Re: [tcmtf] BoF feedback: Application-limited TCP

["Jose Saldana" <[e-mail]>]

This is something I tried to explain during the BOF, but perhaps I wasn't
able to set it clear: when we are talking about multiplexing TCP flows, we
are not thinking about normal TCP flows, but about very specific ones, in
which the information is generated during the TCP session itself.

These three papers [1], [2], [3] are about this question: A TCP-based online
game generates TCP packets as the player generates new commands. The PUSH
bit of the TCP header is set to 1 in order to make the TCP stack send it as
soon as possible, and ACKs are piggybacked onto the packets from the server
and vice versa.

But there are some TCP features that do not work properly for these flows,
since they are thought for "network-limited" TCP flows, whereas these games
generate "application-limited" TCP flows (as Mirko explained in the online
games tutorial on Thursday morning):

- Some TCP mechanisms directly deteriorate the experience of the players
(delayed ACK, Nagle algorithm)

- Some other TCP mechanisms do not work efficiently for MMORPGs (cwnd
reduced due to the application having nothing to send)

So which would be the effect of an additional multiplexing delay on a bunch
of "application-limited" TCP flows? I am currently doing NS2 simulations for
a paper I am preparing for IEEE CCNC 2014. I have some preliminary results I
will share here, just if they can shed some light to this (interesting)
debate. I am summarizing them in another e-mail.

Best regards,

Jose


[1]	C-C. Wu K-T. Chen, C-M. Chen, P. Huang, and C-L. Lei, "On the
Challenge and Design of Transport Protocols for MMORPGs," Multimedia Tools
and Applications (special issue on Massively Multiuser Online Gaming Systems
and Applications), Vol. 45, No. 1, pp. 7-32, 2009.
[2]	C. Griwodz and P. Halvorsen. "The fun of using TCP for an MMORPG,"
Proceedings of international workshop on Network and operating systems
support for digital audio and video (NOSSDAV '06). ACM, New York, NY, USA,
2006.
[3]	K-T. Chen, C-Y. Huang, P. Huang and C-L. Lei, "An Empirical
Evaluation of TCP Performance in Online Games", Proceedings of  the 2006 ACM
SIGCHI international conference on Advances in computer entertainment
technology ACE 06, Hollywood, California, USA, 2006.