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Send Media IP as subscriber rather than the phone ip


i got a tricky question but i will try my best to make sense.

we have a sip trunk that is connected to our voice provider. we dont use cube.

The VOIP sees our cucm cluster (1 PUB and 4 SUB)

the trunk has the Media Termination Point Required unticked so i believe our codec is 711ulaw.

The VOIP is set to accept 711ulaw.

if i do a test call, i get one way audio. Looking at the logs, our VOIP receive a media ip shown as the phone rather than one of our SUB.

I need to find a way to send a media ip shown as one of our SUB instead of the phone ip as VOIP doesnt know the phone ip.

any idea?

we are on cucm 10.5


Chris Deren
Hall of Fame Master

It is expected as media flows directly from devices (IP phone and your SIP trunk), if you do require the media to flow through CUCM then you need to check MTP required on the sip trunk, though that is typically not desired.  Another option is to change the header of the SIP packet to reflect the IP of CUCM server. This would be straight forward with CUBE via sip profiles, but since you don't have one your other option assuming you are on somewhat new version of CUCM is to develop LUA script and apply it to the SIP trunk.

Is having IP address of the phone on the packet breaking something for you?

thanks Chris.

yes we try to avoid to use MTP

i will see what i can find on LUA script

as our sip provider dont know each phone subnets we end up having one way audio.

so either i get a lua or provide all our subnet to sip provider. but we got like 50 subnets :-(

thanks for your answer

Well, if there is no routing from the provided to the phones adjusting the header to "fake" it is not going to help you as you still will have the actual IP address of the phone in the SDP header which is where the media is sent to and the only way to avoid it is to invoke an MTP.  So, your options are:

  1. allow routing from provider directly to/from your phones
  2. invoke MTP on each call
  3. Use Border element i.e. CUBE with Media Flow-through enabled
Mohammed Khan
Cisco Employee

This is working as desgin. You have to invoke CUCM based Software MTP to present CUCM's Media IP.


Mohammed Noor

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