
            !@#$%^&*!@#$%^&*!@#$%^&*!@#$%^&*!@#$%^&*!@#$%^&*!@#$%^
            @                                                    &
            #   General Information on LANs (Topologies, Etc.)   *
            $                                                    !
            %           An Official THUG Production.             @
            ^   Written by Laughing Gas For Solsbury Hill BBS.   #
            &                                                    $
            * (Please keep the name THUGLAN2.TXT where possible) %
            !@#$%^&*!@#$%^&*!@#$%^&*!@#$%^&*!@#$%^&*!@#$%^&*!@#$%^

                            Released: 7-31-91

:: Foreward ::

Well, in the previous file on LANs, I said that the next one (*this one*) would
have a complete list of all the programs availible a Novell LAN system, and
description of each.  Well, that was at the end of the school year, and I
didn't have access to a Novell LAN over the summer.  However, I do have a
LANtastic lan set up here at home..  So I'll probably release a file on that
soon..  However, since I've been doing work with this LAN, and research and so
on, I started to write a file about topologies, etc, and since someone else
mention it on a local BBS, I figured I'd release this file, which is basically
an introductory guide to topologies and network access methods.  This file is
basically released to the computer underground, however, it might be found more
interesting by a LAN manager than a hacker.  It doesn't really have anything on
breaking in, or security.  Oh well.  Here it is.  Oh, by the way, when school
starts up in about a month, I'll get back to the Novell information.

The basic subjects of this file (as mentioned above) are:

LAN Topologies
Network Access Methods
General Wiring Information

(I threw in the wiring information, because it doesn't really have anything to
do with hacking, and neither does the rest of the file.. and it might be
interesting to anyone interested in the rest of the file..)

:: LAN Topologies ::

What is a topology?  It's the way a LAN is set up, _physically_.

Before we get into the different types, you have to know a couple of vocabulary
terms here.

Workstation - A Workstation is a single computer on the LAN, which uses the
LAN's server's resources.

Server - A Server is a computer on the LAN which allows it's resources (disk
drives, printers, modems, etc) to be accessed by a workstation.  There are a
couple of basic types of servers:

        Network Server:  This is a computer usually with a large hard drive,
                         which acts as the main "HUB" of the network, and all
                         of the workstations have access to it.  The majority
                         of shared files are on this machine, and the majority
                         of resources are attached to this machine.

        Print Server:  This is a machine attached to one or more printers with
                       the job of handling all print spooling requests.
                       (Although the print queues can often be controlled by a
                        superuser from another machine)

        Communications Server: This is the machine or machines with the modem
                               or modems in it, and is responsible for handling
                               all of the outside communication.

        File Server: This is just a machine with a hard drive dedicated to the
                     network.

Non-dedicated Server: This is a server that is also a workstation.  (Ie, you
can sit down at the server and log into the network..)

Dedicated Server: This is a server which is dedicated to the network.  (You can
log in FROM it)

Node - A Node is ANY computer, OR device on the LAN.  Any workstation, or
server is a node, as well as any printer, modem, etc.

Well, thats about it for terms to know.

There are three basic LAN topologies.  BUS, RING and STAR.

* BUS 

If a LAN is set up with a BUS topology, there is one long cable, the ends of
which are NOT connected to ANYTHING.  Each Node is connected directly to
this cable.

(Check out this lame ascii diagram..)


                Node 1 ---         Node 3 ---
                          |                  |
        *-----------------------------------------------------------*
                                |                   |
                                 --- Node 2          --- Node 4

Get the idea?

A bus topology is a reliable method of setting up a network.  If a node on
the network goes down, all the other nodes can still communicate.

* RING

A ring topology is just what it sounds like, the nodes are connected in a
circular or ring fashion.  Node 1 connected to Node 2 connected to Node 3
connected to node 1 again.

Lame diagram:

          .-- Node 2 --.
         /              \
     Node 1            Node 3
         \              /
          `-- Node 4 --'

Got it?

A ring topology is not usually a good idea.  If one node goes down, other nodes
may not be able to communication with nodes that are connected through the down
node.  In the case above, it's fairly simple, but for arguments sake, if node 1
went down, node 2 could communicate with node 3, and node 3 could communicate
with nodes 2 and 4, and node 4 could communicate with node 3, but node 2 and 4
could not communicate... Well, technically they could, but in a larger network,
two or more nodes could go down, one on either side of a node, blocking it from
the other nodes, or if the system was designed to find the shortest path, it
might find that one of the nodes in that direction was down.  Unless it was
designed to find alternate routes, it might be stuck.

* STAR

In a star topology there is a main network server, and each node is wired
directly to the server.

Something like this:

                        Node 1
                          |
                          |
             Node 4  -- Server -- Node 2
                          |
                          |
                        Node 3

A star topology is better than a ring topology, but not as good as a bus
topology.  In a star topology, any one of the nodes could go down, and the rest
of the lan would still be able to function, but if the server goes down, NONE
of the rest of the lan would function.


:: Network Access Methods ::

There are two major network access methods that I know of, however I suspect
there are more that I don't know about.  (hey, I never said I knew everything.)

First of all, what is a network access method?  It's the method used to send
data around the network.  Network Access Methods are meant to keep data from
colliding with other data.

The two major types I know of are Token Ring Passing, and Contention.

* TOKEN RING PASSING

Token Ring Passing is used primarily with (you guessed it..) Token Ring
Networks.  Token Ring Networks are usually set up with a ring topology,
although I would assume that token ring passing could occur not matter what
your topology.

When token ring passing is in use, an electronic signal, called a token signal
is continously sent around the network.  When a node wants to send a packet of
data, it must attach it to this token.  The data then rides the token around
the network until it gets to the node it was intended for.

* CONTENTION

Contention is used most often with CSMA/CD (Carrier Sensing Multiple Access
with Collision Detection) set ups.   I like to call it the "waiting" method.
Basically, a node sends a packet of data out, if another packet of data is at
the same point, whichever one got there first keeps going, the other one
bounces back to the node it originated from, waits for a second (well, not
literally, but just for the tinyest microsecond) then bounces back to see if
the way is clear.



:: General Wiring Information ::

There are three main types of wiring for LANs.  Twisted Pair, Coaxial Cable,
and Fiber Optic wiring.

Twisted Pair wiring consists of two insulated copper wires twisted around
each other.  It's basically just phone wire.  This is a common easy way to set
up a LAN, also very inexpensive (just buy phone wire..)  However, it is the
least efficent method, and can't handle the load or speed that other types of
wire can handle.

Coaxial Wiring or Fiber Optik lines are better, they can hold a larger capacity
of data, and transmit much faster with no errors.  However, these types of wire
are much more expensive, and often need to be wired into the walls, or floor,
and that makes them even MORE expensive.

There is one other way of setting up a LAN, which is what I've done here at
home... That's using serial or parralell ports, or even modems, to connect the
computers.  In my case, it's not much of a LAN, an IBM XT w/ 40 megs and an IBM
386SX w/ 80 megs hooked together through the serial ports with a null modem.  A
serial/parralell/modem connection is going to be MUCH MUCH MUCH slower than a
direct connection.  Not only is the data transfered slower, but when you use
other types of cable, the cable has to connect through a NIC, or Network
Interface card.  Not only does the NIC connect the wires together, but it also
has the extra power to allow your computer to access the network with no slow
downs.  Of course, this method is much cheaper.. $5 or less for a null modem
cable, and the price of the LAN software (LANtastic is the only one I know of
that works with serial/parralell/modem connections, with it's E-Z-LAN software,
which is what I use..), although that only applies if you pay for the software.

:: Conclusion ::

Oh well, not a very underground file... Feel free to distribute it to whomever
you like.. although I'd apprieciate it if you left it entirely intact, or at
least left my name on it.  Feel free to publish this in any electronic or
non-electronic form of publication, just leave it intact.  If you find any
errors or whatever, contact me on my board, Solsbury Hill, in the 301 area
code.

As the warez dudez say, Greetz to ......
        Elk, and Insight.. You're learning fast..
        Phusionman.. Sorry your friend didn't get served at Maggies (snicker)
        Weapons, TRG, Gentry.. Good to see you again (at Maggies)
        Tuc.. where are you?

Laughing Gas, 7-31-91.
