MTP can be software or hardware. The selection is based on the codecs used, dsp availability, etc. It placed in the media path due to many reasons such as supplementary services interoperatability, moh, fast/slow start, dtmf relay mismatch etc.
CUCM will decide whether to deploy MTP or not based on need. To enforce it, you need to enable trusted point relay.
To make it clear, here is more details about what i have tried, the following two scenarios in both cases CUCM (Private IP) is located behind a Firewall, meaning remote end points use a Public IP to register into CUCM.
1) Two Cisco IP communicators located behind a firewall (Nated to reach the internet) Control protocol is SCCP
Registration: Successful (OK).
Call established with No audio in both cases, enforcing trusted point relay had no effect.
2) Two Cisco IP communicators and Third party SIP phone (linksys spa 941) located behind a firewall (Nated to reach the internet) Control protocol is SIP:
As per my research MTP is used for SIP & H323 media streaming endpoints so what about SCCP?
And my second question is Is it possible to register SIP phones into CUCM behind NAT ?
The problem is two fold. Firstly, the phone won't know about the NAT device, so when it registers to callmanger and says "My IP Address is x.x.x.x" It's giving its local IP address, and not the public NATed to address.
Secondly, audio uses RTP which runs over UDP. UDP & NAT don't work very well.
Yes of course devices get reistered using its private IPs and I can see this on cucm page for the SCCP devices., but when making calls, audio supposed to go directly between these devices and since there's no connectivity ther's no audio, what I'm thinking of is to get the CUCM in the RTP so it shouldn't go directly between endpoints. Endpoint 1 -- CUCM -- Endpoint 2
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.