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Data Communications and Computer Networks IS 370

Instructor: Dr. Mohammed Alnuem Copyright Notice: Some parts of this presentation, including figures, are either directly quoted or adapted from the PowerPoint presentation for educators provided by “Tanenbaum , computer networks 4th edition” . Other references include: presentation provided by Mr. Mourad Benchikh, IS dept., CCIS, KSU. Data communications and Networking by Behrouz A Forouzan.

Introduction to Computer Networks

IS370 - Dr.Mohammed Alnuem

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What is a computer network? • Old models: one big computer serves all company’s seeds. • This has been replaced with large set of smaller computers interconnected via a computer network. • In this course we will study the definition, use, and design of such networks. IS370 - Dr.Mohammed Alnuem

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What we use computer networks for? • Business applications. – Resource sharing (Printers, CD, Files) – Tele Data communication between different branches (email). – Client-Server model (Servers to store company information). – E-commerce, doing business electronically.


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What we use computer networks for? • Home applications. – Remote access to information (e.g. Newspapers) – Direct communication between people (MSN, P2P). – Entertainment (specially Interactive like online games) – Buying ,selling over the Internet (Ecommerce). • • • •

B2C B2B G2C C2C IS370 - Dr.Mohammed Alnuem

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What we use computer networks for? • Mobile applications. – Mobile Office (e.g. using a notebook with 3g connection ). Sending email, files..etc. while moving. – Wireless network in the university (you can check email or surf the web from anywhere) – Some companies prefer to use wireless network in instead of installing a wired network (e.g. in old buildings). – Wireless Application Portable (WAP1&2) found to allow web surfing using mobile devices. – m-commerce (Mobile commerce). Emerged with the increase of using mobile and wireless networks. (e.g. mobile banking). – Wireless sensors. (e.g. weather reports) IS370 - Dr.Mohammed Alnuem

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What we use computer networks for? • Social Aspects – Who controls the network content (the users or the network operator).

• Any other types of applications? • (Government, , Military..etc.)


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Computer networks types • First let us start with basic definitions • Packet :is the name of the message in a computer network. Data are sent from source computer to destination computer using packets. • Network Topology : Network shape or organization. • Mbps : measurement of network speed (megabits/seconds) or how much data the link can transform per second. IS370 - Dr.Mohammed Alnuem

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Computer networks types Communication techniques • Broadcast networks. – Single communication channel. – All computers hear the message but only one/some accept it. – Example flight announcement at an airport (All passengers hear the announcement but only those in the flight will accept/respond to it). – Broadcast: when all machines are actually the receivers, so all of them should accept the message. This can be implemented by setting a bit in the address filed of the message (Packet). – Multicast: Group communication. When the message should go the machines in subscribed to the group and not other machines even if they are connected to the same communication link. The packet (message) should hold the group number so that only machines in the same group will process the message. IS370 - Dr.Mohammed Alnuem

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Computer networks types Communication techniques

• Point to point networks. – Unicast: Unicaset communication is the most common form of communication in today’s networks. Unicast communication happens when the sender sends a packet that carries the address of the destination machine (usually IP address). No other machine will process this packet and the packet will pass through many intermediate machines called routers. This like usual mail where the letter is addressed to one mail box, however it may go through several mail sorting centers on the way to the destination. IS370 - Dr.Mohammed Alnuem

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Computer networks types Network Hardware

• Local Area Networks (LANs). – Usually private (in home, small company or college). – Used for sharing resources (files, printers, etc..) – Usually small in size high speed (10Mbps to 10Gbps). Mbps: Megabits/second. Gbps: gigabits/second.


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Computer networks types Network Hardware – Can take different topologies (i.e. network shapes, configurations) like: • Bus topology: only one machine is allowed to send. If two or more machines tried to send at the same time a conflict occur. Ethernet (IEE 802.3). is a standard used to resolve the conflict. After each conflict each machine waits a random time and then tries to send again. A conflict is recognized when a packet is received corrupted. This type is a called also dynamic allocation. IS370 - Dr.Mohammed Alnuem

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Computer networks types Network Hardware • Ring topology: Only the machine which has a token can transmit. This type is called also static allocation.


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Computer networks types Network Hardware • Metropolitan Area Networks (MANs). – Cover bigger areas like cities. – MANs can be wireless. Exp. Wireless MANs or WiMAX (IEEE 802.16).


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• Wide Area Networks (WANs). – Covers large geographic areas like country or continent. – Two main components: Hosts and Subnets. – Hosts: usually are end users. – Subnets: have mainly two components: Links and Switching Elements (Routers). IS370 - Dr.Mohammed Alnuem

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Source: http://www.technologyuk.net/networks/wide_area_networks.html

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Wireless and Mobile networks • Not new : 1901 Morse code sent from a ship. • Categories of wireless networks: • System interconnection: Exp. wireless mouse, W.Keyboard.. etc • Wireless LANs: Exp. College wireless LAN (IEEE 802.11). • Wireless WANs: Exp. Mobile 3G data networks and WiMAX .

Network Software Protocol Hierarchies

Protocol Hierarchies • Networks built as stack of layers. • Each layer has a different function. • There is an interface between each two layers which make possible their communication. • Each layer should be able to receive information from adjacent layer without knowing how actually they work. • A peer on one machine (layer n) communicate to other peer on another machine but both should be on the same layer (i.e. both should be on layer n). • Peers should follow a specific Protocol in order to communicate.

Protocol Hierarchies (3)

• Example information flow supporting virtual communication in layer 5.

Protocol Hierarchies • The set of layers and protocols are called Network Architecture. • Example “see. Tanenbaum, P 30,31”: Layer 5 want to transmit message M and give it to layer 4 for transmission. Layer 4 then adds a header in front of the message to identify the message and passes it to layer 3. The header includes control information, such as sequence numbers, to allow layer 4 on the destination to deliver messages in the right order if the lower layers do not maintain sequence. In some layers, headers can also contain sizes, times, and other control fields.

Protocol Hierarchies • Layer 3 break the messages into smaller parts (packets) because of size limitations and adds header to each packet. In this example, M is split into two parts, M1 and M2. • Layer 3 choose the outgoing lines to use and passes the packets to layer 2. • Layer 2 a header and a trailer, and gives the resulting unit to layer 1 for physical transmission. • When the message reaches the receiver it moves upward, from layer to layer, with headers being removed at each layer so that no headers for layer n will go up to layer n+1.

Connection-Oriented and Connectionless Services • Connection oriented: more reliable but may introduce overhead. Exp. The sender requires acknowledgment from the receiver. • Connection less: no acknowledgment is required (so no over head). But less reliable (if packet is lost the sender may not know).

Service Primitives

• Five service primitives for implementing a simple connection-oriented service.

Service Primitives (2)

• Packets sent in a simple client-server interaction on a connection-oriented network.

Services to Protocols Relationship • Services: operations provided by each layer in the same machine.. • Protocol: rules of communication between layers in different machines.

The OSI reference model.

The TCP/IP reference model

Examples • Protocols and networks in the TCP/IP model initially.

Physical Layer

Source: http://www.uapconex.co.cc/category/computer

Physical Layer • Physical Layer : is used to move bits from one machine in the network (node) to the next one over a physical medium . • Usually the machines are in the same network. • Defines the characteristics of the interface between the devices and the transmission medium. • Defines the type of transmission medium. • Defines the encoding technique for bits into either electronic or optical signals. • Defines sending rate, number of bits per second. • Configure host-to-host synchronization. • Defines network topology (bus, ring, etc.) • Defines the transmission direction (duplex, half-duplex or simplex).

Data Link Layer Physical Addressing

Source:http://p-hardware.blogspot.com/2008/04/network-card.html

Data Link Layer • Moves frames (not bits) between hops. • Maintains the physical addressing (MAC address). • Divides the stream of bits received from the physical layer into frames. • Responsible for moving frames between machines if they are in same networks. • Flow Control: is used to prevent fast machines from overflowing slower machines. Data link layer apply a flow control to prevent overflowing the receiver. • Detects damaged and duplicate frames. • Medium Access Control (MAC): part of the data link layer. Controls the link sharing when more than one device are sharing the same link.

Network Layer

Source: http://www.oreillynet.com/pub/a/network/2001/04/13/net_2nd_lang.html

Network Layer • Delivers packets from one host to another specially if they are in different networks. • Source-to-Destination communication. • Responsible for routing packet between different networks. • Responsible to allow heterogeneous network to be interconnected.

Transport Layer

Transport Layer •Delivers packets from one program (process) in one host to another program in another host process-to-process communication. •Uses another address (port address) to deliver message to the destination program. • Messages in transport layer are divided into segments. •Provides both reliable (connection oriented) and non-reliable (connection less) services. •Connection oriented service are provided through protocols like TCP (Transmission Control Protocol). •Connection less services are provided through protocol like UDP (Used Datagram Protocol). •Provides end-to-end flow control. •Provides end-to-end error control. •Error control make sure that packet are received undamaged and there are no duplications.

Session Layer • Dialog control : Who is next to transmit. • Token Management: prevent two processes from entering critical operation at the same time. • Synchronization/Check pointing: allow long transmission to continue from where they stop.

Presentation Layer • Responsible of the Syntax (structure and representation of data) and Semantics (the meanings) of information. •Solve issues of different syntax and Semantics between different machines. Exp: one byte may means one thing on Mac Os while it means another thing on WindowsXP.

Summary

Source: Mr. Mourad Benchikh presentation.