Networking Explained, Second Edition
An in-depth explanation of all things networking.
TABLE OF CONTENTS Networking Explained, Second Edition
Chapter 13: Switched Multimegabit Data Service (SMDS)
Highlights
In this chapter, we present information about switched multimegabit data service (SMDS), a data service that never achieved popularity in the United States. Our main purpose in discussing SMDS is twofold. First, the service is interesting in its own right and deserves attention. Perhaps more important, though, is SMDS's technical design and specifications. SMDS is based on IEEE 802.6, a data link layer protocol for metropolitan area networks (MANs). Called Distributed Queue Dual Bus (DQDB), this protocol is quite different from other protocols we have considered and merits examination. An outline of the main topics we address follows:
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SMDS Overview (Questions 1 2, 6)
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SMDS and Local and Interexchange Carriers (Questions 3 5)
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The DQDB and SMDS Protocols (Questions 7 9)
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SMDS Addressing (Questions 10 11)
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SMDS Applications (Question 12)
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SMDS vs. Frame Relay and ATM (Questions 13 14)
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Current Status and Future of SMDS (Question 15)
SMDS Overview
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What is SMDS?
Switched multimegabit data service is a cell-based, connectionless, high-speed, public, packet-switched, broadband, metropolitan area data network service designed for LAN-to-LAN connectivity. It is also a data service, which means that it can only transmit data (although it is capable of transmitting voice and video).
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What do you mean by "cell-based?"
SMDS uses fixed-length cells as its basic unit for transmitting data. These cells are similar to ATM cells, namely, they contain 53 bytes a 44-byte payload plus a 7-byte header and a 2-byte trailer. (See Chapter 14 for more information about ATM.) As a connectionless data service, SMDS does not...
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