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Introduction to Information Technology

LECTURE 9: COMPUTER NETWORKING

Local Area NetworksWide Area Networks

IT 101 Section 3 Department of Electrical and Computer Engineering

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Course Outline

Understanding terminology Examples of information systems Significance of digital technology

Module I

INTRODUCTION TO INFORMATION

SYSTEMS Representing numbers, text, images, and video in binary

Converting analog to digital

Module II

BINARY REPRESENTATION AND INFORMATION CODING

Module III Module IV

The phone system VoIP Transmission

Local area networks Wide area networks The Internet Network security

COMPUTER NETWORKING

Module V

TELECOMMUNICATIONS

History of computing

Computer system components

Computer software

COMPUTER ARCHITECTURE

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Computer Networking Questions

How is information transmitted from point A to point B?

What, physically, are the three basic types of communications media? Fiber, copper wire, and free space (Chapters 14-16)

What’s a LAN? What’s a WAN? (Chapters 18 and 19) How does the Internet work? (Chapters 2 and 20)

?

NEW TOPIC

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Local Area Network (LAN)

Spans a limited area such as a building Typically spans no more than a mile Varies from serving a few users to thousands of

users Usually serves a single organization Supports desktop computers, laptops, servers, personal

devices Allows access to many resources

Printers File Servers Internet Access Mainframe Storage

A LAN is a computer network that provides access to shared services in a limited area.

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LAN Speeds

LANs are very fast, moving data at speeds from 10 Mbps to Gbps+

Why so much faster than WAN speeds? A sizable percentage of computer communications (in

business) still occurs within a local environment Some estimate the percentage to be 80% versus 20% outside

LAN (?) Lower costs (ease of installation, shorter transmission

distances, etc.)

100 MbpsLAN

100 MbpsLAN

WAN Connection

Speeds: 56 Kbps

1.544 Mbps

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LAN Characteristics Requires very little wiring, typically with a single cable

connecting to each device Uses twisted pair, fiber, coax, or wireless

A NIC inside a computer attaches to the network wiring

Different types of LANs use different wiring configurations like “ring,” “bus,” and “star”

Software facilitating operation of the LAN Windows NT Server, Novell NetWare

Physical LAN equipment includes intelligent wiring hubs, bridges, LAN switches, routers

Different types of LANs use different “access methods”

Physical Medium

Topology

Network Operating System

(NOS)

Network Interface Card (NIC)

Access Control

LAN Equipment

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LAN Physical Building Blocks

Requires consistent and hierarchical wiring structures

Compliance with specs. Flexibility/modularity/reconfigurability! Spare capacity for growth Secured access

Physical Medium:Copper.. Fiber..

Conduit/inter-building

pathways

Wallplates/jacks

There’s a lot behind the walls.Wiring Closets:Cable terminationEquipment racks

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LAN Topologies

LAN Topology describes how the network is constructed and gives insight into its strengths and limitations

Bus Star Branching Tree Ring

Note: there’s a difference between “topology” and physically how the network is wired. For example, a single wire could extend from a hub to each computer in a star configuration, but still logically act as a “ring” because of how it’s connected at the hub. (Logical versus Physical topology)

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Bus Topology

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Star Topology

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Branching Tree

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Ring

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Access Control Methods

Like in a noisy room -- it’s difficult to communicate if every computer tries to simultaneously transmit

Two primary access control methods Non-Contentious Access: Token Access Contentious Access: Carrier Sense Multiple Access

with Collision Detection (CSMA/CD)

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Token-Based Access

Used in Bus and Ring topologies (e.g. Token Ring) A token is placed on the network and passed to each network

node The token consists of a specific bit pattern The computer in possession of the token may transmit information The message is sent to all other members of the network The member the message is addressed to “hears” the message

and all others ignore the message Once the information is delivered, the token is available for use

Deterministic Approach

A B C D E

T

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CSMA/CD Access

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

Usually used in a “bus” topology; Used in Ethernet LANs All stations can send whenever they have data to transmit First, a station listens to the network, if idle (that is, no one is

talking), data is transmitted But, it is possible for two stations to transmit simultaneously,

thinking that the channel is clear When this happens, a collision occurs The first station to detect a collision sends a special signal The stations in contention then wait a random time to again

attempt transmission Performance degrades as network traffic increases

Non-Deterministic

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CSMA/CD

A B C D

A B C D

A B C D

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Examples of LANs

Ethernet

Token Ring

FDDI

Topology?

Access Method?

Medium?

Speeds?

Cost?

Popularity?

Distance?

# Devices Supported?

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Ethernet

Developed by Xerox in 1976 (PARC - Palo Alto Research Center) Robert Metcalfe considered the inventor of Ethernet Eventually became an IEEE standard (IEEE 802.3)

Known as “10Base-T” Bus Topology CSMA/CD access method Medium - coaxial cable, twisted pair, fiber, or wireless

Originally used coax, now primarily over UTP Speeds range from 10 Mbps to Gigabit speeds

MOST POPULAR LAN IMPLEMENTATION

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Types of Ethernet LANs

Wireless (Mbps speed range) IEEE 802.11 2.4 GHz frequency range Also uses CSMA/CD access method

10Base-T (First digit is speed in Mbps; T means UTP) Operates at 10 Mbps IEEE 802.3

Fast Ethernet Operates at 100 Mbps Referred to as 100 Base-T Same IEEE 802.3 frame format, size, and error-detection

mechanism Gigabit Ethernet

1 Gbps Uses multimode fiber

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Ethernet Frame Structure

8 bytes

Preamble

6 bytes

Destination Address

6 bytes

Source Address

2 bytes

Type Field

4 bytes

Frame Check

Sequence

46 to 1500 bytes

Data

Ethernet is based on the datagram, or “frame”

Note the 26 bytes of “overhead”

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Ethernet Frame Structure

Preamble: Repeating Flag that IDs the sequence as an Ethernet frame (10101010 7 times followed by 10101011)

Destination Address: 6-byte address uniquely identifies the recipient (NIC) of the datagram

Source Address: 6-byte address that uniquely identifies the sender (NIC)

Type Field: 2-byte identifier of what kind of datagram is being received (IP, UDP, etc) and length of data

Data: Actual transmitted information (46 to 1500 bytes)

Frame Check Sequence: 4-byte field used for error detection

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Ethernet Concepts: Padding & Overhead

If a message has less than 46 bytes of data, “padding” is added

If only 42 bytes of data require transmission, 4 bytes of padding are added.

Bytes extraneous to the data we are interested in sending are called “overhead”

Ethernet has 26 bytes of overhead in each datagram (frame)

If you had 100 bytes of data to send, you’d have to send 126 bytes of data

How much overhead is transmitted within the 126 bytes of data?

26/126 = 21%

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Ethernet NIC

48 - bit unique address

Permanently attached to NIC

IEEE assigns addresses

Organizationally Unique Identifiers (OUIs)

Also known as MAC (Medium Access Control) Address

Represented in Hexadecimal e.g. 02608CBBDCA7

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Wireless LANs

What’s a WLAN? WLAN = Wireless Local Area Network Generic term for a LAN that uses radio frequency

communication rather than copper cables or fiber optic cables.

What are the pros and cons of WLANs?What’s Wi-FI??

2.4 GHz

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IN-CLASS DISCUSSION OF WIRELESS LANS

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Token Ring – IEEE 802.5

Developed by IBM in 1970s Token passing network Logical topology - ring Medium - UTP, STP Deterministic – possible to calculate the maximum time that will pass

before any end station will be able to transmit Usually 16 Mbps

A B C D ET

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Data – limited by ring token holding time Frame Check Sequence (FCS) End Delimiter – End of Frame Frame Status – 1 byte terminating a command/data frame

Token Ring – IEEE 802.5

Start Delimiter

1 byte

AccessControl1 byte

End Delimiter

1 byte

FrameControl1 byte

DestinationAddress6 bytes

SourceAddress6 bytes

Data>=0

FCS4 bytes

FrameStatus1 byte

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Fiber Distributed Data Interface – FDDI

Consists of a dual ring Uses the token passing access method Operates on Multimode fiber optic cable Achieves speeds of 100 Mbps Supports up to 1000 nodes Up to 200 km

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FDDI Frame

Preamble – 8 byte frame synchronization pattern Start Delimiter Frame Control Source and Destination Address Data Frame Check Sequence End Delimiter Frame Status

Preamble8 byte

StartDelimiter

1 byte

End Delimiter

1 byte

FrameControl1 byte

DestinationAddress6 bytes

SourceAddress6 bytes

Data>=0

FCS4 bytes

FrameStatus

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Campus Networks

Sometimes a LAN that operates over a “campus” or multi-building environment is referred to as a campus network.

Interconnects multiple LANs Is still privately operated and used by a single organization High speed networks like gigabit Ethernet are used in

campus networks.

A business housed in a multi-building, proximate setting would

install a “campus” network.

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Case Study - Designing the GMU Network

In-class, real world case study of designing a campus network.

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LAN Interconnection Devices

Repeater Bridge Router Gateway

It’s helpful to discuss these relative to the “OSI Model” What’s the OSI Model?

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The OSI Model

The Open Systems Interconnection (OSI) model is a theoretical framework for understanding and explaining networking protocols.

Originally an effort by the ISO (International Standards Organization) to standardize network protocols.

TCP/IP became the dominant set of standards but the OSI model is widely used to help understand protocols.

The OSI model defines 7 layers of functional communications protocols.

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The OSI Model

1. Physical Layer

2. Data Link Layer

3. Network Layer

4. Transport Layer

5. Session Layer

6. Presentation Layer

7. Application Layer

Provides a network interface for applications

Translates data to standard format

Establishes sessions between computers

Provides error control and flow control

Supports logical addressing and routing

Interfaces with network adapter

Converts information into transmitted pulses

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Repeater Regenerates and propagates all electrical transmissions

between 2 or more LAN segments Layer 1 of the “OSI model”

HigherLayers

Physical

HigherLayers

PhysicalPhysicalRepeater

Workstation A Workstation B

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Bridge

Connects 2 or more LAN segments and uses data link layer addresses to make data forwarding decisions

Layer 2

HigherLayers

Physical

HigherLayers

PhysicalPhysical 1

BridgeData Link

23-01-88-A8-77-45

Physical 2

Data Link Data Link

Workstation A Workstation B

Data Link53-F1-A4-AB-67-4F

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Router Connects 2 or more networks and uses network layer

addresses (like IP address) to make data forwarding decisions

HigherLayers

Physical

HigherLayers

PhysicalPhysical 1

Router

Data Link

Physical 2

Data Link Data Link

Workstation A Workstation B

Data Link

Network145.65.23.102

Network137.22.144.6 Network Network

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Gateway Connects 2 or more networks and provides protocol

conversion so that end devices with dissimilar protocol architectures can interoperate

Gateway

137.22.144.6

145.65.23.102

Netware

TCP/IP

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WANs A network spanning a large geographical area Connects internal company LANs; may connect business to other

businesses, suppliers, and customers Also called “Enterprise Networks” if they support communications for a

large organization Provided by a common carrier (AT&T, Sprint, MCI, etc) or several

carriers. Even large companies can’t afford to install high capacity circuits

everywhere in the world Companies lease service

Fiber Optic, Satellite, cable, microwave carries the service At capacities needed: T1, T2 (6.176 Mbps), T3 (44.736 Mbps),

OC1 (51.84 Mbps), OC192 (9,953.28 Mbps) From and to locations desired to implement the WAN WAN services include Internet, frame relay, ATM (Asynchronous

Transfer Mode)

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Example

Sprint

Network

LA

Runs a 100 Mbps LAN

DC

Runs a 1Gbps LAN

Sprint provisions a T-1 connection (1.544 Mbps) into their network

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What’s a T1? The T-Carrier System

Format is called DS1, carrier is called T1 24 channels (DS0 – 64kbps) multiplexed together Each channel – 8 bits

7 bit for data 1 bit for control

DS1 Frame is 193 bits every 125µsec = 1.544Mbps 24 x 8 bits = 192 bits 1 bit for frame synchronization – pattern 010101010101….

DS1 used for data Only 23 channels - data 24th channel – synchronization pattern

……Channel 1

Channel 2

Channel 2

Channel 24

Channel 23

Channel 22

Bit 1 is a framing code

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DS3 - What’s a T3?

44.736 Mbps 7 x DS2 672 DS0 T3

DS1

DS1

DS2

DS2

.

.

.

DS3

.

.

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Synchronous Optical Network - SONET

Bellcore-developed in 1985 International standard for high speed communication

over fiber-optic networks ANSI specification T1.105 Digital Hierarchy – Optical

Interface Rates & Formats Specification (SONET) Technical recommendations – Bellcore GR-253-CORE

Synchronous Optical Network (SONET) Transport Systems: Common Generic Criteria

Defines optical carrier (OC) and electrical equivalents Physical Layer 1 Benefit

Multiple vendors Requires Timing!!

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SONET Multiplexing

STS-1 = 51.840 Mbps Higher rates – combination of STS-1

STS-1A

STS1-C

STS-1B 3:1STS-3

C B A C B A

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Multiplexing

Why Multiplexing is needed? Transmission capacity of channel exceeds single-

signal needs Allows many simultaneous independent signals to

be carried by one transmission channel Many low-speed signals share one high-speed

channel Three types

Frequency Division Multiplexing (FDM) Time Division Multiplexing (TDM) Statistical Multiplexing (SMUX)

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Frequency Division Multiplexing (FDM)

Each signal on unique frequency

FDMMUX

Signal A

Signal B

Signal C

Signal A

Signal B

Signal C

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Time Division Multiplexing (TDM)

Each signal is assigned a recurring time slot Example: DS1, DS3

A

A

AA

AB B B B

C C

CTDMMUX

A B C B

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Statistical Multiplexing (SMUX)

TDM – slot wasted, inefficient for “bursty” data signals SMUX

Recurring slots are filled on an as-needed basis Added Overhead

A

A

AA

AB B B B

C C

CSTDMMUX

A B C Ba bc cb ba