On 26 Sep 2006 at 14:32, Greg Purvis wrote:

> I'm not sure I understand enough about the 'switch' you mentioned.
> 
> I use a Netgear router, is that what you mean by a hub?  I think what 
> you're saying is that a switch is something other than a hub (maybe like 
> Laplink, computer-to-computer)?  Or is a switch found in certain types 
> of routers -- or is a switch some type of physical adaptor? 
> 
> I'm probably over-complicating things as usual.  Maybe you're simply 
> advising me that if I'm using a router, I can expect slower transfer 
> speeds between any other, newer, computer and the Ambra with the older 
> and slower ISA card.  (In that event, how might that transfer rate 
> compare to that of data moving to and from a 3.5 floppy drive?)

  Hubs, switches (also sometimes called bridges, although less so any more) 
and routers are three different devices for networking multiple computers.

  An Ethernet hub is a simple "layer 1 (physical)" device; in principle, you 
could build the necessary circuitry out of a few dozen diodes.  It's a box 
with several (usually four or eight) ethernet ports, and any signal that 
arrives at one port goes out the others.  There's nothing resembling 
intelligence in the electronics, so all of the connected devices must be 
talking at the same speed; usually, the hub is labelled for the speed at 
which it operates.
  [All of the connected devices must also be set for "half duplex", meaning 
that each one listens to its own transmissions to detect if a "collision" 
has occurred, such as when two devices try to send at the same time.]

  A switch (or bridge) looks the same as a hub, but it's a "layer 2 
(datalink)" device, a dedicated computer.  When an attached device sends a 
"packet" of data to the switch, it goes into a memory buffer.  The switch 
looks at header information in the packet, from which it learns what machine 
addresses are connected to each port, and so it can determine which port to 
forward the packet out through to reach its destination.  If there is only 
one device on each port, no collisions can occur, and so the links may 
operate in "full duplex", sending one thing while receiving something else.  
And different links can operate at different speeds, with the switch buffers 
serving to convert from one speed to another.

  A router typically has fewer ports than a hub or switch, but brings more 
computing power to bear; it's a "layer 3 (network)" device.  Each port is on 
a different *network* (which may include switches and hubs); when a device 
wants to send a packet to a device on a different network, it actually sends 
it to a router (also called a gateway, as in "default gateway"), which will 
figure out where to send it to reach the destination (often, this just means 
sending it to ITS default gateway).
  The simplest small home routers have two ports, WAN (connects to a line to 
your ISP) and LAN (connects to your local devices).  It has become common to 
see routers with 4 or 8 LAN ports, and often wireless too; what has actually 
happened is that the manufacturer has incorporated a small switch/bridge 
into the box, attache to the LAN side of the router circuitry.

  SO:  If your router has multiple LAN ports, you can pretty much assume 
that it incorporates a bridge and that your various computers will talk 
through it just fine.  If the router only has one LAN port, you will need to 
provide your own switch or hub, and a switch is the superior solution; if 
you already have a hub, it can work but may be more limited than you'd like.

  I'm fairly certain that even 10 Mbps Ethernet is faster than a floppy 
drive, even without counting the time it takes to insert and remove the 
disk.

David Gillett

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