Page 175 - CISSO_Prep_ Guide

individual packets and then buffering them at the far end, the
data could be easily re-assembled.

The first real standard used for this type of communications was
X.25. This is an excellent standard, especially for use with low-
quality voice-grade cables. X.25 employed error protection at
each point along the way, so errors would be corrected before
the data was further down the network. X.25 is still in some
limited use today, but it has been phased out of most regions of
the world. It is limited to data only and cannot handle other
types of traffic.

Then came the development of frame relay. A packet of data at
the data link layer is commonly called a "frame," and the
purpose of frame relay was to pass (relay) these frames over the
network. In the meantime, a lot of the old poor quality cable had
been replaced with fiber. This meant that the error-correcting
feature of X.25 was no longer needed since error-correcting
could be made at the endpoints instead of at each node along the
way. This resulted in faster speeds.

Another technology was the development of ATM
(asynchronous transfer mode). ATM traffic is divided into fixed-
length cells instead of variable length frames. This also
permitted better speeds and more efficient handling of the data.
The introduction of these packet-switched networks did have a
disadvantage in that traffic speeds were variable. For some
organizations with defined business and network requirements,
this may not be a deal. Just when the network is needed most, it
may be very slow. The solution to this was to create a fixed path
that the data of an organization would take through the packet-
switched network. This would create a virtual circuit that would