[asterisk-dev] NFAS Implementation Spanning Multiple Servers

Paul Cadach paul at odt.east.telecom.kz
Fri Feb 3 00:06:57 MST 2006


John Todd wrote:

> Just thinking out loud here, but why couldn't this work with some
> type of modified TDMoE (*) driver setup that handles just the D
> channels?

Signalling is not so timing critical in comparsion to speech channels, so it
could be done without TDM. For example. specific UDP-based protocol (like
SIGTRAN) could be able to handle D-channel distribution and aggregation over
server cluster. Also, SS7 ideology very like to NFAS one where single signalling
link (D-channel in ISDN terminology) can handle more than one bearer link (E1/T1
link), but NFAS is more fail-safe just because it allows to have backup
signalling channels.

For implementation issues, there is should be possible to re-associate
signalling channel from TDM-link with another transport system (network, etc.).
It would allow to handle such types of signalling distribution/aggregation
within Asterisk or standalone application, so there could be possible to declare
"virtual" channels and specify them at zapata.conf configuration file, for
      signalling => net: # for UDP transport
      signalling => unix:/var/lib/asterisk/trunk1.sock # for Unix sockets
      signalling => zaptel:16 # for existing TDM channels

IMHO it's not so complex to implement in the current Asterisk's design (just
because at implementation level access to zaptel's timeslot is done over special
file /dev/zap/<channel>, so all internals will be the same except for handling
of file operations (open, close, read/recvfrom, write/sendto).


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