Policy-based forward error correction in packet networks

FIELD OF THE INVENTION

P-0001[0001] This invention relates to a communications system for classifying and forwarding packets for transmission over a digital communication channel.

BACKGROUND OF THE INVENTION

P-0002[0002] With the evolution of communication services toward a greater penetration of packet transmission, a packet network may need to support a plurality of applications for voice services and video services. However, different types of services have different requirements in order to achieve the objectives of quality of service (QoS). Time latency and packet error rate (PER) are often used to describe the QoS objectives. Voice services typically require a small time latency (which is associated with the delay of the voice signal). On the other hand, entertainment broadcast video typically requires a small packet error rate but does not require a small time latency. Moreover, the processing required for providing a small packet error rate often entails substantial error correcting processing when the signal is transmitted over an imperfect communication channel. If a packet network serves entertainment broadcast video, one would configure the packet network to have a large degree of error correcting capability in order to guarantee a small packet error rate at the expense of a greater time latency. However, this policy may not provide satisfactory support for voice service if the same packet network is concurrently serving applications for voice services.

P-0003[0003] With the prior art, a single forward error correction (FEC) path is often chosen that is a compromise between a reasonable packet error rate and a reasonable delay; however, this approach is not an optimal solution because either there is more delay for voice signals than desired or a higher packet error rate than is desirable for video services. Another conventional approach is to utilize more one than one forward error correction path; however, only one FEC path can be used at a given time. In other words, FEC paths cannot be used concurrently. However, a packet switch may serve different types of services at a given time.

P-0004[0004] There is a need for a packet network to have the capability of selecting the FEC path that best meets the QoS objectives for applications supporting different services such as video services and voice services.

SUMMARY OF THE INVENTION

P-0005[0005] The present invention provides a method and apparatus for a communications system that classifies packets that are transmitted over a digital communication channel with at least one error-correcting transmission path. Quality of Service (QoS) objectives are used to select the appropriate transmission path that satisfies the relevant metrics of service quality such as packet latency, variance of the packet latency, information throughput, and packet error rate (PER). One transmission path supports forward error correction with an associated amount of time latency that is consistent with the QoS objectives of an originating application. The communications system manages, monitors, and prioritizes packets and allocates bandwidth with a packet network in order to satisfy the QoS objectives associated with the originating application. The communications system configures the transmission path according to QoS objectives and bandwidth requirements and selects a transmission path that is associated with QoS objectives best matched to the QoS objectives as required by the originating application. The processing of the packet optionally includes scrambling and interleaving of the packet. A packet can be reclassified with respect to QoS and bandwidth requirements in order to adjust the policy-based communications system to varying service demands. Alternatively, available bandwidth can be re-allocated among the plurality of transmission paths. The receiver, in accordance with the present invention, utilizes corresponding inverse functions to deliver packets to the terminating application.

BRIEF DESCRIPTION OF THE DRAWINGS

P-0006[0006]FIG. 1 shows an architecture of a communications system using forward error correction in a packet network;

P-0007[0007]FIG. 2 shows an architecture that utilizes Reed-Solomon coding and interleaving in accordance with the architecture shown in FIG. 1;

P-0008[0008]FIG. 3 shows a functional diagram for implementing the present invention in conjunction with DSL;

P-0009[0009]FIG. 4 shows a flow diagram in accordance with the functional diagram shown in FIG. 3; and

P-0010[0010]FIG. 5 shows a functional diagram for implementing the present invention in conjunction with Ethernet over VDSL.

DETAILED DESCRIPTION OF THE INVENTION

P-0011[0011]FIG. 1 shows an architecture of a communications system <b>100</b> using forward error correction according to the present invention. Communications system <b>100</b> delivers packets from an application that supports a service (e.g. video-conferencing) for a user. Packet <b>101</b> is delivered from data port <b>102</b> to transmission medium <b>137</b>. Communications system <b>100</b> utilizes a mechanism (comprising system configuration and control unit <b>107</b>, packet classifier <b>105</b>, and forwarding switch <b>111</b> as described later) in order to process and transport packet <b>101</b> in accordance with the desired level of quality of service. Transmission medium <b>137</b> can assume one of different media forms including a radio link (wireless), a cable connection, a microwave connection, or a fiber optic connection. Moreover, packet <b>101</b> can be transported by tandeming different forms of transmission media to form transmission medium <b>137</b>.

P-0012[0012] Packet <b>101</b> is delivered according to a policy in which a level of quality of service (QoS) is associated with a user generating packet <b>101</b>, with the service that the user is requesting, and with the application (software program and as identified by the UDP port number, for example) supporting the service. The quality of service is determined by one or more attributes that include time latency of the packet, variation of the time latency, information throughput for the user, and the packet error rate (PER). Some applications (e.g. entertainment video) require a very low packet error rate but do not require a small time latency (i.e. delay of packets). On the other hand, there are other applications (e.g. voice) that typically require a small time latency but can tolerate a greater packet error rate. With a number of applications, one can trade the performance of one QoS attribute (e.g. time latency) for another QoS attribute (e.g. forward error correcting robustness) in order to satisfy the needs of a particular application.

P-0013[0013] With communications system <b>100</b>, database <b>103</b> provides policy information to system configuration and control unit <b>107</b> about the QoS level and the bandwidth allocated for the user of the application that provides a service. The policy is a set of assignment rules associated with a user and a desired QoS level. Typically, the policy is constructed in accordance with a service agreement between the user and a service provider. As an example, user A may have a higher QoS level than user B, in which packets are delivered quicker for user A than user B with the same packet error rate and in which user A has a greater throughput bandwidth than user B. The policy may have finer granularity by distinguishing the service and application being utilized for a given user. Packet <b>101</b> contains a priority indicator (such as a p value as supported in Standard IEEE 802.1Q). Packet classifier <b>105</b> receives packet <b>101</b> from the application and utilizes the priority indicator and policy information that is provided by system configuration and control unit <b>107</b> from database <b>103</b> over bus <b>109</b> to determine the QoS level and bandwidth allocation that is to be associated with packet <b>101</b>. Packet classifier <b>105</b> determines required transmission attributes that must be provided by a transmission path (which will be discussed subsequently) and forwards packet <b>101</b> with the required transmission attributes to forwarding switch <b>111</b>.

P-0014[0014] In order to adjust communications system <b>100</b> to varying service demands, packet classifier <b>105</b> can reclassify packet <b>101</b> with respect to QoS and bandwidth objectives. Configuration and control unit <b>107</b> determines a current demand of bandwidth resources by monitoring the buffer status on bus <b>127</b>. For example, if the policy associates a time latency of 1.5 msec and a PER of 1% for packet <b>101</b> and communications system <b>100</b> is experiencing traffic congestion, packet classifier <b>105</b> may redirect packet <b>101</b> to a transmission path (not illustrated in FIG. 1) that provides a time latency of 2 msec and a PER of 2% until the traffic congestion is allayed. At that point of time, packet classifier <b>105</b> may redirect packet <b>101</b> to the original transmission path having a time latency of 1.5 msec and a PER of 1%. Alternatively, system configuration and control unit <b>107</b> may instruct frame formatter <b>129</b> to increase the bandwidth allocated to the current transmission path. While maintaining the desired quality of service for the user, this approach may temporarily disrupt transmitting other packets in the frame.

P-0015[0015] Forwarding switch <b>111</b> may also receive additional information such as the current bandwidth usage of communications system <b>100</b> over bus <b>113</b> from system configuration and control unit <b>107</b> for directing packet <b>101</b> to a transmission path. Forwarding switch <b>111</b> consequently directs packet <b>101</b> to a specific transmission path (<b>190</b>, <b>191</b>, or <b>192</b>). FIG. 1 depicts three transmission paths: transmission path <b>190</b> comprising buffer <b>115</b> and error correction unit (EC) <b>121</b>; transmission path <b>191</b> comprising buffer <b>117</b>, error correction unit <b>123</b>; and transmission path <b>192</b> comprising buffer <b>119</b> and error correction unit <b>125</b>. Transmission paths <b>190</b>, <b>191</b>, and <b>192</b> can differ in that each path can be associated with different levels of quality of service. Buffers <b>115</b>, <b>117</b>, and <b>119</b> stores packet <b>101</b> if a previously transmitted packet is currently being processed by the associated error correction unit. Error correction units <b>121</b>, <b>123</b>, and <b>125</b> process packet <b>101</b> by adding coding bits that are used at the receiving side in order to correct any errors resulting from the transmission of packet <b>101</b> over transmission medium <b>137</b>. Even though transmission paths <b>190</b>, <b>191</b>, and <b>192</b> are separate logical paths, each path can be implemented as separate physical paths.

P-0016[0016] Frame formatter <b>129</b> receives processed packets from transmission paths <b>190</b>, <b>191</b>, and <b>192</b> and multiplexes the packets (such as processed packet <b>101</b>) into a frame. The bandwidth associated with a particular transmission path is directly related to the number of bits associated with a particular transmission path in the frame. The bandwidth allocated to a particular transmission path is increased by increasing the number of bits allocated in the frame for the given transmission path. The bandwidth allocation can be modified by system configuration and control unit <b>107</b> instructing frame formatter <b>129</b> through bus <b>131</b>. The frame is encoded into symbols and modulated by symbol encoder/modulator <b>133</b>, and the resulting signal is transmitted over transmission medium <b>137</b>.

P-0017[0017]FIG. 2 shows an architecture that utilizes Reed-Solomon coding and interleaving in accordance with the architecture that is shown in FIG. 1. Numbered components in FIG. 2 correspond to similarly-numbered components in FIG. 1. However, transmission path <b>290</b> comprises buffer <b>215</b>, scrambler <b>216</b>, and Reed-Solomon coder <b>221</b>; transmission path <b>291</b> comprises buffer <b>217</b>, scrambler <b>218</b>, Reed-Solomon coder <b>223</b>, and interleaver <b>224</b>; and transmission path <b>292</b> comprises buffer <b>219</b>, scrambler <b>220</b>, Reed-Solomon coder <b>225</b>, and interleaver <b>226</b>. Scramblers <b>216</b>, <b>218</b>, and <b>220</b> randomize the bits in packet <b>201</b> in order to achieve a uniform usage of the frequency spectrum of transmission medium <b>237</b>. Reed-Solomon coder <b>221</b>, <b>223</b>, and <b>225</b> encode scrambled packet <b>101</b> using a Reed-Solomon code. Reed-Solomon coding is well known in the art. A Reed-Solomon code is chosen according to the number of information bits in packet <b>201</b> and the code robustness that is necessary for providing the desired packet error rate. However, a greater degree of robustness typically corresponds to a greater time latency resulting from the processing of packet <b>201</b> by Reed-Solomon coder <b>221</b>, <b>223</b>, and <b>225</b>. Interleaver <b>224</b> and <b>226</b> reorder processed packet <b>201</b> so that no two adjacent bits, group of bits, or bytes are adjacent after reordering. As known in the art, interleaving provides greater immunity to burst errors and is used in conjunction with block coding (e.g. Reed-Solomon code, Bose, Chaudhuri, and Hocquenghem code, or Hamming code).

P-0018[0018] The architecture in FIG. 2 also includes header generator <b>228</b>. A header is multiplexed into the physical frame structure of the frame by frame formatter <b>229</b>. The header includes information such as the encoding algorithm utilized by error correction units <b>221</b>, <b>223</b>, and <b>225</b> and the boundaries within the frame that are associated with each of the transmission paths <b>290</b>, <b>291</b>, and <b>292</b>.

P-0019[0019] As can be appreciated by one skilled in the art, the architectures depicted in FIGS. 1 and 2 can be implemented with hardware such as Application Specific Integrated Circuit Chips (ASIC), with software using a microprocessor or a digital signal processor, or with a combination of hardware and software.

P-0020[0020]FIG. 3 shows a functional diagram for implementing the present invention in conjunction with a Digital Subscriber Line (DSL). DSL can provide a subscriber of a telephone high-speed data access of as much as 8 Mbps downstream and somewhat fewer bits per second upstream. Numbered components in FIG. 3 correspond to similarly-numbered components in FIG. 2. Transmission path <b>390</b> (comprising buffer <b>315</b>, scrambler <b>316</b>, and Reed-Solomon coder <b>321</b>) is designated a “fast path” because transmission path <b>390</b> is associated with a small time latency. Transmission path <b>391</b> (comprising buffer <b>317</b>, scrambler <b>318</b>, Reed-Solomon coder <b>323</b>, and interleaver <b>324</b>) is designated a “slow path” because transmission path <b>391</b> is associated with a greater time latency while providing a lower PER than transmission path <b>390</b>. Packet classifier <b>305</b> classifies packet <b>301</b> in accordance with the priority indicator (p value). Standard IEEE 802.1Q supports eight levels of priority varying from 0 to 7. Packet classifier directs packet <b>301</b> to the fast path (transmission path <b>390</b>) for higher priority levels (larger p values) and to the slow path (transmission path <b>391</b>) for lower priority levels (smaller p values).

P-0021[0021] Frame formatter <b>329</b> multiplexes packets (e.g. packet <b>301</b>) with header information that is generated by header generator <b>328</b> into a frame. The frame is subsequently symbol encoded and modulated so that a signal conveying the frame can be transmitted over transmission medium <b>337</b> (typically a metallic medium with DSL offerings).

P-0022[0022]FIGS. 1, 2, and <b>3</b> show various embodiments associated with the transmission of a packet in accordance with the present invention. Moreover, in accordance with the present invention, a corresponding receiver utilizes components that perform the inverse function of the corresponding component of the transmitting portion. For example, a scrambler corresponds to a de-scrambler; a Reed-Solomon encoder corresponds to a Reed-Solomon decoder; and an interleaver corresponds to an inverse-interleaver. The receiver uses the header (generated by the header generator <b>228</b> or <b>328</b>) as received in the frame to direct the packet to the appropriate transmission path. (FIG. 5, which is discussed later, illustrates both transmitting and receiving a packet over a transmission medium in accordance with one embodiment of the present invention.)

P-0023[0023]FIG. 4 shows a flow diagram in accordance with the functional diagram shown in FIG. 3. Packet <b>301</b> is provided to packet classifier <b>305</b> through data port <b>302</b> in step <b>401</b>. In step <b>403</b>, packet classifier <b>305</b> utilizes the priority indicator in packet <b>301</b> and the policy information provided by database <b>303</b> through system configuration and control unit <b>307</b>. Typically, policy information is configured by the system administrator in accordance with a service agreement between the service provider and the user. In step <b>405</b>, packet classifier <b>305</b> determines whether packet <b>301</b> should be routed to a fast transmission path or a slow transmission path. In the exemplary embodiment, a fast transmission path corresponds to low time latency and a larger PER probability and a slow transmission path corresponds to a larger time latency and a smaller PER probability. However, alternative embodiments may utilize more than two transmission path types with varying values of QoS attributes. In the exemplary embodiment, transmission path <b>390</b> corresponds to a fast transmission path, and transmission path <b>391</b> corresponds to slow transmission path.

P-0024[0024] If step <b>405</b> determines that a fast transmission path is required, step <b>407</b> determines whether the bandwidth allocation for the fast transmission path is adequate. If not, step <b>409</b> causes the bandwidth of the fast transmission path to be increased by increasing the bit allocation in the frame as instructed to frame formatter <b>329</b>. With a variation of the exemplary embodiment, packet classifier <b>305</b> can redirect packet <b>301</b> to a slow transmission path if traffic congestion exists at that point in time. In step <b>411</b>, packet <b>301</b> is directed to the appropriate transmission path by forwarding switch <b>311</b>. In step <b>413</b>, scrambler <b>316</b> randomizes packet <b>301</b>, and processed packet <b>301</b> is encoded by Reed-Solomon coder <b>321</b> in step <b>415</b>. Processed packet <b>301</b> is subsequently multiplexed by frame formatter <b>329</b> in step <b>417</b>. In step <b>431</b>, the frame is modulated so that the corresponding signal (conveying the frame and consequently packet <b>301</b>) is transmitted over transmission medium <b>337</b>.

P-0025[0025] If step <b>405</b> determines that packet <b>301</b> should be processed by a slow transmission path, analogous steps are executed in steps <b>419</b>, <b>421</b>, <b>423</b>, <b>425</b>, <b>427</b>, <b>417</b>, and <b>431</b>. However, step <b>429</b> provides the interleaving of packet <b>301</b> in order to provide greater robustness to burst errors. Additionally, the encoding parameters for the Reed-Solomon encoding in step <b>427</b> result in more robust forward error correction coding at the expense of added time latency.

P-0026[0026]FIG. 5 shows a functional diagram for implementing the present invention in conjunction with Ethernet over Very-high-bit rate DSL (VDSL). VDSL provides data rates on the downstream from 13 Mbps to 51 Mbps depending on transmission distance and typically a slower data rate on the upstream. The association of packets <b>501</b> and <b>502</b> is provided by system software as part of an overall QoS policy as determined by the policy management system. For example, video broadcast packets (such as packet <b>501</b>) may have a priority indicator (p value) of “1”, while voice packets (such as packet <b>502</b>) may have a p value of “2.” Packet classifier <b>505</b> reads the priority indicators in packets <b>501</b> and <b>502</b> and routes video packets (with p value of 1) to transmission path <b>534</b> that is designated as the “slow path” and routes voice packets (with p value of 2) to transmission path <b>535</b> that is designated as the “fast path.” FIG. 5 does not show the processing components of transmission paths <b>534</b> and <b>535</b>; however, the explanations discussed in conjunction with FIGS. 1, 2, <b>3</b>, and <b>4</b> are applicable. Frame formatter <b>529</b> multiplexes packets <b>501</b> and <b>502</b> into a frame, and front-end <b>533</b> encodes symbols and modulates a signal for transmission over transmission media <b>537</b>.

P-0027[0027] The VDSL receiver corresponds to front-end <b>553</b>, frame de-multiplexer <b>549</b>, transmission path <b>532</b>, transmission path <b>534</b>, buffer <b>515</b>, and buffer <b>517</b>. Front-end <b>553</b> performs the inverse function of front-end <b>533</b>; frame de-multiplexer performs the inverse function of frame formatter <b>529</b>; transmission path <b>532</b> performs the inverse function of transmission path <b>512</b>; and transmission path <b>534</b> performs the inverse function of transmission path <b>514</b>. Received packet <b>501</b> is stored in buffer <b>517</b> for the terminating video application, and received packet <b>502</b> is stored in buffer <b>515</b> for the terminating voice application.

P-0028[0028] It is to be understood that the above-described embodiment is merely an illustrative principle of the invention and that many variations may be devised by those skilled in the art without departing from the scope of the invention. It is, therefore, intended that such variations be included with the scope of the claims.