network protocols handbook.pdf

223Protocols GuideMAN ProtocolsProtocol NameSMDS: Switched MultimegabitData ServiceProtocol DescriptionSwitched Multimegabit Data Service (SMDS) is a broadbandnetworking technology developed by Bellcore based on theIEEE 802.6 DQDB (Distributed Queue Dual Bus) MAN technology.SMDS can use fiber- or copper-based media. It supports speedsof 1.544 Mbps over DS-1, or 44.736 Mbps over DS-3. In addition,SMDS data units are large enough to encapsulate entireIEEE 802.3, IEEE 802.5, and Fiber Distributed Data Interface(FDDI) frames. SMDS operates by accepting high-speed customerdata in increments of up to 9,188 octets, and dividing itinto 53-octet cells for transmission through the service provider’snetwork. These cells are reassembled, at the receiving end,into the customer data.The SMDS Interface Protocol (SIP) is a three-level protocol,based on IEEE 802.6 DQDB, which controls the customer’s accessto the network. SIP Levels 3 and 2 operate at the MediaAccess Control (MAC) sublayer of the data link layer of the OSIreference model. SIP Level 1 operates at the physical layer ofthe OSI reference model. SIP Level 3 receives and transportsframes of the upper layer protocol information. SIP Level 2 controlsaccess to the physical medium. SIP Level 1 includes thePLCP and the transmission system.Protocol StructureThe SIP Level 3 PDU is shown in the following diagram.36