Codec selection on ip?


I know how to make a order based on users wich codec to be used and wich not.
But can it be done also by host tcp/ip ?
Say, tcp/ip is in same LAN, codec -> ulaw.
tcp/ip not from the same LAN, codec -> gsm.
Basically, ppl who are at the office get the best quality codec, but when they go home with their laptop, they get the lower quality codec.
Hope I explained it enough to understand wht I mean. :smile: