Data Communications Networking Devices - 4th Ed.pdf

666 _________________________ WIDE AREA NETWORK DATA CONCENTRATION EQUIPMENTBandwidth utilizationInef®cient T1 and E1 multiplexers assign data to the carrier facility using 64 kbpsDS0 channels for each data source as illustated in Figure 6.26a). In this examplethe assignment of input data sources is ®xed to prede®ned channels, resulting in theinability of the multiplexer to take advantage of the inactivity of different datasources.More ef®cient multiplexers employ a variety of demand assigned bandwidthtechniques to make more ef®cient use of the composite carrier bandwidth. This isillustrated in Figure 6.26b), in which a basic demand assignment feature of amultiplexer dynamically assigns bandwidth based upon the activity of the datasources. In this example it was assumed that several 9.6 kbps data sources becameactive along with two PCM digitized voice conversations and were dynamicallyassigned to the carrier bandwidth in their order of activation. Note that this methodof bandwidth assignment normally results in an increase in available bandwidthsince the probability of all inputs becoming active at one time is usually very low. Inaddition, having the capability to allocate bandwidth based upon the data rate of theFigure 6.26 Demand assigned bandwidth.a) Conventional bandwidth allocation withPCM digitization.b) Demand assigned bandwidth with PCM digitization.c) Demandassigned bandwidth with ADPCM digitization