Transcript L_06_ch_13_DLL_LAN_Ethernet

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expanded by Jozef Goetz, 2012
The McGraw-Hill Companies, Inc., 2006
Jozef Goetz, 2012
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.
•Standard 802 adopted by ANSI and approved by ISO is
a way of specifying functions of the physical layer and
the data link layer of major LAN protocols.
Topics discussed in this section:
Data Link Layer
Physical Layer
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INTRODUCTION
LANs usually are owned by the organization
that is using the network to interconnect
equipment.
LANs have much greater capacity than WAN.
The key technology ingredients that
determine the nature of a LAN are:
[1] Topology
[2] Transmission medium
[3] Medium access control technique
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LAN ARCHITECTURE
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•In OSI terms, higher-layer protocols
(layer 3/4 & above) are independent of
network architecture and are applicable to LANs &
WANs.
SCOPE OF IEEE 802 STANDARDS
[1] LOGICAL LINK CONTROL (LLC)
[2] MEDIUM ACCESS CONTROL (MAC)
[3] PHYSICAL LAYER
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Figure 13.1 IEEE standard for LANs
Note: there is one LLC sublayer for all IEEE LANs
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LAN ARCHITECTURE
Physical Layer
[1] Encoding/decoding of signals
[2] Preamble generation/removal (synch)
[3] Bit transmission/reception
Medium Access Layer (MAC)
[1] On transmission, assemble data into a frame with
address and error-detection fields.
[2] On reception, disassemble frame, and perform
recognition and error detection.
[3] Govern access to the LAN transmission medium
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LAN ARCHITECTURE
Logical Link Control (LLC)
[1] Provide an interface to higher layers and perform
flow and error control.
LAN Protocols in Context
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Figure 13.2 HDLC (typical DLL protocol) frame compared with
LLC and MAC frames in the 803 IEEE standard
PDU – protocol data unit
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LOGICAL LINK CONTROL
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3 services are provided by LLC:
[1] Connection-mode service
A logical connection is set up between users. Flow/error control.
Extended HDLC format.
[2] Acknowledged connectionless service
No connection is setup up, but datagrams are acknowledged.
[3] Unacknowledged connection service
Simple, the delivery of data is not guaranteed.
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LOGICAL LINK CONTROL
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LOGICAL LINK CONTROL
Most upper-layer protocols such as IP
don’t use the services of LLC
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Ethernet Cabling
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(a) Linear – from room to room,
(b) Vertical Spine – from the basement to the roof with
cables on each floor connected by repeaters,
(c) Tree,
(d) Segmented – see max in the previous slide
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repeaters are the physical layer device – amplifies signals in both
directions
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Gigabit Ethernet
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(a) A two-station Ethernet.
(b) A multistation Ethernet.
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LAN TOPOLOGIES
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The common topologies for LANs are
bus, tree, ring, and star.
BUS
TREE
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RING
STAR
Three generations of Ethernet
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13-2 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.
•We briefly discuss the Standard (or traditional) Ethernet in
this section.
Topics discussed in this section:
MAC Sublayer
Physical Layer
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Figure 13.3 Ethernet evolution through four generations
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Ethernet
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• A thick coax cable was used for data
transmission.
• The coax could be up to 2.5km long (with
repeaters every 500 meters).
• 256 machines could connect to the cable.
• A cable with multiple machines is called a
multidrop cable.
• The original throughput was 2.94 Mbps
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IEEE 802.3
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Based on 1-persistent CSMA/CD with some extra
features.
More commonly (but incorrectly) referred to as
Ethernet.
Ethernet is the original product designed by Xerox
PARC based on Bob Metcalfe's idea
It was later upgraded to 10 Mbps by Xerox, Intel and
DEC.
This formed the basis for the IEEE 802.3 standard.
 Which then became an ISO standard.
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Ethernet – IEEE 802.3 in ’83.
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LAN Architecture of the original Ethernet.
A multidrop cabel
A computer first listened to the cable to see if someone
was already transmitting.
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If so, then back off and wait a random time before retrying
If a 2nd collision happen, the random waiting time is doubled
Other standards a token bus (IEEE 802.4) and a token
ring (IEEE 802.5)
Ethernet (most popular LAN) won a war between Ethernet, token
bus, token ring
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Ethernet
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• What happens when there is a collision
on Ethernet?
• The terminals listen while
transmitting,
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and if they don’t hear the same thing that they
transmitted, they jam the cable to alert the
other terminals that a collision has
happened.
• They then back off and wait a random
time before trying again.
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Ethernet Cabling
4 kinds of Ethernet cabling.
10Base5 => 1st one =10 means 10 Mbps – the speed in Mbps; Base = baseband transmission, 3rd one is its length rounded to 100 m
(a) 10Base5,
(b) 10Base2 – much cheaper and easier to install,
(c) 10Base-T – cheapest, no share cable.
(d) 10Base-F – fiber optic, excellent noise immunity, good security
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IEEE 802.3 10-Mbps Specs (ETHERNET)
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MAC FRAME FORMAT
The MAC layer receives a block of data
from the LLC layer and is responsible for
performing functions related to medium
access and for transmitting the data.
MAC control
ex. Priority level
PDU – protocol data unit
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802.3 MAC frame
Minimum and maximum length
Preamble is added
at the physical layer
Start
Frame
Delimiter
physical
physical
Data encapsulated from
the upper-layer
protocols
next length
or PDU (protocol data unit) packet
•Ethernet does not provide any mechanism for acknowledging received frames,
making it what is known as an unreliable medium.
•Acknowledgments must be implemented at the higher layers.
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802.3 MAC frame
Minimum and maximum length
Preamble is added
at the physical layer
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next length
or PDU packet
Defines a number to which a higher layer protocol or application is
bound to at the destination, e.g. IP
SSAP = Source Service Access Point
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physical
physical
DSAP = Destination Service Access Point
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Start
Frame
Delimiter
Tells the destination which SAP to send back the response to, e.g. IP
Control information depends on the service type
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Type 1 – no other information required
Type 2 – full sliding window protocol implementation with extensions
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Type 3 – basic stop and wait protocol information
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Ethernet addresses in hexadecimal notation
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Each station on an Ethernet network
(such as a PC, workstation, or printer) has
its own Network Interface Card (NIC).
The NIC fits inside the station and
provides the station with a 6-byte
physical address.
written in hexadecimal notation using a
hyphen to separate bytes from each other
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Figure 13.6 Example of an Ethernet address in hexadecimal notation
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Unicast and multicast addresses
•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.
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Note
The broadcast destination address is a
special case of the multicast address in
which all bits are 1s.
FF:FF:FF:FF:FF:FF
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Example 13.1
Define the type of the following destination addresses:
a. 4A:30:10:21:10:1A
b. 47:20:1B:2E:08:EE
c. FF:FF:FF:FF:FF:FF
Solution
•To find the type of the address, we need to look at the second
hexadecimal digit from the left.
•If it is even, the address is unicast.
•If it is odd, the address is multicast.
•If all digits are F’s, the address is broadcast.
Therefore, we have the following:
a. This is a unicast address because A in binary is 1010.
b. This is a multicast address because 7 in binary is 0111.
c. This is a broadcast address because all digits are F’s.
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Example 13.2
Show how the address 47:20:1B:2E:08:EE is sent out on
line.
Solution
•The address is sent left-to-right, byte by byte;
•for each byte, it is sent right-to-left, bit by bit, as shown
below:
e.g. 47 = 0100 0111 => 1110 0010
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Physical layer
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AUI
NIC – Network Interface Card
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Function of MAU (transceiver)
AUI – Attachment Unit Interface
MAU – Medium Attachment Unit
MDI – Medium Dependent Interface
PLS – Physical Layer Signaling
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NIC – Network Interface Card
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Function of MAU (transceiver)
•It creates the appropriate
signal for each particular
medium.
•There is a MAU for each type
of medium used in 10-Mbps
Ethernet.
•the coaxial cable needs its
own type of MAU,
• the twisted-pair medium
needs a twisted-pair MAU,
and
•
•fiber-optic cable needs a
fiberoptic MAU.
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MDI – Medium Dependent Interface
PLS – Physical Layer Signaling
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NIC Evolution
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Volumes for Ethernets NICs became huge
NIC becomes cheaper than the AUI
cable!
Moved from 3 separate components to
one integral NIC card
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Categories of traditional Ethernet cables
Thick coaxial
one segment
is 500m long
max
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Thin coaxial
one segment
is 185m long max
UTP category 5
100m max P2P
Unshielded Twisted-Pair
Optical Fiber
2km max P2P
P2P = point-to-point
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BUS LANs
4 media that can be used for a
bus LAN:
[1] Twisted pair,
[2] Baseband coaxial cable,
[3] Broadband coaxial cable,
[4] Optical fiber.
10BASE 5 - thick cable
10BASE2 - thin cable
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Figure 13.10
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10Base5 implementation
Connection of a station to the medium using 10Base5
AIU cable
the size of the cable, which is roughly the size of a garden hose
and too stiff to bend with your hands
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Figure 13.11
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10Base2 implementation
Connection of stations to the medium using 10Base2
AIU cable
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Connection of stations
to the medium using
10Base5
uses a bus topology with
1. an internal transceiver
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2.
Note that if the station uses an internal transceiver, there is no need for an AUI
cable.
a point-to-point connection via an external transceiver
•
If the station lacks a transceiver, then an external transceiver can be used in
conjunction with the AUI - Attachment Unit Interface.
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Figure 13.12
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10Base-T implementation
Connection of stations to the medium using 10Base-T
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A repeater hub connects segments of a LAN.
A repeater forwards every frame;
it has no filtering capability.
uses a physical star topology. The stations are connected to a repeater
1. an internal transceiver
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2.
hub with
Note that if the station uses an internal transceiver, there is no need for an AUI cable.
a point-to-point connection via an external transceiver
•
If the station lacks a transceiver, then an external transceiver can be used in
conjunction with the AUI - Attachment Unit Interface.
Each UTP (Unshielded Twisted-Pair) cable can be up to 100m long (max network size =
200m)
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Ethernet
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Ethernet now looks like a star network
from a physical perspective
Hub is a half duplex device –
“effectively a small piece of coaxial cable”
Collisions on a hub can still take place
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Figure 13.13
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10Base-F implementation
Connection of stations to the medium using 10Base-FL
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AUI cabel
uses a star topology. The stations are connected to a repeater
1. an external transceiver (a point-to-point connection)
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hub with
The standard is normally implemented using an external transceiver called fiberoptic MAU.
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The station is connected to the external transceiver by an AUI cable.
• 2012
The transceiver is connected to the hub by using two pairs of fiber-optic cables
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Comparison of Connection of stations to the medium
10Base5
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10Base2
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Table 13.1
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Summary of Standard Ethernet implementations
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13-3 CHANGES IN THE STANDARD
•The 10-Mbps Standard Ethernet has gone through
several changes before moving to the higher data rates.
•These changes actually opened the road to the evolution
of the Ethernet to become compatible with other highdata-rate LANs.
Topics discussed in this section:
Bridged Ethernet
Switched Ethernet
Full-Duplex Ethernet
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A network with and without a bridge
•The first step in the Ethernet evolution was the division of a LAN by bridges.
•Bridges have two effects on an Ethernet LAN:
•They raise the bandwidth and separate collision domains.
•Without bridging, 12 stations contend for access to the medium;
•with bridging only 6 stations contend for access to the medium.
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Sharing bandwidth
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•In an unbridged Ethernet network, the total capacity (10 Mbps) is shared
between all stations with a frame to send;
•If only one station has frames to send, it benefits from the total capacity (10
Mbps).
•But if more than one station needs to use the network, the capacity is shared.
•For example, if 2 stations have a lot of frames to send, they probably alternate in
usage.
•When one station is sending, the other one refrains from sending (a and b).
•We can say that, on average, each station sends at the rate of 5 Mbps.
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A network with and without a bridge
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A bridge divides the network into two or more networks.
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Bandwidthwise, each network is independent.
a network with 12 stations is divided into two networks, each with 6 stations.
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Now each network has a capacity of 10 Mbps.
The 10-Mbps capacity in each segment is now shared between 6 stations
(actually 7 because the bridge acts as a station in each segment), not 12 stations.
In a network with a heavy load, each station theoretically is offered 10/6
Mbps instead of 10/12 Mbps, assuming that the traffic is not going through the
bridge.
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Collision domains in a nonbridged and bridged network
each station is now offered 10/3 Mbps, which is
4 times more than a nonbridged network.
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Hub
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In an Ethernet network there are 4 devices that from the outside look very
similar.
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A hub is the simplest of these devices.
Any data packet coming from one port is sent to all other ports.
It is then up to the receiving computer to decide if the packet is for it.
Imagine packets going through a hub as messages going into a mailing
list.
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The biggest problem with hubs is their simplicity.
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The mail is sent out to everyone and it is up to the receiving party to
decide if it is of interest.
Since every packet is sent out to every computer on the network, there is a lot of
wasted transmission.
This means that the network can easily become bogged down.
Hubs are typically used on small networks where the amount of data
going across the network is never very high.
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Bridge
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Bridge
A bridge goes one step up on a hub in that it looks at
the destination of the packet before sending.
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A bridge only has one incoming and one outgoing
port.
To build on the email analogy above, the bridge is
allowed to decide if the message should continue on.
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If the destination address is not on the other side of the bridge
it will not transmit the data.
It reads the address [email protected] and decides if there is a
[email protected] on the other side.
If there isn’t, the message will not be transmitted.
Bridges are typically used to separate parts of a
network that do not need to communicate regularly,
but still need to be connected.
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Bridges Basic
Filtering
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Detect which frames need to go from one LAN to another
Forwarding
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Send those frames from the incoming LAN to the outgoing LAN
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“Drop” those frames that don’t need to be forwarded
Loop Prevention
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Avoid issues with networks where a frame can keep going round and round
Types of Bridges
Static
Dynamic – called learning bridges
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BRIDGES
In virtually all cases, there is a need to expand
beyond the confines of a single LAN, to provide
interconnection to other LANs and to WAN.
The bridge is a simpler device
than a router and provides a
means of interconnecting
similar LANs.
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BRIDGES
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BRIDGES - FIXED ROUTING
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Each bridge must make a decision whether or
not to retransmit the frame on its other LAN, in
order to move it closer to its intended destination.
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Switch
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A switch steps up on a bridge in that it has multiple
ports.
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This leads to increased efficiency in that packets are
not going to computers that do not require them.
Now the email analogy has multiple people able to
send email to multiple users.
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When a packet comes through a switch it is read to
determine which computer to send the data to.
The switch can decide where to send the mail based on the
address.
Most large networks use switches rather than hubs
to connect computers within the same subnet.
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ROUTER
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A router is similar in a switch in that it forwards
packets based on address.
 But, instead of the MAC address that a switch
uses, a router can use the IP address.
 This allows the network to go across different protocols.
The most common home use for routers is to share
a broadband internet connection.
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The router has a public IP address and that address is
shared with the network.
When data comes through the router it is forwarded to the
correct computer.
This comparison to email gets a little off base.
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This would be similar to the router being able to receive a
packet as email and sending it to the user as a fax.
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Switched Ethernet
•The idea of a bridged LAN can be extended to a switched LAN.
•Instead of having two to four networks, why not have N networks,
where N is the number of stations on the LAN?
•A layer 2 switch is an N-port bridge with additional sophistication
that allows faster handling of the packets
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HUBs & SWITCHES
•Hubs are commonly used to connect segments of a LAN.
•A hub contains multiple ports.
•When a packet arrives at one port, it is copied to the other ports so that all
segments of the LAN can see all packets.
HUB
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SWITCH
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Full-duplex switched Ethernet
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One of the limitations of 1OBase5 and 1OBase2 is that
communication is half-duplex (1OBase-T is always full-duplex);
The next step in the evolution was to move from switched
Ethernet to fullduplex switched Ethernet = to 20 Mbps
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No Need for CSMA/CD
In full-duplex switched Ethernet, there is
no need for the Carrier Sense Multiple Access with
Collision Detection - CSMA/CD method.
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Each station or switch can send and receive independently
without worrying about collision.
Each link is a point-to-point separate dedicated path between
the station and the switch.
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There is no more need for carrier sensing; there is no more need for
collision detection.
-’s: There is no explicit flow control or error control to
inform the sender that the frame has arrived at the
destination without error. .
To provide it, a new sublayer, called the MAC control, is
added between the LLC sublayer and the MAC
sublayer.
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13-4 FAST ETHERNET – IEEE 802.3u
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•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
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13-4 FAST ETHERNET CONCEPT
- The
whole idea in the evolution of Ethernet from 10 to
100 Mbps is to keep the MAC sublayer untouched.
-The access method is the same (CSMA/CD).
-for full-duplex there is no need for CSMA/CD.
-Backward compatibility with traditional Ethernet.
-Frame format, minimum and maximum frame lengths,
and addressing are the same for 10- and 100-Mbps
Ethernet.
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Figure 13.19
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Fast Ethernet topology
autonegotiation
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A new feature added to Fast Ethernet
It allows to have :
 a station or a hub a range of capabilities
 a station to check a hub's capabilities.
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to negotiate the mode or data rate of
operation.
purposes: to allow incompatible devices to connect
to one another.
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For example, a device with a maximum capacity of 10
Mbps can communicate with a device that is designed for
100 Mbps (but can work at a lower rate).
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Fast Ethernet implementations
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Fast Ethernet can be categorized as either a two-wire or a fourwire implementation.
The two-wire implementation is called 100Base-X, which can
be either twisted-pair cable (100Base-TX) or fiber-optic
cable (100Base-FX).
The four-wire implementation is designed only for twistedpair cable (100Base-T4).
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IEEE 802.3 100-Mbps Specs (ETHERNET)
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Fast Ethernet 802.3u
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The original fast
Ethernet cabling.
4 twisted pairs per station
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Uses “Category 3 UTP”
clock @ 25 MHz
Uses “Category 5 UTP”
clock @ 125 MHz
2 twisted pairs per station
or 100m
hubs not permitted
• People needed to go faster than 10Mbps, so we needed a faster Ethernet.
• Instead of going with a new protocol, it was decided to just make regular Ethernet
go faster – IEEE 802.3u.
•This was done by reducing the bit time from 100nsec to 10 nsec
•and keeping backward compatible – frame formats, interfaces and rules
• Note: that 10Base2 and 10Base5 were not included – it was based only on
10BaseT
• Only two lines are used – one wire in and one wire out of the station.
• This makes 100BaseTX full-duplex – able to handle 100 Mbps in either direction at
the same time.
•all switches can handle a mix of 10- and 100 Mbps stations
• The (slower) 100BaseT4 and 100BaseTX are collectively referred to as “100BaseT”
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Fast Ethernet physical layer
the AUI was replaced
with (MII)
The MII is an improved interface
that can be used with both a 10- and 100.
•RS in Fast Ethernet replaces the PLS sublayer in 10-Mbps Ethernet.
•Encoding and decoding, which were performed by the PLS,
are moved to the PHY sublayer (transceiver) because
encoding in Fast Ethernet is medium-dependent.
•The reconciliation sublayer RS is responsible
for the passing of data in 4-bit format (nibble) to the MII
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MII
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transceiver in Fast Ethernet is responsible for
encoding and decoding.
can be external or internal.
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An external transceiver is installed close to
the medium and is connected via an MII
cable to the station.
An internal transceiver is installed inside the
station (on the interface card) and does not
need an MII cable.
transceiver is medium-dependent,
a mediumdependent interface (MDI) is just
a piece of hardware that is
implementationspecific.
100Base-TX implementation
The transceiver is responsible for
•transmitting,
•sending,
•detecting the collision, and
•encoding/decoding.
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Encoding and decoding in 100Base-TX
•To maintain synchronization, the encoder first performs block
encoding.
•The 4 parallel bits received from the NIC is encoded into 5 serial
bits using 4B/5B.
•This requires a bandwidth of 125 MHz (125 Mbps).
•The data at the 125-Mbps rate are then encoded into a signal using
MLT-3
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100Base-FX implementation
100Base-TX implementation
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Encoding and decoding in 100Base-FX
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Encoding and Decoding 100Base-FX uses two levels of encoding
•To maintain synchronization, the encoder first performs block encoding.
•The 4 parallel bits received from the NIC is encoded into 5 serial bits using 4B/SB.
•This requires a bandwidth of 125 MHz (125 Mbps).
•The data at the 125-Mbps rate are then encoded into a signal using NRZ-I
Encoding and decoding in 100Base-TX
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100Base-T4 implementation
•it requires the use of category 5 UTP or STP (shielded twisted-pair) cable.
•A new standard, called 100BaseT4, was designed to use category 3 or higher UTP.
•The implementation uses four pairs of UTP for transmitting 100 Mbps.
100Base-FX implementation
100Base-TX implementation
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Using four wires in 100Base-T4
•Transmission Using Four Wires The 8B/6T encoding reduces the bandwidth from 100 to
75 Mbaud (ratio of 8/6).
•However, a voice-grade UTP is not capable of handling even this bandwidth.
•100Base-T4 is designed to operate on 25-Mbaud bandwidths.
•It cuts to 4 pairs – see the picture
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Summary of Encoding for Fast Ethernet implementation
13.84
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Table 13.2
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Summary of Fast Ethernet implementations
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13-5 GIGABIT ETHERNET – IEEE 802.3z
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.
It allows the internet interconnection of existing LANs
into a Metropolitan Area Network (MAN) or a Wide
Area Network (WAN)
Topics discussed in this section:
MAC Sublayer
Physical Layer
Ten-Gigabit Ethernet
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Gigabit Ethernet


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(a) A two-station Ethernet.
(b) A multistation Ethernet.
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Figure 13.22 Topologies of Gigabit Ethernet
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Gigabit Ethernet implementations
Shielded Twisted-Pair
Unshielded Twisted-Pair
•Gigabit Ethernet can be categorized as either a two-wire or a fourwire implementation.
•The two-wire implementation is called 1000Base-X, which can
use shortwave optical fiber (1000Base-SX),
•long-wave optical fiber (1000Base-LX), or
•short copper jumpers (1000Base-CX).
•The four-wire version uses twisted-pair cable (1000Base-T).
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Gigabit Ethernet

Gigabit Ethernet cabling.
0.85 and 1.3 micron laser
1.3 micron laser
• 10 times faster than fast Ethernet and still is backwards compatible.
•supports both copper and fiber cabling
• All configurations are point-to-point.
•Compatible with technologies: FrameRelay and ATM
• It supports two modes – full-duplex and half-duplex.
• Full-duplex
– no collisions
– uses a switch
• Half-duplex
– has collisions
– uses a hub
Encoding rules called 8B/10B
•each 8-bit byte is encoded on the fiber as 10 bits hence the name 8B/10B
•Manchester encoding required a 2 Gbaud at 1 Gbps, so
>> too wasteful of bandwidth
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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.
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IEEE 802.2: LLC Logical Link Control
(a)
Position of LLC.

(b)
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Hides the differences between various kind of 802 networks by
providing a single format and interface to the network layer
Protocol formats.

LLC header contains: a destination access point, a source access point and
a control field which contains a seq and acknowledgement numbers
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Physical layer in Gigabit Ethernet
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1000Base-X implementation
•Both 1000Base-SX and 1000Base-LX use two fiber-optic cables.
•The only difference between them is that the former uses
shortwave laser and the latter uses long-wave laser.
• designed with an
internal
transceiver, so there is no
external GMII cable or connector.
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1000Base-T implementation
1000Base-X implementation
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Encoding in 1000Base-T
•5 levels of pulse amplitude modulation are used.
•The technique is very complicated and beyond the scope of this book.
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Summary: Encoding/decoding in Gigabit Ethernet implementations
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Table 13.3
Summary of Gigabit Ethernet implementations
Standard IEEE 802.3z
Table 13.4
Summary of Ten-Gigabit Ethernet implementations
Standard IEEE 802.3ae
•Ten-Gigabit Ethernet uses fiber optic cable over long distances and operates
in full duplex mode which means there is no need for contention;
•CSMA/CD is not used in Ten-Gigabit Ethernet.
•Make it compatible with Standard, Fast, and Gigabit Ethernet
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Ethernet advantages
1.
2.
3.
simple and flexible
reliable
cheap


4.
easy to maintain


5.
twisted pair wiring is relatively inexpensive
interface cards are low cost
no software to install (other than drivers)
no configuration table to manage
interworks easily with TCP/IP


IP is a connectionless protocol, so fits perfectly with
Ethernet
IP fits much less well with ATM, which is connection
oriented
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Summary
UTP - unshielded twisted-pair cable
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Summary
Table 13.1 Summary of Standard Ethernet implementations
Table 13.2 Summary of Fast Ethernet implementations
Table 13.3 Summary of Gigabit Ethernet implementations
Table 13.4 Summary of Ten-Gigabit Ethernet implementations Standard IEEE 802.3ae
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