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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