== MGCP Endpoints

MGCP organizes the switching resources in so called endpoints. Each endpoint is
referenced by its unique identifier. While RFC 3435 specifies a naming scheme, the
actual identifier naming is subject to the implementation and configuration.

=== RTP proxy / RTP bridge endpoints

OsmoMGW implements a freely configurable number of `rtpbridge` endpoints. Those
endpoints are able to host two connections at a time to model the functionality
of a tandem switch.

RTP bridge endpoint identifiers are referenced by the string `rtpbridge/`, a
hexadecimal number without leading zeros and a domain name (configurable).

----
rtpbridge/<number>@<domain>
----

.Example: List of virtual endpoints
----
rtpbridge/1@mgw
rtpbridge/2@mgw
rtpbridge/3@mgw
rtpbridge/4@mgw
rtpbridge/5@mgw
rtpbridge/6@mgw
rtpbridge/7@mgw
rtpbridge/8@mgw
rtpbridge/9@mgw
rtpbridge/a@mgw
rtpbridge/b@mgw
rtpbridge/c@mgw
rtpbridge/d@mgw
rtpbridge/e@mgw
rtpbridge/f@mgw
rtpbridge/10@mgw
----

=== E1/T1 endpoints

OsmoMGW supports E1 subslot multiplexing as specified by I.460. All possible
subslot combinations are mapped on individual endpoints. The endpoint names
are prefixed with `ds/e1-` followed by the trunk number and the E1 timeslot.
The subslot is defined by a bit rate and a bit offset.

----
ds/e1-<trunk>/s-<timeslot>/su<bitrate>-<bitoffset>@<domain>
----

.Example: List of endpoints on E1 trunk 0 at E1 timeslot 2
----
ds/e1-0/s-2/su64-0@mgw
ds/e1-0/s-2/su32-0@mgw
ds/e1-0/s-2/su32-4@mgw
ds/e1-0/s-2/su16-0@mgw
ds/e1-0/s-2/su16-2@mgw
ds/e1-0/s-2/su16-4@mgw
ds/e1-0/s-2/su16-6@mgw
ds/e1-0/s-2/su8-0@mgw
ds/e1-0/s-2/su8-1@mgw
ds/e1-0/s-2/su8-2@mgw
ds/e1-0/s-2/su8-3@mgw
ds/e1-0/s-2/su8-4@mgw
ds/e1-0/s-2/su8-5@mgw
ds/e1-0/s-2/su8-6@mgw
ds/e1-0/s-2/su8-7@mgw
----

When creating connections on endpoints that reside in one E1 timeslot the call
agent must make sure that no overlapping endpoints are used. It is for example
not possible to use `ds/e1-0/s-2/su16-2@mgw` and `ds/e1-0/s-2/su8-3@mgw` at the
same time because they overlap.

.Subslot overlapping
[options="header"]
|===
| Bit offset  4+| Subslots
| 0 | 8k .2+| 16k .4+| 32k .8+| 64k
| 1 | 8k
| 2 | 8k .2+| 16k
| 3 | 8k
| 4 | 8k .2+| 16k .4+| 32k
| 5 | 8k
| 6 | 8k .2+| 16k
| 7 | 8k
|===

NOTE: The current implementation (December 2020) only implements TRAU frame
encoding/decoding for 16K and 8K subslots. Endpoints with other bitrates are
not yet useable.

NOTE: the VTY command "show mgcp" can be used to get a list of all available
endpoints (including identifiers)

=== The `null` endpoint

OsmoMGW offers a special `null@<domain>` endpoint which can be audited at all times.
This is useful for MGCP clients who wish to submit requests to OsmoMGW
periodically to find out whether it is still reachable and in a working state.