# Patent

## Title
Apparatus and method for transmitting data to a network based on retransmission requests

## Abstract

An apparatus for transmitting to a network comprises a queue, packetization logic, interface logic, and queue logic. The packetization logic is configured to packetize data into a plurality of data packets and to store, to the queue, entries pointing to the data packets. The interface logic is configured to read the entries from the queue. The interface logic, for each of the read entries, is configured to retrieve one of the packets pointed to by the read entry and to transmit the retrieved packet to a network socket. The queue logic is configured to limit, based on a number of retransmission requests detected by the queue logic, a number of entries that the packetization logic may store to the queue during a particular time period thereby controlling a transmission rate of the apparatus.

## Background
RELATED ART
In some communication systems, such as networked graphical rendering systems, for example, large amounts of data are transmitted from a transmitting unit through a network to at least one receiving unit. For example, a graphics application at a transmitting unit may transmit graphical data to at least one remote receiving unit that renders the graphical data to form a rendered image. In such a system, communication of large amounts of graphical data at a relatively high transmission rate may be needed in order to provide a suitable frame rate for the rendered image.
Performance of a system's transmitting and receiving units in transmitting data to and receiving data from a network is typically an important factor in whether graphical data can be successfully rendered via a remote receiving unit at suitable frame rates. Unfortunately, achieving a suitable transmission rate for the data communicated from the transmitting unit to the receiving unit or units can sometimes be problematic, particularly in instances where a large number of receiving units are to receive the graphical data. In such situations, the transmitting unit may be configured to transmit each graphics command multiple times through the network (e.g., once for each destination receiving unit that is to receive the command). The multiple transmissions of the graphics commands can significantly increase the amount of data that is to be communicated through the network.
SUMMARY OF THE INVENTION
Thus, better techniques for communicating with a network to achieve a higher network throughput are generally desirable. Generally, embodiments of the present invention pertain to an apparatus and method for transmitting data to a network based on retransmission requests.
An exemplary apparatus in accordance with one embodiment of the present invention comprises a queue, packetization logic, interface logic, and queue logic. The packetization logic is configured to packetize data into a plurality of data packets and to store, to the queue, entries pointing to the data packets. The interface logic is configured to read the entries from the queue. The interface logic, for each of the read entries, is configured to retrieve one of the packets pointed to by the read entry and to transmit the retrieved packet to a network socket. The queue logic is configured to limit, based on a number of retransmission requests detected by the queue logic, a number of entries that the packetization logic may store to the queue during a particular time period thereby controlling a transmission rate of the apparatus.
An exemplary method in accordance with another embodiment of the present invention comprises storing, to a queue within a transmitting apparatus, entries pointing to data packets, reading the entries from the queue, transmitting, based on the entries read from the queue, the data packets to a network socket, and controlling a number of the entries stored to the queue during a particular time period such that a rate at which the apparatus receives retransmission requests from at least one receiving apparatus remains within a specified range.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the invention. Furthermore, like reference numerals designate corresponding parts throughout the several views.
FIG. 1 is a block diagram illustrating an exemplary embodiment of a communication system in accordance with the present invention.
FIG. 2 is a block diagram illustrating an exemplary communication session, such as is depicted in FIG. 1.
FIG. 3 is a block diagram illustrating an exemplary pointer entry, such as is depicted in FIG. 2.
FIG. 4 is a block diagram illustrating an exemplary computer system that may be employed to implement a transmitting unit, such as is depicted in FIG. 1.
FIG. 5 is a block diagram illustrating an exemplary data packet that may be communicated by a communication system, such as is depicted in FIG. 1.
FIG. 6 is a block diagram illustrating an exemplary receiving unit, such as is depicted in FIG. 1.
FIG. 7 is a block diagram illustrating an exemplary receiver, such as is depicted in FIG. 6.
FIG. 8 is a block diagram illustrating an exemplary pointer entry, such as is depicted in FIG. 7.
FIG. 9 is a block diagram illustrating an exemplary computer system that may be employed to implement a receiving unit, such as is depicted in FIG. 7.
FIG. 10 is a flow chart illustrating an exemplary architecture and functionality of queue logic, such as is depicted in FIG. 2.
FIG. 11 is a flow chart illustrating an exemplary architecture and functionality of packet delivery logic, such as is depicted in FIG. 7.



DETAILED DESCRIPTION
FIG. 1 depicts a communication system 100 in accordance with an exemplary embodiment of the present invention. As shown by FIG. 1, the system 100 comprises a transmitting apparatus or unit 111 that is configured to transmit data packets through a network 114 to at least one receiving apparatus or unit 117 via a packet transfer protocol, such as internet protocol (IP), for example. Although other types of data may be communicated by the system 100, the system 100 will be described hereafter, for illustrative purposes, as communicating graphical data from the transmitting unit 111 to the receiving units 117 such that components of the receiving units 117 may render such graphical data.
As shown by FIG. 1, the transmitting unit 111 preferably comprises a graphics application 121 that produces graphical data according to known or future-developed techniques. Buffer logic 124 within the transmitting unit 111 stores the graphical data into blocks 126 of memory 128, referred to as “buffers.” A process, referred to hereafter as the “communication session 139,” retrieves the graphical data from the buffer 126 and packetizes the retrieved data, thereby forming a plurality of data packets for transmission across the network 114 to at least one receiving unit 117. Exemplary techniques for storing to and retrieving from the buffers 126 are described in co-pending and commonly-assigned U.S. patent application entitled “Data Buffering Apparatus and Method,” and filed on Feb. 8, 2003, which is incorporated herein by reference.
In a preferred embodiment, the communication session 139 enables the data packets to be selectively transmitted via one of a plurality of transport protocols. As an example, in an embodiment that will be described in more detail hereafter, the communication session 139 enables each packet to be selectively transmitted via user datagram protocol-multicast (UDPM) or transmission control protocol (TCP). However, it should be emphasized that the communication session 139 may enable the data packets to be transmitted via other types of transport protocols in other embodiments.
In the embodiment shown by FIG. 2, the communication session 139 comprises packetization logic 145 that is configured to retrieve graphical data from the buffers 126 of FIG. 1. Packetization logic 145 within the session 139 shown by FIG. 2 then packetizes the retrieved data into a plurality of data packets for transmission to the network 114 (FIG. 1). Depending on the type of transport protocol employed for the transmission of the data packets to the receiving units 117, it may be desirable to retransmit various ones of the data packets (e.g., data packets that are lost during transmission through the network 114) in response to retransmission requests from the receiving units 117.
As an example, UDPM is a type of transport protocol that does not guarantee the successful arrival of a transmitted packet at its destination. For such protocols, the packetization logic 145 is preferably configured to temporarily store, into a block 132 of memory 128, a copy of each data packet packetized by the packetization logic 145. As will be described in more detail hereafter, the packets stored in the memory blocks 132 may be used to retransmit data packets in response to retransmission requests generated by the receiving units 117. If a data packet is to be communicated from the transmitting unit 111 via another transport protocol, such as TCP, for example, that guarantees successful arrival of the packet at its destination, then the packetization logic 145 may be configured to transmit the packet to the network interface 148 without writing the packet to a memory block 132.
As shown by FIG. 2, the network interface 148 comprises a network protocol layer 151 and a network interface card (NIC) 152. The network protocol layer 151 is preferably configured to interface data packets with the network 114 via various transport protocols and to enable the packetization logic 145 or other component of the session 139 to select which type of transport protocol is to be used to communicate a particular packet through the network 114. The NIC 152 preferably comprises various hardware components (not shown) for interfacing data with the network 114. For each packet to be interfaced with the network 114, the network protocol layer 151 drives the packet through the NIC 152 to the network 114.
Specifically, in the exemplary embodiments described herein, the network protocol layer comprises a UDPM socket 154 and a TCP socket 156. The UDPM socket 154 is configured to communicate data packets through the NIC 152 and to the network 114 using UDPM. Moreover, by writing a data packet to the UDPM socket 154, the data packet is ultimately communicated through the network 114 to each of a specified set of receiving units 117. However, the UDPM socket 154 and NIC 152 do not ensure that the data packet is successfully received by each of the specified receiving units 117.
The TCP socket 156, on the other hand, is configured to communicate data packets through the NIC 152 and to the network 114 using TCP. Thus, each data packet written to the TCP socket 156 is communicated to a specified receiving unit 117, and the TCP socket 156 and NIC 152 ensure that the data packet successfully arrives at and is received by the specified receiving unit 117.
It should be noted that there are various techniques that may be employed by the transmitting unit 111 to interface data packets with the network interface 148. In an exemplary embodiment shown by FIGS. 1 and 2, the memory blocks 132 are pre-allocated, and the communication session 139 comprises a packet pointer pool 149 storing a plurality of packet pointer entries 157 that point to the memory blocks 132. In this regard, each pointer entry 157 in the packet pointer pool 149 preferably points to an available one of the memory blocks 132 (i.e., one of the memory blocks 132 that may be written to without corrupting data within the memory block 132). Initially, all of the memory blocks 132 are available, and the packet pointer pool 149 comprises a pointer entry 157 for each of the memory blocks 132. However, when a memory block 132 is written to, as will be described in more detail hereinbelow, the pointer entry 157 associated with (i.e., pointing to) this memory block 132 is pulled from the pool 149 and is not returned until the associated memory block 132 is again available. Thus, the entries 157 of the packet pointer pool 149 may be analyzed to determine to which of the memory blocks 132 may be written.
Note that it is not necessary for the blocks 157 to be pre-allocated. In this regard, it is possible for the packetization logic 145 to dynamically allocate a memory block 132 and an associated pointer entry 157 for each packet generated by the packetization logic 145. However, the allocation of memory blocks 132 and packet pointer entries 157 consumes time and processing resources, potentially slowing the rate at which the packetization logic 145 can process data packets. Thus, pre-allocating memory blocks 132 and pointer entries 157 helps to improve the performance of the packetization logic 145 by eliminating the step of dynamically allocating memory for the data packetized by the packetization logic 145.
For each TCP packet packetized by the packetization logic 145, the logic 145 writes the TCP packet to the TCP socket 156. The TCP socket 156 then communicates the packet to its intended destination over network 114 via known or future-developed TCP techniques.
For each UDPM packet packetized by the packetization logic 145, the logic 145 pulls one of the pointer entries 157 from the packet pointer pool 149 and stores the data defining the packet to the memory block 132 pointed to by the pulled entry 157. The packetization logic 145 also stores the sequence indicator 161 of the foregoing packet into the pulled entry 157 and writes the pulled pointer entry 157 to an input port 158 of an ordered queue 159. As shown by FIG. 3, each pointer entry 157 preferably comprises a sequence indicator 161 that uniquely identifies the corresponding packet (i.e., the packet pointed to by the entry 157) and a pointer 162 that points to the memory block 132 where the corresponding packet is stored.
Queue logic 163 generally controls when data packets may be input and output from the queue 159. Except when servicing a retransmission request, as will be described in more detail hereinbelow, the queue logic 163 outputs the pointer entries 157, via a UDPM output port 164, in the same order that such entries are input to the queue 159 via the input port 158. For each pointer entry 157 output via the UDPM output port 164, UDPM interface logic 165 reads the pointer entry 157 and retrieves the packet stored at the memory block 132 identified by the pointer 162 of the pointer entry 157. The interface logic 165 then writes the retrieved data packet to the UDPM socket 154 of the network protocol layer 151. As described above, this socket 154 drives the data packet through the NIC 152 to the network 114, which transmits the data packet to a specified set of receiving units 117 according to UDPM communication techniques.
When a pointer entry 157 is output via the UDPM output port 164 and read by the interface logic 165, the queue logic 163 preferably retains the pointer entry 157 in the queue 159 until it can be ensured that a retransmission request for the entry's corresponding packet will not be received from one of the receiving units 117. Once it can be ensured the such a retransmission request will not be received, the queue logic 163 classifies the entry 157 as “expired.” Further, the queue logic 163 is configured to return each expired entry 157 to the packet pointer pool 149. Returning an expired entry 157 to the packet pointer pool 149 has the effect of freeing the memory block 132 pointed to by the expired entry 157. In this regard, once an entry 157 is returned to the pointer pool 149, the entry 157 may be pulled by the packetization logic 145, and the corresponding memory block 132 may be used by the packetization logic 145 to store another data packet that is packetized by the logic 145.
During operation, the receiving units 117 may generate retransmission requests for missing or lost UDPM data packets (e.g., packets that do not arrive at their destination receiving units 117). Each such retransmission requests identifies the missing or lost data packet or packets (e.g., includes data indicating the sequence indicators 161 of the lost or missing packets) and are transmitted back to the transmitting unit 111, which retransmits the identified missing or lost data packets in response to the retransmission requests. In addition, each receiving unit 117 may also periodically generate an acknowledgment that it has successfully received a particular packet. For example, a receiving unit 117 may generate an acknowledgement for each 50th data packet successfully received by receiving unit 117 although other numbers of successfully received data packets may trigger an acknowledgment in other embodiments. The acknowledgments, like the retransmission requests, identify the data packet at issue (e.g., include the sequence indicator 161 of the received data packet) and are received by the transmitting unit 111.
Each acknowledgement and retransmission request received by the transmitting unit 111 is preferably provided to the queue logic 163. For each retransmission request, the queue logic 163 outputs, from the queue 159, the entry 157 corresponding to the packet identified by the retransmission request. If the retransmission is to occur via UDPM, the queue logic 163 outputs the foregoing entry 157 via UDPM output port 164. As a result, the UDPM interface logic 165 reads the foregoing entry 157 and, in response, retrieves the packet pointed to by the entry's pointer 162 (FIG. 3). The interface logic 165 then writes the retrieved packet to the UDPM socket 154, which communicates the retrieved packet across the network 114 via UDPM.
However, if the aforementioned retransmission of a missing or lost UDPM data packet is to occur via TCP, then the queue logic 163 outputs the foregoing entry 157 via a TCP output port 173 to TCP interface logic 175. The TCP interface logic 175 is configured to retrieve the packet pointed to by each entry 157 output from the TCP output port 173 and to write the retrieved packet to the TCP socket 156, which communicates each such packet over network 114 via TCP. Thus, the packet pointed to by the aforementioned entry 157 output from the TCP port 173 in response to the retransmission request is transmitted over network 114 via TCP rather than UDPM.
Furthermore, for each retransmission request and acknowledgment received by the queue logic 163, the queue logic 163 assumes that each of the data packets transmitted from the transmitting unit 111 prior to the packet or packets identified by the received acknowledgment or retransmission request has been successfully received by its destination receiving unit or units 117. Thus, the queue logic 163 classifies the entries 157 corresponding to the earlier transmitted packets (i.e., the packets transmitted prior to the packet or packets identified by the acknowledgment or retransmission request) as expired, and the logic 163 returns these expired entries 157 to the packet pointer pool 149. Thus, the packetization logic 145 may use the memory blocks 132 pointed to by these expired entries 157 to store future data packets packetized by the logic 145.
The queue logic 163 may also be used to control the transmission rate of the session 139 such that a more optimum rate is achieved. In this regard, it is generally desirable to have the session 139 communicate at higher rates in an effort to increase throughput. However, it is possible for the transmission rate to be set at a level substantially higher than the rate at which the receiving units 117 can successfully receive packets. In such a situation, a large number of retransmission requests may be generated thereby increasing the amount of traffic communicated between the transmitting unit 111 and the receiving units 117. Thus, decreasing the transmission rate of the session 139 may actually increase throughput by reducing the number of retransmission requests generated by the receiving units 117.
In an exemplary embodiment, the queue logic 163 is configured to enable the packetization logic 145 to periodically insert only a limited number of entries 157 into the queue 159 in order to control the transmission rate of the session 139. As an example, the queue logic 163 may be configured to enable the packetization logic 145, every three-hundred (300) micro-seconds (or some other time period), to buffer, for transmission over network 114, up to one-hundred (100) pending entries 157 (or some other maximum number of pending entries 157) in the queue 159 at a time. As used herein, a “pending entry” refers to an entry 157 that has been inserted into the queue 159 but has yet to output from the queue 159. Note that the maximum number of pending entries 157 that may be buffered by the queue 159 preferably does not include any entries 157 that have been previously output from the queue 159 and are being retained in the queue 159 for the purposes of servicing retransmission requests. Thus, regardless of the number of entries 157 that the packetization logic 145 is ready to insert in the queue 159, the logic 145 is enabled, by the queue logic 163, to insert a limited number of entries 157 within the queue 159 during a particular time period.
Moreover, by controlling the maximum number of entries 157 that may be periodically inserted by the packetization logic 145, the queue logic 163 can control the transmission rate of the session 139. In this regard, to determine whether to change the transmission rate of the session 139, the queue logic 163 can count the number of retransmission requests that are received during a particular time period and compare this count to an upper threshold (“THH”). Note that THH is preferably established such that it is generally desirable to reduce the transmission rate of the session 139 when THH is exceeded in order to reduce the number of retransmission requests that are occurring. Thus, if the count exceeds THH, the queue logic 163 may be configured to decrease the maximum number of pending entries 157 that may be buffered by the queue 159. The foregoing has the effect of enabling less data packets to be transmitted during a particular time period thereby decreasing the transmission rate of the session 139.
Conversely, to determine whether to increase the transmission rate of the session 139, the queue logic 163 can compare the number of retransmission requests that are received during a particular time period to a lower threshold (“THL”). Note that THL is preferably established such that it is generally desirable to increase the transmission rate of the session 139 when the count falls below THL. Such a situation arises when the number of retransmission requests is low enough to indicate that the transmission rate of the session 139 can be increased without generating an unacceptable number of retransmission requests. Thus, if the count falls below THL, the queue logic 163 may be configured to increase the maximum number of pending entries 157 that may be buffered by the queue 159. The foregoing has the effect of enabling more data packets to be transmitted during a particular time period thereby increasing the transmission rate of the session 139. Note that levels of THH and THL are design choices based upon retransmission rate tolerance.
It should be noted that the graphics application 121, network interface 148, and each set of logic 124, 145, 163, 165, and 175 depicted by FIGS. 1 and 2 may be implemented in hardware, software, or any combination thereof. In an exemplary embodiment illustrated by way of example in FIG. 4, the graphics application 121 and buffer logic 124 are implemented in software and run on an operating system (OS) thread 166 of a computer system 168. Furthermore, the network protocol layer 151 and each set of logic 145, 163, 165, and 175 are implemented in software and run on an OS thread 167 that is separate from the OS thread 166.
Note that any portion of the graphics application 121, network protocol layer 151, and the logic 124, 145, 163, 165, and 175 when implemented in software, can be stored and transported on any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch and execute instructions. In the context of this document, a “computer-readable medium” can be any means that can contain, store, communicate, propagate, or transport a program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable-medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. Note that the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.
As shown by FIG. 4, the computer system 168 comprises memory 128 that stores the software components of the transmitting unit 111. The system 168 further comprises at least one conventional processing element 170, such as a digital signal processor (DSP) or a central processing unit (CPU), that communicates to and drives the other elements within the system 168 via a local interface 171, which can comprise one or more buses. Furthermore, an input device 172, for example, a keyboard or a mouse, can be used to input data from a user of the system 163, and an output device 174, for example, a screen display or a printer, can be used to output data to the user.
Note that having the graphics application 121 and the software components of the communication session 139 run on separate OS threads 166 and 167 can help to improve the performance of the graphics application 121. In such an embodiment, the OS thread 166 running the graphics application 121 is not burdened with the tasks of interfacing, with the network 114, the graphical data produced by the application 121 once such data has been written to the buffers 126 (FIG. 1). Thus, the tasks of interfacing the graphical data with the network 114 do not usurp substantial processing resources from the graphics application 121, enabling the graphics application 121 to be processed at a relatively fast rate even when the session 139 is burdened with interfacing a large amount of data with the network 114.
As shown by FIG. 5, each data packet 177 transmitted by the transmitting unit 111 of FIG. 1 comprises a data portion 181 and a header 183. The header 183 may comprise various control information that can be used to control the transmission of the data packet 177 through the network 114 (FIG. 1) to its intended destination. The header 183 also preferably comprises a retransmission indicator 185 indicating whether or not the data packet 177 is a retransmission of a packet previously transmitted to the network 114 by the transmitting unit 111. In addition, the header 183 preferably comprises the packet's sequence indicator 161, which is indicative of the data packet's position within a sequence of packets transmitted by the transmitting unit 111. The header 183 also preferably comprises a value, referred to as a “packet count 187.” Utilization of the retransmission indicator 183, the sequence indicator 185, and the packet count 187 will be described in more detail hereinbelow.
Each packet transmitted by the transmitting unit 111 to the network 114 is preferably routed, by the network 114, to the receiving unit 117 associated with an address included in the header 183 of the packet. As shown by FIG. 6, each receiving unit 117 comprises at least one receiver 201 for receiving data packets from the network 114. Each receiver 201 preferably writes the data portion 181 of each received packet into a block 205 of memory 206, referred to as a “buffer 205.” In this regard, each packet having data from the same buffer 126 of FIG. 1, is preferably stored to the same buffer 205 of FIG. 6.
To achieve the foregoing, the packetization logic 145 of FIG. 2 may be configured to determine the total number of packets used to transmit the data retrieved from a particular buffer 126 (FIG. 1), and the logic 145 may be configured to store this value in the header 183 (FIG. 5) of each such packet as the packet count 187. Further, the transmitting unit 111 is preferably configured to consecutively transmit each such packet to the receiving unit 117. Thus, by analyzing the packet counts 187 of the packets, the receiver 201 can identify each packet that comprises data from the particular buffer 126. In this regard, upon receiving the first packet comprising data from the particular buffer, the receiver 201 can determine that the next y number of consecutively received data packets also comprise data from the particular buffer 126, where “y” corresponds to a value one less than the value of the packet count 187. Thus, the receiver 201 may store the data of each such packet into the same buffer 205.
Buffer logic 208 preferably retrieves the data stored in the buffers 205 and provides this data to other devices at the receiving unit 117. In the instant example where graphical data is packetized at the transmitting unit 111 of FIG. 1 and transmitted to the receiving unit 117 shown by FIG. 6, each set of buffer logic 208 corresponds to and communicates with a rendering element 211, as shown by FIG. 6. Further, each set of buffer logic 208 retrieves, from the buffers 205, graphical data that is to be rendered by its corresponding rendering element 211, and the corresponding rendering element 211 then renders such data according to known or future-developed techniques.
As shown by FIG. 7, each receiver 201 preferably comprises a network interface 215 that receives data packets from the network 114 of FIG. 1. The network interface 215 of FIG. 7 comprises a network protocol layer 217 and a network interface card (NIC) 219, which may comprise various hardware components (not shown) for communicating data with the network 114. The network protocol layer 217 preferably enables communication with the network 114 via various transport protocols, as will be described in more detail hereafter.
In an exemplary embodiment shown by FIGS. 6 and 7, the memory blocks 213 are pre-allocated, and each receiver 201 comprises a packet pointer pool 221 that stores a plurality of packet pointer entries 228 that point to the memory blocks 213 of FIG. 6. In this regard, as shown by FIG. 8, each pointer entry 228 in the packet pointer pool 221 preferably has a pointer 232 that points to an available one of the memory blocks 213 (i.e., one of the memory blocks 213 that may be written to without corrupting data in the memory block 213). Initially, all of the memory blocks 213 are available, and the packet pointer pool 221 comprises a pointer entry 228 for each of the memory blocks 213. However, when a memory block 213 is written to, as will be described in more detail hereinbelow, the pointer entry 228 associated with (i.e., pointing to) this memory block 213 is pulled from the pool 221 and is not returned until the associated memory block 213 is again available. Thus, the entries 228 of the packet pointer pool 221 may be analyzed to determine which of the memory blocks 213 may be written to.
Note that it is not necessary for the blocks 213 to be pre-allocated. In this regard, it is possible for the receive logic 224 to dynamically allocate a memory block 213 and an associated pointer entry 228 for each packet received by the receive logic 224. However, the allocation of memory blocks 213 and packet pointer entries 228 consumes time and processing resources potentially slowing the rate at which the receive logic 224 can process data packets. Furthermore, slowing the packet processing rate of the receive logic 224 can increase the number of lost data packets thereby resulting in a higher number of retransmission requests that can significantly degrade the performance of the communication system 100. Thus, pre-allocating memory blocks 213 within the pool 221 helps to improve the performance of the receive logic 224 and of the system 100 as a whole.
When the receive logic 224 receives a packet from the network interface 215, the logic 224 pulls an entry 228 from the packet pointer pool 221 and stores the data packet to the memory block 213 pointed to by the pointer 232 of the pulled entry 228. In addition, the receive logic 224 stores the sequence indicator 161 of the received packet into the pulled entry 228 and writes the pulled entry 228 to an input port 230 of an ordered queue 222. The receive logic 224 also transmits the sequence indicator 161 and the retransmission indicator 185 of the received packet to flow control logic 225, which will be described in more detail hereinbelow.
As shown by FIG. 7, the queue 222 comprises an output port 226 from which packet delivery logic 227 reads or pulls pointer entries 228 from the queue 222. For each such entry 228 pulled or read from the queue 222, the packet delivery logic 227 retrieves the packet stored at the memory block 213 pointed to by the entry's pointer 232 and writes this data to buffers 205 (FIG. 6). As described above, the packet delivery logic 227 preferably writes, to the same buffer 205, the data portion 181 (FIG. 5) of each packet comprising data retrieved from the same buffer 126 of FIG. 1. Furthermore, after pulling or reading an entry 228 from the queue 222, the packet delivery logic 227 preferably returns the entry 228 to the packet pointer-pool 221. The foregoing has the effect of freeing the memory block 213 identified by the returned entry 228 such that the receive logic 224 may write data from a newly received packet into the identified memory block 213 after pulling the returned entry 228 from the pool 221.
Note that the queue logic 229 preferably orders the entries 228 within the queue 222, based on their sequence indicators 161, such that the sequence indicators 161 of the entries 228 output from the queue 222 are in the same sequence or sequential order as the sequence indicators 161 of the packets transmitted from the transmitting unit 111. Thus, the packet delivery logic 227 stores, to the buffers 205, the data packets in the same sequence or sequential order that the packets were transmitted from the, transmitting unit 111.
In an exemplary embodiment, the packetization logic 145 (FIG. 2) may control or assign the sequence indicators 161 such that the sequence indicator 161 of each packet packetized by the packetization logic 145 is incremented relative to the preceding packet. Further, the logic 145, except when retransmitting a packet in response to a retransmission request, generally transmits packets in the same order that they were packetized by the logic 145. Thus, in general, the difference between the sequence indicators 161 of two data packets consecutively transmitted by the transmitting unit 111 is one (1) unless one of the packets is a retransmission in response to a retransmission request. Accordingly, the queue logic 229 may be configured to order the queue's output such that the next entry 228 output via the output port 226 has a sequence indicator 161 that is one higher than the sequence indicator 161 of the last entry 228 output from this port 226. If the entry 228 having the next sequential indicator 161, as compared to the last entry 228 output from the queue 222, is not yet in the queue 222, then the queue logic 229 preferably waits on this entry 228 until it arrives in the queue 222 before outputting another entry 228. Once the entry 228 having the next sequential indicator 161 arrives in the queue 222, the queue logic 229 writes this entry 228 to the output port 226.
Further, if a new entry 228 is not output via the write port 226 when the packet delivery logic 227 is ready to pull or read a new entry 228 from the queue 222, the packet delivery logic 227 may stall or, in other words, wait until a new entry 228 appears in the output port 226. Thus, if the entry 228 having the next sequential indicator 161 is not in the queue 222 when the packet delivery logic 227 is ready to pull or read a new entry 228 from the queue 222, then the packet delivery logic 227 stalls. Note that an absence of such an entry 228 from the queue 222 generally indicates that the corresponding packet (i.e., the packet pointed to by the entry's pointer 232) is missing or, in other words, has yet to be received by the receiver 201.
Once the missing packet is received thereby prompting the insertion, into the queue 222, of the entry 228 having the next sequential indicator 161, the queue logic 229 outputs the entry 228 via the queue's output port 226, as described above. The packet delivery logic 227 then ends its stall and reads the entry 228 from the output port 226. Upon reading the foregoing entry 228 from the queue 222, the packet delivery element 227 retrieves the corresponding data packet, which is stored in the memory block 213 identified by the entry's pointer 232. The packet delivery logic 227 then stores the data portion 181 (FIG. 5) of this packet in one of the buffers 205 (FIG. 6).
As described above, the receive logic 224 provides, to the flow control logic 225, the retransmission indicator 185 and sequence indictor 161 of each packet stored in the pool 221. Similarly, the packet delivery logic 227 preferably transmits, to the flow control logic 225, the sequence indicator 161 of each entry 228 pulled or read from the queue 222 and, therefore, the sequence indicator 161 of each packet retrieved by the delivery logic 227. Based on the values provided by the receive logic 224 and packet delivery logic 227, the flow control logic 225 may track which packets have been received by the receiver 201 and, more specifically, determine whether there are any packets missing from the packets received by the receiver 201, as will be described in more detail below.
In this regard, the flow control logic 225 may detect a missing packet by determining when the sequence indicators 161 of two consecutive data packets processed by the receive logic 224 are not consecutive. For example, if a set of three consecutively received data packets have sequence indicators 161 corresponding to the values of “10,” “11,” and “12,” then the flow control logic 225 determines that there are no missing data packets between the first and last packets of the set. In particular, the sequence indicator 161 of each consecutive data packet is incremented relative to the sequence indicator 161 of the preceding packet received before it. However, if the set of sequence indicators 161 instead corresponds to the values of “10,” “11”, and “13,” then the flow control logic 225 preferably detects that the packet having a sequence indicator 161 corresponding to “12” is missing.
Moreover, the flow control logic 225 preferably maintains a list 233 of missing data packets. In this regard, for each missing data packet detected by the flow control logic 225, the logic 225 adds the sequence identifier 161 of the missing data packet to the list 233. Once a missing data packet is received by the logic 224, the flow control logic 225 removes the sequence indicator 161 of this packet from the list 233. Therefore, the list 233 identifies each missing data packet detected by the flow control logic 225 until such data packet is received by the receive logic 224. For each missing data packet identified by the list 233, the flow control logic 225 determines when a retransmission request for the missing data packet is to be generated and then communicates such a retransmission request to the transmitting unit 111. Exemplary techniques for determining when to communicate retransmission requests are described in co-pending and commonly-assigned U.S. patent application entitled “Apparatus and Method for Receiving Data from a Network,” and filed on Feb. 8, 2003, which is incorporated herein by reference.
When the transmitting unit 111 receives the aforementioned retransmission request, the transmitting unit 111 retrieves a copy of the missing data packet from one of the memory blocks 132 (FIG. 1) and initiates a retransmission of the missing data packet according to the transport protocol requested by the retransmission request. In this regard, the queue logic 163 (FIG. 2) finds the entry 157 within the queue 159 corresponding with the missing packet. Note that the retransmission request preferably comprises the sequence indictor 161 of the missing packet, and the queue logic 263 finds the entry 157 having the same sequence indicator 161.
If the retransmission of the missing data packet is to occur via UDPM, the queue logic 163 outputs the forgoing entry 157 via UDPM output port 164. In turn, the UDPM interface logic 165 retrieves the missing data packet from the memory block 132 identified by the entry 157 and retransmits this data packet. In particular, the UDPM interface logic 165 writes this data packet to the UDPM socket 154, which drives the data packet through the NIC 152 to the network 114. The network 114 then communicates the retransmitted packet to the UDPM socket 220, and the receive logic 224 reads and processes the retransmitted packet according to the techniques described herein. In particular, the receive logic 224 pulls an entry 228 from the packet pointer pool 221 and writes the packet to the memory block 213 identified by the pulled entry 228. The receive logic 224 then inserts the pulled entry 228 into the queue 222 for processing according to the techniques described herein.
However, if the retransmission of the missing data packet is to occur via TCP, the queue logic 163 outputs the forgoing entry 157 via the TCP output port 173 instead of the UDPM output port 164. In turn, the TCP interface logic 175 retrieves the missing data packet from the memory block 132 identified by the entry 157 and retransmits this data packet. In particular, the TCP interface logic 175 writes this data packet to the TCP socket 156, which drives the data packet through the NIC 152 to the network 114. The network 114 then communicates the retransmitted packet to the TCP socket 223, and the flow control logic 225 reads the retransmitted packet from the TCP socket 223. In this regard, the flow control logic 225 pulls an entry 228 from the packet pointer pool 221 and writes the packet to the memory block 213 identified by the pulled entry 228. The flow control logic 225 then inserts the pulled entry 228 into the queue 222 for processing according to the techniques described herein.
Note that by having the flow control logic 225 read TCP packets from the TCP socket 223 and the receive logic 224 read UDPM packets from the UDPM socket 220 it is not necessary for the receive logic 224 to switch between reading the UDPM socket 220, and the TCP socket 223. Thus, inefficiencies and latencies pertaining to switching between reading the UDPM socket 220 and the TCP socket 223 are preferably not incurred by the receive logic 224, helping the receive logic 224 to read packets from the UDPM socket 220 at a more efficient rate.
It should be noted that the network interface 215 and each set of logic 208, 224, 225, 227, and 229 depicted by FIGS. 6 and 7 may be implemented in hardware, software, or any combination thereof. In an exemplary embodiment illustrated by way of example in FIG. 9, the network protocol layer 217 and each set of logic 208, 224, 225, 227, and 229, along with their associated methodology, are implemented in software and stored in memory 206 of a computer system 243. Note that any portion of the network protocol layer 217 and the logic 208, 224, 224, 227, and 229, when implemented in software, can be stored and transported on a computer-readable medium.
As shown by FIG. 9, the computer system 243 comprises at least one conventional processing element 246, such as a digital signal processor (DSP) or a central processing unit (CPU), that communicates to and drives the other elements within the system 243 via a local interface 248, which can comprise one or more buses. Furthermore, an input device 252, for example, a keyboard or a mouse, can be used to input data from a user of the system 243, and an output device 254, for example, a screen display or a printer, can be used to output data to the user.
In addition, as shown by FIG. 9, in order to increase the rate at which packets can be successfully received, the network protocol layer 217 and receive logic 224 preferably run on an operating system (OS) thread 271, and the other software components of the receiver 201 preferably run on at least one different OS thread 274. In particular, the buffer logic 208, flow control logic 225, and packet delivery logic 227 run on OS thread 274 in the embodiment shown by FIG. 9. As a result, the OS thread 271 is not burdened with the tasks of performed by such components but rather is dedicated to tasks for receiving data packets from the network 114 and storing such packets into the packet pool 221. Therefore, the receive logic 224 is able to process data packets at a faster rate thereby decreasing the number of data packets that are lost or, in other words, not successfully received by the receiver 201. The foregoing has the effect of reducing retransmission requests thereby reducing the communication burdens of the system 100.
It should be noted that there may be times when the packet delivery logic 227 is stalled for a significant amount of time despite the efforts described herein for enhancing the communication efficiency of the system 20. For example, successful retransmission of a missing packet to the receiver 201 may be significantly delayed such that the packet delivery logic 227 is stalled for a significant amount of time. In another example, a graphics application 121 may temporarily stop producing data for a significant amount of time causing the queue 222 to empty. Thus, the packet delivery logic 227 may stall until the application 121 resumes and begins to produce graphical data again so that the receive logic 224 begins to receive packets and insert pointer entries 228 into the queue 222.
When the packet delivery logic 227 is stalled, it may be desirable to put the logic 227 to sleep in order to prevent the logic 227 from needlessly consuming the processing resources of the receiver 201. Such an effect can be achieved by submitting a blocking call to the OS thread 274 (FIG. 9) that is running the packet delivery logic 227. As an example, for a Posix-based OS thread, a “select” call may be made in order to put a component, such as the packet delivery logic 227, to sleep. Once the queue 222 outputs an entry 228 to be read by the packet delivery logic 227, the OS thread 274 may be configured to awaken the logic 227 such that the logic 227 resumes its normal operation. However, there is a latency associated with putting the logic 227 to sleep and awakening the logic 227. Further, transitioning of the packet control logic 227 into and out of sleep states consumes processing resources of the receiver 201. It is possible for the cost of putting the packet delivery logic 227 to sleep, as described above, may outweigh the benefits of such an action, particularly when the logic 227 would be put to sleep only for a relatively short amount of time.
Thus, in one exemplary embodiment, the packet delivery logic 227 is preferably configured to remain awake for at least a short amount of time after a stall is initiated. In this regard, as shown by FIG. 7, the packet delivery logic 227 may comprise a timer 278 that may be used to track time in accordance with known or future-developed techniques. The packet delivery logic 227 is configured to activate the timer 278 in response to a stall of the logic 227 in order to determine when a predefined amount of time has elapsed since initiation of the stall. If a new entry 228 is ready to be pulled or read from the queue 222 prior to expiration of the predefined amount of time, then the packet delivery logic 227 is preferably configured to read and process the entry 228, as described above, without entering into a sleep state. However, if no such entry 228 becomes available prior to expiration of the predefined amount of time, then the packet delivery logic 227 is preferably configured to enter into a sleep state. By waiting for expiration of the predefined amount of time before entering into a sleep state, the packet delivery logic 227 is prevented from entering into a sleep state when there is only a short delay in the output of a new entry 228 by the queue 222.
Furthermore, before actually entering into a sleep state, the packet delivery logic 227 preferably notifies the queue logic 229 of its intent to go to sleep. In response to such a notification, the queue logic 229 determines whether the queue 222 has recently received any entries 228 that are about to be output via output port 226. The queue logic 229 then notifies the packet delivery logic 227 whether any such entries 228 exist. If any such entries 228 do exist, then the packet delivery logic 227 preferably refrains from entering a sleep state since any such sleep state would last only for a short amount of time. In this regard, if the packet delivery logic 227 entered into a sleep state, the logic 227 would be awakened a short time later in order to read and process the aforementioned entry 228 that is about to be output from the queue 222. In such a situation, any benefits associated with entering the sleep state would likely be outweighed by the costs of causing the packet delivery logic 227 to transition into and out of the sleep state.
Alternatively, if the queue logic 229 informs the packet delivery logic 227 that it has detected no entries 228 that are about to be output from the queue 222, then the packet delivery logic 227 preferably enters into a sleep state thereby preventing the logic 227 from needlessly usurping the processing resources of the receiver 201. Due to the aforementioned notification previously transmitted from the packet delivery logic 227 to the queue logic 229, the queue logic 229 is aware of when the packet delivery logic 227 enters into a sleep state. In this regard, the packet delivery logic 227 enters into a sleep state when the logic 227 submits a notification of its intent to enter into a sleep state and the when the queue logic 229 responds with an indication that it has detected no entries 228 that are about to be output from the queue 222.
Moreover, when the packet delivery logic 227 enters a sleep state, the queue logic 229 is preferably configured to awaken the packet delivery logic 227 when the queue logic 229 detects an entry 228 that is about to be output from the queue 222. For example, the queue logic 229 may awaken the packet delivery logic 227 when the logic 229 detects the next entry 228 that is to be output from the queue 222. By providing the packet delivery logic 227 with advanced notice that a new entry 228 is about to be output from the queue 227, the transition of the packet delivery logic 227 from a sleep state to an active state may begin before the new entry 228 is output from the queue 222. Thus, the packet delivery logic 227 may be ready to read this new entry 228 sooner than would otherwise be possible had the advanced notice of the entry 228 not been provided by the queue logic 229. By having the packet delivery logic 227 transition into and out of sleep states according to the aforedescribed techniques, the overhead associated with periodically putting the packet delivery logic 227 to sleep in response to stalls of the logic 227 can be reduced thereby helping to improve the efficiency of the receiver 201.
Note that the techniques described above for transitioning the packet delivery logic 227 into and out of sleep states may be employed to transition the interface logic 165 (FIG. 2) into and out of sleep states as well. In this regard, the interface logic 165 may be configured to enter into a sleep state a predefined amount of time after a stall of the interface logic 165 is initiated due to the absence of a new entry 157 to be pulled or read from the queue 159. However, before entering into a sleep state, the logic 165 may first notify the queue logic 163. If the queue logic 163 detects no entries 157 that are about to be output from the queue 159, then the interface logic 165 may enter into a sleep state. Once the interface logic 165 enters a sleep state, the queue logic 163 may be configured to awaken the interface logic 165 in response to a detection of an entry 157 that is about to be output from the queue 159. Thus, the same techniques used to reduce the overhead associated with putting the packet delivery logic 227 of the receiver 201 to sleep may also be employed to reduce the overhead associated with putting the interface logic 165 of the transmitting unit 111 to sleep.
An exemplary use and operation of the communication system 100 and associated methodology are described hereafter.
Assume that the transmitting device 111 of FIG. 1 is configured to transmit graphical data via a sequence of n data packets to a plurality of receivers 201, referred to hereafter as “destination receivers,” residing within a plurality of remote receiving units 117, where “n” is any positive integer number. Furthermore, assume that, except in certain circumstances when retransmitting a missing data packet, the transmitting device 111 and network 114 are configured to transmit the foregoing packets via UDPM, although other types of protocols may be employed in other embodiments.
In the instant example, the graphics application 121 produces graphical data, which is temporarily stored into buffers 126 by buffering logic 124. The communication session 139 retrieves this graphical data from the buffer 126, and the packetization logic 145 packetizes this retrieved data into the data packets that are to be communicated to the receiving units 117.
When packetizing the graphical data, the packetization logic 145 preferably sets the retransmission indicator 185 of each resulting packet to indicate that the packet is not a retransmission but is rather an original transmission of the data contained in the data portion 181. For illustrative purposes, each retransmission indicator is a one-bit value, which is asserted only when its data packet is a retransmission. In such an example, the packetization logic 145 deasserts the retransmission indicator 185 of each of the foregoing packets to be transmitted from the transmitting unit 111.
The packetization logic 145 also sets the sequence indicators 161 of the data packets based on the transmission sequence of the data packets. For illustrative purposes, the packetization logic 145 sets the sequence indicator 161 of the first transmitted packet of the sequence to a value of one (1) and sets the sequence indicator of each consecutively transmitted packet to a successively higher integer value. Thus, the sequence indicator 161 of the second packet of this example is set to two (2), and the sequence indicator 161 of the third packet is set to three (3). Further, the sequence indicator 161 of the fourth packet is set of four (4), and so on.
In order to effectuate transmission of each of the data packets, the packetization logic 145 pulls a pointer entry 157 from the packet pointer pool 149 and writes the packet to the memory block 132 pointed to by the pulled entry 157. In packetizing the data packet, the logic 145 assigns a sequence indicator 161 to the packet and stores this sequence indicator 161 in the packet's header 183 (FIG. 5) as well as in the pulled entry 157. The packetization logic 145 then inserts the pulled entry 157 into the queue 159. In this regard, the packetization logic 145 inserts the entries 157 into the queue 159 such that the data packets are transmitted in the sequential order described above. Noting that the packets are generally transmitted in the same order that corresponding entries 157 (i.e., entries having the same sequence indicator 161) are inserted into the queue 159, the packetization logic 145 inserts the entries 157 into the queue 159 such that the sequence indicators 162 of consecutively inserted entries 157 have successively higher values. Thus, continuing with the instant example, the sequence indicator 161 of the first entry 157 inserted into the queue 159 is one (1), and the sequence indicator 161 of the second entry 157 inserted into the queue 159 is two (2). Further, the sequence indicator 161 of the third entry 157 inserted into the queue 159 is three (3), and so on.
In an effort to set the transmission of the transmitting unit 111 to a more desirable rate, the queue logic 163 preferably limits the number of pending entries 157 that may be stored in the queue 159 during a particular time period. For example, assume that the queue logic 163 is initially configured to enable the packetization logic 145 to insert, into the queue 159, up to one-hundred (100) pending entries 157 every three-hundred (300) micro-seconds. In such an example, as shown by block 281 of FIG. 10, the queue logic 159 initializes a threshold, referred to hereafter as the “entry threshold,” to one-hundred (100), which corresponds to the maximum number of pending entries 157 that may be stored in the queue 159 at any given time until the entry threshold is later changed. For illustrative purposes, each consecutive three-hundred (300) micro-second time period will be referred to hereafter as a “transmission period.”
During the first transmission period, the queue logic 163 enables the packetization logic 145 to insert entries 157 into the queue 159 until the number of pending entries 157 in the queue 159 reaches the entry threshold, as shown by block 284. Once this occurs, the queue logic 163 disables the packetization logic 145 from inserting any more entries 157, at this point, even if the packetization logic 145 has more entries 157 to insert. As an example, assume that the packetization logic 145 initially has two-hundred (200) entries 157 to insert the queue 159. In such an example, the packetization logic 145, during the first period, is enabled to insert the first one-hundred five (100) of these entries 157 into the queue 159.
After the foregoing entries 157 are inserted into the queue 159, the queue logic 163 begins outputting the entries 157 in the same order that they were received by the queue 159. Thus, in block 286, the queue logic 163 writes, to the output port 164, the next pending entry 157 to be output from the queue 159. While this entry 157 is being read by the UDPM interface logic 165, the queue logic 163 determines whether any acknowledgments or retransmission requests have been received, as shown by decision block 288. If any such messages (i.e., acknowledgments or retransmission requests) have been received, then the queue logic 163 may expire one or more entries 157 based on the received acknowledgment or retransmission request, as shown by block 289. In this regard, an acknowledgement or retransmission request preferably comprises data indicative of the sequence indicator or indicators 161 of the packet or packets at issue. Further, the queue logic 159 may assume that any packet transmitted prior to a packet identified by a received acknowledgement or retransmission request has been successfully received by the prior packet's destination if a retransmission request for such a prior packet has yet to be received. Thus, the queue logic 163 preferably expires each entry 157 having a sequence indicator 161 corresponding to any such prior transmitted packet. The queue logic 163 returns each expired packet 157 to the packet pointer pool 149.
As shown by block 291, the queue logic 163 preferably services any retransmission request detected in block 288. In this regard, for such a request, the queue logic 163 finds, in the queue 159, the entry 157 corresponding to (e.g., having the same sequence indicator 161 as) the requested packet. The queue logic 163 then outputs this entry 157 to one of the output ports 164 or 173 depending on the type of protocol that is to be used to retransmit the requested packet. In response, the requested packet is retrieved and retransmitted.
As shown by decision block 293, the queue logic 163 determines whether there are any pending entries 157 to be output from the queue 159. If there are any such entries 157, the queue logic 163 determines whether the current transmission period has expired in block 295. If not, the queue logic 163 repeats blocks 286, 288, 293, and, if appropriate, blocks 289 and 291. However, if the current transmission period has expired, the queue logic 163 proceeds to block 296, which will be described in more detail hereinbelow.
If the queue logic 163 determines, in decision block 293, that there are no pending entries 157 to be output from the queue 159, the queue logic 163 proceeds to block 298 and determines whether the current transmission period has expired. If not, the queue logic 163 determines whether any new acknowledgments or retransmission requests have been received from the receiving units 117. If so, the queue logic 163 expires entries 157 in block 301 and services any new retransmission request in block 302 via the same techniques described above for blocks 289 and 291.
If the queue logic 163 determines, in decision block 295 or 298, that the current transmission period has expired, then the logic 163 determines, in block 296, the total number of retransmission requests that were received during the just expired transmission period. As shown by decision block 305 and block 306, the queue logic 163 increases the entry threshold if the total number of retransmission requests falls below THL. Further, as shown by decision block 308 and block 309, the queue logic 163 decreases the entry threshold if the total number of retransmission requests exceeds THH. After adjusting the entry threshold in blocks 306 or 309, if appropriate, the queue logic 163 proceeds to block 284 and repeats the aforedescribed process such that additional entries 157 can be inserted into the queue 159 thereby initiating the transmission of more data packets.
By implementing the aforedescribed process shown by FIG. 10, the queue logic 163 adjusts the transmission rate of the session 139 such that a more optimum transmission rate is achieved. In particular, if the current transmission rate of the session 139 induces a large number of retransmission requests, then the queue logic 163 may decrease the transmission rate by decreasing the entry threshold thereby reducing the number of retransmission requests that will be generated. Further, if the current transmission rate of the session 139 induces a small number of retransmission requests, then the queue logic 163 may increase the transmission rate of the session 139 by increasing the entry threshold.
As each destination receiver 201 receives the aforementioned data packets, the data packets are written to memory blocks 213 and corresponding pointer entries 228 from the packet pointer pool 221 are inserted into the queue 222. While entries are being passed through the queue 222 and monitored by the queue logic 229, the packet delivery logic 227 is reading and processing the entries 228 output from the queue 222. In this regard, as shown by decision block 411 and block 414 of FIG. 11, for each new entry 228 output from the queue 222, the packet delivery logic 227 reads the entry 228 and retrieves the packet stored in the memory block 213 pointed to by the read entry 228. The logic 227 then stores the data of the packet into one of the buffers 205 (FIG. 6).
If the packet delivery logic 227 does not detect a new entry 228 output from the queue 222 in block 411, then the delivery logic 227 activates the timer 278 and continues checking the queue 222 for a new entry 228, as shown by block 417 and decision block 419. Also, as shown by decision block 422, the packet delivery logic 227 determines when the timer 278 expires (i.e., determines when a predefined amount of time tracked by the timer 278 expires). If the timer 278 expires without a new entry 228 being output from the queue 222, then the packet delivery logic 227 provides the queue logic 229 with a notification indicating that the logic 227 will go to sleep unless there is a new entry 228 about to be output from the queue 222, as shown by block 426.
In response to the foregoing notification, the queue logic 229 determines whether the next entry 228 to be output from the queue 222 has been received by the queue 222. If not, the queue logic 229 provides the packet delivery logic 227 with an indication that it has detected no entries 228 that are about to be output from the queue 222. In response to this indication from the queue logic 229, the packet delivery logic 227 goes to sleep, as shown by decision block 432 and block 434. However, if the queue logic 229 determines that the next entry 228 to be output from the queue 222 has been received by the queue 222, then the queue logic 229 provides the packet delivery logic 227 with an indication that a new entry 228 is about to be output from the queue 222. In response to such an indication, the packet delivery logic 227 proceeds to block 411 without entering into a sleep state.
If the packet delivery logic 227 enters into a sleep state in block 434, the queue logic 229 awakens the logic 227 when the queue logic 229 detects that the next entry 228 to be output from the queue 222 has been received by the queue 222. Upon transitioning from the sleep state into an active state, the packet delivery logic 227 repeats the process depicted by FIG. 11.

## Claims

1. An apparatus for transmitting data to a network, comprising:
a queue;
packetization logic configured to packetize data into a plurality of data packets and to store, to the queue, entries pointing to the data packets;
interface logic configured to read the entries from the queue, the interface logic, for each of the read entries, configured to retrieve one of the packets pointed to by the read entry and to transmit the retrieved packet to a network socket; and
queue logic configured to limit, based on a number of retransmission requests detected by the queue logic, a number of entries that the packetization logic may store to the queue during a particular time period thereby controlling a transmission rate of the apparatus, wherein the queue logic is configured to establish a threshold based on the number of retransmission requests and to delay, based on a comparison of the threshold to a value indicative of a number of entries stored to the queue during a particular time period, storage of at least one entry to the queue for a sufficient period of time such that the transmission rate is reduced.

2. The apparatus of claim 1, wherein the queue logic is configured to expire at least one of the entries stored in the queue based on one of the retransmission requests.

3. The apparatus of claim 1, wherein the queue logic is configured to expire at least one of the entries stored in the queue based on an acknowledgment indicating that one of the data packets has been received by a remote receiving apparatus.

4. The apparatus of claim 1, wherein the queue logic is configured to enable the packetization logic to store entries to the queue until the number of entries stored to the queue during a particular time period reaches an entry threshold.

5. The apparatus of claim 4, wherein the queue logic is configured to adjust the entry threshold based on the number of detected retransmission requests.

6. An apparatus for transmitting data to a network, comprising:
a queue;
packetization logic configured to packetize data into a plurality of data packets and to store, to the queue, entries pointing to the data packets;
interface logic configured to read the entries from the queue, the interface logic configured to retrieve the respective packets associated with the entries and to transmit the retrieved packets to a network socket; and
queue logic configured to control a number of the entries that the packetization logic stores to the queue thereby controlling a transmission rate of the apparatus such that a rate at which the apparatus receives retransmission requests from at least one receiving unit remains within a specified range, wherein the queue logic is configured to establish a threshold based on the rate at which the apparatus receives retransmission requests from the at least one receiving unit and to delay, based on a comparison of the threshold to a value indicative of a number of entries stored to the queue during a particular time period, storage of at least one entry to the queue for a sufficient period of time such that the transmission rate is reduced.

7. The apparatus of claim 6, wherein the queue logic is configured to expire at least one of the entries stored in queue based on one of the retransmission requests.

8. The apparatus of claim 6, wherein the queue logic is configured to expire at least one of the entries stored in the queue based on an acknowledgment indicating that one of the data packets has been received by a remote receiving apparatus.

9. An apparatus for transmitting data to a network, comprising:
means for packetizing data into a plurality of data packets and storing, to a queue, entries pointing to the data packets;
means for reading the entries from the queue, the reading means, for each of the read entries, configured to retrieve one of the packets pointed to by the read entry and to transmit the retrieved packet to a network socket; and
means for limiting, based on a number of retransmission requests detected by the limiting means during a particular time period, a number of entries that the packetizing means may store to the queue during a particular time period thereby limiting a transmission rate of the apparatus such that a rate at which the queue logic receives retransmission requests from at least one receiving unit remains within a specified range, wherein the limiting means is configured to establish a threshold based on the number of retransmission requests and to delay, based on a comparison of the threshold to a value indicative of a number of entries stored to the queue during a particular time period, storage of at least one entry to the queue for a sufficient period of time such that the transmission rate is reduced.

10. A method for transmitting data to a network, comprising:
storing entries to a queue within a transmitting apparatus, the entries pointing to data packets;
reading the entries from the queue;
transmitting, based on the entries read from the queue, the data packets to a network socket;
receiving, at the transmitting apparatus, retransmission requests from at least one receiving apparatus;
limiting a number of the entries that may be stored during a particular time period based on a number of the retransmission requests received via the receiving thereby controlling a transmission rate of the transmitting apparatus;
establishing a threshold based on the number of retransmission requests; and
comparing the threshold to a value indicative of a number of entries stored to the queue during a particular time period,
wherein the limiting comprises delaying storage of at least one entry to the queue.

11. The method of claim 10, further comprising expiring at least one of the entries stored in the queue based on one of the retransmission requests.

12. The method of claim 10, further comprising expiring at least one of the entries stored in the queue based on an acknowledgment indicating that one of the data packets has been received by a remote receiving apparatus.

13. A method for transmitting data to a network, comprising:
storing, to a queue within a transmitting apparatus, entries pointing to data packets;
reading the entries from the queue;
transmitting, based on the entries read from the queue, the data packets to a network socket; and
controlling a transmission rate of the apparatus by limiting a number of the entries stored to the queue during a particular time period such that a rate at which the apparatus receives retransmission requests from at least one receiving apparatus remains within a specified range;
establishing a threshold based on the rate at which the apparatus receives the retransmission requests; and
comparing the threshold to a value indicative of a number of entries stored to the queue during a particular time period,
wherein the controlling comprises delaying storage of at least one entry to the queue.

14. The method of claim 13, further comprising expiring at least one of the entries stored in the queue based on one of the retransmission requests.

15. The method of claim 13, further comprising expiring at least one of the entries stored in the queue based on an acknowledgment indicating that one of the data packets has been received by a remote receiving apparatus.

16. A method for transmitting data to a network, comprising:
receiving retransmission requests;
storing, to a queue within a transmitting apparatus, entries pointing to data packets;
transmitting, based on the entries, the data packets to a network socket;
establishing a threshold based on the retransmission requests;
determining a value indicative of a number of the entries stored to the queue during a particular time period;
comparing the threshold to the value; and
delaying, based on the comparing, storage of at least one entry to the queue for a sufficient period of time such that a transmission rate of the transmitting apparatus is reduced.

17. The method of claim 16, further comprising updating the threshold based on a number of the retransmission requests received during a particular time period.

18. The method of claim 16, wherein the determining comprises counting the number of the entries stored to the queue during the particular time period.