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Old 12-21-2007, 08:18 AM
Brad R Brad R is offline
Linux Member
Join Date: Apr 2007
Location: Ontario
Posts: 607
Arrow TCP/IP tweaks

xplornetsuck sent me some info last week about tweaking TCP/IP settings for better satellite performance. Actually, I haven't been able to find much regarding Xplornet tweaks, and I haven't had success tweaking my own settings, so this is really not ready to be put into a FAQ. I'm just opening this up for discussion.

First, here's the link xplornetsuck sent me, a tool to tweak TCP/IP settings on Windows PCs:

Surfing around a bit I found this tool to report your TCP/IP settings:
The problems are, (a) if you have a home router it won't report the correct numbers, and (b) even if you bypass the router it doesn't report the correct numbers. Their FAQ says:

There are still some routers and cable/dsl modems in use that modify the maximum packet size (MTU) regardless of Registry settings. If the Analyzer reports a smaller MTU and you're behind a router, you might want to try updating its firmware, or looking through its management interface for an MTU value.
Which makes me think that the Xplornet modem (basically a modified cable modem) is changing the MTU and RWIN values.

Here's the report I'm seeing from the analyzer:
? SpeedGuide.net TCP Analyzer Results ?
Tested on: 12.21.2007 07:24
IP address: 208.114.xxx.xxx

TCP options string: 020405a80101040203030001
MSS: 1448
MTU: 1488
TCP Window: 32768 (NOT multiple of MSS)
RWIN Scaling: 0
Unscaled RWIN : 32768
Reccomended RWINs: 63712, 127424, 254848, 509696
BDP limit (200ms): 1311kbps (164KBytes/s)
BDP limit (500ms): 524kbps (66KBytes/s)
MTU Discovery: ON
TTL: 239
Timestamps: OFF
IP ToS: 00000000 (0)
However, my PC is set to MTU=1500 and RWIN=131071.

RWIN is important because it affects download speed, especially on satellite systems. Basically, RWIN must be at least as large as your bandwidth * latency (ping time). See this FAQ. But I gather that most operating systems now adjust RWIN automatically, so it's not something you need to tweak. (Maybe on Win 9x boxes...I don't know.) If you can get your full plan download speed at 2 a.m., then you can assume your RWIN is big enough to support that data rate. (Not a perfect test, because ping times are smaller in the quiet hours.)

More info as I find it...
4G Fixed Wireless Formerly Echostar 17 "Jupiter"; Rogers Rocket Hub; Everus 3.5 GHz Wireless; Telesat Kazam plan; HughesNet Ku.
A computer without Windows is like a chocolate cake without mustard. http://www.goodbyemicrosoft.net
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