A New Internet-Draft is available from the on-line Internet-Drafts directories.
Title : Analysis of SPDY and TCP Initcwnd
Author(s) : Greg White
Dan Rice
Filename : draft-white-httpbis-spdy-analysis-00.txt
Pages : 34
Date : 2012-07-06
Abstract:
Making the Internet faster is the goal of many product and service
companies. Many strategies exist, from data caching to packet
switching, performance improvements in Internet browser clients and
server software, without forgetting the transport network scaling
from the fiber core to the access edges.
This report investigates two proposed protocol enhancements aimed at
making the web browsing user experience better by optimizing the
transport of web objects and thereby reducing the page load time.
The two enhancements are SPDY, a replacement of the HyperText
Transfer Protocol (HTTP) requiring client and server changes, and a
TCP tune-up, an increase in the TCP initial congestion window
accomplished by a setting change on the web servers. Both show
promise, but there are some caveats, particularly with SPDY. SPDY is
a candidate for standardization as HTTP/2.0.
In addition to a discussion of the two enhancements, this report
provides the results of laboratory testing on SPDY version 2 and the
proposed increase in the TCP initial congestion window in a variety
of simulated conditions, comparing the page load time when using the
proposed enhancement to the page load time for the default case of
HTTPS and current initial congestion window settings.
The proposed enhancements generate mixed results: web page load times
were reduced in some scenarios but increased significantly in others.
The performance improvement (or degradation) varied depending on the
number of servers, configuration of the initial TCP congestion
window, and especially any network packet loss. The following
results were obtained across all scenarios comparing SPDY and
congestion window enhancements to standard HTTPS.
o Average reduction in page load time was 29%
o Best improvement was over 78% reduction in page load time
o Worst cases showed a negative impact, resulting in a 3.3x increase
in page load time
These results lead us to the following conclusions:
o The SPDY protocol is currently a moving target, and thus it would
be challenging to realize a return on investment for general-
purpose usage in web servers.
o Protocol improvements, standardization in the IETF and wider
adoption by the client/server software may warrant a second look
at SPDY.
o Some applications in controlled environments may gain by
leveraging SPDY. SPDY might be a valuable tool where the a single
entity provides the servers, the client software, and the web
content.
o If SPDY were adopted very widely it may have some secondary
benefits for network operators through improved infrastructure
scalability due to a significant reduction in concurrent TCP
sessions, as well as a reduction in Packets Per Second.
o The proposed increase in the TCP initial congestion window is
straightforward, requires no client modifications, and on its own
provides consistent (albeit modest) performance gains.
This report is available in a somewhat more detailed form in
[SPDY-ANALYSIS].
The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-white-httpbis-spdy-analysis
There's also a htmlized version available at:
http://tools.ietf.org/html/draft-white-httpbis-spdy-analysis-00
Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/
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