Data Communications Networking Devices - 4th Ed.pdf

66 _______________________________ FUNDAMENTAL WIDE AREA NETWORKING CONCEPTSTable 1.21cont.)V.27 bis 4800/2400 bps modem with automatic equalizer standardized for use on leasedtelephone-type circuits.V.27 ter 4800/2400 bps modem standardized for use in general switched telephonenetwork. Similar to the Bell 208B.V.28 Electrical characteristics for unbalanced double-current interchange circuits de®nedby V.24; similar to and operational with RS-232).V.29 9600 bps modem standardized for use on point-to-point four-wire leasedtelephone-type circuits. Similar to the Bell 209.V.31 Electrical characteristics for single-current interchange circuits controlled by contactclosure.V.32 Family of 4800/9600 bps modems operating full-duplex over two-wire facilities.V.33 14.4 kbps modem standardized for use on point-to-point four-wire leasedtelephone-type circuits.V.34 28.8/33.6 kbps modem standardization for operating full duplex over two-wirefacilities.V.35 Data transmission at 48 kbps using 60±108 kHz group band circuits. CCITT balancedinterface speci®cation for data transmission at 48 kbps, using 60±108 kHz group bandcircuits. Usually implemented on a 34-pin M block type connector M 34) used to interface toa high-speed digital carrier such as DDS.V.36 Modems for synchronous data transmission using 60±108 kHz group band circuits.V.37 Synchronous data transmission at a data signalling rate higher than 72 kbps using60-108 kHz group band circuits.V.40 Error indication with electromechanical equipment.V.41 Code-independent error control system.V.42 Error control for modems.V.42 bis Data compression for use in switched network modems.V.50 Standard limits for transmission quality of data transmission.V.51 Organization of the maintenance of international telephone-type circuits used fordata transmission.V.52 Characteristic of distortion and error-rate measuring apparatus for data transmission.V.53 Limits for the maintenance of telephone-type circuits used for data transmission.V.54 Loop test devices for modems.V.55 Speci®cation for an impluse noise measuring instrument for telephone-type circuits.V.56 Comparative tests of modems for use over telephone-type circuit.V.90 56 kbps modem standardization for operating downstream and 33.6 kbps upstreamover two-wire facilities.policy third-party vendors had to design communications equipment,such asmodems,that was compatible with the majority of equipment in use.As some third-party vendor products gained market acceptance over otherproducts,vendor licensing of technology resulted in the development of de factostandards. Another area responsible for the development of a large number of defacto standards is the Internet community. In this section we will examine bothvendor and Internet de facto standards.