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September 1999 P/N 880-503284-001-A1 - page 59 / 65





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Table 5-6

Troubleshooting Tips Trouble


Signal loss

  • verify that a T1 circuit is connected to the network port.

  • verify that a proper cable is used, T1 circuits utilize pins 1,2,4 and 5 when

presented in an RJ-45 connector.

  • use a straight through cable (1 to 1, 2 to 2, etc.) on the network side of

the CSU. Use a crossover cable on the DSX-1 equipment side.

  • the smart jack (network termination device) may be in a loopback.

Frame loss

  • in a new installation, T1 circuits are often patched out at a carrier’s DACS

or switch until completely turned up. In this case a pattern of unframed all ones (AIS) is kept on the T1 as a keep-alive signal. Contact the carrier and request that they “normal up” the circuit.

  • the CSU must be optioned for the same type of framing as the T1 carrier

is providing. Framing can not be changed arbitrarily by the user. Contact the carrier and verify the type of framing used on the T1.

CRC errors and BPVs

reported on a new installation

  • when a T1 presents symptoms of CRC errors and BPVs, with no other

alarms, it often is traced to problems with wiring inside the customer premise.

  • when the smart jack is a considerable distance from the CSU (over 50

feet), there is the risk that the high level (hot) signals in the transmit pair will induce echo into the lower level (long) signals in the receive pair. This condition is called crosstalk and is a leading cause of T1 problems.

  • as telephone carriers move toward a policy of housing all smart jacks in

one location within commercial buildings, crosstalk related complaints are becoming more common.

  • to prevent crosstalk related issues the transmit pair and the receive pair

must be isolated from each other.

CRC errors

  • the recommended cable for T1 uses individually shielded, twisted pairs;

each pair has shielding around it—the cable therefore has two shields inside it, one for each pair.

  • if shielded twisted pair cable is not available, try to route the transmit pair

and the receive pair in different cables as they traverse the building.

  • if the transmit and receive pairs must be routed through a multi-pair

cable, such as the 25 pair or 50 pair cables found in large office buildings, select pairs which are not near each other in the cable.

  • many smart jacks offer an option “regeneration”. This causes the smart

jack to increase the amplitude of the signal received from the network before handing it off to the CSU. Try to get the carrier to turn on this option.

  • ESF T1 circuits offer CRC-6 error checking as a means of detecting

changes in data which occur on the T1 circuit.

  • if CRC errors are reported, the errors are occurring at some point

between the two CSUs. Verify in-house wiring as indicated above.

  • contact the carrier and request they monitor the circuit. Carriers can

monitor a T1 circuit for CRC errors without disrupting user data.

Verilink NCC 2020 User Manual


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