[cf-dev] Problem while using Netem for benchmarking large-large post in

[Abhijan Bhattacharyya <abhijan.bhattacharyya@xxxxxxx>]

Dear list,
We are trying to do some bench marking
of a typical large-large post scenario under different bandwidth and losses.
We are using Californium. However, we are experiencing an apparently bizarre
problem. 

We are running the client and server
in two VMs and routing the packets through a third VM. We are observing
the exchanges in Wireshark at both client and server ends. The exchanges
happen as usual. However, whenever we are incorporating loss in the 3rd
VM we see the problem. 

We are using the following command for
incorporating loss in the 3rd VM (this one is configured with 2 interfaces)

sudo tc qdisc add dev eth0 root netem loss <n>%

As soon as the loss is incorporated we see that after exchange of one or two blocks (or some time not even a single one) the exchange stalls and the client is getting Null pointer exception. Actually, the server is responding, but the client is not able to receive the packets and the application layer, rather than doing retransmits, is somehow crashing. Is Netem doing something with the state machine?
If anyone has faced this problem or has any idea regarding this may please respond.


 
Regards
Abhijan Bhattacharyya
Associate Consultant
Scientist, Innovation Lab, Kolkata, India
Tata Consultancy Services
Mailto: abhijan.bhattacharyya@xxxxxxx
Website: http://www.tcs.com
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