[e2e] Multiple TCP-friendly Sessions and Cong. Control in user-mode?

[Shivkumar Kalyanaraman]

2 questions:

1. What is the current thinking about instantiating multiple TCP-friendly
flows between the same pair of src-dest IP addresses? Is it
good/bad/friendly-to-TCP ?

The reason I ask is that we have found it to be useful for video
streaming and other such apps (incl large file transfer) -- which can
monitor the RTT/rate/volatility/loss-rate of each TCP-friendly flow and
map traffic on a packet-by-packet basis to different flows. Each flow is
TCP friendly and follows a congestion control scheme like TFRC or binomial
CC (with some end-system randomization extensions we have developed to
counter synchronization over drop-tail queues). Are any commercial video
streaming software opening up multiple TCP sessions?

2. As part of congestion manager or earlier attempts to manage
non-TCP flows, have folks considered the impact of implementing congestion
control schemes at the user-mode (and not kernel mode like TCP). If busy
video servers implement congestion control above RTP, there would be
significant OS process scheduling jitter which would add to the
burstiness. We have observed severe burstiness effects in our experimental
studies even with just about 50 odd threads (especially since we use a
non-real-time OS like Linux).... Looks like another argument to go for the
congestion manager approach.

cheers
-Shiv
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Shivkumar Kalyanaraman
Associate Professor, Dept of ECSE, Rensselaer Polytechnic Institute (RPI)