Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Utility Patent
1997-11-06
2001-01-02
Harrison, Jessica J. (Department: 3713)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S468000
Utility Patent
active
06169738
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to communications and, more particularly, to a communications system for transporting packet voice.
BACKGROUND OF THE INVENTION
Asynchronous transfer mode (ATM) networks carry fixed sized cells within the network irrespective of the applications being carried over ATM. At the network edge or at the end equipment, an ATM Adaptation Layer (AAL) maps the services offered by the ATM network to the services required by the application. There are a number of industry standards and proposed standards covering various AALs. In particular, “B-ISDN ATM Adaptation Layer Type 2 Specification,” draft Recommendation I.363.2, November 1996, of ITU-T (herein referred to as AAL2) provides for efficient ATM transport of small, delay-sensitive packets in such applications as packet voice systems. AAL2 is partitioned into two sublayers, the Common Part Sublayer (CPS) and the Service Specific Convergence Sublayer (SSCS).
In an AAL2/SSCS packet voice system, the peak required raw bandwidth of voice, coded in accordance with ITU-T standard embedded ADPCM G.727 (hereafter referred to as G.727), is 32 thousands of bits per second (kb/s). However, other types of voice-band type traffic are also carried in this system besides voice itself. For example, G3 facsimile (fax) traffic may be conveyed requiring a typical bandwidth of 9.6 kb/s. Also, data traffic may be carried with required bandwidths of as much as 64 kb/s in the case of 56 kb/s modem technology.
As a result, an AAL2/SSCS packet voice system multiplexes a variety of traffic types onto an outgoing ATM virtual circuit (VC) pipe, which has a fixed bandwidth allocation in accordance with an ATM service category, e.g., ATM Constant Bit Rate (CBR), ATM Real-Time Variable Bit Rate (rt-VBR). (This bandwidth is typically fixed, or static, and negotiated with a distant ATM endpoint at setup of the VC.) Once the VC is set up, new calls may be admitted to the VC in accordance with a call admission algorithm. In this call admission algorithm, all traffic is treated in a homogeneous fashion in one extreme. A new call is admitted simply by comparing the current number of calls in the respective VC to a predetermined call threshold value. If the current number of calls is less than this call threshold value, then the new call is admitted. Otherwise, the new call is blocked.
Unfortunately, as new calls are admitted to the pipe, traffic loads may necessitate the use of congestion relief algorithms for the voice traffic such as bit dropping or dropping entire AAL2 voice packets. (It is presumed that only voice traffic is throttled to relieve congestion and that non-voice traffic is not targeted for packet dropping in order to provide for congestion relief.) For example, as congestion begins to occur, voice packets are typically queued for transmission in a buffer, or queue. If the number of these queued voice packets exceeds a predetermined threshold, bit dropping for voice traffic begins to occur in accordance with, e.g., G.727. If the congestion continues to worsen, then entire AAL2 voice packets are dropped. (Also, it should be noted that if the above-mentioned thresholds are too small, bit dropping occurs too soon, and if the above-mentioned thresholds are too large, bit dropping occurs too late. In this latter case, there is almost little, or no, benefit from bit dropping (in the context of G.727) because of the already incurred large packet delay by the time bit dropping begins to start.)
SUMMARY OF THE INVENTION
In view of the above, we have observed that a call admission control strategy that treats all calls in a homogenous fashion either admits too few calls—thus causing some calls to be blocked even though capacity exists—or too many calls—with concomitant congestion effects. As such, we have realized that a call admission control strategy should take into account different call types in order to provide for efficient bandwidth management. In particular, and in accordance with the invention, call admission is dynamically performed as a function of call type.
In an illustrative embodiment, an AAL2/SSCS packet voice system multiplexes various forms of voice-band traffic including voice packets, fax packets, and data packets into a virtual circuit (VC). This AAL2/SSCS packet voice system executes a dynamic call admission algorithm that takes into account call type in deciding whether to admit a new call to the VC. In particular, this approach takes into account different bandwidth needs for different call types.
In accordance with a feature of this invention, at least one queue parameter is dynamically varied as a function of capacity (or link bandwidth). An example of a queue parameter is a threshold.
REFERENCES:
patent: 4914650 (1990-04-01), Sriram
patent: 5570355 (1996-10-01), Dail et al.
patent: 0648035 (1995-04-01), None
Mauger, R., et al., “ATM Adaptation Layer Switching”, ISS '97, World Telecommunications Congress (International Switching Symposium), Global Network Evolution: Convergence or Collision? Toronto, Sep. 21-26, 1997, vol. 1, Sep. 21, 1997, pp. 207-217 XP000720525.
Sriram Kotikalapudi
Wang Yung-Terng
Harrison Jessica J.
Lucent Technologies - Inc.
Nguyen Kim T.
Opalach J. J.
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