Sharing a switch port

Sharing a switch port
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Subject Author Date
Sharing a switch port J 08-30-2008
Posted by J on August 30, 2008, 3:17 pm
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we have 20 new PCs being setup in a conference room. We have only 5
jacks in the room wired to our ethernet switch in the wiring closet.
The powers that be want to just buy a 24 port switch, plug the new PCs
into the switch and use 1 port on the switch connected to 1 of the
existing jack that goes back to the switch in the wiring closet. The
switch in the wiring closet is connected to a router to the internet
and internet browsing is going to be a big use here. My concern is
that performance will suffer due to all 20 PCs going through 1 port.
Shouldn't we at least buy five 4 port switchs and make use of all 5
jacks in the conference room.

Or, connect a wireless router to 1 of the jacks and put wireless NICs
in the PCs (Vista Home Basic o/s). Does that buy us anything?
Thanks for any advice and please let me know if the scenario needs
clarification.
TIA

Posted by Albert Manfredi on August 30, 2008, 4:26 pm
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> we have 20 new PCs being setup in a conference room. =A0We have only 5
> jacks in the room wired to our ethernet switch in the wiring closet.
> The powers that be want to just buy a 24 port switch, plug the new PCs
> into the switch and use 1 port on the switch connected to 1 of the
> existing jack that goes back to the switch in the wiring closet. =A0The
> switch in the wiring closet is connected to a router to the internet
> and internet browsing is going to be a big use here. =A0My concern is
> that performance will suffer due to all 20 PCs going through 1 port.
> Shouldn't we at least buy five 4 port switchs and make use of all 5
> jacks in the conference room.

If those 5 jacks in the conference room all wind up going to the same
IP router anyway, and if traffic between the PCs in the conference
room is negligible compared with traffic from those PCs going through
one router to the Internet, then I don't think you'll see that much
difference. The bottleneck will most likely be the single router. I am
assuming here that the router is connected internally via 100 Mb/s
Ethernet, as are all the PCs to the switch.

> Or, connect a wireless router to 1 of the jacks and put wireless NICs
> in the PCs (Vista Home Basic o/s). =A0Does that buy us anything?
> Thanks for any advice and please let me know if the scenario needs
> clarification.
> TIA

Going this route will give you less performance than what you
described before, because the actual throughput of the wireless will
be less than the 100 Mb/s I am assuming for your wired network.
However, it is certainly a good way to go, IMO. If your wireless LAN
is 802.11g, you should get about 25-26 Mb/s of actual throughput,
shared by all the PCs in the conference room.

Bert

Posted by jpd on August 30, 2008, 5:58 pm
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> we have 20 new PCs being setup in a conference room. We have only 5
> jacks in the room wired to our ethernet switch in the wiring closet.
> The powers that be want to just buy a 24 port switch, plug the new PCs
> into the switch and use 1 port on the switch connected to 1 of the
> existing jack that goes back to the switch in the wiring closet. The
> switch in the wiring closet is connected to a router to the internet
> and internet browsing is going to be a big use here. My concern is
> that performance will suffer due to all 20 PCs going through 1 port.

What is the bandwidth of your uplink (router<->internet)?

If it's less than the bandwidth to a single pc, then there's no issue.

Also, making sure that the switch<->router link is faster than the
individual pc<->switch links (eg. 1Gbit vs. 100Mbit) would take care of
most issues, but that only makes sense if the uplink is faster than a
single individual pc<->switch link.


> Shouldn't we at least buy five 4 port switchs and make use of all 5
> jacks in the conference room.

Not necessairily. If the five most active pcs happen to be on one switch
that still doesn't help you much. And (again) if your uplink isn't fast
enough the entire point is moot.

Also, one managed switch is easier to deal with than five. Unmanaged...
the small cheap 5-port stuff can be quite annoying. With five switches
you have a five times higher probability one will fail, but only one
fifth of the network will be affected. Pick your priorities.


> Or, connect a wireless router to 1 of the jacks and put wireless NICs
> in the PCs (Vista Home Basic o/s). Does that buy us anything?

As pointed out, due to a variety of issues wireless is likely to be
(much) slower than wired, so if speed is a concern it'd be pretty low on
my list of things to look at. It certainly does have uses, but for your
stated goal it's unlikely to gain you much.


You should describe the speeds of the various links in more detail. Your
uplink speed relative to the rest of the network is the key here.


--
j p d (at) d s b (dot) t u d e l f t (dot) n l .
This message was originally posted on Usenet in plain text.
Any other representation, additions, or changes do not have my
consent and may be a violation of international copyright law.

Posted by J on August 30, 2008, 10:02 pm
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> Begin =A0<8efd7320-3104-4565-afaa-e95f641e5...@w1g2000prk.googlegroups.co=
m>
>
ote:
> > we have 20 new PCs being setup in a conference room. =A0We have only 5
> > jacks in the room wired to our ethernet switch in the wiring closet.
> > The powers that be want to just buy a 24 port switch, plug the new PCs
> > into the switch and use 1 port on the switch connected to 1 of the
> > existing jack that goes back to the switch in the wiring closet. =A0The
> > switch in the wiring closet is connected to a router to the internet
> > and internet browsing is going to be a big use here. =A0My concern is
> > that performance will suffer due to all 20 PCs going through 1 port.
>
> What is the bandwidth of your uplink (router<->internet)?
>
> If it's less than the bandwidth to a single pc, then there's no issue.
>
> Also, making sure that the switch<->router link is faster than the
> individual pc<->switch links (eg. 1Gbit vs. 100Mbit) would take care of
> most issues, but that only makes sense if the uplink is faster than a
> single individual pc<->switch link.
>
> > Shouldn't we at least buy five 4 port switchs and make use of all 5
> > jacks in the conference room.
>
> Not necessairily. If the five most active pcs happen to be on one switch
> that still doesn't help you much. And (again) if your uplink isn't fast
> enough the entire point is moot.
>
> Also, one managed switch is easier to deal with than five. Unmanaged...
> the small cheap 5-port stuff can be quite annoying. With five switches
> you have a five times higher probability one will fail, but only one
> fifth of the network will be affected. Pick your priorities.
>
> > Or, connect a wireless router to 1 of the jacks and put wireless NICs
> > in the PCs (Vista Home Basic o/s). =A0Does that buy us anything?
>
> As pointed out, due to a variety of issues wireless is likely to be
> (much) slower than wired, so if speed is a concern it'd be pretty low on
> my list of things to look at. It certainly does have uses, but for your
> stated goal it's unlikely to gain you much.
>
> You should describe the speeds of the various links in more detail. Your
> uplink speed relative to the rest of the network is the key here.
>
> --
> =A0 j p d (at) d s b (dot) t u d e l f t (dot) n l .
> =A0 This message was originally posted on Usenet in plain text.
> =A0 Any other representation, additions, or changes do not have my
> =A0 consent and may be a violation of international copyright law.

Thanks for the posts.
All PCs are connecting at 100mpbs;
The uplink from switch to router is 100mpbs.
We have a fractional T1 at 768kbps.

"but that only makes sense if the uplink is faster than a
single individual pc<->switch link."
Can you explain this in more detail (to a novice). Each PC connects
to the switch at 100MBPS.
Thanks!

Posted by jpd on August 31, 2008, 2:24 am
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> Thanks for the posts.
> All PCs are connecting at 100mpbs;
> The uplink from switch to router is 100mpbs.
> We have a fractional T1 at 768kbps.
>
> "but that only makes sense if the uplink is faster than a
> single individual pc<->switch link."

You *should've* trimmed the rest of the post instead of quoting all the
material then quoting some of it again. Please see RFC1855 (google for it).
There are also specific netiquette guidelines for google posters, though
those are generally summarized as ``find yourself a real news server''.


> Can you explain this in more detail (to a novice). Each PC connects
> to the switch at 100MBPS.

Well, your question relates that you are concerned that the connection
between switch and router is the same speed as the links between each pc;
meaning that in the worst case, when all 20 pcs are trying to use their
link at full speed, they will be able to use at most 100Mbps/20=5Mbps.


pc -\
pc -- [switch] -- [router] -- { internet }
pc -/


So, you have pcs connected to a switch at 100Mbps, one switch connected
to a router at 100Mbps, and one router to the rest of the internet, at
768kbps. One can observe that when the primary use is internet use[1],
the most important connection is the router <-> internet one, and also
that 100Mbps / 20pcs is much larger than 768kbps / 20 pcs.

What I implied above was that the router <-> internet connection was
likely to be much slower than 100Mbps anyway (that turns out to be true)
so that upgrading your internet connection would be required before
worrying about the switch <-> router connection starts making sense.


[1] Presumably meaning ``world wide web browsing'', -- the WWW is not the
same as the internet, but built on top of the internet. WWW-browsing
tends to spurts of traffic whenever someone clicks on something, making
contention unlikely unless people start to download large blobs of data.

--
j p d (at) d s b (dot) t u d e l f t (dot) n l .
This message was originally posted on Usenet in plain text.
Any other representation, additions, or changes do not have my
consent and may be a violation of international copyright law.

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