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New Member

Using of the G.729 instead of G.711 in a CME + 7912G ip-phones environment.

Hi!

I'm sorry, but unable to attach a file,so doing scheme here:

[IP Phone Cisco CP-9712G]

|

[PC-based router]

|

[Modem Zyxel U336-S]

|

|

ppp, leased line

|

|

[Modem Zyxel U336-S]

|

[Cisco AS-2511-RJ]

|

---------------

| |-----[Phone CP-7912G]

| L A N |

|______________|-----[Phone CP-7912G]

|

[Cisco 2811 with CCME 3.1]

CCME is 3.1 version, IOS is 12.3(8)T8

With phone connections in LAN everything is OK. But when I'm making a call from the phone at the remote far end (ppp), the connection is ok, but the voice quality is extremely bad and "croaking".

When I used SnifferPro at the remote PC-based router during a call, it diagnosed:

[VoIP] RTP - High jitter

Jitter values in packets are 130-180 ms., and

SnifferPro was configured to set alarm when jitter is over 100 ms.

On the other hand ITU-T G.114 standart says that jitter under 200 provides more or less normal voice quality. So, I guess problem is not with jitter.

Next, I used Ethereal to capture packets while making a call from the remote phone to the phone in LAN. Two packets from router with CCME in part of SCCP had such description fields:

packet 1:

MessageID : OpenRecieveChannel

PayloadCapability : G.711 u-law 64k

EchoCancelType : EchoCancellation_on

G.723BitRate : Media_G723BRate_6_4

packet 2:

MessageID :StartMediaTrasmission

RemoteAddress : xxx.yyy.zzz.xzxz

PayloadCapability : G.711 u-law 64k

SilenceSuppression:Media_SilenceSupression_off

MaxFramesPerPacket : 1712

G.723BitRate : Media_G723BRate_6_4

And one packet from phone to phone had in part of RTP such field:

Payload type : ITU-T G.711 PCMU

So I wonder, G.711 needs 64kbps for normal work, but ppp in my case cannot provide such rate. So i think it'll be preferable to use G.729 with it's 8 kbps requirement.

Is it possible to solve this problem somehow?

Because, there are about 30 users on ppp lines via modems, and it will be far expensive to get voice gateway w/CCME to all of them.

Thank you.

Best regards,

Alex.

DAO21-RIPE
3 REPLIES
Bronze

Re: Using of the G.729 instead of G.711 in a CME + 7912G ip-phon

alex,

you are working with an unsopperted design:))

normaly cme is designed for ip telephony in a location where the phones are connected to the same lan.

in cme you havent the possiblity to configure codec capabilitys between ip phones. your default codec is G711.

you need with g711 and with ppp as layer2 over 80 kbit/sec for a call.

greetings

mehmet

New Member

Re: Using of the G.729 instead of G.711 in a CME + 7912G ip-phon

msolak,

you mean, that in such environment (modems, ppp, different voice lans) it is impossible at all?

I was recently told about an opportunity of using Cisco ATA 186/188 on the subscribers part that will provide usage of G.723.1 that is also supported by CCM... But phones do not! So I guess it'll be no way.

Thanks for your attention!

Best regards,

Alex.

DAO21-RIPE

Re: Using of the G.729 instead of G.711 in a CME + 7912G ip-phon

For G.711 you shold budget 80kbps per call

For G.729 you should budget 24kbps per call

I don't see how the Zyxel U336-S would be supported, usually a modem takes G.711/PCM and compresses/decomporesses with high latency. How are the modems doing QoS, etc?

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