Home / server / Questions / 99675
Accepted
atroon
Asked: 2010-01-06 09:06:04 +0800 CST

How do I use ISDN debug on a Cisco router to troubleshoot PRI phone issues?

  • 772

We have a Cisco 2811 with UCM E 7.0 running our phone system. It is connected to the PSTN by a VWIC2-1MFT-T1/E1 card connected to a PRI from the phone company.

From time to time of late, we are experiencing fast-busy signals when trying to make outgoing calls (dial 9 for secondary dial-tone). At these times as well, the AL light on the VWIC card lights and the CD light goes out. To my rudimentary sensibilities, this means that there is some sort of issue where the phone company has gone down since our system appears to be fine.

After several rounds of monitoring with the phone company they are talking about errors that they see from the CSU (which, if I'm not mistaken, means the T1 Card on the 2811) and they are able to loop the circuit continuously with test patterns on all 23 channels without errors. So it seems conceivable that our router has trouble of its own. The question, I guess, is how do I determine what that trouble is?

I know there are a large number of debug commands for checking what's what, but I am much more out of my depth dealing with a PSTN interface vs. an internet interface. Telecom terminology and methods are unfamiliar to me. I realize that even as I ask this question, I will need to provide more info, but I am not sure what to add at this point other than the basics: 

(C2800NM-ADVIPSERVICESK9-M), Version 12.4(22)T, RELEASE SOFTWARE (fc1)

Cisco 2811 (revision 53.50) with 247808K/14336K bytes of memory.
Processor board ID FTX1119A4KS
2 FastEthernet interfaces
24 Serial interfaces
1 terminal line
1 Channelized/Clear T1/PRI port

Version 7.0(1)
Cisco Unified Communications Manager Express

I hope I've provided enough information to be of use to someone with more experience here than I have.

Edit: Requested sh int data:

Serial0/0/0:23 is up, line protocol is up (spoofing)
  Hardware is DSX1
  MTU 1500 bytes, BW 64 Kbit/sec, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation PPP, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:09, output never, output hang never
  Last clearing of "show interface" counters 4w0d
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/1/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 48 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     287135 packets input, 1452745 bytes, 0 no buffer
     Received 0 broadcasts, 56961 runts, 0 giants, 0 throttles
     129163 input errors, 129163 CRC, 0 frame, 0 overrun, 0 ignored, 64394 abort
     287962 packets output, 1463850 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out
     67 carrier transitions
  Timeslot(s) Used:24, SCC: 0, Transmitter delay is 0 flags

And here's the interface section of sho run that matches:

interface Serial0/0/0:23
 no ip address
 encapsulation ppp
 isdn switch-type primary-ni
 isdn incoming-voice voice
 isdn supp-service name calling

...

dial-peer voice 100 pots
 description PSTN
 destination-pattern 9T
 port 0/0/0:23
cisco

1 Answers

  1. Best Answer

    You are seeing a TON of input errors , like ALOT of them. The first thing that stands out is your encapsulation on your serial interface. I've only seen 'ppp' encapsulation for data T1's. Generally voice T1's should be configured with HDLC encapsulation.

    If your telco really and truely wants you to be PPP encapsulated. You should run some loopback tests on the CSU to verify it is working correctly.

    • 1