Chapter 3

Hardware Introduction and LAN Media

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Chapter 3 talks about the different types of LAN media that you can use to create a network.  There are three basic types of media.  Copper, Fiber and Wireless.  Each of these types of media have there own characteristics, and limits.  We'll discuss media selection criteria, as well as media errors.

Media, Connectors, Jacks, Etc... (Conducted Media)

Phone Cable - This is a flat (non-twisted) four wire cable.

Category V Cable - Twisted cable with four pair, Unshielded Twisted Pair (UTP).  This one is plenum.

Category V Cable - This one is Shielded Twisted Pair (STP)

Category VI - Twisted cable with four pair, Notice the plastic divider to keep the four pair separate.

Category VII Cable - Flat cable with four twisted pair.

RJ-11 - Used for phone cable RJ = Registered Jack

RJ-45 - Used for CAT III, IV, V and VI cable

RJ-45 - With a molded boot and CAT V cable

RJ-45 - Without a molded boot. (notice the color pattern - EIA/TIA 568b)

Fiber - The top is an SC Type end; the lower is ST type end.

RG-58 (Coaxial Cable) - With BNC (Bayonet Neill-Concelman) connector, T and terminator.

Keystone Jack - Notice this is color coded for the EIA/TIA 568b pattern

EIA/TIA 568a and 568b Patterns

Cable 1, 2, 3, & 6 Send and Receive Data

Wireless Media (Non Conductive Media)

  • Broadcast Radio - This type of connection is used in cell phones, pagers, and low orbit non geosynchronous satellites.  Transmission speeds are usually low on this type of connection, usually 19,200 bps or slower.

  • Microwave Radio - With speeds of 10 Mbps or higher Microwave is a good solution for people that need to go a long distance.  This connection is insecure and can easily be interrupted by weather and other radio signals.

  • Spread Spectrum Radio - This is a slower connection (2 Mbps) over a shorter distance (1000ft)  This will either transmit at multiple frequencies at once (direct sequencing) or continuously change (frequency hopping)  A lot of cordless phones use this type of connection.  This is the most secure.

  • Infrared Transmission - Most remote controls use this type of connection.  This connection requires line of site and is slow (10 Mbps or lower).  Most laptops have an infrared port and newer operating systems support transferring files or printing via IR.

  • IEEE 802.11 Wireless Standard - This has become mainstream over the past few years as a solution for home networks.  802.11b will allow you to transmit up to 11 Mbps and operates at 2.4Ghz, 802.11g also transmits at 2.4Ghz with speeds up to 54Mbps.  802.11a transmits at 5-6Ghz with speed up to 54 Mbps.  At this point the 802.11x standards are not very secure.  The first mainstream device that helped make the 802.11b standard popular was the Airport from Apple.

  • Bluetooth - This is a relatively new standard.  This will allow for the creation of PAN (Personal Area Networks) Bluetooth operates at 2.4Ghz and has a distance limitation of about 30ft.

My House

Below are pictures taken of my home network.  This network is a small one and should be easy to understand.  We will be following a CAT V cable from a PC to the switch and all the steps in between.

We start at the computer.  The Category V cable is circled.

The cable then goes to the wall jack.  The wall jack's cable runs to the basement.

All the cables run through the basement and end up at the patch panel.

The patch panel has cable coming from all over the house going into the top.  Then out of the bottom comes the cables to the switch.

Close up of wall mount patch panel.  Note the color patterns, even though they are not in the 568b order this is a 568b patch panel. The wires are rearranged to make it easy to punch down.

Here you can see the cables go from the wall mount patch panel to the switch (bottom box).  The switch connects to the router (top box) and the router plugs into the cable modem. (box to the left.)

The switch connects all the PC's in the house together.  The switch connects to the router which connects to the cable modem.

A close up of the switch.  The lights tell you information about the client hooked to it, I.e. speed, transmission mode. etc...

Here we can see the cable plugs the cable modem into the router and the router into the switch.  The third cable goes to another switch.

This is the upstairs switches that has the server plugged into as well as the WAP (Wireless Access Point) 802.11b

Also connected to the upstairs switch is the Jet Direct box witch turns my printer into a network printer.

Here is a map of the whole network so you can see how everything is connected.  This diagram omits keystone jacks and patch panels.

Corporate Network

Below is a group of pictures from a large network that uses fiber.  The pictures show two separate ways to convert copper to fiber.  Click on the picture to see the full image.

We start with the back of a rack mount patch panel.  Remember all the computers in the surrounding area are coming to the patch panel(s)

 Here is the front of the patch panel (bottom).  The ports on the patch panel plug into the hub.  Each hub is plugged into the switch (top).  The switch converts to fiber and sends the signal to the center closet.

The fiber comes out of the switch and plugs into this wall mount fiber patch panel.  The fiber then runs to the center closet.

Here we see where the fiber comes too in the center closet.  This is a rack mount fiber patch panel.

The fiber goes to the fiber transceiver (both orange [fiber] and yellow [cat V] cable is plugged into this)  The Cat V then plugs in to the switch.  This is how each location talks to each other.  (Note: Below is a hub and patch panel that is where the local computers plug into.)

Here is a diagram that shows the path from a client to the server in this network

Media Selection Criteria

  • Cost - You'll want to choose a media that is within your budget.  But don't forget to think about the cost of expanding later if needed.  Will it be more economical to provide a faster network now instead of possibly replacing parts later?
  • Speed - You'll want to make sure you have a medium that will provide a good response time for your users.  In Chapter 2 we talked about characteristics of a LAN.  One of the characteristics was transparent use.  If you have a low response time you will have transparent use for the users.
  • Expandability - Will you be able to add onto this network?  Some networks have a limit, for example an ARCNET LAN has a limit of 255 nodes. 
  • Error Rates - Some media types are more prone to errors at higher speeds.
  • Security - If high security is a must you will probably not use a wireless media.  Copper is easy to tap into without disrupting the service.  Fiber might be the medium you choose.
  • Distance - All media has length limitations.  Most can be over come with repeaters.
  • Environment - Will you be running near any devices that give off a high amount of electromagnetic interference?  If so you may have to choose STP or fiber.
  • Application - Some devices that you want to deploy might require a certain media type.

Error Sources

  • White Noise - or Thermal Noise, is directly related to heat.  As the temperature of the medium increases so does the amount of White Noise.  On a phone system this will sound like static.  This usually effects wireless mediums.
  • Impulse Noise - This is a spike in the service, usually caused by lightening, or jarring a connection.  This can also be caused by machines with electric motor continuously powering up and down near the medium.
  • Crosstalk - This is caused when two cables are next to each other and the signal from one bleeds over to the other.
  • Echo - Usually seen in Coaxial cable without a terminator.  It is the reflection of the signal.
  • Attenuation - The weakening of the signal due to distance or other characteristics of the medium.  A repeater will usually fix this problem.

Error Detection

  • Parity Checks - Vertical Redundancy Check (VRC) The data is sent in a series of 1's and 0's.  With a VRC a bit will be added to the end of a block of bits that tells the computer weather their is an odd or even number of 1's in that block.  If there is an even number a 1 is added as the parity bit.  If there is an odd number, a 0 is added as the parity bit.  This way if a bit is changed the computer knows the data is corrupt and asks for the data to be sent again.
  • Longitudinal Redundancy Check (LRC)- The VRC will fail of a 0 turns to a 1 and a 1 turns to a 0.  Because of the the LRC was created to do another level of checking.  If you have a group of bit blocks like in the VRC stacked on top of each other the LRC will count all the 1's first bits of the bit blocks and follow the same rules as the VRC to create a Block Check Character (BCC)

Below is an example of VRC and LRC



  • Cyclic Redundancy Check (CRC) - A CRC is generated for a block of data.  The receiving end computes the CRC for the data received and compares it to the CRC sent.  If they are different the packet is rejected and retransmitted.  They way the CRC is generated is beyond the scope of this course.

  • Sequence Checks - Sequence Checks are primarily the task of the transport layer in the OSI model.  If a file is broken down into five packets each packet would be labeled as 1/5, 2/5, 3/5, 4/5, and 5/5.  If a packet is missed the receiving computers asks to have it retransmitted.

  • Error-Correction Codes - Redundant information is sent with the data so if some of the data is corrupt the data may be able to be recovered without requesting a resend.

Error Correction

  • Message Acknowledgement - If the receiving computer verifies that all data sent to it was correct it will reply with an ACK packet.  This is an acknowledgment packet saying that everything was received ok.  If data is lost during transmission and the receiver knows it it will send a NAK packet.  This is a negative acknowledgement telling the sender to retransmit the message.
  • Retry Limit - If the receiving computer keeps on receiving errors in the packets with will time out after a predetermined number of NAK's  This will prevent an infinite loop on the network caused by errors.

This is a photo that was sent to me by a friend of mine.  This shows a fiber switch (bottom) with 5 copper switches (stacked on top) plugged into fiber switch.  The copper switches have fiber transceivers built into them that allow the copper switches to connect to the fiber switch.  Each of these switches will go out into remote wiring closets.  This is a good photo that you can use as a model for your final project.  It illustrates how all the computers will be physically connected to each other.

More Information


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