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EEE 448

Computer Networks

Lecture #1

Dept of Electrical and Electronics Engineering

Çukurova University

Why Learn about Networking?

• Indispensable part of modern society

– Commercial – e-commerce, banking, inventorying,

telecommunications, archiving, health

– Social – critical infrastructure, homeland security, policing

– Human interaction/communication – email, chat,

videoconferencing, social networking, entertainment

• Appears in every facet of engineering

– Modern trend – Network every (electronic) device (computers,

phones, sensors, planes, cars, TVs, appliances, heart monitors,

…)

• Prolific field to pursue graduate studies

– Many problems remain unsolved

– Research funding is still strong 2

What is this Course All About

• Principles of Computer Networks

• First course – Broad coverage of topics

(important topics in depth)

• Topics categorized to:

– network architectures - technologies

– protocols

– Applications in C#

• We will not discuss specific implementations:

e.g., how to configure the latest cisco routers

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Course Objectives • Develop a fundamental understanding of the network

design principles and performance metrics

• Become familiar with the mechanisms and protocols

for reliable data communication via a computer

network

• Be able to evaluate the performance of various network

technologies and protocols

• Think as an engineer: What technologies should be

employed to build a network with particular

specifications?

• Develop interest in performing research in the area of

Computer Networks 4

Topics to be covered

• Network architectures, performance metrics, layering

• Medium access control

• Internetworking, routing

• End-to-end protocols, flow control

• Congestion control and resource allocation

• Applications

• Network security 5

Course Logistics

• Textbook “Computer Networks: A Systems Approach”

L. Peterson, and B. Davie, 5th edition.

• Additional References “Data Networks”D. Bertsekas, and R. Gallager, 2nd edition

“Computer Networks”, S. Tanenbaum and D. Wetherall, 5th edition,

• Course Website :eembdersler.wordpress.com Lectures, Homework, Useful links,

Supplementary material, Announcements

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Where to find me

• My Office:

• EEE bldg: Room 305

• Office Hours by appointment

• My Email: turgayibrikci@hotmail.com

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When the class

• Monday

– EEE bld Computer Lab: Room 205

– 9:30 – 12:00 AM

• Thursday

– EEE Bld Computer Lab: Room 205

– 13:00 – 16:00 PM

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Class Expectations

• Class participation – Your input is needed for good discussion

• Keep up with reading material

• Present your presentation clean and understandable

• Submit clean, organized, concise and on time your project (back

of a flyer is not ok!)

• Identify potential project partner early (in one week, if possible)

• Brush up prior knowledge (Probability theory, C# Programming)

• Follow academic integrity code (Remember EEE117)

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Presentation: At least a 90 mins-presentation (How to use the time, to present the details, to answer the questions will be graded)

Midterm and Final Exam: will be setup by the department- Closed books and

materials

Grading Scheme

Assignment Points

Presentation 30% 40% of

Midterm 10% 40% of

Project 50% 60% of

Final Exam 10% 60% of

Total 100% 100

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DATA COMMUNICATIONS

•The term telecommunication means communication

at a distance.

•The word data refers to information presented in

whatever form is agreed upon by the parties creating

and using the data.

•Data communications are the exchange of data

between two devices via some form of transmission

medium such as a wire cable.

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Characteristics that define effectiveness of

data communications

• Delivery

• Accuracy

• Timeliness

• Jitter

A data communications system must transmit data

to the correct destination in an accurate and timely

manner.

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Five components of data communication

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Components of Data Communication System

• Message is the information (data) to be

communicated (text, numbers, images, audio, and

video).

• Sender is the device that sends the data message

(computer, mobile phone, video camera and so on).

• Receiver is the device that receives the message.

• Transmission medium is the physical path by which

a message travels from sender to receiver (twisted-

pare, coaxial, fiber-optic cables and radio waves).

• Protocol is an agreement between the communicating

devices on how communication is to proceed.

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Data flow modes

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Data flow modes

• Simplex as one-way street. Only one of the

two devices on a link can transmit; the other

can only transmit.

• Half-duplex, each station can both transmit,

but not at the same time.

• Full-duplex (or duplex), both stations can

transmit and receive simultaneously.

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Networks

• Computer Network is a collection of

devices (nodes) interconnected by a single

technology (transmission medium link).

• Node can be a computer, printer, or any other

device capable of sending and/or receiving

data generated by other nodes on the network.

• Interconnected computers are two or

more computers that able to exchange

information.

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Computer network example

Networks

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• Internet is the network of networks (connection of

two or more networks)

• Intranet is a private business network.

• Most networks use distributed processing, in

which a task is divided among multiple computers.

• Distributed System is a software system built on

top of a network.

• World Wide Web is a distributed system that runs

on top of the Internet.

Networks

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Networks criteria

• Performance can be measured in many ways, including:

1)Transit time (time required for a message to travel from one device to another);

2) Response time (elapsed time between inquiry and response).

Performance is often evaluated by two networking metrics:

Throughput and delay.

To enhance performance we need more throughput and less delay.

• Reliability is measured by :

1) accuracy of delivery;

2)frequency of failure;

3) time it takes a link recover from failure.

• Security include:

1) protecting data from unauthorized access;

2) protecting data from damage;

3) development recovery policies and procedures.

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Business Applications

- Resource Sharing (printers, scanners,

storage devices, and sharing information,

(client-server model))

- Communication Medium (E-mail)

- Being able to place orders in real time

(Purchase)

- E-Commerce, M-Commerce

Benefits of Computer Networks I

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Business Applications of Networks

A network with two clients and one server.

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Home Network Applications

- Access to remote information (e.g. Google)

- Person to person communication

- Using social networks (e.g. Facebook)

- Interactive entertainment

- E- commerce, M-Commerce

Benefits of Computer Networks II

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Network attributes: 1 - Types of connection

• Point-to-point

• Multipoint (or multidrop, e.g. broadcasting networks)

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Network attributes: 2 –Topology

The topology of the network is the geometric

representation of the relationship of all the links

and nodes to each other.

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Categories of networks

The most common classification of networks is based on its

physical size (scale).

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LAN is a network within a single building or

campus of up to a few kilometres in size.

LANs share the following characteristics:

- their transmission media

- their size (restricted small size)

- their topology (Bus, Ring, Star)

- their setting up cost is low

- Data transfer rate is high (10Mbps,

100Mbps, 10Gbps)

Local Area Network (LAN)

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LAN example

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A fully connected mesh topology (five devices)

We need n(n-1)/2 duplex-mode point-to-point links to connect n devices

LAN topologies: Mesh (1)

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LAN topologies: Mesh (2)

Advantages of mesh topology:

•Eliminating traffic problem (each link is dedicated to pair of devices);

•Robustness (break in one line does not lead to break of all network);

•Privacy and security;

•Fault identification and isolation is easy.

Disadvantages of mesh topology:

•Large amount of cabling and I/O ports are required;

•Wiring can be greater than available space;

•It is expensive.

Mesh mainly is used to connect servers of a hybrid topology

network that can include several other topologies.

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LAN topologies: Star (1)

Star topology uses point-to-point connections (station-hub).

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LAN topologies: Star (2)

In a Star topology, each station is directly connected to

a central controller – hub.

The hub acts as exchange: device sends data to hub,

which then relays the data to other device.

Advantages of star topology:

•Less expensive than mesh;

•Less cabling;

•Easy maintenance.

Disadvantages of star topology:

•One single point of failure – hub.

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An isolated LAN connecting 12 computers to a hub in a closet

LAN topologies: Star (3)

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LAN topologies: Bus (1)

Bus topology is multipoint. One large cable acts as a

backbone to link all devices in a network.

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LAN topologies: Bus (2)

In a bus topology, all stations are attached to a liner

transmission medium (bus) through appropriate hardware

interface (tap).

Advantages of star topology:

•easy to install;

•efficient use of wiring;

Disadvantages of bus topology:

•One single point of failure – backbone cable.

•Difficult maintenance.

IEEE 802.3 (Ethernet) is an example of bus topology.

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LAN topologies: Ring (1)

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In a Ring topology, each station on the network is connected to two

other stations, forming a loop or ring.

It uses token (signal circulating in a ring) to control transmission.

Advantages of ring topology:

•To add or delete a device requires changing only two

connections.

•Fault isolation is simplified

•No conflict in the transmission of data.

Disadvantages of ring topology:

- if one connection fails, the rest of the network will fail.

To avoid this a dual ring could be used.

IEEE 802.5 ( IBM Token Ring) & FDDI (Fiber Distributed Data

Interface) are examples.

LAN topologies: Ring (2)

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LAN topologies: Hybrid

A hybrid topology: a star backbone with three bus networks

Network topology • Advantages and Disadvantages of Network Topologies

Topology Advantages Disadvantages

Bus Cheap. Easy to install.

Difficult to reconfigure.

Break in bus disables entire network.

Star Cheap. Easy to install.

Easy to reconfigure.

Fault tolerant.

More expensive than bus.

Ring Efficient. Easy to install.

Reconfiguration difficult.

Very expensive.

Mesh Simplest. Most fault tolerant.

Reconfiguration extremely difficult.

Extremely expensive.

Very complex.

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MAN is a network with a size between a

LAN and a WAN. It normally covers a

city.

Examples of a MAN:

1) part of the telephone company

network that can provide a high-speed

DSL line to the customer;

2) cable TV network.

Metropolitan Area Network (MAN) (1)

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MAN based on cable TV

Metropolitan Area Network (MAN) (2)

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Relation between hosts on LANs and the subnet.

Wide Area Network (WAN) (1)

The main differences between WAN and LAN are:

- LAN is fully controlled by the owner whilst the WAN needs

the involvement of another authority like Telephone Company.

- The transfer rate of LAN is higher than the transfer rate of

WAN.

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WAN network spans a large geographical

area, it contains a collection of hosts that are

connected by a communication subnet.

Host is a machine that is used to run user

(i.e., application) program and is owned by the

customers.

Subnet consists of transmission lines and

switching elements, and its job is to carry

messages from host to host.

Wide Area Network (WAN) (2)

46 A stream of packets from sender to receiver.

Wide Area Network (WAN) (3)

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Subnet is typically owned and operated by a

telephone company or Internet service

provider.

Transmission lines move bits between

machines, they can be made of copper wire,

optical fiber, or even radio links.

Switching elements are specialized

computers that connect three or more

transmission lines and they called Routers.

Wide Area Network (WAN) (4)

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Wide Area Network (WAN) (5)

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- Users have a dream to connect their

notebooks to the network without having to be

plugged into a telephone wall socket.

- To achieve a true mobility there is a need

to use a radio (or infrared) signals for

communication.

Three main categories:

1- System interconnection

2- Wireless LANs

3- Wireless WANs

Wireless Networks (1)

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(a) Bluetooth configuration

(b) Wireless LAN

Wireless Networks (2)

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- System interconnection, it is about

interconnecting the components of a computer

using a short-range radio that uses the master-

slave paradigm.

Example:

- Bluetooth is a short-range wireless network

that allows digital components to connect to a

computer by merely being brought within range.

Wireless Networks (3)

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- Wireless LAN, it is a system where every

computer has a radio modem and antenna with

which it can communicate with other systems.

- Wireless LANs are used in small offices,

homes, older office building , conference rooms

and other places.

- IEEE 802.11 (WiFi) is a standard for wireless

LANs.

Wireless Networks (4)

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Wireless LAN

Wireless Networks (5)

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- Wireless WAN, it is similar to wireless LAN

system, but with lower bandwidth and is used in a

wide area systems.

- Three generations of Wireless WAN :

the first one was analog and for voice only

the second one was digital and for voice only

the third one is digital and for both voice and

data

- IEEE 802.16 (WiMAX) is a standard for

wireless WANs.

Wireless Networks (6)

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- Every device in the home will be capable of

communicating with every other device, and all of

them will be accessible over the Internet.

- Examples of devices that are capable of being

networked:

1- Computers (PC, Notebook, PDA)

2-Entertainment (TV, DVD, Camera...)

3-Telecommunications (telephone, intercom...)

4-Appliances (microwave, refrigerator, lights…)

5- Telemetry (smoke alarm, thermostat,

babycam…)

Home Networks

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Internetwork or internet is a collection of interconnected networks

that provides universal service among heterogeneous communication

networks.

Internetworks

A heterogeneous

network made of four

WANs and two LANs

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TCP/ IP is a protocol suite in the Internet.

The main Internet applications are:

E-mail, News, Remote Login, File transfer, World Wide

Web (WWW)

The Internet (1)

The Internet has revolutionized many aspects of our

daily lives. It has affected the way we do business as well as

the way we spend our leisure time. The Internet is a

communication system that has brought a wealth of

information to our fingertips and organized it for our use.

History of Internet:

Beginning in 1969. It was called ARPANET.

58 Hierarchical organization of the Internet

The Internet (2)

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- The Internet today is run by private companies, not the

government.

- The national Internet service providers are backbone

networks created and maintained by specialized companies.

- These backbone networks are connected by complex

switching stations (normally run by a third party) called

network access points (NAPs).

- Local ISPs can be connected to a regional or national

service provider.

- Most end users are connected to the local ISPs.

The Internet (3)

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The Internet (4)

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Networking Standards (1)

In this section, we define two widely used terms: protocols

and standards. First, we define protocol, which is

synonymous with rule. Then we discuss standards, which are

agreed-upon rules. A protocol is a set of rules that governs data communication;

the key elements of a protocol are syntax, semantics, and

timing.

- The term syntax refers to the structure or format of the data,

meaning the order in which they are presented.

- The word semantics refers to the meaning of each section

of bits. How is a particular pattern to be interpreted, and what

action is to be taken based on that interpretation?

- The term timing refers to two characteristics: when data

should be sent and how fast they can be sent. 62

Networking Standards (2)

Advantages of standards

• A standard assures that there will be a large market for

a particular piece of equipment or software.

• A standard allows products from multiple vendors to

communicate.

Disadvantages of standards

• A standard tends to freeze the technology.

• There are multiple standards for the same thing.

Standards are necessary to ensure that products from

different manufacturers can work together as expected.

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Networking Standards (3)

Standards are developed through the cooperation of standards

creation committees, forums, and government regulatory

agencies.

The ISO, ITU-T, ANSI, IEEE, and IETF are some of the

organizations involved in standards creation.

ISO - International Organization for Standardization

ITU-T - International Telecommunication Union-Telecommunication

Standards Sector

ANSI - American National Standards Institute

IEEE - Institute of Electrical and Electronics Engineers

IETF - Internet Engineering Task Force

- Forums are special-interest groups that quickly

evaluate and standardize new technologies.

- A Request for Comment (RFC) is an idea or concept

that is a originator to an Internet standard. 64

The 802 working groups. The important ones are marked with

*. The ones marked with are hibernating. The one marked

with † gave up.

Networking Standards (4)