[ns] Questions on IFQ of mobile node and mobile-ip

[Diepchi T Tran <Diepchi.T.Tran@lerc.nasa.gov>]

Hi ns-users,
I am working on a wired+wireless network including mobile-ip. I am facing
two following problems and not sure if they are bugs or something wrong in
my simulation

1)Some TCP packets are dropped after received by TCP receiver (which is a
mobile node in my simulation) because of no buffer space in IFQ. The length
time between the packet received and packet dropped are varied from 80 sec
to 30 sec. I think that it is a bug because when a tcp packet is received
by a receiver, it can not be sent back down to IFQ to cause the queue
overloaded.

2)When the mobile node is in domain of a foreign agent (FA), the home agent
(HA) doesn't encapsulate and forward a packet but it encapsulates and
forwards the packet before and after that packet. For example, home agent
receives packet number 4 and 5 but only encapsulates and forwards packet
#4. When the ack of packet # 4 comes back, TCP source send packet # 6 to
home agent. Home agent encapsulates and forwards packet # 6 to foreign
agent. Then after a time out, tcp source resend packet # 5 to home agent
and it is encapsulated and forward to foreign agent. I think that it is a
bug because when packet # 4, 6 are forwarded to foreign agent, home agent
should also forward the packet # 5 since there is no indication of
congestion on the link between HA and FA at the time HA hold packet #5

When I change packet size from 1000 Bytes to 512 bytes, I don't have the
two above problems. Do you think there are bugs in the code or something
else going wrong?. please help

Thank you very much,
Cindy
Diepchi Tran 
Phone (216) 433-8861
Fax   (216) 433-8705