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Quick NOOB CUCM-Voice Gateway Config question

Brian Betourney

          Okay, I lied, its not that "quick"  a question!

Bringing up a small (100) cadre of VoIP Phones in a single cluster.  Phones external access is via a Cisco 2921 ISR with dual PRI's (connecting to two different exchanges).  Call Control is a UCS C210 running a Pub/Sub/and Unity.  

The network has a L3 switch with connection to 5 access switches and DHCP and DNS servers. This l3 switch terminates the voice/data vlans and serves as a de facto DG for the network.    The UCS server is connected to an access switch on floor, the Voice gateway is connected to another access switch on another floor. 

Whats Good-----

- Voice Gateway endpoints register properly with Call manager via MGCP

- Internal Calls are good VoIP-VoIP

-  PRI's are up, synched, and zero errors (verified with show ISDN Status)

- Using a simple 9.XXXXXXX as the sole RP during testing (This pattern is in a "Local PSTN" partition)

- All VoIP DN's (not the phones) have CSS with the Local PSTN RP Partition.

- Calls to 9.XXXXXX  appear to match pattern

Whats Bad----

- PSTN bound calls go to reorder tone immediately after pattern match.

- Monitoring the PRI indicates that no B channels are seized for an outbound call.

My questions---

- Does the voice gateway need to be in the voice VLAN ?

- Does the Call Manager  need to be in the voice VLAN ?

- Should the VoIP phones have the Default Gateway as the voice Gateway router?

- Do the VoIP Phones need to be in a partition and the Gateways have the CSS to that partition?

MGCP and TFTP obliviously work between CCM and Gateway,  but concerned that the gateway cannot communicate directly with the phones causing the reorder when the pattern is matched.     We do not manage the network and concerned they may not be trunking properly, and/or their DG is fubar.

Appreciation in Advance for any responses and troubleshooting assistance!


Scott Leport
Rising star
Rising star

If you are certain the call is being passed to your voice gateway, do the following:

"debug isdn q931"

"Term Mon"

Make the call and you should see what the disconnect cause is.

If you don't know, a quick check of the dialled number analyzer within CUCM Servicability using the called number should at least tell you the dial string is hitting a route pattern configured within CUCM.

If you send your gateway configuration that would help.

With regards to your questions:

No, the voice gateway doesn't have to be in the voice VLAN, though it does make sense to have them in the same VLAN as your IP phones, especially if you run SRST.

No, Call Manager doesn't need to be in the voice VLAN either. For example, you could have a call processing VLAN where you have your Call Managers, Voice / Analog Gateways etc and another one (e.g. your Voice VLAN) where you place your IP phones.

The Default Gateway for the IP phones will be whatever the Voice VLAN SVI / Subinterface is on the network equipment. You may need to ask your network team what that is, but quick "show ip route", or "traceroute from your voice gateway should also confirm what that is.

Hi there,

You still needing help with this or are you good?

I realised I forgot to answer your last question. Have a look at this forum for some helpful information about Gateway CSS's and how they are used.

It might help to try the following when making a test call:

show voice call sum

show voice call status

The first command will tell you which channel on the PRI is being seized (if any at all)

The second command will give you a brief description of calls on the gateway at that time.

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