The Passport 4400 provides channel-side frame relay pass-through services, which allows third-party FRADs to connect transparently through the Passport wide area network. The frame relay pass-through services use switched virtual circuits (SVC) to terminate FR DCE configured ports connected to the third-party devices (see the illustration below).
The diagram below shows two third-party FRADs communicating with each other over a frame relay backbone.
In effect, the Passport 4400 provides connectivity between FRADs and the Passport network. The Passport 4400 unit appears as a frame relay user-network interface (FRUNI) switch to the FRAD and provides the necessary buffering and flow control mechanisms to maintain delivery of user data between the attached devices.
The Passport 4400 allows data traffic originating from a FRAD to be combined with other traffic from the same site, such as voice and LAN, and carried to a Passport network over a single low speed link. The traffic can then be transported over the network to a FRAD at a remote location which is also serviced by a Passport 4400 unit (see the illustration above).
The frame relay pass-through service performs the following functions:
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