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From: Jose Luis Domingo Lopez <lartc@24x7linux.com>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] general shaping rules
Date: Sat, 15 Oct 2005 19:17:50 +0000	[thread overview]
Message-ID: <20051015191749.GA23409@localhost> (raw)
In-Reply-To: <43514A80.6050109@inway.cz>


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On Saturday, 15 October 2005, at 20:29:20 +0200,
Jorge Sanchez wrote:

> Any router performing a shaping function should be the bottleneck on the 
> link, and should be shaping slightly below the maximum available link 
> bandwidth. This prevents queues from forming in other routers, affording 
> maximum control of packet latency/deferral to the shaping device.
> 
In the Internet, traffic flows through a number of router between source
and destination, routers you can not control. In the router closest to
your network (if using ADSL, the local telephone witching central with
DSLAM adapters) sometimes the ISP or telco applies buffering to each
subscriber. That is, to get tranfer rates up it is very easy to allocate
and indeterminate (but usually large) buffer for incoming traffic.

This way, when you download at full speed you get, well, full speed, but
the telco is getting more data at a rate greater than you can, so it
buffers traffic in excess. So, if the sending box somewhat slows down
(network congestion), your telco still has data to send and keep your line
100% full. So statistics show you get a fantastic service bandwitdh wise,
but not so good with respect to latency.

The only way to prevent those buffer to even start filling is shaping
traffic to/from your network some Kbps bellow your nominal maximun
transfer rate. You have to "be" the bottelneck to be able to control
bandwidth allocation and keep latency to a minumun.

Hope I made an understandable explanation. Greetings,

-- 
Jose Luis Domingo Lopez
Linux Registered User #189436     Debian Linux Sid (Linux 2.6.14-rc3-git7)


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      reply	other threads:[~2005-10-15 19:17 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-10-15 18:29 [LARTC] general shaping rules Jorge Sanchez
2005-10-15 19:17 ` Jose Luis Domingo Lopez [this message]

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