flex codec complexity and g729

[ciscoforum]

Does anybody know that in flex mode(default codec complexity) in GW 28xx, is it g729a or g729 if we specify g729 under dial-peer?

[Majdi Harb]

hi

first On Cisco IOS gateways, the variant to use (G.729 or G.729A) is related to the codec complexity configuration on the voice card. It does not show up explicitly in the Cisco IOS command line interface (CLI) codec choice. For example, the CLI does not show g729ar8 ("a" code) as a codec option. However, if the voice-card is defined as medium-complexity, then the g729r8 option is the G.729A codec.

now in default flex on GW 28xx, as known it eliminates the requirement to specify the codec complexity A DSP in flex mode accepts a call of any supported codec type, as long as it has available processing power (millions of instructions per second (MIPS))

Cisco IOS performs a MIPS calculation for each call received and subtracts MIPS credits from its budget whenever a new call is initiated. The number of MIPS consumed by a call depends on the codec of the

call, both calls of G.729 and G.729a needs 30 MIPS per call each...

hope this helps

/majdi

[ciscoforum]

Thanks for your reply. I do agree with this that the variant to use (G.729 or G.729A) is related to the codec complexity configuration on the voice card.

The reason I am asking this question is that we want to use G729 because it has more MOS(mean opinion score). But since it is flex, I don't know what is used. Here is my scenario:

analog phone-PBX1-PRI-28xxGW---IPwan---28xxGW-PRI-PBX2-analog phone

Do you think it will G729 if there is enough MIPS?

and the following is a table for MOS using different G729 variant for reference.

codec MOS

G.729 CS-ACELP 3.92

G.729a CS-ACELP 3.72