i have 2 servers in 2 locations and i am using VPN to connect these 2 FreePBX server 12 with Asterisk 11.
i have IAX trunk between both and every thing work fine . and due to the slow connection between the 2 branches i used ilbc only for the IAX . but none of my endpoint phone in both branches support ilbc .
so my question is . do i have to have ilbc on these 2 phones . or is the traffic between these 2 servers will be IAX and from each server to each phone will be normal codec?
what is the codec and call flow in this design ?
is it (phone ) G711 â> IAX ( server ) ---- IAX (server ) <----- G711 (phone )
or somthing else
Itâs as you expect. Asterisk is doing transcoding from ulaw to ilbc over the iax trunk.
You can see this by doing âcore show channelsâ and then picking an IAX channel thatâs going between the machines, and going âcore show channel IAX/âŚwhateverâ and youâll see the codec in use.
However, I would like to point out, I find it extremely unlikely that itâll make that much of a difference in bandwidth. Youâll actually have better audio quality and be more tolerant of dropped packets if you switch to G722.
Hi Rob - thatâs an interesting âpearl of wisdomâ. Can you explain briefly why that would be? Since the majority of our endpoints are wifi handheld devices (on the move), Iâm interested in anything that would minimise in-call dropouts.
Thanks xrobau . but for sure ILBC will consume less bandwidth plus G722 will take traffic as the G711 . yes HD audio . but still i limited to bandwidth
G722 is quite tolerant of dropped packets - much more so than G711. This is something you can play with yourself, by the way, in software.
If your handset has the IP Address 192.168.99.88:
iptables -A OUTPUT -d 192.168.99.88 -m statistic --mode random --probability 0.1 -j DROP
If you run that on your FreePBX machine, thatâll drop 10% of all traffic heading 192.168.99.88 so you can hear the changes yourself. Note that 10% is a lot of traffic to drop. More real-world is 1%, which would be --probability 0.01
To remove it, replace the -A (add) with -D (delete).
If you wanted to be even MORE accurate, you should drop packets both ways, which would be this:
iptables -A OUTPUT -d 192.168.99.88 -m statistic --mode random --probability 0.005 -j DROP
iptables -A INPUT -s 192.168.99.88 -m statistic --mode random --probability 0.005 -j DROP
That emulates a network thatâs dropping 1% of packets in both directions. (Note the -s[ource] and -d[est] differences there, too)