Add I/O plugin for mISDN stack that is included in the linux kernel
since version 2.6.27.
The in-kernel mISDN stack uses a socket based interface (AF_ISDN),
data and control commands are exchanged via datagram messages.
This makes writing a driver that doesn't use a separate (per-span)
thread to handle all incoming events a bit tricky, because responses
to control messages and incoming data are mixed and interfacing
with the synchronous FreeTDM I/O API is problematic.
B(*)/D-channel handling:
The current version uses misdn_wait() to poll() for activity on
the non-blocking channel sockets and misdn_read() to receive and
handle all pending events up to the first PH_DATA_IND (data) message
(which is what the caller of the read method is actually after).
In case no data has been received, misdn_read() returns FTDM_SUCCESS
with *datalen = 0, which is OK for all the signalling modules tested
(ftmod_libpri and (out-of-tree) ftmod_isdn).
To send data, misdn_write() is called, which just sends a PH_DATA_REQ
message to the mISDN channel socket.
(*) B-channels use a per-channel timerfd as a timing reference for
'ready-for-write' poll()ing in misdn_wait().
This is a workaround for a limitation of mISDN sockets, which do not
support POLLOUT waiting on b-channel sockets (in a useful way).
Sending/receiving of data works the same way as on d-channels, otherwise.
The module has received some minimal testing using a beronet
single-port HFC E1 and a HFC4-S quad-port BRI card on linux-3.0.x.
--- Limitations ---
- Only the most basic features have been implemented (alarms,
sending/receiving data/audio).
- Spans are limited to E1 and BRI/BRI_PTMP trunk types.
- D-Channels only work on 16 for PRI and 3 for BRI.
- NT/TE mode information is not available from freetdm.conf /
at configure_span()-time so the module assumes TE mode,
which should be only a problem for cards that can change
the port configuration (pin-out) from software.
- Current design (b-channel timerfd / misdn_wait()/_read()/_write())
should be fine for most SoHo use-cases
(scalability / cpu usage / timing precision).
--- Requirements ---
- mISDNif.h header (/usr/include/mISDN/mISDNif.h), provided by mISDNuser
(http://isdn.eversberg.eu/download/lcr-1.7/mISDNuser-20100525.tar.gz).
- Linux kernel with mISDN and timerfd enabled (>= 2.6.27)
and libc with timerfd support.
mISDN options can be found in the:
"Device Drivers" -> "ISDN support" -> "Modular ISDN driver"
section of make menuconfig. Timerfd is usually enabled by default.
The FreeTDM configure script will check for missing mISDNif.h
header and timerfd support and print a message.
You should see the following in the summary screen on success:
ftmod_misdn........................ yes
NOTE: Forcing mISDN support using the "--with-misdn" configure option,
will cause the configure script to fail on the first missing
dependency.
--- Usage ---
To use the module, make sure you have mISDN support in the kernel
(kernel modules loaded or kernel with built-in mISDN running),
the "misdn_info" application shipped with mISDNuser will output
a list of available mISDN ports on your system, e.g.:
Found 5 ports
Port 0 'hfc-4s.1-1': TE/NT-mode BRI S/T (for phone lines & phones)
2 B-channels: 1-2
B-protocols: RAW HDLC X75slp
...
Port 4 'hfc-e1.2': TE/NT-mode PRI E1 (for phone lines & E1 devices)
30 B-channels: 1-15 17-31
B-protocols: RAW HDLC X75slp
NOTE: ftmod_misdn will print an error message if mISDN support is not available,
or if there are no ports installed.
- Example freetdm.conf settings
[span misdn BRI_1]
trunk_type => BRI_PTMP
b-channel => 0:1,2
d-channel => 0:3
[span misdn PRI_1]
trunk_type => E1
b-channel => hfc-e1.2:1-15,17-31
d-channel => hfc-e1.2:16
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>
NOTE: There is bugs in libpri, even latest 1.4.12 as of this writing if you use NI2. So rightnow it only work in DMS100/ATT mode. Email me to get the NI2 patch (really stupid error).
NOTE2: The way libpri is build doesn't allow to do advance feature with the SERVICE feature, so if you put an channel out of service, and the far end send an restart, it will be bring back in service. Lot of changes in libpri is required to allow this. I need to figure out what would be the best steps to take since I don't have commit access to libpri release.
NOTE3: You need to enable this feature by setting service_message_support to true on the span
