Media Introduction

1 Ethernet Overview
2 Common Network Cabling
3 Physical Network Communication Mediums
3.1 Twisted-Pair Cable
3.2 Unshielded Twisted-Pair Cable
3.3 Shielded Twisted-Pair Cable
3.4 Coaxial Cable
3.5 Fiber Optic
4 Wiring Diagrams and Schematics

Ethernet Overview

Ethernet has been with us since 1980. Early Ethernet was carried over stiff coax and later more malleable thin coax. Coax Ethernet installations require that the cable be snaked past each network device and that the device tap into the cable as it goes past. Although this wiring scheme reflects the way Ethernet uses a shared media to allow network communications, the station to station coax has serious real-world reliability problems. 10BASE-T was introduced in 1990 to address these problems. 10BASE-T uses durable and inexpensive twisted pair cable. Two pairs are required for each station: one pair for incoming traffic and one for outgoing. Home runs from each station to a central concentrator carry data to and from each station. With 10BASE-T, the vulnerable shared media portion of the network is now safely hidden in the closet and is not strewn all across the office. In a 10BASE-T system, a wiring fault typically takes out network service only to a single station.

10BASE-T includes diagnostic indicators that allow wiring faults to be easily identified. Because 10BASE-T offers both reliability and cost advantages over the original coax, most new Ethernet installations are of the twisted pair variety.

The newer Fast Ethernet used by CobraNet is wired just like 10BASE-T except that it has ten times the bandwidth, requires a slightly higher grade cable and has some distance limitations not found in 10BASE-T.

Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media Access Control (MAC)/Data Link Layer, and a common addressing format.

Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. It has been in use from the 1990s to the present, largely replacing competing LAN standards such as token ring, FDDI, and ARCNET. In recent years, Wi-Fi, the wireless LAN standardized by IEEE 802.11, is prevalent in home and small office networks and augmenting Ethernet in larger installations.

Ethernet is used in most, but not all, computer networking situations. It is a standard which defines rules that all computers follow to allow successful and efficient communication.

Common Network Cabling

Cable is a medium which provides physical path for data transmission. Several types exist. Some networks use the same type, other use multiple types. A common early cable was the RS-232 D Serial cable. It transmitted one bit at a time, very slow connection. Parallel cables can talk at one bit per line at a time – an 8 pin cable can have 8 bits at once assuming one bit is one line and software handles all handshaking.


RJ-11 is the terminator typically used on plugin phone cables. This cable type has been used for many years by TELCOs all over the world – six pin cable schmatics to follow at a later date.

RJ-45 connectors now terminate most common cables used for hub based or star style TCP/IP networks. RJ-45 terminated cable ends are shown to right. Schematics to follow at a later date. Now that we understand what cables are used the next step is to learn signal processing.

Early TCP/IP networks functioned with looped coax cables or very thick D connector style cables running from one computer to the next rather than via centralized star style hub components.

Physical Network Communication Mediums

Twisted-Pair Cable

Twisted-pair cabling is a copper wire that comes in two forms, shielded and unshielded. It is the most common form of wiring used in a network. It uses 8 wires twisted into pairs to cancel the effect of crosstalk (Noise from the adjacent wires). It is a relatively inexpensive form of LAN cabling. It can accommodate different topologies, but is mostly implemented in a star topology.

Unshielded Twisted-Pair Cable

UTP relies on the cancellation effect of twisting the wires to reduce Electromagnetic Interference (EMI). It is required to have a certain amount of twists per meter and it is connected using a Registered Jack 45 Connecter (RJ-45). UTP can run for 100 meters before the signal needs to be refreshed. UTP has advantages that make it ideal in some networks.

  • Easy to Install
  • Small, it does not take up much space in wiring ducts.
  • Cheapest type of cable.

UTP has 6 Categories.

  • Category 1:
    • Only reliable for transmitting telephone communications, not regular data transmissions.
  • Category 2:
    • Previously used in token rings. Speeds only up to 4kbit
  • Category 3:
    • Works in 10BASE-T networks.. Transfer rate of 10mbit
  • Category 4:
    • Used on 16mbit token ring networks.
  • Category 5:
    • Transfer rate of 100mbit. Unreliable for 1000BASE-T networks.
  • Category 5e:
    • Transfer rate of 1000mbit. Used in Gigabit Ethernet networks.
  • Category 6:
    • Same as Cat 5e but made to a higher standard

Shielded Twisted-Pair Cable

Shielded Twisted-Pair Cable uses twisted pairs along with a metallic foil shielding to reduce the crosstalk and EMI. It is usually connected using an STP connecter but can also be connected with an RJ-45. Although it reduces the interference better than UTP, STP has many drawbacks that keep it from having a mainstream use.

  • More Expensive
  • Must be grounded at both ends
  • Harder to install

Because of these drawbacks it is rarely implemented in Ethernet networks. It is more common in Europe.

Coaxial Cable

Coaxial Cable uses a copper wire for the conductor, on top of this is insulation for the wire. The third layer consists of a metallic foil or woven copper braid as a shielding, followed by a rubber jacket on the top. It is often referred to as Thicknet or Thinnet, depending on the specification. Coaxial cable was found in early Ethernet networks (~1980).


  • It costs less to buy than Fiber Optic
  • It has speeds of 10mb/s to 100mb/s.
  • It costs more to install Coaxial cable.

Fiber Optic

Installation of fiber optic cabling is not the rocket science it once was. Great strides have been made in the durability cost and ease of termination of this media. Fiber optic cable offers two main advantages over twisted pair cable. First, data may be carried much further over fiber. Second, fiber is immune to electromagnetic interference.

There are two basic types of fiber in use today: Multimode and Single Mode. Multimode fiber is used extensively in the data communications industry. Fast Ethernet carried over multimode fiber is known as 100BASE-FX. Ethernet may be carried up to 2 kilometers on this fiber. Single mode fiber is used extensively in the telecom industry. Single mode fiber allows much greater run lengths than multimode fiber. Although there is no official standard for carrying Ethernet over single mode fiber, numerous datacom products offer this capability.

Two strands are required for each Ethernet link; one for transmit and one for receive. Both multimode and single mode fiber cables are available with varying numbers of strands. 4-strand cable costs about $0.80/meter.

Transfer rates of up to 10GB/s and a distance of up to 1000 meters. This is an expensive type of medium and takes a special connector to terminate the signal. It has higher bandwidth possibilities and is best suited for backbone installations. It has 3 parts to the cable: Core, Cladding and Buffer.

  • Core:
    • This is where the light is transmitted
  • Cladding:
    • Just outside the core it traps the light inside the core and helps guide it around corners.
  • Buffer:
    • The hard plastic coating on the outside of the cable that protects the core from moisture and physical damage.

Fiber optic uses include grounding and bonding for:

  • LIghting protection systems
  • Grounding electrode systems
  • Electrical bonding and grounding
  • Power protection
  • Telecom bonding and grounding
  • Telecom circuit protector

Wiring Diagrams and Schematics

RJ-45 Color Codes

RJ-45 modular connectors (AKA “8 Position 8 Contact” or “8P8C”) are the default standard for Ethernet connectivity.

Very Important Note: The T-568B is the current default standard for almost all applications.


RJ-45 Crossover Cable Pinout

A crossover swaps the transmit and receive pairs. Important Note: A crossover cable is not the same as a reverse polarity cable.



RJ-45 Reverse Polarity Cable Pinout

A polarity cable swaps the positive and negative signals on the transmit and receive pairs. Important Note: A polarity cable is not the same as a cross over cable.



Solid color versus banded/striped wiring cross reference

Wiring is usually solid color or banded/striped. Below are the the first three wire pairs and their respective colors.


RJ-11/RJ-14 Color Codes and Wiring

RJ-11 and RJ-14 Female Jack from the outside looking in. RJ-11 is the common standard for most phones and POTS devices.


RJ-11/RJ-14 Wall Plate Jack

Standard RJ-11/RJ-14 Wall Plate Jack.


Swapping Inner and Outer Pairs on an RJ-11 Wall Plate

Some modems are designed to receive the DSL signal on the “outer pairs” (pins 2 and 5) instead of the “inner pairs” (pins 3 and 4) of an RJ-11 jack. You can use a line swapper or you can rewire your wall plate as shown. Note: If you rewire the wall plate as shown you will not be able to use most standard equipment that requires the “inner pairs”.


IFITL (PCDATA) Installation and Connections

IFITL (Integrated Fiber In The Loop) is a 10Mb ethernet connection and does not require a DSL modem. It does however require a PPPoE client for connectivity. You can use a stand alone client such as BellSouth Connection Agent, RasPPPoE, or the native PPPoE client on Windows XP on the computer. You can also use a router as shown here.

IFITL requires a specialized, dedicated 10Base-T Protector and IFITL EBN (Entrance Bridge Network) be placed inside the customer’s NID. Since IFITL installation use a completely separate line there is no need for inline microfilters on the POTS devices.

Important Note: IFITL also requires a crossover be built into the wiring before the NIC. The guidelines for placing the crossover varies and can be wired at the 10base-T protector, the IFITL EBN, or the wall plate inside the house. Most (but not all) technicians rewire the wall plate as the crossover point so standard CAT5 wiring can be used between the wall plate and the NIC or router (if present).




Standard POTS NID (Network Interface Device) Schematic

NIDs (or TNIs) come in a variety of styles as shown here. Depending on the age of the NID and type of the wiring used, the color codes and connections can vary. Please reference these FAQs for more information:

•RJ-11 Color Codes
•RJ-11 Wall Plate Schematic



Telco Wiring Color Code.

Telco color code.

  • B=blue
  • O=orange
  • G=green
  • Br=brown
  • S=slate (not grey)
  • W=white
  • R=red
  • Bk=black
  • Y=yellow
  • V=violet (not purple)

Tip: Pairs

  • White 1-5
  • Red 6-10
  • Black 11-15
  • Yellow 16-20
  • Violet 21-25

Ring: Pairs

  • Blue First Pair 1,6,11,16,21
  • Orange Second Pair 2,7,12,17,22
  • Green Third Pair 3,8,13,18,23
  • Brown Fourth Pair 4,9,14,19,24
  • Slate Fifth Pair 5,10,15,20,25


  • B/W 1-25
  • O/W 26-50
  • G/W 51-75
  • Br/W 76-100

And on and on.

FWIW Telco cable is built in 25 pair groups or binders. Any cable over 25 pairs will have binders which are the 25 pairs twisted and then wrapped in a multi-colored colored string (old days) or two colored plastic binders.

For example a pair in a 25 pair cable consisting of a black wire with blue stripe mated with a blue wire with a black stripe is pair 11. Now lets go to a cable with over twenty five pairs and lets say the same pair was in a binder/group wrapped with a brown/white string it would be pair 86. Make sense?

How do I install DSL filters?

Best Filter Installation Advice:

Due to basic differences in design, it is best to consult the installation instructions and diagrams provided by your ISP or filter manufacturer. It is critical that you install the filters correctly. Failure to do so will create poor performance and speeds. It may even keep the modem from synching at all.

Typically, there are two common types of DSL filters:

  1. Dual Line Filter – One line input and two outputs. One output is marked “Phone” and is used to connect to all POTS devices. The other ouput is marked “DSL/HPN” or “Data” and is used to connect the DSL modem.
  2. Single Line Filter – One line input and one phone only output. The single output marked “Phone” is used to connect to all POTS devices (not modems).


Feedback received on this FAQ entry:

A dual line filter means its designed for a two lines (not that it has two jacks)..Single line 1 line system


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