creating a loss system for voice data in Linux

how do I create a system that takes in voice data(rtp) and then creates loss in this data(like delay or packet drop/loss)? The output of the system(data) should be readable which made me think i might not be ab开发者_如何学Cle to use ns-2.Also, ns-2 does not support VBR(needed for voice). I might be wrong in this aspect though. How can I achieve this loss condition in linux environment? please give suggestions.

NIST Net looks as if it will do what you want.