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BRI L2 dropping

We have an installation which drops the L2 on BRI voice connection. The connection is to Telkom and we can establish a call and talk but after the call is dropped, L2 drops and the port is left without multi-frame established. The following is an ISDN q931 debug of an outgoing call. The BRI config is below, at present its MGCP but we have also been testing with H323. From the debug 'Ux_DLRelInd: DL_REL_IND received from L2' seems to drop L2, it only comes back from a shut or Clear command. Does anyone know of an ISDN command which will reset the L2 after a call or keep it up.

Just for interest I tried switch-type Basic-ni, this does a reset after the L2 goes down and works without going calls, but on incomming calls I get Incompatible Destination and the call does not establish, L2 stays up.



Oct 13 12:56:48: ISDN BR0/3/1 Q931: Applying typeplan for sw-type 0x1 is 0x0 0x0, Calling num 36565
*Oct 13 12:56:48: ISDN BR0/3/1 Q931: Applying typeplan for sw-type 0x1 is 0x0 0x0, Called num 0824547562
*Oct 13 12:56:48: ISDN BR0/3/1 Q931: TX -> SETUP pd = 8  callref = 0x07
        Bearer Capability i = 0x8090A3
                Standard = CCITT
                Transfer Capability = Speech 
                Transfer Mode = Circuit
                Transfer Rate = 64 kbit/s
        Channel ID i = 0x81
                Preferred, B1
        Progress Ind i = 0x8183 - Origination address is non-ISDN 
        Display i = 'VOIP TEST VAUGHAN'
        Calling Party Number i = 0x0081, '36565'
                Plan:Unknown, Type:Unknown
        Called Party Number i = 0x80, '0824547562'
                Plan:Unknown, Type:Unknown
        Sending Complete
*Oct 13 12:56:49: ISDN BR0/3/1 Q931: RX <- CALL_PROC pd = 8  callref = 0x87
        Channel ID i = 0x89
                Exclusive, B1
*Oct 13 12:56:54: ISDN BR0/3/1 Q931: RX <- ALERTING pd = 8  callref = 0x87
*Oct 13 12:56:56: ISDN BR0/3/1 Q931: RX <- CONNECT pd = 8  callref = 0x87
        Date/Time i = 0x0A0A0D0F2F00
                Date (dd-mm-yr)   = 10-10-13
                Time (hr:mnt:sec) = 15:47:00
*Oct 13 12:56:56: %ISDN-6-CONNECT: Interface BRI0/3/1:1 is now connected to 0824547562 N/A
*Oct 13 12:56:56: ISDN BR0/3/1 Q931: TX -> CONNECT_ACK pd = 8  callref = 0x07
*Oct 13 12:56:59: ISDN BR0/3/1 Q931: RX <- DISCONNECT pd = 8  callref = 0x87
        Cause i = 0x8090 - Normal call clearing
        Progress Ind i = 0x8288 - In-band info or appropriate now available
*Oct 13 12:56:59: %ISDN-6-CONNECT: Interface BRI0/3/1:1 is now connected to 0824547562 N/A
*Oct 13 12:56:59: %ISDN-6-DISCONNECT: Interface BRI0/3/1:1  disconnected from 0824547562 , call lasted 3 seconds
*Oct 13 12:57:01: ISDN BR0/3/1 Q931: TX -> RELEASE pd = 8  callref = 0x07
*Oct 13 12:57:01: ISDN BR0/3/1 Q931: RX <- RELEASE_COMP pd = 8  callref = 0x87
*Oct 13 12:57:03: %ISDN-3-LAYER2_DOWN: Layer 2 for Interface BR0/3/1, TEI 104 changed to down
*Oct 13 12:57:03: ISDN BR0/3/1 Q931: Ux_DLRelInd: DL_REL_IND received from L2

interface BRI0/3/1
description ###Telkom - BRI-7###
no ip address
isdn switch-type basic-net3
isdn overlap-receiving
isdn point-to-point-setup
isdn incoming-voice voice
isdn bind-l3 ccm-manager service mgcp
isdn send-alerting
isdn sending-complete
isdn static-tei 0
no isdn spoofing

New Member

Re: BRI L2 dropping

Could be the following:

CSCsc76080 Bug Details

MGCP gateway fails to bring up backhaul, when BRI is in power  save mode


Gateway fails to bring up L1/L2 for  BRI MGCP backhaul


Callmanager 4.1(3) 
IOS Gateway configured for BRI Backhaul
Telco performs 'power save' on  the line (brings down L1/L2 when no activity on  line)


Configure IOS gateway for H323 and add  following command to POTS peer :
"no dial-peer outbound status-check  pots"

Further Problem Description:

This issue occurs after  the Telco performs 'power save' on L1.
When Callmanager then sends an  Establish Request to bring up the BRI backhaul, the gateway will fail to bring  up L1/L2 with 'Q931: Ux_DLRelInd: DL_REL_IND received from L2'

Hall of Fame Super Gold

Re: BRI L2 dropping

It is perfectly normal that L1 and L2 drops on ISDN BRI, it is the the CO switch that deactivates them after a short timeout.

However, as soon a call is attempted in either directions, the router must be able to re-establish the connection immediately.

If thta doesn't happen, you likely have a buggy IOS. Also note, MGCP is especially weak with BRI, your best choice is to use H.323 or SIP.

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