Throughput comparison of one TCP stream with and without ECN

Throughput comparison of TCP streams with TWO points of congestion, with and without ECN

Goal:
to estimate the gain introduced by ECN, in terms of throughput, with more TCP stream and TWO points of congestion.

Equipment:
- Pool of Linux hosts, v. 2.9.4: ECN and SACK capable
- Pool of Solaris hosts, v. 2.7: NON-ECN and NON-SACK capable
- One IBM workstation, AIX v. 5.1: ECN and SACK capable (Amsterdam)
- chain of intermediate ecn-capable routers (Cisco 7500 and C7200), IOS: 12.1(4)E (experimental version) - in this test first and second router are ecn-capable with the same configuration
Test description:
Topology:
topology consists in a chain of ecn-capable routers connecting a pool of TCP senders (on the left of the chain) and a pool of TCP receivers (on the right), like in this map
Bandwidth bottleneck: 50 Mbps
Parameters
Traffic profile

Summary:

when ECN is enable, the average aggregated throughput is quite higher than without ECN
the performance of TCP stack with SACK and ECN enable are better than performance of TCP stack which is SACK and non-ECN capable. This underlines the real benefit carried by ECN implementation
the results confirm the improvement obtained with two points of congestion on experimental LAN.

Comments:

Observing Table 1 and 2, we can see that the aggregated throughput (30 TCP streams) with ECN has a confidence interval quite greater than one with all non-ECN capable streams.
While observing the contribution of 10 TCP ECN capable streams, we can notice that they significantly increasing the aggregated throughput.

	*Throughput with 30 TCP streams with* ECN ( Mbps )**
	10 ECN and SACK streams	10 non-ECN and non-SACK streams	10 non-ECN and non-SACK streams	Aggregated throughput
mean	15.745	13.746625	13.7452	43.236825
variance	2.627396154	4.424486446	5.304216318	26.81437697
dev standard	1.620924475	2.103446326	2.30308843	5.178260033
median	15.9	13.9	14.15	44.2


confid interv	(15.243 ; 16.247)	(13.095 ; 14.399)	(13.032 ; 14.458)	(41.635 ; 44.839)

Table 1: confidence interval of mean throughput with 30 TCP concurrent streams with ECN and TWO points of congestion

	*Throughput with 30 TCP streams without* ECN ( Mbps )**
	10 non-ECN and SACK streams	10 non-ECN and non-SACK streams	10 non-ECN and non-SACK streams	Aggregated throughput
mean	14.6495	13.238425	14.9618	42.849725
variance	1.937483436	3.862969892	7.652202882	22.9443519
dev standard	1.391935141	1.965443943	2.766261535	4.790026294
median	14.9	13.7835	15.4	44.0715


confid interv	(14.219 ; 15.081)	(12.629 ; 13.847)	(14.105 ; 15.819)	(41.315 ; 44.285)

Table 2: confidence interval of mean throughput with 30 TCP concurrent streams without ECN and TWO points of congestion

Serena Alessandrini and Tiziana Ferrari, August 13 2002