HP auroraTempo, User Manual

Page: 217 / 300

Issue 1a - 10/99 8-3
Introduction to Frame Relay
With X.25, as information moves across each point in the
network it is checked for errors. Any errors which occur
are corrected by means of retransmitting the data. Error
detection and correction of this type virtually guarantees
the transmission of a ‘clean’ data stream and this makes
X.25 very suitable for use over lines which have a high
error rate.
However, nowadays, hardware improvements and the
availability of digital transmission facilities mean
relatively ‘error free’ transmission. Error rates in the
order of 1 x 10
9 , for example, are easily achieved.
Frame Relay takes advantage of these low error rates by
omitting the constant error detection and correction
associated with X.25. If errors do occur Frame Relay
relies on the intelligent end user systems, running higher
level protocols, to detect the fact that an error has
occurred and to request frame retransmission.
By removing this processing overhead Frame Relay can
achieve approximately 10 times the packet throughput of
X.25 networks. Thus, Frame Relay can be thought of as
a ‘stripped-down’ version of X.25, providing higher-
speed communications with less overhead.
Statistical Multiplexing and Bandwidth
Frame Relay is also characterized by its more efficient use of
bandwidth, in comparison to TDM (Time Division
Multiplexing)-based solutions.
TDM solutions reserve a fixed amount of bandwidth,
based on defined timeslots for each user or application,
regardless of whether they have anything to send or not.
This means that available bandwidth often remains
unused.