[ns] Priority for TCP and CBR

["Leyla TOUMI" <Leyla.Toumi@imag.fr>]

 Hi all !
 I'm simulating a network which uses two sources, each of them send 10
flows,
 the first source sends FTP/TCP flows, and the second one RTP/CBR flows. The
 sources send to a same sink node. The topology is as the following :

 node0_________
                                  |
                              Router 1-----------Router2-------------Sink
                                 |
 node1_________|


 The flows are 1Mbits. The packet size is 250 bytes for all flows. Link
 between node0 and Router1 is 1Mbps. Link between node1 and Router1 is
1Mbps.
 The other links are 2Mbps.
 Flows are exponentially distributed, with the same distribution mean.

 For now, I use the DropTail queues, and I measured the mean packet delay of
 each flow, in the first router...I mean that I measured the time between
 packet enters the router, and the time the packet leaves the router. In
 theory, because there is no priority given to any flow, I wouldn't find
 different values for TCP packets delay and CBR packets delay.....but
 something strange happens : I always find the CBR delay greater than the
TCP
 one, which is abnormal....this result means that TCP has more priority than
 CBR wich isn't true....

 Can anyone explain me why do I find this strange result ?

 Many thanks in advance for your help !!!

 Sincerely,

 Leyla Toumi
 PhD Student - Grenoble, France