Download Business Data Communications and Networking

Chapter 6
Local Area Networks
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Outline
Introduction
Ethernet
Switched Ethernet
Wireless Ethernet
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Discussion Questions
What are the components for a small LAN?
What is topology?
What is CSMA/CD?
How to improve the performance of a LAN?
Compare and contrast 10Base-2, 10Base-5,
10-Base-T, 100Base-T, 1GbE, 10 GbE and 40
GbE.
What is “hidden node” problem in Wireless
LAN and how to solve it?
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Networking Experiment
Networking schemes



Construct a LAN with a hub
Construct a LAN with a router
Network two PCs directly
Questions



What is the network topology?
What parameter do we need to set up the
network?
What features does the router provide?
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Dedicated Server LANs
A dedicated server LAN has one or more
computers that are permanently
assigned to being the network
server(s).
In a dedicated server LAN, the server’s
usual operating system is replaced by a
network operating system.
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Peer-to-Peer Networks
Do not require a dedicated server
Have less capability
Support a more limited number of
computers
 Provide less sophisticated software
 More difficult to manage than dedicated
server LANs.

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LAN Components
There are five basic components to a LAN
Client
Server
Network Interface Cards
Network Cables and Hubs
Network Operating Systems
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LAN Components
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Network Interface Cards
Network Interface Card (NIC)
Allows the computer to be physically
connected to the network cable, which
provides the physical layer connection among
computers in the network. Most NICs are
installed inside the computer.
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Network Cable
Unshielded twisted pair (UTP) wire
Shielded twisted pair (STP)
Coaxial cable
Fiber optic cable.
Many LANs use a combination of shielded
and unshielded twisted pair.
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Network Cable
Name
Type
Mbps Dist(m)
Used by
------------------------------------------------------------------------Cat 1
UTP
1
90
Modem
Cat 2
UTP
4
90
Token Ring-4
Cat 3
UTP
10
100 10Base-T Ethernet
Cat 4
STP
16
100 Token Ring-16
Cat 5
UTP
100 200 100Base-T Ethernet
Cat 5
STP
100 200 100Base-T Ethernet
RG-58
Coax
10
185 10Base-2 Ethernet
RG-8
Coax
10
500 10Base-5 Ethernet
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Network Hubs
Serve two purposes:


Provide an easy way to connect network cables
and expand a network.
Act as repeaters or amplifiers to prevent
attenuation.
Some hubs are “smart”, because they can
detect and respond to network problems.
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Network Operating Systems
Definition: The software that controls the
network.
Every NOS provides two sets of software:
one that runs the network server(s), and
one that runs on the network client(s).
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Network Operating Systems
The server version
Enables the file server, printer server, database server to operate.
Usually the computer’s own operating system.
Typically replaced the normal operating system on the server
Examples: Windows NT Server, NetWare
The client version
Provides the data link and the network layer
Must interact with the application layers and the computer’s own
operating system.
Examples: Windows NT Workstation, Window 98
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LAN Technology in A Layered
Model
Application Layer
Applications, such as http. Ftp,
email, etc.
Transport Layer
Network Layer
NT network (TCP/IP)
Novell NetWare (IPX/SPX)
Data Link Layer
Ethernet, Token Ring, ARCNET,
Wireless LAN (IEEE 802.11), AppleTalk
Physical Layer
Network Interface Card, cabling, hub, etc.
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Ethernet (IEEE 802.3)
The Ethernet LAN standard was originally
developed by DEC, Xerox, and Intel, but
has since become a formalized standard
by the Institute of Electrical and
Electronics Engineers as IEEE 802.3
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Topology
Topology is the basic geometric layout of the network
-- the way in which the computers on the network
are interconnected.
Two kinds of topologies:


Physical – cable scheme
Logical – data flow
Topologies




Bus
Star
Tree
Ring
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Ethernet Topology
Ethernet uses a bus topology (a high speed circuit and
a limited distance between the computers, such as
within one building).
From the outside, an ethernet LAN appears to be a star,
because all cables connect to the central hub.
Most ethernet LANs span sufficient distance to require
several hubs, but some ethernet LANs are build
without the use of hubs (coax bus).
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Media Access Control
Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
Wait until the bus is free and then transmit.
If no collision, transmission is completed.
If the collision is detected, send a jamming signal.
Wait a random amount of time, then re-broadcast.
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Types of Ethernet
10BASE-T (10 Mbps)

Uses a twisted-pair cable with maximum distance of 100 meters
100BASE-T (100Mbps)

Based on 10Base-T standard, 10 times faster
Three new types of Ethernet. They can use Ethernet traditional
half-duplex approach, but most are configured to use fullduplex. Also they can run over fiber-optic cables.



1000Base-T Ethernet, sometimes is called 1 GbE.
10 GbE
40 GbE
Some old Ethernet standards:


10Base-5 (Thicknet), using thick coaxial cable, 500M
10Base-2 (Thinnet/Cheapnet), using RG-58 coaxial able, 185M
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100Base-T Ethernet (IEEE
802.13)
It gives a 100 Mbps data rate using the standard
Ethernet bus topology, data link packets and
CSMA/CD media access protocol.
Three versions of 100Base-X differing only at the
physical layer:



100BaseTX uses cat 5 UTP
100BaseFX uses fiber optic cable
100BaseT4 uses 4 sets of cat 3 UTP (inverse
multiplexed)
100Base-T Ethernet can co-exist with 10Base-T
Ethernet.
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Wireless LANs (IEEE802.11)
Wireless LANs are growing very rapidly. Wireless
LANs transmit data through the air (space) rather
than through wire or cable.
New terms:


WLAN (Wireless LAN)
LAW (Local Area Wireless Network)
IEEE 802.11 standard is likely to be the dominant
standard for wireless LAN
It is easy to connect wireless LANs to Ethernet. So, it
is usually called wireless Ethernet
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Wireless LANs (IEEE802.11)
Topology. The same as traditional Ethernet. It is both
a physical star and a logical bus.

A central wireless access point (AP) is a radio transceiver
that plays the role of hub. The maximum range is 100-500
feet depending on interference
Wireless LANs use CSMA/CA (Carrier Sense Media
Access with Collision Avoidance) similar to CSMA/CD
by Ethernet. Two methods are simultaneously used:


Physical carrier sense method. Packets are sent using stopand-wait ARQ. Receiver waits less time to send ACK than
other computers waiting for available time slots.
Virtual carrier sense method. Using AP, hidden node problem
must be solved. It is optional.
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Hidden Node Problem
When one computer transmits packets, a computer in another
side of AP may not detect the signal and send packets as well.
This causes collision at AP.
So, AP is the only device that is able to communicate with both
computers. To solve the problem, AP uses controlled access
method instead of the contention based method. A computer
wanting to send packets must send a request (RTS) to AP. If no
other computer is using the circuit, AP will respond with a clear
to transmit (CTS) specifying the amount of time for the circuit
reserved for the computer.
All other computers hear the CTS and remain silent for the
specified time period.
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Hidden node problem
?
Access
Point
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Types of Wireless Ethernet
IEEE 802.11b. Two basic forms:
IEEE 802.11a. Expected to run at 5 GHz. Takes more time to be
develop. Products became available now (D-Link)
IEEE 802.11g. Speed is five times of 11b with the same
frequency – 2.4GHz, up to 54Mbps (Linksys WRT54G, D-Link
DWL-2000AP)
Other type of wireless LANs:

Infrared wireless LAN. Less flexible because most require direct line
of sight between transmitters and receivers.
 The primary advantage: the reduction of wiring.
 The primary disadvantage: the low speed (1-4 Mbps).

Bluetooth. Provide seamless networking of devices in a very small
area (up to 30 feet)
 Small, cheap
 Called Piconet with no more than 8 devices
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IEEE 802.11b
Two basic forms:


Direct-sequence spread-spectrum (DSSS), in 2.4 GHz band.
Transmits signals through a wide spectrum of radio
frequencies simultaneously. The signal is divided into many
different parts and sent on different frequencies. 1, 2, 5.5,
11 Mbps speeds. 20 Mbps version is in the way out.
Frequency-hopping spread-spectrum (FHSS). Uses the same
band, but once each frequency in turn. Sender and receiver
synchronize in a frequency. So, minimizes jamming and
eavesdropping. 1 Mbps and 2 Mbps.
They are shared media implementation. As the
number of devices increases the speed will be
reduced.
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*IEEE LAN Standards
IEEE 802.2: Logic link control (LLC) layer of data link layer
IEEE 802.3: Ethernet
IEEE 802.4: Token bus, an old protocol
IEEE 802.5: Token ring
IEEE 802.6: Distributed queue dual bus (DQDB) protocol, similar
to FDDI
IEEE 802.9: Integrated voice and data networking, including
ISDN, Iso-ethernet
IEEE 802.12: 100Base-VG
IEEE 802.13: 100Base-X
IEEE 802.16
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Improving LAN Performance
Why: When most computers in an organization
are on LANs, performance can be a problem.
How: In order to improve performance, you
must locate the bottleneck, the part of the
network that is restricting the data flow.
Generally speaking, this bottleneck is in one of
two places:


The network server
The network circuit
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Improving LAN Performance
Step one:
Identify Where the bottleneck lies
If in the server The server utilization during periods of poor
performance is high (60-100%).
If in the network circuit The server utilization during periods of poor
performance is low (10-40%).
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Improving LAN Performance
Step two:
Applying the following solutions:
Solution 1 - Increase Server Performance
Solution 2 - Increase Circuit Capacity
Solution 3 - Reduce Network Demand
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Tiered LANs
Cost of attachment to a LAN tends to
increase with data rate
Alternative to connecting all devices is
to have multiple tiers
Multiple advantages



Higher reliability
Greater capacity (less saturation)
Better distribution of costs based on need
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Tiered LAN Diagram
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*NetBIOS vs. NetBEUI
NetBIOS has 18 commands for PC
connections.
NetBEUI adds 8 more and is used as a
transport protocol. It is faster and more
efficient than NetBIOS
When NetBEUI is in use, NETBIOS becomes
API that invokes NetBeui.
They can support a LAN with less than 200
PCs.
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*Windows Network Model
Windows Network Model
Internet Model
Application layer:
I/O
Named Pipes Mail Server
Environment Subsystem
FTP, TELNET,
HTTP, etc.
Transport layer:
TCP, UDP
Network layer: IP
Data link layer
Physical layer
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Layer 7
Layer 6
Provider Interface
NetBIOS (Redirector)
TDI
NetBEUI
WINSOCK
Layer 5
Layer 4
TCP/IP
Layer 3
NDIS 3.0
NDIS Environment
and Drivers
Layer 2
Layer 1
802.2 802.3 802.4 802.5
NDIS: Network Driver Interface Specification
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*NDIS
NDIS (Network Driver Interface
Specification) is a Windows specification
for how communication protocol
programs (such as TCP/IP) and network
device drivers should communicate with
each other.
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*NetBIOS
NetBIOS (Network Basic Input/Output
System)
Created by IBM for its early PC Network, was adopted
by Microsoft, and has since become a de facto industry
standard.
A program that allows applications on different
computers to communicate within a local area network
(LAN).
Used in Ethernet, token ring, and Windows NT
networks.
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*NetBEUI
NetBEUI (NetBIOS Extended User
Interface)
Developed by IBM for its LAN Manager product and
has been adopted by Microsoft for its Windows NT,
LAN Manager, and Windows for Workgroups
products.
A new, extended version of NetBIOS, the program
that lets computers communicate within a local area
network.
Formalizes the frame format (or arrangement of
information in a data transmission) that was not
specified as part of NetBIOS.
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*NetBIOS over TCP/IP
NetBIOS over TCP/IP runs over the TCP/IP, so that you
can share drives and printers over the Internet.
In the "Network" configuration window in Windows 95,
there is no option for NetBIOS over TCP/IP, but a
"NetBEUI" entry, with which Microsoft actually means
NetBIOS over NetBEUI.
With the installation of TCP/IP protocol, Windows
automatically installs the "NetBIOS over TCP/IP”.
If you do want the TCP/IP protocol, but not "NetBIOS
over TCP/IP" (because of security problem), you should
uncheck "Files and Printer Sharing" in the Bindings tab
of the TCP/IP entry in Network Configuration.
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