Re: why upload with adsl is faster than 100M ethernet ?

[Jay Hennigan <jay () west net>]

On Fri, 15 Oct 2004, Joe Shen wrote:

> Hi,
>
> the network path is:
>
>
>          |-(ADSL)--------\
> customer/                 --Edge_router---...---Japan
> Server
>         \-(100Methernet)-/
>
>
> So, from edge_router to Japan server the path is
> identical.
>
> Yes. But, for ftp  TCP control real end-to-end
> transmission speed.
>
> I attached a monitor computer to our core router along
> the path between customer's site and server.
> Monitoring computer ping customer's site by targeting
> both ends of ADSL line and ethernet line. The
> measuring is scheduled 20packet per 20seconds, we also
> ping each hop address along the path to server. The
> result shows there is no packet loss along from
> monitoring computer to customer site, but packet loss
> increase at a special hop along the path to server in
> japan.
>
> So, we think the bottleneck is not inside our network.
> And, TCP connection between customer's computer and
> its server should be affacted by same bottleneck. So,
> the uploading speed should be similar (?), but it
> shows so much difference!

I can think of three possible things:

1. MTU over the ethernet and ADSL lines is different and there is
   fragmentation occuring when the ethernet link is used.  Look at
   packet sizes with your sniffer and/or try sweeping a range of
   ping sizes.

2. Somewhere in the path there are parallel load-balanced paths with
   variable delay resulting in packets arriving out-of-order more
   frequently when sent over the ethernet link, due to the packets
   arriving more frequently in bursts when originating from the faster
   link.  Do you have a group of load-sharing per-packet links in
   your core over which the traffic flows?  Could also be beyond your
   control.  Ethereal at the receiving end might show this.

3. As was previously suggested, aggresive rate-limiting or policing
   happening along the long-haul.

--
Jay Hennigan - CCIE #7880 - Network Administration - jay () west net
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