gigabit switches in a mixed Gigabit - Fast-Ethernet LAN

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milleron

I just had a gigabit network switch die, and I've been researching the
inexpensive units meant for unmanaged home LANs. It turns out that some
of the brand-name units like Netgear models do NOT provide gigabit
networking in a mixed environment -- i.e., if just one device connected
to the switch is 10 or 100 Mbs only, then the switch runs ALL of its
connections at that slower rate, even if the other computers have
gigabit NICs. (This probably explains the disappointing results I
experienced after connecting my Buffalo Gigabit LinkStation (NAS) to the
computers on my LAN via two inexpensive Netgear gigabit switches.)

I'm having a problem identifying WHICH replacement to buy because the
manufacturers do not specify whether their products actually do provide
gigabit switching in mixed environments.

I'm hoping to spend less than $70 for such a product, and I want one
that doesn't require configuration. Does anyone have experience with a
switch like that in a mixed environment -- some computers with gigabit
NICs and some with only older 100Mbs NICs?

Ron
 
Hi
I assume that you are aware that Giga us Not Really functional Giga.
I.e on peer-to-peer network with client OS you get some where between
25-35MB/sec. transfer (The word Giga implies 125MB/sec. transfer).
If all the computer on the Giga switch are Giga capable it would yield good
transfer so use out your old 1100 NICs on the Router or an other old switch
and plug all the Giga Computers to the Giga switch.
Jack (MVP-Networking).
 
Jack said:
Hi
I assume that you are aware that Giga us Not Really functional Giga.
I.e on peer-to-peer network with client OS you get some where between
25-35MB/sec. transfer (The word Giga implies 125MB/sec. transfer).
If all the computer on the Giga switch are Giga capable it would yield
good transfer so use out your old 1100 NICs on the Router or an other
old switch and plug all the Giga Computers to the Giga switch.
Jack (MVP-Networking).
Click to expand...

Yes, the rate-limiting factor with large file transfers will be the read
and write speeds of the respective HDs, whereas the rate-limiting factor
with Fast Ethernet is actually the Ethernet connection. Is that
correct? However, I've never gotten anywhere near 25 MB/sec using
base-level Netgear gigabit switches. It takes about 16 minutes to move
a 4.38 GB file, and that's no more than 4.6 MB/sec, terribly
disappointing for a "gigabit" network. I thought there was something
wrong with the cabling (5e, about three years old), but after reading
users' experiences posted on retailer Web sites, I now believe that
these switches probably identified gigabit NICs properly and then
proceeded to transmit files at 100Mbs speeds because there were 100Mbs
Ethernet devices connected to both of the switches involved.

Ron
 
I just had a gigabit network switch die, and I've been researching
the inexpensive units meant for unmanaged home LANs. It turns out
that some of the brand-name units like Netgear models do NOT
provide gigabit networking in a mixed environment -- i.e., if
just one device connected to the switch is 10 or 100 Mbs only,
then the switch runs ALL of its connections at that slower rate,
even if the other computers have gigabit NICs. (This probably
explains the disappointing results I experienced after connecting
my Buffalo Gigabit LinkStation (NAS) to the computers on my LAN
via two inexpensive Netgear gigabit switches.)

I'm having a problem identifying WHICH replacement to buy because
the manufacturers do not specify whether their products actually
do provide gigabit switching in mixed environments.

I'm hoping to spend less than $70 for such a product, and I want
one that doesn't require configuration. Does anyone have
experience with a switch like that in a mixed environment -- some
computers with gigabit NICs and some with only older 100Mbs NICs?

Ron
Click to expand...

Are you referring to the "Head-of-Line Blocking" phenomena?
<http://en.wikipedia.org/wiki/Head-of-line_blocking>
While the above article addresses contention issue, the same phenomena
occurs when a high-speed port communicates to a low-speed port.

Some manufacturers specify head-of-line blocking prevention. For
example the Linksys EG008W ($80). (NB: I have no personal experience
with this product.)

<http://www.linksys.com/servlet/Sate...nksys/Common/VisitorWrapper&lid=8881522279B10>

HTH,
John
 
John said:
Are you referring to the "Head-of-Line Blocking" phenomena?
<http://en.wikipedia.org/wiki/Head-of-line_blocking>
While the above article addresses contention issue, the same phenomena
occurs when a high-speed port communicates to a low-speed port.

Some manufacturers specify head-of-line blocking prevention. For
example the Linksys EG008W ($80). (NB: I have no personal experience
with this product.)

<http://www.linksys.com/servlet/Sate...nksys/Common/VisitorWrapper&lid=8881522279B10>

HTH,
John
Click to expand...

Thanks! That's a very cogent reply, because I was unfamiliar with the
concept. I don't think that's my problem, though, because the Wikipedia
article states that HOL blocking limits throughput to about 60%. In my
current situation, I have computers with gigabit NICs connected through
a gigabit switch that is wired to another gigabit switch in another
room. That second switch is connected to a Buffalo Gigabit LinkStation
NAS device. With Cat 5e cabling and jacks, I should be able to achieve
transfer speeds of at LEAST 25 megabytes per second between the computer
and the NAS, but the fastest I've ever been able to get is about 4.5
megabytes/second. That's MUCH slower than the read/write speeds of the
HDs and much slower than 60% of the nominal throughput of a Gigabit
network. My best guess now is that the "gigabit" switches (Netgear
home-use models), while indicating gigabit connections (as does Windows
XP and the NAS), are actually transferring data at only Fast Ethernet
speeds because there are 100-Mbs devices (a print server and a router)
attached to the switches.

Is that a reasonable guess?

Ron
 
Thanks! That's a very cogent reply, because I was unfamiliar with
the concept. I don't think that's my problem, though, because the
Wikipedia article states that HOL blocking limits throughput to
about 60%. In my current situation, I have computers with gigabit
NICs connected through a gigabit switch that is wired to another
gigabit switch in another room. That second switch is connected
to a Buffalo Gigabit LinkStation NAS device. With Cat 5e cabling
and jacks, I should be able to achieve transfer speeds of at LEAST
25 megabytes per second between the computer and the NAS, but the
fastest I've ever been able to get is about 4.5 megabytes/second.
That's MUCH slower than the read/write speeds of the HDs and much
slower than 60% of the nominal throughput of a Gigabit network.
My best guess now is that the "gigabit" switches (Netgear home-use
models), while indicating gigabit connections (as does Windows XP
and the NAS), are actually transferring data at only Fast Ethernet
speeds because there are 100-Mbs devices (a print server and a
router) attached to the switches.

Is that a reasonable guess?
Click to expand...

First, the 60% quoted in the wikipedia article is assuming the
effects of HOL blocking due only to collisions and not to speed
differentials. Switches should not slow all traffic down simply
because slower speed devices are attached. In your situation,
consider where there is a device on the first switch trying to send
traffic to the [slow] router on the second switch at the same time a
device on the first switch is trying to transfer data to the fast NAS
device on the second switch. Both streams of data have to pass
through the common port (wire) between the two switches. When
packets arrive at the FIFO at the input to the second switch from the
first switch, the fast traffic gets "stuck" behind the packets going
to the slow router and won't be delivered until the packet in front
of it is delivered [at the slow speed] to the slow router. The
effect is that the Gigabit traffic is slowed to near 100-Base-T
rates.

It's like having a slow dump truck ahead of you on the single-lane
offramp of a super freeway -- but it shouldn't be a problem if you
don't need to take that offramp.

I can't say for sure that this is your problem but if you were
looking to purchase a new switch, Head-of-Line block prevention is a
feature that might be desirable to look for (all else being the
same).

HTH,
John
 
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