MGCP and H323 redundancy calling issue......

[Rupesh Kshirsagar]

I have call Manager 7.1 and there is 2 MGCP gateways registered on the CUCM. Each gateway has 1 PRI line and this setup is working fine. Now I am adding new PRI line for redundancy prospect. So I had added the new E1 card for each gateway and then I have created the H323 trunk between the Voice gateway and CUCM. I have configured the Route Group and Route list for MGCP and H323.If primary MGCP is down call auto routed to H323.

Now when MGCP is down, call is auto routed to H323 and its hitting on the proper PRI port but call is not getting established and incoming is working fine.

Kindly find the isdn debug for your reference:

DEL-2921-ROUTER(config)#

DEL-2921-ROUTER(config)# debug isdn q931

Jan 31 16:52:34.655: ISDN Se0/0/0:15 Q931: Ux_DLRelInd: DL_REL_IND received from L2

Jan 31 16:52:44.655: ISDN Se0/0/0:15 Q931: Ux_DLRelInd: DL_REL_IND received from L2

Jan 31 16:52:47.267: ISDN Se0/2/0:15 Q931: Applying typeplan for sw-type 0x12 is 0x0 0x0, Calling num 6272

Jan 31 16:52:47.267: ISDN Se0/2/0:15 Q931: Sending SETUP callref = 0x00AC callID = 0x802D switch = primary-net5 interface = User

Jan 31 16:52:47.267: ISDN Se0/2/0:15 Q931: TX -> SETUP pd = 8 callref = 0x00AC

Sending Complete

Bearer Capability i = 0x8090A3

Standard = CCITT

Transfer Capability = Speech

Transfer Mode = Circuit

Transfer Rate = 64 kbit/s

Channel ID i = 0xA9839F

Exclusive, Channel 31

Calling Party Number i = 0x0081, '6272'

Plan:Unknown, Type:Unknown

Called Party Number i = 0x80, '09821444335'

Plan:Unknown, Type:Unknown

Jan 31 16:52:47.295: ISDN Se0/2/0:15 Q931: RX <- RELEASE_COMP pd = 8 callref = 0x80AC

Cause i = 0x82D2 - Identified channel does not exist

Jan 31 16:52:54.675: ISDN Se0/0/0:15 Q931: Ux_DLRelInd: DL_REL_IND received from L2

DEL-2921-ROUTER(config)#

THANKS IN ADVANCE.....

[Andrey Chertolyas]

Hello Rupesh,

This message indicates that the requested channel (timeslot number 31) is not in use, most likely due to a fractional PRI configuration. Try to configure the PRI timeslots utilization algorirm as "top-down".

Kind regards,
Andrew C.

[Rupesh Kshirsagar]

Hi Andrew,

Thanks for reply...

It is already configured the TOP-DOWN algorirm in route group.

[Andrey Chertolyas]

Rupesh,

It's not about the route-group distribution algoritm, it's about PRI timeslot selection. Go to Device/gateway/your gateway and check the Channel Selection Order option here. I do not have an MGCP-configured gateway at the moment, cannot provide you with a screenshot, but this option should be somewhere here.

Kind regards,
Andrew C.

[Rupesh Kshirsagar]

Andrew,

I have find there is option of NFAS configuration: In my case how do I config the NAFS......

[Andrey Chertolyas]

Hi Rupesh,

No, you don't have to configure NFAS, please take a look at the screenshot.This is CUCM 9.x, but I am pretty sure that in 7 you have just the same.

Kind regards,
Andrew C.

[Nishant Savalia]

Hi Rupesh,

The cause code "Idenfied channel does not exist" means:- This code indicates a call attempted on a channel that is not configured on the far end. This could happen if you are using a fractional PRI

Please ask to remote end for the number of channels configured and you can configure that number of channels accordingly at your end.

In CUCM 7.1 there is a service parameter which will help you to use the number of channel as per your requirement and rest of the channels you can mark it as busy so that CUCM won't select that channel.

Service Parameters > Call Manager > Advanced > CTRL-F > "maintenance"

In that you will find "Change B-Channel Maintenance Status" and mark channel as 1 which you don't want you to use.

For further information regarding this parameter you can click on that parameter and you will get more information.

And to enable above mentioned parameter, go to MGCP Gateway configuration page and check the box "Enable Status Poll"

Regards,

Nishant Savalia

[Ayodeji Okanlawon · Accepted solution]

Rupesh,

You could also change the channel selection order on your gateway...to ascending...In which case the gateway will choose channel 1 first...

conf t

interface serial 0/0/0:15

isdn bchan-number-order ascending

NB: This is not a recommended practice because typically the Telco provider sends calls to you starting from channel 1. That means you could potentially experience glare (a condition when outbound and inbound call attempts to use the same channel)...

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[Nishant Savalia]

Yes and in telcommunication industry they call it as Dual-seizure where the call originates from any of the side at the same time and uses the same channel and gets conflict.

So for general practice, as aokanlawon has suggested don't alter the channel selection from your end unless and until Telco agrees to change channel selection from their side.

Note:- For better practice always use channel selection in opposite manner of PSTN or any other remote end.

Regards,

Nishant Savalia

[Rupesh Kshirsagar]

Thank you all....

Really appriciate all your support...........