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Trouble establishing layer 2 on PRI line H323 Gateway

We have a PRI being brought in on a 2851 router running 12-4-15-T5 code. It is configured as an h323 gateway. The controller shows up clean and the serial interface shows layer 2 going up and down. When I do a "sh isdn status" it shows it in TEI_ASSIGNED and after a few seconds goes to AWAITING_ESTABLISHMENT and after a little while it goes to MULTIPLE_FRAME_ESTABLISHED. After being in that state for a few seconds it fails back to TEI_ASSIGNED and goes through the same process again. I have included a debug isdn q921 in the attachment.

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Trouble establishing layer 2 on PRI line H323 Gateway

If nothing has changed in the configuration from when it was working and you have replaced all of the hardware on your side, it has got to be a provider issue. That would have been the most likely issue to begin with, but considering the troubleshooting steps you have taken, it is the only possibility left.

16 REPLIES
New Member

Re: Trouble establishing layer 2 on PRI line H323 Gateway

Can you post a sh run and a sh isdn status ?

New Member

Re: Trouble establishing layer 2 on PRI line H323 Gateway

sh run is as follows:

boot-start-marker

boot-end-marker

!

card type t1 0 0

logging buffered 1000000

no logging rate-limit

no logging console

!

no aaa new-model

clock timezone CST6 -6

clock summer-time CDT6 recurring

network-clock-participate wic 0

network-clock-select 1 T1 0/0/0

dot11 syslog

!

isdn switch-type primary-4ess

!

voice-card 0

dspfarm

dsp services dspfarm

!

!

!

voice service voip

allow-connections h323 to h323

allow-connections h323 to sip

allow-connections sip to h323

allow-connections sip to sip

redirect ip2ip

h323

h450 h450-2 timeout T1 750

sip

no call service stop

!

!

voice class codec 1

codec preference 1 g729r8

codec preference 2 g711ulaw

!

!

!

voice class h323 1

h225 timeout tcp establish 2

!

application

global

service alternate DEFAULT

!

controller T1 0/0/0

framing esf

linecode b8zs

pri-group timeslots 1-24

!

voice-port 0/0/0:23

!

!

interface Serial0/0/0:23

no ip address

encapsulation hdlc

isdn switch-type primary-4ess

isdn protocol-emulate network

isdn incoming-voice voice

no cdp enable

!

New Member

Re: Trouble establishing layer 2 on PRI line H323 Gateway

show isdn status changes every few seconds. It bounces back and forth between the following three statuses:

gwshellrock#sh isdn status

Global ISDN Switchtype = primary-4ess

ISDN Serial0/0/0:23 interface

dsl 0, interface ISDN Switchtype = primary-4ess

Layer 1 Status:

ACTIVE

Layer 2 Status:

TEI = 0, Ces = 1, SAPI = 0, State = TEI_ASSIGNED

Layer 3 Status:

0 Active Layer 3 Call(s)

Active dsl 0 CCBs = 0

The Free Channel Mask: 0x807FFFFF

Number of L2 Discards = 4, L2 Session ID = 232

Total Allocated ISDN CCBs = 0

gwshellrock#sh isdn status

Global ISDN Switchtype = primary-4ess

ISDN Serial0/0/0:23 interface

dsl 0, interface ISDN Switchtype = primary-4ess

Layer 1 Status:

ACTIVE

Layer 2 Status:

TEI = 0, Ces = 1, SAPI = 0, State = AWAITING_ESTABLISHMENT

Layer 3 Status:

0 Active Layer 3 Call(s)

Active dsl 0 CCBs = 0

The Free Channel Mask: 0x807FFFFF

Number of L2 Discards = 4, L2 Session ID = 232

Total Allocated ISDN CCBs = 0

gwshellrock#sh isdn status

Global ISDN Switchtype = primary-4ess

ISDN Serial0/0/0:23 interface

dsl 0, interface ISDN Switchtype = primary-4ess

Layer 1 Status:

ACTIVE

Layer 2 Status:

TEI = 0, Ces = 1, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHED

Layer 3 Status:

0 Active Layer 3 Call(s)

Active dsl 0 CCBs = 0

The Free Channel Mask: 0x807FFFFF

Number of L2 Discards = 4, L2 Session ID = 233

Total Allocated ISDN CCBs = 0

gwshellrock#

VIP Super Bronze

Re: Trouble establishing layer 2 on PRI line H323 Gateway

hi,

Why do you have "isdn protocol emalate network on your s0/0/0:23"

If your circuit is connected to the PSTN, then the PSTN is most times the network side while your end is the user side. YOu may want to remove this and hten test again

Please rate all useful posts "The essence of christianity is not the enthronement but the obliteration of self --William Barclay"
New Member

Re: Trouble establishing layer 2 on PRI line H323 Gateway

The telco requested we change the router to the network side to see if we could bring it up that way and they changed their side to user. We have since changed the router back to user and the telco has changed their side back to network as the change did not help at all. The debugs and sh isdn status are from after we changed our side back to user. The show run was just a little old. Sorry for the mixup.

Thanks,

Bud

VIP Super Bronze

Re: Trouble establishing layer 2 on PRI line H323 Gateway

Hi,

Have you tried a different encapsulation on the serial interface..eg encapsulation point-to-point (not sure of the exact command)

Please rate all useful posts "The essence of christianity is not the enthronement but the obliteration of self --William Barclay"
New Member

Re: Trouble establishing layer 2 on PRI line H323 Gateway

I tried "encapsulation ppp" on the serial interface and i continuted to get the same exact issues in teh q921 debug and the sh isdn status. The pri had been working for several months and it was always encapsulation hdlc while it was working.

VIP Super Bronze

Re: Trouble establishing layer 2 on PRI line H323 Gateway

Ok,

If it has always ben working then it could be a hadrware problem. If you have a spare t1 card, you may want to change the card and try again...

Please rate all useful posts "The essence of christianity is not the enthronement but the obliteration of self --William Barclay"
New Member

Re: Trouble establishing layer 2 on PRI line H323 Gateway

We swapped out the card already and still saw the exact same issue. We even swapped out the router for a replacement and that didn't help either. We've replaced about everything we can at this point.

New Member

Re: Trouble establishing layer 2 on PRI line H323 Gateway

I tried "encapsulation ppp" on the serial interface and i continuted to get the same exact issues in teh q921 debug and the sh isdn status. The pri had been working for several months and it was always encapsulation hdlc while it was working.

Re: Trouble establishing layer 2 on PRI line H323 Gateway

If nothing has changed in the configuration from when it was working and you have replaced all of the hardware on your side, it has got to be a provider issue. That would have been the most likely issue to begin with, but considering the troubleshooting steps you have taken, it is the only possibility left.

New Member

Re: Trouble establishing layer 2 on PRI line H323 Gateway

That was kind of my guess. Unfortunately convincing the Telco that this is the case is the hard part.

Re: Trouble establishing layer 2 on PRI line H323 Gateway

Hello,

I am guessing that when you call telco to have the PRI tested, they tell you that they test clean to the CSU with no errors. And that may be correct, but that is only testing Layer 1 connectivity. Your issue is at Layer 2, when you open the ticket with telco, advise them that the problem is in the switch itself, and not on the physical layer. In looking at the debug, when layer 2 is down, the router is sending frames to telco, but it doesnt appear the the switch is sending them back.

Hope that helped, if so please rate.

Silver

Re: Trouble establishing layer 2 on PRI line H323 Gateway

A guess, But I noitce you have not set the clock source line commend on the Controller for the link?

Hall of Fame Super Gold

Re: Trouble establishing layer 2 on PRI line H323 Gateway

It is never necessary to set "clock source line", because that is the default.

Most likely cause of the problem is an issue with the circuit, even if the SP is in denial.

Remember, you need to have a clean and stabe "show controllers T1" before looking at anything else.

New Member

Re: Trouble establishing layer 2 on PRI line H323 Gateway

Here are a few thoughts..

Possible timing issue. What is your timing source?

Possible configuration mismatch - If the Service Provider is sending ESF, B8ZS, wink/wink - you need to be configured for that.

Possible hardwire issue. If it's a copper circuit - - one of the transmit or receive wires could be off or not making good contact. (Pins 1-2 / 4-5)

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