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New Member

ISDN BRI problems

We are having problems with ISDN BRI connections. We are in the UK and using basic-net3 switch type. When the line is connected it goes through the correct setup and ends up with layer 2 in Multiple Frame Established state. However after around 30 seconds the switch sends a DISCp and the status changes to TEI_ASSIGNED. The Telco has checked their end and said its all ok but this is now happening on three separate routers on three separate ISDN lines. However the fourth one is ok !! Any help would be appreciated. The configs are identical for the BRI on all four routers

3 REPLIES
Cisco Employee

Re: ISDN BRI problems

Typically in Europe, the isdn switches de-activate the layer 1 or 2 if no calls are active on the isdn line.In such situations, it is necessary to configure "isdn tei-negotiation first-call" under the BRI interface, so that TEI negotiation can occur when the first ISDN call is placed or received to re-activate the layer 2.

To make sure which side is de-activating layer 2, we need "debug isdn q921" from the router..Also make sure with your telco that not to reset layer 2 at all..

So debug isdn q921 with sh run for bri interface will help to go ahead...Thx..Tejal

New Member

Re: ISDN BRI problems

Tejal,

Here is the debug isdn q921 output and the config for the bri interface as requested

*Mar 2 08:17:14.267: ISDN BR0/0: TX -> IDREQ ri=1463 ai=127

*Mar 2 08:17:14.291: ISDN BR0/0: RX <- IDASSN ri=1463 ai=87

*Mar 2 08:17:14.295: ISDN BR0/0: TX -> SABMEp c/r=0 sapi=0 tei=87

*Mar 2 08:17:14.307: ISDN BR0/0: RX <- UAf c/r=0 sapi=0 tei=87

*Mar 2 08:17:24.303: ISDN BR0/0: RX <- RRp sapi=0 tei=87 nr=0

*Mar 2 08:17:24.307: ISDN BR0/0: TX -> RRf sapi=0 tei=87 nr=0

*Mar 2 08:17:34.307: ISDN BR0/0: TX -> RRp sapi=0 tei=87 nr=0

*Mar 2 08:17:34.315: ISDN BR0/0: RX <- RRp sapi=0 tei=87 nr=0

*Mar 2 08:17:34.319: ISDN BR0/0: TX -> RRf sapi=0 tei=87 nr=0

*Mar 2 08:17:34.319: ISDN BR0/0: RX <- RRf sapi=0 tei=87 nr=0

*Mar 2 08:17:44.319: ISDN BR0/0: TX -> RRp sapi=0 tei=87 nr=0

*Mar 2 08:17:44.327: ISDN BR0/0: RX <- RRp sapi=0 tei=87 nr=0

*Mar 2 08:17:44.331: ISDN BR0/0: TX -> RRf sapi=0 tei=87 nr=0

*Mar 2 08:17:44.331: ISDN BR0/0: RX <- RRf sapi=0 tei=87 nr=0

*Mar 2 08:17:54.331: ISDN BR0/0: TX -> RRp sapi=0 tei=87 nr=0

*Mar 2 08:17:54.339: ISDN BR0/0: RX <- RRp sapi=0 tei=87 nr=0

*Mar 2 08:17:54.343: ISDN BR0/0: TX -> RRf sapi=0 tei=87 nr=0

*Mar 2 08:17:54.343: ISDN BR0/0: RX <- RRf sapi=0 tei=87 nr=0

*Mar 2 08:18:04.323: ISDN BR0/0: RX <- DISCp c/r=1 sapi=0 tei=87

*Mar 2 08:18:04.327: ISDN BR0/0: TX -> UAf c/r=1 sapi=0 tei=87

sh run int bri 0/0

interface BRI0/0

description ISDN number is xxxxxxxxxx

no ip address

encapsulation ppp

dialer rotary-group 1

isdn switch-type basic-net3

cheers, David

Cisco Employee

Re: ISDN BRI problems

From the debug it loks to me that we got the TEI 87. So at that point the router will go for Multiple_frame_established on layer 2 if you type "sh isdn status".

Since router receive from switch

*Mar 2 08:18:04.323: ISDN BR0/0: RX <- DISCp c/r=1 sapi=0 tei=87

Which will inform the router ro mark layer 2 down.

Pl. visit here for more explanation

http://www.cisco.com/warp/public/129/bri-layer2.html

Here's what you can do to capture the layer 2 source of problem.

1)turn on "debug isdn q921"

2)wait for a 20 secs or so and do "clear interface bri0/0"

3)"sh isdn status" after about 1 min from step 2

For backup issue

================

Now how do you manage the backup..i.e. using the "backup" command or else.?

Now turn on

debug dialer

debug isdn q921

debug isdn q931

before you try to make a call. Also port "sh isdn status" along with "sh interface dialer 1" Now make a callout using a ping or so..Now wait till about 30-40 secs or so.Capture all the debug and post it for review...Thx..Tejal

Since this issue is going towards more of troubleshooting, pl. take a help from Cisco's TAC engineers by opening a case at

http://www.cisco.com/tac

Thx..Tejal

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