[e2e] Question on TCP throughput and host's access speed

[Jing Shen]

Hi,

thanks for all your help. 

The bottleneck does not locate with access line but a
link between China Telecom and Verio(Japan). To upload
a file of 5MB, it takes 170seconds(average) for ADSL
while  420seconds(average)  for fiber.

Asymetric route  exists between our site and server in
japan.To our measurement there is no packet loss
between ADSL/Fiber and core router of our ISP, while
point to point delay between our computer and ISP's
core router differs a little (<0.2ms, fiber link is
faster).

But, what makes me confused is : if TCP modifies its
sending window according to ACK received,and
bottleneck link would not distinguish between ADSL
subscribers and Fiber  link subscribers, no matter how
asymetric is routing path or how much difference
between access line,  TCP on both end should behave
similar (?). Why there exist so much difference ? 

thanks

Jing Shen

--- Lynne Jolitz <lynne at telemuse.net> µÄÕýÎÄ£º
> Dennis is correct. Here's a little story from a
> manager of international datacenters in Japan and
> the US to illustrate how complicated the issue can
> become:
> 
> "There was a weak laser in an inexpensive optical
> ethernet LAN connection used to convey a WAN from
> one floor of a datacenter in Ariake to the other,
> resulting in a significant increase in bit error
> rate. While the laser was within spec for the
> product, the product was used on a fibre at the edge
> of the distance of the link - but still also within
> spec.
> 
> The simplest thing to do was to replace it with an
> optical ethernet WAN connection more suited to the
> use. Unfortunately, the datacenter insisted that you
> could only use this inadaquate connection to go
> between floors. The rule could not be changed to
> repair this situation. Everyone along the path
> acknowledged the problem, as they all were blamed,
> but still the rule 'could not be changed'.
> 
> This problem impacted Japanese consumers using one
> of the most heavily trafficed Japanese websites at
> the time. The problem persisted for months until we
> were able to consolodate on one floor only." (from
> my book on datacenter management and operations). 
> 
> Regards,
> Lynne.
> 
> > -----Original Message-----
> > From: end2end-interest-bounces at postel.org
> > [mailto:end2end-interest-bounces at postel.org]On
> Behalf Of Dennis Rockwell
> > Sent: Thursday, October 14, 2004 5:54 AM
> > To: Jing Shen
> > Cc: end-to-end list
> > Subject: Re: [e2e] Question on TCP throughput and
> host's access speed
> > 
> > 
> > On 14 Oct, Jing Shen wrote:
> > 
> > > We use two leased line from ISP. One is a 2Mbps
> ADSL
> > > the other is a 100Mbps fiber link. [ ... ]
> > 
> > > packet loss and retransmission happen more
> frequently
> > > when I use Fiber link.
> > 
> > Retransmissions kill TCP throughput rather
> thoroughly,
> > especially in long (high delay) paths.
> > 
> > > Analizing routing path between
> > > our computer and server in jappan, we found
> there is
> > > no difference between ADSL access and Fiber Link
> > > beside the access method.
> > 
> > What you have discovered is that your 2Mbps link
> is not the
> > bottleneck; that lies elsewhere in your network
> path.  The
> > extra bandwidth of the fiber link cannot help this
> > application.
> > 
> > Good luck!
> > 
> > Dennis
> > 
> >  

=====
Jing Shen

Data Communication Center
HangZhou TeleCom 
HangZhou ZJ 310027
P.R.China

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