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osmux: Use local/remote CID terminology 

This terminology is much more common and used in other protocols, like
PFCP.

Related: SYS#5987
Change-Id: Ia5eb833c296c504555f273a7fc3af5d746af19c0
This commit is contained in:
Pau Espin 2022-09-14 13:48:55 +02:00
parent 35b5e27b02
commit 1ab6dbc62a
5 changed files with 20 additions and 20 deletions
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14
common/chapters/osmux/mgcp_extension_osmux.adoc
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@ -19,11 +19,11 @@ their respective response messages.
In request messages, the value part of `X-Osmux` specifies the CID to be used by
OsmoMGW to _send_ Osmux frames to the remote peer for that connection, also
known as _sendCID_.
known as the MGW's _remote CID_ or the peer's _local CID_.
In response messages, the value part of `X-Osmux` specifies the CID where
OsmoMGW expect to _receive_ Osmux frames from the remote peer for that
connection, also known as _recvCID_.
connection, also known as the MGW's _local CID_ or the peer's _remote CID_.
.Example: `X-Osmux` format with a known CID 3.
----
@ -39,12 +39,12 @@ X-Osmux: *
If the MGCP client is willing to use Osmux for a given connection, it shall
specify so during `CRCX` time, and not later. If at `CRCX` time the MGCP client
doesn't yet know the _sendCID_, it can use an astersik (*) and provide
_sendCID_ later within `MDCX` messages.
doesn't yet know the MGW's _remote CID_, it can use an astersik (*) and provide
_remote CID_ later within `MDCX` messages.
All subsequent `MDCX` messages sent towards an Osmux connection must contain the
original _sendCID_ sent during `CRCX`. The same way, all `MDCX` response shall
contain the _recvCID_ sent during `CRCX`.
original MGW's _remote CID_ sent during `CRCX`. The same way, all `MDCX` response shall
contain the _local CID_ sent during `CRCX`.
The other required connection address parameters, such as IP address, port, and
codecs, are negotiated through MGCP and SDP as usual, but in this case the IP
@ -72,7 +72,7 @@ a=rtpmap:112 AMR/8000/1
a=ptime:20
----
.Example: response to `CRCX` containing the <<recvCID>>
.Example: response to `CRCX` containing the MGW's _local CID_
----
200 189 OK
I: 07E41584

4
common/chapters/osmux/mo_call_osmux_aoip.msc
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@ -14,7 +14,7 @@ msc {
# Allocate MGW/MSC Osmux endpoint
m_sc -> mgw_msc [label="MGCP CRCX rtpbridge/*@mgw, X-Osmux: *"];
mgw_msc box mgw_msc [label="Bind to MGW-local Osmux Port (1984)\nAllocate new endpoint 1, recvCID 5"];
mgw_msc box mgw_msc [label="Bind to MGW-local Osmux Port (1984)\nAllocate new endpoint 1, MGW's local CID 5"];
mgw_msc -> m_sc [label="MGCP CRCX rtpbridge/1@mgw OK (MGW:1984, X-Osmux: 5)"];
bsc <- m_sc [label="BSSAP ASSGN REQ (3GPP AoIP, extension IE: Osmux CID 5)"];
@ -37,7 +37,7 @@ msc {
...;
mgw_bsc <- bsc [label="MGCP CRCX rtpbridge/2@mgw (MSC:1984, X-Osmux: 5)"];
mgw_bsc box mgw_bsc [label="Bind to MGW-local Osmux Port (1985)\nConnect to MSC:1984\nAllocate new recvCID 7"];
mgw_bsc box mgw_bsc [label="Bind to MGW-local Osmux Port (1985)\nConnect to MSC:1984\nAllocate new MGW's local CID 7"];
mgw_bsc -> bsc [label="MGCP CRCX rtpbridge/2@mgw OK (MGW:1985, X-Osmux: 7)"];
...;

4
common/chapters/osmux/mo_call_osmux_sccplite.msc
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@ -12,7 +12,7 @@ msc {
# Allocate MGW/MSC Osmux endpoint
m_sc -> mgw_msc [label="MGCP CRCX *@mgw, X-Osmux: *"];
mgw_msc box mgw_msc [label="Bind to MGW-local Osmux Port (1984)\nAllocate new endpoint 1, recvCID 5"];
mgw_msc box mgw_msc [label="Bind to MGW-local Osmux Port (1984)\nAllocate new endpoint 1, MGW's local CID 5"];
mgw_msc -> m_sc [label="MGCP CRCX rtpbridge/1@mgw OK (MGW:1984, X-Osmux: 5)"];
bsc <- m_sc [label="BSSAP ASSGN REQ (CIC:1)"];
@ -39,7 +39,7 @@ msc {
# MSC configures BSC-MGW MSC-side of the endpoint through MGCP UDP forwarding
mgw_bsc <- m_sc [label="MGCP CRCX 1@mgw (MSC:1984, X-Osmux: 5)"];
mgw_bsc box mgw_bsc [label="Bind to BTS-local Osmux Port (1985)\nAllocate new recvCID 7"];
mgw_bsc box mgw_bsc [label="Bind to BTS-local Osmux Port (1985)\nAllocate new MGW's local CID 7"];
mgw_bsc -> m_sc [label="MGCP CRCX 1@mgw OK (MGW:1985, X-Osmux: 7)"];
mgw_bsc <- m_sc [label="MGCP MDCX 1@mgw (recvonly) "];
mgw_bsc box mgw_bsc [label="Connect Osmux socket to remote (MSC) Osmux Port"];

4
common/chapters/osmux/mo_call_osmux_sccplite_nat.msc
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@ -18,7 +18,7 @@ msc {
# NAT: MGW/MSC Osmux endpoint
#bscnat -> bscnat [label="MGCP CRCX *@mgw, X-Osmux: *"];
mgw_msc box mgw_msc [label="Bind to MGW-local Osmux Port (1984)\nAllocate new endpoint 2, recvCID 5"];
mgw_msc box mgw_msc [label="Bind to MGW-local Osmux Port (1984)\nAllocate new endpoint 2, MGW's local CID 5"];
#mgw_msc -> m_sc [label="MGCP CRCX rtpbridge/1@mgw OK (MGW:1984, X-Osmux: 5)"];
bsc <- bscnat [label="BSSAP ASSGN REQ (CIC:2)"];
@ -48,7 +48,7 @@ msc {
# MSC configures BSC-MGW MSC-side of the endpoint through MGCP UDP forwarding
bscnat <- m_sc [label="MGCP CRCX 1@mgw (MSC:3000)"];
bscnat box bscnat [label="Allocate new endpoint 2\nAllocate new recvCID 5\nBind to local Osmux Port (1984)\nBind to local RTP port 4000"];
bscnat box bscnat [label="Allocate new endpoint 2\nAllocate new MGW's local CID 5\nBind to local Osmux Port (1984)\nBind to local RTP port 4000"];
mgw_bsc <- bscnat [label="MGCP CRCX 2@mgw (MSC:1984, X-Osmux: 5)"];
mgw_bsc -> bscnat [label="MGCP CRCX 2@mgw OK (MGW:1985, X-Osmux: 7)"];
bscnat -> m_sc [label="MGCP CRCX 1@mgw OK (MGW:4000)"];

14
common/chapters/osmux/osmux.adoc
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@ -50,13 +50,13 @@ connections alive.
=== CID allocation
Each peer (BSC/MGW and MSC/MGW) allocates its own _recvCID_, and receives from
the peer through the used GSM protocol the peer's _recvCID_, which becomes
the local _sendCID_ for that connection.
Each peer (BSC/MGW and MSC/MGW) allocates its own _local CID_, and receives from
its peer a _remote CID_ (aka the peer's _local CID_) through the used GSM
protocol. This _remote CID_ is then used to send Osmux frames to that peer.
----
BSC/MGW(recvCID=Y,sendCID=?)<-X--MSC/MGW(recvCID=X,sendCID=?)
BSC/MGW(recvCID=Y,sendCID=X)--Y->MSC/MGW(recvCID=X,sendCID=Y)
BSC/MGW(localCID=Y,remoteCID=?)<-X--MSC/MGW(localCID=X,remoteCID=?)
BSC/MGW(localCID=Y,remoteCID=X)--Y->MSC/MGW(localCID=X,remoteCID=Y)
----
This way each peer is responsible for allocating and managing their own local
@ -75,13 +75,13 @@ localPort>` tuple, allowing for 256 Osmux CIDs per BSC and hence call legs per
BSC. Each of the peers could actually have more than one Osmux socket towards
the other peer, by using a pool of ports or IP addresses, so there's really not
limit if required as long as there's a way to infer the initially negotiated
`<srcIP, srcPort, dstIP, dstPort, sendCID>` tuple from the received audio
`<srcIP, srcPort, dstIP, dstPort, remoteCID>` tuple from the received audio
packets.
However, due to some constrains from in between NATs explained in section above,
BSC/MGW IP address and port are not a priory known, and could change between
different connections coming from it. As a result, it is difficult to infer the
entire tuple, so for now MGW needs to allocate its Osmux _recvCID_ in a clever
entire tuple, so for now MGW needs to allocate its Osmux _local CID_ in a clever
way, in order to be able to identify the full tuple from it.
Hence, currently OsmoMGW CID allocation implementation shares CID between all