| A high-speed packet switching
protocol used in wide area networks (WANs). Providing a granular service of up to DS3
speed (45 Mbps), it has become very popular for LAN to LAN connections across remote
distances. Services are offered by all the major carriers. Frame relay is much faster than
X.25 networks, the first packet-switching WAN standard, because frame relay was designed
for today's reliable circuits and performs less rigorous error detection. Although X.25
was never widely used in the U.S., frame relay has become a major wide area technology.
The name comes from the fact that frame relay does not do any processing of the content of
the packets; rather, it relays them from the input port of the switch to the output port. Voice over frame relay enables voice to be packetized and travel over a frame relay network, often providing significant cost savings but at some sacrifice in voice quality, depending on the network configuration. In 1998, the Frame Relay Forum finalized its voice over frame relay specfication. FRF.11 defines the frame formats, and FRF.12 defines the ability to divide large frames into smaller ones so that realtime voice can be interleaved with data on slower connections. Frame relay provides permanent and switched logical connections, known as Permanent Virtual Circuits (PVCs) and Switched Virtual Circuits (SVCs). These are logical connections provisioned ahead of time (PVCs) or on demand (SVCs). The connections are identified by a Data Link Connection Identifier (DLCI) number that is significant to the local frame relay switch, which will change the number as it passes the packet on to its destination, because the receiving switch uses a different DLCI for its end of the same connection. Every DLCI requires a Committed Information Rate (CIR), which is a pledge on the part of the network to provide a certain amount of transmission capacity for the connection. CIRs are adjusted with experience. A customer attaches to the frame relay network via a frame relay access device (FRAD) which resides on the customer's premises. The FRAD may be a separate device or software built into the router. The FRAD connects to a port on a frame relay switch on the service provider's network via an interface known as the User-to-Network Interface (UNI). This line/port is typically some multiple of 64 Kbps, and all traffic for one customer generally travels through the same port. The frame relay switches may interconnect via point-to-point lines, but they often use an ATM backbone. A Frame Relay Network |