Reliability Comparison of WAN Technologies

Reliability Comparison of WAN Technologies

Technology Reliability
Asynchronous dial-up Low
X.25 High
ISDN Moderate
Frame Relay Moderate
Leased lines Moderate
DSL Moderate
Cable modem Moderate

Examining this table further, it’s important to consider each factor of reliability. Dial-up connections
cannot recover errors within packets and cannot automatically find a new path through the
network, except when the circuit is emulated over ATM or another technology within the carrier’s
cloud. X.25 is considered highly reliable by most—including Cisco—because the protocol provides
for error correction and other mechanisms to protect data without relying on upper layer protocols.
The technologies rated with moderate reliability are typically quite robust and will work for
most users without any problems. Historically, however, Cisco presented the position that these
technologies were more prone to problems, including lower service guarantees. Although none of
the technologies rated moderate provide for error correction as X.25 does, the quality of cables,
equipment, and software makes errors very rare and easily addressed by the upper level protocols.

Note: Carriers are turning to Multi-Protocol Label Switching (MPLS) for their voice
and data clouds and IP datagrams for all services. This will eventually position
each of these technologies as a last-mile service; the technology within the
cloud will be transparent to the user and data. Table 22.8 focuses on the endto-
end use of the noted technologies.