[Ham-Computers] RE: Routers vs. Switches

Tue, 13 Aug 2002 11:33:06 -0700

I'll start with some basic terms and move up...

Hub - A simple "non-intelligent" device used primarily in "star"
configuration networks.  This is where all the devices on the network
connect to.  The ports on a hub are non-selective...all packets entering one
port will be spit out to all the other ports on the hub.  Hubs are typically
a bottleneck in networks; if data is being sent/received on one port, all
other ports are also repeating the data so no one else can transmit.  In
short, everyone "sees" everyone and only one person can "talk" at any one
time.  Think of it as a radio repeater...only one person can transmit at a
time while everyone listens.

Bridge - A simple "intelligent" device that passes network packets (data)
from one physical network segment to another physical segment (such as
connecting two offices together on two different floors); however, both
segments are still on the same logical network.  The difference from a hub?
A bridge is selective in passing packets...it only allows packets to "cross
the bridge" if it needs to.  This reduces the total amount of network
traffic seen on the segments since one device "talking" on one segment won't
prevent another device from "talking" on another segment.  Sorta like a
large conference room divided by a partition.  Two different people can be
speaking at the same time without disturbing the other.  But, you still have
the option of "going to the other side" if you need to.

Switch - An "intelligent" device that replaces a Hub.  The difference is
that a switch keeps a table of what device(s) is connected to what port.
So, packets entering one port are scanned and the switch outputs the packet
on the port the destination device is connected to.  This reduces the
overall network traffic and reduces the amount of "collisions" seen on the
network.  It also increases network throughput since all devices connected
to the switch can send data at the same time and not experience any
collisions - the switch as a memory cache that holds the data until the
appropriate port the destination device is connected to is "open".  The
larger the cache and the faster the switching time, the more expensive the
switch.

Router - An "highly intelligent" device that replaces a Bridge.  The main
difference is a router logically seperates the network segments so each
network can use a different network "number".  Also, routers works with
other routers to get the data packet to it's destination in the shortest
amount of "hops".  It's like a switch, but on a much grander scale; however,
unlike a switch, a router usually has only 2 ports.  Routers reduce network
traffic by segmenting networks and making sure packets get to it's
destination the quickest way possible.  Using the conference room example
again, let's say the room was divided into 4 smaller rooms like this:
1-2-3-4.  If I needed to get a message from room #1 to room #4, I could
either act like a router and have a messenger walk straight from room #1 to
room #4, or, I could act like a bridge and just pass the message to somone
in room #2, he/she will pass to room #3, and it will finally be passed to
room #4.  You can see the efficiency of a router as opposed to a bridge.
However, this comes at a cost - $$$.  Good network routers run in the
thousands while even high-end network bridge programs will fit on a floppy
and run on old PC's with two NIC's.  Yes, there are low cost routers (and
even single disk Linux routers), but let's compare $$$ with equivilent
performance routers/bridges - the router will always be much more $$$.

To get a general idea of the routing, you can do the following in Windows
9x/Me/2K.  Start a command prompt and type "TRACERT www.google.com" (without
the qoutes) and press <enter>.  You'll slowly get a listing of all the
routers your data packets need to go through before reaching www.google.com.
There are thousands of routers on the 'net, so image if we were using
bridges instead of routers.  Remember, bridges don't work with each other,
so it just keeps passing the data to the next nearest bridge it can talk to.
It might take hundreds or thousands of hops if we only had bridges to work
with.  I think you get the general idea.

FYI, the typical network configuration would be:

Network attached devices <--> hub/switch <--> bridge/router <--> some
internetwork link (aka a "backbone") <--> bridge/router <--> hub/switch <-->
Network attached devices.

Note: the "internetwork link" may be a combiniation of additional routers
and physical links.

I've tried to make these definitions as simple as possible.  I can get more
detailed if need be, but I'm definitely not a networking expert!  There are
lots of websites out there that can also fill you in better detail.  Just do
a Google search on "network router hub switch bridge" and I'm sure you'll
get a ton of hits.

73,

  - Aaron Hsu, NN6O (ex-KD6DAE)
    {nn6o}@arrl.net
    {athsu}@unistudios.com
    No-QRO Int'l #1,000,006
    . -..- - .-. .-   ".... . .- ...- -.--"

p.s.  Again, I'm not a networking expert so please excuse any errors that
may have crept in.  Comments and corrections are ALWAYS appreciated!

-----Original Message-----
From: Jonathan D Thawley [mailto:[email protected]]
Sent: Tuesday, August 13, 2002 8:51 AM
To: [email protected]
Subject: [Ham-Computers] Routers vs. Switches

Can someone explain to me what the difference is between a router and a
switch, if any?

Thank-you.

73,
Jonathan

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