On Mar 22, 2007, at 7:17 PM, Avinash Sridharan wrote:
Hi Phil,
A few more questions more on the bandwidth allocation between the
client and forwarder in the forwarding engine.
The forwarder effectively has a depth of FORWARD_COUNT (set to 5)
in the FIFO queue and the client has a depth of 1. As you mentioned
in your mail below this implies the client gets only 1/6 th of the
bandwidth.
Isn't this inherently unfair. In the sense that the forwarded
packets would always get 5 times the bandwidth as compared to the
source itself. I did a simple experiment with the following linear
topology:
1<----2<----3
This was done on TOSSIM, I kept an application level queue of size
50 for the forwarder 2. Both 2 and 3 were generating packets that
were destined for the sink 1.
It turned out that for every 3-5 packets forwarded by node 2 to
node 1 that originated from node 3 you would have a single packet
forwarded sent from node 2 to 1. Thus the bandwidth allocation was
quiet uneven.
CTP is not intended to provide node-level fairness under high
bandwidth. If you look closely, none of the protocols that lots of
people use do (e.g., MintRoute, etc.). There are a couple of
transport protocols that propose ways to do so -- IFRC, Ee's paper in
SenSys 2004, ARC in Mobicom 2001. The two general approaches are to
maintain per-child state or rate-limit at packet sources.
Phil
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