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COE 342 - 1 Data and Computer Communications


Amount of data to be sent at one time. Data format. Dealing with errors. Term 042 ... A suite of communications protocols used to connect hosts on the Internet. ... – PowerPoint PPT presentation

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Title: COE 342 - 1 Data and Computer Communications

COE 342 - 1 Data and Computer Communications
  • Data Communications Networking Overview

Communication Model
Communication Model
  • Fundamental purpose of communications system is
    exchange of data between two parties
  • The key elements of a communication model are
  • Source Generates data to be transmitted
  • Transmitter Converts data into transmittable
    signals (modulation, encoding, )
  • Transmission System Carries data
  • Receiver Converts received signal into data (the
    opposite of the Transmitter role)
  • Destination Takes incoming data

Communications Tasks
  • Transmission system utilization
  • Interfacing
  • Signal generation
  • Synchronization
  • Exchange management
  • Error detection and correction
  • Flow control
  • Addressing
  • Routing
  • Recovery
  • Message formatting
  • Security
  • Network management

Communications Tasks
  • Transmission system utilization
  • Making efficient use of transmission facilities
  • Multiplexing is used to allocate the total
    transmission medium among number of users
  • Congestion control is needed to assure that the
    transmission system is not overwhelmed
  • Interfacing Interfacing here refers to how to
    interface communicating devices to the
    transmission system
  • Signal generation Most forms of computer
    communication depend on the use of
    electromagnetic signals propagated over
    transmission media. Thus, we need to generate
    signals from the data to be transmitted.

Communications Tasks
  • Synchronization The receiver needs to know when
    the signal start and ends. Also, it needs to know
    the duration of each signal
  • Exchange management The communicating parties
    need to agree on a variety of requirements to
    communicate usefully. Such conventions include
  • Signal timing
  • How to start/end conversation
  • Simultaneous transmission or taking turns
  • Amount of data to be sent at one time
  • Data format
  • Dealing with errors

Communications Tasks
  • Error detection and correction
  • In all communication system there is a potential
    for error (signal distortion, attenuation,
  • In most cases, error in transmission is not
    accepted (tolerated)
  • We need to have a technique to detect errors in
    transmission and even better to have a technique
    to correct errors
  • Flow control Flow control is required to assure
    that the source does not send information too
  • Addressing When more than two devices share
    transmission facility
  • Each system need to have unique address.
  • Source need to identify the destination by its

Communications Tasks
  • Routing the transmission system must assure that
    the destination system receive the data
  • Recovery Recovery is needed when the information
    exchange is interrupted or to restore the system
    to the point prior to the beginning of the
  • Message formatting Communicating parties need to
    agree on the form of data to be transmitted such
    as the binary code for characters
  • Security
  • Data sender need to assure that only the intended
    destination receive the data.
  • Destination need to be sure that what he recived
    was sent actually by the purported sender.
  • Destination need to be sure that the data has not
    been altered

Communications Tasks
  • Network management Network management is needed
  • configure the system
  • Monitor the system status
  • React to failures and overload
  • Plan for future growth

Data Communication
  • Sending an email (simplified)
  • User A wrote an email message and he wants to
    send it to B
  • When the user click send, the email program will
    prepare binary message that has the digital
    equivalent of email body, B address and some
    control bit streams.
  • The computer will send the bit stream as a
    digital signal to the transmitter (modem for
  • Transmitter will convert the digital signal to a
    signal suitable for the transmission system
    (analog signal for example)
  • Transmission system will carry the signal to the
    destination recover.
  • The receiver convert the received signal to a
    binary signal and send it to the computer
  • Destination computer will take the received
    signal convert it to binary data and store it in
    the memory
  • Email program will read the binary data removes

Simplified Data Communication Model
Direct point to point connection
Direct point to point connection
Computer network
  • Computer network is a group of computer systems
    linked together.
  • Computer networks can be classified in different
    ways. Follows is a classification that depends
    on the geographical position of the computers
  • WAN wide-area network The computers are farther
    apart and are connected by telephone lines or
    radio waves.
  • MAN metropolitan-area network A data network
    designed for a town or city.
  • CAN campus-area network The computers are
    within a limited geographic area, such as a
    campus or military base.
  • LAN local-area network The computers are
    geographically close together (in the same
  • HAN home-area network A network contained
    within a user's home that connects a person's
    digital devices.

Local-area network
  • A computer network that spans a relatively small
  • Most LANs are confined to a single building or
    group of buildings.
  • A LAN can be connected to other LANs over any
    distance via telephone lines or radio waves. A
    system of LANs connected in this way is called a
    wide-area network (WAN).
  • Most LANs connect workstations and personal
  • Each node (individual computer ) in a LAN has its
    own CPU with which it executes programs, but it
    also is able to access data and devices anywhere
    on the LAN.
  • Users can share devices, such as printers, as
    well as data.
  • Users can also use the LAN to communicate with
    each other, by sending e-mail or engaging in chat
  • There are many different types of LANs examples
  • Ethernets being the most common for PCs.
  • AppleTalk is most common for Apple Macintosh

  • A local-area network (LAN) architecture developed
    by Xerox Corporation in cooperation with DEC and
    Intel in 1976.
  • Ethernet uses a bus or star topology
  • Ethernet data transfer rates
  • Ethernet 10 Mbps.
  • Fast Ethernet 100 Mbps.
  • Gigabit Ethernet 1 gigabit (1,000 megabits) per
  • The Ethernet specification served as the basis
    for the IEEE 802.3 standard
  • It is one of the most widely implemented LAN

Wide Area Network
  • A computer network that spans a relatively large
    geographical area.
  • Typically, a WAN consists of two or more
    local-area networks (LANs).
  • Computers connected to a wide-area network are
    often connected through public networks, such as
    the telephone system.
  • They can also be connected through leased lines
    or satellites.
  • The largest WAN in existence is the Internet.

Metropolitan Area Network
  • A data network designed for a town or city.
  • In terms of geographic breadth, MANs are larger
    than local-area networks (LANs), but smaller than
    wide-area networks (WANs).
  • MANs are usually characterized by very high-speed
    connections using fiber optical cable or other
    digital media.

Wireless network
  • Wireless network is a type of network that uses
    high-frequency radio waves rather than wires to
    communicate between nodes.
  • Hybrid wireless network is an emerging networking
    that consists of wireless components that
    communicate with a network that uses cables in a
    mixed-component network.
  • Wireless network is now common in
  • Business LANs
  • WAN (voice data)
  • Advantages of using wireless network
  • Easy to install and configure.
  • Provides mobility

Network technology
  • Circuit switching
  • Packet switching
  • Frame relay
  • Asynchronous Transfer Mode (ATM)

Circuit switching
  • A type of communications in which a dedicated
    channel (or circuit) is established for the
    duration of a transmission.
  • The most famous circuit-switching network is the
    telephone system, which links together wire
    segments to create a single unbroken line for
    each telephone call.
  • Circuit-switching systems are ideal for
    communications that require data to be
    transmitted in real-time such as live audio and
  • Circuit-switching networks are sometimes called
    connection-oriented networks.

Packet switching
  • Communication method that divides messages into
    packets and sends each packet individually.
  • Each packet is then transmitted individually and
    can even follow different routes to its
  • Once all the packets forming a message arrive at
    the destination, they are recompiled into the
    original message.
  • Packet-switching networks are more efficient if
    some amount of delay is acceptable. as e-mail
    messages and Web pages.
  • The Internet is based on a packet-switching
    protocol, TCP/IP.
  • Most modern Wide Area Network (WAN) protocols,
    including TCP/IP, X.25, and Frame Relay, are
    based on packet-switching technologies.

Frame relay
  • Packet switching systems have large overheads to
    compensate for errors.
  • Modern systems are more reliable (dramatically
    lower errors rate)
  • Errors can be caught in end system
  • Most overhead for error control is stripped out
  • Frame relay is a packet-switching protocol that
    uses much lesser overhead for error control.
  • Frame Relay networks can support data transfer
    rates up to 2 Mbps (compared to 64Kbps for
    regular packet switching)
  • Frame Relay is quite popular in the U.S. because
    it is relatively inexpensive. However, it is
    being replaced by faster technologies, such as

Asynchronous Transfer Mode (ATM)
  • A network technology based on transferring data
    in cells or packets of a fixed size.
  • The cell used with ATM is relatively small
    compared to units used with older technologies.
  • The small, constant cell size allows ATM
    equipment to transmit video, audio, and computer
    data over the same network, and assure that no
    single type of data hogs the line.
  • ATM creates a fixed channel, or route, between
    two points whenever data transfer begins.
  • ATM attempts to combine the best of both worlds
    -- the guaranteed delivery of circuit-switched
    networks and the robustness and efficiency of
    packet-switching networks.
  • Speed up to Gbps range

Transmission Control Protocol/Internet Protocol
  • A suite of communications protocols used to
    connect hosts on the Internet.
  • TCP/IP uses several protocols, the two main ones
    being TCP and IP.
  • TCP/IP establishes a connection between two hosts
    so that they can send messages back and forth for
    a period of time.
  • TCP is a protocols that enables two hosts to
    establish a connection and exchange streams of
  • TCP establishes a virtual connection between a
    destination and a source.
  • TCP guarantees delivery of data and also
    guarantees that packets will be delivered in the
    same order in which they were sent.
  • IP specifies the format of packets, also called
    datagrams, and the addressing scheme.
  • IP is like the postal system It allows you to
    address a package and drop it in the system, but
    there's no direct link between you and the

  • Subscriber connection
  • Telephone network
  • DSL
  • Cable TV
  • Satellite
  • SONet Synchronous Optical Network, a standard
    for connecting fiber-optic transmission systems.