Re: [re-ECN] Charter Question

[Bob Briscoe <[e-mail]>]

Stewart,

At 06:38 08/05/2010, Stewart Bryant wrote:
>On 08/05/2010 01:19, Woundy, Richard wrote:
>>So now let's add Conex marking, in which the end hosts add markings 
>>to send feedback about end-to-end congestion into the network. Now 
>>the CMTS has a new data point -- information about whether there is 
>>upstream (ECN) or downstream (Conex) congestion 
>>experienced/expected for a particular packet flow. The CMTS can 
>>count 'total bytes' as well as 'congestion bytes' on a per modem 
>>basis. As a result, the backend system can make a much better 
>>determination about whether a subscriber's overall traffic is 
>>dominated by LEDBAT or non-LEDBAT applications, without resorting 
>>to DPI and other such schemes. And the CMTS only maintains another 
>>set of packet counters, without disrupting its primary job of 
>>packet forwarding.
>>
>>-- Rich
>This sounds like a relatively slow process - i.e. over a few packets 
>the host tell anyone who wishes to listen that it is seeing 
>congestion on a flow. That sounds like it could be addressed by 
>having the host send an OAM packet from time to time over the path 
>rather than including the information in every packet.
>
>Stewart

An OAM based solution would be in scope as a solution to the ConEx 
problem statement. However, we would need someone to write up a 
protocol spec in detail, including inter-domain, then prove it is 
resistant to cheating, etc etc. If this happens (unlikely) the w-g 
can choose between candidate solutions.

Anyway, granular isn't necessarily bad. For instance, operators 
generally use data volume on slow timescales, but a volume counter 
still has to accumulate packet by packet. Congestion-volume is no 
different - except you just count the volume of packets that are 
congestion marked.

We should be open to any solution, whether granular or coarse, as 
long as it solves the problem ConEx aims to address: that network 
operators currently have no reliable way (fast or slow) to measure 
which users contribute how much to congestion - at least not in cases 
where the congestion is occurring at a different point to where it is 
being measured and controlled - whether the two points are within 
your own network, as in Rich's example, or in different networks.



Bob

PS. sorry for late reply.

PPS. The only feasible OAM-based system I am aware of is Katerina 
Argyraki's (ref  below). I'm sure the IESG would not want this level 
of complexity in the Internet. Also it only solves one side of 
congestion accountability: network to users, whereas re-ECN aims to 
make networks accountable to users *and* users accountable to networks.

Argyraki, K., Maniatis, P., Irzak, O., Ashish, S. & Shenker, S., 
"Loss and Delay Accountability for the Internet," In: Proc. IEEE 
International Conference on Network Protocols IEEE (October 
2007)  URL: http://www-dsg.stanford.edu/papers/astra/astra-hotnets04-paper.pdf



________________________________________________________________
Bob Briscoe,                                BT Innovate & Design