iv) are enough identified relevant servers available from the process of obtaining prior segment/s? (v) if no, identifying enough relevant servers; (vi) if yes, requesting enough fragments from the identified relevant servers, optionally in parallel and according to the sequential order of the segments; (vii) if less than enough fragments are obtained from the identified relevant servers, go back to step iv and identify additional relevant server/s; (viii) reconstructing the segment/s from the obtained fragments; and (ix) optionally, go back to step i to obtain the next segments.
In one embodiment, a method for obtaining erasure-coded fragments from fractional-storage servers to reconstruct a segment in a burst mode includes the following steps: (i) identifying the next segment to be obtained; (ii) optionally, determining the minimum number of fragments needed to reconstruct the segment; (iii) are more than the minimum number of relevant servers available from the process of obtaining prior segment/s? (iv) if no, identifying more than the minimum relevant servers; (v) if yes, requesting more than the minimum number of fragments needed to reconstruct the segment; if less than enough fragments are obtained, go back to step iv and identify additional relevant server/s; (vi) reconstructing the segment from the obtained fragments; and (vii) optionally, go back to step i to obtain the next segment.
The various methods for obtaining erasure-coded fragments from the fractional-storage servers for reconstructing one or more segments may be combined as needed. In one example, the initial segment/s are obtained using a burst mode and the following segments are retrieved without requesting extra fragments. In another example, the initial segment/s are obtained approximately in parallel and optionally using a burst mode, and the following segments are obtained one by one and optionally without requesting extra fragments. The fragments may be obtained using a pull protocol and/or a push protocol. Moreover, the servers from which to retrieve the fragments may be selected according to one or more of the various discussed methods for selecting the servers and/or load balancing the servers.
FIG. 16 illustrates one embodiment in which the bandwidth amplification factor is increased by allowing assembling device 420a (which may be a user-premises server) to continue and forward erasure-coded fragment 310a to additional assembling devices 420aa and 420ab. A larger layered cluster is possible, where more than two layers of distribution are supported. Each assembling device participating in the layered cluster (which is somewhat similar to a distribution tree) 420a, 420aa, and 420ab store the erasure-coded fragment 310a, and can then send it to any assembling device. Similarly, server 399a may send assembling device 520a some unique erasure-coded fragments generated from the same segment (320a′, 320a′′, and 320a′′′). Assembling device 520a stores erasure-coded fragment 320a′ and forwards erasure-coded fragments 320a′′ and 320a′′′ to additional assembling devices 520aa and 520ab. 
FIG. 17 illustrates one embodiment of a streaming cluster utilizing a fragment pull protocol. Optional content source 260 provides streaming content to a first layer of CDN servers 262, optionally through server 261. In one embodiment, the outgoing bandwidth of the first layer of CDN servers 262 is amplified using a second layer of CDN servers 263, having a total outgoing bandwidth higher than that of the first layer of CDN servers 262.
In one embodiment, the outgoing bandwidth of the second layer of CDN servers 263 is amplified using at least one layer of peer clients 265, having a total outgoing bandwidth higher than that of the second layer of CDN servers 262. The peer clients utilize a fragment pull protocol to retrieve a plurality of erasure-coded fragments from a plurality of servers, and optionally from other peer clients as well. For example, peer client 266 retrieves erasure-coded fragments from the second layer of CDN servers 263 and from peer clients 267a and 267b. 
FIG. 18 illustrates one embodiment of a server 268 which retrieves a plurality of unique erasure-coded fragments (Frag #1 to Frag #N) from a plurality of sources, optionally utilizing a fragment pull protocol. Then, the server 268 decodes the erasure-coded fragments and generates new unique erasure-coded fragments (Frag #N+1 to Frag #N+K). The new unique erasure-coded fragments are retrieved by the next layer, which may be the next layer of the bandwidth amplification streaming cluster, and/or assembling devices which ultimately present the content.
Usually, a broadcast tree operates (i) a task for maintaining the broadcast tree, and (ii) a task for propagating the broadcast data through the tree. In one embodiment, different contents are distributed through different paths. In one embodiment, different contents are propagated though the same broadcast-like layered cluster and have different storage gains. In one embodiment, a cluster of servers is divided into two or more coexisting broadcast-like layered clusters, such that the same server may be associated with two different layers in two different broadcast-like clusters. In the case of server congestion, the server assigns higher priority to requests for erasure-coded fragments from servers in the initial layers of the cluster over requests for erasure-coded fragments from servers in the end layers of the cluster, in order to suffocate the layered cluster as little as possible. In one example, the priority mechanism implemented by each retriever supplies its layer identification, which enables the server to locate the retrievers from the initial layers of the cluster.
FIG. 19 illustrates one embodiment of a broadcast-like layered cluster having a low propagation delay used to distribute unique erasure-coded fragments to a plurality of peer clients. A full copy of the segment is distributed through the broadcast-like layered cluster on the left, which includes servers 270a, 272a-272n, and 274a-274n. Each server generates a plurality of unique erasure-coded fragments from the segment, which are distributed to its associated peer clients, for example, server 270a distributes to peer clients in group 271a, server 272a distributes to peer clients in group 273a, and so on. An assembling device can reconstruct the segment by retrieving enough erasure-coded fragments from any of the groups of peer clients. Optionally, the peer clients store erasure-coded fragments associated with hot contents with medium or higher storage gain and high redundancy factor.
In one embodiment, a server layered cluster comprising a first layer and a second layer. The first layer comprising fractional-storage servers, having a first aggregated outgoing bandwidth, and storing a plurality of unique erasure-coded fragments. The second layer comprising fractional-storage servers having a second aggregated outgoing bandwidth, and having outgoing bandwidth that is significantly larger than the first aggregated outgoing bandwidth. Optionally, the second layer comprises significantly more fractional-storage servers than the first layer. Wherein, at least some of the fractional-storage servers from the second layer are programmed to retrieve at least some of the erasure-coded fragments from the first layer using a fragment pull protocol, whereby the server cluster provides a broadcast-like effect.
In one embodiment, a bandwidth amplification cluster comprising a plurality of servers utilizing a fragment pull protocol to retrieve erasure-coded fragments, wherein most of the servers can be used both for bandwidth amplification purposes and for distributed storage system purposes.
In one embodiment, each node in the broadcast-like layered cluster receives entire segments for re-encoding new fragments to the next nodes. After forwarding the new fragments, the node saves only some of the unique fragments and deletes the segment. Therefore, the end result is a broadcast-like layered cluster storing unique fragments in each level, and a high storage gain distribution of unique fragments between the nodes on the broadcasting layers.
In one embodiment, the fractional-storage system is approximately insensitive to the mixture of the consumed contents as long as the aggregated throughput is below the total throughput of the fractional-storage servers.
In one embodiment, the fractional-storage system is approximately insensitive to the mixture of the consumed contents as long as the aggregated throughput is below the total throughput of the fractional-storage servers.
FIG. 20 illustrates one example of a fractional-storage server array, including N servers (399a to 399(N)), and storing content A, which includes erasure-coded fragments 310a to 310(N), and content B, which includes erasure-coded fragments 320a to 320(N). Each server is connected to the network 300 with a fragment delivery bandwidth capability B 339. Therefore, the N servers have an aggregated bandwidth of B×N. A first group of assembling devices 329a consumes content A at an average bandwidth Ba 349a. A second group of assembling devices 329b consumes content B at an average bandwidth Bb 349b. Since all of the servers participate in the transmission of the two contents, the first and second groups can potentially consume all server bandwidth, up to the limit where Ba+Bb=N×B, with any ratio of demand between the first and second contents, and with no special provisions to be made when storing the erasure-coded fragments related to the two contents in the fractional-storage server array.
FIG. 21 illustrates the case where the first group 328a, which consumes content A, becomes larger than 329a, with a larger bandwidth Ba 348a. The second group 328b, which consumes content B, becomes smaller than 329b, with a smaller bandwidth Bb 348b, such that Ba is about the same as Bb. In this case, the array can still be exploited up to the aggregated bandwidth, since, as before, Ba+Bb can still be almost as high as N×B. FIG. 22 illustrates the case where the first group has disappeared, allowing the second group 327b, which consumes content B, to extract an aggregated bandwidth of Bb 347b that can potentially reach the limits of the server array, such that Bb=N×B. Again, this is achieved without updating the erasure-coded fragments associated with content A and content B, and without using inter-server interaction.
In some embodiments, the ability to utilize the aggregated bandwidth of approximately all of the participating servers, for the delivery of about any mixture of contents with about any mixture of content bandwidth demand, is made possible by one or more of the following: (i) each assembling device selecting a subgroup of the least loaded fractional-storage servers from which to retrieve the necessary number of erasure-coded fragments to reconstruct a segment or several segments (least-loaded server selection criterion); or (ii) each assembling device approximately randomly selecting a subgroup from which to reconstruct a segment or several segments, such that when many assembling devices select at random, the various fractional-storage servers are selected approximately the same number of times (or in proportion to their available resources, such as unutilized bandwidth), which in turn balances the load between the participating servers (random server selection criterion). It is noted that (i) the selections may be made by either the assembling devices themselves, or may be made for the assembling devices by a control server, which then communicates the selections to each of the assembling devices; (ii) the selections may be made approximately for each segment, or for a group of segments, or only once per content at the beginning of the content; (iii) some assembling devices may use an approximately random server selection criterion, while other assembling devices may use least-loaded server selection criterion; (iv) the least-loaded selected servers may be selected out of a portion of all available fractional-storage servers. For example, the least-loaded servers may be selected from fractional-storage servers with low latency response or with low hop count to the assembling device; (v) the least-loaded servers may include servers having the most unutilized bandwidth. Additionally or alternatively, it may include servers having any unutilized bandwidth left to serve additional assembling devices; (vi) an approximately random or least-loaded selection of servers may be made such that all servers are selected to determine a subgroup, or it can be made such that every time selections are made, only some servers are selected, while the others remain as before. In these cases, the assembling device runs a process in which only a small portion of the servers currently in the serving subgroup are reselected. In the case of approximately random selection, the assembling device may randomly select the number of servers in the serving subgroup for random selection (reselection in this case, since they are replacing other servers already in the serving subgroup of the specific assembling device), such that eventually, over time, all servers within the serving subgroup have the chance to be randomly reselected. In the case of least-loaded server selection, only the most loaded servers within the serving subgroup may be selected and replaced by less-loaded servers.
FIG. 23 illustrates one embodiment of using the entire aggregated bandwidth of the fractional-storage servers for delivering multiple contents. Approximately any number of contents having any mixture of bandwidth demand per content may be delivered, as long as the aggregated bandwidth demand does not exceed the aggregated bandwidth of the fractional-storage servers. In one example, broadcast-like streams 3101, 3102, and 3103 are delivered to multiple assembling devices via multiple fractional-storage servers. Each stream is a live TV channel carrying multiple TV programs. For example, stream 3101 comprises TV programs 3110 to 3112, each spanning a specific time interval. The other streams comprise of multiple TV programs as well. Before time T1, stream 3130 has a bandwidth demand of 3130′ (meaning that all assembling devices that are currently retrieving stream 3130′ use a total bandwidth of 3130′ out of the fractional-storage servers). The other streams 3120 and 3110 have bandwidth demands of 3120′ and 3110′ respectively. The total bandwidth demand of the three streams 3130′+3120′+3110′ does not exceed the aggregated bandwidth of the fractional-storage servers 3150, and therefore all streams are fully delivered to the assembling devices. The load of the three streams is spread approximately equally among the participating fractional-storage servers, optionally because of a mechanism that selects the least-loaded servers to serve each assembling device, and/or a mechanism that approximately randomly selects servers to serve each assembling device. At time T1, TV program 3120 ends, and TV program 3121 starts. Program 3121's demand 3121′ is higher than the previous demand 3120′, and therefore a higher aggregated bandwidth is drawn from the fractional-storage servers. Still, the aggregated bandwidth demand of all three streams (3130′+3121′+3110′) is lower than the maximum possible 3150, and therefore the newly added bandwidth demand is fully supported by the servers. Optionally, the additional demand created by TV program 3121 (3121′ minus 3120′) is caused by the addition of new assembling devices that join stream 3102 and retrieving additional erasure-coded fragments. Additionally or alternatively, the additional demand created by TV program 3121 is caused by a higher bandwidth demand of TV program 3121, such as 3D data or higher resolution. Newly added assembling devices may choose fractional-storage servers from which to retrieve, according to a least-loaded server selection criterion and/or an approximately random server selection criterion, and therefore the total load is still spread approximately equally among the participating servers. At time T2, TV program 3110 ends, and a new program 3111 begins, which is less popular, and therefore creates a lower bandwidth demand 3111′. The result is a decrease in the total delivered bandwidth. At time T3 TV program 3130 ends, and TV program 3131 starts with a higher bandwidth demand of 3131′. At time T4 both TV programs 3111 and 3121 end, and two new programs 3112 and 3122 start. TV program 3112 is highly popular and therefore generates a large bandwidth demand 3112′. Program 3122 is not popular, and therefore generates a limited bandwidth demand 3122′. Some of the additional bandwidth needed by program 3112 is taken from servers that stop serving assembling devices previously retrieving program 3121, such that the aggregated bandwidth of all three streams (3131′+3122′+3112′) is still below the maximum possible bandwidth 3150, despite the fact that program 3112 is generating a large bandwidth demand. This example illustrates how the fractional-storage servers support almost any demand mixture, as long as the aggregated demand of all streams is kept below the aggregated maximum capacity of the servers 3150. Consequently, the distribution of all of the streams to the fractional-storage servers is approximately unrelated to the changes in bandwidth demand for programs carried by each stream; each stream can be regarded as a sequence that is segmented, erasure-encoded, and distributed to the participating servers. There is no need to account for demand variations during the distribution of each stream, nor is there a need to know in advance the bandwidth demand for each stream or for each program within each stream. It is noted that the demand variations are illustrated as instant variations, but may also be gradual and may occur during a program and not necessarily when one program ends and the other begins.
FIG. 24 illustrates one embodiment of real time streaming content retrieval from fractional-storage servers, wherein erasure-coded fragments 720a to 720(K) are retrieved in a fast cycle, meaning that several erasure-coded fragments are obtained approximately in parallel. As a result, the interval T2 minus T1 is more or less limited only by the download bandwidth of the assembling device's modem. Referring to the example of FIG. 3, T2 minus T1 can be reduced from 0.77 seconds to 0.15 seconds, if the modem operates at 5 Mbps (instead of 1 Mbps).
In one embodiment, T1 to T2 represents a fragment fetch cycle that corresponds to the beginning of streaming content to be presented (in that case, segment 710a is the first segment of the content, and presentation 700 corresponds to the beginning of the streaming content), or corresponds to a certain point within the streaming content to be presented starting this point onwards (in that case, segment 710a is a segment within the content, and presentation 700 corresponds to playing the content starting not from the beginning, but rather from segment 710a, located somewhere within the content). This is also known as trick play. In one embodiment, erasure-coded fragments 720(a) to 720(K) are obtained such as to result in approximately a maximum utilization of the download capabilities of the assembling device, and such that the rate of requesting erasure-coded fragments results in a data arrival rate that on average utilizes the assembling device's maximum download bandwidth.
In one embodiment, the fragment pull protocol request includes a priority indication. A high priority indication means that the servers should give a preference to responding with a fragment transmission. High priority requests are served before other requests. Optionally, high priority requests are served even if the server's bandwidth quota is exceeded. In one embodiment, the high priority requests are used by the assembling devices for receiving priority in the reception of the first segment, or several first segments, in order to facilitate fast starting of content presentation after content request by the user (either when starting to play a content, or in trick play mode, when starting to play a content from a certain point).
FIG. 25 illustrates one embodiment of a fragment pull protocol. Assembling device 861 (also represented by protocol diagram element 810b) obtains erasure-coded fragments from fractional-storage servers 899a to 899(N) (also represented by protocol diagram element 898), utilizing the following steps: (i) deciding 810a which segment to retrieve; (ii) device 861 sending requests to some of the fractional-storage servers for erasure-coded fragments associated with the desired segment. For example, requests 880a to 880(K) for erasure-coded fragments 890a to 890(K), from servers 899(a) to 899(K), correspondingly; and (iii) the servers respond by sending the requested erasure-coded fragments. For example, servers 899a to 899(K) send 881a to 881(K) erasure-coded fragments 890a to 890(K) to device 861. The fragment request and receipt process begins at T1c and ends at T1d. At time T1d, device 861 has enough erasure-coded fragments (K) to reconstruct the segment selected at 810a. In one embodiment, the process from T1c to T1d occurs in real time, in support of streaming content presentation.
FIG. 26 illustrates a similar process to FIG. 25, where requests for erasure-coded fragments are loaded into one aggregated request 870, that is sent to one of the fractional-storage servers (the receiving server is illustrated as protocol diagram element 888a, and will be also referred to as a “relay server”). In one example, if the relay server is 899(N), then, it will forward the request to additional servers 899a to 899c (protocol element 888b) via new requests 870a to 870c (on behalf of assembling device 861). Servers 899a to 899c will then respond by sending the erasure-coded fragments 890a to 890c (871a to 871c) to the assembling device 861. Server 899(N) will send 871(N) fragment 890(N) to the assembling device.
The term “fragment pull protocol for high latency” as used herein denotes a protocol enabling an assembling device to request one or more fragments from one or more providing sources, wherein the time to transmit the one or more fragments in response to the assembling device request, through the slowest communication link connecting the responding source and the assembling device, is smaller than the round trip communication delay between the assembling device and the responding source, excluding the processing time of the providing source. For example, if the round trip communication delay between Israel and the USA is about 200 ms, the assembling device requests one fragment sized about 1500 bytes, and the slowest communication link is an ADSL line connecting the assembling device at 1.5 Mbps, then the time it takes to transmit the requested fragment through the slowest communication link is about 1500*8/1500000=8 ms, which is much smaller than the round trip delay. Many of the disclosed embodiments using fragment pull protocol may use fragment pull protocol for high latency for retrieving the fragments.
FIG. 27 illustrates a similar process to FIG. 25, where request 890b fails to result in a reception of erasure-coded fragment 890b for any reason (such as a server fault, network congestion, or abnormal latency conditions). Assembling device 861 therefore issues another request 882(K+1) for erasure-coded fragment 890(K+1) in response, and receives 883(K+1) the additional erasure-coded fragment 890(K+1) needed to reconstruct the segment.
FIG. 28 illustrates a similar process to FIG. 25, where one or more extra erasure-coded fragments (in addition to the needed K) are requested in advance (illustrated as request 880(K+1) for erasure-coded fragment 890(K+1)), such that if, as an example, request 890b fails to result in a reception of erasure-coded fragment 890b, assembling device 861 does not have to request new erasure-coded fragments to reconstruct the segment, since there are still at least K erasure-coded fragments that were successfully received and therefore the segment can be reconstructed.
Still referring to FIG. 28, in one embodiment, more fragments than needed to reconstruct a segment are requested, such that the additional requested fragments approximately compensate for fragment failure conditions. If, statistically, F fragment requests are expected not to result in the reception of a fragment (i.e. fragment loss), out of a total number of K+F fragment requests (wherein K is the minimal number of fragments needed to reconstruct a segment), then it is possible to request K+F fragments instead of just K. In one embodiment, more than K+F fragments are requested, since the quantity of the received fragments is a statistical variable. In this case, K+F+S fragments are requested, wherein S is a safeguard amount of additional requests to assure that at least K fragments are received. In one embodiment, the fragment loss F changes over time, and the assembling device handles the change by increasing or decreasing the number of fragments requested per segment. In one embodiment, the assembling device may determine F based on previous fragment failure rates.
In one embodiment, requesting K+F+S fragments for a segment will almost always result in the reception of at least K fragments, and therefore the assembling device may request K+F+S without being concerned about which fragment has not arrived, and without trying to actively compensate for fragment failures by issuing additional fragment requests. In this case, the assembling device requests the fragments in an “open loop” fashion, meaning that it requests the K+F+S fragments, and moves on to another segment. In one embodiment, even when requesting K+F, or K+F+S fragments per segment, it is still possible not to receive the needed K fragments. Therefore, the assembling device may compensate for undelivered fragments by issuing additional fragment requests (a “closed loop” operation).
In one embodiment, the K+F, or K+F+S fragment requests are issued approximately in parallel, in order to achieve the fastest response possible for reconstructing a segment. In this case, the fragments start to arrive at the assembling device a short while after being requested, such that as soon as at least K out of the requested fragments arrive, the assembling device may immediately proceed with reconstructing the segment.
In one embodiment, a method includes the steps of obtaining, by an assembling device from fractional-storage servers, erasure-coded fragments associated with a segment of streaming content; detecting a first quantity of at least one fragment associated with the segment, which have failed to arrive at the assembling; requesting via a fragment pull protocol for high latency approximately the first quantity fragments; and repeating the steps of detecting and requesting until enough fragments have been obtained for reconstructing the segment. Optionally, the steps are repeated approximately sequentially on the segments. Optionally, the streaming content comprises approximately sequential segments. Optionally, detecting the failure comprises determining which fragment has failed after not obtaining the fragment within a predetermined period from issuing its request, and/or receiving a message that does not contain the actual fragment's payload. And optionally, the fragments are obtained via sub-transmissions transmitted by the servers.
In one embodiment, a method for retrieving erasure-coded fragments includes the steps of: determining, by an assembling device, the time remaining to reconstruct a segment of streaming content; estimating the probability of receiving a sufficient quantity of already-ordered erasure-coded fragments to reconstruct the segment during the remaining time; and if the estimated probability is below a predefined threshold, issuing one or more additional fragment requests, using a fragment pull protocol, until the estimated probability equals or passes the predefined threshold. Optionally, the already-ordered fragments and the additional fragment requests are received from fractional-storage CDN servers. Optionally, the already-ordered fragments are received via at least two sub-transmissions transmitted by the servers. Optionally, the already-ordered fragments are received via a fragment pull protocol. And, optionally, estimating the probability includes considering the probability of each request to result in a fragment reception during the remaining time.
In one embodiment, an assembling device may aggregate several fragment requests into one message. The aggregated message is then sent to a fractional-storage server, possibly in a payload of a single packet, and optionally in order to conserve outgoing bandwidth and/or to reduce the number of packets needed to convey the requests. The fractional-storage server may then read the aggregated message and act accordingly by sending a plurality of fragment responses to the assembling device. The fragment responses may include one fragment at each payload, as is the case of responding to a single fragment request, or it may include an aggregated response including multiple fragments at each payload.
In one embodiment, multiple segments of content, which, in one example, is streaming content, are reconstructed by an assembling device retrieving multiple erasure-coded fragments associated with the multiple segments. Since a fragment request does not always result in a reception of the fragment, some requested fragments may fail to arrive at the assembling device. Therefore, the assembling device checks (from each of the segments for which fragments have already been requested) which requested fragments have failed to result in a correct reception of a fragment. For each such failure, the assembling device issues an additional request for a fragment. The additional requests are associated with segments for which fragments have already been requested before, and therefore, in one example, the resulting fragment retrieval process includes the following two sub-processes: a first sub-process of requesting fragments associated with new segments to be reconstructed, and a second sub-process of requesting additional fragments needed to complement already requested fragments, in order to reconstruct the segments. The first and second sub-processes work together, such that the second sub-process may complement fragments associated with a first segment, while the first sub-process runs ahead in an attempt to obtain fragments needed to reconstruct a second segment; wherein the second segment is located ahead of the first segment. The first and the second sub-processes can also be described as two different quantities of fragments being requested: a first quantity associated with the first sub-process requests, and a second quantity associated with the second sub-process requests.
In one embodiment, an assembling device may control the erasure-coded fragment reception throughput by controlling the rate of fragment request. For example, each of n fragments has a known size S1 to Sn. Therefore, issuing n requests over a period of T will result in an average fragment reception throughput of (S1+S2 . . . +Sn)/T. In one example, if each fragment is 1500 Bytes, and 64 fragment requests are issued over a period of 0.5 seconds, then the average expected fragment arrival throughput is (64×1500×8)/0.5=1.53 Mbps. The fragment requests do not need to be uniformly spread over the period of 0.5 seconds, although such a spread may result in a more stable throughput, which means that less communication buffering will be needed. Using the above-described rate-control technique may result in one or more of the following: retrieving the content at a target fragment reception throughput; preventing communication buffer spill at the last mile network resulting from uncontrolled fragment requests; and/or reducing fragment loss due to averaging the fragment traffic.
In one embodiment, an assembling device operating trick play modes needs to obtain new erasure-coded fragments within a short period, to replace lost erasure-coded fragments. Therefore, the new fragments are retrieved from one or more nearby fractional-storage servers having low latency responses to the assembling device. The nearby fractional-storage servers should have sufficient bandwidth to supply the new fragments needed for the trick play, but because most of the fragments are not obtained from the nearby servers, these nearby servers may have relatively low bandwidth and may store relatively small portions of the information.
In one embodiment, a distributed system is located in a few to dozens of data centers (also known as server farm or datacenter), located close to or on the Internet backbone, together housing at least 100 fractional-storage CDN servers. The servers store erasure-coded fragments associated with approximately sequential segments of streaming contents, with a storage gain of at least 5, and transmit the stored fragments on demand to assembling devices approximately according to the sequential order of the segments. In many cases, the data centers provide a convenient place to place the CDN servers close to or on the Internet backbone. A data center can be also a collocation center, or an Internet Exchange Point. In one example, a single data center can house many fractional-storage CDN servers.
In one example, a streaming system comprising at least several hundreds of fractional-storage CDN servers located close to or on the Internet backbone, storing erasure-coded fragments encoded with a redundancy factor greater than one, and associated with approximately sequential segments of streaming contents. At least 100,000 assembling devices concurrently obtain fragments from the CDN servers, wherein the system achieves efficient load balancing and fault tolerance between the various CDN servers by determining for each of the assembling devices from which servers to obtain the fragments.
In one example, a system comprising at least 1,000 fractional-storage CDN servers is connected to the public Internet. The servers store erasure-coded fragments associated with approximately sequential segments of streaming contents, with a storage gain greater than 5, and transmit the stored fragments on demand to assembling devices approximately according to the sequential order of the segments. Wherein the aggregated bandwidth utilized by the servers for transmitting the fragments to the assembling devices exceeds 1 Giga bit per second times the number of the CDN servers. In one optional example, the system comprises at least 10,000 fractional-storage CDN servers and the aggregated bandwidth utilized by the servers exceeds 10 Giga bit per second times the number of the CDN servers.
By using a pull protocol or a push protocol with multiple sub-transmissions, the assembling device can obtain erasure-coded fragments from one, two or more different arrays of CDN servers and/or bandwidth amplification devices seamlessly.
FIG. 29 illustrates one embodiment in which fractional-storage servers 399a and 399b are part of a server array. Fractional-storage servers 399a and 399b store erasure-coded fragments 310a and 310b of a first content, and erasure-coded fragments 320a and 320b of a second content. Server 393 is a control server that manages a pool of twelve registered bandwidth amplification devices surrounded by ellipse 599. One or more of the twelve bandwidth amplification devices may be assigned to one or more of the fractional-storage servers participating in the array. In the initial stage, no assignments have been made, and the twelve bandwidth amplification devices in pool 599 are ready to receive instructions. Next, the control server 393 allocates six bandwidth amplification devices of group 610aa to server 399a, and six bandwidth amplification devices of group 610bb to server 399b. Registering the bandwidth amplification devices with the servers may be processed using any appropriate method. From groups 610aa and 610bb, three bandwidth amplification devices 610a and 610b are allocated to store erasure-coded fragments 310a and 310b respectively (and, optionally, other erasure-coded fragments associated with consequent segments of the content); and three bandwidth amplification devices 620a and 620b are allocated to store erasure-coded fragments 320a and 320b respectively (and, optionally, other erasure-coded fragments associated with consequent segments of the content). After these allocations have been made, fractional-storage server 399a forwards erasure-coded fragment 310a to group 610a, and erasure-coded fragment 320a to group 620a. Fractional-storage server 399b forwards erasure-coded fragment 310b to group 610b, and erasure-coded fragment 320b to group 620b. At the end of the allocation and forwarding process, the bandwidth amplification devices are ready to act as bandwidth amplifiers to the fractional-storage server array 399a and 399b. Optionally, the allocation of bandwidth amplification devices to specific contents is performed by either the control server 393, or each fractional-storage server 399a and 399b. 
It is noted that each bandwidth amplification device is not restricted to storing and serving erasure-coded fragments associated with a single content, and it is possible for each bandwidth amplification device to store and serve multiple erasure-coded fragments associated with multiple contents. The tradeoff in this case is that the more erasure-coded fragments from more contents are stored and served, the lower the bandwidth amplification factor, since the rate of forwarding fragments from the server to the bandwidth amplification devices increases, while the outgoing bandwidth available for each bandwidth amplification device remains the same.
In one embodiment, when a CDN server receives a request for an erasure-coded fragment, it may supply the erasure-coded fragment or supply an address of a bandwidth amplification device having an image of the requested erasure-coded fragment. Optionally, a bandwidth amplification device storing one erasure-coded fragment of a specific content also stores an image of some or all other erasure-coded fragments associated with the specific content (which are stored on the specific CDN server). Alternatively, the bandwidth amplification device stores unique erasure-coded fragments generated from the same segments used for generating the erasure-coded fragments stored on the specific CDN server. In these cases, the assembling device may approach the bandwidth amplification devices instead of the CDN server for the relevant erasure-coded fragments of the specific content until (i) the end of the content; (ii) a predefined time period elapses; (iii) receiving an appropriate message; or (iv) a combination of the aforementioned.
In one embodiment, an assembling device tries to obtain an erasure-coded fragment or sub-transmission from the relevant server, and if the server does not have the necessary bandwidth to respond with fragment/s, the server relays the fragment request/s to relevant bandwidth amplification devices. The relevant bandwidth amplification devices can then send the fragment/s directly to the assembling device.
In one embodiment, unique erasure-coded fragments can be distributed between two types of devices: (i) high bandwidth fractional-storage servers, such as CDN servers, and (ii) relatively low bandwidth and storage devices acting as bandwidth amplification devices, such as peer-to-peer (P2P) devices. Since the fragments distributed between the two types of devices are unique, any combination of devices, from both types, can be used to obtain a decodable set of fragments, if the combination of devices stores a decodable set of fragments. In one embodiment, there are at least ten times more bandwidth amplification devices than high bandwidth servers, and the redundancy factor used in decoding the fragments is greater than 10. In this case, the servers can be used all or most of the time, and the bandwidth amplification devices can be used from time to time, according to bandwidth requirements, and according to the availability of the bandwidth amplification devices. In one embodiment, the processes of obtaining a fragment from a server and from a bandwidth amplification device are essentially the same, and the fragments are essentially identical in construction and format. In one embodiment, the high redundancy factor needed to support a large hybrid array of servers and bandwidth amplification devices is achieved using rateless coding techniques.
In one embodiment, the bandwidth amplification devices are used to supplement the streaming capabilities of the servers during peak traffic periods. In this case, the aggregated bandwidth of the fixed bandwidth lines connecting the servers to the Internet need not account for the full bandwidth demand. In one example, 1,000 CDN servers are connected to the Internet via fixed bandwidth lines having a total capacity of 10 Tbps. Demands above 10 Tbps, which occur during a 3-hour period in the evening, are met by utilizing additional fragment delivery bandwidth of P2P devices acting as bandwidth amplification devices.
In some embodiments, the assembling devices may obtain the fragments from the servers and/or from the P2P devices using a fragment pull protocol, a fragment pull protocol for high latency, and/or multiple sub-transmissions.
In one embodiment, a distributed streaming system comprising: fractional-storage servers and bandwidth amplification devices configured to store, correspondingly, a first and a second portions of rateless-coded fragments associated with approximately sequential segments of streaming content, shortly after the segments are progressively made available by a streaming source. Decodable sets of fragments associated with the segments can be obtained from approximately any combination of servers and bandwidth amplification devices storing fragments associated with the segments shortly after the segments are made available by the streaming source.
In one embodiment, the first and the second portions comprise unique rateless-coded fragments encoded with a redundancy factor that is determined according to the estimated popularity of the content being encoded, whereby the higher the popularity of the content, the higher the redundancy factor used to encode the content into fragments, and the larger the number of bandwidth amplification devices that store the fragments associated with the content.
In one example, two contents are encoded into fragments using rateless-coding. The first content is encoded with a redundancy factor greater than 100, and the second content, which is estimated to be more popular, with a redundancy factor greater than 1,000. Approximately all fragments are unique. The first content's fragments are distributed to 100 fractional storage servers and to about 10,000 bandwidth amplification devices. The second content's fragments are distributed to the same 100 fractional storage servers and to about 100,000 bandwidth amplification devices. Assuming that the fragment delivery bandwidths of each server and amplification device are 100 Mbps and 1 Mbps respectively, the first content has a potential delivery bandwidth of (100×100 Mbps)+(1,000×1 Mbps)=11 Gbps, and the second content has a potential delivery bandwidth of (100×100 Mbps)+(10,000×1 Mbps)=20 Gbps. If different popularities are expected, or alternatively different popularities are encountered during streaming of the contents, then different redundancy factors may be used, and different numbers of amplification devices per content may be utilized accordingly.
In one embodiment, different quantities of erasure-coded fragments are generated per different segments. In one embodiment, some segments store data that is considered more important than data stored in other segments, and relatively more erasure-coded fragments are generated from the segments storing the more important data than from the segments storing the less important data.
In one example, a compressed video content is segmented into segments storing i-frames and segments storing p-frames. Optionally, all segments are approximately of the same size, and more erasure-coded fragments are generated from the segments storing the i-frames than from the segments storing the p-frames. Alternatively, the segments storing the i-frames are shorter than the segments storing the p-frames, and approximately the same quantity of erasure-coded fragments are generated from the segments storing the i-frames and from the segments storing the p-frames.
In one example, a DCT content is segmented into segments storing low frequencies and segments storing high frequencies. Optionally, all segments are approximately of the same size, and more erasure-coded fragments are generated from the segments storing the low frequencies than from the segments storing the high frequencies, where in addition, the size of the erasure-coded fragments generated from the segments storing the low frequencies is smaller than the size of the erasure-coded fragments generated from the segments storing the high frequencies. Alternatively, the segments storing the low frequencies are shorter than the segments storing the high frequencies, and approximately the same quantity of erasure-coded fragments are generated from the segments storing the low frequencies and from the segments storing the high frequencies.
In some embodiments, generating different quantities of erasure-coded fragments per different segments may provide different probabilities to recover the different segments, may require less storage space because smaller quantities of erasure-coded fragments are generated from the less important data, may provide a more efficient infrastructure for coping with peak demand, and/or may enable the fractional-storage system to operate with a lower redundancy factor because the less important data will probably be damaged first.
In one embodiment, different segments are encoded differently. For example, a video content is segmented to segments storing pixel data and segments storing audio data. Because audio data is generally more sensitive to errors than the pixel data, it may be advantageous to encode the audio-related erasure-coded fragments with a high redundancy factor. Therefore, the segments storing the audio data are encoded using rateless Raptor code while the segments storing the pixel data are encoded using fixed rate Tornado code. In another example, different objects of a Scalable Video Coding (SVC) extension of H.264/AVC/MPEG-4 Part 10 are segmented into different segments, which are encoded using different erasure codes.
In one embodiment, in order to reduce the time to play from requesting a content until the content begins playing, or the time from jumping to a specific location within the content until playing from that location, the assembling device may significantly increase its average consumption rate of erasure-coded fragments for some time, for example, 2 to 50 times higher than its steady state consumption rate of erasure-coded fragments. When many assembling devices simultaneously attempt to retrieve the same content using high consumption rate of erasure-coded fragments, some servers may become saturated because of the peak in the demand. Therefore, in one embodiment, the number of unique erasure-coded fragments a fractional-storage server can supply in such cases is increased. Moreover, in one embodiment, the erasure-coded fragments are retrieved from nearby servers in order to achieve low latency; but the nearby servers may not store sufficient unique erasure-coded fragments per the required segments. Therefore, an extra quantity of erasure-coded fragments is generated from segments expected to require the higher consumption rate of erasure-coded fragments, such as the segments at the beginning of a content, and/or segments at some predefined trick play start points. In one embodiment, the extra quantity of erasure-coded fragments is distributed among more servers. As a result, the load of retrieving the erasure-coded fragments is distributed among more servers, which in turn, weakens the peak effect.
FIG. 30 illustrates the process of generating a larger quantity of erasure-coded fragments in the vicinity of the fast start points. The content 100 is segmented into segments 251. The segments 251 that are in the vicinity of the one or more fast start points, marked in dashed lines, are encoded by the erasure encoder 252 into a larger quantity of erasure-coded fragments (illustrated by more rectangles in part 253), which may then be distributed 255 among fractional-storage servers. FIG. 31 is a schematic view of generating erasure-coded fragments from the content 100, wherein larger quantities of erasure-coded fragments are generated in the vicinity of the fast start point(s).
In some embodiments, the content is segmented into a plurality of segments to enable beginning to play the content as it is being obtained, and optionally enable trick play. The different segments may or may not be of the same size.
The following embodiments discuss different methods for segmenting the content. In one embodiment, at least one portion of the content is segmented into multiple segments in sizes within a first size range, and the remainder of the content is segmented into a plurality of segments in sizes within a second size range (additional size/s may be added similarly). The sizes included in the second size are larger than the sizes included in the first size range. Pluralities of erasure-coded fragments are generated from each of the segments. The segments of sizes within the first size range are better suited for fast retrieval, and the segments of sizes within the second size range are better suited for high-gain storage. In one example, the segments in sizes within the first size range belong to approximately the beginning of the content. In one example, the segments in sizes within the first size range belong to locations within the content requiring trick play access. In one embodiment, the segments of the first type are encoded into fewer fragments than the segments of the second type. This allows a fast retrieval of the shorter segments.
In one embodiment, a first sub-group of the servers stores segments of the first type, and a second sub-group of the servers stores segments of the second type, whereby the first and the second sub-groups may overlap. In one example, the sub-group storing the short segments comprises a large number of servers, in order to facilitate high level of availability and responsiveness.
In one embodiment, the segments of the first type are encoded with a first redundancy factor, and the segments of the second type are encoded with a second redundancy factor, where the first redundancy factor is significantly higher than the second redundancy factor. In one example, the high redundancy factor allows the fragments of the short segment to be available on a large number of servers. In one example, the fragments associated with the first type of segments are stored on a significant amount of the servers, such that an assembling device can potentially retrieve a decodable set of fragments from nearby servers.
In one embodiment, an assembling device reconstructs segments of streaming content by obtaining, from fractional-storage servers, decodable sets of erasure-coded fragments associated with the first or the second type of segments. Each type of segment requires different amount of fragments in order to be decoded. The assembling device obtains the fragments according to information describing the position of the different types of segments within the streaming content. In one example, the information contains the number of fragments needed to decode the different types of segments. In one example, content is composed of one initial short segment requiring 20 fragments for reconstruction, followed by 1,000 long segments, each requiring 200 fragments for reconstruction. The assembling devices receive information from a control server regarding the above structure, and obtain at least 20 fragments for the first segment, followed by at least 200 fragments for each additional segment.
In one example, the content 100 is a 1 GByte encoded H.264 file, storing a 2-hour motion picture, and is segmented into approximately 10,000 segments of approximately 100 Kbytes each. In another example, the content 100 is a 4 MByte web-site information (HTML, FLASH, or any other combination of information that encodes the presentation of a website), and is segmented into 4 segments of approximately 1 MByte each.
In one example, the content supports streaming presentation, and the segments are small enough to enable presentation shortly after beginning the reception of the first segment(s). For example, each segment may include 96 KByte, allowing a 5 Mbps receiver to download the segment in approximately 0.2 seconds, and optionally begin the presentation shortly thereafter. In one embodiment, the time to play is reduced by segmenting certain portions of the content into smaller segments, while the remaining portions are segmented into larger segments. A smaller segment can be retrieved faster, while a larger segment may be better optimized for storage gain and/or efficient transmission.
In one embodiment, the short segments are 96 Kbytes in size, and the long segments are 960 Kbytes in size. The redundancy factors used for encoding short and long segments into fragments are 100 and 5 respectively. 1500 Bytes fragments are used for both sizes. The short segments are therefore encoded into (96K/1500)×100=6,400 fragments, from which only about 64 are needed for reconstruction, and the long segments are encoded into (960K/1500)×5=3,200 fragments, from which only about 640 are needed for reconstruction. Short segments are reconstructed more quickly than long ones, as they require fewer fragments to be decoded. Optionally, each fragment is stored on a different server, resulting in a storage gain of 64 for short segments, and 640 for long segments.
FIG. 32 illustrates one example in which the content 100 is segmented into segments, such that the first segment 104a is smaller than the consecutive segment 104b, which is smaller than following segments 104c and 104d. In another example, the content 100 is segmented into segments, such that the first several segments (e.g. 104aa and 104bb, which are the same size), are smaller than consecutive segments (e.g. 104cc and 104dd, which are the same size).
FIG. 33 illustrates one example in which the content 100 is segmented into cyclic sets of successive segments increasing in size. For example, 105b is equal or larger in size than 105a, and so on, up to segment 105d; 105f is equal or larger in size than 105e, and so on, up to segment 105h. In one example, segment 105e is equal in size to segment 105a. Point 105EP represents the ending of the first set, and the beginning of the second set.
In some embodiments, the content is segmented according to its components and/or properties. FIG. 34 illustrates one embodiment in which a content 2800 is a compressed video file. The component comprising Intra-Coded Pictures (i-frames) 2801 and 2802 is processed as one sequence 2820 directed to a first set of segments 2820′, while the component comprising Predicted Pictures (P-Frames) and/or Bi-Predictive Pictures (B-Frames) 2811 to 2814 is processed as a separate sequence 2830 directed to a second set of segments 2830′. Since any segment and segment sequence can be decoded independently of other segments or segment sequences, the i-Frame component can be separately decoded from segment sequence 2820′, without decoding the P/B-Frames that are placed in segment sequence 2830′. In one example, i-Frame component can be decoded to present only the i-frame-related video sequence, while P/B-frames component may be obtained and decoded only when it is available.
In one embodiment, the content is compressed using Discrete Cosine Transform (DCT). The low frequencies component is directed to a first set of segments, while the higher frequencies component is directed to a second set of segments.
In one embodiment, the content is available in different compressions, sometimes known as different rates, and the different compression components are directed to different sets of segments.
In one embodiment, the content includes one or more of the following components: video pixel data, audio data, or other data such as control data, meta-data, or Internet communication. Different components may be directed to different sets of segments and/or stored on different servers. For example, different dubbing of the same movie may be stored on different segments. In one embodiment, the content is encrypted and certain encryption elements are stored in certain segments. FIG. 35 illustrates one example of a compressed multimedia file 2900 containing both video pixel data 2901 to 2903, and audio data 2911 to 2913 (the two types of data are illustrated as being interlaced, but they may also be encapsulated side by side, in a sequence, or simply be contained in two separate files or containers). The video pixel data is processed as a single component 2920 directed to a first set of segments 2920′, while the audio data is processed as a separate single component 2930 directed to a second set of segments 2930′. An assembling device needs to separately obtain and separately decode segments in order to obtain both the video pixel and audio data.
In one embodiment, the content is composed of different descriptions, in which the more descriptions received, the better the quality, as in the case of Multiple Description Coding (MDC) or Layered Coding (LC). Each description component may be encoded, stored, and/or assembled separately. For example, the different descriptions may be stored in different segments, encoded with different erasure-codes, and/or retrieved independently. FIG. 36 illustrates one example of an Audio/Video content 3000 encoded using MDC into multiple description components 3001 to 3009. The first description 3001 may be the base description, meaning that it is only necessary to obtain the base description in order to enable basic presentation of content 3000. As more descriptions are obtained, a better quality of presentation is possible, up to the maximal quality possible by obtaining all descriptions 3001 to 3009. Each description is independently segmented, such that segment sequences 3010 to 3090 correspond to descriptions 3001 to 3009 respectively. Every description may be obtained by retrieving and decoding the appropriate segment sequence.
In one embodiment, segments are created on-the-fly, such as during a live event or when the content is made available to the segmentation process as an on-going stream. In one embodiment, the content supports streaming presentation, and the segments are of the small size, to enable content presentation shortly after beginning the reception of the first segment (or any other segment). In addition, the erasure-coded fragments are kept as small as possible, while still enabling efficient transport over an IP network. For example, each erasure-coded fragment is about 1500 Bytes and can be transported using one IP packet.
It is to be noted that streaming content may also be manifested as an intermediate product of a process. For example, in a case where a video camera outputs erasure-coded fragments that can be decoded into streaming content, the intermediate data from which the erasure-coded fragments are generated is considered to be streaming content (even if the video camera does not output that intermediate data). Moreover, streaming content may include: content that is produced and then immediately transmitted to a receiving server, content that is produced but stored for any length of time before being transmitted to a receiving server, content that is transmitted to a receiving server and then immediately sent from the receiving server to a client, content that is transmitted to a receiving server, then buffered for some time at the receiving server and then sent from the receiving server to a client, content that is solely played at a client, and content that is manipulated or changed or reacted to at the client while a continuation of the content is still being played at the client.
In one embodiment, an assembling device obtains first and second sets of erasure-coded fragments from fractional-storage servers, decodes the first and second sets of fragments into a first and second set of segments belonging to a first and second components of streaming content, correspondingly, and progressively combines the first and second components, obtained from the segments, into the content. Both components include data relevant to most of the content's duration. In one embodiment, the assembling device obtains less than all sets of fragments when the servers are approximately overloaded. In one example, the assembling device decodes the first set using a first erasure-coding, and the second set using a second erasure-coding that is different from the first erasure-coding.
In one example, the first component comprises video pixel data and the second component comprises audio data. In one example, the streaming content is encoded using multiple description coding (MDC) or layered coding (LC), and the first and the second components of the content are different descriptions or layers. In one example, the streaming content is compressed video; the first component comprises Intra-Coded Pictures (i-frames), and the second component comprises Predicted Pictures (p-frames). In one example, the compressed streaming content comprises Discrete Cosine Transform (DCT); the first component comprises mainly low DCT frequencies, and the second component comprises mainly higher DCT frequencies. In one embodiment, the assembling device is located at the user premises, and the servers are fractional-storage CDN servers. In one embodiment, the assembling device is configured to obtain the fragments using a fragment pull protocol. In one embodiment, the assembling device is configured to obtain the fragments using sub-transmissions.
FIG. 37 illustrates one embodiment, wherein segment 101a of content 100 is encoded into erasure-coded fragments 390a to 390(M), such that any sufficient subset of the fragments can be used to reconstruct segment 101a. Fragments 390a to 390(N) are stored in fractional-storage servers 399a to 399(N) respectively, and fragments 390(N+1) to 390(M) are stored in streaming server 399S. In one example, fragments 390(N+1) to 390(M) form a group of fragments which are sufficient to reconstruct segment 101a. Subsequent segments 101b to 101j of content 100 may be similarly encoded into additional fragments stored on the servers (not illustrated). Assembling device 309 uses two different protocols approximately simultaneously to retrieve fragments for segment reconstruction: (i) a push protocol, and (ii) a fragment pull protocol. The push protocol 301S is used to deliver fragments 390(N+1) to 390(M) to assembling device 309. The push protocol may be RTP based or TCP-connection based, or any other type of transmission that does not require assembling device 309 to explicitly ask for each of fragments 390(N+1) to 390(M). In one example, fragments 390(N+1) to 390(M) are delivered to the assembling device using a single RTP stream 301S, such that upon reception of the fragments from the stream, the assembling device can immediately reconstruct segment 101a. The fragment pull protocol is used by the assembling device to retrieve additional fragments that may be needed to reconstruct segment 101a if one or more fragments out of fragments 390(N+1) to 390(M) fail to reach the assembling device. In one example, fragment 390(N+2) fails to reach the assembling device due to Internet packet loss conditions (referred to as fragment loss). The assembling device, after concluding that fragment 390(N+2) is missing, uses a fragment pull protocol to retrieve a substitute fragment out of one of the fractional-storage servers 390a to 390(N), and uses this fragment to complete the reconstruction of the segment 101a (any one of fragments 390a to 390(N) will do). For example, the assembling device chooses fragment 390a as the one additional fragment, by requesting and receiving it 303a from server 399a, using a fragment pull protocol. If more fragments out of fragments 390(N+1) to 390(M) fail to reach the assembling device 309, it may compensate by pulling substitute fragments from some or all of servers 399a to 399(N), illustrated as fragment pull protocol requests and responses 303a to 303(N)).
In one embodiment, the fragment pull protocol requests for additional needed fragments are not made to fractional-storage servers 399a to 399(N), but are rather made to server 399S. In this case, the assembling device asks server 399S to retransmit the fragment which has failed to arrive. In this embodiment, only fragments that fail to reach the assembling device via the push transmission 301S cause an added communication overhead in the form of explicit fragment pull protocol requests, such that if no fragments are actually lost over transmission 301S, there is no need for fragment pull requests 303a to 303(N).
In some embodiments, the push protocol is implemented using one or more sub-transmissions. Optionally, a push protocol transmission is implemented using multiple sub-transmissions, each transporting a fraction of the fragments transmitted by the push protocol transmission. A sub-transmission may be transported using an IP stream such as RTP, an HTTPS session, or any other form of transporting a sequence of fragments between a source server and a destination assembling device.
In the claims, sentences such as “wherein the assembling device is configured to use a fragment pull protocol to obtain the fragments” and “wherein the assembling device is configured to use sub-transmissions to obtain the fragments” are to be interpreted as open claim language. Therefore, an assembling device configured to use a fragment pull protocol to obtain fragments may also obtain fragments using sub-transmissions, and vice-versa.
FIG. 38 illustrates one example of geographically distributed fractional-storage servers 399a to 399n, in which servers 399a to 399c are located in Europe 676, servers 399d to 399g are located on the east coast of the US 677, servers 399h to 399i are located on the west coast of the US 678 and servers 399k to 399n are located in Japan 679. Assembling devices all over the world obtain erasure-coded fragments from the globally distributed fractional-storage servers. The characteristics of the fractional-storage system, according to some embodiments, allow the globally distributed assembling devices to exploit the outgoing bandwidth of the globally distributed fractional-storage servers approximately up to the point where all servers 399a to 399n utilize their available outgoing bandwidth for content delivery.
In one embodiment, the main demand for fragments shifts between the different global locations as the day elapses. For example, at 8 pm Pacific Standard Time, the main fragment demand is generated from the US west coast. At that time, the local time in the east coast is late evening, the time in Europe and Japan is early morning and noon respectively, and thus very little fragment demand is generated from these regions. The high fragment demand load generated from the west coast is spread across all of the fractional-storage servers. As the day elapses, the load generated from the west coast declines, and the main load shifts to Japan as time there becomes afternoon. When that happens, the servers are still able to supply all content demands, as they are still able to deliver maximal bandwidth to assembling devices in Japan. As the cycle continues, the main load shifts again from Japan to Europe, from Europe to the US east coast, and from there back to the US west coast, following a 24-hour cycle. In some embodiments, the servers are able to deliver maximal fragment traffic, resulting from peak demands occurring during a day cycle, to anywhere on the globe.
In one example, there are 14 globally distributed fractional-storage servers; each server has a bandwidth of B, and the total capacity of the array is 14×B. Assuming the total global peak demand during the daily cycle does not exceed Bg, then the system is balanced and can meet all demands during the daily cycle if Bg<14×B, meaning that B>Bg/14. In this example, all servers may be at, or may approach, their peak bandwidth capabilities for a relatively long period, and feature relatively short idle periods. In one example, the number of servers in the global array is 10,000, from which 2,500 are located on the US west coast, 2,500 on the east coast, 2,500 in Europe and 2,500 in Japan. In one example, the number of servers in the global array is 1,000, from which 100 are located on the west coast, 700 on the east coast, 100 in Europe and 100 in Japan.
In one embodiment, multiple contents originating from multiple global locations (and therefore expected to require high loads at different times of day), are all stored on the globally distributed fractional-storage servers. Therefore, the system's bandwidth capacity equals the aggregated bandwidth of its server members, optionally regardless of which content generates high load, regardless of when the load is generated during the day, and regardless of where the load is generated from.
In one embodiment, at some point in time, some portions of the Internet may become congested at some global locations. The global system assures that servers not affected by the congestion handle the excess load, such that operation close to peak bandwidth performance is still possible.
In one embodiment, the globally distributed assembling devices retrieve fragments from the fractional-storage servers using a fragment pull protocol, and determining which servers deliver fragments to which assembling devices load balances the distributed system. In one embodiment, the globally distributed assembling devices obtain fragments from fractional-storage servers using a push protocol with multiple sub-transmissions, and determining which servers deliver fragments via the sub-transmissions to which assembling devices load balances the distributed system.
FIG. 39 illustrates one embodiment in which assembling devices distributed over different time zones together induce fragment traffic having a reduced peak-to-average traffic ratio, as compared to the fragment traffic induced by assembling devices located in any single time zone. Graph 1602 illustrates the fragment traffic induced by assembling devices located at a first time zone. The peak of graph 1602 occurs during the late afternoon, local time of the first time zone. Similarly, graphs 1603 and 1604 illustrate induced traffic from second and third time zones. Since the first, second and third time zones are different, the peak traffic of each graph occurs at a different time. The peak-to-average fragment traffic ratios of graphs 1602 to 1604 are relatively high, since most of the traffic is generated close to the peak demand. In the case of video traffic, a daily peak-to-average traffic ratio of about six is expected during one day, starting at T1 and ending at T2. The combined traffic induced by all assembling devices is the sum of graphs 1602 to 1604, which is schematically illustrated as graph 1601. Since the peaks of graphs 1602 to 1604 occur at different times, the combined traffic 1601 behaves much more smoothly and has peaks close to the peaks of graphs 1602 to 1604, resulting in a much lower peak-to-average traffic ratio, which in some embodiments is about two or three. This means that the fractional-storage servers can be utilized during longer periods of the day when servicing assembling devices located at different time zones. In one embodiment, the distribution of the assembling devices to the different time zones results in an approximately flat traffic during the day, having a peak-to-average traffic ratio approaching one. Such a distribution is challenging in real life deployments, but can be approached by engineering the distribution of the assembling devices over the globe.
Still referring to FIG. 39, in one embodiment, the severs are connected to the Internet using guaranteed fixed bandwidth communication links, and can together deliver to the Internet fragment traffic of 1610 all day. In this case, it is clear that traffic graph 1601 utilizes the fixed bandwidth capacity 1610 better than any of the graphs 1602 to 1604, since it approaches the maximal capacity for longer periods over the day.
In one embodiment, the servers are spread over two or more continents, and some of the fragments associated with the same segments are stored on different servers located on different continents. This achieves content placement diversity, and results in better immunity to different network and server faults.
FIG. 40 illustrates one embodiment in which US-based fractional-storage servers 399a′ to 399n′ deliver erasure-coded fragments to assembling devices spread over the globe. The assembling devices spread over the globe induce a total fragment traffic from the US-based servers having a reduced peak-to-average traffic ratio, as compared to the fragment traffic induced by assembling devices located in any single time zone. In one example, 5,000 fractional-storage servers are located in the US and service 10 million assembling device subscribers spread over the globe. At a first period during the day, the servers deliver erasure-coded fragments concurrently to 2 million assembling devices located primarily in Japan. At a second period during the day, the servers deliver erasure-coded fragments concurrently to 2 million assembling devices located primarily in Europe. At a third period during the day, the servers deliver erasure-coded fragments concurrently to 2.5 million assembling devices located primarily on the East Coast, and 1⁄2 million assembling devices located primarily on the West Coast. At a fourth period during the day, the servers deliver erasure-coded fragments concurrently to 1⁄2 million assembling devices located primarily on the East Coast, and 2.5 million assembling devices located primarily on the West Coast. According to this example, the servers are capable of delivering a peak fragment traffic resulting from the demand of at least 3 million assembling devices concurrently.
In one embodiment, the servers are spread over different time zones. Different servers located at different time zones usually encounter peak load conditions at different times, especially if they share resources, such as communication link to the Internet, processing resources, storage, Tier-1 ISP networks, backbone networks, or any other resources with local servers delivering general Internet traffic. Load conditions may refer to actual load on the servers, load on a communications link connecting the server to the Internet, load on a local backbone or Tier-1 network, or any type of condition in which additional fragment traffic will contribute to service degradation. In the case of a load condition, it is advantageous to refrain from obtaining fragments from servers that directly contribute to the load, and to try to obtain fragments from servers that do not directly contribute to the load. Servers encountering load conditions below a certain threshold are usually found somewhere, as they are spread over different time zones, and these servers are the preferred fragment sources.
FIG. 41 illustrates one example of different loads at different times for different time zones. Graphs 641a, 641b, 641c and 641d represent load levels encountered by server groups 679, 676, 677 and 678 respectively, located in the Far East, Europe, the US east coast, and the US west coast respectively. In one example, the loads refer to traffic levels on communication links connecting the data centers, in which the servers are placed, to the Internet. In this case, the traffic may be general Internet traffic generated by servers and other application/s not necessarily related to fragment delivery, and the communication links can also be referred to as shared links, as they are used to transport both fragment traffic and general Internet traffic. During a 24-hour period, all encountered load levels complete one cycle. The load level graphs are shifted in time in respect to each other, according to the time shifts between the various time zones around the world in which the different server groups are located. As an example, graph 641a represents load encountered by the servers in the Far East, with a peak load occurring about 7 hours before graph 641b representing load encountered by the servers in Europe.
At each arbitrary point in time, server groups around the world may encounter different load conditions. As an example, at point 642a, server group 679 encounters medium load conditions, server group 676 encounters peak load conditions, and server groups 677 and 678 encounter low load conditions. Therefore, at the point in time 642a, it is beneficial for assembling devices to obtain erasure-coded fragments only from server groups 677, 678, and maybe 679. Server group 676 encounters peak load conditions, and therefore will not be approached by the assembling devices. At a different point in time 642b, the worldwide load conditions change, such that server groups 679 and 676 encounter low load conditions, and server groups 677 and 678 encounter high load conditions. At this point, assembling devices will obtain fragments from servers groups 679 and 676 and will refrain from approaching server groups 677 and 678.
In one embodiment, the load conditions encountered by each server group, or by specific servers, are published by the servers. In one embodiment, the load condition level encountered by each server is sent to each assembling device as a response to an erasure-coded fragment request.
In one embodiment, the communication link transporting fragments from a server or group of servers to the Internet is owned by a data center operator. The data center operator publishes the load condition associated with the link. The published information is used to select servers that transmit fragments via relatively unloaded links as compared to other links.
In one embodiment, the load conditions encountered by a server are detected by an outside source, such as an assembling device or a control server, using one of the following methods: (i) detecting an increased latency in responding to a request such as a fragment pull protocol request, (ii) detecting a certain level of latency variance, (iii) detecting a certain level of packet or fragment loss, and/or (iv) detecting outages in server's traffic.
FIG. 42 illustrates one embodiment of data centers communicating via shared links. Fractional-storage servers 1699a to 1699c are collocated with at least one general server 1698 in a data center 1671. All the servers are connected to the Internet via a shared communication link 1681. Therefore, erasure-coded fragment traffic transmitted by the fractional-storage servers and general Internet traffic transmitted by the general server are mixed together on the shared link 1681. Similarly, fractional-storage servers 1699d to 1699g are collocated with at least one general server 1699 in a data center 1672, and share the same communication link 1682 to the Internet. In one embodiment, the fractional-storage servers are selected for fragment transmittal when the communication link through which they transmit fragments to the Internet is loaded below a certain level. This principle is demonstrated by the following example: assuming that any three fractional-storage servers out of 1699a to 1699g store a decodable set of fragments, the three servers will be selected according to the load of the link through which they communicate. If the general server 1698 transmits a high level Internet traffic via link 1681, and this traffic is close to the maximum capacity of the link, then using any of servers 1699a to 1699c is not advisable. Instead, in a case where the general server 1699 does not create a high level traffic and link 1682 is relatively free to transport fragments, any three servers out of servers 1699d to 1699g may be used. When the fractional-storage servers deliver fragments to many assembling devices, servers transmitting via relatively unloaded links are preferred, such that the end effect is that servers 1699d to 1699g deliver a higher fragment load than servers 1699a to 1699c. In other words, servers 1699d to 1699g participate in more sub-sets of servers delivering decodable sets of fragments to assembling devices than servers 1699a to 1699c. 
In one embodiment, the data center, such as 1671 and/or 1682, is an Internet service provider connected to the Internet via a fixed bandwidth link, which is used as a shared communication link to servers transmitting general Internet traffic and fractional-storage servers transmitting fragments. In one embodiment, the data center is a colocation center, having a limited link capacity to the Internet. In one embodiment, the data center or the shared link is operated by an Internet bandwidth provider. In one embodiment, the data center is operated by an ISP.
FIG. 43 illustrates one embodiment of alternative servers communicating via shared networks. Fractional-storage servers 1699a′ to 1699c′ transmit erasure-coded fragment traffic over Internet backbone networks or Tier-1 networks 1661 and 1662. The fragment traffic and the general Internet traffic transported via the networks are mixed together on the networks. Similarly, fractional-storage servers 1699d′ to 1699g′ are connected to Internet backbone networks or Tier-1 networks 1663 and 1664. In one embodiment, the fractional-storage servers are selected for fragment transmittal when the networks through which they transmit fragments to the Internet are loaded below a certain level. This principle is demonstrated by the following example: assuming that any three fractional-storage servers out of 1699a′ to 1699g′ store a decodable set of fragments, the three servers will be selected according to the load of the network through which they communicate. If the general Internet traffic transported via networks 1661, 1662 is close to the maximal capacity of the networks, then using any of servers 1699a′ to 1699c′ is not advisable. Instead, in a case where networks 1663, 1664 are relatively unloaded with general Internet traffic, any three servers out of servers 1699d′ to 1699g′ may be used. When the fractional-storage servers deliver fragments to many assembling devices, servers transmitting via relatively unloaded networks are preferred, such that the end effect is that servers 1699d′ to 1699g′ deliver a higher fragment throughput than servers 1699a′ to 1699c′. In other words, servers 1699d′ to 1699g′ participate in more sub-sets of servers delivering decodable sets of fragments to assembling devices than servers 1699a′ to 1699c′. 
In one embodiment, after obtaining some data regarding some of the loads, availabilities, losses, costs, preferences, and/or any other data that may influence the selection of the servers, algorithms and/or theorems such as Minimax (also known as Minmax) may be used for optimizing the selections.
FIG. 44 illustrates one embodiment of fractional-storage servers 697a to 697(N), wherein each server, or a group of servers, may be owned and/or connected to the Internet in any combination and by different entities. The following 3 examples illustrate how the assembling devices balance the load on the fractional-storage servers.
In a first example, servers 697a and 697b, server 697c, and servers 697(N−1) and 697(N) are connected to the Internet 300 via first, second, and third Internet backbone operators (689a, 689b, and 689c) correspondingly. Assembling device 661, assembling a content stored in the array, can select the servers from which to retrieve regardless of its Internet backbone operator connection, and in a manner that combines erasure-coded fragments coming from different Internet backbone operators.
In a second example, assembling device 661 can select the servers regardless of the hosting ISP, and in a manner that combines fragments from several ISPs.
In a third example, servers 697a and 697b are owned by a private corporate 689a, server 697c is hosted by an ISP 689b and servers 697(N−1) and 697(N) are connected to the Internet 300 via an Internet backbone operator. Assembling device 661 can select the servers regardless of the hosting entity, and in a manner that combines fragments from servers hosted in private corporate, ISP and backbone operators.
Still referring to FIG. 44, in one example servers 697a and 697b, server 697c, and servers 697(N−1) and 697(N) are connected to the Internet 300 via first, second, and third hosting providers (689a, 689b, and 689c) correspondingly. Assembling device 661 can select the servers regardless of the hosting provider, and in a manner that combines erasure-coded fragments from several hosting providers. At any point in time, the operator of the distributed storage system can perform a cost effectiveness analysis of the hosting and data transport services provided by each hosting provider, and look for new hosting providers as candidates for replacement of one or more of the current hosting providers. If such a replacement is found, such as when a better hosting deal can be obtained, the distributed storage operator can terminate the services of such hosting provider(s), and replace it with a better deal.
In one example, if the second hosting provider 689b is found to be too expensive, it can be replaced with a fourth provider (not illustrated), while the first and third providers are still maintained, and provide service to the distributed storage system via remaining servers 697a, 697b, 697(N−1) and 697N. Server 697c will be terminated, and optionally replaced by other servers belonging to the fourth hosting provider. Optionally, the entire process is performed without affecting the streaming to the assembling device 661, or any other client groups, and no inter-server cooperation may be necessary throughout the process of replacing the hosting provider.
In the claims, a sentence such as “the erasure-coded fragments support source-selection diversity” is to be interpreted as fragments encoded using any kind of erasure-code that can produce N unique fragments, from which C combinations of decodable sets of fragments can be selected, wherein C is much greater than N. Standard parity checks, standard checksums, and standard cyclic redundancy checks (CRC) are examples of codes that do not support source-selection diversity.
In this description, numerous specific details are set forth. However, the embodiments of the invention may be practiced without some of these specific details. In other instances, well-known hardware, software, materials, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. In this description, references to “one embodiment” mean that the feature being referred to may be included in at least one embodiment of the invention. Moreover, separate references to “one embodiment” or “some embodiments” in this description do not necessarily refer to the same embodiment. Illustrated embodiments are not mutually exclusive, unless so stated and except as will be readily apparent to those of ordinary skill in the art. Thus, the invention may include any variety of combinations and/or integrations of the features of the embodiments described herein.
Although some embodiments may depict serial operations, the embodiments may perform certain operations in parallel and/or in different orders from those depicted. Moreover, the use of repeated reference numerals and/or letters in the text and/or drawings is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. The embodiments are not limited in their applications to the details of the order or sequence of steps of operation of methods, or to details of implementation of devices, set in the description, drawings, or examples. Moreover, individual blocks illustrated in the figures may be functional in nature and do not necessarily correspond to discrete hardware elements. While the methods disclosed herein have been described and shown with reference to particular steps performed in a particular order, it is understood that these steps may be combined, sub-divided, or reordered to form an equivalent method without departing from the teachings of the embodiments. Accordingly, unless specifically indicated herein, the order and grouping of the steps is not a limitation of the embodiments. Furthermore, methods and mechanisms of the embodiments will sometimes be described in singular form for clarity. However, some embodiments may include multiple iterations of a method or multiple instantiations of a mechanism unless noted otherwise. For example, when a controller or an interface are disclosed in an embodiment, the scope of the embodiment is intended to also cover the use of multiple controllers or interfaces.
Certain features of the embodiments, which may have been, for clarity, described in the context of separate embodiments, may also be provided in various combinations in a single embodiment. Conversely, various features of the embodiments, which may have been, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.
Embodiments described in conjunction with specific examples are presented by way of example, and not limitation. Moreover, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the embodiments. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope of the appended claims and their equivalents.

## Claims

1. A method comprising:
distributing erasure-coded fragment associated with segments of streaming content to fractional-storage servers, until each server stores at least one fragment and less than the minimum data required to decode the fragments;
obtaining, by an assembling device, an indication of a segment associated with the fragments that were already distributed; and
pulling fragments usable to decode the indicated segment, by the assembling device from the servers, before fragments associated with at least one following segment of the streaming content are being distributed to the servers; wherein the pulling is pulled at an average rate that essentially follows the average rate at which fragments associated with new segments of the streaming content are distributed to the servers, although the assembling device operative to have enough incoming bandwidth to pull the fragments at a rate significantly greater than the average rate.

2. The method of claim 1, wherein most of the time the assembling device requesting fragments having sizes for which the time to transmit each fragment in response to the assembling device request, through the slowest communication link connecting the responding server and the assembling device, is smaller than the round trip communication delay between the assembling device and the responding server, excluding the processing time of the responding server; and the average fractional-storage server operative to have an outgoing bandwidth of at least 10 times the incoming bandwidth of the average assembling device.

3. The method of claim 1, wherein the indication is for segments that have just been distributed, most of the time the assembling device requesting fragments having sizes for which the time to transmit each fragment in response to the assembling device request, through the slowest communication link connecting the responding server and the assembling device, is smaller than the round trip communication delay between the assembling device and the responding server, excluding the processing time of the responding server; and further comprising reconstructing the segments from the pulled erasure-coded fragments at a rate that essentially maintains a fixed distance in segments between the currently reconstructed segment and the segment whose fragments have just been distributed to the servers, although the assembling device operative to have enough incoming bandwidth and computational resources to pull and reconstruct the fragments at a rate significantly greater than the fixed distance rate.

4. The method of claim 1, wherein pulling the fragments comprises pulling the fragments at a rate that essentially follows the corresponding rate at which the streaming content is played, although the assembling device operative to have enough incoming bandwidth to pull the fragments at a rate significantly greater than the corresponding playing rate.

5. The method of claim 4, further comprising reconstructing, by the assembling device, at least a portion of the streaming content, and forwarding the portion, or a transcoded version of the portion, to a client device associated with the assembling device.

6. The method of claim 1, wherein the erasure-coding is rateless-coding.

7. An apparatus comprising:
an assembling device configured to obtain essentially concurrently from a plurality of servers erasure-coded fragments usable to reconstruct a first nonempty set of segments of streaming content, at a rate that essentially follows the rate at which the obtained fragments are being stored on the servers, although the assembling device operative to have enough incoming bandwidth to obtain the fragments at a rate significantly greater than the rate that essentially follows the rate at which the obtained fragments are being stored on the servers; and
the assembling device is further configured to obtain the fragments before fragments associated with at least one following segment of the streaming content are being stored in the servers, and to obtain from each server an amount of fragments smaller than one-hundredth of the server's fragment delivery bandwidth, such that the fragment load of the assembling device on each server is small.

8. The apparatus of claim 7, wherein the assembling device is further configured to obtain the fragments using a fragment pull protocol, each fragment pull request associated with a specific segment.

9. The apparatus of claim 8, wherein the assembling device is further configured to reconstruct the segments from the obtained fragments on-the-fly to create a broadcast-like effect.

10. The apparatus of claim 8, wherein the assembling device is configured to obtain from each server an amount of fragments smaller than one-thousandth of the server's fragment delivery bandwidth, such that the fragment load of the assembling device on each server is tiny.

11. The apparatus of claim 8, wherein the erasure-coding is rateless-coding.

12. The apparatus of claim 7, wherein the assembling device is configured to obtain the fragments using sub-transmissions.

13. The apparatus of claim 12, wherein the assembling device is configured to obtain from each server an amount of fragments smaller than one-thousandth of the server's fragment delivery bandwidth, such that the fragment load of the assembling device on each server is tiny; and the erasure-coding is rateless-coding.

14. An apparatus comprising:
an assembling device configured to receive an indication of allowance to obtain, essentially concurrently from a plurality of servers, erasure-coded fragments associated with a first segment of streaming content;
the assembling device is further configured to obtain fragments associated with subsequent segments as the access to the segments is allowed essentially sequentially as time progresses and to reconstruct segments from the obtained fragments at an average rate that essentially follows the average rate at which the segments are allowed to be accessed, although the associated fragments of the first segment and the subsequent segments are pre-stored on the servers, and although the assembling device operative to have enough incoming bandwidth to obtain the fragments at a rate significantly greater than the allowance rate.

15. The apparatus of claim 14, wherein the assembling device is further configured to obtain the fragments using a fragment pull protocol, each fragment pull request associated with an indicated segment.

16. The apparatus of claim 15, wherein the assembling device is configured to obtain from each server an amount of fragments smaller than one-thousandth of the server's fragment delivery bandwidth, such that the fragment load of the assembling device on each server is tiny.

17. The apparatus of claim 16, wherein the first reconstructed segments of the streaming content are played before the last segments are allowed to be accessed, and the rate at which the subsequent segments are allowed to be accessed essentially follows the rate at which segments are being used for continuous playing of the streaming content.

18. The apparatus of claim 14, wherein the assembling device is configured to obtain the fragments using sub-transmissions.

19. The apparatus of claim 14, wherein the first segment is the most recent segment to which access was allowed out of all of the segments of the streaming content, and the fragments associated with the first segment are obtained shortly after access to the first segment is allowed; the assembling device is further configured to reconstruct the first segment and provide a playable stream of the first segment shortly after it is obtained.