Re: Why do we need congestion control?

assume your goals are
a. efficiency
b. fairness

where to meet a, 
you must not waste capacity on the links up to the bottleneck 
(for type 1 flow, this means not too much packet loss)
and to meet b,
you can use the Jain fairness equation.

now assume flows of type 2 can start and stop at some point.
what level of FEC do you use when there is 0, 1, or 2 flows of type 2?

now have a mix of flows of type 1 & 2
what level of FEC do you use when there is 
0, 1 or 2 flows of type 1 andor type 2?

repeat for 1million flows.

In missive <[email protected]>, Detlef Bosau typed:

 >>Am 03.04.2013 11:41, schrieb Jon Crowcroft:
 >>> lets do a simple thought experiment lets say you have two users 
 >>> sharing at least one router's output port/link as part of their path, 
 >>> and both users are greedy lets say you have a choice in each user 
 >>> whether to use either 1) feedback based rate adjustment (don't care if 
 >>> its VJCC cwnd or TFRC based) or 2) a rateless erasure code you could 
 >>> have both users' flows use 1 or both 2 or a mix, i.e. 3 cases 1+1, 2+2 
 >>> or 1+2 now, how do you choose the code to get max goodput for the 3 
 >>> cases... 
 >>
 >>
 >>Hm. Maybe I miss something essential. However, I don't know whether 
 >>there is "that only" and "simple" answer to this question. As Joe wrote 
 >>some days ago, in networks with huge (R)TT, FEC dominated approaches 
 >>would often be prefarable, so perhaps 2+2. In networks with small (R)TT, 
 >>ARQ based approaches would be preferable, so perhaps 1+1.
 >>
 >>However: What about two flows which only share a part of their paths, so 
 >>one flow has a huge RTT, the other a small one?
 >>
 >>And one point is missing: In case 2+2, we have to distribute the path's 
 >>capacity. "Somehow". In case 1+1, it is VJCC which distributes available 
 >>resources among the flows.  How is this achieved in 2+2?
 >>
 >>

 cheers

   jon