I like everything I have read about G.722, but am a little confused about some of the benefits. If my Polycom VVX500 negotiates in SDP for G.722, will it automatically use G.722.1 or G.722.2 if the other side can agree?
There are various specifications for how much bandwidth G.722 can use. We engineered for G.711 at a constant bandwidth of about 84 kbps (after overheads). In practice, it seems that G.722 never uses more than that. But some customers want G.729 because they think they will get more simultaneous calls in the same thin pipe (e.g.. 1.544 Mbps T1). I would much rather they used G.722. Will G.722 automatically lower the bandwidth it uses if it encounters packet losses? Is there a way I can set my VVX500 phones to use a more frugal variant of G.722?
THANKS in advance for reading my question,
Here's what I have figured out so far:
- To see which codecs your phone supports, go to the phone's internal web site, e.g. http://192.168.7.23, login and then choose "Settings" / "Audio Codec Priority".
- Or read the UC Software 4.x Administrator's Guide, Table 7-7 "Supported Audio Codecs"
- In the G.72x series, Polycom VVX 500 supports G.722, G.722.1, and G.722.1C
- None of those codecs are Adaptive Multi-Rate (AMR), but they do give you a choice of several fixed speeds
- G.722 is the old, original WideBand codec . . . able to represent frequencies up to 7,000 Hz.
- G.722.1 has fixed speeds at 16, 24, or 32 Kbps. To my ear, G.722.1 at 32Kbps seems much better than G.711 at 64 Kbps. Your mileage may vary.
- G.722.1C is even wider band, able to represent frequencies up to 14,000 Hz, but my ears are too old for high frequencies.