Frame Relay
Frame Relay is a standardized wide area network (WAN) technology that specifies the physical and data link layers of digital telecommunications channels using a packet switching methodology.
The Frame Relay network handles the transmission over a frequently changing path transparent to all end-user extensively used WAN protocols.
With the advent of Ethernet over fiber optics, MPLS, VPN and dedicated broadband services such as cable modem and DSL, Frame Relay has become less popular in recent years.
For most services, the network provides a permanent virtual circuit (PVC), which means that the customer sees a continuous, dedicated connection without having to pay for a full-time leased line, while the service-provider figures out the route each frame travels to its destination and can charge based on usage.
[1] Frame Relay has its technical base in the older X.25 packet-switching technology, designed for transmitting data on analog voice lines.
The Frame Relay network exists between a LAN border device, usually a router, and the carrier switch.
When offered load is high, due to the bursts in some services, temporary overload at some Frame Relay nodes causes a collapse in network throughput.
To do so, special congestion control bits have been incorporated into the address field of the Frame Relay: FECN and BECN.
Frame Relay provides an industry-standard encapsulation, utilizing the strengths of high-speed, packet-switched technology able to service multiple virtual circuits and protocols between connected devices, such as two routers.
X.25 remained the primary standard until the wide availability of IP made packet switching almost obsolete.
Frame Relay networks can dynamically allocate bandwidth at both the physical and logical channel level.
Initial proposals for Frame Relay were presented to the Consultative Committee on International Telephone and Telegraph (CCITT) in 1984.
Lack of interoperability and standardization prevented any significant Frame Relay deployment until 1990, when Cisco, Digital Equipment Corporation (DEC), Northern Telecom, and StrataCom formed a consortium to focus on its development.
Datalink connection identifiers (DLCIs) are numbers that refer to paths through the Frame Relay network.
Individual network interfaces and the end nodes attached to them, for example, can be identified by using standard address-resolution and discovery techniques.
In addition, the entire Frame Relay network appears to be a typical LAN to routers on its periphery.
LMI virtual circuit status messages provide communication and synchronization between Frame Relay DTE and DCE devices.
Multicasting saves bandwidth by allowing routing updates and address-resolution messages to be sent only to specific groups of routers.
In more recent years, Frame Relay has acquired a bad reputation in some markets because of excessive bandwidth overbooking.
[citation needed] When multiplexing packet data from different virtual circuits or flows, quality of service concerns often arise.
