420 Networking Explained, Second Edition
equipment, which gave SMDS the reputation of being an expensive service. Contributing
to this reputation was SMDS’s initial lack of support for low data rates (less than DS-1).
Many organizations that could have beneﬁted from SMDS service were locked out
because they could not afford (or justify) the high cost associated with high speeds and the
potential wasted bandwidth. Although some LECs now offer low-speed SMDS, which
makes the service more attractive to companies with limited resources and bandwidth
requirements, it’s a matter of too little too late since these companies are opting instead for
From a technology perspective, insufﬁcient attention also was given to how neighbor-
ing LECs would interconnect their SMDS networks. This led to incompatible methods
that made customers with LANs that crossed LATA boundaries hesitant to subscribe to
SMDS. Although this issue also has been addressed, it is once again a matter of too little
too late. Since the SMDS market never materialized, commitment to SMDS among the
LECs has been spotty at best. LECs have been opting instead to concentrate on frame
relay and ATM. For example, in the United States, among the various LECs, Verizon Com-
munications (formerly Bell Atlantic) offers SMDS service. Furthermore, among the major
IXCs (AT&T, MCI WorldCom, and Sprint), only MCI WorldCom offers nationwide
SMDS service. This lack of support makes customers wary of the service and less likely to
subscribe to it. In fact, the ﬁnal nail in SMDS’s cofﬁn was AT&T’s decision to provide
frame relay and ATM instead of SMDS.
Another reason for SMDS’s lack of market share in the broadband community is it
was never designed to support isochronous data, which is needed to transmit real time dig-
ital voice and video applications. SMDS was to eventually support voice and video in
addition to data. Its DQDB access method provides the necessary technology for this sup-
port. However, it doesn’t appear that SMDS will be further developed to incorporate sup-
port for isochronous services. Finally, although SMDS has built-in security that enables it
to use a shared, public network as the backbone for a private network, this concept has
been overshadowed by the Internet and virtual private networks (VPNs), as we discussed
in Chapter 7.
15. What is the current status and future of SMDS?
From all accounts, SMDS is probably “dead” in the United States. Consider, for exam-
ple, the following:
1. The SMDS Interest Group, which was the biggest promoter of SMDS,
folded in 1997.
2. In Data Communications’ 25th anniversary issue (October 21, 1997),
SMDS was identiﬁed as one of the top 25 ﬂops. “Switched multimegabit
data services were designed to deliver LAN-like performances over the
wide area. And it’s just what they did, to the dismay of users who got high
bandwidth, lots of ﬂexibility—and the variable delays associated with
Ethernet. Now the SMDS Interest Group has folded, presumably for lack
of interest” (p. 143).
3. MCI WorldCom is the only interexchange carrier that offers SMDS.
Chapter 13: Switched Multimegabit Data Service (SMDS) 421
4. Some local exchange carriers have discontinued offering SMDS service.
US West, for example, cited a dearth of customer demand as its reason for
On the other hand, since it is a service, SMDS can coexist with ATM and frame relay.
That is, SMDS subscribers can migrate to ATM or use ATM or frame relay as the underly-
ing technology for their SMDS service. It is uncertain, though, whether this will ever
come to fruition on a large-scale basis in the United States. From all accounts it is unlikely
that SMDS will grow in market share or be developed further. It might, however, survive
as a niche market.
Although SMDS is not in widespread use in the United States, it is still popular in
Europe. Providers include British Telecommunications (London), Telecom Eireann (Irish
Republic), France Telecom (Paris), Belgacom (Brussels), and Deutsche Telekom (Bonn).
Other countries in which SMDS deployment is high include Denmark, Switzerland, Aus-
tria, Italy, Sweden, and Australia.
This concludes our brief discussion on SMDS. For additional information about this ser-
vice, you are encouraged to consult the references listed in the appendix. You also might
want to review Chapter 12 (Frame Relay) and Chapter 14 (ATM) to compare SMDS to
these two technologies.
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