Frame Relay
Frame Relay is a fast packet-switching technology
introduced in 1992. fast packet-switching means,
high-speed
communications
and
low-delay
networking. Fast packet is a "hold and forward"
technology designed to reduce delay, reduce
overhead and processing, improve speed, and reduce
costs. It is designed to run on high-speed circuits with
low (or no) error rates. Errors are corrected at the two
ends, instead of every step along the route
Frame Relay versus X.25
Frame Relay, as stated, is a fast packet-switching
technology used for the packaging and transmission of
data communications. Moreover, Frame Relay packages
the data into a data link layer frame used to carry the
data across the network on a permanent virtual circuit
(PVC) without all the handling of the X.25 networks.
Although X.25 acknowledges every packet traversing the
network, Frame Relay does not use acknowledgments
(ACKs) or negative acknowledgments (NAKs). Also, when
an X.25 packet is corrupted, the network node requests a
retransmission, which is not so on Frame Relay. Both of
the services do, however, use a statistical TDM concept.
Table 11-1 is a summary of the comparison of X.25 and
Frame Relay services.
Summary of Frame Relay and X.25
Frame Relay’s Frame
The beginning of the frame starts with an opening flag,
the opening flag depicts that the frame is started. Next, a
two-byte sequence defines the addressing of the frame.
This is called the Data Link Connection Identifier (DLCI). By
very nature of the title (DLCI), we can assume that Frame
Relay works at the data link layer. Following the data field
in the Frame Relay frame is a cyclic redundancy check
(CRC) used only to check for corruption. The CRC
determines if the frame or the address information is
corrupt. If so, the frame is discarded; if not, the frame is
forwarded. There is no ACK or NAK in the Frame Relay
transmission along the route. Lastly, there is a closing flag
on the frame, indicating that the transmission of the
frame is ended
Frame
Figure
Asynchronous Transfer Mode (ATM)
Overview
In 1992, a group of interested parties developed a
set of standards-based specifications called the
Asynchronous Transfer Mode (ATM). This was a step
at developing a single set of standards for the
integration of voice, data, video, and multimedia
traffic on a single backbone network. Prior to this
development, the industries offered separate
standards and networks for voice, others for data,
and still others for video communications.
ATM
What Is ATM?
ATM is a member of the fast packet-switching family called cell
relay As part of its heritage, it is an evolution from many other
sets of protocols. In fact, ATM is a statistical time-division
multiplexed (TDMed) form of traffic that is designed to carry
any form of traffic and enables the traffic to be delivered
asynchronously to the network. When traffic in the form of
cells arrives, these cells are mapped onto the network and are
transported to their next destination. When traffic is not
available, the network will carry empty (idle) cells because the
network is synchronous.
ATM is one technology for voice, data, video and multimedia. It
provides bandwidth on demand as needed
Mapping Circuits Through an ATM
Network
Mapping Circuits Through an ATM Network. The
connection is built into a routing table in each of
the switches involved with the connection from
end to end. As such, the switches only need to
look up a table for the incoming port and
channel and then determine the mapping (in
the same table) for the output port and channel.
Using virtual path identifiers (VPI) and virtual
channel identifiers (VCI),