The Frame Relay Forum has ratified a specification for the interconnection of Frame Relay and Asynchronous Transfer Mode networks, which is claimed to bring significant advantages over the earlier Frame Relay/Asynchronous Transfer Mode Permanent Virtual Circuit Network Interworking Agreement adopted in January (CI No 2,595). Northern Telecom Ltd’s John Casadonte, a member of the forum, said one of the major advantages of the new specification compared with that agreed in January, is that the code typically resides in the public network switches, whereas with the Virtual Circuit Network stuff, lives in the customer premises equipment. Because of this, the earlier version required the Frame Relay equipment to have the necessary software to interface to Asynchronous Transfer Mode at both ends of the connection. By having it located at the switch, the new specification enables translation from Frame Relay to Asynchronous Mode, and vice versa, without requiring any modification to users’ equipment. Because of this, said Casadonte, the Service Internetworking Agreement gives users more flexibility to migrate only those portions of their networks to Asynchronous Transfer that would benefit from the upgrade. Casadonte cited a scenario where a Frame Relay network connects 400 locations, but where only a handful of these would gain from Asynchronous Mode. Whereas the first version would require all 400 locations to add code to their customer premises equipment, the new one requires an upgrade only at the public network switches where the connections are interfacing to Asynchronous Mode, he said. Nevertheless, Casadonte did still feel that the Network Internetworking Agreement will have a place for users, for example in very simple networks where upgrading the customer equipment is not a big issue. The new agreement describes interworking functions, including frame formatting and delimiting; discard eligibility and cell loss priority mapping; congestion indication; command-response mapping; and Data Link Connection Identifier-to-Common Part Indicator/Virtual Connection Identifier mapping. Two optional encapsulation modes are supported for each pair of interoperable Frame Relay and Asynchronous Mode Private Virtual Circuits: transparent mode is said to forward unaltered encapsulations; and translation mode is said to support interworking of routed or bridged protocols. The Internetworking Agreement is available free over the Internet at http://frame-relay.indiana.edu.
