Traffic policing in broadband networks

Details Traffic policing in broadband networks Traffic policing in broadband networks

1998-07-29

2001-03-06

Olms, Douglas W. (Department: 2732)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S508000

Reexamination Certificate

active

06198743

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a method of traffic policing in broadband cell-based networks, such as ATM (Asynchronous Transfer Mode) Networks
DESCRIPTION OF THE RELATED ART
In ATM networks, service providers rely on User Parameter Control (UPC) to protect network resources from malicious and unintentional misbehavior which can affect the Quality-of-Service (QoS) of other established connections.
One popular implementation of UPC is the Generic Cell Rate Algorithm (GCRA) as defined in ‘ATM Forum Traffic Management Specification’, Version 4.0, April 1996, which is herein incorporated by reference, and ‘Broad Band Switching System (BSS) Generic Requirement’, Bellcore GR-1110-CORE, Sept. 1994.
It is presented as GCRA(I, L) with two parameters, the increment I and the Limit time L. When it is used to police the Peak Cell Rate (PCR) of a connection, it becomes GCRA(1/PCR, CDVT); when it is applied to police Sustainable Cell Rate (SCR), it becomes GCRA(1/SCR, BT).
In one version, the GCRA is a virtual scheduling algorithm that updates the Theoretical Arrival Time (TAT) of a cell, which is the nominal arrival time of the cell assuming that the active source sends equally spaced cells. If the actual arrival time of a cell is not “too” early relative to the TAT, and in particular if the actual arrival time is after TAT-L, then the cell is considered conforming, otherwise it is considered non-conforming.
At the arrival time of the first cell t
a
(1), the theoretical arrival time is initialized to the current time, t
a
(1). For subsequent cells, it the arrival time of the k
th
cell, t
a
(k), is actually the current value of TAT then the cell is conforming and TAT is updated to the current time t
a
(k), plus the increment I. If the arrival time of the k
th
cell is greater than or equal to TAT-L but less than TAT, then again the cell is conforming, and the TAT is increased by the increment I. Lastly, if the arrival time of the k
th
cell is less than TAT-L (i.e., if TAT is greater than t
a
(k)+L, then the cell is non-conforming and the TAT is unchanged.
In ATM networks, a risk exists that a cell delay variation tolerance (CDVT) that is not large enough may be specified at user-network and network-network interfaces because cell delay variation (CDV) is ubiquitous due to the slotted nature of cell transmission, multiplexing and clock variation. Also slight rate shifting can occur because of mismatched clocks.
A policing algorithm such as GCRA is too stringent to end-users because it is so sensitive to minor violations that the end-users may receive a transmission capacity significantly lower than what they have paid for. In the worst case, it can be only one-half of what they have paid for. Furthermore, to end-users, the unfairness to VCs (virtual Channels) violating traffic contracts is not acceptable because a VC with minor rate violation may get penalized far more than a VC with large rate violation.
The paper “Proceedings of the International Switching Syposium”, vol. 1-2, 25 October 1992, Institute of Electronics; Information and Communication Engineers, pages 316-320 discusses a virtual scheduling algorithm for ATM networks. This proposal does not, however, address the unfairness problems associated with the GCPA algorithm.
BRIEF SUMMARY OF THE INVENTION
An object of the invention is to alleviate the disadvantages of the GCRA algorithm, such as unfairness and sensitivity to minor contract-violation.
According to the present invention there is provided A method of traffic policing in packet-based, broadband asynchronous networks, such as ATM networks, comprising the steps of measuring the actual arrival time t
a(k)k
of incoming cells k, providing a reference clock that maintains a time representing the theoretical arrival time of a current incoming cell, determining whether the current incoming cell is conforming or non-conforming to a predetermined condition, advancing said clock by an increment I after the arrival of each conforming cell to determine the theoretical arrival time of the next incoming cell, and if the current incoming cell is late by an amount greater than its theoretical arrival time plus the value of the increment I, updating the theoretical arrival time for the current cell to the actual arrival time for the current cell prior to advancing said reference clock.
The new method is more robust than GCRA. It resolves the drawbacks in the GCRA algorithms such as unfairness to VCs slightly violating their traffic contracts, and sensitivity to CDV which is dependent on unknown aggregate traffic behavior; on the other hand it bounds the CDV or BT (Burst Tolerance) of the conformed cell-stream. The method in accordance with the invention provides end users with a more gracious network environment than GCRA at the expense of limited extra bandwidth and buffering requirements on networks and user-end equipment.
The method brings the end-user an admitted rate much closer to the PCR (Peak Cell Rate). Although an increase on cell-clumping in the delivered traffic is expected as fewer cells are discarded, the increase is bounded and the impact on switch resource allocation and the AAL (ATM Adaptation Layer) cell-assembly buffer is also limited.
The invention also provides a user parameter control moduler for implementing traffic policing in packet-based, broadband networks, such as ATM networks, comprising means for monitoring the arrival of incoming cells, means for advancing a reference clock on a step of I if an arrival is late but not later than I, where I is an increment, and if an arrival is later than I assuming a new busy period and means for setting the reference clock at the arrival time.


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