[ns] TCP Simulation

[gokul ramasubramanian <ramasubr@eta.cis.ohio-state.edu>]

Hi All,

I am running a simulation and the topology is something like this.


n0-----
      |
n1    | 10Mbps
      |
n2    |           10Mbps
      |-------n5----------n6---------n7
n3    |
      |
n4----|


All nodes n0,n1,n2,n3,n4 are connected to n5. Nodes n0 to n4 are the TCP
sources.  Each of the links
n0->n5,n1->n5, n2->n5, n3->n5 ,n4->n5   are 10Mbps link with
delay of 5ms.  The link  from n5 to n6 is also 10Mbps.

For simulation, I've attached CBR agents to all nodes. they generate
traffic at the rate of 2500 packets/sec. each packet size is 500 bytes. So
this fully utilizes bandwidth of 10Mbps.
I monitor the queue at n5 which is droptail.

I've some questions abt the results i got.

i) When i view the simulation in nam, I see that not all sources are
sending
at the same time, although i start the simulation at the same time for all
of them.
 No packets were dropped when i checked the trace file!!! how can this
be possible? The link from n5 to n6 has bandwidth of only 10Mbps.  and all
the 5 TCP sources are sending at total rate of 50Mbps. On checkign the
queue size , it never gets above 48 so no packets are dropped.
  IS there something wrong i am doing??

ii) Also in the trace file, i find that totally 281336 packets were
removed from the queue, but only 187708 were received by the sinks. why is
that so


Any ideas are greatly appreciated.

Gokul.


***************************
R.GOKUL,
Graduate Student,
Dept. of CIS,
Ohio State University,
Columbus, OH.
Office - 474, Dreese Labs
Phone 614-292-8578
***************************