Re: [tcpm] On the deployment of Explicit Rate Notification protocols
Dino LOPEZ <dino.lopez <at> unice.fr>
2011-10-10 07:54:35 GMT
Thank you for your comments and questions. I hope this email will
clarify the points where, we believe, IP-ERN can provide important benefits.
One of the objectives of the IP-ERN architecture is to improve the
performance of TCP by trying to use router-assisted protocols (more
precisely, by mean of Explicit Rate Notification protocols).
As reported in some papers (e.g. in , just to give an example), using
such ERN protocols, it's possible to compute a cwnd which will allow to
grab all the available bandwidth, remains stable at that point and avoid
congestion. Hence, if we grab all the bottleneck capacity, avoid losses
(we consider losses due to congestion), and therefore, retransmission
and cwnd reductions, we improve the performance of TCP without being
more aggressive. For instance, in links with high propagation delay
(e.g. satellite links) the FastRet/FastRec mechanism of TCP has a strong
impact on the performance of TCP. Getting the rigth cwnd value to fully
use the available bandwidth and avoid FastRet/FastRec would be just great.
It seems like is very difficult to agree about a level of aggressiveness
which can be considered safe for Internet, so IP-ERN does not advise the
use of any high speed TCP version, does not make TCP more aggressive.
IP-ERN only makes mandatory to implement one E2E congestion control
protocol. The choice of the E2E CC is taken by the user or the
programmer (like in a Window Vista OS the user can enable CTCP if he
wants, one can use IP-ERN with CTCP or CUBIC).
Another good reason of allowing the deployment of ERN protocols is the
convergence of flows (e.g. 1 CUBIC and 1 CTCP flows could never