Data Communications Networking Devices - 4th Ed.pdf

512 _________________________________ WIDE AREA NETWORK TRANSMISSION EQUIPMENTTable 4.38RS-232 interface DCE)DSU interchange circuitsV.35 interface DCE)Pin Signal Pin Signal1 Chassis ground P Transmit data A)2 Transmit data STransmit data B)3 Receive data R Receive data A)4 Request-to-send T Receive data B)5 Clear-to-send C Request-to-send6 Data set ready D Clear-to-send7 Signal ground H Data terminal ready8 Carrier detect E Data set ready9 Positive voltage B Signal ground10 Negative voltage F Receive line signal detect15 Transmit clock Y Transmit timing A)17 Receive clock AA Transmit timing B)20 Data terminal ready V Receive timing A)24 External transmit clock X Receive timing B)UExternal transmit timingWExternal transmit timingLLocal loopbackwideband, 56 kbps device utilizes a 34 pin ITU, V.35 Winchester) female typeconnector. Table 4.38 lists the RS-232 and V.35 interchange circuits commonlyused by most DSUs. Since DTEs are normally attached to the DSU, the latter'sinterface is normally con®gured as data communications equipment DCE) by themanufacturer.Prior to deregulation, the CSU was provided by the communications carrier,while the DSU could be obtained from the carrier or from third-party sources.This resulted in an end-user connection to the DDS network similar to thatillustrated in the top portion of Figure 4.87 where the CSU terminated the carrier'sfour-wire loop and the DSU was cabled to the CSU. In this con®guration the CSUterminates the carrier's circuit. In addition, a separate CSU was designed toperform signal regeneration, monitor incoming signals to detect bipolar violationsand perform remote loopback testing. Interfacing between the DSU and CSU isaccomplished by the use of a 15-pin female D-type connector which utilizes theFigure 4.87DSU/CSU connection