CÁC CÔNG NGHỆ ETHERNET (MẠNG máy TÍNH cơ bản SLIDE)

CHƯƠNG 7
CÁC CÔNG NGHỆ ETHERNET
ETHERNET TECHNOLOGIES

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Overview
• Ethernet has been the most successful LAN
technology largely because of its simplicity of
implementation
compared
to
other
technologies. Ethernet has also been
successful because it has been a flexible
technology that has evolved to meet changing
needs and media capabilities. This module
introduces the specifics of the most important
varieties of Ethernet. The goal is not to
convey all the facts about each type of
Ethernet, but rather to develop a sense of
what is common to all forms of Ethernet.
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• Changes in Ethernet have resulted in major

improvements over the 10-Mbps Ethernet of
the early 1980s. The 10-Mbps Ethernet
standard remained virtually unchanged until
1995 when IEEE announced a standard for a
100 Mbps Fast Ethernet. In recent years, an
even more rapid growth in media speed has
moved the transition from Fast Ethernet to
Gigabit Ethernet. The standards for Gigabit
Ethernet emerged in only three years. An
even faster Ethernet version, 10 Gigabit
Ethernet, is now widely available and still
faster versions are being developed.
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• In these faster versions of Ethernet, MAC
addressing, CSMA/CD, and the frame
format have not been changed from earlier
versions of Ethernet. However, other
aspects of the MAC sublayer, physical
layer, and medium have changed. Copperbased network interface card (NICs)
capable of 10/100/1000 operation are now
common. Gigabit switch and router ports
are becoming the standard for wiring
closets. Optical fiber to support Gigabit
Ethernet is considered a standard for
backbone cabling in most new installations.
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• Students completing this module should
be able to:
– Describe the differences and similarities
among
10BASE5,
10BASE2,
and
10BASE-T Ethernet.
– Define Manchester encoding.
– List the factors affecting Ethernet timing
limits.
– List 10BASE-T wiring parameters.
– Describe the key characteristics and
varieties of 100-Mbps Ethernet
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– Describe the evolution of Ethernet.
– Explain the MAC methods, frame formats, and
transmission process of Gigabit Ethernet.
– Describe the uses of specific media and
encoding with Gigabit Ethernet.
– Identify the pinouts and wiring typical to the
various implementations of Gigabit Ethernet.

– Describe the similarities and differences
between Gigabit and 10 Gigabit Ethernet.
– Describe
the
basic
architectural
considerations of Gigabit and 10 Gigabit
Ethernet.
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7.1.10-Mbps and 100-Mbps Ethernet
7.1.1. 10Mbps Ethernet
• 10BASE5, 10BASE2, and 10BASE-T
Ethernet
are
considered
Legacy
Ethernet. The four common features of
Legacy Ethernet are timing parameters,
frame format, transmission process,
and a basic design rule

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• 10BASE5, 10BASE2, and 10BASE-T all
share the same timing parameters, as
shown in the figure (1 bit time at 10
Mbps = 100 nsec = 0.1 µsec = 1 tenmillionth of a second.)

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• 10BASE5, 10BASE2, and 10BASE-T also
have a common frame format.

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• The Legacy Ethernet transmission
process is identical until the lower part

of the OSI physical layer. The Layer 2
frame data is converted from hex to
binary. As the frame passes from the
MAC sublayer to the physical layer,
further processes occur prior to the bits
being placed from the physical layer
onto the medium. One important process
is the signal quality error (SQE) signal. 
SQE is always used in half-duplex. SQE
can be used in full-duplex operation but
is not required.
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• SQE is active:

– Within 4 to 8 microseconds following a
normal transmission to indicate that the
outbound
frame
was
successfully
transmitted
– Whenever there is a collision on the medium
– Whenever there is an improper signal on the
medium. Improper signals might include
jabber, or reflections that result from a cable
short.

– Whenever a transmission has been
interrupted
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• All 10 Mbps forms of Ethernet take octets
received from the MAC sublayer and
perform a process called line encoding.
Line encoding describes how the bits are
actually signaled on the wire. The
simplest encodings have undesirable
timing and electrical characteristics. So
line codes have been designed to have
desirable transmission properties. This
form of encoding used in 10 Mbps
systems is called “Manchester.”
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• Manchester encoding relies on the
direction of the edge transition in the
middle of the timing window to determine
the binary value for that bit period. The
top waveform has a falling edge, so it is
interpreted as a binary 0. The second
waveform shows a rising edge, which is

interpreted as a binary 1. In the third
waveform, there is an alternating binary
sequence. With alternating binary data,
there is no need to return to the previous
voltage level.
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•

As can be seen from the third and
fourth wave forms in the graphic, the
binary bit values are indicated by the
direction of change during any given bit
period. The waveform voltage levels at
the beginning or end of any bit period
are not factors when determining binary
values.

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• Legacy
Ethernet
has
common
architectural features. Networks usually
contain multiple types of media. The
standard ensures that interoperability is
maintained. The overall architectural
design is of the utmost importance
when implementing a mixed-media
network. It becomes easier to violate
maximum delay limits as the network
grows.
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• The timing limits are based on
parameters such as:
– Cable length and its propagation
delay
– Delay of repeaters
– Delay of transceivers
– Interframe gap shrinkage
– Delays within the station
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• 10-Mbps Ethernet operates within the
timing limits offered by a series of not
more than five segments separated by
no more than four repeaters. This is
known as the 5-4-3 rule. No more than
four repeaters may be connected in
series between any two distant stations.
There can also be no more than three
populated segments between any two
distant stations.
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7.1.2. 10Base5
• The original 1980 Ethernet product
10BASE5 transmitted 10 Mbps over a
single thick coaxial cable bus. 10BASE5
is important because it was the first
medium used for Ethernet. 10BASE5
was part of the original 802.3 standard.
The primary benefit of 10BASE5 was
length. Today it may be found in legacy
installations, but would not be
recommended for new installations.
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• 10BASE5 systems are inexpensive and
require no configuration, but basic
components like NICs are very difficult
to find as well as the fact that it is
sensitive to signal reflections on the
cable. 10BASE5 systems also represent
a single point of failure.

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• 10BASE5 uses Manchester encoding. It
has a solid central conductor. Each of
the maximum five segments of thick
coax may be up to 500 m (1640.4 ft) in
length. The cable is large, heavy, and
difficult to install. However, the distance
limitations were favorable and this
prolonged
its

use
in
certain
applications.
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• Because the medium is a single coaxial
cable, only one station can transmit at a
time or else a collision will occur.
Therefore, 10BASE5 only runs in halfduplex resulting in a maximum of 10
Mbps of data transfer.

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