Frame Relay is a
standardized wide area network technology that
specifies the physical and logical link layers of digital telecommunications
channels using a packet switching methodology. Originally designed
for transport across Integrated Services Digital Network (ISDN)
infrastructure, it may be used today in the context of many other network
interfaces. It is also a protocol standard for LAN
internetworking which provides a fast and efficient method of transmitting
information from a user device to LAN bridges and routers.
The designers of Frame Relay aimed to provide a
telecommunication service for cost-efficient data transmission for intermittent
traffic between local area
networks (LANs) and between end-points in a wide area
network (WAN). Frame Relay puts data in
variable-size units called "frames" and leaves any necessary error-correction (such as
re-transmission of data) up to the end-points. This speeds up overall data
transmission. 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.
Frame
relay is based on the older X.25 packet-switching
technology which was designed for transmitting analog data such as
voice conversations. Unlike X.25 which was designed for analog signals, frame
relay is a fast packet technology, which means that the
protocol does not attempt to correct errors. When an error is detected in a
frame, it is simply "dropped." (thrown away). The end points are
responsible for detecting and retransmitting dropped frames. (However, the
incidence of error in digital networks is extraordinarily small relative to
analog networks.)
Frame Relay works at
the data link layer to reduce the overhead associated with the movement of data
across the wide area. Because we refer to Frame Relay as a WAN technology, it
is natural that the protocols will work with the improvements made in the
network over the past decades. It relays packets at the Data Link
layer of the Open Systems Interconnection (OSI)
model rather than at the Network layer.
A frame can incorporate packets from different protocols such as Ethernet and X.25. It
is variable in size and can be as large as a thousand bytes or more.
When the Frame Relay
specification was developed, the primary goal was to carry data over the WAN. To handle this
form of wide area communications, the core protocols for Frame Relay were established
using the revised version of the data link protocols. Instead of using the
network layer protocols, Layer 3 was gleaned down to efficiently carry the
traffic while performing the same function as the network layer. Moreover, the
data link layer was also streamlined to offer less overhead and processing on a
link−by−link basis because the circuits across the wide area are much more
reliable and error−free (thanks to fiber optics).
Newer wireless services known as the
General Packet Radio Services (GPRSs) are designed around the movement
of IP datagrams (always−on Internet access) from a cell phone or personal
digital assistant (PDA) to the public Internet or a VPN connection to an
intranet. Regardless of the direction that the data is going to flow, the use
of the IP services from the handset enables us to use the network ad hoc. When
an IP is created, it is packaged in a radio message. Once this message gets to
the base station, it is then encapsulated into a Frame Relay frame to be
carried across the wireless carrier's network to a router.
References:
Broadband Telecommunications Handbook (Regis J. Bates)
