|author||Neels Hofmeyr <firstname.lastname@example.org>||2018-08-26 23:14:21 +0200|
|committer||Neels Hofmeyr <email@example.com>||2018-08-26 23:49:42 +0200|
OsmoMGW: document the 'X-Osmo-IGN' MGCP extension
See also Ia6fe5ead4b601931c1bf41b29fc1b237aac37d2c in osmo-mgw.git, which changes the initial single-character implementation to match this specification of string tokens separated by spaces. Change-Id: If15a88c3b5b40fd1d24ad0f94f3231f678669ab1
2 files changed, 70 insertions, 0 deletions
diff --git a/OsmoMGW/chapters/mgcp_extensions.adoc b/OsmoMGW/chapters/mgcp_extensions.adoc
new file mode 100644
@@ -0,0 +1,68 @@
+== MGCP Extensions
+The MGCP protocol is extendable. The following non-standard extensions are
+understood by OsmoMGW.
+`X-Osmo-IGN` indicates to OsmoMGW that specific items of an endpoint should be
+ignored, so that it is lenient on mismatching values that would normally
+indicate collisions or configuration errors.
+==== `X-Osmo-IGN` Format
+The value part of X-Osmo-IGN must be one or more items separated by one or more
+spaces. Each item consists of one or more non-whitespace characters.
+.Example: `X-Osmo-IGN` format with three ficticious items "X", "abc" and "123".
+X-Osmo-IGN: X abc 123
+`X-Osmo-IGN` must be issued in the MGCP section (typically as its last item),
+before the SDP section starts.
+==== Supported `X-Osmo-IGN` Items
+Currently, the following `X-Osmo-IGN` items are supported:
+* `C`: ignore CallID mismatches, i.e. differing "C" values between connections
+ on the same endpoint.
+`X-Osmo-IGN` does not support ignoring mismatches on the domain part of
+an endpoint name, e.g. ignoring a mismatch on "example.com" in
+`firstname.lastname@example.org`. Instead, you may globally configure OsmoMGW
+with `mgcp` / `domain *` to permit all domain parts.
+===== `X-Osmo-IGN: C`
+By default, OsmoMGW verifies that all CallIDs ("C" values) match for all
+connections on any one given endpoint. To ignore CallID mismatches, pass a `C`
+in the `X-Osmo-IGN` header, for the first or the second `CRCX` on an endpoint.
+When the `X-Osmo-IGN: C` is sent for any one `CRCX` on an endpoint, CallID
+mismatches will be ignored for that and all subsequent messages for that
+endpoint. Hence this header only needs to be included once per endpoint, in any
+`CRCX` message that precedes or coincides with a CallID mismatch.
+This is particularly useful for a BSC that is connected to an A/SCCPlite MSC,
+where the BSC and MSC each are expected to configure their respective own
+connection on a shared endpoint. For A/SCCPlite, it is impossible for the BSC
+to know the CallID that the MSC will use, so CallID mismatches are inevitable.
+See also OsmoBSC, which will by default pass the `X-Osmo-IGN: C` header for
+endpoints associated with an A/SCCPlite MSC.
+.Example: `CRCX` message that instructs OsmoMGW to ignore CallID mismatches
+CRCX 2 rtpbridge/123abc@mgw MGCP 1.0
+c=IN IP4 22.214.171.124
+m=audio 5904 RTP/AVP 97
diff --git a/OsmoMGW/osmomgw-usermanual.adoc b/OsmoMGW/osmomgw-usermanual.adoc
index 69dc005..6030023 100644
@@ -18,6 +18,8 @@ include::../common/chapters/logging.adoc