To MTP or to not MTP, that is the question

[Tommer Catlin]

Im trying to decipher some docs on CCO.    I always thought that if you put a call on hold, it requires an MTP to hold the RTP stream at the CUCM server (if you are using the MTP software at CUCM).  Same goes for transfers, etc.

If I had an h323 remote site, I would put register an MTP IOS with CUCM for that site, order it in the MRG/MRGL and let the phones use this MTP for when they put a call on hold, transfer, etc.

But looking at some docs, "

An  MTP service can provide supplementary services such as hold, transfer,  and conferencing when the service is using gateways and clients that do  not support the H.323v2 feature of EmptyCapabilitiesSet."

The main goal im trying to determine here is if Call Park, Hold, Transfers would require an MTP source.  I could use CUCM, but then if I use this, the RTP stream will be pegged up on the CUCM server in the MRG/MRGL through the WAN causing traffic.  Where as if I use IOS MTP (hardware/software) at the branch office router, it stays at the site.  Similar to Conference Bridges in IOS at the site.

Am I short on coffee this morning and missing something or am I correct.  Put an MTP source at the branch office for these services.  Or are they nto required and will not cause additional RTP traffic on the WAN when these services are used (CallPark, Hold, Transfers, etc).

I would use MTP if the branch office had SIP for DTMFs, etc, but they are all PRIs

[Chad Stachowicz]

You need more coffee   Those services you mention definitely use MTP.

I highly suggest using software MTP session on each branch router.  Trust me, you will solve plenty of issues you wont even know you would have had by doing this.  I mainly say this because the CUCM MTP's are terrible.  They barely work... and often don't work at all when having to truly use MTP over the WAN (not recommended anyways).

Cheers,

Chad

[Tommer Catlin]

Thanks for inserting some common sense into my coffee.    I was going over some configurations and looking at Callparks.. where they use individual CUCM servers for ranges. And I was thinking... Cant I create one range for CallPark cluster wide, then shift the MTP sources to the routers.  When CallPark in invoked, the IOS MTP resource is called up for duty. (rather than the individual CUCM server)

[Tommer Catlin]

I had another though dawn on me with a fellow engineer.  If the call is on Hold or callpark, it should be getting a multicast stream from the router (if configured).  Hence, it would *not* use an MTP source then.  Correct?

[Chad Stachowicz]

Well no it would use an MTP, because that stream is only going to the caller, its still being held at the persons phone who put it on hold.  Your only thinking of the other side

Chad

[arunkum3]

Hi Tommer,

First, a few basics about MTP from CUCM 8.X SRND :

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/8x/media.html#wp1046314

Media Termination Point (MTP)

A media termination point (MTP) is an entity that accepts two full-duplex media streams. It bridges the streams together and allows them to be set up and torn down independently. The streaming data received from the input stream on one connection is passed to the output stream on the other connection, and vice versa. MTPs have many possible uses, such as:

•Re-Packetization of a Stream

•DTMF Conversion

•Protocol-specific usage

–DTMF Relay over SIP Trunks

–H.323 Supplementary Services

–H.323 Outbound Fast Connect

Now coming to your question. Each action like Hold or transfer is different and it is important to know what happens in the background. E.g.,  when a call is put on hold, the UCM instructs the phone to connect to a MoH stream (in case of multicast) or contact the MoH server (in case of Unitcast). There is no MTP at play.

Similarly during transfer , the user presses the transfer button. What this does is, it puts the other party on hold and creates a new call leg to the party being transfered to. Again No MTP in play.

The reason why people get comfortable using MTP resources is that they don't want to bother too much about their call flows.

One thing to remember while using software MTP resources on a CUCM is that it supports only G.711 codec streams only (like re-packetization of G.711 streams, DTMF mismatch for G.711 codec etc). Usage of other codecs require a hardware MTP resource on a Gateway.

So choosing an MTP resources really need an understanding of the call flows. It boils down to what features do you like to use or what your applications expect. E.g., if you would like to use H.323 fast start or want to interoperate with H.323v1 devices, you do need certainly need an MTP resource. If there are DTMF mismatches, or re-packetization is required, again MTP becomes a must.

For a CUCM communicating with a H.323 endpoint (slow start), an MTP is not required for call hold /park/transfer because most of the gateways H.323 version is 4.

Do let me know if this clarifies your question.

Regards,

Arun Kumar

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