I believe it's not possible. This question is well discussed here but could not reach to conclusion.
[URLnofo]http://serverfault.com/questions/54483/how-can-i-monitor-per-user-bandwidth-on-linux[/URLnofo]
Alternatively, if you are using Ubuntu then following is the solution.
[URLnofo]http://askubuntu.com/questions/28926/how-to-monitor-network-bandwidth-per-user-on-ubuntu-server[/URLnofo]
However, per user bandwidth measurement is not necessary then you can install command-line tools like nethogs Nload, iftop, iptraf. These tools allows users to monitor the incoming and outgoing traffic separately.