BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the nature of the present invention, its features and advantages, the subsequent detailed description is presented in connection with accompanying drawings in which:
FIG. 1 is a diagram of a network capable of transmitting a real-time media stream;
FIG. 2 is the network diagram of FIG. 1 showing routers as nodes in the network;
FIG. 3 is diagram of a network on which the method of the preferred embodiment may be implemented showing the preferred embodiment activated between two intermediate nodes;
FIG. 4 is a flowchart showing a method of the preferred embodiment;
FIG. 5 is a diagram of a network showing the preferred embodiment activated between an endpoint an intermediate node;
FIG. 6 is a diagram of a typical packet format;
FIG. 7 is a flowchart showing a method of an alternative embodiment;
FIG. 8 is a flowchart showing a method of an additional alternative embodiment;
FIG. 9 is an additional network diagram capable of implementation of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 3 illustrates a network diagram of FIG. 2 that can implement the preferred and alternative embodiments. Network 32 comprises router 26 that contains components as is known in the art of network interfaces, printed circuit boards, and processors used for reception and transmission of network media streams. For purposes of explanation, routers 26 and 28 are exemplary network nodes and assumed to have equivalent hardware components and software capabilities to implement the present invention. Further, each node on the network is assumed to contain a processor such as an integrated circuit (IC), central processing unit (CPU), reduced-instruction set computer (RISC), or an equivalent processor capable of programming and controlling the transmission of a network media stream to implement the preferred and alternative embodiments. In FIG. 3, exemplary nodes include IP phones 18 or 24 (which are also endpoints), media gateway 20, router 28, router 26, and wireless access point (AP) 22.
Steps for the method of the preferred embodiment for network 32 are included in the flowchart diagram of FIG. 4. The preferred method is intended for use during transmission of a real-time media stream transmitted over a network beginning in step 50. This transmission in occurs between two endpoints such as between IP phone 18 and IP phone 24 over the nodes in the network. One or more nodes in the network monitors communication channels for adverse network transmission problems 52 such as packet loss, delay, corruption, etc. (for purposes of describing the preferred embodiment it is assumed that packet loss is the adverse network event detected in a communication channel). Each node monitors the media stream in the channel it is receiving from its upstream network link.
If packet loss is not detected 54 above a tolerable level for the network, then the node continues packet transmission in its normal operational mode 56 and continues to monitor channels for problems 52. If packet loss is detected 54, then the node detecting the loss activates the preferred method of operation to reverse the adverse network effects on the media stream. This is termed the “robust mode” in flowchart step 58. In a network running RTP/RTP-XR media streams of voice, video, audio, and/or data payloads, the robust mode 58 may be activated on one or more specific links in the network that are experiencing the packet loss, delay, etc., and not necessarily on the entire end-to-end communication path. FIG. 3 illustrates such an implementation only on the link 32 between routers 26 and 28 when that link is experiencing packet loss and the remaining network links are not experiencing loss. If packet loss is occurring on the wireless link between AP 22 and phone 24, then FIG. 6 illustrates the robust mode operating on the link 48 between those two nodes. In a packet network, when packet loss is detected 54 and the node enters the robust transmission mode 58, the RTP (Real-Time Protocol) and its associated control protocol (CP) RTCP or RTP-XR (RPT extended Reporting) packets destined for that particular communication channel are duplicated 60 by the transmitting node for that channel. Duplication 60 of packets is performed to improve the probability that sufficient packets are arriving at a downstream node that will produce a high-quality replication of the original voice, video, audio, or data that was originally packetized at the upstream endpoint 20. The duplication 60 operations may be performed by any methods known in the art, such as according to Request for Comments (RFC) 2198 “RTP Payload for Redundant Audio Data” or equivalent packet duplication method.
One method is for the node in robust mode 58 to generate appropriate replacement RTP/RTP-XR packet headers for the original packet it has already received. A typical packet format is illustrated in FIG. 5. Packet 34 comprises a header 36 and a payload 38. An IP header 36 includes an IP address frame 40, a user datagram protocol (UDP) frame 42, and a Real Time Protocol (RTP) frame 44. UDP serves as an application interface to the IP and since it has no reliability, flow control, or error-recovery capabilities, also serves as a multiplexer/demultiplexer for the receiving and sending of IP traffic. Payload 38 includes multiple frames 46 of voice, video, or audio data. The payload message format 46 for RTP supports various types of codecs, such as ITU G.729, G.711 and other protocols known in the art. If a different type of network, such as frame relay, implements the preferred embodiment, then the appropriate frame headers or signal identifiers are changed without changing the data portion.
The embodiment preferably only changes the header portion 36 of a packet. Codecs used to encode, decode, or transcode the media payload 38 are not required at the nodes implementing the preferred embodiment. The codecs used for transmission protocols between endpoints would remain as expected in the transmission. This further serves a purpose of not interfering with the specialized protocols used in a VOIP call or other media transmissions. Such interference with the codecs of payload by a node could potentially create delay or loss of payload at the receiving endpoint 26. However, if transcoding is desired at an intermediate node in the network channel either by an application or by a network operator, codecs could be present at the desired intermediate node without compromising the node from taking advantage of the features of the present invention.
The preferred method duplicates packets even though the duplicating node may not be the originating or terminating endpoint for the media stream. Once an intermediate node duplicates packets 60 on the channel experiencing loss, the node forwards the duplicated packet in step 62 to the next downstream node or endpoint. The node will continue to monitor the channel experiencing loss to determine 64 if, after implementing the robust operations 58, the losses in the channel decrease to an acceptable rate. If the losses are not acceptable then the node continues in robust mode in step 66 and continues to monitor the channel 64. If during monitoring 64 the channel losses are lowered to an acceptable rate, the node de-activates robust mode 68 and returns to transmission of packets normally while continually monitoring the channel for network problems 52.
Although the preferred method implements a packet duplication operation 60 at an intermediate node, alternative embodiments may implement other error-correction schemes on one or more intermediate links in the media transmission. An alternative embodiment of a method for inter-nodal robust mode is illustrated in the flowchart of FIG. 7. The alternative method is also intended for inter-nodal real-time media stream on a network. Step 50 in FIG. 7 begins with transmission of a packet stream 50 with one or more nodes monitoring channels 52 for network problems. Again, a problem with packet loss on the network is illustrated and described but this could be any type of adverse network event replay problems including delayed packets, lost packets, packet corruption, etc. After packet loss is detected 54 and the activation of robust mode 58 at an intermediate node on the network 32, the node activates a forward error correction (FEC) scheme for packets in the channel experiencing loss. The node then forwards the FEC-encoded packets downstream 72 to the next node. When packet loss in the channel is deemed acceptable 64, the FEC-encoding is stopped at the node by de-activating the robust mode 68.
FIG. 8 contains a flowchart illustrating steps of an additional alternative embodiment that can be implemented at a node that may not be the originating or terminating endpoint during a real-time media stream transmission. The process begins with multiple nodes monitoring a transmission stream channel 74 for a problem with the network, for example packet loss above an acceptable rate. As is understood from the preferred embodiment, this method is applicable for other network transmission problems as is known in the art such as lost packets, delayed packets, and corruption. If the packet loss parameters are not detected 76, then the node continues with packet transmission 78 in normal operation and continues monitoring channels for packet loss 74. If the packet loss parameters are detected as unacceptable 76 by multiple nodes, then those nodes on the channel links experiencing problems decide to active the robust mode 80 as described in the preferred embodiment. Thus, in this scenario there is a node, such as router 28, that has entered robust mode and a downstream node, such as router 26 that has entered robust mode of their downstream links. When the channel in the destination link over which a node in robust mode is forwarding packet in question is determined by that node to have an acceptable packet loss 82, then that node may de-activate robust mode transmission 86 only if that node participated in the decision to enter robust mode that in a channel that it was monitoring directly.
In FIG. 3, this would be the case where router 26 participated in the decision to enter robust mode for the destination link between itself and AP 22. If steps 82 and 86 are satisfied, then router 26 could terminate the redundant packets 60 or FEC encoding 70 of packets it is receiving from router 28. If the destination link from router 26 does not have an acceptable level of packet loss 82, then the router 26 continues in robust mode 84 while monitoring the destination link. The alternative method terminating robust mode by an intermediate node that participated in the decision to enter the robust mode is extremely advantageous. This method removes the possibility that an intermediate node will terminate the transmission of duplicate packets when an upstream link requires them and the upstream node is not able to monitor and activate the a robust mode by itself.
FIG. 9 illustrates a more detailed view of a view of an exemplary network that could implement the present invention. Endpoint 88 is connected to broadband network 12 through router 90. Router 92 is part of a home network and connects to broadband network 12 through a cable or DSL network interface card 94. Router 92 transmits on a wireless LAN connection 96 to any one or all of additional networks, applications, or devices that comprise the home network. These include applications and devices for Global System for Mobile Communications (GSM) 98, Internet Protocol 100, WLAN 102, Internet Mail Service (IMS) 104, and a voice/data router (VDR) 106. If the connection between router 90 and router 92 experiences unacceptable packet loss etc., router 92 enters the robust mode 58 for transmissions from router 92 and the devices and applications of the home network described above.
The present invention has numerous advantages that are extremely important to improving the transmission of real-time media streams over a network. These include bandwidth savings in the network by eliminating redundancy on network links that do not require a redundancy scheme in order to maintain quality of service. Additionally, the processing overhead required to implement the invention is minimal. Processing is performed in a distributed fashion, in one or more processors at each node on the network links. The nodes capable of robust mode may also communicate with one another using control signaling from a central location or with inter-nodal signaling or with indicators within the packet headers. This has an advantage of notifying all nodes in the destination links that they can expect to process packets transmitted in the robust mode and to insure proper reporting to a network operator of what links activate robust mode and how often. Once the need to activate a robust mode is detected by a network node, the node will generate the appropriate replacement headers for the original packet that is has already received. There is no requirement for re-transmission or duplication of packets starting from an originating endpoint nor is acknowledgement of receipt of duplicate packets required.
Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.
Patent Application
20070280217
