Patent Description:
<CIT> describes a communication link where a first transceiver transmits a first set of packets at a predetermined rate with a first error resistance level and, on receiving a retransmission request, retransmits the relevant data using one or more packets encoded with a second error resistance level that is higher than the first error resistance level. A second transceiver receives the packets and forwards the data received in the packets according to its original order after a fixed delay. Another example of a transceiver configured to indicate delays added to packets due to retransmission events, is disclosed by the document <CIT>.

In one embodiment, a transceiver configured to indicate delays added to packets due to retransmission events, includes: a first scheduler, memory, a retransmission module, a second scheduler, a delay indicator module, and a physical layer module; the first scheduler is configured to receive multiple packet streams, multiplex them into a first multiplexed packet stream, and to add time indications; the memory is configured to store the first multiplexed packet stream together with time indications; the retransmission module is configured to receive a retransmission request and to select data for retransmission; the second scheduler is configured to receive the first multiplexed packet stream and the data for retransmission, and to multiplex them into a second multiplexed packet stream; the delay indicator module is configured to utilize the time indications to calculate delays added to packets of the second multiplexed packet stream as a result of fulfilling the retransmission request in order to achieve an approximately fixed transmission latency with latency variation below <NUM> microseconds; the delay indicator module is further configured to add the calculated delays to at least some of the packets of the second multiplexed packet stream; and the physical layer module is configured to transmit the second multiplexed packet stream.

In another embodiment, a method for indicating delays added to packets due to retransmission events, includes: receiving multiple packet streams and multiplexing them into a first multiplexed packet stream; storing in memory the first multiplexed packet stream together with time indications; receiving a retransmission request and selecting data for retransmission; multiplexing the first multiplexed packet stream and the data for retransmission into a second multiplexed packet stream; utilizing the time indications for calculating delays that were added to packets of the second multiplexed packet stream as a result of fulfilling the retransmission request in order to achieve an approximately fixed transmission latency with latency variation below <NUM> microseconds; adding the calculated delays to at least some of the packets of the second multiplexed packet stream; and transmitting the second multiplexed packet stream.

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> illustrates one embodiment of retransmitting a packet whose header and tail feature a higher error resistance than its payload. Certain types of packets (#<NUM>, #<NUM>, #<NUM>, #<NUM>) of a first transmission are encoded to have a packet error rate much worse than the target packet error rate, while the retransmitted packets are encoded such that their packet error rate is approximately equal to or better than the target packet error rate. The source <NUM> sends packets to sink <NUM> at a predetermined rate. The source <NUM> stores the data transmitted through the packets for a period of time approximately equal to or longer than the round trip delay. The sink <NUM> receives the packets, checks the received packets for errors and/or missing packets, and requests retransmission of the erroneous packets (where erroneous packets also include the missing packets). Meanwhile, the source <NUM> continues to send packets at the predetermined rate, and sends the next packet(s) (in this example, packet #<NUM>), until it retransmits the erroneous packet (in this example, packet #<NUM>). Optionally, the payload of the retransmitted packet #<NUM>' is encoded using error resistance higher than the error resistance of packet #<NUM>, in order to ensure that no additional retransmissions will be required. After sending packet #<NUM>' to replace the erroneous packet #<NUM>, the source <NUM> sends the next unsent packet #<NUM> according to the original order. On the receiving side, the sink <NUM> maintains the original order of the data by replacing the payload of the erroneous packet #<NUM> in buffer <NUM> with the payload of the retransmitted packet #<NUM>'.

Different sections of the packet may feature different error resistances as a result of implementing different encoding schemes, as discussed, for example, in <CIT>. Alternatively, different sections of the packet may feature different error resistances as a result of implementing Forward Error Correction (FEC) techniques.

In one example, the communication link illustrated in <FIG> is used to transmit HDMI signals. In order to exploit the link to its maximum extent, the first set of packets delivers the HDMI data with a packet error rate of 1e-<NUM> and CRC-<NUM>, and the retransmitted packets are delivered with a packet error rate of 1e-<NUM>, which is better than the packet error rate of 1e-<NUM> required by the HDMI standard.

<FIG> is a flow diagram illustrating one method for operating a communication link close to its maximum capacity while maintaining the original order of transmitted data. The method comprises the following steps: In step <NUM> transmitting at least one stream of data at a predetermined rate; the transmitted data featuring a first error resistance level. In step <NUM>, storing the received data in a buffer. In step <NUM>, requesting data retransmission upon detection of an error. In step <NUM>, retransmitting the data with a second error resistance level that is higher than the first error resistance level. And in step <NUM>, inserting the retransmitted data into the proper location in the buffer so as to maintain the original order of the data. In one embodiment, the method is operated over each hop of a network that maintains the original order of the data and features a short and approximately fixed latency with latency variation below <NUM> microseconds (usec). In one embodiment, the detected error includes a missing packet error, and further comprising identifying the missing packet using a packet identification code that is assigned according to a predefined series of codes. In one embodiment, the stream comprises time-sensitive data, and the method ensures approximately fixed latency with latency variation below <NUM> usec.

<FIG> illustrates a network that implements the method illustrated by <FIG> over each hop. Thus, the entire network maintains the order of the transmitted packets, and requests for retransmissions are responded to using packets with improved error resistance and, for the most part, without adversely affecting the original streams transmitted from the sources <NUM> and <NUM>. Optionally, the sources <NUM> and <NUM> transmit the original streams approximately according to a fixed transmission rate. Optionally, the network approximately ensures a fixed latency with latency variation below <NUM> usec. Optionally, the sources <NUM> and <NUM> receive the data from end devices that do not support retransmission.

In one embodiment, the switches <NUM>, <NUM>, and <NUM> of the network illustrated in <FIG> comprise buffers and therefore the network can operate well with legacy end devices <NUM>, <NUM>, <NUM>, and <NUM> that do not support retransmission. In this embodiment the total latency of the network may also be reduced when retransmission is not required over at least one of the hops.

<FIG> illustrates one embodiment of source and sink devices supporting retransmissions and fixed delay for at least some of the streams. On the source side, the source's scheduler <NUM> receives a first stream to be protected by the retransmission mechanism (marked by a solid line) and a second stream that is not to be protected by the retransmission mechanism (marked by a dashed line). The source's retransmission module <NUM> optionally adds additional packet identification data to the first stream packets in order to identify their sequential order, and then stores a section of the first stream in the source's buffer <NUM>. The first and second streams are transmitted by the source's physical layer component <NUM> over the link <NUM>, and are received on the sink side by the receiver's physical layer component <NUM>. The receiver's retransmission module <NUM> forwards the packets of the second stream to the receiver's scheduler <NUM>, with or without a CRC check, and forwards the packets of the first stream to the receiver's buffer <NUM>. Upon detection of a CRC error in a first stream packet, or detection of a missing packet, optionally based on a gap in the additional packet identification data, the receiver's retransmission module <NUM> sends a proper retransmission request to the source. The source's retransmission module <NUM> extracts the required packet from the source's buffer <NUM>, re-encodes the packet to feature a better error resistance, and sends the retransmitted packet to the sink. In order to maintain the original order of the packets, the receiver uses the receiver's buffer <NUM> to introduce latency on all protected packets, proper or erroneous, and the receiver's retransmission module <NUM> inserts the retransmitted packet into its original position in the receiver's buffer <NUM>. After the required latency period passes, the packets from the receiver's buffer <NUM> are forwarded to the receiver's scheduler <NUM>.

In one embodiment, the communication link illustrated in <FIG> carries multimedia signals. The video pixel data is protected by retransmissions, while latency sensitive data that does not have to be synchronized to the video pixel data is transmitted over the second stream that is not to be protected by the retransmission mechanism, and therefore without the fixed delay. In this case, neither the transmitter, nor the receiver needs to store the unprotected packets in the retransmission buffer. In one embodiment, the retransmission protection mechanism is not required because the unprotected data types are transmitted using a much higher error resistance level, such as lower PAM, than the initial protected packets. For example, link control messages and video DDC signals and may be transmitted with a high error resistance and without the retransmission mechanism.

In one embodiment, a first video stream is protected by the retransmission mechanism and a second video stream is not protected by the retransmission mechanism. Therefore, the unprotected video stream features a shorter link delay than the protected video stream. In one embodiment, the maximal link delay determines the maximum number of retransmissions, which determines the amount of traffic to be protected by the retransmission mechanism.

There are cases where it is necessary to utilize a communication channel approximately to its maximum capacity, while maintaining the order of the transmitted packets and a fixed and short latency. In order to utilize the communication channel approximately to its maximum capability, the data cannot be protected only by Forward Error Correction (FEC) code, which consumes extra bandwidth when the interference over the communication link cannot be accurately predicted. Therefore, erroneous packets that cannot be corrected by the optional FEC code have to be retransmitted. And in order to maintain the order of the transmitted packets and a fixed and short latency, the retransmitted packets should be requested as soon as the receiver identifies an error in a received packet, and/or identifies a missing packet.

In one embodiment, a communication link comprises first and second transceivers. The first transceiver transmits a first set of packets at a predetermined rate with a first error resistance level and stores the transmitted data in a buffer. The second transceiver receives the first set of packets, checks the packets for errors, and upon detecting an erroneous packet, requests retransmission of the erroneous packet. The first transceiver receives the retransmission request and retransmits the relevant data using one or more packets encoded with a second error resistance level that is higher than the first error resistance level. Then the second transceiver forwards the data received in the packets according to its original order approximately after a fixed delay. In one embodiment, the average throughput and maximum burst of the retransmissions are controlled such as not to over a predefined amount, not to overload the link, not to interfere with the proper transmission of the first set of packets, to bring the maximal throughput of the transmissions of the first set of packets and the retransmitted packets to the maximum capacity of the communication link, and/or not to increase the delay above a certain value. The retransmissions may be controlled by the first transceiver, the second transceiver, and/or any other appropriate element. In one embodiment, the retransmitted packets are transmitted with a priority higher than the priority of the first set of packets. Retransmitting the packets with a higher priority may reduce the latency of the communication link by shortening the time between requesting a retransmission and receiving the retransmitted packet. The embodiments may be implemented over a variety of mediums, such as a wired medium, a wireless medium, or an optical medium. Moreover, the embodiments may be used to create a network that ensures an approximately fixed latency with latency variation below <NUM> usec. Such a network may also operate well with end devices that do not support retransmission.

In one embodiment, a receiver comprises a packet buffer coupled to a packet processing element. The packet buffer stores the received packets and the packet processing element detects erroneous packets and sends a retransmission request upon detection of an erroneous packet. Optionally, the packets include a packet identification code that is assigned according to a predefined series of codes and the packet processing element identifies the missing packets by comparing the packet identification codes of the received packets with the expected packet identification codes of the series. When receiving the retransmitted packet, the packet processing element maintains the original order of the packets by inserting the retransmitted packet to its proper location.

In one embodiment, a network switch includes multiple transceivers supporting packet retransmissions with a higher error resistance than the initial transmitted packet. The retransmissions are initiated by the receiver side and a network comprising at least two links and at least one such switch maintains the original order of the packets and features a short and approximately fixed latency with latency variation below <NUM> usec. In one embodiment, the network carries one or more main streams, and the maximum amount of retransmitted packets is determined so as not to interfere with the proper transmission of the main streams. In one embodiment, the network's latency is reduced by retransmitting the packets with a priority higher than the priority of most of the initial transmitted packets.

<FIG> illustrates one embodiment of a transceiver <NUM> configured to indicate delays added to packets due to retransmission events. The transceiver <NUM> includes at least a first scheduler <NUM>, memory <NUM>, a retransmission module <NUM>, a second scheduler <NUM>, a delay indicator module <NUM>, and a physical layer module <NUM>.

The first scheduler <NUM> receives one or more packet streams (denoted Str #<NUM>, Str #<NUM>, Str #<NUM>); the packet streams may be received, for example, from input ports or from processes running in the transceiver. The first scheduler <NUM> multiplexes the received packet streams (Str #<NUM>, Str #<NUM>, Str #<NUM>) into a first multiplexed packet stream 7a, and adds time indications for at least some of the packets. The memory <NUM> receives and stores the first multiplexed packet stream 7a and its corresponding time indications.

The retransmission module <NUM> receives retransmission requests <NUM> and selects data for retransmissions. Optionally, the retransmission requests <NUM> are received from a second transceiver that communicates with the transceiver <NUM> over a communication link, such as a wired communication link. The retransmission requests <NUM> are received for data that was already transmitted by the transceiver to the second transceiver.

The second scheduler <NUM> receives the first multiplexed packet stream 7a and the data for retransmission 7b, and multiplexes them into a second multiplexed packet stream 7c. The second scheduler <NUM> may also receive link management data <NUM> and multiplex it into the second multiplexed packet stream 7c. Examples of link management data <NUM> include self-initiated retransmissions, link management packets, and known data used for learning and maintaining the communication link.

The delay indicator module <NUM> utilizes the time indications to calculate the delays added to packets of the second multiplexed packet stream 7c as a result of fulfilling the retransmission request. In one example, the time indications are a function of the local clock of transceiver <NUM>, and the delay indicator module <NUM> calculates the delay that is added to a packet that belongs to the second multiplexed packet stream 7c by subtracting the current local clock time from the time indication associated with that certain packet. The delay indicator module <NUM> adds the calculated delays to at least some of the packets of the second multiplexed packet stream. In one example, the delay indicator module <NUM> adds the calculated delays to all the packets of the second multiplexed packet stream. In another example, the delay indicator module <NUM> adds the calculated delays only to some of the packets of the second multiplexed packet stream, such as only to packets for which the calculated delay exceeds a predetermined threshold. In still another example, the calculated delay accounts for the time from receiving a packet at the first scheduler until it is forwarded to the physical layer for transmission. Then the physical layer module <NUM> transmits the second multiplexed packet stream to the second transceiver, optionally over a wired communication link.

Optionally, the transceiver <NUM> transmits to the second transceiver payloads of packets that were not retransmitted using a first error resistance level, and transmits to the second transceiver payloads containing retransmitted data using a second error resistance level. The second error resistance level is higher than the first error resistance level in order to reduce the probability for another retransmission. In some cases the second error resistance level is strong enough to ensure that a single retransmission is enough to transmit successfully the retransmitted data.

In one optional embodiment, the second transceiver receives the packets from the transceiver, transmits the non-retransmitted packets after a fixed delay with a first error resistance level to a third transceiver over a wired communication link, stores the payloads in a second memory, receives a second retransmission request for a second payload that is included in the payloads stored in the second memory, and retransmits the second payload using a second retransmission packet encoded with a second error resistance level that is higher than the first error resistance level. Optionally, the second error resistance level may be strong enough to ensure that a single retransmission is enough for transmitting successfully the second payload.

Optionally, the clocks of the transceiver and the second transceiver are not synchronized, and the second transceiver uses the calculated delays, which are stored in the packets it receives, to adjust the order and idle durations between the packets it receives in order to compensate for at least some of the delays incurred as a result of the a retransmission event at the transceiver <NUM>.

Optionally, the memory <NUM> is a shared memory, and the data for retransmission is selected from the first multiplexed packet stream stored in the memory.

<FIG> illustrates one embodiment of a transceiver <NUM> having at least two memories. The transceiver <NUM> includes at least: a first scheduler <NUM> similar to the first scheduler <NUM>; a buffer <NUM> that stores the first multiplexed packet stream 8a while waiting for transmission; a retransmission memory <NUM> that stores the already transmitted packet 8d while waiting for possible retransmission; a retransmission module <NUM> that receives remote retransmission requests <NUM>, may issue local retransmission requests <NUM>, and selects the data to be retransmitted from the retransmission memory <NUM> using command line <NUM>; a second scheduler <NUM> that is similar to the second scheduler <NUM>; a delay indicator module <NUM> that is similar to the delay indicator module <NUM>; and a physical layer module <NUM> that is similar to the physical layer module <NUM>.

The second scheduler (<NUM>, <NUM>) may further receive link management packets, and multiplex them into the second multiplexed packet stream. Link management packets are packets generated by the transceiver for operating the link, such as a request for a retransmission issued by the transceiver, link control massages, massages for learning the link properties, and massages for handling interferences.

Optionally, the first scheduler, the retransmission module, the second scheduler, and the delay indicator module are implemented using one or more processors. Optionally, the retransmission module and the memory are designed to support multi retransmission events for the same data. Alternatively, the retransmission module and the memory are designed to support just a single retransmission event for the same data. Optionally, the physical layer module is an HDBaseT® physical layer module, and the second multiplexed packet stream is an HDBaseT® stream.

In one embodiment, the transceiver (<NUM>, <NUM>) is incorporated in a network switch that supports retransmissions having latency variation below <NUM> usec. The transceiver <NUM> may be connected through a second switch to a sink device, such as a device that displays video that is streamed through the switch transceiver <NUM>. Optionally, the retransmission module <NUM> may add additional packet identification data to the packet stream in order to identify the sequential order of the packets.

<FIG> illustrates one embodiment of a method for indicating delays added to packets due to retransmission events. The method includes the following steps: In step <NUM>, receiving, by a transceiver, multiple packet streams and multiplexing them into a first multiplexed packet stream. In step <NUM>, storing in memory the first multiplexed packet stream together with time indications. In step <NUM>, receiving a retransmission request and selecting data for retransmission. In step <NUM>, multiplexing the first multiplexed packet stream and the data for retransmission into a second multiplexed packet stream. In step <NUM>, utilizing the time indications for calculating the delays that were added to packets of the second multiplexed packet stream as a result of fulfilling the retransmission request. In step <NUM>, adding the calculated delay to at least some of the packets of the second multiplexed packet stream. And in step <NUM> transmitting by the transceiver the second multiplexed packet stream. Optionally, the retransmission request is received from a second transceiver to which the data for retransmission was already transmitted by the transceiver. Optionally, the memory is a shared memory, and the data for retransmission is selected from the first multiplexed packet stream stored in the memory. And optionally, the method may further include receiving link management packets, and multiplexing them into the second multiplexed packet stream.

Herein, a predetermined value, such as a predetermined confidence level or a predetermined threshold, is a fixed value and/or a value determined any time before performing a calculation that compares a certain value with the predetermined value. A value is also considered to be a predetermined value when the logic, used to determine whether a threshold that utilizes the value is reached, is known before start of performing computations to determine whether the threshold is reached.

In this description, references to "one embodiment" (and its variations) mean that the feature being referred to may be included in at least one embodiment of the invention. Moreover, separate references to "one embodiment", "some embodiments", "another embodiment", and "still another embodiment" may refer to the same embodiment, may illustrate different aspects of an embodiment, and/or may refer to different embodiments.

The embodiments of 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 order of steps of the methods, or to details of implementation of the devices, set in the description, drawings, or examples. Moreover, individual blocks illustrated in the figures may be functional in nature and therefore may not necessarily correspond to discrete hardware elements. In the claims, the terms "first", "second" and so forth are to be interpreted merely as ordinal designations, and shall not be limited in themselves.

Claim 1:
A transceiver (<NUM>) configured to indicate delays added to packets due to retransmission events, comprising:
a first scheduler (<NUM>), memory (<NUM>), a retransmission module (<NUM>), a second scheduler (<NUM>), a delay indicator module (<NUM>), and a physical layer module (<NUM>);
the first scheduler (<NUM>) is configured to receive packet streams, multiplex the packet streams into a first multiplexed packet stream, and to add time indications;
the memory (<NUM>) is configured to store the first multiplexed packet stream together with the time indications;
the retransmission module (<NUM>) is configured to receive a retransmission request (<NUM>) and to select data for retransmission;
the second scheduler (<NUM>) is configured to receive the first multiplexed packet stream and
the data for retransmission, and to multiplex the first multiplexed packet stream and the data for retransmission into a second multiplexed packet stream;
the delay indicator module (<NUM>) is configured to utilize the time indications to calculate delays added to packets of the second multiplexed packet stream, as a result of fulfilling the retransmission request, in order to achieve an approximately fixed transmission latency with latency variation below <NUM> microseconds;
the delay indicator module (<NUM>) is further configured to add the calculated delays to at least some of the packets of the second multiplexed packet stream; and
the physical layer module (<NUM>) is configured to transmit the second multiplexed packet stream.