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DATA COMMUNICATIONS

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DATA COMMUNICATIONS Data Communications and Networking, Behrouz A Forouzan, 4th edition, 2006, TMH Mrs P Lavanya Asst. Prof. E. C. E. Dept. – PowerPoint PPT presentation

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Title: DATA COMMUNICATIONS


1
DATA COMMUNICATIONS Data Communications and
Networking, Behrouz A Forouzan, 4th edition,
2006, TMH
Mrs P Lavanya Asst. Prof. E. C. E. Dept.
2
  • Data refers to information presented in
    whatever form is
  • agreed upon by the parties creating and
    using the
  • data.
  • Communication process of exchanging information
  • Data Communications are the exchange of data
    between two devices via some form of transmission
    medium.
  • For data communications to occur, the
    communicating devices must be part of a
    communication system made up of a combination of
    hardware (physical equipment) and software
    (programs).

3
  • Effectiveness of data communications system
    depends on four fundamental characteristics
  • Delivery The system must deliver data to the
    correct destination
  • Accuracy The system must deliver the data
    accurately.
  • Timeliness the system must deliver data in a
    timely manner.
  • Jitter refers to the variation in the packet
    arrival time. It should be
  • zero.

4
UNIT - I
5
Contents
  • Introduction
  • - Components
  • - Data Representation
  • - Data Flow
  • Networks
  • - Network Criteria
  • - Physical Structures
  • - Categories of Networks
  • The Internet
  • Protocols and Standards
  • Network Models
  • - Layered Tasks
  • - The OSI Model
  • - Layers in the OSI Model
  • - TCP/IP Protocol Suite
  • - Addressing

6
Introduction(1)
  • Components
  • - A data communications system has five
    components.
  • 1. Message it is the information to be
    communicated.
  • 2. Sender It is the device that sends the
    data message.
  • 3. Receiver It is the device that receives
    the message.
  • 4. Transmission medium It is the physical
    path by which a
  • message travels from sender to
    receiver.
  • 5. Protocol It is a set of rules that govern
    data communications.

7
Introduction(2)
Fig. 1.1 Five components of data communication
8
Introduction(3)
  • Data Representation
  • - Information comes in different forms such as
    text, numbers, images,
  • audio, and video.
  • Text ASCII(American Standard Code for
    Information Interchange)
  • Unicode
  • Numbers represented by bit patterns.
  • number is directly converted to a binary
    number
  • Images represented by bit patterns.
  • color images RGB, YCM
  • Audio refers to the recording or broadcasting
    of sound or music.
  • It is different from
    text, numbers, or images.
  • It is continuous, not discrete.
  • Video refers to the recording or broadcasting
    of a picture or movie.

9
Introduction(4)
  • Data Flow
  • - Communication between two devices can be
    simplex, half-duplex, or
  • full-duplex
  • Simplex Communication is unidirectional
  • - entire capacity of the channel
    is used
  • - Ex Keyboards, Traditional Monitors

10
Introduction(5)
  • Half-Duplex each station can both transmit and
    receive, but not
  • at the same time.
  • - entire capacity of the channel is taken
    over by whichever of the two devices is
    transmitting at the time
  • - Ex Walkie-talkies and CB radio

11
Introduction(6)
  • Full-Duplex both stations can transmit and
    receive simultaneously
  • - capacity of the link is shared
  • - Ex Telephone

12
Networks(1)
  • A network is a set of devices (often referred to
    as nodes) connected by communication links.
  • A node can be a computer, printer, or any other
    device capable of sending and/or receiving data
    generated by other nodes on the network.
  • Distributed Processing
  • Network Criteria
  • A network must be able to meet a certain number
    of criteria. The most important of these are
    performance, reliability, and security.

13
Networks(2)
  • Performance performance of a network depends
    on a number of factors, including the
    number of users, the type of transmission
    medium, the capabilities of the connected
    hardwares, and the efficiency of the
    software.
  • It is often evaluated by two networking metrics
    throughput and delay
  • We need more throughput and less delay.
  • Reliability It is measured by frequency of
    failure in addition to accuracy of
    delivery
  • Security include protecting data from
    unauthorized access, protecting
    data from damage and development, and
    implementing policies and procedures for recovery
    from breaches and data losses.

14
Networks(3)
  • Physical Structures
  • Type of Connection
  • - A network is two or more devices connected
    through links.
  • - A link is a communications pathway that
    transfers data from one
  • device to another.
  • - For visualization purposes, it is simplest to
    imagine any link drawn
  • between two points.
  • - For communication to occur, two devices must
    be connected in
  • some way to the same link at the same time.

15
Networks(4)
  • There are two types of connections
    point-to-point and multipoint.
  • Point-to-point
  • - there is a dedicated link between two
    devices.
  • - entire capacity of the link is reserved for
    transmission between
  • those two devices.
  • - connection can be a physical wire or cable or
    a microwave or a
  • satellite link

16
Networks(5)
  • Multipoint
  • - also called multidrop
  • - more than two specific devices share a single
    link
  • - capacity of the channel is shared, either
    spatially or temporally.
  • - if several devices can use the link
    simultaneously
  • spatially shared connection
  • - if users must take turns time shared
    connection

17
Networks(6)
  • Physical Topology
  • Refers to the way in which a network is laid out
    physically.
  • Two or more devices connect to t link
  • Two or more links form a topology.
  • Topology of a network is the geometric
    representation of the relationship of all the
    links and linking devices to one another.

18
Networks(7)
  • Mesh
  • - every device has a dedicated point-to-point
    link to every other device.
  • - to have a mesh network with n nodes, n(n-1)/2
    physical links are
  • needed.
  • - to accommodate that many links, every device
    on the network must
  • have n-1 input/output (I/O) ports
  • - Advantages
  • 1. use of dedicated links eliminate traffic
    problems
  • 2. robust
  • 3. there is the advantage of privacy or
    security.
  • 4. fault identification and fault isolation
    easy
  • - Disadvantages
  • 1. installation and reconnection are difficult.
  • 2. the sheer bulk of the wiring can be greater
    than the available space
  • 3. hardware required to connect each link is
    prohibitively expensive
  • - limitedly used

19
Fig. A fully connected mesh topology
20
Networks(8)
  • Star
  • - every device has a dedicated point-to-point
    link only to a central
  • controller, usually called a hub.
  • - devices are not directly linked to one
    another.
  • - does not allow direct traffic between devices.
  • - the controller acts as an exchange If one
    device wants to send data to
  • another, it sends data to the controller,
    which then relays the data to the
  • other connected device.
  • - Advantages
  • 1. less expensive than mesh, each device needs
    only one link and one I/O port to connect it
    to any number of others.
  • 2. easy to install and reconfigure
  • 3. Far less cabling is needed to mesh
  • 4. robustness
  • 5. easy fault identification and fault
    isolation

21
Networks(9)
  • Star
  • - Disadvantages
  • 1. dependency of the whole topology on one
    single point, the hub.
  • 2. more cabling is required than in some other
    topologies
  • - used in LANs

Fig. A star topology
22
Networks(10)
  • Bus
  • - It is multipoint
  • - one long cable acts as a backbone to link all
    the devices in a network
  • - Nodes are connected to the bus cable by drop
    lines and taps.
  • - a drop line is a connection running between
    the device and the main cable
  • - a tap is a connector that splices into the
    main cable
  • - as a signal travels along the backbone, some
    of its energy is transformed
  • into heat.
  • - therefore, the signal becomes weaker and
    weaker as it travels farther and
  • farther.
  • - for this reason there is a limit on the number
    of taps a bus can support and
  • on the distance between those taps.
  • - Advantages
  • 1. ease of installation
  • 2. uses less cabling than mesh or star

23
Networks(11)
  • Bus
  • - Disadvantages
  • 1. difficult reconnection and fault isolation
  • 2. difficult to add new devices.
  • 3. signal reflection at the taps can cause
    degradation in quality.
  • 4. a fault or break in the bus cable stops all
    transmission
  • - used in the early LANs.

Fig. A bus topology
24
Networks(12)
  • Ring
  • - each device has a dedicated point-to-point
    connection with only the two
  • devices on either side of it (each device is
    linked to only its immediate
  • neighbors either physically or logically).
  • - a signal is passed along the ring in one
    direction, from device to device,
  • until it reaches its destination.
  • - each device in the ring incorporates a
    repeater.
  • - when a device receives a signal intended for
    another device, its repeater
  • regenerates the bits and passes them along

Fig. A ring topology
25
Networks(12)
  • Ring
  • - Advantages
  • 1. relatively easy to install and reconfigure
  • 2. fault isolation is simplified
  • - Disadvantages
  • 1. unidirectional traffic
  • 2. a break in the ring can disable the entire
    network
  • - used in Token ring LANs

26
Networks(13)
  • Hybrid Topology
  • - a network can be hybrid.

Fig. A hybrid topology a star backbone with
three different networks
27
Networks(14)
  • Categories of Networks
  • - a network is a group of connected
    communicating devices such as
  • computers or printers etc.
  • - the category into which a network falls is
    determined by its size.
  • - a LAN normally covers an area less than 2 mi.
  • - a WAN can be worldwide.
  • - networks of size in between are referred to as
    MANs and span tens of
  • miles

28
Networks(15)
  • LAN
  • - usually privately owned
  • - links the devices in a single office,
    building, or campus
  • - a LAN can be as simple as two
  • PCs and a printer connected
  • together in someones home
  • office or it can extend
  • throughout a company and
  • include audio and video
  • peripherals.
  • - designed to allow resources to
  • be shared between PCs or WSs.

29
Networks(16)
  • LAN
  • - resources to be shared can be hardware,
    software, or data.
  • - in addition to size, LANs are distinguished
    from other types of networks
  • by their transmission media and topology.
  • - a given LAN uses only one type of transmission
    medium.
  • - most common LAN topologies are bus, ring, and
    star
  • - today, LANs data rates are normally 100 or
    1000 Mbps
  • - Wireless LANs are the newest evolution in LAN
    technology

30
Networks(17)
  • WAN
  • - provides long-distance transmission of data,
    image, audio and video
  • information over large geographic areas
    that may comprise a country, a
  • continent, or even the whole world.
  • - a WAN can be as complex as the backbones that
    connect the Internet
  • or as simple as a dial-up line that connects a
    home computer to the
  • Internet
  • - normally refer to the first as a switched WAN
    and to the second as a
  • point-to-point WAN

31
(No Transcript)
32
Networks(18)
  • WAN
  • - swithced WAN connects the end systems, through
    a router to another
  • LAN or WAN.
  • - point-to-point WAN is normally a line leased
    from a telephone or cable
  • TV provider that connects a home computer or a
    small LAN to an Internet
  • Service Provider (ISP).
  • - Wireless WAN is becoming more and more popular
    today.

33
Networks(19)
  • MAN
  • - covers the area
  • inside a town or
  • a city.
  • - designed for
  • customers who
  • need a high-
  • speed
  • connectivity,
  • and have end-
  • points spread
  • over a city or
  • part of city.

Fig. a MAN
34
internet
  • Interconnection of Networks internetwork
  • - when two or more networks are connected, they
    become an
  • internetwork, or internet.

35
Internet(1)
  • The Internet
  • - the Internet is a communication system that
    has brought a wealth of
  • information to our fingertips and organized it
    for our use.
  • - the Internet is a structured, oraganized
    system
  • - the most notable internet is called the
    Internet, a collaboration of more
  • than hundreds of thousands of interconnected
    networks
  • - private individuals, government agencies,
    schools, research
  • facilities, corporations, and libraries in
    more than 100 countries use the
  • Internet.

36
Internet(2)
  • - millions of people are users.
  • History
  • - this extraordinary communication system came
    into being in 1969.
  • - the Advanced Research Projects Agency (ARPA)
    in the Department
  • of Defense (DoD)
  • - Network Control Protocol (NCP)
  • - Transmission Control Protocol (TCP)
  • - Transmission Control Protocol (TCP) and
    Internetworking Protocol
  • (IP)

37
Internet(3)
  • The Internet Today
  • - today, Internet is not a simple hierarchical
    structure
  • - It is made up of many wide- and local-area
    networks joined by
  • connecting devices and switching stations.
  • - It is difficult to give an accurate
    representation of the Internet because it
  • is continually changing
  • - today most end users who want Internet
    connection use the services of
  • Internet Service Providers (ISPs).
  • - there are international service providers,
    national service providers,
  • regional service providers, and local service
    providers.
  • - The Internet today is run by private
    companies, not the government.

38
Internet Today
  • ISP (Internet service providers)
  • NISP (national ISP)
  • NAP (network access point)

1-38
39
Internet(4)
  • International Internet Service Providers
  • - at the top of the hierarchy are the
    international service providers that
  • connect nations together.
  • National Internet Service Providers
  • - these are backbone networks created and
    maintained by specialized
  • companies.
  • - these networks are connected by complex
    switching stations called
  • network access points (NAPs).
  • - some national ISP networks are also connected
    to one another by private
  • switching stations called peering points
    (normally operate at a high data
  • rate upto 600Mbps.

40
Internet(5)
  • Regional Internet Service Providers
  • - these are smaller ISPs that are connected to
    one or more national ISPs.
  • - they are at the third level of the hierarchy
    with a smaller data rate.
  • Local Internet Service Providers
  • - provide direct service to the end users.
  • - local ISPs can be connected to regional ISPs
    or directly to national ISPs.
  • - a local ISP can be a company that provides
    Internet services, a
  • corporation with a network that supplies
    services to its own employees, or
  • a nonprofit organization, such as a college or
    a university, that runs its
  • own network.

41
Protocols and Standards(1)
  • Protocols
  • - a protocol is a set of rules that govern data
    communcations.
  • - a protocol defines what is communicated, how
    it is communicated, and
  • when it is communicated.
  • - key elements of a protocol are syntax,
    semantics, and timing.
  • Syntax
  • - refers to the structure or format of the data,
    meaning the order in which
  • they are presented.
  • Semantics
  • - refers to the meaning of each section of bits.

42
Protocols and Standards(2)
  • - How is a particular pattern to the
    interpreted, and what action is to be
  • taken based on that interpretation?
  • Timing
  • - refers to two characteristics when data
    should be sent and how fast
  • they can be sent.

43
Protocols and Standards(3)
  • Standards are essential in
  • - creating and maintaining an open and
    competitive markets for equipment
  • manufacturers
  • - guaranteeing national and international
    interoperability of data and
  • telecommunications technology and
    processes.
  • - provide guidelines to manufacturers, vendors,
    government agencies, and
  • other service providers to ensure the kind of
    interconnectivity necessary in
  • todays marketplace and in international
    communications.
  • - they are fall into two categories de facto
    and de jure.

44
Protocols and Standards(4)
  • De facto
  • - meaning by fact or by convention
  • - these are the standards that have not been
    approved by an organized
  • body but have been adopted as standards
    through widespread use.
  • De jure
  • - meaning by law or by regulation
  • - standards that have been legislated by an
    officially recognized body

45
Standards Organizations
  • Standards are developed by
  • Standards creation committees
  • Forums
  • Regulatory agencies
  • Standards committees forums
  • Standards committees are slow moving
  • Forums are made up of interested corporations
  • Forum are able to speed acceptance of a
    particular technology

1-45
46
Standards Committees
  • ISO
  • Voluntary international organization
  • ITU-T
  • Formerly, CCITT formed by UN
  • ANSI
  • Private non-profit corporation in the US
  • IEEE
  • The largest engineering society in the world
  • EIA
  • Non-profit organization in the US

1-46
47
Internet Standards
  • IETF (Internet Engineering Task Force)
  • Internet Draft
  • working document with no official status
  • with a 6-month lifetime
  • RFC (Request for Comment)
  • Edited, assigned a number, and made available to
    all interested parties

48
UNIT I(B)
49
Contents
  • Introduction
  • - Components
  • - Data Representation
  • - Data Flow
  • Networks
  • - Network Criteria
  • - Physical Structures
  • - Categories of Networks
  • The Internet
  • Protocols and Standards
  • Network Models
  • - Layered Tasks
  • - The OSI Model
  • - Layers in the OSI Model
  • - TCP/IP Protocol Suite
  • - Addressing

50
Network Models
  • A network is a combination of hardware and
    software that sends data from one location to
    another.
  • Hardware consists of the physical equipment that
    carries signals from one point of the network to
    another.
  • Software consists of instruction sets that make
    possible the services that we expect from a
    network.
  • Computer networks are created by different
    entities.
  • Standards are needed so that these heterogeneous
    networks can communicate with one another.

51
Network Models Layered Tasks(1)
Fig.Tasks involved in sending a letter
52
Network Models Layered Tasks(2)
  • - the tasks involved in data exchange are
    grouped as hierarchical
  • layers.
  • - each layer uses the services of the layer
    immediately below it.
  • - the two layered models that dominated data
    communications and
  • networking are Open Systems Interconnection
    (OSI) model and
  • TCP/IP protocol suite.

53
Network Models OSI Model(1)
  • - An ISO standard that covers all aspects of
    network communications is
  • Open Systems Interconnection (OSI) model
  • - First introduced in late 1970s.
  • - It is a set of protocols that allows any two
    different systems to
  • communicate regardless of their underlying
    architecture.
  • - It is a model for understanding and designing
    a network architecture that
  • is flexible, robust, and interoperable.
  • - It consists of seven ordered, separate but
    related layers, each of which
  • defines a part of the process of moving
    information across a network.

54
OSI Model
  • ISO is the organization. OSI is the model

55
Network Models OSI Model(2)
  • - Each layer defines a family of functions
    distinct from those of the other
  • layers.
  • - Within a single machine, Layer 3 uses the
    services provided by layer 2
  • and provides services for layer 4.
  • - Between machines, layer x on one machine
    communicates with layer x on
  • another machine.
  • - This communication is governed by an
    agreed-upon series of rules and
  • conventions called protocols.
  • - The processes on each machine that communicate
    at a given layer are
  • called peer-to-peer processes.

56
Interaction between layers in the OSI model
  • Layer and interface

57
Network Models OSI Model(3)
  • - At the physical layer, communication is
    direct.
  • - Each layer in the sending device adds its own
    information to the
  • message it receives from the layer just above
    it and passes the whole
  • package to the layer just below it.
  • - At layer 1 the entire package is converted to
    a form that can be
  • transmitted to the receiving device.
  • - At the receiving machine, the message is
    unwrapped layer by layer, with
  • each process receiving and removing the data
    meant for it.
  • - Each interface defines the information and
    services a layer must provide
  • for the layer above it.

58
Network Models OSI Model)
  • - physical, data link and physica layers
    network support layers.
  • - session, presentation and application layers
    user support layers.
  • - At layer 1 the entire package is converted to
    a form that can be
  • transmitted to the receiving device.
  • - At the receiving machine, the message is
    unwrapped layer by layer, with
  • each process receiving and removing the data
    meant for it.
  • - Each interface defines the information and
    services a layer must provide
  • for the layer above it.

59
An exchange using the OSI model
  • Encapsulation with header and possibly trailer

2-59
60
Physical Layer
  • The physical layer is responsible for movements
    of individual bits from one hop (node) to the
    next
  • Mechanical and electrical specification, the
    procedures and functions

2-60
61
Physical Layer Duties
  • Physical characteristics of interfaces and media
  • Representation of bits
  • Data rate
  • Synchronization of bits
  • Line configuration
  • Physical topology
  • Transmission mode

2-61
62
Data Link Layer
  • The data link layer is responsible for moving
    frames from one hop (node) to the next
  • Transform the physical layer to a reliable
    (error-free) link

2-62
63
Data Link Layer Duties
  • Framing
  • Physical addressing
  • Flow control
  • Error control
  • Access control

2-63
64
Hop-to-Hop Delivery
2-64
65
Network Layer
  • The network layer is responsible for the delivery
    of packets from the source host to the
    destination host

2-65
66
Network Layer Duties
  • Logical addressing and routing

Data Communications, Kwangwoon University
2-66
67
Transport Layer
  • The transport layer is responsible for delivery
    of a message from one process to another

2-67
68
Transport Layer Duties
  • Service-point (port) addressing
  • Segmentation and reassembly
  • Connection control
  • Flow control
  • Error control

2-68
69
Reliable Process-to-Process Delivery of a Message
2-69
70
Session Layer
  • Session layer is responsible for dialog control
    and synchronization

2-70
71
Presentation Layer
  • Presentation layer is responsible for
    translation, compression, and encryption

2-71
72
Application Layer
  • Application layer is responsible for providing
    services to the user

2-72
73
Application Layer Services
  • Network virtual terminal
  • Mail services
  • File transfer, access, and management
  • Directory services

2-73
74
Summary of Layers
2-74
75
TCP/IP and OSI Model
2-75
76
TCP/IP Protocol Suite
  • Host-to-network Physical and data link layer
  • No specific protocol
  • Network layer
  • IP(Internet Protocl), ARP(Address Resolution
    Protocol), RARP(Reverse ARP), ICMP(Internet
    Control Message Protocol), IGMO(Internet Group
    Message Protocol)
  • Transport layer
  • TCP(Transmission Control Protocol), UDP(User
    Datagram Protocl), SCTP(Stream Control
    Transmission Protocol),
  • Application Layer
  • Combined session, presentation, and application
    layers

2-76
77
Addressing
  • Four levels of addresses in TCP/IP protocols
  • Physical (link), logical (IP, network), port, and
    specific addresses

2-77
78
Relationship of Layers and Addresses
2-78
79
Physical Address
  • A node with physical address 10 sends a frame to
    a node with physical address 87. The two nodes
    are connected by a link (bus topology LAN). As
    the figure shows, the computer with physical
    address 10 is the sender, and the computer with
    physical address 87 is the receiver.

070102012C4BA 6-byte (12 hexadecimal
digits) physical address.
2-79
80
Logical (IP) Address
  • The physical addresses will change from hop to
    hop, but the logical addresses usually remain the
    same

2-80
81
Port Address
  • The physical addresses change from hop to hop,
    but the logical and port addresses usually remain
    the same

2-81
82
Specific Address
  • Some application have user-friendly addresses
    that are designed for that specific address
  • Example 1 e-mail address kchung_at_kw.ac.kr
  • Defines the recipient of an e-mail
  • Example 2 URL (Universal Resource Locator)
    www.kbs.co.kr
  • Used to find a document on the WWW

2-82
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