[Asterisk-biz] Modem Over IP: solutions ?

[Jean-Michel Hiver]

trixter aka Bret McDanel a écrit :

>On Sat, 2005-10-22 at 23:59 +0400, Jean-Michel Hiver wrote:
>  
>
>>Link latency is about 300ms with no more than 10ms jitter. If you have a 
>>solution please let me know!
>>    
>>
>
>10ms is too high for any 'fast' modem connection and may be too high for
>slower (sub 4800 bps) connections.  Modems rely on more exact timing
>which is available due to the properties of the TDM network.  Jitter of
>a few ms will break the newer protocols although it may be suitable
>otherwise.
>  
>
OK. Question: Isn't it possible to use a large jitter buffer to smoothe 
out jitter issues?

>I am working to expand iaxmodem to support not just fax but also modem
>data.  I currently dont have the time I would like and have done little
>omre than look at the code and talk to Lee in a few emails, but that
>should change soon.
>  
>
OK.

>What modem protocol is used?  
>  
>
I don't know yet - I have to go and study customers' equipment. I will 
let you know once I know more myself!

>Keep in mind its way better to run iaxmodem on the asterisk server
>itself over Zap channels as timing between iaxmodem and asterisk is very
>critical.  
>  
>
I didn't know about the iaxmodem module! I'm going to check it out.

>Now if he is switching to IP how is that accomplished?
>
That's what I'm trying to figure out. My first thought was to use IAX 
with ulaw but after some reading it sounds that would be shabby. Since 
the bloke is transmitting alarm informations, reliability is important.

>If the device itself is being modified to use IP why not send a packet or two instead
>of modem data?  That would save bandwidth, cut response time, etc.
>
Yes I agree and I will study this possibility. However there is a 99% 
chance that it will be some crappy, closed, un-hackable hardware which 
will need to be treated like a "black box".

>Or was the plan to not modify the device instead just supply a small cheap
>sip terminal? 
>  
>
Of course this would be ideal but it might not be doable...

>If the latter is the case then why not see if you are capable of running
>everything needed on the sip terminal and send off a SIP IM or something
>to a better equipped system?
>  
>
I'm not sure to understand you here.

>Just trying to see if there is a better way, VoIP is not always the best
>solution for a given problem, at least not right now.
>  
>
Well the biggest issue for the customer is that they have 2,500 short 
modem calls per day, and that France Telecom charges almost 10 cents 
"connection fee" for each call... although technically speaking, France 
Telecom TDM network is a very good solution for modem calls, it's so 
damn expensive!

Cheers,
Jean-Michel.