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Lesson #6: Exploring Ethernet Specifications
Key Terms |
Ethernet
CSMA/CD
IEEE 802.3
IEEE 802.3µ
IEEE 802.3z
NIC
DIX
AUI
shared memory
I/O address
interrupt
BIA
boot PROM
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spanning tree
RG 8 Coax
RG 58 A/U Coax
fiber optic cable
UTP (CAT 3, 4, 5, 5e, 6, 6a)
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, 1000Base-T
RJ45 connector
RJ45 pin-out
UTP cable categories
UTP wire colors
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| Most images are "clickable"
links to larger, clearer images. |
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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, 100, 1,000, and even 10,000 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. These name are also reflected in the company's name
"3Com" (three companies).
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.
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, government, and home network installations.
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
(Click on the links for higher resolution
or alternate images).
Some of the features of these cards are:
BNC -
AUI - RJ45
(Click on the links for higher resolution
or alternate images)
 
Ethernet cards can have one, two, or possibly all three of the
following connectors:
- Bayonne Neil Councelman (BNC)
connectors support 10Base2 coax cabling
- DIX/AUI connectors support
10Base5 external transceivers and AUI cables
- RJ45 modular plugs can
support Cat 3, 4, 5, 5e, and Cat6 (UTP) cabling
In many cases today, Ethernet NICs will auto configure
themselves using Plug-n-Play. But
for multi-NIC servers and other hi-end uses, the NICs may
have DIP switches or blocks of jumpers which are are used to
select the active connector, NIC number, and other features.
On most NICs however, these settings can now also be
selected using configuration software.
A limitation of 1,024 host nodes (physical addresses)
per network address exists on an Ethernet network. Addresses
are assigned by IEEE to the vendor for the first (three
bytes) 24-bits of the (six-byte) 48-bit
physical address. The vendor is responsible
for assigning the remainder of the address and ensuring
unique IDs. These unique Burned-In
Addresses are called the Machine Address
Control or MAC addresses.
As with the Token Ring cards, the card's
manufacturer "burns in" a unique node address into a ROM
on each NIC. Ethernet NICs call this physical address the "MAC"
address (Token-Ring calles this hardware address a BIA (Burned In Address).
Unless you override the MAC address in software, using
what are called Locally Administered Addresses (LAA), address conflicts
should not occur on an Ethernet network. Vendors sometimes label their cards
with the MAC (node) address. If the address is not visible, use the diagnostic
disk supplied by the vendor.
A variety of cables can be used to implement Ethernet networks.
In the past, Ethernet networks were cabled with
coax cables of specific types like
RG 8 for 10Base5
networks and RG 58 A/U for 10Base2
networks.
 
Fiber optic cables
like (FOIRL) Fiber Optic Inter-Repeater Link
and (FDDI) Fiber Distributed Data Interface
are now frequently employed to extend the geographic range
of Ethernet networks.
 
The contemporary interest in using Unshielded
Twisted Pair (UTP) wiring has resulted in a standard
scheme for cabling using unshielded twisted pair. 10Base-T,
100Base-TX, and 1000Base-T all use this standard cabling
layout, which uses UTP in a physical star topology,
which is described later.
 
Older Ethernet installations were primarily cabled with coaxial
cable. The two types of coaxial cable that are still in use
in both small and large environments are ThinNet (also known
as cheapernet) and ThickNet. These Ethernet networks have
different limitations based on which ThinNet or ThickNet cable
specifications are used. Following are typical specifications
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.
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}
The IEEE 802.3 10Base5, ThickNet, technology uses an
external transceiver to attach
to the network interface card. The NIC attaches to the
external transceiver using an AUI cable
attached to the DIX/AUI connector on
the NIC. Some external transceivers clamp to the ThickNet
cable with very sharp metal points that resemble a vampire's tooth
(vampire tap), others connect with standard TNC or
N-series barrel connectors. As with
10Base2, each coax network segment must have terminators at both ends
with only one end using a grounded terminator. The layout
and specifications for an Ethernet 10Base5 ThickNet network are shown
below. Click on the graphic for a
larger and clearer image.
The IEEE 802.3 name for ThickNet Ethernet is
10Base5. This naming 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
Click on the image for a larger and clearer image.
The IEEE 802.3, 10Base2 ThinNet technology uses an on-board transceiver (radio) on the Network
Interface Card (NIC) to translate the signals to and from the
rest of the network. 10Base2 cabling uses RG-58 A/U coaxial cable,
50 Ohm terminators (terminating resistors), and
BNC T-connectors that directly attach to the BNC connector
on the NIC. A grounded terminator must be used on only
one end of the coax network segment. The layout and
specifications for an Ethernet 10Base2 ThinNet network are shown below.
Click on the graphic for a larger and
clearer image.
STUDY NOTE: A transceiver
is a device that takes the digital signal from the
host node and translate it to communicate on the analog baseband
cabling system. NICs that support thin 10Base2 coax cable have
built-in transceivers. External transceivers are used for
thick 10Base5 coax cable.
The IEEE 802.3 name for ThinNet Ethernet is
10Base2. This naming 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...
@grin@ 200 yards! @grin).
The 10Base2 cabling scheme and components are shown below
Click on the image for a larger and clearer image.
The trend in wiring Ethernet networks today is to use
Unshielded Twisted Pair (UTP) cable. UTP cable has
a much lower cost than coax. And since UTP is smaller than coax,
it relieves congestion of wiring conduits.
UTP based Ethernet is wired in a star-shaped design where all
cabling runs returns back to a central connecting hub. This
is referred to in the technical world as a "physical
star". The cable uses RJ45
(8p8c modular plug) connectors, and the NICs
have RJ45 jacks built into them.
An external transceiver attached to a DIX/AUX connector can
also be used to connect older Ethernet devices into a twisted
pair, physical star topology network.
The figure below shows a 10Base-T Ethernet network cabled
together using UTP cables and a concentrator
(Ethernet hub).
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.
STUDY NOTE:
10Base-T requires that the UTP cable system be compliant with a minimum
rating of Category 3. RJ45 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.
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.
| 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
On 1000Base-T (Gigabit Ethernet) and 10GbE (10 Gigabit Ethernet)
and higher, all 4 pair may be used.
As specified for 10Base-T (CAT3 minimum) & 100Base-TX (CAT5 minimum),
cables should be 100 Ohm unshielded or shielded/screened twisted pair (UTP
or ScTP) 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.
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.
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.
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
- RJ45 crimp-on connectors (Qty. 6)
- Set the Coax wire stripper to the RG-58 setting. (RG-59 & RG-62 are
the same diameter)
- 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.
- Crimp the center pin of the BNC connector onto the end of the center
conductor.
- Slide the crimp ferrule over the coax cable.
- Slip the body of the BNC connector under the braided shield as far as it
will go.
- Slide the crimp ferrule over the braided shield up to the BNC body
shoulder.
- Use the ratchet crimping tool to evenly and completely crimp the ferrule
to the BNC body.
- Repeat for the other end of the cable.
- Use a digital multimeter to test your cable for shorts. (any Ohm reading
other than infinity)
- Using a BNC butt-splice and terminating resistor, also test for a perfect
50 Ohm reading.
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.
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.
| 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 |
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 Network
cable test tool.
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Categories for UTP cable:
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Lesson #7 - Token Ring
This page is maintained by:
Prof.
Michael P. Harris, CCNA, CCAI
