Frame Relay
Over the past few years Frame Relay has been one of the most
popular remote-access technologies. It offers a high-speed connection between a
central office and a branch office.
One of Frame Relay's benefits is built-in congestion control to
combat bursty traffic. As bandwidth needs have increased over the years, this
technology has proven very popular. Also, Frame Relay circuits can be ordered
from providers in a variety of bandwidths. Starting at 56 kbps, these are
usually fractions of a T1. This allows for flexibility when planning.
Some of the services that can be used over Frame Relay networks
are data, voice over IP, voice over Frame Relay, and IP Multicast.
Frame Relay operates at Layer 2 by encapsulating Layer 3
traffic such as IP within a Frame Relay frame. To improve performance, Frame
Relay relies on higher-layer protocols such as TCP to overcome corrupt or
dropped frames that occur during transmission. This is different from protocols
such as X.25 that have built-in error checking/correction. Often Frame Relay is
described as a successor to X.25.
Frame Relay employs its own addressing scheme at Layer 2 to
specify a frame's destination. This feature is called a Data Link Connection Identifier (DLCI). This field in the Frame Relay header
tells the Frame Relay switch where to route the frame. The DLCI can be thought
of as the Media Access Control (MAC) address in the Frame Relay network.
Another advantage of Frame Relay is its capability to establish
one-to-many connections. This is often called point-to-multipoint. This capability can potentially
allow the redirection of traffic around an outage, provided that a
partially-meshed network exists.
One of Frame Relay's drawbacks is the high cost of provisioning
links. The high cost can possibly be justified in a branch office scenario, but
it might be unsuitable for single remote users.
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