Why is MTP use discouraged?

[travlmoore]

Hello all,

I'm currently troubleshooting an issue with our PSTN SIP trunk.  Right now we are converting from SIP to H.323 at the CUBE using a MTP required.  I am trying to convert to an end-to-end SIP path so that we can play Multicast MOH to PSTN caller.  (You cannot play Multicast MOH through an MTP).

We are running into issues and it looks like even if we convert to a full SIP trunk to the PSTN we may be stuck using an MTP resource.

Aside from the Music On Hold Issues,  why is using MTP required so frowned upon?  In every training video I watch or forum I read everyone say's they do not like to use MTP and to avoid it if possible.  I have never heard a why.

What are all of the caveats and disadvantages of using an MTP required at PSTN gateways and trunks?

[Brandon Pierce · Accepted solution]

MTPs in general soak up DSP resources that could otherwise be used for transcoding or conferencing.  If you are running T1s and your PVDMs are lesser in quantity you can end up robbing channels without upgrading to higher density PVDMs.  Basically, in the gateway you have to allocate resources and the more you put to MTPs the less you are going to have for everything else.  I guess this doesn't matter as much for those upper end PVDMs but I just don't like seeing all those sessions.

[travlmoore]

Thank you.   Another engineer also mentioned to me that if you are using CUCM software MTP resources you need to consider that you will be adding additional routing complexity by having to place your media streams through your CUCM servers.  

[Wilson Samuel · Accepted solution]

Just adding to to Brendon's point.  PVDMs are very expensive items, and for Transcoding (and/or Trans-rating) it is less frequently used (how many transcoding calls will anyone will have in a given site at a given time?

Same goes for Conferencing..

However if you select MTP required, every single call will need MTP (or PVDMs) and it can be easily reached 20 - 30 calls at a time, placing a tax on the PVDMs and if you are using PVDM3s, then one can easily understand it is very pricey, hence it is always suggested to use "MTP if required" option

HTH

[travlmoore]

Thank you for the reply.  I see the full scope of the problem now.  In our environment we happen to have the all of the resources available to implement MTP without the chance of a performance hit but I can see where in other environments where it would be necessary to ration the uses of router and CUCM resources wherever possible.