[asterisk-dev] NFAS Implementation Spanning Multiple Servers

Kevin P. Fleming kpfleming at digium.com
Thu Feb 2 18:28:55 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?  
> The system with the "primary" D channel would then be told which 
> machines had which "trunk groups", and then messages for each of those 
> systems would be split off using a single DS0 TDMoE connection to each 
> of the respective platforms.

This is the original idea that I had, which I shared with Matt a few 
months back. I too agree that this would be a reasonable course to take 
and not terribly difficult to implement, presuming that each Q.931 
message that travels across the D-channel has adequate information for 
it to be 'bridged' in this fashion.

One concern is with this model is that if that 'main' Asterisk instance 
was to stop operating, the entire NFAS group would become 
non-functional. My original idea was to still have the telco provide one 
or two backup D-channels, and each Asterisk server would have access to 
all of them via this bridging method, so each server sees a primary and 
a backup (and maybe another backup) channel.

> I don't know where the concept of "remotely registering phones" would 
> factor into this, or "RTP" for that matter.  If you are using the TDM/IP 
> boxes as SIP registrars and mixing things up, I think that is a separate 
> problem that need not be addressed at all by the NFAS portion of the 
> code.

This is a separate issue that has come up during our discussions 
revolving around SS7 implementations, STPs, media gateways, etc. I think 
this is a side issue, and that basic 'bridging' implementation could be 
put together without too much headache. It's certainly not trivial to 
do, but it could be done.

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