[Asterisk-biz] $19.95/mo unlimited US IAX termination

[alex at pilosoft.com]

On Thu, 7 Apr 2005, Brian West wrote:

> FYI iax works behind ultramonkey with sticky sessions....
Uh, I didn't say it doesn't, and I said that there are people with enough 
clue to do it. Just not everyone. :)

However, it is still a faint cry from proper SIP SBC redundancy - if an 
IAX box handling a call in the cluster fails, those calls are dropped 
hard. SIP SBCs will replicate the status of the call in progress to other 
cluster members, and if one SBC fails, others will be able to keep the 
call active. 

Correct me if I am wrong, but to my knowledge, IAX does not make a 
difference between call control path and media path. Thus, once IAX 
transfer happens, the box in the "middle" of the transfer will be 
completely out of the path, and won't be able to signal, for example, one 
endpoint to drop the call (such as necessary for prepaid card, if time 
expired). This results in requirement that the box that handles media path 
needs to handle control. 

Proper softswitches make a distinction between "Media Gateway"  (MG) and
"Media Gateway Controller" (MGC). MG is a fairly stupid device that has
TDM and VoIP dsps and is controlled for call establishment by MGC. Once
call is established, MGC is not involved until the teardown. This spreads 
the load and the risk - MG is less likely to fail because it is a fairly 
stupid device, and MGC is a) not involved in media path and b) replicated 
to other MGCs in cluster.

-alex