Network Bandwidth - Gigabit Vs. 100M

Hello Everyone,
I have a really strange problem at hand and am hoping to find
someone that could shed some light on it. I run a few lan centers with
approximately 40 PCs in each location. I am not a networking guru and
am hoping to find someone that is.

Problem:
A few month ago, we opened a new location that used Gigabit ethernet
PCs vs. the old 100Mbit PCs. From day one, we started to experience
serious lag on the network of which we assumed was the problem of our
T1 provider. To make a long story short we never resolved it (lots of
finger pointing). The only thing that we figured out was that one PC
can actually max out the entire T1 line and if a second PC came on
line, it did not a share of the line which should be half the
bandwidth. The first PC just continues to max out the line until its
finished!

We just recently upgraded one of our old stores with new PCs. Before
the upgrade, we had over 30 PCs on line at the same time with
absolutely no lag and lots of bandwidth un-used. But just as soon as
the PCs were switched to Gigabit ethernet PCs, the same lag as I
described above showed up. The only difference in the two stores now
is that the new store has gigabit switches and the upgraded store has
100Mbit switches.

Question:
Can anyone figure out what is wrong? The PCs are sent to autosense and
do. The upgraded store PCs do switch down to 100Ms but something
causes just one PC to utilize the entire bandwidth. Essentially
something that used to cause the old PCs to share the line, goes away.
What??? What is different in between 100Mbit and 1Gbit protocal?

It's driving me crazy and my customers out of the store...

(E-Mail Removed) wrote:
> Hello Everyone,
> I have a really strange problem at hand and am hoping to find
> someone that could shed some light on it. I run a few lan centers with
> approximately 40 PCs in each location. I am not a networking guru and
> am hoping to find someone that is.
>
> Problem:
> A few month ago, we opened a new location that used Gigabit ethernet
> PCs vs. the old 100Mbit PCs. From day one, we started to experience
> serious lag on the network of which we assumed was the problem of our
> T1 provider. To make a long story short we never resolved it (lots of
> finger pointing). The only thing that we figured out was that one PC
> can actually max out the entire T1 line and if a second PC came on
> line, it did not a share of the line which should be half the
> bandwidth. The first PC just continues to max out the line until its
> finished!

How are your PCs connected to the T1 line?

>
> We just recently upgraded one of our old stores with new PCs. Before
> the upgrade, we had over 30 PCs on line at the same time with
> absolutely no lag and lots of bandwidth un-used. But just as soon as
> the PCs were switched to Gigabit ethernet PCs, the same lag as I
> described above showed up. The only difference in the two stores now
> is that the new store has gigabit switches and the upgraded store has
> 100Mbit switches.
>
> Question:
> Can anyone figure out what is wrong? The PCs are sent to autosense and
> do. The upgraded store PCs do switch down to 100Ms but something
> causes just one PC to utilize the entire bandwidth. Essentially
> something that used to cause the old PCs to share the line, goes away.
> What??? What is different in between 100Mbit and 1Gbit protocal?

Probably that gigabit ethernet uses all 4 pairs of wires in the cable.

Robert

>
> It's driving me crazy and my customers out of the store...
>

On 26 Apr 2007, in the Usenet newsgroup comp.os.linux.networking, in article
<(E-Mail Removed) .com>,
(E-Mail Removed) wrote:

>A few month ago, we opened a new location that used Gigabit ethernet
>PCs vs. the old 100Mbit PCs. From day one, we started to experience
>serious lag on the network of which we assumed was the problem of our
>T1 provider.

What have you got for a router between your LAN and the "T1" provider,
and how big are the pipes? A "T1" is 1.544 Megabit/Second, and even
the _predecessor_ to Thick Ethernet (10Base5) from the 1970s can fill
a T1 in a heartbeat.

>To make a long story short we never resolved it (lots of finger
>pointing). The only thing that we figured out was that one PC can
>actually max out the entire T1 line and if a second PC came on line,
>it did not a share of the line which should be half the bandwidth. The
>first PC just continues to max out the line until its finished!

TCP Window? Jumbo Frames? The first box is cramming a whole bunch of
data over the local wire, and the router is buffering this. That may
leave no room for the extra packets from the "other" systems unless
the router is doing traffic shaping.

>We just recently upgraded one of our old stores with new PCs. Before
>the upgrade, we had over 30 PCs on line at the same time with
>absolutely no lag and lots of bandwidth un-used. But just as soon as
>the PCs were switched to Gigabit ethernet PCs, the same lag as I
>described above showed up. The only difference in the two stores now
>is that the new store has gigabit switches and the upgraded store has
>100Mbit switches.

And you may have selected the high performance options to allow the
maximum bandwidth on your Gigabit end, while your downstream is still a
soda straw maximum. ifndef Blivit...

>Can anyone figure out what is wrong?

I'd use a packet sniffer, and look specifically at the window sizes. I'm
guessing you'd see one box absolutely stuffing the pipe full, and if you
were able to look at the ACK numbers, you'd see that the limiter is your
upstream. Think what it's like to have ten-twenty boxes talking very
well on 10 Megabit, but that isn't going to help when your connection
to the world is a 56k modem. Now, scale those numbers. 1.544M/56k 27:1
10Base? 27:1 = what?

>It's driving me crazy and my customers out of the store...

If you are trying to demo gigabit speed, do it locally, or pay a bunch
of bux for a wide pipe outside.

Old guy