tcp congestion window

[Adib Bashir Motiwala <adibm@cs.tamu.edu>]

I am trying to modify TCP's congestion response....
Instead of the normal cwnd = cwnd/2 on packet loss
 and cwnd = cwnd + 1/cwnd on successful transmission 

i have to use modifications such as cwnd = 3/4 cwnd on loss and
cwnd = cwnd + 1/(2*cwnd)

i have to compare performance with TCP Reno.
I have a config of 4 senders and 4 recivers connected via 2 routers.

My questions are:
1)Is TCP REno the default config of TCp...ie cwnd = cwnd/2 on loss and
additvie increase by 1/cwnd on success of transmitting packet.

2)I have just started with ns...for the problem above do i need to change
the code of tcp.cc or just adjust parameters in my tcl script.

advice appreciated