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IT305: Computer NetworksLecture 0: Course Overview

Lecturer DetailsDr. Walid KhedrEmail: khedrw@yahoo.comWeb: www.staff.zu.edu.eg/wkhedrDepartment of Information TechnologyCourse InfoCourse Name: Computer NetworksCourse Number: IT305Course Group: www.facebook.com/groups/it300305Office Hours: 11 am 12 pm, ThursdayTools: Cisco Packet Tracer 6 simulator, Wireshark 1.1 protocol analyzerPrerequisite: CS260 (Operating Systems)Course Materials:Text BookLecture Notes

Grading PolicyYour final grade will be calculated as follows: Term Work: Assignments / Homework / Quizzes / Midterm exam (20 points)Lab Exams (20 points)Oral Exam, Attendance and Participation (20 points)How to participate?Ask questionsAnswer questionsMake commentsTotal is 150 points

Grading RulesFinal exam is cancelled if attendance < %75If final exam grade is less than %30, your final grade will be just your final exam grade.What is Computer NetworkA computer network or data network is a telecommunications network which allows computers to exchange data. In computer networks, networked computing devices exchange data with each other along network links (data connections). The connections between nodes are established using either cable media or wireless media. The best-known computer network is the Internet.Why computer networks is importantAmong all of the essentials for human existence is the need to interact with others.Communication is almost as important to us as our reliance on air, water, food.The creation and interconnection of robust Data Networks is having a profound effect.

Why computer networks is importantCurrent data networks have evolved to carry voice, video streams, text, and graphics between many different types of devices

CommunicationBefore beginning to communicate with each other, we establish rules or agreements to govern the conversation.An identified sender and receiverAgreed upon method of communicating (face-to-face, telephone, letter)Common language and grammarThe Elements of Digital CommunicationMessage sources devices that need to send a message to devices.A channel, consists of the media that provides the pathway over which the message can travel from source to destination.Messages can be sent across a network by first converting them into binary digits, or bits. These bits are then encoded into a signal that can be transmitted over the appropriate medium.

The Elements of Digital Communication

The Elements of Digital Communication

The Elements of Digital Communication

The Elements of Digital Communication

The Elements of Digital Communication

The Elements of Digital Communication

The Elements of Digital Communication

The Elements of a NetworkDevicesThese are used to communicate with one anotherMediumThis is how the devices are connected togetherMessagesInformation that travels over the mediumRulesGoverns how messages flow across network

The Elements of a NetworkNetwork HardwareNetwork Software

Network HardwareNetwork edge:hosts: clients and serversservers often in data centersNetwork core: interconnected routersswitches

Network MediaCommunication across a network is carried on a medium3 types of Media:Metallic wires within cablesGlass or plastic fibers (fiber optic cable)Wireless transmission

21Network HardwareNetworks can be classified by their scale:ScaleTypeVicinityPAN (Personal Area Network) Building LAN (Local Area Network) CityMAN (Metropolitan Area Network) CountryWAN (Wide Area Network) PlanetThe Internet (network of all networks)An internetwork is any larger network made up of smaller component networks. The Internet (with a capital I) is the set of all connected networks.22Personal Area NetworkConnect devices over the range of a personExample of a Bluetooth (wireless) PAN:

Local Area NetworksConnect devices in a home or office buildingCalled enterprise network in a company

Wireless LAN with 802.11

Wired LAN withswitched EthernetMetropolitan Area NetworksConnect devices over a metropolitan areaExample MAN based on cable TV:

This is a common way in which home subscribers obtain access to the Internet in the US.25Connect devices over a countryExample WAN connecting three branch offices:

Wide Area Networks (1)The company probably leases the transmission lines (since most companies do not have their own lines).26Wide Area Networks (2)An ISP (Internet Service Provider) network is also a WAN.Customers buy connectivity from the ISP to use it.

Now the company/customer buys service from an ISP who uses its own lines to deliver packets.27Network SoftwareProtocol layers Service primitives Relationship of services to protocols Rules that Govern Communications (Protocols)Communication in networks is governed by pre-defined rules called protocols. These protocols are implemented in software and hardware that is loaded on each host and network deviceNetworking protocols suites describe processes such as: The format or structure of the messageHow and when error and system messages are passed between devices The setup and termination of data transfer sessionsProtocol Layers (1)Protocol layering is the main structuring method used to divide up network functionality.

Each protocol instance talks virtually to its peer Each layer communicates only by using the one below Lower layer services are accessed by an interface At bottom, messages are carried by the medium

30Protocol Layers (2)Example: the philosopher-translator-secretary architectureEach protocol at different layers serves a different purpose

Protocol Layers (3)Each lower layer adds its own header (with control inform-ation) to the message to transmit and removes it on receive

Why Using Layer ModelsTo visualize the interaction between various protocols, it is common to use a layered model.Benefits of doing so:Helps break down network function.Create standard for equipment manufacturing.Allows vendors to focus in specialized areas of the networkService Primitives (1)A service is provided to the layer above as primitivesHypothetical example of service primitives that may provide a reliable byte stream (connection-oriented) service:

Service Primitives (2)Hypothetical example of how these primitives may be used for a client-server interactionClientServerLISTEN (0)ACCEPT RECEIVESEND (4)DISCONNECT (6)CONNECT (1)SENDRECEIVEDISCONNECT (5)Connect requestAccept responseRequest for dataReplyDisconnectDisconnect(2)(3)The primitives are called at the client and server by the higher layer using the service. The layer implements the primitives by sending messages using the services of the lower layer; these messages are assumed to be reliable for simplicity and the lower layer service is not otherwise described.

This is similar to the way that simple Web browsers and Web servers work today.35Relationship of Services to ProtocolsRecap:A layer provides a service to the one above[vertical]A layer talks to its peer using a protocol [horizontal]

Reference ModelsReference models describe the layers in a network architecture

OSI reference model TCP/IP reference model Model used for this text OSI Reference ModelA principled, international standard, seven layer model to connect different systems

Provides functions needed by users Converts different representations Manages task dialogs Provides end-to-end delivery Sends packets over multiple links Sends frames of information Sends bits as signalsTCP/IP Reference ModelA four layer model derived from experimentation; omits some OSI layers and uses the IP as the network layer.

IP is the narrow waist of the InternetProtocols are shown in their respective layersThe comment about the narrow waist refers to the fact that the network layer of the Internet is IP (Internet Protocol) such that the network layer is called the Internet layer. The significance is that all Internet devices speak IP, which provides a point of interoperability that enables innovation both above (new applications and transports) and below (new link technologies).39Model Used in this BookIt is based on the TCP/IP model but we call out the physical layer and look beyond Internet protocols.

Protocol Data Units (PDU) and Encapsulation

41Protocol Data Units (PDU) and Encapsulation

The Process of Sending and Receiving (F2.4.6.1)

43Example NetworksThe Internet 3G mobile phone networks Wireless LANs RFID and sensor networks ContentsIntroductionpresents the basics of communication and how networks have changed our lives.Application Layer Functionality and Protocolsintroduces you to the top network model layer, the Application layer.Transport Layerintroduces you to the Transport LayerNetwork Layerintroduces the OSI Network layer.CCNA1 : Network Fundamentals ContentsData Link Layerdiscusses the services provided by Data Link layerPhysical Layer introduces the Physical layer

Offline Course Materials

Packet Tracer Simulation ToolA powerful network simulation program developed by Cisco that allows students to experiment with network behavior.

Wireshark 1.10Wireshark is the world's foremost network protocol analyzer, and is the standard across many industries and educational institutions.http://www.wireshark.org/

ReadingChapter 1 Download and study Packet Tracer 5.3 Next LectureChapter 1Questions