Date: Wed, 25 Apr 2001 05:40:42 -0400 From: "Mark" <offworld@richnet.net> To: "Brooks Davis" <brooks@one-eyed-alien.net> Cc: "'freebsd-small@freebsd.org'" <freebsd-small@FreeBSD.ORG> Subject: Re: Is BSD capable?? Message-ID: <006f01c0cd6b$ceba8960$6b95efd1@quick> References: <002001c0cc6d$be9aee20$8995efd1@quick> <01042421341401.14955@offworld1.net> <20010424145138.B30762@Odin.AC.HMC.Edu> <01042503542301.15147@offworld1.net> <20010424210332.A30795@Odin.AC.HMC.Edu>
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I would say that the system is far from being oversubscribed. I would call
it the "hidden node" problem. These are not smart radios, more like bridges.
The upload problem is not a big one and all users are happy as of now. I am
just looking forward to the time when I get the system loaded down.
Regardless to how the units are performing, dumping the half duplex units
onto a full duplex backbone can only be of benefit. If I could do this with
a BSD router and equipment on hand, life would be good and I would be doing
something that most are not. I need to get my routers replaced with the BSD
boxes soon any way. I am using the cable / DSL routers now out at the remote
sites and in all candor, they suck!! Very limited in features. They work and
are not crashing but place to many limits on the system and they appear to
be adding some unnecessary latency into the system.
On Wed, Apr 25, 2001 at 03:50:33AM -0400, Mark wrote:
> What I have here is a network set up something like the following
(simplified
> the best I can). Here at the NOC I have a half duplex Access Point (AP1).
> This is linked to Remote Site 1 (RS1). Connected to RS1 are 2 more Access
> Points (AP2, AP3). All are half duplex. End users connect to AP2 and AP3.
What
> happens is, that when a user connects to say AP2 and starts a download,
and a
> user connected to AP3 attempts to send an MP3 to his bud up in Spider
Breath
> MO., AP2 and AP3 both attempt to access the gateway, RS1, in two separate
> directions at the same time into a half duplex back haul link.
>
> In practice, one or the other suffers, and when you have 3 doing a
download
> and one fighting upstream, guess which one loses. That is because there is
> no control between AP2 and AP3. Neither one knows what the other is doing.
> Being able to install a full duplex link in the backbone would give me a
> big boost in overall network performance. Trouble is that a full duplex
> link is thou$and$ of dollars more than 2 half duplex links. If this can
> be done, great, If not, I start saving my pennies.
Ok, so if I understand correctly, you have an oversubscribed half duplex
link that gets pounded by collisions when in heavy (bi-directional) use.
If that's the case, you might try cranking the rts threshold way down
on both ends of the link (that's the -r option to {wi,an}control).
This introduces a bit more latency by forcing both ends to ask nicely
before they send anything, but if most of you're traffic is big it could
be a hugh win. Enabling it on my access point raised ping latench from
1.9ms to 2.1ms, enabling it on my Cisco 340 card turned off the pipe so it
appears there's some work to be done in that driver. ;-) If that works,
then you could use the money you would have spent building a full-duplex
link to double your link speed. ;-)
-- Brooks
--
Any statement of the form "X is the one, true Y" is FALSE.
PGP fingerprint 655D 519C 26A7 82E7 2529 9BF0 5D8E 8BE9 F238 1AD4
----- Original Message -----
From: Brooks Davis <brooks@one-eyed-alien.net>
To: Mark <mark@offworld1.net>
Cc: <freebsd-small@FreeBSD.ORG>
Sent: Wednesday, April 25, 2001 12:03 AM
Subject: Re: Is BSD capable??
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