A TRP is a point inserted into the RTP media stream which is used as a proxy between the endpoints in a conversation. Think of it like this, you have two networks, both can reach a UCM cluster, but have no route between each other for whatever reason. You can use a TRP for these devices to establish media even though they cannot route to each other.
You have different media resources, in the list you have MTP and TRP.
MTP stands for media termination point.
TRP stands for trusted relay point.
MTP can be a software (CUCM Media resource) or a hardware (Router PVDM Resources) entity which basically terminates signals example: when you put a call on hold you terminate the signal in a point, MTP can make TRANSRATING but no TRANSCODING an example is the following.
If you have a call leg with G711ulaw and another call with G711alaw, both codecs are similar but they sample different, so you need an entity which basically makes the work to convert the leg to another, do not get confused with TRANSCODERS which basically convert from one codec to another Example: G711ulaw to --> G729r8 which are different codecs.
Another example is when you have same codecs but different sample size Example: G.711ulaw 20ms and the other call leg G711ulaw 30ms you will need an MTP there too in order to make the transrating.
A TRP in the other hand basically is an MTP which acts as a proxy entity, which is inserted in the audio path, a basic example is the following.
Suppose you have two ip phones registered to the same CUCM cluster, one uses extension 1001 and the other one extension 1002. the default behavior is the following:
Remember that a call has two basic phases: 1. Signaling, 2. Media exchange
In the signaling phase CUCM will be in the middle negotiating the signaling attributes/capabilities, etc...
but in the media exchange phase the media (RTP packets) does not go through the CUCM it is directly the two phones.
If you add a the CUCM as a TRP you override this behavior sending the SIGNALING and RTP packets through the CUCM.
A TRP can be a software MTP (CUCM RESOURCES) or a hardware MTP (Router Dspfarm profile, PVDM)
Manuel Arias Soto