Someimes, during a call, layer 2 negotiation fails and the call is dropped.

Unanswered Question
Feb 8th, 2007

I have a 2811 running 12.4.11T (CME) and a vic2-2bri that is connected to an alcatel pbx configured with qsig.

BRIs are Network side:

interface BRI0/1/0

no ip address

isdn switch-type basic-qsig

isdn timer T310 120000

isdn overlap-receiving

isdn protocol-emulate network

isdn point-to-point-setup

isdn layer1-emulate network

isdn incoming-voice voice

isdn static-tei 0

isdn skipsend-idverify

!

!

voice-port 0/1/0

compand-type a-law

timeouts interdigit 5

bearer-cap Speech

!

There is no problem in establishing a call from the router to the PBX or vice versa, but sometimes out of nowhere, there is a problem in q921 negotiation between bri and alcatel and the call drops.

Here is the debug

Succesfull Call

*Feb 6 12:26:00.165: ISDN BR0/1/0 Q921: Net TX -> RRf sapi=0 tei=0 nr=0

*Feb 6 12:26:01.089: ISDN BR0/1/0 Q921: L2_EstablishDataLink: sending SABME

*Feb 6 12:26:01.089: ISDN BR0/1/0 Q921: Net TX -> SABMEp sapi=0 tei=0

*Feb 6 12:26:01.185: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 6 12:26:01.185: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 6 12:26:02.089: ISDN BR0/1/0 Q921: Net TX -> SABMEp sapi=0 tei=0

*Feb 6 12:26:02.205: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 6 12:26:02.205: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 6 12:26:03.089: ISDN BR0/1/0 Q921: Net TX -> SABMEp sapi=0 tei=0

*Feb 6 12:26:03.101: ISDN BR0/1/0 Q921: Net RX <- UAf sapi=0 tei=0

*Feb 6 12:26:03.221: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 6 12:26:03.225: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 6 12:26:13.225: ISDN BR0/1/0 Q921: Net TX -> RRp sapi=0 tei=0 nr=0

*Feb 6 12:26:13.237: ISDN BR0/1/0 Q921: Net RX <- RRf sapi=0 tei=0 nr=0

*Feb 6 12:26:23.237: ISDN BR0/1/0 Q921: Net TX -> RRp sapi=0 tei=0 nr=0

*Feb 6 12:26:23.241: ISDN BR0/1/0 Q921: Net RX <- RRp sapi=0 tei=0 nr=0

Dropped Call

*Feb 6 12:30:19.570: ISDN BR0/1/0 Q921: L2_EstablishDataLink: sending SABME

*Feb 6 12:30:19.570: ISDN BR0/1/0 Q921: Net TX -> SABMEp sapi=0 tei=0

*Feb 6 12:30:19.658: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 6 12:30:19.658: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 6 12:30:20.570: ISDN BR0/1/0 Q921: Net TX -> SABMEp sapi=0 tei=0

*Feb 6 12:30:20.678: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 6 12:30:20.678: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 6 12:30:21.570: ISDN BR0/1/0 Q921: Net TX -> SABMEp sapi=0 tei=0

*Feb 6 12:30:21.698: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 6 12:30:21.698: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 6 12:30:22.570: ISDN BR0/1/0 Q921: Net TX -> SABMEp sapi=0 tei=0

*Feb 6 12:30:22.718: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 6 12:30:22.718: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 6 12:30:23.570: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0/1/0, TEI 0 changed to down

*Feb 6 12:30:23.570: ISDN BR0/1/0 Q931: Ux_DLRelInd: DL_REL_IND received from L2

*Feb 6 12:30:23.574: ISDN BR0/1/0 Q921: Net TX -> IDCKRQ ri=0 ai=0

*Feb 6 12:30:23.590: ISDN BR0/1/0 Q921: Net RX <- IDCKRP ri=0 ai=0

*Feb 6 12:30:58.734: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 6 12:30:58.734: ISDN BR0/1/0 Q921: S4_SABME: Sending UA

notice that there is no UAf reply from alcatel and Layer 2 is down casusing the call to drop.

Any ideas?

I have this problem too.
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Paolo Bevilacqua Thu, 02/08/2007 - 05:58

Hi DTW, nice trace.

for one, seems that the router is quite swift in repeating sabme and ua, so relaxing the T200 timer and N200 counter could help. These are hidden commands.

Also, one would need to understand in first place why layer2 is going down, being the router network side it should not happen.

dwtcp Thu, 02/08/2007 - 06:19

Here are the default values of the timers. What do you suggest me to do?

Besides, that is exactly my question, too:

Why is the router keep sending the sabme query during an active call? Souldn't this happen ONLY at the beginning, when network side tries to establish multiframe?

ISDN BRI0/1/0 Timers (dsl 2) Switchtype = basic-qsig

*** interface Network side configuration ***

ISDN Layer 2 values

K = 1 outstanding I-frames

N200 = 3 max number of retransmits

T200 = 1.000 seconds

T203 = 10.000 seconds

ISDN Layer 3 values

T302 = 15.000 seconds

T301 = 300.000 seconds

T303 = 6.000 seconds

T304 = 120.000 seconds

T305 = 30.000 seconds

T306 = 30.000 seconds

T307 = 180.000 seconds

T308 = 6.000 seconds

T309 = 90.000 seconds

T310 = 120.000 seconds

T313 = 6.000 seconds

T314 = 6.000 seconds

T316 = 120.000 seconds

T318 = 4.000 seconds

T319 = 4.000 seconds

T322 = 4.000 seconds

T3OOS = 5.000 seconds

TGUARD= 3.000 seconds, Expiry = REJECT_CALL

keep in mind, that this behaviour in not happening at a 2801 router connected to the same pbx with a vic2-2bri!

The problem is that i am not responsible in dealing with alcatel so i am not sure what is happening on the other side.

Do you thing that changing from qsig to basic-net3 would help?

Anthony

Paolo Bevilacqua Thu, 02/08/2007 - 06:29

Yes sabme is sent at link establishment only, that is why I was wondering about what is bringing down the the link in first place.

Would you check controller status and interface status. For BRI cabling please try to use proper cabling as the cat5 patch cable has a different twisting.

For tweaking, I would try N200 to 4 and T200 to 2 sec.

What IOS is running the 2801 ?

I don't think switching from qsig would help.

dwtcp Thu, 02/08/2007 - 06:41

2801 is running 12.4(4)XC4.

How do you change the n200?

In fact, i am using a cat5 patch cable about 15 feet long.

Could that be a problem?

dwtcp Thu, 02/08/2007 - 07:36

Hi,

ia have changed the T200 to 2 (i cannot find anywhere how to change N200 timer!!)

and here is what changed:

*Feb 8 15:19:22.065: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 8 15:19:22.069: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 8 15:19:32.069: ISDN BR0/1/0 Q921: Net TX -> RRp sapi=0 tei=0 nr=0

*Feb 8 15:19:32.081: ISDN BR0/1/0 Q921: Net RX <- RRf sapi=0 tei=0 nr=0

*Feb 8 15:19:42.082: ISDN BR0/1/0 Q921: Net TX -> RRp sapi=0 tei=0 nr=0

*Feb 8 15:19:42.086: ISDN BR0/1/0 Q921: Net RX <- RRp sapi=0 tei=0 nr=0

*Feb 8 15:23:16.354: ISDN BR0/1/0 Q921: Net TX -> RRp sapi=0 tei=0 nr=0

*Feb 8 15:23:16.442: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 8 15:23:16.442: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 8 15:23:17.462: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 8 15:23:17.462: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 8 15:23:27.463: ISDN BR0/1/0 Q921: Net TX -> RRp sapi=0 tei=0 nr=0

*Feb 8 15:27:11.839: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 8 15:27:11.839: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 8 15:27:12.859: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 8 15:27:12.859: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 8 15:27:13.880: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 8 15:27:13.880: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 8 15:27:23.880: ISDN BR0/1/0 Q921: Net TX -> RRp sapi=0 tei=0 nr=0

*Feb 8 15:29:08.096: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 8 15:29:08.096: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 8 15:29:09.116: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 8 15:29:09.116: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 8 15:29:10.136: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 8 15:29:10.136: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 8 15:29:11.156: ISDN BR0/1/0 Q921: Net RX <- SABMEp sapi=0 tei=0

*Feb 8 15:29:11.156: ISDN BR0/1/0 Q921: Net TX -> UAf sapi=0 tei=0

*Feb 8 15:29:21.156: ISDN BR0/1/0 Q921: Net TX -> RRp sapi=0 tei=0 nr=0

*Feb 8 15:29:29.156: ISDN BR0/1/0 Q921: L2_EstablishDataLink: sending SABME

*Feb 8 15:29:29.156: ISDN BR0/1/0 Q921: Net TX -> SABMEp sapi=0 tei=0

*Feb 8 15:29:29.172: ISDN BR0/1/0 Q921: Net RX <- UAf sapi=0 tei=0

voicegw#

voicegw#

voicegw#

*Feb 8 15:29:39.172: ISDN BR0/1/0 Q921: Net TX -> RRp sapi=0 tei=0 nr=0

*Feb 8 15:29:39.176: ISDN BR0/1/0 Q921: Net RX <- RRp sapi=0 tei=0 nr=0

*Feb 8 15:29:39.176: ISDN BR0/1/0 Q921: Net TX -> RRf sapi=0 tei=0 nr=0

*Feb 8 15:29:39.184: ISDN BR0/1/0 Q921: Net RX <- RRf sapi=0 tei=0 nr=0ter no mon

voicegw#

Now, it is the user side who sends the SABME and the network side( our router ) responds with UAf!!!

Is this normal?

Why the two parties need to establish multiframe again and again...?

Anthony

Paolo Bevilacqua Thu, 02/08/2007 - 10:59

Both user and network side can send sabme, and it was happening even in the previous trace. The PBX may be reinitializing the link because it is receiving errors. Please use a cable with proper pair polarity and twisting, following the BRI pinout as published in the TAC troubleshooting guides.

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