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Acknowledgment Timing tests (ACK Timing or Sensitivity Range)

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JCLW

Member
Joined
Apr 1, 2002
So I find myself in a rental house for eight months, and can't really pull cable from the office (DSL modem) to my media computer/file server in the family room.

Modem (and router) is a Sagemcom f@st 2864 bought from my ISP (Teksavvy/Bell) and comes with basically no documentation or spec sheet.

Not wanting a little USB wifi thingy, I started looking for a dedicated client bridge (which are apparently widely known as media bridges now) for the media computer/file server but they all seem to be in the ~$60 price range.

DLink DIR-615 routers (DD-WRT compatible) are on sale for $18, so I figure for that price you can't go wrong for a name brand N-300 router.

Get it home, flash DD-WRT, set it up as a client bridge. DIR-615 shows link speed in the 117~130 mbps range - I figure the Sagemcom f@st 2864 modem/router is just N-150 (later proven wrong).

Start copying some holiday pictures onto the file server - s l o w . . . I'm writing at 3~5 MB/s which is not much faster then my laptop with a 54g connection.

I then try playing with some DD-WRT settings, particularly the ACK timing.

Results (as reported by the client bridge DIR-615):

TX Rate (mpbs) - RX Rate (mbps) - Signal Quality

Sagemcom <- DIR-615 (ACK=2000): 130 - 117 - 42%
Sagemcom <- DIR-615 (ACK=1000): 240 - 162 - 45%
Sagemcom <- DIR-615 (ACK=100): 300 - 216 - 43%
Sagemcom <- DIR-615 (ACK=20): 300 - 243 - 43%

Big improvement. From about 9.5 MB/s read 5.5 MB/s write to 11.5 MB/s read 8.5 MB/s write.

There is no way to change the ACK timing in the Sagemcom.

But the Sagemcom kept dropping the wireless link every ~12hrs (regardless of the ACK setting), and would require a reboot before the link could be re-established so I ran out and picked up another DIR-615 to use as the main router (switched the Sagemcom into bridge mode so it just acts as the modem).

Results (as reported by the original client bridge DIR-615):

TX Rate (mpbs) - RX Rate (mbps) - Signal Quality

DIR-615 (ACK=2000) <- DIR-615 (ACK=20): 270 - 243 - 42%
DIR-615 (ACK=1000) <- DIR-615 (ACK=20): 270 - 270 - 44%
DIR-615 (ACK=100) <- DIR-615 (ACK=20): 300 - 270 - 47%
DIR-615 (ACK=20) <- DIR-615 (ACK=20): 300 - 300 - 49%

With ACK timing on both set to 20m the link is very stable at 300 mbps, and throughput is consistent at ~11.5 MB/s read and write.

Note that a setting of 20m the wifi signal gives a very limited range (20m = ~60ft), so going this low is probably not for everyone, but it works well for me (phones/tablets still connect and work well anywhere in the house - maybe I'll try some longer distance speed tests as well another day).

So if your wifi speeds are not what you think they should be try playing with the ACK timing.
 

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