Call Manager MTP's and IOS MTP's

Unanswered Question
Jun 21st, 2010

In a multi site central call  processing model of CUCM, would it be best practice to have hardware  media termination points configured on all branch routers??

Up  until recently, I've kind of had a hard time understanding what role  they play.  I understand that they seperate call legs etc etc, but I  don't really get what they're actually used for or how they work in real  life.

For example - tick the MTP box of a H323 gateway - don't  know what that does  Or if you're running a SIP trunk off the gateway  router - you need to set up an MTP - don't know what that does.

To  put it simply this is how I understand it - So if an MTP was configured  on a branch router, if an external call into that branch is put on  hold, the held call is terminated at the router.  Without an MTP and  depending on your MRGL's, is it moved to the MTP on the Call Manager  server (ie through the WAN) until it's taken off hold?



I have this problem too.
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Robert Thomas Mon, 06/21/2010 - 12:39


MTPs are are very big discussion. Originally MTPs were designed to dive suplementary feature support for H323v2 devices, so you put a call on hold and to prevent the call from disconnecting an MTP was involved to maintain the call leg. However pretty much all IOs devices are right now support H323v4 with should not invoque a MTP for call hold. Nowadays MTP are used most because of DTMF relay method selected specially RFC2833 for SIP.

neilobrien Mon, 06/21/2010 - 12:45

Thanks Robert .  But am I right in thinking that when a call comes into a remote site and that call is put on hold the call leg is temp moved to the server mtp across the WAN??  That's the only real use I can see form them??

Aaron Harrison Mon, 06/21/2010 - 13:43

Hi Neil

If you use an MTP, the call stream goes from origin, to MTP, to endpoint (phone) and back for the return transmission path. It's not invoked when you invoke hold; it's invoked at the start of the call, for the duration of the call, in case you invoke a hold or transfer that requires it.

So if you have MTP only running on the centralised CCMs, calls run accross the WAN even if the origin and endpoint are on the same remote site.



neilobrien Mon, 06/21/2010 - 13:51

Hi Aaron - thanks for the info, though now I have a concern!

I'm going to have to test this because I was sure that wasn't the case and if it is I have a bit of work to do!!

So call comes in on PSTN of remote site, signals CUCM server, server signals phone to ring, pick up phone and call is connected.  I was under the impression that the only call legs once the call is connected is between the phone and gateway and gateway and external caller??  What exactly would be going over the WAN??



Aaron Harrison Mon, 06/21/2010 - 13:54


If your MTP is over the WAN, and you force use of an MTP, then the voice streams will go over the WAN.

Whilst the CCM runs an MTP service, other devices can as well - you can run an MTP on the local gateway. Whether or not you need an MTP in the call path is another question - what makes you think you do?


neilobrien Mon, 06/21/2010 - 14:02

Hi Aaron - I'm not forcing the use of them at all, they're not in any of my MRGL's.

I know I can run an MTP on my gateway, but I don't.  And that's kind of my original question - I don't know that I do need one becuase I don't fully grasp what situations require them.  I just thought that I'd be saving on bandwidth by configuring them locally for calls being put on hold but I don't know why else I'd configure one.

As you said, I may or may not need one - obviously I don't need one if I don't have one configured.


neilobrien Mon, 06/21/2010 - 14:11

11 sites with h323 gateways and in production and working.  No MTP's!!

Aaron Harrison Mon, 06/21/2010 - 14:16

Well - I know some 'click happy' engineers would hit the 'force mtp' button as a matter of course, but if you bear in mind that it's adding a third party to each media stream you'll realise it's a kind of last resort to resolve interop issues.

Generally it gets turned on if you experience problems with hold/transfer type functions, usually in interop scenarios. It's basically a solution to a problem you don't have, so don't worry about it :-)

In terms of saving bandwidth local provisioning of conference resource, gateway-sourced moh, or transcoding at the central site if you use the CCM software conf bridge so you can run G729 to it might be more productive depending on your business...


Please rate helpful posts and mark answered questions that you've got a satisfactory response from to help identify useful content in the forums...

neilobrien Mon, 06/21/2010 - 14:19

by forcing do you mean the "require MTP" check box on teh gateway config page of CUCM?

ANyway - as you said, a problem I don't have.  I do have conferencing the moh resources run locally so that's the best I can do.

Thanks for your time and explanation.



Aaron Harrison Mon, 06/21/2010 - 14:53

Hi Neil

Yep - 'require MTP' - was paraphrasing as I don't have the interface in front of me.




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