me soon. MSU (modem sharing unit) A device that permits two or more terminals to share a single modem. MTBF (mean time between failures) The average length of time for which a system, or a component of a system, works without fault. MTP (Message Transfer Part) Part of SS7 used for communication in the PSTN. MTP is responsible for the correct and reliable end-to-end data transport of SS7 messages between munication partners. MTP Level 2 (MTP2) corresponds to OSI Layer 2, and MTP Level 3 (MTP3) corresponds to OSI Layer 3. MTS (mobile telephone service) MTS (mobile telephone service) A telephone service provided between mobile stations and the PSTN in which radio transmission provides the equivalent of a local loop. MTSO (mobile telephone switching office) A component in the cellular radio system that links the base transceiver stations with the terrestrial local exchanges to complete calls over the PSTN. MTTR (mean time to repair) The average time required to perform corrective mainte- nance on a failed device. MTU (maximum transmission unit) The maximum packet size that can be transmitted over a LAN or an internet. mu-law encoding Encoding according to ITU-T recommendation G.711 that is used with 24-channel PCM systems in the United States and Japan. It is similar to A-law encoding, but the two differ in the size of the quantizing intervals. multicarrier modulation A modulation scheme that uses and aggregates a certain amount of bandwidth and then subdivides it into subbands. Each subband is encoded by using a single- carrier technique, and bitstreams from the subbands are bonded together at the receiver. multicasting Simultaneous distribution of data to a defined subset of all receive points in a network. The subset may be redefined for each transmission and range from one to all receive points. multichannel Pertaining to broadcasting media capable of carrying multiple different televi- sion and radio channels. multidrop A communications arrangement in which multiple devices share a common trans- mission channel,