Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-04-02
2001-08-14
Ton, Dang (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S352000, C370S392000, C370S397000
Reexamination Certificate
active
06275493
ABSTRACT:
TECHNICAL FIELD
This invention relates to the routing of real-time service requests through Asynchronous Transfer Mode (ATM) transport networks and, in particular, to the rapid establishment of a communications connection through an ATM network using cached switched virtual connections (SVCs) and ATM switching using cached cross-connections.
BACKGROUND OF THE INVENTION
In telecommunications systems, the current trend is to use an ATM protocol in the backbone transport network. The ATM protocol is based on a data structure called a “cell”. Cells are data packets having a fixed length of 53 octets. Each cell includes a header of 5 octets and a payload of 48 octets. The header is used to direct the cell through the network and the payload is the useful information portion of each packet.
ATM cells are routed through the network using routing information in the cell header. The routing information consists of a Virtual Path Identifier (VPI) and a Virtual Channel Identifier (VCI). The VPI and VCI pair have only local significance on the link between ATM nodes. ATM nodes, which include ATM switches and cross-connect apparatus, use routing tables to map VCI and VPI values received in an incoming cell to outgoing values used to select an outgoing link as a way of routing the associated cell through the ATM node. A Virtual Circuit Link (VCL) is a logical link between two nodes in the ATM network and is identified by a VCI value. A Virtual Path Link (VPL) is a logical link between two nodes in the network and is identified by a VPI value. A Virtual Circuit Connection (VCC) is identified by a Virtual Circuit Connection Identifier (VCCI). The VCC is an end-to-end connection between two nodes in the network and is formed by the concatenation of VCLs.
When real-time connection-oriented traffic is transferred to an ATM transport backbone, a path must be set up through the backbone network to provide a connection over which cells are routed. Each communication request may also be associated with a service characteristic which may guarantee a specific bandwidth to a communication connection. One way to set up a path through the network is to define a VPC between each pair of ingress/egress points in the network. A VPC generally reserves adequate bandwidth to accommodate an anticipated traffic load for a specific communications application. The VPC eliminates most connection setup signaling and processing but tends to waste network resources because the VPC lacks the granularity required for efficient use of the network capacity.
Network capacity can be utilized more efficiently if a Switched Virtual Circuit (SVC) is used for each communication connection. However, it is well known that the signaling involved in setting up an SVC consumes a certain overhead in the network and may cause connection processing delays. For example, when voice traffic is transported over an ATM network, the setup of SVCs is known to sometimes cause unacceptable call setup delays. This problem is particularly acute during peak busy hours when ATM switches may not be able to sustain a peak time call setup rate.
Solutions have been invented to overcome this problem. For example, U.S. Pat. No. 5,719,863 which issued Feb. 17, 1998 to Hummel describes a method and arrangement for fast through-connect of virtual connections in ATM communication systems. Hummel proposes that virtual connections be set up using cells containing call-associated signaling information. The signaling information is communicated using cells defined as administration and maintenance cells. A permanent virtual connection is set up from an originating to a destination ATM communication terminal equipment. Cells containing the signaling information are labelled as administration and maintenance cells. They are transmitted via the permanent virtual connection. Using the permanent virtual connection for setting up SVCs facilitates and accelerates SVC setup. A drawback of this solution is that a certain portion of the network bandwidth is reserved exclusively for signaling and that portion of the network cannot be used for other purposes even when signaling requirements are minimal. A further disadvantage is that SVC setup still takes time and uses resources in every node involved in the connection.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method and apparatus for rapidly establishing communications connections through an ATM network which ensures minimal delay in the setup of communications connections while ensuring efficient usage of network capacity.
It is another object of the invention to provide a method and apparatus for rapidly establishing cross-connections through an ATM switch which ensures minimal delay in the setup of cross-connections while ensuring efficient usage of switch capacity.
It is a further object of the invention to provide a method and apparatus for establishing a communications connection through an ATM network which permits the caching of SVCs.
It is another object of the invention to provide a method and apparatus for establishing a cross-connection through an ATM switch which permits the caching of cross-connections.
It is yet a further object of the invention to provide a method and apparatus for rapidly establishing a communications connection through an ATM network which permits the intelligent caching of SVCs using application-specific parameters.
It is yet another object of the invention to provide a method and apparatus for rapidly establishing a cross-connection through an ATM switch which permits an intelligent caching of cross-connections using application-specific parameters.
It is yet a further object of the invention to provide a method and apparatus for rapidly establishing a communications connection through an ATM network which proactively responds to the level of use of an ATM network by any given real-time communications application to ensure that network resources are efficiently utilized.
It is yet another object of the invention to provide a method and apparatus for rapidly establishing a cross-connection through an ATM switch that proactively responds to the level of usage of the switch fabric by any communications application to ensure that switch resources are efficiently utilized.
These and other objects of the invention are realized in a method of rapidly establishing a communications connection through an asynchronous transfer mode (ATM) network, comprising the steps of:
a) setting up at least one switched virtual circuit connection (SVC) between a first and second ingress/egress point in the ATM network;
b) caching the at least one SVC for use by either the first or second ingress/egress points when a request for a communications connection through the ATM network is received by one of the ingress/egress points;
c) selecting an appropriate one of the at least one cached SVCs when the request for a communications connection through the ATM network is received by one of the ingress/egress points, if an appropriate cached SVC is available; and
d) using the cached SVC to rapidly establish the communications connection through the ATM network.
The invention is practised using an apparatus for rapidly establishing a communications connection through an asynchronous transfer mode (ATM) network, comprising at least one machine programmed to perform the functions of:
a) a switched virtual circuit connection (SVC) control agent which is responsible for SVC setup and release at an ingress/egress point for the ATM network;
b) an SVC caching manager that maintains an SVC cache table in which a record of each cached SVC is stored; and
c) an SVC selector that processes operation requests from a communications application which seeks to establish an SVC through the ATM network, or release an SVC that is no longer required, the SVC selector selecting an available cached SVC from the SVC cache table or requesting the SVC control agent to establish a new SVC through the network when a process operation request is received from the communications application.
In accordance wi
Hayward Kenneth Gary
Li Li
Morris Todd Douglas
Nortel Networks Limited
Swabey Ogilvy Renault
Ton Anthony
Ton Dang
Wood Max R.
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