SMDS

            SMDS stands for switched multi-megabit data service. By definition, SMDS is a high-performance, connectionless telecommunications service for packet switched data transport. An important thing to keep in mind about this service is that it is neither a protocol nor a technology. The SMDS service provider has absolute control over the use of more unique addresses, however the customer has absolute control over individual addresses. An Individual Address is a media access control layer (MAC) address in an E.164 format, and the customer can assign several addresses (up to sixteen for each individual SNI) to a single Customer Premise Environment (CPE) or assign assign a group address to several hardware devices. SMDS is often compared with ATM because of certain similarities. Both use cell relay transport, however ATM has a maximum length, which are 56,347 octets larger than SMDS. A common usage of SMDS is to have it run as a server within an ATM network. This is beneficial because it creates a connectionless datagram service with SMDS, and still utilizes all the benefits of an ATM network. .
             When compared to the OSI model, most of the work done by SMDS is operating at the data link level, which we remember is the level in which data is encoded and decoded into bits, it is also broken down into two sub-layers. These sub-layers are known as the LLC sub-layer and the MAC sub-layer. The LLC controls frame synchronization and error checking, while the MAC sub-layer controls how a computer gains access to data and permission to transport it.
             Today's SMDS uses DQDB (Distributed Queue Dual Bus) technology to transport its cells which are 53 octets in length across a network. DQDB has integrated a plethora of positive features including; Duel-bus architecture, Cell relay transmission, Compatibility with LANs and FDDI, The ability to use sever different types of media including coaxial cable to fiber optics, Fault tolerance, rates from 1.