[plug] OT: 10/100 hubs

[Brian Tombleson]

I'll have a crack at this one for you, Russell.  Someone feel free to
correct me if I'm wrong :)

Hubs come in 3 main flavours.
1. You can get your basic 10Base-T hub doing 10 Mb/s.
2. You can get your basic 100Base-T hub doing 100Mb/s
  - This won't talk to anything doing 10Mb.
3. You can get 10/100 Hubs that will run at 100Mb/s if everything attached
runs at 100Mb/s and then drop to 10Mb/s if any one device talks at this
speed.

If you want 'Auto-sensing' on seperate ports, you will probably need to get
a 'switch' or 'managed huib'... or one of several other terms that are
floating around for them.

Hub operation:
  Get data on one port -> re-broadcast data on all ports.

Switch operation:
  Get data on one port, check the destination hardware address, look in
cache to see if we know where it is.  Do we know where it is?
    - Yes : deliver it to that port only
    - No : broadcast it (and remember/work out where that address is).

Obviously switches are much beter.  But in a hub, if you have two devices
talking at 100Mb but another device on the network only talking 10Mb, even
just the two fast devices talking to each other means that there is a
back-log of data needing to be kept for the slower port(s) .. This is why it
is only operating at 100Mb when everything is 100Mb.

A switch, on the other hand, can talk independantly to each device and so
can talk at the slowest speed required for only the devices talking.

HTH.
Brian.

----- Original Message -----
From: "Russell Steicke" <r.steicke at bom.gov.au>
To: "Perth Linux Users Group" <plug at plug.linux.org.au>
Sent: Tuesday, April 10, 2001 3:36 PM
Subject: [plug] OT: 10/100 hubs


> While thinking about buying hardware for a home network, the following
> question came up: Do all 10/100 hubs do speed translation between a
> device on one port at 10 Mbit and a device on another port at 100 Mbit,
> or do some of them only handle all 10 Mbit devices or all 100 Mbit
> devices? Is this sort of translation a standard feature of 10/100 hubs,
> or something one needs to look for?
>
> Thanks,
> Russell Steicke