Switched Multimegabit Data Service. SMDS is a connectionless service used to connect LANs, MANs, and WANs at rates up to 45 Mbps. SMDS is cell-oriented and uses the same format as the ITU-T B-ISDN standards. The internal SMDS protocols are SIP-1, SIP-2, and SIP-3. They are a subset of the IEEE 802.6 standard for MANs, also known as DQDB.