ISDN2 Point to Point or Point to Multipoint - Failed inbound calls

[Steve Baker]

Hi,

We have an office setup with an H323 voice gateway and 4 ISDN2 lines. We currently have an issue where incoming calls will not always work.

Sometimes when the mainline is called the caller will hear the call ringing but none of the phones in the office will actually ring. I have tried replicating this and monitored it on the voice gateway using the debug isdn q931 command. When a successful call comes through I can see it process normally. When a failed call happens and it just keeps ringing I do not see the call it hit the voice gateway at all.

The telco povider has asked me if we are using point to point or point to mulit point. I have no idea how to find this out. Is anyone hear able to offer some advice?

Using CUCM 10.5

Voice Gateway is Cisco 2921 configured as H323

4 ISDN2 lines allowing 8 concurrent calls with a range of 10 DDI's

Thanks

Steve

[Jitender Bhandari]

Hi Steve,

Can you attach the show run and below debug from h323 gateway for working \ non working call.

debug voip ccapi inout
debug h225 q931
debug h225 asn1
debug h245 asn1

Mention the calling \ called number for working \ non-working call.

JB

[Steve Baker]

Hi JB,

Here's the SH Run. I'll try and get some debugs for the calls today and post them.

Thanks

Steve

[Steve Baker]

OK and here is the debug results from a working call.

Calling number was 07786251277

Called number was 0035316344850

Translates to call extension number 4850

Thanks

Steve

[Steve Baker]

OK I managed to get a couple of calls where it didn't work and just kept ringing. When this happened there was no output on the debug what so ever. I am guessing this means that the call never even hit the gateway?

[Gordon Ross]

Yes, so you need to talk to your telco about where the call is going. With ISDN, their switch should know if the link is up or down, so should give N/U if all the links are down.

GTG

[Gordon Ross]

The telco povider has asked me if we are using point to point or point to mulit point. I have no idea how to find this out. Is anyone hear able to offer some advice?

I can't see how to show in on an interface, other than by looking at its configuration

#sh run int  BRI0/1/0:0 
....
interface BRI0/1/0:0
 isdn switch-type basic-net3
 isdn point-to-point-setup
 isdn incoming-voice voice

GTG

[Steve Baker]

Hi Gordon,

This is the output for the interfaces:

DUB-2921#
DUB-2921#sh run int bri0/1/0
Building configuration...

Current configuration : 247 bytes
!
interface BRI0/1/0
no ip address
isdn switch-type basic-net3
isdn tei-negotiation first-call
isdn point-to-point-setup
isdn incoming-voice voice
isdn calling-number 4850
isdn sending-complete
isdn static-tei 0
trunk-group BRI-TG 3
end

DUB-2921#sh run int bri0/1/1
Building configuration...

Current configuration : 247 bytes
!
interface BRI0/1/1
no ip address
isdn switch-type basic-net3
isdn tei-negotiation first-call
isdn point-to-point-setup
isdn incoming-voice voice
isdn calling-number 4850
isdn sending-complete
isdn static-tei 0
trunk-group BRI-TG 4
end

DUB-2921#sh run int bri0/0/0
Building configuration...

Current configuration : 247 bytes
!
interface BRI0/0/0
no ip address
isdn switch-type basic-net3
isdn tei-negotiation first-call
isdn point-to-point-setup
isdn incoming-voice voice
isdn calling-number 4850
isdn sending-complete
isdn static-tei 0
trunk-group BRI-TG 1
end

DUB-2921#

[Gordon Ross · Accepted solution]

I have tried replicating this and monitored it on the voice gateway using the debug isdn q931 command. When a successful call comes through I can see it process normally. When a failed call happens and it just keeps ringing I do not see the call it hit the voice gateway at all.

Then this is a ISDN side problem, rather than a H.323 side issue.

I'd start by unplugging three of the ISDNs and concentrate on just one interface. It could be that the telco has screwed up the hunting between the ISDN bearers. (Been there, done that...) If your telco is half decent, they may even have engineering numbers for each bearer that do not roll-over, so testing individual circuits is easier.

I see you've got both "isdn tei-negotiation first-call" & "isdn static-tei 0". Do you need both? On my system, I just have "isdn static-tei 0".

Also, according to Cisco's IOS doc, "isdn sending-complete" is only required in a few locations.

GTG