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freetdm: Add documentation for SS7 native bridge

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James Zhang 2012-04-03 11:27:25 -04:00
parent b324f86797
commit 339c45b2cb
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libs/freetdm/docs/ss7-native-bridge.txt Normal file
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SS7 Native Bridge
Native bridge is enabled on 2 conditions:
* The SIP header FreeTDM-TransUUID is set in the originating leg and matches a freetdm channel
* The variable freetdm_native_sigbridge is true and the originating leg is also a freetdm channel
Some coding rules apply to this feature:
- Each channel is responsible for clearning its own peer_data and event queue
at the end of the call (when moving to DOWN state)
- Each channel dequeues messages only from its own queue and enqueues messages
in the peer's queue, with the only exception being messages received before
the bridge is stablished (IAM for sure and possible SAM messages) because
if the bridge is not yet stablished the messages must be queued by the channel
in its own queue temporarily until the bridge is ready
- When the bridge is ready it is the responsibility of the incoming channel to
move the messages that stored temporarily in its own queue to the bridged peer queue
- During hangup, each channel is responsible for moving itself to DOWN. The procedure
however differs slightly depending on the hangup conditions
If the user requests hangup (ie, FreeSWITCH) the request will be noted by setting the
FTDM_CHANNEL_USER_HANGUP flag but will not be processed yet because call control is
driven only by the link messages (so no hangup from ESL or command line allowed)
When REL message comes, the channel receiving it must move to TERMINATING state and:
- If the user has not hangup yet (FTDM_CHANNEL_USER_HANGUP flag not set) then
notify the user via SIGEVENT_STOP and wait for the user to move to HANGUP
state by calling ftdm_channel_call_hangup() before sending RLC
- If the user did hangup already (FTDM_CHANNEL_USER_HANGUP flag is set) then
skip user notification and move to HANGUP state directly where the RLC message
will be sent
- On HANGUP state the RLC is sent and the channel is moved to DOWN, final state
The peer channel will forward the REL message and wait for RLC from the network, when
RLC is received the channel can move straight to DOWN itself because the peer channel
is completing its own shutdown procedure when it received the REL message