Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Patent
1996-08-02
1998-07-14
Nguyen, Chau
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
370394, 370412, H04L 1256
Patent
active
057815321
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates generally to packet-switched networks, and more particularly to a data link interface, such as may be incorporated in a router for connection to a frame relay network.
Frame relay is a packet switching technology designed to require the minimum processing. Frame relay networks provide dynamic bandwidth allocation by switching framed data between connection segments. The networks are based on virtual connections, which can either be switched or permanent. The present invention is concerned with permanent virtual connections (PVCs).
Permanent virtual connections (PVCs) are end-to-end logical connections across a frame relay network composed of a sequence of PVC segments between pairs of frame relay DCEs (data connection ends) or frame relay DCE and a frame relay DTE (data terminal end).
Each end of PVC segment is called a data link connection (DLC). A DLC is identified on a frame relay port with a locally unique number called the data link connection identifier (DLCI).
On frame relay networks, there is potential for downstream network congestion. Frame relay switches use a backward explicit congestion notification bit (BECN) bit to notify user devices of congestion. The BECN bit is included in the address header of each Q.922 frame. Conventional routers ignore the BECN bit and congested permanent virtual connections. They continue to send out data over frame relay links to the network as if the PVCs were not congested, and as a result, packets are dropped, causing expensive retransmissions and down time for applications.
N. J. Muller (INTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, vol. 2., No. 2, Jun. 1992, UK pages 87-99) discloses the adjustment of transmission rate in the presence of network congestion. However, Muller does not disclose any means of making optimum use of the bandwidth available in the presence of congestion.
An object of the invention is to alleviate the aforementioned problems.
SUMMARY OF THE INVENTION
According to the present invention there is provided a data link interface for sending and receiving data over a virtual connection in a packet-switched network, comprising means for detecting congestion in the network, and means for adjusting the transmission rate in response to the detection of said congestion so as to reduce congestion in the network, characterized in that it further comprises means for sorting traffic by conversation between two endpoints, and means for re-ordering packets from different conversations on a common link in the presence of congestion while maintaining the order of transmission for each conversation in order to achieve fair allocation of bandwidth among different conversations.
Preferably the network is a frame relay network, and the means for detecting congestion in the network comprises a congestion bit detector, preferably a backward explicit congestion bit (BECN) detector. The virtual connection may be a permanent virtual connection.
Preferably, upon detection of a BECN bit, the interface, which is normally a router drops the transmission rate to a predetermined rate known as the committed information rate (CIR). Traffic is then prioritized according to type, with bandwidth guaranteed to critical applications even during periods of severe congestion.
Unlike most routers, which treat all data equally, a router operating in accordance with the invention sorts traffic by conversation between user data devices, and then allocates bandwidth fairly between active conversations. Heavy usage applications, such as bulk file transfers, are forced to share link capacity fairly with lighter usage applications.
The router can therefore offer reliable frame relay data transmission and protection for high priority calls. Network behavior is stabilized during congestion, resulting in increased speed and reduced overheads.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:
FIG.1 is block diagram of a p
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patent: 5014265 (1991-05-01), Hahne et al.
patent: 5231633 (1993-07-01), Hluchyj et al.
patent: 5335224 (1994-08-01), Cole et al.
patent: 5506839 (1996-04-01), Hatta
patent: 5600798 (1997-02-01), Cherukuki et al.
Newbridge Networks Corporation
Nguyen Chau
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