American Telecom AM64/128A manual System Overview

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System Overview	AM64/128A User Manual

3.SYSTEM OVERVIEW

The AM64/128A baseband modem uses the digital transmission system designed and developed by ATL Telecom Ltd. in Cardiff. It is intended for operation on 2-wire local telephone network circuits, such as those meeting BT EPS-9 (2-Wire). It will operate satisfactorily on unloaded lines having a wide range of characteristics; bridge taps can be tolerated, dependent upon their characteristics. Although the system requires a baseband circuit, a continuous DC loop is not required. The system can transmit data at 71 kbps (64k rate) or 142.2 kbps (128k rate) ; the lower rate is useful in situations where the transmission performance is being limited by attenuation or noise.

The line signal comprises AMI encoded data and an embedded synch pattern which is used for timing control; the data consists of user data and a control channel for the systems own use. Echo cancellation is used to eliminate the unwanted reflections of the transmitted signal from the receiver input. The echo canceller can eliminate echoes of up to 16 bit periods duration. To counteract the signal distortion inherent in long lines the system employs adaptive decision feed back equalisation to eliminate trailing inter-symbol interference; this also has a span of 16 bit periods. A fixed linear equaliser is incorporated to control the received pulse waveform and to reduce the effect of the long tails of both echo and transmission responses.

Digital signal processing is used throughout to achieve high performance reproduction. A block diagram of the unit is shown in figure 3.1 above.

The line is connected to the transmission circuit via a line transformer which acts as a balun and provides isolation ; there is surge protection across the transformer line connections. The transmission circuit utilises a custom IC and a number of proprietary components to perform the signal processing described above.

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Contents Base Band Modem ATL Part No /203/002/610 Issue 4 SeptemberInformation Contained This Document is Confidential to Contents Appendix B International Models IntroductionBaseband Modems Constructional DetailsInterface Modules System Overview System Overview Self Test Pass InstallationTesting BBM to BBM LinkLink Mode LTU Ready No Alarm LTU Not ReadyBBM to Line Card Link Network ModeMenu Operation Front Panel FeaturesLoop back On Loop back OffOver all Status Status MenuLoop Active CD Fail Alarm StatusNo Alarm No Signal Receiving AIS No Alignment LOS/CD FailLine Rate User RateInterface Status Link Mode Network Mode Operating ModeLoc Loop On Test MenuLocal loop Local loop from menu Top level display shows Loc Loop OffLoopback On LoopbackLocal loop from DTE Loopback is applied by selecting the display Loopback OffRem Loop On Remote LoopRemote Loop from menu Rem Loop OffRemote loop from DTE Binary PatternsBin Keys Off Sending Bin Operation Error Count Bit Error Rate BER = User Data Rate x TimeData Test OverviewData Test Errors nnnnnnErrors s000001 ErrorsInjecting 1s Injection ModeTransparent Mode Injecting 0sTime If the count is stopped the display is Stop Service TestSvc Test Comms Evp Rx Evp TxSelf Test Lamp TestComm Loop Off Communication Channel LoopbackRate 4.8K Rate MenuMaster 64K BT Slave 4.8K 2 X.21bis Option MenuSignalling Rate Asynchronous Mode3 G.703 Char Len Character LengthMaster Slave Configuration MenuLine Rate Modem 3 X.21 Loop ControlSynchronisation Type for software versions below Internal Clk Synchronisation Type for software version V1.3 and aboveExt Byte Clk Ext Bit ClkPower Level 5 64k ModeMenu Lock Glossary of Terms Band circuits General Specifications Way D-type X.21 V.11 Connector pin allocation Way D type X.21 bis V.24 / V.28* Connector pin allocationAppendix a Interface Pin Connections Way D-type V.36 Connector pin allocation Mrac Connector Pin allocationLine Connector Way D-type RS-530 Connector pin allocationAppendix B Internal Link Settings Page Interface Module Interface Modules21bis Interface Module RS530 Interface ModuleFrame Structure Service Test FacilitiesAppendix C In Service Test TTE Network and Safety statements LVD Safety Statements21 bit timing cable 15 way to 15 way D type plugs Appendix E24 / V.28 bit timing cable 25 way to 25 way D type plugs 21 byte timing cable 15 way to 15 way D type plugs35 bit timing cable 34 way to 34 way Mrac plugs RS530 bit timing cable 25 way to 25 way D type plugs 21 bis V.36 bit timing cable 37 way to 37 way D type plugsAppendix F Troubleshooting Rate 64K Slave Mode 64K RatePower 10dBm Master Mode C 64K Rate