[cisco-voip] signaling very average bandwidth

[Vladimir Litovka (vlitovka)]

> 	Knowing that there were no lost packets in my media is far more
> important than the signaling overhead.  In most cases the signaling
> doesn't need to be immediate (eg: 60ms vs 600ms) doesn't matter.

My customer is going to build a kind of cutted network, when voice payload goes through PSTN, but signaling - over IP, through centralized SPS. It isn't good idea, but I think they know, what they are doing. In this case all bandwidth will be dedicated to signaling.

> 	If you're trying to get an idea, i'd look at the options
> messages which are frequently used as keepalives during NAT
> operations.

An idea is simple. If don't look at relatively rarely used requests (REGISTER, CANCEL, SUBSCRIBE/NOTIFY, etc), which don't make weather on link (this is as I think :-) ), then there are few another commands, which is in frequent use: INVITE, ACK, BYE, PRACK, INFO (?), UPDATE and responces (200 OK, etc), which, as I think, give average size from 400 to 600 bytes not counting ip/udp overhead. Lets think about 500 bytes per message

So, in the simpliest case

1) INVITE / 200 OK - 2 times (to central SPS and backward)
2) ACK
3) BYE / 200 OK
4) INFO (to SPS about session finish)

where 2nd and 3rd steps don't use WAN link.

which supposed to be 1000 bytes (1st step) + 500 bytes (4th step). For 5cps this gives required bandwidth 60Kbps. More complex  cooperation between users will give much more bandwidth requiremens... Not bad :-)

I feel, that I've missed somewhere. Any comments?

/doka