DYNAMIC PERMANENT VIRTUAL CONNECTION (DPVC) AT USER-TONETWORK INTERFACES IN FRAME RELAY NETWORKS
FIELD OF THE INVENTION
The present invention relates to data communication networks and more particularly to a method of dynamically establishing/clearing a permanent virtual connection at both user-to-network interfaces within a frame relay network. 10 This is termed a dynamic permanent virtual connection or DPVC.
BACKGROUND OF THE INVENTION
Data networks used to transport data between distant end 15 users can employ any of a number of technologies in transferring the data across intervening, interconnected systems. One well-known technology is frame relay technology which can be used to transport variable length data messages between the end users. In a frame relay network, a virtual 20 link or virtual connection (VC) exists across the entire network between the communicating end users. This virtual connection provides the bi-directional transfer of data messages from an originating end user to a destination end user with the order preserved. This is done on the basis of a label 25 attached to each data message called a data link connection identifier (DLCI). Each end associates the virtual connection with its own DLCI. The DLCI may be the same or different from the DLCI used at the other end.
Each DLCI is associated with a user-to-network interface (UNI). A UNI is a interface between a frame relay network and an end user. It includes a physical interface on the end user device, a physical interface on the frame relay network equipment, and the physical line between them. 35
Network nodes within the frame relay network communicate across network-to-network Interfaces or NNIs. The details of UNIs and NNIs are not important to an understanding of the present invention but may, if desired, be found in a number of documents available from known 4Q standards organizations. Representative documents include Frame Relay Forum FRF 1.1, Frame Relay Forum FRF 2.1, ITU X.76, ITU X.36, ITU Q.933 Annex A, and Frame Relay Forum FRF.10.
In known networks, data routing devices are typically 45 interconnected using frame relay permanent virtual connections or PVCs. The descriptor "permanent" means that the resources for the connection remain committed for the life of the connection between the end users and are thus unavailable for use by others even when those resources are not 50 actually needed. PVCs are an inefficient use of network resources and increase network operating costs for both network service providers and end users.
To provide more effective utilization of network resources, switched virtual connections (SVCs) can be 55 implemented within and between frame relay networks. In the case of switched connections, network resources are committed for the duration of the connection. When there is no data to be transferred, the user can clear the virtual connection, releasing the network resources and making 60 them available to other connections. Details of SVCs can be found in ITU X.36, X.76, Q.933; Frame Relay Forum FRF.4 and FRF.10. While SVCs are highly flexible, they are also costly to implement at a UNI and provide more functionality than is required by many existing network devices. 65
It is possible to provide a PVC service to the end users using SVC processing within and between frame relay
networks. The resulting VC is called a switched permanent virtual connection (SPVC). The SPVC appears to the end users as a PVC, but is connected through the frame relay network(s) as an SVC. Although the SVC provides high resiliency and a reduction in network provisioning requirements, the service to the end user is still that of a PVC which means that network resources are committed to the VC even when there is no data to send. The end user has no means of notifying the frame relay network whether the resources of the SPVC are needed or not.
SUMMARY OF THE INVENTION
To provide the flexibility of connections that can be dynamically established and cleared for a specific end user without the attendant costs and complexities of switched virtual connections, a dynamic permanent virtual connection or DPVC has been developed. DPVCs support usercontrolled establishment and clearing of frame relay SPVCs without having to implement a full data link layer and sophisticated signaling state machine. DPVCs offer a service similar to that of a standard PVC in that no parameter or addressing signaling is done.
The invention is implemented in a method for use in a data communication network having at least two end users connected to a frame relay network. The FR network consists of one or more sub-networks. Sub-networks are connected to each other at network-to-network interfaces (NNIs). Each end user is connected to at least one network node through a user-to-network interface or UNI. Adynamic permanent virtual connection is comprised of a DPVC segment at the originating UNI, an SPVC segment between the originating network node and the destination network node, and a DPVC segment at the destination UNI.
The DPVC segments and the connection parameters (DLCI, committed information rate (CIR), committed burst size (Be), excess burst size (Be), etc.) are provisioned, similar to an SPVC. The end users can control the establishment and clearing of the SPVC segment via the DPVC signaling mechanisms at the UNI.
In setting up a DPVC between the end users, the originating end user requests the network to activate the DPVC. The network establishes an SPVC to the destination network node and activates the destination and origination DPVC segments, and acknowledges the request. The PVC status management procedures (i.e. Q.933 Annex A) informs the end users that the DPVC is active and can transfer data.
When the end users have completed data transfer the end users initiate deactivation of the DPVC which clears the SPVC segment and releases the network resources.
BRIEF DESCRIPTION OF THE DRAWINGS
While this specification concludes with claims that particularly point and distinctly claim that which is regarded as the present invention, details of a preferred embodiment of the invention may be more readily ascertained from the following detailed description when read in conjunction with the accompanying drawings wherein:
FIG. 1 is a schematic illustration of a virtual connection between two end systems showing the points at which dynamic permanent virtual connection segments established in accordance with the present invention would be used;
FIG. 2 is a block diagram representation of major functional components required in a system which is to implement dynamic permanent virtual connections;
FIG. 3 is a schematic representation of the preferred structure of messages employed in establishing and clearing dynamic permanent virtual connections;