What does it do?
Unlike X.25, which has three protocol layers, the Frame Relay standard only specifies two layers, the physical layer, and the data link layer. Therefore the routing, flow control and error recovery services handled by the higher protocol layers are absent. Frame Relay benefits from this simplicity, in that it can offer much higher transfer rates than X.25. It operates on the assumption that modern digital circuits are very reliable, and expects higher level protocols to deal with issues of data corruption and flow control.

Frame relay currently supports only Permanent Virtual Circuits (PVCs). This means that a pre-established path through the network is established and can only be changed manually. As standards mature for switched circuits, this capability is expected to become available.

Frame relay interfaces with higher level protocols in much the same way as Token-Ring or Ethernet. Data from these upper level protocols is segmented into packets called frames. An address conversion between the upper-layer network address and the frame relay address format is performed, and the addressed frames are transmitted across the virtual circuit.

Frame relay services are usually identified by a committed information rate (CIR), which specify the amount of bandwidth the customer expects to use. Users are allowed to exceed this rate on an occasional basis, when they have short-term needs to transfer large quantities of data. this is termed bursting. This amounts to the customer being able to temporarily increase their bandwidth, which is called dynamic bandwidth allocation. With a standard T-1 line, a customer was required to pay for the full 1.5 Mb/sec bandwidth all the time, whether they were using it or not.

The data rates for Frame Relay extend from 56 Kb/sec to 1.3 Mb/sec.

How is it used?
Frame Relay is an excellent technology for making LAN-to-LAN connections, because of its relatively high speed. It can be implemented on leased lines, or connections can be made to a limited number of public Frame Relay services. Frame relay interfaces are generally achieved through bridges or routers on the LAN.

Where do I get more information?
Contact your local CBV Office.