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#131764 - 03/18/04 08:04 PM WAN's & LAN's
Nick Offline
Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
Can we begin a discussion about these things here? I am not sure where to start. Scott, I was looking at your LAN diagram and I understand the hook up's but I would like to know more about the inner workings of these things. I have networked computers together at home and on job sites, I know how to terminate CAT5 cable but I don't feel I have a grasp on what is really going on. Any Ideas?
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#131765 - 03/29/04 06:14 AM Re: WAN's & LAN's
Scott35 Offline

Broom Pusher and
Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA

Sorry for the latency on this subject also!

A discussion on LAN principles and connections would be great, and very helpful to those browsing for at least some basic information regarding Local Area Networking equipment, cabling and etc.

I'll get the ball rolling!

Refer to Basic LAN Map #1 in the Technical Reference area, for items referred to throughout this message.

For this beginning discussion, I will cover the 10BASE-T protocols and type of Ethernet system - which will open the doors for the rest of the network types - including Tolken Ring and 100BASE-TX.

Per the LAN Layout plan, the network topology is the more commonly used Star topology.
In this case, the network is an Ethernet network - based on the IEEE 802.3 standard - more correctly, the IEEE 802.3i standard which is more commonly known as 10BASE-T (the "T" refers to the use of twisted pair cabling).

What is going on with this network in a basic sense, is there are a bunch of "Listeners and Talkers".
A normal computer (referred to for now on as a Work Station) is both a Listener and a Talker - it can send and receive data.
A Printer on the other hand is normally just a Listener - as it only receives data.
The "Words" spoken on the network is the data.

In order for data to reach its destination correctly, each Listener needs to have a unique "Name". The unique "Name" is the Listener's Address.

So with this basic description in mind, if i wanted to send data from one Workstation to another Workstation, I would send it to that W/S's Address.

Data is transferred from the "Talking" Workstation - the Transmitting or Sending "Location", to the "Listening" Workstation - the Receiving "Location" in the form of BIT streams - or Serial data transmission (like a Serial port does).
The data is sent in a "Packet" which contains the usable data, Address headers and Parity check Bits.

All "Listeners" on the network will see data being sent, but only the one with the correct Address will be receiving the data.

The Cable connections between each device (the CAT-5 UTP cable) is simply a Serial data path. This means there's only two wires used for data transmission in each direction.
Pin #1 = Transmit Data +,
Pin #2 = Transmit Data -,
Pin #3 = Receive Data +,
Pin #6 = Receive Data -.
(pins 4, 5, 7 and 8 are unused for 10BASE-T)

The problem with this method (I have only covered an extremely brief description of the Ethernet workings) is there's nothing stopping all Talkers to send out data at the same time - while another Workstation is sending data on the Serial COM Line.
When this happens, the "Packets" collide, and the data is lost - requiring it to be resent.
This is known as "Data Collision, and really sucks when it happens on your network!

Methods and Protocols have been implemented to reduce the problems of Data Collisions - which I will describe in the next discussion message.

So to recap things on this basic intro, each piece of equipment on the network listens for a message to be sent to it. The message is the data to be transmitted.

Data can be anything which is wanted to be placed at a new location, or to perform some specific task - such as printing.

Workstations (computers) can both Listen and Talk, whereas devices like Printers only Listen. The reason for this is because Workstations and Servers normally "Share" Data with other Workstations / Servers, so they need to listen and talk.
Devices like Printers just print out hard copies, so they only need to listen for a message addressed to them.

By Addressing the data, it gets sent to the correct location instead of going to all locations (or no locations).

The Data information being sent to another location is compiled into a Packet, which includes the destination address, the sender's address, parity check bits, and the actual data.

Each Packet is sent on the network cabling in Serial format.
Serial format is a single line of data, which flows in a "Bit Stream" from sender to receiver. The data flows like a Train - more like many Trains of similar size, all running the same direction on the same track, but separated by an equal space behind and in front of another Train.

For the 10BASE-T network, the data flows at a maximum speed of 10 Mega Bits per second, meaning that if you were to stand above the COMBUS (Com Lines) and were able to see the data pass by - and it was continuous, you would count 10,000,000 Bits passing one point in one second.
This is only a theoretical speed, so don't expect to see that volume of data passing through like this!

A "Bit" (short for "BINARY DIGIT") is a value of either "1" (Hi / Yes), or "0" (Low / No).
A "Nibble" (half a Byte) is 4 Bits, a "Byte" is 8 Bits.
There's more complex data - such as a "Word" which is 16 Bits, and "Double Word" which is 32 Bits.

A few examples of values for a Nibble:
Nibbles have a maximum value of 16 (0-15).

The Number "1" would be:

The Number "2" would be:

The Number "4" would be:

And the Number "8" would be:

See how this works? This is "Boolean Algebra". It works by placing the "1" into a value position. In the case of the Nibble (and the first half of the Byte), the value positions from Left to Right are:
"8" - "4" - "2" - "1"

To make the number "1", the very first Bit becomes "Hi" - or becomes a "1" Bit.
To make the number "2", the "1" Bit gets bumped to the next position, and the "1" position becomes "0"
For the number "4", bump the "1" Bit to the 3rd position, and place a "0" Bit on the "2" position.
For the number "8", the "1" Bit goes to the last position, and a "0" is placed at the "4" position.

To make the number "3", the Bits would be:
This has a value of "1" and a value of "2" being added together - resulting in the number "3"

To make the number "10" the Bits would be:
Here we have the number "8" and the number "2" being added together - resulting in the number "10".

Bytes have a maximum value of 256 (0-255), and use 8 Bits to compile these values.

Words have a maximum value of 65,536 (0-65535), and use 16 Bits to compile these values.

Double Words have a maximum value of 4,294,967,296 (0-4294967295), and use 32 Bits to compile these values.

To deal with the extremely large values of Words and Double Words (along with 64 and 128 Bit info), Decimal numbers are used in conjunction with Hexadecimal numbers.
Hexadecimal values contain numbers 0-9 and letters A-F to derrive some astonishingly high values!

Will end here, and compile the next discussion message off-line, then post later.
Let me know what you think and if you have any suggestions.

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#131766 - 03/30/04 06:54 PM Re: WAN's & LAN's
Nick Offline
Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
Thanks Scott! That is a great start. Please keep this going as time permits.
#131767 - 03/31/04 08:34 AM Re: WAN's & LAN's
Mean Gene Offline
Registered: 10/20/03
Posts: 137
Loc: Ohio, USA
Just wait untill he gets in protocols, such as NetBEUI and TCP/IP. Then, you better have your seatbelt on!!
#131768 - 03/31/04 04:02 PM Re: WAN's & LAN's
Nick Offline
Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
Thats exactly the kind of stuff I'm after! Bring it on
#131769 - 04/18/04 05:09 PM Re: WAN's & LAN's
Scott35 Offline

Broom Pusher and
Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Hello everyone,

Now that the recent Family situations are completed, I can take some time and compile the 2nd part of this discussion.

Looks like the general consensus is leaning towards Protocols, so I'll cover the 7 layers of the OSI, and a few other things.

Many of these items may require drawings, so if needed I'll add a few simple ones. Might embed drawings or link to them.

Will only be able to cover things in brief - as they are extremely complex in nature! As always, I suggest finding a few good books on the subject(s), which will "fill in the gaps".

Per commonly known Protocols, I will cover the ones typical to Ethernet and what's known for Internet stuff - like NetBEUI, IPX/SPX, TCP/IP, etc.

Will get to work on this ASAP!

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#131770 - 05/08/04 09:14 PM Re: WAN's & LAN's
JOAN Offline
Registered: 11/13/01
Posts: 10
Loc: Jersey City, New Jersey
Scott, your explanations are great. When are you writing your "LAN for Dummies"?
#131771 - 09/18/04 12:25 PM Re: WAN's & LAN's
jooles Offline
Registered: 09/18/04
Posts: 98
Loc: brussels, belgium
On the whole this is a good explaination but I don't agree with this statement:

>> Workstations (computers) can both Listen and Talk, whereas devices like Printers only Listen.

Indeed printers do both Tx and Rx (transmit and receive), rather than only receiving. The reason they need to transmit is to relay back to the workstation that submitted the job status information (e.g. the number of pages completed in the print job, out-of-paper conditions, low ink/toner warnings, paper misfeeding errors, paper stock available for different paper sizes, and so on). Modern printers in particular offer a very wide set of features such as duplexing, different paper source selection, and so on, all of which are remotely controllable via the network, and this requires a two-way dialog with the controlling workstation.


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