PPP with VoIP - Echo problems

[somwicked]

Simple PPP WAN between remote site and main office. We have a solid data connection running across a T1 (full).

There is an Inter-Tel Axxess VoIP box in the main office and phones located in the remote office.

Per another user's recommendation, I used the following for VoIP prioritization.

class-map match-all VOIP

match access-group name VoiceOverIP

!

policy-map SET_PRECEDENCE

class VOIP

set ip precedence 5

!

interface FastEthernet0

service-policy input SET_PRECEDENCE

Everything seems to be working fine except there is a terrible echo when using the phones. I believe the Axxess system is SIP based but am not entirely sure since a 3rd party handles that portion.

Any ideas how I can handle this better, or cancel the echo?

[dgahm]

QOS problems on your WAN link would result in garbled or distorted audio, not echo.

Echo is caused when reflected audio is present and is delayed enough to be noticable. Reflected audio with no delay is sidetone, and is not annoying. IP telephony has to buffer voice to compensate for the variable latency (jitter) that is normal in a packet network. This buffer delay means that any reflections will be perceived as echo if the level is high enough.

There are 2 kinds of echo, acoustical and electrical. If the echo is heard when the Inter-Tel phones talk to each other you have acoustical echo meaning the audio is feeding back from the earpiece (or speaker) to the mic. Cisco phones have built in echo cancellers to deal with acoustic echo. If the echo is heard on outside calls, then it may be electrical, which occurs in analog circuits like home phone lines (POTS). All Cisco gateways (interface to analog or TDM network) have echo cancellers to handle this when it happens.

Bottom line, the solution lies with the Axxess system or it's gateway to the PBX or PSTN. If an analog 2 wire interface is used the impedance may be misconfigured which would cause echo.

[somwicked]

Wow. You pretty much summed up all of the information I spent hours scouring for today - many, many hours of reading. Thanks.

I understand its not WAN related - now to trace down more understanding of where and when the echo occurs.

So far I know ..

The echo is not heard by the outside (i.e. me calling them).

The echo is heard on the sets in the remote location - not sure about the main site, yet. Soon.

Thanks again.