CIS 304
LAN Hardware/Wiring & Installation

Lesson 6 - Exploring Ethernet Specifications

Instructor: Michael P. Harris

  Key Terms  
Ethernet
CSMA/CD
IEEE 802.3
IEEE 802.3u
NIC
DIX AUI
shared memory
I/O address
interrupt
BIA
boot PROM
spanning tree
RG 8 Coax
RG 58 A/U Coax
fiber optic cable
UTP (CAT5)
The 5-4-3 Rule
10Base2, ThinNet
on-board transceiver
50 Ohm terminator
BNC
BNC T-connector
EIA/TIA 568
10Base5, ThickNet
external transceiver
AUI cable
DIX connector
N-series connector
10Base-T, 100Base-TX
RJ-45 connector
RJ-45 pin-out
UTP cable categories
UTP wire colors
Applications:   Coax Lab   CAT5 Lab   Cross-Cable Lab
All images are "clickable" links to larger, clearer images.

[Top] Ethernet

Ethernet was originally developed by DIX - the Digital Corporation, the Intel Corporation, and the Xerox Corporation in the early 1970s. Ethernet is known as a spanning tree topology because the networks expand by branching in tree structures that do not allow redundant paths between nodes. Ethernet uses the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) media contention access method and supports a maximum throughput of 10 or 100 Mbps. The original Ethernet and later IEEE 802.3 protocols are similar but not usually interchangeable.

STUDY NOTE: The origins of Ethernet are commemorated in the initials DIX, which is a 15-pin connector used to interface Ethernet components (also called the AUI - Attachment Unit Interface). The acronym "DIX" is derived from the combination of leading letters of the founding Ethernet vendors -- Digital, Intel, and Xerox.

The term Ethernet commonly refers to original Ethernet (now most frequently identified as Ethernet II) as well as the IEEE 802.3 standards. However, Ethernet and the IEEE 802.3 standards differ in ways significant enough to make standards incompatible in terms of packet formats. At the Physical Layer, Ethernet and IEEE 802.3 are generally compatible in terms of cables, connectors, and electronic devices.

RG 58 A/U Coax cable

Ethernet is generally used on light to medium traffic networks, and performs best when a network's data traffic is sent in short bursts. Ethernet is the most popular network standard. It has become especially popular in many university and government installations.

[Top] Ethernet Board Settings

Most versions of Ethernet NICs are configured using jumpers to set addresses and interrupts. Certain models of newer type Network Interface Cards (NICs) can be configured using a diagnostic program that allows changing of interrupt and memory address settings stored in a special memory chip on the NIC.

An example of an Ethernet NIC is shown above. Some of the features of these cards are:

Ethernet cards can have one, two, or possibly all three of the following connectors:

  • DIX/AUI connectors support 10Base5 external transceivers
  • BNC connectors support 10Base2 coax cabling
    (Bayonne Neil Councelman also commonly called
    British Naval Connector)
  • RJ-45 connectors support 10Base-T/100Base-TX (UTP) cabling

In many cases, DIP switches or blocks of jumpers are used to select the active connector. With some cards, however, the active connector can be selected with configuration software.

A limitation of 1,024 nodes (physical addresses) per network address exists on an Ethernet network. Addresses are assigned by IEEE to the vendor for the first three bytes of a six-byte address. The vendor is responsible for assigning the rest of the address and ensuring unique IDs. These unique addresses are called Burned-In Addresses  (BIA).

As with the Token Ring cards, the card's manufacturer "burns in" a unique node address into a ROM on each NIC. Unless you override the burned-in address (using what are calles Locally administered Addresses - LAA), address conflicts should not occur on an Ethernet. Vendors sometimes label their cards with the node address. If the address is not visible, use the diagnostic disk supplied by the vendor.

[Top] Ethernet Cabling

A variety of cables can be used to implement Ethernet networks. Traditionally, Ethernets have been cabled with coax cables of several different types (similar to RG 8 for 10Base5 and RG 58 A/U for 10Base2). Fiber optic cables (FOIRL) Fiber Optic Inter-Repeater Link; are now frequently employed to extend the geographic range of Ethernets.

The contemporary interest in using twisted pair wiring (UTP) has resulted in a new scheme for cabling using unshielded twisted pair. The 10Base-T cabling standard, which uses UTP in a star topology, is described later.

Ethernet remains closely associated with coaxial cable, however. Two types of coaxial cable still used in small and large environments are thin net (also known as cheapernet) and thick net. The Ethernet networks have different limitations based on thinnet and thicknet cable specifications. The best way to remember the requirements is to use the following rule of thumb for each cable type.

Typical Ethernet coax cable specifications:
  • RG-58 A/U, stranded conductor, CL2, 95%+ copper braided shield, PVC jacket, nominal 50 ohm impedance, 29.5 nominal capacitance/ft.

  • RG-58 A/U, stranded conductor, CL2P, 95%+ copper braided shield, Plenum jacket, nominal 50 ohm impedance, 27.0 nominal capacitance/ft.

  • RG-58/U, solid conductor, CL2, 90%+ copper braided shield, PVC jacket, nominal 50 ohm impedance. 26.0 nominal capacitance/ft.

  • Thick Ethernet Yellow Trunk Cable, solid conductor, CL2, double foil and braided shield, PVC jacket, nominal 50 ohm impedance, 26.0 nominal capacitance /ft.

[Top] The 5-4-3 Rule

The 5-4-3 rule  states that between any two nodes in the Ethernet network can be:

  • Up to (5) five segments in a series
  • Up to (4) four concentrators or repeaters
  • Up to (3) three populated segments (coax only)
    {cable that contain nodes}

[Top] 10Base2 (ThinNet)

The 10Base2, thinnet  topology generally uses the on-board transceiver of the network interface card to translate the signals to and from the rest of the network. Thin net cabling uses RG-58 A/U coaxial type cable, 50 Ohm terminators, and BNC T-connectors that directly attach to the connector on the NIC. A grounded terminator must be used on only one end of the network segment. The components of a thin net network are shown below.

STUDY NOTE: A transceiver   is a device that takes the digital signal from the node and translates it to communicate on a baseband cabling system. NICs that support thinnet or 10Base-T/100Base-TX cable have built-in transceivers. External transceivers are used for 10Base5 thick Ethernet.

  • Remember: several additional rules must be adhered to in 10Base2 thinnet Ethernet environments, including the following:

    • The minimum cable distance between workstations must be 1.5 feet or .5 meters.

    • Pig tails, also known as drop cables, from BNC T-connectors should not be used to connect to the BNC connector on the NIC. The BNC T-connector on the coax must be connected directly to the NIC.

    • You may not go beyond the maximum network segment limitation of 607 feet or 185 meters (not the 200 meters commonly stated).

    • The entire network cabling scheme cannot exceed 3,035 feet or 925 meters.

    • The maximum number of nodes per network segment is 30 (this includes workstations and repeaters).

The IEEE 802.3 standard  for thinnet is 10Base2. This standard describes a 10 Mbps baseband network with a maximum segment length of approximately 200 meters (the actual limit, as stated above is 185 meters).

[Top] 10BASE5 (ThickNet)

The 10Base5, thicknet topology uses an external transceiver  to attach to the network interface card. The NIC attaches to the external transceiver by an AUI cable to the DIX connector on the card. Some external transceivers clamp to the thick net cable with metal points that resemble a vampire's teeth (vampire tap), others connect with standard BNC  or N-series barrel connectors. As with thin net, each network segment must be terminated at both ends with one end using a grounded terminator. The components of a thicknet network are shown in the figure below.

  • Remember: several additional guidelines along with the 5-4-3 rule must be followed in 10Base5 thicknet Ethernet networks:

    • The minimum cable distance between transceivers is eight feet or 2.5 meters.

    • You may not go beyond the maximum network segment length of 1,640 feet or 500 meters.

    • The entire network cabling scheme cannot exceed 8,200 feet or 2,500 meters.

    • One end of the terminated network segment must be grounded.

    • The maximum number of nodes per network segment is 100. (This includes all repeaters.)

The IEEE 802.3 standard  that describes thicknet is 10Base5. This standard describes a 10 Mbps baseband network that can have segments up to 500 meters long.

The 10Base5 cabling scheme and components are shown below.

[Top] 10Base-T/100Base-TX (Twisted Pair Ethernet)

The trend in wiring Ethernet networks is to use unshielded twisted pair (UTP) cable. UTP cable has a lower cost than coax. Another significant advantage is that UTP is smaller than coax, which relieves congestion of wiring conduits. UTP Ethernet is wired in a star-shaped design and is referred to in the technical world as 10BaseT. The cable uses RJ-45 connectors, and the network interface card can have RJ-45 jacks built into the back of the cards. External transceivers attached to a DIX connector can also be used to connect standard Ethernet cards into a twisted pair topology.

The figure below shows 10Base-T Ethernet cabled using twisted pair and a concentrator.

STUDY NOTE: Networks with star wiring topologies can be significantly easier to trouble shoot and repair than bus wired networks. With a star network, a problem node can be isolated from the rest of the network by simply disconnecting the cable and directly connecting it to the cable hub. If the hub is considered "intelligent", management software developed for that hub type can disconnect the suspect port.

  • The additional rules for a 10Base-T network are as follows:

    • The maximum number of network segments is 1,024.
    • The maximum unshielded cable segment length is 328 feet or 100 meters.

STUDY NOTE: 10Base-T requires that the UTP cable system be compliant with a minimum rating of Category 3. RJ-45 connectors wired with two pairs (4 wires) on pins 1,2,3, & 6 are used with 10Base-T. Level IV is cable certified to operate at 10Base-T required throughput.

[Top] Fast Ethernet

An extension of the popular 10Base-T Ethernet standard, Fast Ethernet transports data at 100 Mbps. With rules defined by the IEEE 802.3u standard, Fast Ethernet leverages the familiar Ethernet technology and retains the CSMA/CD protocol of 10 Mbps Ethernet. Three types of Fast Ethernet are available: 100Base-TX, which runs over Category 5 UTP; 100Base-T4 which runs over existing Category 3 UTP; and 100Base-FX, which operates over multimode fiber optic cabling.

[Top] EIA/TIA T568B Color Codes & Pin-out for the
10Base-T & 100Base-TX RJ-45 connector

1 2 3 4 5 6 7 8
TD+ TD- RD+ N/C N/C RD- N/C N/C

Pins 1 & 2 - Pair #1 Transmit Data
Pins 3 & 6 - Pair #2 Receive Data
Pins 4, 5, 7, & 8 - Not Connected

As specified for 10Base-T (CAT3 minimum) & 100Base-TX (CAT5 minimum), cables should be 100 Ohm unshielded or shielded twisted pair (UTP or STP) wire of AWG gauge 24, 26, or 28. Maximum length is 100 meters. IBM Type-1 cable and other 150 Ohm STP cables are not suitable.

[Top] Categories for UTP cable:

Category 3 - The characteristics are specified up to 16 MHz. They are typically used for voice and data transmission rates up to and including 10 Mbps, e.g. IEEE 802.5 4-Mbps UTP (Token Ring) and IEEE 802.3 10Base-T (Ethernet).

Category 4 - The characteristics are specified up to 20MHz. They are typically used for voice and data transmission rates up to and including 16 MHz, e.g. IEEE 802.5 16-Mbps UTP (Token Ring).

Category 5 - The characteristics are specified up to 100 MHz. They are typically used for voice and data transmissions up to and including 100 Mbps e.g. the 100Base-TX Fast Ethernet, 100 MBps Fast ARCnet, and others.

[Top] Ethernet Trouble shooting

Look for the following things when trouble shooting Ethernets:

  • With 10Base-T & 100Base-TX, make sure that the cable used has the correct number of twists to meet the data grade specifications.

  • Electrical interference can be caused by tying the network cable together with monitor and power cords. Outside interference also can be caused by fluorescent lights, electric motors, and other electrical devices.

  • Make sure that connectors are pinned properly and crimped tightly.

  • Check the cable lengths to make sure that distance specifications are not exceeded.

  • If excess shielding on coax cable is exposed, it may be grounding out the connector.

  • Make sure that coax cables are not coiled tightly together.

  • Check the grade of the cable being used. For thinnet, RG-58 A/U is required. Thick net cable must meet Ethernet specifications.

  • If using a linear bus setup, make sure that the topology rules are followed.

  • Check for missing terminator or terminators with improper impedance ratings.

  • Make sure that all the component cables in a segment are connected together. A user who moves his workstation and removes the T-connector incorrectly can cause a broken segment.

10Base2, thinnet and 10Base5, thick net cable can be combined to extend the distance of an Ethernet network topology (spanning tree topology). The following formula can be used to define the maximum amount of thinnet cable that can be used in one network segment combination:

Maximum length of thinnet that can be used =
1,640 feet (length of new network
segment to be added)

NOTE: A linear bus topology is economical to wire because it is not necessary to have a separate cable run for each workstation. However, some local problems on a linear bus have the capability of bringing the entire network down.

If a break is in the cable or a streaming (beaconing) NIC is in the channel, the entire network can go down. Streaming is more frequently referred to as a broadcast storm. This occurs when a network card fails, and the transmitter floods the cable with traffic, just like a faucet that is stuck open. At this point, the network becomes unusable.

[Top] Application Projects:

We will be building a typical coax cable for 10Base2 thinnet for our first hands-on lab project for this lesson. We will then build a typical UTP patch-cable for 10Base-T & 100Base-TX Ethernet for our second project. Then we will build a cross-cable (sometimes called a 10Base-T / 100Base-TX null-modem cable) for directly connecting two 10Base-T or 100Base-TX NICs together without then need for a concentrator.

From your LAN-Wire materials kit locate the:

  • 6' length of RG-58A/U coax cable
  • RG-58 A/U crimp-on BNC connectors (Qty. 3)
  • Two 6' lengths of four-pair (8 wire) UTP cable
  • RJ-45 crimp-on connectors (Qty. 6)

[Top] Project #1 - 10Base2 coax cable

  1. Set the Coax wire stripper to the RG-58 setting. (RG-59 & RG-62 are the same diameter)
  2. The dual-set blades of the coax wire stripper will strip the end of the coax cable with a precise two-stage cut. Strip the ends of your RG-58 cable using a rotary motion with the coax stripper.
  3. Crimp the center pin of the BNC connector onto the end of the center conductor.
  4. Slide the crimp ferrule over the coax cable.
  5. Slip the body of the BNC connector under the braided shield as far as it will go.
  6. Slide the crimp ferrule over the braided shield up to the BNC body shoulder.
  7. Use the ratchet crimping tool to evenly and completely crimp the ferrule to the BNC body.
  8. Repeat for the other end of the cable.
  9. Use a digital multimeter to test your cable for shorts. (any Ohm reading other than infinity)
  10. Using a BNC butt-splice and terminating resistor, also test for a perfect 50 Ohm reading.

[Top] Project #2 - 10Base-T/100Base-TX patch-cable

Technically, as long as you build your 10Base-T/100Base-TX patch-cable with straight-through connections for pins 1, 2, 3, & 6 it will work. But there is a EIA/TIA 568 standard that specifies minimum recommendations for telecommunications wiring within a structure, including telecommunication outlets, and between structures in a campus environment. It specifies a wiring system with a recommended topology and distances. It specifies media by parameters which determine performance and specifies connectors and their pin assignments to ensure interconnectability.

     

Using the USOC/PDS wiring pair color codes and the EIA/TIA T568B (AT&T 258A) wiring scheme assemble a standard 10BaseT cable with straight-through wiring using pins 1, 2, 3, & 6. Use the Paladin twisted pair tester to insure connection integrity.

usoc Universal Service Ordering Codes (USOC): are a series of Registered Jack (RJ) wiring configurations developed by the Bell System for connection of customer premise equipment to the public network.

[Top] Banded & Solid / Wiring Pair Color Codes:

Pair # ID Pin #
T568B
Band
code
Pin #
USOC
Solid
code
1 T1 5 White/Blue 5 Red
R1 4 Blue(White) 4 Green
2 T2 1 White/Orange 6 Black
R2 2 Orange(White) 3 Yellow
3 T3 3 White/Green 7 Orange
R3 6 Green(White) 2 Blue
4 T4 7 White/Brown 8 Gray (or White)
R4 8 Brown(White) 1 Brown

[Top] Project #3 - 10Base-T/100Base-TX Cross-cable

To direct-connect two 10BaseT NIC's for testing or trouble shooting you will assemble a 10Base-T/100Base-TX cross-cable (sometimes called a UTP null-modem cable or plug-to-jack cable). This cable will allow you to connect two 10Base-T or 100Base-TX nodes together without the need for a concentrator. This can create a two-node LAN. Be sure to check the wiring with the Padadin test tool.


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