Data Communications Networking Devices - 4th Ed.pdf

658 _________________________ WIDE AREA NETWORK DATA CONCENTRATION EQUIPMENTTable 6.7Time slotEuropean G703/732 frame structureType of information0 Synchronizing1±15 PCM encoded speech16 Signaling17±31 PCM encoded speechTable 6.8 Signaling characteristics comparisonT1 E1 G703/732Composite data rate Mbps) 1.544 2.048Number of channels 24 32Channel data rate kbps) 64 64Synchronization Frame bit Channel 0Signaling Eighth bit in sixth frame Channel 16synchronization, whereas the G703/732 system provides a separate 64 kbps channelfor this function. Table 6.8 compares the signaling characteristics of the T1 andG703/732 systems. Due to these major differences between systems, many T1multiplexers designed for operation in North America will not perform properly ifused in Europe, while other T1 multiplexers can operate correctly on both sides ofthe Atlantic. Readers are referred to Section 4.11 for additional informationconcerning the E1 system.The T1 multiplexerWhen T1 became available for subscriber use in 1984, it was initially relegated touse in voice networks. This limited utilization was based upon the lack of equipmentto ef®ciently combine voice and data on one T1 facility as well as the availabilityof telephone company equipment designed exclusively for the combinationof voice channels onto one T1 circuit. Due to the cost of less than 20 analog circuitsused for transmitting data equaling the cost of one T1 facility while providingapproximately 6% of the capacity of a T1 facility, many communications equipmentmanufacturers developed T1 multiplexers designed to economically multiplex bothvoice and data onto a composite T1 or E1 channel.In addition to performing data multiplexing, most T1 multiplexer manufacturersoffer users a variety of optional voice digitization modules that can be used todigitize voice signals at data rates ranging from the standard 64 kbps PCM rate todata rates as low as 2.4 kbps. Such modules can be employed to increase the numberof voice channels that can be transmitted on a T1 line by a factor of two to four ormore over the normal 24 or 30 channels obtainable when PCM digitization isemployed. The use of these multiplexers enables organizations to effectivelyintegrate voice, data and video information onto a common T1 facility. Prior to