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Oct 12 / Greg

Cisco – Troubleshoot T1 PRI

So we have been turning up a new PRI lately and had HUGE amounts of trouble with it. It all came down to the fact that the telco told us to use the wrong PRI type, but that’s the fix…the fun was in the journey. Here are the steps we took to resolve the issue.

We first do a show isdn status. You want to see MULTIPLE_FRAME_ESTABLISH. This means that everything is hunky dory.

shisdnstat

Next we want to check the layer 3 ISDN info, so issue the debug isdn q931 command. Here you can see what would happen when we tried to make inbound calls.

Note the disconnect pri2

As you can see, we were getting a disconnect message right after we received the status message from the telco. It just looks like the router no likey…but it turns out it was call manager that no likey.

If you issue the debug ccm-manager backhaul packets command, you would notice that the telco would send us status. Then the router would send an MGCP message to the callmanager. The callmanager would promptly reply with the disconnect message. The router would then pass this disconnect message to the telco. The line type was supposed to be NI2, so the router has the configuration set as such:



    
	
  1. network-clock-participate wic 1
    2. 
	
  2. network-clock-select 1 T1 0/0
    3. 
	
  3. voice-card 0
    4. 
	
  4.  dspfarm
    5. 
	
  5. isdn switch-type primary-ni
    6. 
	
  6. !
    7. 
	
  7. controller T1 0/0
    8. 
	
  8.  framing esf
    9. 
	
  9.  linecode b8zs
    10. 
	
  10.  pri-group timeslots 1-24 service mgcp
    11. 
	
  11. !
    12. 
	
  12. mgcp
    13. 
	
  13. mgcp call-agent 1.1.1.1 2427 service-type mgcp version 0.1
    14. 
	
  14. mgcp dtmf-relay voip codec all mode out-of-band
    15. 
	
  15. mgcp rtp unreachable timeout 1000 action notify
    16. 
	
  16. mgcp modem passthrough voip mode nse
    17. 
	
  17. mgcp package-capability rtp-package
    18. 
	
  18. no mgcp package-capability res-package
    19. 
	
  19. mgcp package-capability sst-package
    20. 
	
  20. no mgcp package-capability fxr-package
    21. 
	
  21. no mgcp timer receive-rtcp
    22. 
	
  22. mgcp sdp simple
    23. 
	
  23. mgcp fax t38 inhibit
    24. 
	
  24. no mgcp explicit hookstate
    25. 
	
  25. mgcp rtp payload-type g726r16 static
    26. 
	
  26. !
    27. 
	
  27. dial-peer voice 100 pots
    28. 
	
  28.  application mgcpapp
    29. 
	
  29.  port 0/0:23
    30. 
	
  30. !
    31. 
	
  31. interface Serial0/0:23
    32. 
	
  32.  description [CID]
    33. 
	
  33.  no ip address
    34. 
	
  34.  no logging event link-status
    35. 
	
  35.  isdn switch-type primary-ni !**this is for ni or ni2**
    36. 
	
  36.  isdn incoming-voice voice
    37. 
	
  37.  isdn bind-l3 ccm-manager
    38. 
	
  38.  no cdp enable
    39.

The fix was to set the pri type to 5E8 in the callmanager. Device -> Gateway -> MYGateway: PRI Type 5E8. Originally we had it set to NI2, as the carrier told us, but it doesn’t work that way. We would receive the status message which meant nothing to callmanager and we would disconnect.

Filed under CallManager, Cisco, Networking, VOIP
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