DISCARDING TRAFFIC IN IP NETWORKS TO OPTIMIZE THE QUALITY OF SPEECH SIGNALS

Abstract: A method for discarding data within an IP-network communications link (10) in a manner that optimizes the quality of speech data contained in the IP-network communications link (10). Initially, the IP-network communications link (10) is monitored to determine the occurrence of an overload condition. At least a portion of a plurality of data packets (30) within the IP-network communications link (10) are selected in response to detection of the overload condition. The selected portions are discarded from the IP-network communications link (10), and the remainder of the packets (30) transmitted on the link (10).

Description: DISCARDING TRAFFIC IN IP NETWORKS TO OPTIMIZE THE QUALITY OF SPEECH SIGNALS BACKGROUND OF THE INVENTION Technical Field of the Invention The present invention relates to overload situations within IP-network communications links, and more particularly, to a method for relieving an overload situation within an IP-network communications link in a manner that optimizes the quality of speech signals within the communications link. Description of Related Art In a cellular access network 10, signals are transmitted through an air interface portion 15 and an IP transmission network 20 as shown in FIGURE 1. The IP transmission network 20 utilizes IP -network communications links to move data through the network 20. In the cellular access network 10, the speech quality considerations are essentially due to the quality of signal (QOS) degradation occurring over the air interface 15. QOS degradation in the IP transmission network 20 must be negligible when compared to degradation on the air interface 15 or speech signal quality becomes unacceptable. The main signal degradation problem arising in IP-network communications links of the IP transmission network 20 occurs during certain overload situations which require the IP transmission network to discard traffic. This involves the discarding of data packets from the IP-network communications links. The overload situation may be triggered by a link failure or other re-rerouting actions in the IP transmission network 20. In many cases, the overload situation may be only temporary such as in the case of statistical multiplexing. However, in all of these situations, the overflow traffic must be discarded in such a way as to avoid the lowering of speech signal quality. The problem with existing IP based networks arises from the fact that they are optimized for a best-effort application that provides the best overall signal quality. The quality of signal mechanism is optimized in a similar manner. While this type of quality of signal mechanism might be appropriate for the overall signal, this system is not necessarily appropriate from the speech quality point of view. The current method is optimized in the flow control mechanisms of the TCP-protocol such that routers will discard packet traffic in a random manner enabling the system to control traffic in a fair way that randomly discards packets without giving particular preference to any type of packet or the associated connection. While this may be acceptable to overall traffic performance, this can have a detrimental effect on the speech signal quality. By discarding packets in a random manner, poor behavior may be imported on the quality of speech signals as a whole. Thus, if one or several speech signals causes an overflow condition and initiates the discard of traffic from 100 other real-time flows consisting of a number of speech packets, the overall quality for all users on the 100 real-time flows can be degraded below an acceptable threshold for high quality speech signals. Some manner of limiting the effects of overload conditions on overall speech signal quality is needed. SUMMARY OF THE INVENTION The present invention overcomes the foregoing and other problems with a method for discarding data within an IP -network communications link in a manner that optimizes the quality of speech data on the communications link. An IP -network communications link is monitored for the occurrence of an overload condition on the link. In response to detection of an overload condition, specific groups of data are selected within the IP-network communications link. In a first embodiment, the packet payloads of data packets within the communications link are separated into important parameters and less important parameters. The less important parameters are selected and discarded from a plurality of data packets within the IP -network communications link. In a second embodiment, select groups of data packets referred to as real-time flow sessions containing data packets having the same source and destination IP addresses and source and destination ports, and consisting of encapsulated video, audio, etc. signals, are selected and deleted from the IP-network communications link. In this manner, only a single or a few real-time flow session need be eliminated from the link, and the remaining links remain unaffected. BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention, reference is made to the following Detailed Description taken in conjunction with the accompanying drawings wherein: FIGURE 1 is a block diagram illustrating a cellular access network; FIGURE 2 is a block diagram illustrating the transmission of data packets over a IP -network communications link; FIGURE 3 is an illustration of a first embodiment of the present invention wherein a portion of a plurality of packet payloads are deleted from data packets within the IP -network communications link; FIGURE 4 is a block diagram illustrating the method of FIGURE 3; FIGURE 5 illustrates an alternative embodiment of the present invention wherein data packets from a single real-time flow are deleted from the IP -network communications link; and FIGURE 6 is a flow diagram illustrating the method of FIGURE 5. DETAILED DESCRIPTION Referring now to the drawings, and more particularly to FIGURE 2, there is illustrated a single IP-network communications link 25 on an IP transmission network 20 (FIGURE 1). Upon the communications link 25 are multiple data packets 30 including a packet header 35 and a payload 40. The packet header 35 includes information enabling the data packet 30 to be transmitted over the IP -network communications link 25. The payload 40 comprises the information being transmitted over the IP-network communications link 25 between source and destination locations. The packet header 35 includes fixed value parameters 45 and non-fixed value parameters 50. The fixed value parameters do not often change during a call and only need to be sent a few times during a call. The non-fixed value parameters 50 change frequently during a call and are coded and always transmitted in a compressed header. This manner of only transmitting the fixed values a few times during a call is referred to as header compression. This is accomplished by including a record 55 at each end of the IP -network communications link 25 that includes the fixed parameters 45 which are not being transmitted. There is one record made for each real-time flow proceeding from a source location to a destination location. Referring now to FIGURE 3, there is illustrated a first embodiment of the invention wherein an overload condition detected on the IP-network communications link 25 may be alleviated without degrading the quality of speech signals (i.e., the manner in which the audio signals are perceived at a receiving end is not severely degraded) on the communications link 25. An overload condition occurs when more traffic (i.e., data packets) are present on the communications link than can be handled. During an overload condition, multiple data packets 30 on the IP -network communications link 25 have their packet payloads 40 sorted to determine the important parameters 70 and less important parameters 75 contained in each data packet 30. The designation of important and less-important parameters is normally performed before or during packetization of the data. The less important parameter 75 from each packet payload 40 are selected and discarded from each data packet 30 by local routers within the IP network such that the full data packet 30 becomes a truncated data packet 30a including only the important parameters 70 of the data payload 40 and the packet leader 35. In this way, each data packet 30 is transmitted as a truncated or partial packet 30a rather than the full packet originally provided. The quality of the speech signals within the IP-network communications link 25 is maintained at a high level despite the fact that the less important parameters are deleted. The divisions into important and less important parameters are carried out normally by the signal processing protocol, but other methods for prioritizing the parameters may be used. Referring now to FIGURE 4, there is illustrated a flow diagram describing the method of FIGURE 3. The IP -network communications link 25 is monitored at step 80 for the occurrence of an overload condition. Upon detection of an overload condition, the important and less important parameters of the packet payload 40 within the data packet 30 are noted at step 85 as discussed above. The less important parameters are selected at step 90 from a plurality of the data packets 30, and the selected parameters are discarded at step 95. In an optional step, the packet headers may also have header compression applied at step 100, and the truncated packets 30a are transmitted at step 105 over the IP -network communications link 25. In an alternative embodiment, rather than deleting a portion of the packet payloads 40 within a number of data packets 30, a number of data packets 30 may be entirely deleted from the IP-network communications link 25. In this embodiment, a determination is made by the local routers of the IP networks of the real-time process flows to which each packet 30 within the IP-network communications link 25 is associated by reading the information contained within packet headers 35. A real-time process flow comprises a plurality of data packets having the same source and destination IP addresses and the same source and destination ports. A real-time process flow may also comprise portions of a multiplexed data flow which come from a single data flow source before multiplexing. Each data packet 30 having this same information is considered to be from the same real-time process flow. A single IP -network communications link 25 can have a plurality of real-time flows associated therewith as illustrated in FIGURE 3 by reference number 30a, 30b and 30c. From a speech signal quality point of view, it is better to drop a single one of the real-time flows, for example 30b, rather than to drop packets from each of the real-time flows. Thus, by dropping the real-time flow represented by 30b, the IP- network communications link 25 would be converted to include only the real-time flows 30a and 30c as shown. While the signal for the real-time flow 30b would be entirely lost, the quality of signal for real-time flows 30a and 30c would remain unaffected. A determination of which real time flow to drop may be made at random or based upon any number of methods. The methods include but are not limited to dropping flows based upon prioritizations within the packet header; assigning certain addresses to have a higher priority; having control signals dynamically select parameters to be deleted; providing priority to particular bearer protocols; or discarding from a last connected real time flow. Referring now to FIGURE 6, there is illustrated a flow diagram describing the method of FIGURE 5. The IP -network communications link 25 is monitored for the occurrence of an overload condition at step 120. Upon detection of the overload condition, the determination of real-time flows presently supported by a IP -network communications link 25 are determined at step 125. After determination of at least one real-time flow, a single real-time flow is selected at step 130 by routers of the IP network, and the selected real-time flow is discarded from the IP -network communications link 25 at step 135. The optional step of packet header compression may be performed on the remaining data packets 30 at step 140, and the remaining packets are transmitted over the IP-network communications link at step 145. Although preferred embodiments of the method and apparatus of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it is understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.

Claims: WHAT IS CLAIMED IS: 1. A method for discarding data within an IP -network communications link in a manner that optimizes a quality of speech data on the IP -network communications link, comprising the steps of: monitoring the IP-network communications link for occurrence of an overload condition; selecting at least a portion of a plurality of data packets within the IP- network communications link in response to the overload condition, wherein deletion of said selected at least one of a plurality of data packets would not substantially degrade a quality of speech signals on the link; and discarding the selected portions of the plurality of data packets from the IP-network communications link. 2. The method of Claim 1 , wherein the step of selecting further comprises the steps of: dividing a packet payload into a first group of parameters and a second group of parameters; and selecting the second group of parameters in response to the overload condition. 3. The method of Claim 2, wherein the step of discarding comprises discarding the selected second group of parameters from the packet payloads of the IP- network communications link. 4. The method of Claim 2, wherein the discarding of the selected parameters does not substantially degrade an audio signal perceived by a listener at a receiving end of the IP network communications link. 5. The method of Claim 2, further comprising the step of storing at each end of the IP -network communications link records containing the second group of parameters. 6. The method of Claim 1 , wherein the step of selecting further comprises the steps of: determining at least one real-time flow session upon the IP -network communications link; selecting the determined at least one real-time flow session in response to the overload condition. 7. The method of Claim 6, wherein the step of discarding further comprises the step of discarding the selected real-time flow session from the IP- network communications link. 8. The method of Claim 6, wherein the real-time flow session comprises a group of data packets having a same source and destination IP-addresses and source and destination ports. 9. The method of Claim 1, further including the step of compressing packet headers on the IP-network communications link. 10. A method for discarding data within an IP-network communications link in a manner that optimizes a quality of speech data on the IP network communication link, comprising the steps of: monitoring the IP -network communications link for occurrence of an overload condition; dividing a packet payload into an important group of parameters and a less important group of parameters; selecting the less important group of parameters in response to the overload condition; and discarding the less important group of parameters from a plurality of data packet payload of the IP-network communications link. 11. The method of Claim 10 further including the step of compressing packet headers on the IP -network communications link. 12. The method of Claim 10, wherein the discarding of the less important group of parameters does not substantially degrade an audio signal perceived by a listener at a receiving end of the IP network communications link. 13. A method for discarding data within an IP-network communications link to optimize a quality of speech data on the IP -network communications link, comprising the steps of: monitoring the IP -network communications link for occurrence of an overload condition; determining a plurality of data packets having a same source and destination IP addresses and a same source and destination ports; and discarding the determined plurality of data packets from the IP -network communications link in response to the overload condition. 14. The method of Claim 13 further including the step of compressing packet headers on the IP -network communications link. 15. The method of Claim 13, wherein the discarding of the determined plurality of data packets does not substantially degrade an audio signal perceived by a listener at a receiving end of the IP network communications link.

Inventors: WESTBERG LARS, WESTBERG, LARS
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Application year: 2000
Main classification: H04L12
IPC codes: H04L12, H04L29