frame relay
Frame Relay
(communications)Frame Relay is the result of wide area networkingrequirements for speed; LAN-WAN and LAN-LANinternetworking; "bursty" data communications; multiplicityof protocols and protocol transparency. Theserequirements can be met with technology such as optical fibre lines, allowing higher speeds and fewer transmissionerrors; intelligent network end devices (personal computers,workstations, and servers); standardisation and adoptionof ISDN protocols. Frame Relay could connect dedicated linesand X.25 to ATM, SMDS, BISDN and other "fast packet"technologies.
Frame Relay uses the same basic data link layer framing andFrame Check Sequence so current X.25 hardware still works.It adds addressing (a 10-bit Data Link Connection Identifier(DLCI)) and a few control bits but does not includeretransmissions, link establishment, windows or errorrecovery. It has none of X.25's session layer but adds somesimple interface management. Any network layer protocol canbe used over the data link layer Frames.
Frame Relay Resource Center.
frame relay
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 popular for LAN to LAN connections across remote distances, and services are offered by most major carriers.Frame relay (FR) is much faster than X.25, the first packet-switched WAN standard, because frame relay was designed for reliable circuits and performs less error detection (X.25 was never widely used in the U.S.). Frame relay does not process the packets; it relays them from the switch's input port to the output port, hence the name.
The FRAD (Frame Relay Access Device)
Attachment to a frame relay network is made via a FRAD on the customer's premises, which may be a separate device or software in the router. The FRAD connects to a switch port on the service provider's network via the User-to-Network Interface (UNI). All traffic for one customer generally travels over the same line, which is typically a multiple of 64 Kbps. Frame relay switches interconnect via point-to-point lines or an ATM backbone.
Permanent and Switched Circuits
Frame relay provides Permanent Virtual Circuits (PVCs) and Switched Virtual Circuits (SVCs). They are logical connections provisioned ahead of time (PVCs) or on demand (SVCs).
Connections are identified by a Data Link Connection Identifier (DLCI) number that is significant only to the local FR switch, which changes the number as it passes the packet on to its destination. 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.
Voice Over FR
Voice can be packetized to travel over a frame relay network, often providing significant cost savings with some sacrifice in voice quality, depending on network configuration. In 1998, the Frame Relay Forum finalized the Voice Over FR specification. FRF.11 defines the formats, and FRF.12 subdivides large frames in order to interleave real-time voice with data on slow connections.
A Superb Resource
"Frame Relay for High-Speed Networks" by Walter Goralski is must reading not only to learn about frame relay, but about wide area networking in general. Goralski factors in history, trends and related networking technologies. Published by John Wiley & Sons, Inc., ISBN 0-471-31274-6.
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| A Frame Relay Network |
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| This illustration depicts the customer and service provider sides of a frame relay network. An ATM backbone is shown, because it is a common method of interconnecting FR switches. The FRAD may be a separate device (left side of illustration) or software built into the router (right). |