[AccessD] OT: Hubs attached to Routers

John

I only have a minimal amount of technical experiences with hubs, switches
and routers, but the following is true:

On a router (and a switch), the bandwidth is processed in a parallel manner
... i.e., for a 100 mbps unit, each port operates at 100 mbps. On a hub, the
bandwidth is shared ... i.e., for a 100 mbps unit, the maximum total for all
active ports is 100 mbps; port 1 may be at 32, port 3 may be at 16, etc ...
but the sum will not exceed the hub's capability. Also, a hub is limited by
the LOWEST attached connection. If you have an 8-port hub, and 7 of those
are to 100 mbps NIC's and the 8th is to a 10 mbps NIC, the entire hub will
operate at the maximum sum of 10 mbps. I personally might argue against that
last statement, but it is what I was told by the *experts* (ex = has been,
spurt = drip under pressure). While the hub may not be actually 'reduced' to
the lowest speed, there is DEFINITELY a major drop in throughput when a
10-card is attached.

And yes, they use MAC addresses for identification and IP addresses for
unique connectivity.

Regards,

Bob Gajewski

-----Original Message-----
From: accessd-admin at databaseadvisors.com
[mailto:accessd-admin at databaseadvisors.com]On Behalf Of John W. Colby
Sent: Friday, February 07, 2003 17:54
To: AccessD
Subject: [AccessD] OT: Hubs attached to Routers


My understanding of things network is minimal although I do understand
Electronics.  However...

My understanding of a Router is that it is a cross point switch matrix.  It
literally connects one input to one output.  Thus traffic between two jacks
is not imposing on any other jacks (physical connectors), i.e. port 1 can
talk with port 2 (or any other port) at 100 mbps, at the same instant in
time that port 3 is talking to port 4 at 100 mbps.  There is no traffic
collisions since there is no connection between the circuits supporting the
two conversations.  IOW any port can hold a private conversation with any
other port.  Since this is the case, any remaining port can hold another
separate conversation with any remaining port.  Etc. Etc. until all ports
are busy.  It appears then that a 4 port router can create two separate
private conversations, an 8 port router can create 4 separate circuits etc.

How it does this I never understood, but that was the way it was explained
to me.

A Hub on the other hand simply connects all of the ports together all of the
time.  Therefore while Port 1 is talking to Port 2, no other ports can talk
without traffic collisions.

Before I go on, I need to ask if this is truly the case?

I would also appreciate a simple explanation of how the router knows that
data coming in on port 1 is "going to" the machine on port X.  I have to
assume that (using TCP/IP) each machine has a 192.168.x.x address (or
something similar) and that address is part of the packet.  The router knows
which machine is associated with each of those addresses, and therefore
simply closes a switch to "route" the packet to the right place?

Next, what happens when I connect a hub to port 1 (for example)?

My understanding is that all machines on the hub can only talk to one
machine at a time, but that if you take that into account, any machine on
the hub could still talk to port 2, while port 3 was talking to port 4.

My question really is, am I slowing down the network for ALL other devices
on the router?  My understanding is no.  However all machines on the HUB
share a connection to the router.  Kind of like a party line (in telephone
terminology).  The hub is a party line, the router is a private line?



John W. Colby
Colby Consulting
www.ColbyConsulting.com


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