Scenario 4: Dirty Phone Line

A dirty phone line usually does not have the same symptoms as frequent retrains and disconnects; however, they do occur. In this case, the primary issue that the client reports is that the speed of the connection is unacceptable. The same outputs as "Scenario 3: Frequent Retrains and Disconnects" are provided here, except that these outputs show a modem that is connected to a dirty phone line. Again, the command to use is show modem operational-status while having the client attempt a connection. The output is shown in Example 8-5.

Example 8-5. The show modem operational-status Output with a Dirty Phone Line

 Parameter #5  Call Timer:  10682 secs  Parameter #6  Total Retrains:  12 <output  omitted>  Parameter #8  Connected Standard:  V.34+  Parameter #9  TX,RX Bit Rate:  26400, 26400 <output  omitted>  Parameter #21 Signal Noise Ratio:  35 dB <output  omitted>  Parameter #39 Robbed Bit Signalling (RBS) pattern:  0  Parameter #40 Digital Pad:  None,  Digital Pad Compensation: None 

There are many retrains over the length of the call, the speed is much lower, and the signal-to-noise ratio is lower. The line shape from the end of the show modem operational-status output shows just how bad the line is, as shown in Example 8-6.

Example 8-6. Line Shape from a Dirty Phone Line

 ...........................* .................................* .................................* ................................* ...............................* ...............................* ..............................* ..............................* .............................* ............................* ...........................* ...........................* ..........................* ..........................* .........................* ........................* ........................* .......................* .......................* ......................* .....................* .....................* ....................* ..................* ............* 

The line tapers off drastically compared to that of a clean line. Because of this reaction, bandwidth is significantly limited, which makes the connection slower. You can use this data to tell the client that their phone line is the problem.

The recommended fix is for the user to notify his telco of this problem and, if possible, have it resolved. In most cases, the telco will first test the line to see where a possible problem might exist. A wide variety of things might need to be fixed, including replacing a bridge tap or repeater. The problem might also exist in a faulty line card at the central office (CO). The telco might even change the pair of wires that your phone is delivered on.

Not all problems can be resolved by the telco. In cases where the distance between the CO and home is too great, there is no fix for slow connections.