[ns] How to set TCP receiver buffer? (10Gbps issue)

[Giovane]

Dear all,

In the Linux kernel there are two variables that specify buffer size of TCP
sender and receiver.

For instance, in the case of receiver, this variable is tcp_rmen
(/proc/sys/net/ipv4/tcp_rmem). It contains the following values:
4096    87380   4194304

which stand for the minimum, default and maximum receive buffer for each TCP
socket, respectively  (values in bytes).
In this example, the maximum value allowed for each TCP socket is 4MB.

I would like to know to it is possible to set this values on a ns-2
TCP-sink.

I conducted a simulation with the following receiver (using TCP LINUX/Cubic
as a sender):
set sink [new  Agent/TCPSink/Sack1/DelAck]
$sink set ts_echo_rfc1323_ true
$ns attach-agent $n4 $sink
$ns connect $tcp $sink

I'm asking because I'm simulating on 10Gbps speeds and packets are arriving
out-of order, and I cannot see any discard on the receiver side (so it must
be buffering the data until it receives the missing packet).

Analyzing the trace, I calculated the amount of packets that arrived before
the missing packet finally arrived, which was 550810.
Each packet in my case has a size of 1500 bytes, so the receiver buffer
stored 826.215 MB!

I would like to limit this receiver buffer side to see how it would perform
when there is no more buffer space left.

Thanks for your attention,

Giovane