Are you using m0n0 on both ends.  I've had some similar problems where I 
have m0n0 on one end and a Netopia router handling the other end of the 
tunnel. The hardware simply couldn't handle the encryption / decryption 
of the link.

gramels wrote:
> keep in mind, that voip over vpn has some pitfalls in respect tu mtu
> size etc... I had some bad expierences here independent of the
> available bandwith. I would check for that first. What are the jitter
> values on jour fones? (on cisco 79xx with sip image press the info key
> twice to see iinfo about jitter for ongoing calls)
> 
> 
> On Mon, 27 Sep 2004 21:19:28 +0200, kjetilla <kjetil underscore larsen at broadpark dot no> wrote:
> 
>>My scenario:
>>
>>Using m0n0 1.1 CD/Floppy on two standard PC :
>>
>>VoIPgateway ---- Lan1 --- m0n01 ---- internet ---- m0n02 ----Lan2 ----- VoIP
>>Phones ( 10 pcs)
>>
>>IPsec is used to connect lan1 with lan2. Working perfect!
>>
>>Traffic shaping is enabled and setup was done using the wizard.
>>
>>It is working very well when traffic is coming to/from the internet. VoIP
>>quality is very good.
>>
>>But when traffic is coming thru the IPsec channel between the two m0n0's
>>VoIP quality drops to unacceptable level and becomes unusable.
>>
>>Is ViOP traffic wrapped into ESP before the traffic shaper starts processing
>>and therefore it cannot differenced between any combos of ports / source
>>/target IP's within the ESP package?
>>
>>I've tried to use traffic shape rules on LAN side instead of WAN, without
>>any luck, but I might overlooked something..
>>
>>Is there any way to get this to work? Any suggestions are welcomed.
>>
>>Thanks, Kjetil
>>
>>