Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Patent
1997-10-27
2000-06-13
Nguyen, Chau
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
370412, 370468, H04L 1256
Patent
active
06075771&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method of fairly controlling the excess usage of a finite resource, for example the usage of available bandwidth by permanent virtual circuits in frame relay networks.
In frame relay networks, permanent virtual circuits are set up through the network and frames are routed at each node in accordance with a virtual circuit id carried in the packet header. Available bandwidth is of course determined by the physical links and as a result congestion can occur in the network. When this happens frame relay may discard packets, which then must be retransmitted.
Existing frame relay networks (based upon current frame relay standards) have a problem with regards to the way in which spare/free bandwidth is allocated. Virtual circuits competing for excess bandwidth are not subject to fairness. Frames received by the switching mechanism are switched out to an outgoing transmit queue. If the transmit queue is congested (i.e. virtual circuits on that piece of bandwidth are transmitting more than the resource can handle) then the number of frames in the transmit queue will increase, potentially eventually overflowing. Essentially, the virtual circuit transmitting the most frames will get to consume the most bandwidth and the most transmit and buffering resources.
Current technologies, for example, as illustrated in the paper by D. B. Grossman entitled "An Overview of Frame Relay communications", CONFERENCE ON COMPUTERS AND COMMUNICATIONS, March 1991, and the paper by K. S. R. Mohan "Enterprise Networking using Frame Relay", PACIFIC TELECOMMUNICATIONS CONFERENCE, vol. 1, January 1993, in this area rely upon the Committed Information Rate and congestion procedures defined in the ANSI specifications. These procedures allow the user devices in a network to be policed to a committed information Rate (CIR), but burst up to an excess information rate (EIR). Excess burst traffic is marked as excess in frame relay by setting a DE (discard eligible) bit. DE frames are discarded in preference to non DE frames.
Other situations arise where the `excess` usage of any resource by competing users needs to be controlled.
An object of the invention is to provide a method of fairly controlling the excess usage of a finite resource.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of controlling, in a digital communications system, flow of traffic into a resource having a shared input queue of finite capacity, and further having a flow of traffic which originates from a plurality of information sources, and wherein a committed information rate is pre-established for each source and the traffic from each source carries an excess indication when it is flowing at a rate in excess of said committed information rate, the method comprising, for each source, carrying out steps of at call set up, defining a fair burst Bf representing a number of bits that may be transferred from the source within a predetermined time interval T such that the sum of the fair bursts Bf for all sources does not exceed resource queue size, and a fair information rate Bf/.DELTA.T, and .DELTA.T is a time interval over which a burst rate is measured; determining whether traffic from said source carries an excess indication; determining whether the resource is experiencing congestion; if step b determined that the traffic carried an excess indication and step c determined that the resource in congested, subsequently measuring a current information rate of traffic carrying an excess indication and determining if said current rate of incoming traffic is greater than the fair information rate; and of the current information is greater than said fair information rate, discarding the incoming traffic.
In a preferred embodiment, the method of controlling the "fair " excess information rate is based upon the "leaky bucket" approach, although other bandwidth admissions procedures can be employed. This makes the allocation of excess resources `fair` between competing virtual circuits. A
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Wall Wayne
Wolff Mark
Newbridge Networks Corporation
Nguyen Chau
Wilkow Frederic D.
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