Why do we need to have MTP?

[Ralph John Tampilic]

Hi Cisco Experts,

Good day! Here is the scenario: We migrated the WAN link from Frame relay to IP VPN connection. We have successfully migrated the connection to VPN however, there is an issue on the VoIP calls.

The setup is: IP Phones > CUCM > VG > Frame Relay > VG > Analog FXS phone. = No issue vice versa.

                    IP Phones > CUCM > VG > IP VPN > VG > Analog FXS phone. = IP phone users can dial analog phone users however, the analog user

                                                                                                                    can't dial IP phone users.

After we check the MTP required Checkbox on CUCM the issue resolved.

May we know if you can help me on explaining why do we need to have MTP on IP VPN setup?

Thank you very much for your kind assistance.

Regards,

RJ

[baskaranm]

Hi,

This MTP type can convert G.711 mu-law to G.711 a-law and vice versa.

This MTP type can packetize conversion for a given codec; for example, when one call leg uses 20-ms sample size and the other call leg uses 30-ms sample size.

• for more details, please go through the below link,
  

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/7x/media.html#wp1046314

[Ralph John Tampilic]

Hi baskaranm,

Thanks for your reply.

However, may we know why the Frame Relay connection no issue even the MTP is not enabled?

Best Regards,

RJ

[mkchandak]

With the information provided here, if the only change is with replacing the Framce relay, I dont see a reason why MTP would be required. Maybe what you are noticing is not the issue. When you enable the check box for MTP required, the call routing through your MTP server and not directly between the endpoint. With your VPN configuration, there would be a path/routing enabled betweent he endpoints and CUCM (I'm assuming it is using Software MTP on CUCM) ant the same is not allowed between the enspoints, I'd recommend doing the following checks first:

1. From the default gateway of the IP phone, do an extended ping (Using IP Phone default gateway as source) to the VG which has analog phone registered and vise-versa.

2) If the above works, then check if there is a firewall in between which does is blocked UDP ports 16000-32000.

Hope this helps.

Regards,

Mahesh

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[William Morales]

Hi,

• Is the gateway on the remote site registered to CUCM?
• If it is, what protocol is it using to register?
• Where exactly are you enabling the MTP required option?

An MTP doesn´t do transcoding, some of it´s possible uses are:

• Relay calls that are routed through SIP or H.323 endpoints or gateways.
• CUCM to use early offer.
• DTMF issues.

If the analog port is not registered to CUCM, let´s say that it´s an H323 gateway, it should have a dial peer pointing to CUCM. You need to check what DTMF method have you configured there.

Regards.

[Ralph John Tampilic]

Hi William,

Thanks for the reply.

Here are my answers:

• Is the gateway on the remote site registered to CUCM? Yes
• If it is, what protocol is it using to register? H323
• Where exactly are you enabling the MTP required option? from the CUCM GUI > Gateways >Configuration of the VG there is a checkbox for Media Termination Required.

Before enabling that we found out that IP phone only can dial the analog phone, but when the analog phone will dial they only hear "Your call can't completed as dialed". I think the DTMF is not incomplete/no signal passing thru the CUCM.

After checked the MTP required, the issue was resolved. That's why we need to know why the Frame Relay no issue only on IP VPN connection.

Thanks for your kind assistance.

Best Regards,

RJ

[Ralph John Tampilic]

Hi Cisco Experts,

May we ask if you know how to explain this?

Thanks

Regards,

RJ

[William Morales]

Hi Ralph,

"Your call can't be completed as dialed" means that the inbound Calling Search Space that gateway is using doesn't have access to the partition where the called number is. That is a generic CUCM message that has that function.

If this was a codec issue you would just get a fast busy tone. I guess someone has added the correct Partition the the CSS, you can check it disabling the MTP required option, if it still works then you have solved it.

Regards.