A DSL customer has subscribed to a service that provides 2 mbps downstream and 256 kbps upstream. The cable length is 10 kft (3 km). The customer reports that file transfers on the DSL line seem slower than normal in recent days. After reviewing the DSL profile parameters for the DSL port, and the actual status of the line, what is the possible reason why the subscriber’s data rates are slower than usual?DSLAM#show dsl int atm 1/1DMT profile parametersMaximum Bitrates:Interleave Path: downstream: 2048 kb/s, upstream: 256 kb/sFast Path: downstream: 0 kb/s, upstream: 0 kb/sMinimum Bitrates:Interleave Path: downstream: 0 kb/s, upstream: 0 kb/sFast Path: downstream: 0
kb/s, upstream: 0 kb/sMargin: downstream: 6 dB, upstream: 6 dBInterleaving Delay: downstream:
16000 usecs, upstream: 16000 usecsCheck Bytes (FEC):Interleave Path: downstream: 16, upstream:
16Fast Path: downstream: 0, upstream: 0R-S Codeword Size: downstream: auto, upstream: autoTrellis Coding: DisabledOverhead Framing: Mode 3Operating Mode: AutomaticTraining Mode: QuickMinrate blocking: DisabledSNR Monitoring: DisabledStatus:Bitrates:Interleave Path: downstream: 640 kb/s, upstream: 256 kb/sFast Path: downstream: 0 kb/s, upstream: 0 kb/sMargin: downstream: 6 dB, upstream: 9 dBAttenuation: downstream: 45 dB, upstream: 31 dBInterleave Delay: downstream: 16000 usecs, upstream: 16000 usecTransmit Power: downstream: 19.4 dB, upstream: 12.0 dBCheck Bytes (FEC):Interleave Path: downstream: 16, upstream: 16Fast Path: downstream: 0, upstream: 0R-S Codeword Size: downstream: 1, upstream: 8Trellis Coding: Not In UseOverhead Framing: Mode 3Line Fault: NONEOperating Mode: ITU G dmt Issue 1Line Type: Interleaved Only
A.
The signal-to-noise margin on the line will not allow downstream DSL rates faster than 640 kbps. If the subscriber’s service was in fact faster at some time, then something has changed in the line characteristics or noise spectrum.
B.
The subscriber is provisioned for 640 kbps downstream, and the service appears to be working normally.
The problem is apparently not related to the DSL (physical layer) part of the service.
C.
The service is running in G.DMT, and 640 kbps is normal for the subscriber’s cable length. Change the mode to ANSI T1.413 for faster rates.
D.
The DSL profile is set for 16 milliseconds interleave delay. Change the interleave delay to 0, or change the profile to fastpath for faster line rates.