How to find out who is taking more bandwidth in Squid

You could use

acl aclname rep_mime_type mime-type

to block certain mime-types from downloading (eg iso's)

and

reply_body_max_size

to set a ceiling on the biggest files that can be downloaded

you could also use free-sa to analyze your logs to see where the bandwidth is going

http://free-sa.sourceforge.net/

EDIT: Actually squid delay pools will do EXACTLY what you need.

read this article: http://www.howtoforge.com/squid-delay-pools-bandwidth-management

You could set up shaping with rules something like this:

tc qdisc del dev eth0 root

tc qdisc add dev eth0 root handle 1: htb default 1 r2q 160

tc class add dev eth0 parent 1: classid 1:1 htb rate 2000kbit burst 1k
tc class add dev eth0 parent 1:1 classid 1:2 htb rate 2000kbit ceil 2000kbit burst 1k
tc class add dev eth0 parent 1:1 classid 1:3 htb rate 1200kbit ceil 1200kbit burst 1k

tc qdisc add dev eth0 parent 1:2 handle 2: sfq perturb 10
tc qdisc add dev eth0 parent 1:3 handle 3: sfq perturb 10

Then you could use iptables to classify packets into these classes:

iptables -t mangle -A POSTROUTING -o eth0 --set-class 1:2
iptables -t mangle -A POSTROUTING -o eth0 -m tcp -p tcp --dport 80 -j CLASSIFY --set-class 1:3

Note that it's the last matching rule that sets the class, it doesn't short-circuit when one rule matches. It took me a while to grok that.