Joining more than one hub, basic question

I'll soon be getting a broadband router for my internet connection,
this will almost inevitably have a four port hub built into it. I
need more than four ports so I'll use my existing four port hub as
well.

Presumably I just connect it as follows:-


To Internet
|
Router/Hub
| | | |
PC PC PC |
|
|
Second Hub
| | | |
PC X Y Z


X, Y, Z are other things like a print server and spare ports.
Presumably the PCs won't know any different from when they were all on
one hub, they will just see all the devices on the same subnet as they
did before.

Another question occurs to me now, what happens with auto switching
10/100Mbs hubs, if (for example) all the PCs have 100Mb/s ports but
the print server (X) is only 10Mb/s? Does any one 10Mb/s device on
the network slow *all* transfers down to 10Mb/s? If not then how does
it work because, as I understand it, all packets are broadcast to
every device? Single packets could be buffered in the hub and sent
out more slowly than they arrive but this would still slow down a long
transfer of data.

--
Chris Green

In article <(E-Mail Removed)>, "(E-Mail Removed)"
(E-Mail Removed) says...
> I'll soon be getting a broadband router for my internet connection,
> this will almost inevitably have a four port hub built into it. I
> need more than four ports so I'll use my existing four port hub as
> well.
>
> Presumably I just connect it as follows:-
>
>
> To Internet
> |
> Router/Hub
> | | | |
> PC PC PC |
> |
> |
> Second Hub
> | | | |
> PC X Y Z
>
You may need a crossover cable to connect the two hubs, but they will
probably have switchable or uplink ports.
>
> X, Y, Z are other things like a print server and spare ports.
> Presumably the PCs won't know any different from when they were all on
> one hub, they will just see all the devices on the same subnet as they
> did before.

Yes.
>
> Another question occurs to me now, what happens with auto switching
> 10/100Mbs hubs, if (for example) all the PCs have 100Mb/s ports but
> the print server (X) is only 10Mb/s? Does any one 10Mb/s device on
> the network slow *all* transfers down to 10Mb/s?

Depends if it has store-and-forward buffering or not.

> If not then how does
> it work because, as I understand it, all packets are broadcast to
> every device?

If it's not a switching hub then that's how it works.

> Single packets could be buffered in the hub and sent
> out more slowly than they arrive but this would still slow down a long
> transfer of data.
>
Obviously a slow device will take longer to handle data than a fast
device.

Rob Morley <(E-Mail Removed)> wrote:
> In article <(E-Mail Removed)>, "(E-Mail Removed)"
> (E-Mail Removed) says...
> > I'll soon be getting a broadband router for my internet connection,
> > this will almost inevitably have a four port hub built into it. I
> > need more than four ports so I'll use my existing four port hub as
> > well.
> >
> > Presumably I just connect it as follows:-
> >
> >
> > To Internet
> > |
> > Router/Hub
> > | | | |
> > PC PC PC |
> > |
> > |
> > Second Hub
> > | | | |
> > PC X Y Z
> >
> You may need a crossover cable to connect the two hubs, but they will
> probably have switchable or uplink ports.

Yes, OK, my second hub has an uplink port.

> >
> > Another question occurs to me now, what happens with auto switching
> > 10/100Mbs hubs, if (for example) all the PCs have 100Mb/s ports but
> > the print server (X) is only 10Mb/s? Does any one 10Mb/s device on
> > the network slow *all* transfers down to 10Mb/s?
>
> Depends if it has store-and-forward buffering or not.
>
> > If not then how does
> > it work because, as I understand it, all packets are broadcast to
> > every device?
>
> If it's not a switching hub then that's how it works.
>
Even if the hub has store-and-forward buffering then surely a long
transfer between two 100Mb/s NICs will be slowed down to 10Mb/s by any
10Mb/s device on the same subnet won't it because all the packets will
have to be transmitted to that device even though it doesn'e need
them. The buffer in the hub/switch will very rapidly fill up long
before a large file has been copied between the computers.

--
Chris Green

<(E-Mail Removed)> wrote in message news:(E-Mail Removed)...
> Rob Morley <(E-Mail Removed)> wrote:
> > In article <(E-Mail Removed)>, "(E-Mail Removed)"
> > (E-Mail Removed) says...
[snip]
> > > Another question occurs to me now, what happens with auto switching
> > > 10/100Mbs hubs, if (for example) all the PCs have 100Mb/s ports but
> > > the print server (X) is only 10Mb/s? Does any one 10Mb/s device on
> > > the network slow *all* transfers down to 10Mb/s?
> >
> > Depends if it has store-and-forward buffering or not.
> >
> > > If not then how does it work because, as I understand it, all packets
> > > are broadcast to every device?
> >
> > If it's not a switching hub then that's how it works.
>
> Even if the hub has store-and-forward buffering then surely a long
> transfer between two 100Mb/s NICs will be slowed down to 10Mb/s by any
> 10Mb/s device on the same subnet won't it because all the packets will
> have to be transmitted to that device even though it doesn'e need
> them. The buffer in the hub/switch will very rapidly fill up long
> before a large file has been copied between the computers.

AIUI, when a mixture of 10M and 100M devices are attached to some 10/100
hubs, they act like a two port switch connected to a 10M hub (with all 10M
devices attached) and a 100M hub (with all 100M devices attached).

Alex

Alex Fraser <(E-Mail Removed)> wrote:
> <(E-Mail Removed)> wrote in message news:(E-Mail Removed)...
> > Rob Morley <(E-Mail Removed)> wrote:
> > > In article <(E-Mail Removed)>, "(E-Mail Removed)"
> > > (E-Mail Removed) says...
> [snip]
> > > > Another question occurs to me now, what happens with auto switching
> > > > 10/100Mbs hubs, if (for example) all the PCs have 100Mb/s ports but
> > > > the print server (X) is only 10Mb/s? Does any one 10Mb/s device on
> > > > the network slow *all* transfers down to 10Mb/s?
> > >
> > > Depends if it has store-and-forward buffering or not.
> > >
> > > > If not then how does it work because, as I understand it, all packets
> > > > are broadcast to every device?
> > >
> > > If it's not a switching hub then that's how it works.
> >
> > Even if the hub has store-and-forward buffering then surely a long
> > transfer between two 100Mb/s NICs will be slowed down to 10Mb/s by any
> > 10Mb/s device on the same subnet won't it because all the packets will
> > have to be transmitted to that device even though it doesn'e need
> > them. The buffer in the hub/switch will very rapidly fill up long
> > before a large file has been copied between the computers.
>
> AIUI, when a mixture of 10M and 100M devices are attached to some 10/100
> hubs, they act like a two port switch connected to a 10M hub (with all 10M
> devices attached) and a 100M hub (with all 100M devices attached).
>
Yes, I suppose real 'hubs' are pretty rare nowadays. It may well be
that my 100Mb/s 'hub' is really a switch, I haven't actually checked
and (outside of this discussion) I've learnt what the difference
between a switch and a hub is now.

--
Chris Green

In article <(E-Mail Removed)>, "(E-Mail Removed)"
(E-Mail Removed) says...
<snip>
> >
> Even if the hub has store-and-forward buffering then surely a long
> transfer between two 100Mb/s NICs will be slowed down to 10Mb/s by any
> 10Mb/s device on the same subnet won't it because all the packets will
> have to be transmitted to that device even though it doesn'e need
> them. The buffer in the hub/switch will very rapidly fill up long
> before a large file has been copied between the computers.
>
Each device will only send a limited amount of data before waiting for
an acknowledgement from the receiving device. If a slow device hasn't
downloaded all of its data from the buffer then the device sending the
data will pause, freeing up the switch for communication between other
devices.

"Rob Morley" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) t...
> In article <(E-Mail Removed)>, "(E-Mail Removed)"
> (E-Mail Removed) says...
> <snip>
> > Even if the hub has store-and-forward buffering then surely a long
> > transfer between two 100Mb/s NICs will be slowed down to 10Mb/s by any
> > 10Mb/s device on the same subnet won't it because all the packets will
> > have to be transmitted to that device even though it doesn'e need
> > them. The buffer in the hub/switch will very rapidly fill up long
> > before a large file has been copied between the computers.
>
> Each device will only send a limited amount of data before waiting for
> an acknowledgement from the receiving device. If a slow device hasn't
> downloaded all of its data from the buffer then the device sending the
> data will pause, freeing up the switch for communication between other
> devices.

You missed the point - the OP is talking about communication between two
100M devices, not a 100M device talking to a 10M device. You can't sustain
100M between two 100M devices if all frames must be broadcast to all 10M
devices. However, there is no problem if you have switched 10M and 100M
segments, because traffic from the 10M/100M devices is stored and forwarded
to the 100M/10M devices only when it needs to be.

Alex

In article <(E-Mail Removed)>, "Alex Fraser" (E-Mail Removed)
says...
> "Rob Morley" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) t...
> > In article <(E-Mail Removed)>, "(E-Mail Removed)"
> > (E-Mail Removed) says...
> > <snip>
> > > Even if the hub has store-and-forward buffering then surely a long
> > > transfer between two 100Mb/s NICs will be slowed down to 10Mb/s by any
> > > 10Mb/s device on the same subnet won't it because all the packets will
> > > have to be transmitted to that device even though it doesn'e need
> > > them. The buffer in the hub/switch will very rapidly fill up long
> > > before a large file has been copied between the computers.
> >
> > Each device will only send a limited amount of data before waiting for
> > an acknowledgement from the receiving device. If a slow device hasn't
> > downloaded all of its data from the buffer then the device sending the
> > data will pause, freeing up the switch for communication between other
> > devices.
>
> You missed the point

I did rather, didn't I :-\

> - the OP is talking about communication between two
> 100M devices, not a 100M device talking to a 10M device. You can't sustain
> 100M between two 100M devices if all frames must be broadcast to all 10M
> devices. However, there is no problem if you have switched 10M and 100M
> segments, because traffic from the 10M/100M devices is stored and forwarded
> to the 100M/10M devices only when it needs to be.
>
I thought we'd already got past the difference between unswitched and
switched hubs, but obviously not.