C H A P T E R 14
• Tell how SMDS works, and describe its components.
• Describe the operational elements of the SMDS environment, and outline its underlying protocol.
• Discuss related technologies.
• Discuss SMDS access classes and cell formats.
Switched Multimegabit Data Service
Switched Multimegabit Data Service (SMDS) is a high-speed, packet-switched, datagram-based WAN
networking technology used for communication over public data networks (PDNs). SMDS can use fiber-
or copper-based media; it supports speeds of 1.544 Mbps over Digital Signal level 1 (DS-1) transmission
facilities, or 44.736 Mbps over Digital Signal level 3 (DS-3) transmission facilities. In addition, SMDS
data units are large enough to encapsulate entire IEEE 802.3, IEEE 802.5, and Fiber Distributed Data
Interface (FDDI) frames. This chapter summarizes the operational elements of the SMDS environment
and outlines the underlying protocol. A discussion of related technologies, such as Distributed Queue
Dual Bus (DQDB) is also provided. The chapter closes with discussions of SMDS access classes and
SMDS Network Components
SMDS networks consist of several underlying devices to provide high-speed data service. These include
customer premises equipment (CPE), carrier equipment, and the subscriber network interface (SNI).
CPE is terminal equipment typically owned and maintained by the customer. CPE includes end devices,
such as terminals and personal computers, and intermediate nodes, such as routers, modems, and
multiplexers. Intermediate nodes, however, sometimes are provided by the SMDS carrier. Carrier
equipment generally consists of high-speed WAN switches that must conform to certain network
equipment specifications, such as those outlined by Bell Communications Research (Bellcore). These
specifications define network operations, the interface between a local carrier network and a
long-distance carrier network, and the interface between two switches inside a single c