Chapter07 LAN Basic

8/3/2019 Chapter07 LAN Basic

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Data Communicationsand

Computer NetworksA Business Users Approach

Parviz KermaniPolytechnic UniversityParviz KermaniPolytechnic University

Chapter 7 Local Area Networks (LAN):

The Basics


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7- Local Area Networks (LAN): TheBasics

Polytechnic UniversityParviz Kermani 2

Acknowledgement

The original contents of this presentation wereprovided by the publisher, Course

Technology. Additional materials from othersources were added

William Stallings, Business Data Communications,

4th Edition, Prentice Hall publisher


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Objectives

State the definition of a local area network

List the primary function, activities, andapplication areas of a local area network

Cite the advantages and disadvantages of

local area networks

Identify the physical and logical topologies

of local area networks


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Objectives (continued)

Cite the characteristics of wireless local

area networks and their medium accesscontrol protocols

Specify the different medium access

control techniques Recognize the different IEEE 802 frame

formats Describe the common local area network

systems


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Introduction

Local area network - communication network

Interconnects a variety of data communicating

devices within a small geographic area Broadcasts data at high data transfer rates with very

low error rates.

Since the local area network first appeared inthe 1970s, its use has become widespread in

commercial and academic as well homeenvironments.


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Basic Characteristics of LANs

Small geographic area

Broadcast: transmission heard by all

High data rates

Low error rates


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Functions of a Local Area Network

Resource Sharing - To provide access to hardwareand software resources that will allow users to performone or more of the following activities

File server - A large storage disk drive that acts as a centralstorage repository.

Printer server - Provides the authorization to access aparticular printer, accept and queue print jobs, and provides auser access to the print queue to perform administrative duties.

Interconnection - A LAN can provide an interconnection toother systems, LANs, and to wide area networks.


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Functions of a Local Area Network

Video transfers - High speed LANs are capable ofsupporting video image and live video transfers.

Manufacturing support - LANs can supportmanufacturing and industrial environments.

Distributed processing - LANs can support networkoperating systems which perform the operations ofdistributed processing.

Academic support In classrooms, labs, and wireless.

E-mail support.


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Advantages of Local Area Networks

Ability to share hardware and softwareresources.

Individual workstation might survive networkfailure.

Component and system evolution are possible. Support for heterogeneous forms of hardware

and software.


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Advantages of Local Area Networks

Access to other LANs and WANs.

Private ownership.

Secure transfers at high speeds with low errorrates.

Di d t f L l A


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Disadvantages of Local AreaNetworks

Equipment and support can be costly.

Level of maintenance continues to grow.

Private ownership.

Some types of hardware may not interoperate.

Just because a LAN can support two differentkinds of packages (e.g. databases) does notmean their data can interchange easily.

A LAN is only as strong as it weakest link, andthere are many links.


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Basic Network Topologies

Stations on a local area networks are

interconnected using one of four basic

configurations:

1. Bus/tree

2. Star-wired bus3. Star-wired ring

4.

Wireless


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Bus/Tree Topology

The original topology


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Bus/Tree Topology

Workstation has a network interface card (NIC)that attaches to the bus (a coaxial cable) via a

tap.


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Bus/Tree Topology

Data can betransferred using

either baseband digital

signals

Bidirectional

broadband analogsignals

Unidirectional


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Bus/Tree Topology

Basebandsignals are bidirectional and moveoutward in both directions from the workstation

transmitting.


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Bus/Tree Topology

Broadbandsignals are usually unidirectionaland transmit in only one direction. Because of

this, special wiring considerations arenecessary.


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Bus/Tree Topology

In broadband topology, buses can be split and joined,creating trees.


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Advantages of Broadband LAN

Broadband signals easy to amplify

Network extends for 100s to 1000s of meters

Wide bandwidth: support for video and

radio signal transmissions

Multiple concurrent channels

Possible to split and join broadband

cables


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Disadvantages of Broadband LANs

More susceptible to noise

More expensive (than baseband)

Analog transmission

Long average propagation delay

Difficult to plan


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Star-wired Bus Topology

Logicallyoperates as a bus, but physically lookslike a star.

Star design is based on hub. All workstations attach to hub.


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Unshielded twisted pair usually used to connectworkstation to hub.

Hub takes incoming signal and immediatelybroadcasts it out all connected links.


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Hubs can be interconnected to extend size ofnetwork.


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Modular connectors and twisted pair

make installation and maintenance of

star-wired bus better than standard bus.

Hubs can be interconnected with twisted

pair, coaxial cable, or fiber optic cable. Biggest disadvantage(?): when one

station talks, everyone hears it. This is called a shared network. All devices

are sharing the network medium.


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Star-wired Ring Topology

Logically operates as aring

But physically appearsas a star


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Ring Topology

NIC operates as a repeater


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Ring Topology

Star ring topology is based on MAU (multi-station access unit) which functions similarly to

a hub.


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Ring Topology

Where a hub immediately broadcasts allincoming signals onto all connected links, the

MAU passes the signal around in a ring fashion.


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Ring Topology

Like hubs, MAUs can be interconnected toincrease network size.


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Wireless LANs

Not really a specific topology Workstation in a wireless LAN can be

anywhere as long as it is within transmittingdistance to an access point.

Newer IEEE 802.11 standard defines

various forms of wireless LANconnections.

Speed of 11/54 Mbps Speeds up to 20 Mbps available on other

technologies.


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Wireless LANs

Workstations reside within a basic service set,while multiple basic service sets create an

extended service set.


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Wireless LANs

Two basic componentsnecessary:

Client radio: usually a PCcard with an integratedantenna, and

Access point (AP): an

Ethernet port plus atransceiver

The AP acts as a bridgebetween the wired andwireless networks

Can perform basic routingfunctions.

Workstations with clientradio cards reside within abasic service set,

Multiple basic service setscreate an extendedservice set.


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Wireless LANs


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Wireless LANs

With directional antennae designed for

point-to-point transmission (rare), 802.11b

can work for more than 10 miles.

With an omni-directional antenna on a

typical AP, range may drop to as little as100 feet.

Distance is inversely proportional totransmission speed - as speed goes up,

distance goes down.


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Wireless LANs

In actual tests, 11 Mbps 802.11b devices

managed 5.5 Mbps (from a July 2000 test

by Network Computing).

To provide security, most systems use

Wired Equivalent Privacy (WEP), whichprovides either 40- or 128-bit keyprotection.

What will Bluetooths impact be on

802.11b?


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Other Wireless Standards

IEEE 802.11 (older 2 Mbps)

IEEE 802.11b (11 Mbps, 2.4 GHz)

IEEE 802.11a (54 Mbps, 5 GHz, in 2002)

IEEE 802.11g (54 Mbps, 2.4 GHz, in

2002), same frequency as 802.11b

Backward compatible

HiperLAN/2 (European standard, 54 Mbpsin 5 GHz band)


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Comparison of Technologies


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Peer-to-Peer LANs (Ad-Hoc Nets)

Wireless LANs may also be configured

without access point

These configurations are called ad-hoc

Not as common as server-based LANs

Most peer-to-peer LANs still use one ormore servers

Interesting collaborative-type applications(world-wide law firm)


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Medium Access Control Protocols

How does a workstation get its data onto

the LAN medium?

A medium access control protocol is the

software that allows workstations to

take turns at transmitting data. Three basic categories:

1. Contention-based protocols2. Round robin protocols (not in use)

3. Reservation protocols (not in use)


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Medium Access Protocols


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Contention-Based Protocols

Most common example is carrier sense multiple accesswith collision detection (CSMA/CD).

CSMA/CD protocol is based on the ALOHA protocol.


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If no one is transmitting, a workstation cantransmit.

If someone else is transmitting, the workstationbacks off and waits.


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If two workstationstransmit at the sametime, a collision occurs.

When the twoworkstations hear thecollision, they stoptransmitting immediately.

new packets

old packets

channel

Collision?

No

Yes

GS


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ALOHA Performance

Pure ALOHA:

Send the packet when it isgenerated

Period of vulnerability is 2time slots

Maximum efficiency= 18%

Slotted ALOHA

Time is slotted.

Stations can transmit onlyat the beginning of slots

Maximum efficiency= 36%


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ALOHA Performance


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Each workstation backs off a random

amount of time and tries again.

Hopefully, both workstations do not try

again at the exact same time.

CSMA/CD is an example of a non-deterministic protocol.


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Round Robin Protocols

Each workstation takes a turn transmitting Turn is passed around the network from workstation to

workstation.

Most common example is token ring LAN in which asoftware token is passed from workstation toworkstation.


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Token ring is an example of a deterministic protocol.

Token ring is more complex than CSMA/CD. What

happens if token is lost? Duplicated? Hogged? Token ring LANs are losing (have lost!) the battle with

CSMA/CD LANs.


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Reservation Protocols

Workstation places a reservation with centralserver.

Workstation cannot transmit until reservationcomes up.

Under light loads, this acts similar to CSMA/CD.

Under heavy loads, this acts similar to tokenring.

Though a powerful access method but again

losing out to CSMA/CD. Most common example of reservation protocol

is demand priority protocol.


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Medium Access Control Sublayer

Shortcoming of the OSI model for LANs

Routing at the network layer

Interdependence of physical & DLC layers

Need for medium access


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To better support local area networks, the datalink layer of the OSI model was broken into two

sublayers: Logical link control sublayer

Medium access control sublayer


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Medium access control sublayer defines the framelayout and is more closely tied to a specific medium atthe physical layer.

Thus, when people refer to LANs they often refer to itsMAC sublayer name, such as 10BaseT.


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IEEE 802 Frame Formats

The IEEE 802 suite of protocols defines

the frame formats for CSMA/CD (IEEE

802.3) and token ring (IEEE 802.5).

Each frame format describes how thedata package is formed.


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Note how the two frames are different. If

a CSMA/CD network connects to a token

ring network, the frames have to beconverted from one to another.


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LAN Systems: Ethernet

Also known as CSMA/CD.

Most common form of LAN today.

Star-wired bus is most common topology, butbus topology also available.

Ethernet comes in many forms dependingon

medium used

transmission speed

technology.


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Ethernet

Originally, CSMA/CD was 10 Mbps.

Then 100 Mbps was introduced. MostNICs sold today are 10/100 Mbps.

Then 1000 Mbps (1 Gbps) was

introduced. 10 Gbps is now beginning to appear.


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Ethernet

1000 Mbps introduces a few interesting

wrinkles:

Transmission is full duplex (separate transmitand receive), thus no collisions.

Prioritization is possible using 802.1pprotocol.

Topology can be star or mesh (for trunks).


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Ethernet

A few more interesting wrinkles:

Cabling can be either UTP or optical (but 10

Gbps Ethernet may not work over UTP dueto radio frequency interference).

Where 10 Mbps Ethernet has less than 30%utilization due to collisions, 1000 Mbps islimited only by traffic queueing.

Distance with 10 Mbps is limited byCSMA/CD propagation time, whereas 1000Mbps is limited only by media.


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Ethernet Standards


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Wired Ethernet (continued)

One of the latest features is power overEthernet (PoE)

What if you have a remote device that hasan Ethernet connection? It will require a power connection

What if you dont have an electrical outletnearby?

Use PoE Power to drive Ethernet NIC is sent over wiring

along with usual Ethernet signals


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LAN Systems: IBM Token Ring

Deterministic LANoffered at speeds of 4,16 and 100 Mbps.

Experimental 100Mbpsnever made it to market.

Very good throughput

under heavy loads. More expensive

components than

CSMA/CD. Losing (lost!) ground

quickly to CSMA/CD.


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LAN Systems: FDDI

Fiber Distributed Data Interface

Based on the token ring design using 100 Mbps fiberconnections.

Allows for two concentric rings - inner ring can supportdata travel in opposite direction or work as backup.

Token is attached to the outgoing packet, rather thanwaiting for the outgoing packet to circle the entire ring.


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FDDI Dual Ring Topology


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FDDI Reliability

Reconfigured dual-ring network.


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Wireless Ethernet

As we have already seen, IEEE hascreated the 802.11b, 802.11a, and

802.11g wireless standards IEEE 802.11n (100 Mbps) will be ratified

soon and should start appearing inproduct form in 2006 (maybe?)

Latest wireless Ethernet is using MIMO

technology (multiple input multiple output) Sender and receiver have multiple antennas

for optimum reception


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LAN Systems: 100VG-AnyLAN

Deterministic LAN based on demand

priority access method (IEEE 802.12).

Transmits data at 100 Mbps

Uses and supports Ethernet and TR

technologies (Any). Originally designed to run on category 3

(Voice Grade, VG) wires Category 5 is now the preferred cable

S G


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LAN Systems: 100VG-AnyLAN

Similar to hub topology (star design).

Similar to Token Ring, uses round robin

scheduling (enforced by the root hub)

Two levels of priority - normal and high.

Supports a wide-variety of media types.

Losing (has lost!) ground to CSMA/CD.

00VG A LAN T l


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100VG-AnyLAN Topology

LANs In Action : A Small OfficeS l i


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Solution

What type of system will interconnect

twenty workstations to a central server,

which offers: Electronic mail

A database that contains all customerinformation

Internet access

High quality printer access

LANs In Action : A Small OfficeS l i


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Solution

LANs In Action : A Small OfficeS l ti


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Solution



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Solution



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Solution

LANs In Action: A Home OfficeL l A N t k S l ti


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Local Area Network Solution

What if you have two computers at home and want bothto share a printer and a connection to the Internet.

Some type of network-in-a-box solution might solvethis problem.

Essentially a LAN with a 2- or 3-port hub, connectingcables, and software.

In some models, the hub also acts as a router to theInternet.

LANs In Action: A Home OfficeL l A N t k S l ti


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Local Area Network Solution

Wh t l d i thi h t


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What we learned in this chapter

State the definition of a local area network. List the primary function, activities, and application

areas of a local area network.

Cite the advantages and disadvantages of local areanetworks. Identify the physical and logical local area network

topologies. Cite the characteristics of wireless local area networks

and their medium access control protocols. Recognize the difference between client/server

networks and peer-to-peer networks. Specify the different medium access control techniques. Recognize the different IEEE 802 frame formats Describe the common local area network systems

Chapter07 LAN Basic

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