[LARTC] Best way to drop avg packet size?

[Ed Wildgoose]

I am testing VoIP via SIP on my local network and despite a careful 
setup to prioritise the voip packets I am still getting some small 
amounts of breakup when the system is under stress.

I already my patches to HTB to get it to understand ADSL bandwidth (so I 
know that this is being accounted for OK), and also with the HTB code 
patched to not use "hysterisis".  It's also only intermittent and seems 
to affect outbound traffic more than inbound and so I suspect that it's 
down to the average packet size being the default 1500 bytes..?  Sound 
plausible?

So what is the preferred method of reducing the MTU of connections, 
outwards in particular, but inbound would also be nice?  I am currently 
experimenting with a rule in the forward chain on the router which does 
a "--set-mss XXX".  Is this better or worse than simply changing the MTU 
on either the router box of the modem?  Anyone got any experience of the 
problems that can occur here?

The router also runs a small public mail and web server and so I don't 
want to start accidently locking people out, or having connection issues. 

Thanks

Ed W