bài giảng mạng máy tính căn bản chương 7 các công nghệ ethernet ethernet techologies phan vĩnh thuần

Phan Vĩnh Thuần Computer Network 1
CHƯƠNG 7
CÁC CÔNG NGHỆ ETHERNET
ETHERNET TECHNOLOGIES
Phan Vĩnh Thuần Computer Network 2
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.
Phan Vĩnh Thuần Computer Network 3
•
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.
Phan Vĩnh Thuần Computer Network 4
•
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. Copper-
based 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.
Phan Vĩnh Thuần Computer Network 5
•
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
Phan Vĩnh Thuần Computer Network 6
–
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.
Phan Vĩnh Thuần Computer Network 7
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
Phan Vĩnh Thuần Computer Network 8
Phan Vĩnh Thuần Computer Network 9
•
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 ten-millionth of
a second.)
Phan Vĩnh Thuần Computer Network 10
•
10BASE5, 10BASE2, and 10BASE-T also
have a common frame format.
Phan Vĩnh Thuần Computer Network 11
Phan Vĩnh Thuần Computer Network 12
•
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.
Phan Vĩnh Thuần Computer Network 13
•
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
Phan Vĩnh Thuần Computer Network 14
•
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.”

Phan Vĩnh Thuần Computer Network 15
•
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.
Phan Vĩnh Thuần Computer Network 16
•
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.
Phan Vĩnh Thuần Computer Network 17
Phan Vĩnh Thuần Computer Network 18
•
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.
Phan Vĩnh Thuần Computer Network 19
•
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
Phan Vĩnh Thuần Computer Network 20
•
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.

Phan Vĩnh Thuần Computer Network 21
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.
Phan Vĩnh Thuần Computer Network 22
•
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.
Phan Vĩnh Thuần Computer Network 23
Phan Vĩnh Thuần Computer Network 24
•
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.
Phan Vĩnh Thuần Computer Network 25
•
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 half-
duplex resulting in a maximum of 10 Mbps
of data transfer.