Chapter 13
Wired LANs: Ethernet
13.1
13-1 IEEE STANDARDS
In 1985, the Computer Society of the IEEE started a
project, called Project 802, to set standards to enable
intercommunication among equipment from a variety
of manufacturers.
Project 802 is a way of specifying functions of the
physical layer and the data link layer of major LAN
protocols.
Data Link Layer
Physical Layer
13.2
Figure 13.1 IEEE standard for LANs
13.3
HDLC frame compared with LLC and MAC frames
Framing LLC defines a protocol data unit (PDU)
13.4
MAC: IEEE Project 802 has created a sublayer called media
access control that defines the specific access method for each
LAN.
It defines CSMA/CD as the media access method for Ethernet
LANs and the token passing method for Token Ring and Token
Bus LANs
Physical layer
It is dependent on the implementation and type of
physical media used. IEEE defines detailed
specifications for each LAN implementation
13.5
STANDARD ETHERNET
The original Ethernet was created in 1976 at Xerox’s
Palo Alto Research Center (PARC). Since then, it has
gone through four generations.
MAC Sublayer
Physical Layer
13.6
Ethernet evolution through four generations
13.7
Figure 13.4 802.3 MAC frame
Preamble : alerts the receiving system to the coming frame and enables it to
synchronize its input timing. The pattern provides only an alert and a timing pulse.
13.8
Figure 13.5 Minimum and maximum lengths
13.9
Note
Frame length:
Minimum: 64 bytes (512 bits)
Maximum: 1518 bytes (12,144 bits)
13.10
Figure 13.6 Example of an Ethernet address in hexadecimal notation
13.11
Figure 13.7 Unicast and multicast addresses
13.12
Note
The least significant bit of the first byte
defines the type of address.
If the bit is 0, the address is unicast;
otherwise, it is multicast.
13.13
Note
The broadcast destination address is a
special case of the multicast address in
which all bits are 1s.
13.14
Mac Sub Layer Implementation
MAC Sub Layer - Access
Method: CSMA/CD
13.15
Physical Layer Implementation
13.16
Figure 13.10 10Base5 implementation
13.17
Figure 13.11 10Base2 implementation
13.18
Figure 13.12 10Base-T implementation
13.19
Figure 13.13 10Base-F implementation
13.20
Table 13.1 Summary of Standard Ethernet implementations
13.21
13-4 FAST ETHERNET
Fast Ethernet was designed to compete with LAN
protocols such as FDDI or Fiber Channel. IEEE
created Fast Ethernet under the name 802.3u. Fast
Ethernet is backward-compatible with Standard
Ethernet, but it can transmit data 10 times faster at a
rate of 100 Mbps.
Topics discussed in this section:
MAC Sublayer
Physical Layer
13.22
FAST ETHERNET
Fast Ethernet was designed to compete with LAN
protocols such as FDDI.
Fast Ethernet is backward-compatible with
Standard Ethernet, but it can transmit data 10
times faster at a rate of 100 Mbps.
The goals of Fast Ethernet can be summarized as
follows:
1. Upgrade the data rate to 100 Mbps.
2. Make it compatible with Standard Ethernet.
3. Keep the same 48-bit address.
4. Keep the same frame format.
5. Keep the same minimum and maximum frame lengths.
13.23
Figure 13.19 Fast Ethernet topology
13.24
Figure 13.20 Fast Ethernet implementations
13.25
Figure 13.21 Encoding for Fast Ethernet implementation
13.26
Table 13.2 Summary of Fast Ethernet implementations
13.27
13-5 GIGABIT ETHERNET
The need for an even higher data rate resulted in the
design of the Gigabit Ethernet protocol (1000 Mbps).
The IEEE committee calls the standard 802.3z.
Topics discussed in this section:
MAC Sublayer
Physical Layer
Ten-Gigabit Ethernet
13.28
Note
In the full-duplex mode of Gigabit
Ethernet, there is no collision;
the maximum length of the cable is
determined by the signal attenuation
in the cable.
13.29
Figure 13.22 Topologies of Gigabit Ethernet
13.30
Figure 13.23 Gigabit Ethernet implementations
13.31
Figure 13.24 Encoding in Gigabit Ethernet implementations
13.32
Table 13.3 Summary of Gigabit Ethernet implementations
13.33
Table 13.4 Summary of Ten-Gigabit Ethernet implementations
13.34
13.35
