SMDS (Switched Multimegabit Data Service) is a public, packet-switched service aimed at enterprises that need to exchange large amounts of data with other enterprises over the wide-area network on a nonconstant or "bursty" basis. SMDS provides an architecture for this kind of data exchange and a set of services. In general, SMDS extends the performance and efficiencies of a company's local area network (LANs) over a wide area on a switched, as-needed basis.
SMDS is connectionless, meaning that there is no need to set up a connection through the network before sending data. This provides bandwidth on demand for the "bursty" data transmission typically found on LANs.
SMDS packets contain up to 7168 bytes of data, which is large enough to accept the most common LAN packets. Each packet includes the source address and the destination address and is sent separately from other packets.
Each enterprise using SMDS is assigned from one to sixteen unique SMDS addresses, depending on needs. An address is a ten digit number that looks like an ordinary telephone number.
SMDS also provides for broadcasting packets to multiple SMDS addresses. Each SMDS company is assigned one or more group addresses that can be used to define destination groups. Group addressing is similar to LAN multicasting. It lets routing protocols, such as TCP/IP, use dynamic address resolution and routing updates.
Since SMDS is a public service, any SMDS customer can exchange data with any other customer. The SMDS Interest Group, an association of service providers, equipment manufacturers, and users, develops technical specifications, promotes awareness of SMDS, stimulates new applications, and ensures worldwide service interoperability, working with its international affiliates. Their home page provides a list of companies providing SMDS services.