Anthony,
This information is incredibly invaluable!
Is there any other documentation outside of the source code that contains this
kind of “here’s what happens and why” type of info? Just
curious.
Thanks for working on such a great idea.
I’m looking forward to using FreeSwitch in the not-so-distant future.
-MC
P.S. – Before I go drop $2K on a
Sangoma T1 card, has anyone started working on mod_zap for FreeSwitch? I have
a Tormenta2 clone that actually works very well and I don’t want to spend
more $$ on hardware if I don’t have to… J
From: Anthony
Minessale [mailto:anthmct@yahoo.com]
Sent: Wednesday, September 06,
2006 12:02 PM
To:
Subject: Re: [Freeswitch-dev]
Questions regarding the architecture
1. Thread architecture. For a basic
call, why do we need two threads for the sessions (one for each
endpoint)? While the thread in charge of originator is in the
switch_core_standard_on_execute(), the other thread is in the
switch_core_session_run() while loop. What's advantage of
doing this compared to Asterisk's one thread approach? Why do we need the
thread for the originatee?
A)
Every session has a thread which is managed by the state
machine in the core which sees it from creation to destruction.
In the case of a bridged call the existing thread of both sessions are used to
move inbound audio across to the opposite session at the same time.
A one threaded approach such as asterisk will leave you doing poll's on 2
sockets at once and blocking in one direction will impeed the other as
well as forcing you to expose something that can be polled, (not all channels
have sockets)
The states of the orignatee channel are overridden from
the default behaviour to perform the bridge
in this case:
CS_HOLD pauses the thread.
CS_RING moves the state to CS_HOLD where it will wait until it's moved to
CS_LOOPBACK or CS_HANGUP by the originate function.
CS_LOOPBACK runs the audio bridge code sending the audio back to the other
channel.
The originator is in CS_EXECUTE meaning it's running
instructions installed by a dialplan module.
At this point both channels are in the same code reading A
and writing B as well as moving messages and dtmf across one another.
If either is interrupted the functions exits in both
sessions and the originatee state override table
is cleared and the session is moved to the new state where the execution
continues. if this state is hangup
the call ends.
2. What does CS_LOOPBACK really mean? When A calls B, B is in the
LOOPBACK state after the call is established. Yet, the
switch_core_on_loopback() is not really called.
A)
The default for loopback is to echo the audio back to the
channel,
in the case of a bridge it's overridden to send it audio to the other session
instead
of itself.
3. When A calls B and before B answers, the caller session
thread does busy waiting by constantly calling check_channel_status(). Is
there a better approach than this? And with this architecture how
are we going to incorporate with the voice mail and other timer-based
applications?
A)
Yes this is the best approach, the originator has created
the originatee and is waiting for the endpoint module to place it into the
CS_RING state
when this happens because we overrode it we move it to CS_HOLD and wait for it
to be answered or for a timeout to occur.
The point is we have waited for it to be safe for us to control.
4. When the orginatee hangs up, the exosip_kill_channel() was called 3 times
just for the orginatee channel. The same function is called twice for the
originator channel. Is this by design?
A)
The should be as few calls to this as possible once it's
ok to have mutiple calls to it it just calls for any blocking to end
on a read or write operation such as the socket api call "shutdown()"
does
We are not using exosip anymore, we have started coding
mod_sofia which is our preferred sip code.
There are several changes comming up this week you may want to study.
Thanks,
Anthony Minessale II
FreeSWITCH http://www.freeswitch.org/
ClueCon http://www.cluecon.com/
AIM: anthm
MSN:anthony_minessale@hotmail.com
JABBER:anthony.minessale@gmail.com
IRC: irc.freenode.net #freeswitch
FreeSWITCH Developer Conference
sip:888@66.250.68.194
iax:guest@66.250.68.194/888
googletalk:freeswitch@gmail.com
pstn:712-432-7800
----- Original Message
----
From: Alex Guan <alex.guan@prodeasystems.com>
To:
Sent: Wednesday, September 6, 2006 10:13:43 AM
Subject: [Freeswitch-dev] Questions regarding the architecture
Gang,
I am new to freeswitch and have been studying it for the last
week. A few questions regarding the architecture. Any
input will be greatly appreciated.
1. Thread architecture. For a basic call, why do we need
two threads for the sessions (one for each endpoint)? While the
thread in charge of originator is in the
switch_core_standard_on_execute(), the other thread is in the switch_core_session_run()
while loop. What's advantage of doing this compared to
Asterisk's one thread approach? Why do we need the thread for the
originatee?
2. What does CS_LOOPBACK really mean? When A calls B, B is in the
LOOPBACK state after the call is established. Yet, the switch_core_on_loopback()
is not really called.
3. When A calls B and before B answers, the caller session thread does busy
waiting by constantly calling check_channel_status(). Is there a
better approach than this? And with this architecture how are we
going to incorporate with the voice mail and other timer-based applications?
4. When the orginatee hangs up, the exosip_kill_channel() was called 3 times
just for the orginatee channel. The same function is called twice
for the originator channel. Is this by design?
Thanks,
Alex
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