An Investigation into Transport Protocols and Data Transport ...

5.4. Analysis of AIMD Congestion Control 101
RED is wholly implemented on routers and therefore requires no modification
on TCP hosts. The exception is when RED is used in conjunction with
ECN (see Section 5.3.1) whereby a marked packet will be set to include the
CE-bit rather than be physically dropped by the router in order to mitigate
congestion.
5.4 Analysis of AIMD Congestion Control
For bulk transport of data, the dominant factor in the rate at which data is
transported is the congestion avoidance algorithms of TCP. Unfortunately,
the congestion control mechanisms of TCP constrain the congestion windows
that can be achieved by TCP in realistic environments, and hence the
achievable throughput.
The performance of a very long bulk transfer TCP connection is dependent
on the packet loss rate, bandwidth and round trip time, and of a connection.
These are considered in turn:
Packet Loss Rates Standard TCP implementations can only reach the
large congestion windows necessary to fill a an end-to-end path with a
high bandwidth delay product when there is an exceedingly low packet
loss rate. As standard TCP implementations cannot distinguish between
real network loss (e.g. corruption) and losses due to network
congestion 4 , the underlying physical network has to be able to maintain
very low loss rates in order for TCP not to invoke congestion avoidance
when a packet is lost through corruption rather than congestion.
4 Without network feedback such as ECN which would require deployment throughout
bottleneck routers.