By: Dr. N. Ioannides (Feb 2010)CT0004N - L.07 - Computer Networks - pp 1/52 Computer Networks Saroj Regmi Lecture 07 CT0004N Principles of Comms Systems.

By: Dr. N. Ioannides (Feb 2010) CT0004N - L.07 - Computer Networks - pp 1/52

Computer NetworksComputer Networks

Saroj RegmiSaroj Regmi

Lecture 07Lecture 07

CT0004NCT0004NPrinciples of Comms SystemsPrinciples of Comms Systems


Last Lecture: 06Last Lecture: 06Fibre Optic CommunicationsFibre Optic Communications

• Introduction to Optical Communications,

• Technological Developments,

• System & Data Link Considerations,

• System Components,

• Optical Fibre Principle of Operation,

• Types of Optical Fibre,

• Optical Fibre Transmission Characteristics,

• Wavelength Division Multiplexing.


Today’s Lecture: 07Today’s Lecture: 07Computer NetworksComputer Networks

• Computer Hardware Basics,

• Computer Software Basics,

• Computer Operating Systems,

• Computer Codes and Units,

• Digital Bandwidth,

• Networks,

• The ISO / OSI and TCP / IP Layered Models of Communication,

• Local Area Networks, Topologies & Devices,

• Wide Area Networks,

• Addressing.


The The ComputerComputer

• An important building block in a network.

• Small, Discrete Components:

Transistors, integrated circuits (IC), resistors, capacitors, connectors, light emitting diodes (LED), etc.

• Personal Computer Subsystems:

Printed circuit board (pcb), CD-ROM drive, CPU, floppy disk drive, hard disk drive, microprocessor, motherboard, bus, RAM, ROM, system unit, expansion slots, power supply, etc.

• Backplane Components:

Backplane, network card, video card, sound card, parallel port, serial port, mouse port, power cord, etc.

Computer Computer ComponentsComponents


Computer Hardware BasicsComputer Hardware Basics

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• Software describes the programs that are used to operate the computer system.

• A program is a sequence of instructions that describe how data is to be processed.

It instructs the computer on how to operate, i.e. identifying, accessing, and processing information.

Programs vary widely, depending on the type of information that is to be accessed or generated.

• There are two types of software:

Applications,

Operating Systems.

Computer Software BasicsComputer Software Basics


• Applications are programs designed to perform a specific function directly for the user or for another application program.

Examples: word processors, database programs, spreadsheets, web browsers, web development tools, graphic design tools, etc.

• Application Programs allow the completion of tasks.

Examples: writing a report, keeping track of clients, drawing a company logo, displaying web pages, and writing e-mail.

• Application software accepts input from the user and then manipulates it to achieve a result, known as the output.

Application SoftwareApplication Software


• An OS is a program that manages all the other programs in a computer.

Examples: Disk Operating System (DOS); Windows 98, 2000, XP and NT; Linux; Mac OS X; DEC VMS; IBM OS/400.

• OS are software programs that control thousands of operations, provide an interface between the user and the computer, and run applications.

They perform basic tasks like recognizing input from the keyboard or mouse, sending output to the video screen or printer, keeping track of files on the drives, and controlling peripherals.

Operating Systems (OS)Operating Systems (OS)


• Operating systems are platform-specific, i.e. they are designed for use with a specific type of computer. A platform is the computer system on which programs can run:

The Windows operating system (3.1, 95, 98, 2000, or NT) is designed for use with an IBM-compatible pc.

The Mac OS will only work with Macintosh computers.

Operating Systems (OS) (…2)Operating Systems (OS) (…2)


Computer CodesComputer Codes

0• What are computer codes made out of?

1


Number SystemsNumber Systems

Base 10 (Decimal)Base 10 (Decimal)

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Base 2 (Binary)Base 2 (Binary)


Conversion from Decimal To BinaryConversion from Decimal To Binary

• Method 1:

By Successive Halving, starting from the top and working downwards.

By Dividing the Decimal Number by 2.

For Integer Numbers Only.

Read the remainders starting from the bottom up.


• Method 2:

By Subtracting from the decimal number the largest power of 2 which is smaller than the decimal number.

• Example: Consider the decimal number 24.510:

24.510 = (1 × 16) + (1 × 8) + (0 × 4) + (0 × 2) + (0 × 1) + (1 × 0.5)

= (1 × 24) + (1 × 23) + (0 × 22) + (0 × 21) + (0 × 20) + (1 × 2-1)

24.510 = 11000.12

Conversion from Decimal To Binary (…2)Conversion from Decimal To Binary (…2)


Conversion from Binary To DecimalConversion from Binary To Decimal

• Method 1:

By successive doubling of each bit of the binary number starting from the least significant bit (LSB):


• Method 2:

By summing up the powers of 2 corresponding to the 1 bits in the binary number.

• Example: Consider the binary number 10110.12:

10110.12 = 1 × 24 + 0 × 23 + 1 × 22 + 1 × 21 + 0 × 20 + 1 × 2-1=

= 1 × 16 + 0 × 8 + 1 × 4 + 1 × 2 + 0 × 1 + 1 × 0.5 = 22.510

Conversion from Binary To Decimal (…2)Conversion from Binary To Decimal (…2)


ASCII ChartASCII Chart(American Standard Code for Information Interchange)(American Standard Code for Information Interchange)

• The binary number representation of many keyboard and control characters.

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BandwidthBandwidth

• Bandwidth is the term used to describe the AMOUNT of information which flows over a SPECIFIC period of time.

The amount is bits.

The specific period of time is the second.

• Bandwidth is the measure of how much information can flow from one place to another in a given amount of time.

Bits per second is a unit of bandwidth.

• The use of the term bandwidth is used to describe the capabilities of LANs and WANs.


The Importance of BandwidthThe Importance of Bandwidth

• BW is Finite,

• Can save money,

• A key measure of network design and performance,

• A key to understanding the Internet,

• Demand for BW increases constantly.


Units of BandwidthUnits of Bandwidth

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Units of InformationUnits of Information

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Multimedia Bandwidth RequirementsMultimedia Bandwidth Requirements

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Bandwidth & ThroughputBandwidth & Throughput

• Throughput is less or equal to the Digital Bandwidth of a Medium.

• The variables which affect throughput are:

The PC (client),

The Server,

Other users on your LAN,

Routing through the “Cloud”,

The design topology of all networks involved,

Type of data being transferred,

Time of day.


File Transfer Time CalculationsFile Transfer Time Calculations

• Best Download: T = S / BW

• Typical Download: T = S / P

Where:

BW: Maximum theoretical bandwidth of the slowest link between the source host and the destination host, measured in bits per second.

P: Actual throughput at the moment of transfer, measured in bits per second.

T: Time for file transfer to occur, measured in seconds.

S: File size in bits.


Network ExamplesNetwork Examples

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Data Network ProblemsData Network Problems

• Incompatibility.

• Inability to communicate with each other.

SolutionSolution

• The International Organisation for Standardization (ISO) researched network schemes like DECNET, SNA, and TCP/IP in order to find a set of rules.

It created a network model that would help vendors create networks that would be compatible and interoperable with other networks.

• The result was a multi-layered network model.

• The ISO / OSI 7 Layer Reference Model was released in 1984.


Application Layer (7):Application Layer (7): Provides Network Processes to Applications

• email, file transfer, terminal emulation.

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The ISO / OSI 7 Layer ModelThe ISO / OSI 7 Layer Model

Presentation Layer (6):Presentation Layer (6): Data Representation• Insure data is readable by receiving

system,• Format of data,• Data Structures,• Negotiates data transfer syntax for

application layer.

Session Layer (5):Session Layer (5): Interhost Communication• Establishes, manages and terminates

sessions between applications.


Transport Layer (4):Transport Layer (4): End-to-End Connections

• Concerned with transportation issues between hosts,

• Data transport reliability,• Establish, maintain terminate virtual

circuits.• Fault detection and recovery.• Information flow control.

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Network Layer (3):Network Layer (3): Address and Best Path• Provides connectivity and path selection

between two end systems,• Domain of routing.

The ISO / OSI 7 Layer Model (…2)The ISO / OSI 7 Layer Model (…2)


Data Link Layer (2):Data Link Layer (2): Access to Media• Provides reliable transfer of data across

media,• Physical addressing, network topology,

error notification, flow control.

Physical Layer (1):Physical Layer (1): Binary Transmission• Wires, connectors, voltages, data rates.

The ISO / OSI 7 Layer Model (…3)The ISO / OSI 7 Layer Model (…3)


Peer-to-Peer CommunicationsPeer-to-Peer Communications

• Each layer uses its own layer protocol to communicate with its peer layer in another system.

• Each layer's protocol exchanges information, called Protocol Data Units (PDUs), with its peer layers.

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Data EncapsulationData Encapsulation

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• The process of packaging the data prior to transmission.

• Encapsulation wraps data with the necessary protocol information before network transit.

• As the data packet moves down through the layers of the OSI model, it receives headers, trailers, and other information.


Data Encapsulation ExampleData Encapsulation Example

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Local Area Networks (LANs)Local Area Networks (LANs)

• LANs are high-speed, low-error data networks that cover a relatively small geographic area (up to a few thousand meters).

• Connect workstations, peripherals, terminals, and other devices in a single building or other geographically limited areas.

• Provide multiple connected desktop devices (usually PCs) with access to high-bandwidth media.


LAN TopologiesLAN Topologies

• Topology defines the structure of the network.

• There are two parts to the topology definition:

Physical Topology: The actual layout of the media, i.e. Bus, Ring, Star, Extended Star, Hierarchical, and Mesh.

Logical Topology: How the media is accessed by the hosts, i.e. Broadcast and Token-Passing.


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LAN Physical TopologiesLAN Physical Topologies

• The actual layout of the media.


• How the media is accessed by the hosts

Fibre DistributedData Interface

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LAN Logical TopologiesLAN Logical Topologies


LAN Layer 1 Networking MediaLAN Layer 1 Networking Media

UTP

• Media confine network signals to a wire, cable, or fibre.

• Carry a flow of information (bits and bytes) through a LAN.

• Main issues when choosing a medium are: Cable length. Cost. Ease of installation.

• Other media are wireless LANs and PANs.

UnshieldedTwisted

Pair

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Fibre Optic Cable Connectors


Typical Networking MediaTypical Networking Media

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Repeaters:

• Regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media.

LAN Layer 1 DevicesLAN Layer 1 Devices

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. Hubs:

• Regenerate and retime network signals at the bit level to a large number of hosts (e.g. 4, 8, or even 24) using a process known as concentration.

• Also known as multi-port repeaters.



Network Interface Cards (NICs):Network Interface Cards (NICs):

• Provides network communication capabilities to and from a PC.

• Communicates with the network through a serial connection.

• Communicates with the computer through a parallel connection. • Each individual NIC throughout the

world carries a unique code, called a Media Access Control (MAC) address.

• The MAC address is used to control data communication for the host on the network.

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Selection Rules for NIC CardsSelection Rules for NIC Cards

• Important when selecting a network card:

Type of network (Ethernet, Token Ring, or FDDI),

Type of media (twisted-pair, coaxial, or fibre-optic cable),

Type of system bus (PCI or ISA).


Bridges:

• Connect two LAN segments.

• Filter traffic on a LAN based on the unique MAC address on the NIC.


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. Switches:

• Connect many LAN segments.

• Make decisions based on MAC addresses, "switching" data only out the port to which the proper host is connected.

• Also called a multi-port bridge.


LAN Layer 3 DeviceLAN Layer 3 Device

Routers:

• Examine incoming packets (Layer 3 data), choose the best path for them through the network, and then switch them to the proper outgoing port.

• Make decisions based on groups of network addresses (Classes).• Routers are the most important traffic-regulating devices on large networks.

• Enable virtually any type of computer to communicate with any other computer anywhere in the world!

• Routers can also connect different Layer 2 technologies, such as Ethernet, Token-ring, and FDDI.

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Clouds:

• Indicate a way to connect to other networks, without supplying all the details of either the connection or the network.

Layer 1 – 7 DeviceLayer 1 – 7 Device

• Represent a large group of details that are not pertinent to a situation, or description, at a given time.

• A collection of devices that operate at all levels of the OSI model.

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• A WAN is a data communications network that operates beyond a LAN's geographic scope.

• A WAN is different from a LAN in that you must subscribe to an outside WAN service provider to use WAN carrier network services.

• A WAN uses data links, such as Integrated Services Digital Network (ISDN) and Frame Relay, that are provided by carrier services to access bandwidth over wide-area geographies.

• A WAN connects the locations of an organization to each other, to locations of other organizations, to external services (such as databases), and to remote users.

• WANs generally carry a variety of traffic types, such as voice, data, and video.

Wide Area Networks (WANs)Wide Area Networks (WANs)


Wide Area Network Technologies & DevicesWide Area Network Technologies & Devices

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• WAN technologies function at the three lowest layers of the OSI reference model: the physical layer, the data link layer, and the network layer.


Wide Area Network ConnectivityWide Area Network Connectivity

• Telephone and data services are the most commonly used WAN services.

• Telephone and data services are connected from the building Point of Presence (POP) to the WAN provider's central office (CO).

The CO is the local telephone company office to which all local loops in a given area connect and in which circuit switching of subscriber lines occurs.

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WAN ServicesWAN Services

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AddressingAddressing

• Addressing relates to the way by which hosts (computers, servers, switches, etc.) communicate with each other.

• Addressing takes place at the:

Data Link Layer (layer 2)

Network Layer (layer 3).


Addressing (…2)Addressing (…2)

• The Data Link Layer uses a flat addressing scheme based on the Medium Access Control (MAC) address of the Network Interface Card.

It is used for communication between the hosts of a single network.

• The Network Layer uses a hierarchical addressing scheme based on the Internet Protocol (IP) address assigned to each host.

It is based on the network into which a host belongs to and to the address assigned to the actual host.

This scheme is used for communication over the Internet.


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Communication Using MAC AddressingCommunication Using MAC Addressing

• Used for communication between the hosts of a single network.


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Communication Using IP AddressingCommunication Using IP Addressing

• Used for communication over the Internet.


SummarySummary

• Computer Hardware Basics,

• Computer Software Basics,

• Computer Operating Systems,

• Computer Codes and Units,

• Digital Bandwidth,

• Networks,

• The ISO / OSI and TCP / IP Layered Models of Communication,

• Local Area Networks, Topologies & Devices,

• Wide Area Networks,

• Addressing.

By: Dr. N. Ioannides (Feb 2010)CT0004N - L.07 - Computer Networks - pp 1/52 Computer Networks Saroj Regmi Lecture 07 CT0004N Principles of Comms Systems.

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