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					  DATA COMMUNICATION AND
  NETWORKING

            CHAPTER 1 - PRELIM




JUNE 2005      DATA COMMUNICATION AND NETWORKING
DATA COMMUNICATIONS

Is   the   exchange   of data
between two devices via some
form of transmission medium
such as a wire cable.




JUNE 2005   DATA COMMUNICATION AND NETWORING
3 Fundamental Characteristics:
1.    Delivery. The system must
      deliver data to the correct
      destination.
2.    Accuracy. The system must
      deliver the data accurately
3.    Timeliness. The system must
      deliver data in a timely
      manner.
JUNE 2005     DATA COMMUNICATION AND NETWORING
Components

1.      Message. Is the information
        (data) to be communicated.
2.      Sender. Is the device that
        sends the data message.
3.      Receiver. Is the device that
        receives the message.


JUNE 2005      DATA COMMUNICATION AND NETWORING
4.      Medium. Is the physical path
        by which a message travels
        from the sender to receiver.
5.      Protocol. Is a set of rules
        that        govern       data
        communications.            It
        represents    an    agreement
        between   the   communicating
        devices.
JUNE 2005       DATA COMMUNICATION AND NETWORING
     Direction of Data Flow
     Transmission Modes
1.    Simplex Mode, the communication is
      unidirectional. Only one of the two
      devices on a link can transmit; the
      other can only receive.
2.    Half-Duplex, each station can both
      transmit and receive, but not at
      the same time.
3.    Full-Duplex (also called duplex),
      both stations can transmit and
      receive simultaneously.
     JUNE 2005   DATA COMMUNICATION AND NETWORING
 NETWORKS
Is a set of devices (often
referred to as nodes) connected
by communication links.




 JUNE 2005   DATA COMMUNICATION AND NETWORING
Distributed Processing

In which task is divided among
multiple computers. Instead of
a single large machine being
responsible for all aspects of
a process, separate computers
(usually a PC or workstation)
handle a subset.

JUNE 2005   DATA COMMUNICATION AND NETWORING
     Network Criteria

1.       Performance can be measured in many
         ways, including transit time and
         response time. The performance of a
         network depends on a number of
         factors,
          Number of users
          Type of transmission medium
          Capabilities of the connected hardware
          Efficiency of the software
     JUNE 2005        DATA COMMUNICATION AND NETWORING
2.        Reliability is measured by,
                Frequency of failure
                Time it takes to recover from a
                 failure
                Robustness in a catastrophe
3.        Security issues include
          protecting data from,
                Unauthorized users
                viruses
     JUNE 2005           DATA COMMUNICATION AND NETWORING
      Physical Structures
      Line Configuration

A network is two or more devices
connected together through Links.

Link is a communications pathway
that transfers data from one
device to another.


  JUNE 2005   DATA COMMUNICATION AND NETWORING
There are two possible type of
connections/line configurations:
1.   Point-to-point, connection
     provides a dedicated link
     between two devices. The entire
     capacity of the link is
     reserved for transmission
     between those two devices.
     JUNE 2005   DATA COMMUNICATION AND NETWORING
2.      Multipoint (also called
        multidrop)connection is one in
        which more than two specific
        devices share a single link.

        The capacity of the channel is
        shared, either spatially or
        temporally (timeshare).


JUNE 2005       DATA COMMUNICATION AND NETWORING
Physical Topology
Refers to the way in which a network
is laid out physically. Two or more
devices connect to a link; two or more
links form a topology.

Is the geometric representation of the
relationship of all the links and
linking devices (usually called nodes)
to one another.
  JUNE 2005   DATA COMMUNICATION AND NETWORING
Four Basic Topologies:
1. Mesh. Every device has a
   dedicated point-to-point link
   to every other device. A fully
   connected mesh network has n(n-
   1)/2 physical channels to link
   n devices. Every device on the
   network must have n-1
   input/output (I/O) ports.
  JUNE 2005   DATA COMMUNICATION AND NETWORING
Advantages of Mesh:
a) Eliminates the traffic problems that
   can occur when links must be shared
   by multiple devices.
b) Robust. If one link becomes
   unusable, it does not incapacitate
   the entire system.
c) Privacy or Security
d) Makes fault identification and fault
   isolation easy. Traffic can routed
   to avoid links with suspected
   problems.
   JUNE 2005   DATA COMMUNICATION AND NETWORING
Disadvantages of Mesh:
a) Because every device must be
   connected to every other device,
   installation and reconfiguration are
   difficult.
b) The sheer bulk of the wiring can be
   greater than the available space (in
   walls, ceilings, or floors) can
   accommodate.
c) The hardware required to connect
   each link (I/O ports and cable) can
   be prohibitively expensive.
   JUNE 2005   DATA COMMUNICATION AND NETWORING
2.   Star. A topology in which each
     device has a dedicated point-to-
     point link only to a central
     controller, usually called a hub.
     The   controller   acts   as   an
     exchange: if one device wants to
     send data to another, it sends
     the data to the controller, which
     then relays the data to the other
     connected device.
     JUNE 2005   DATA COMMUNICATION AND NETWORING
Advantages of Star:
a) Less expensive than a mesh topology.
b) Each device needs only one link and
   one I/O port to connect it to any
   number of others. Thus, make it easy
   to install and reconfigure.
c) Less cabling needs to be housed, and
   additions, moves, and deletions
   involve only one connection: between
   that device and the hub.
d) Robustness
e) Easy fault identification and fault
   isolation.
   JUNE 2005   DATA COMMUNICATION AND NETWORING
Disadvantages of Star:
Each node must be linked to a
central hub. For these reason more
cabling is required in a star than
in some other topologies (such as
tree, ring, or bus).



  JUNE 2005   DATA COMMUNICATION AND NETWORING
3.   Bus. A network topology in which
     all computers are attached to a
     shared medium (often a single
     cable). One long cable acts as a
     backbone to link all the devices
     in   the   network.   Nodes   are
     connected to the bus cable by
     drop lines and taps. Bus topology
     is multipoint.
     JUNE 2005   DATA COMMUNICATION AND NETWORING
A drop line is a connection running
between the device and the main
cable. A tap is a connector that
either splices into the main cable
or punctures the sheathing of a
cable to create a contact with the
metallic core.



  JUNE 2005   DATA COMMUNICATION AND NETWORING
Advantages of Bus:
a) Ease of installation.

b) Use less cabling than mesh, or
   star topologies.




  JUNE 2005   DATA COMMUNICATION AND NETWORING
Disadvantages of Bus:
a) Difficult reconfiguration and fault
   isolation.
b) A fault or break in the bus cable
   stops all transmission, even between
   devices on the same side of the
   problem. The damage area reflects
   signals back in the direction of
   origin, creating noise in both
   directions.
   JUNE 2005   DATA COMMUNICATION AND NETWORING
4.   Ring. Each device has a dedicated
     point-to-point   connection  only
     with the two devices on either
     side of it. 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.
     JUNE 2005   DATA COMMUNICATION AND NETWORING
Advantages of Ring:
a) Easy to install and
   reconfigure.
b) Fault isolation is simplified.




  JUNE 2005   DATA COMMUNICATION AND NETWORING
Disadvantages of Ring:
a) Unidirectional traffic.

b) A break in the ring (such as
   disabled station) can disable
   the entire network. This
   weakness can be solved by using
   dual ring or a switch capable
   of closing off the break.
  JUNE 2005   DATA COMMUNICATION AND NETWORING
      Categories of Networks
                  Size              Ownership                Distance it
                                                             covers
LAN               Few               Privately owned          Links devices     2 PCs & a
                  kilometers,                                in a single       printer, in a
                  licensing                                  office building   house or
                  restrictions                               or campus         office, 4 TO
                  on the # of                                                  16 Mbps range
                  users per copy                                               up to 100
                  of software or                                               Mbps, voice,
                  access of OS                                                 sound, &
                                                                               video
                                                                               peripherals,
                                                                               Bus, Ring, &
                                                                               star
MAN               3 to 30 miles     Maybe wholly             Entire city,
                                    owned and                may be a single
                                    operated by a            network such as
                                    private company,         cable TV
                                    or it maybe              network, LAN to
                                    service provided         LAN (co. use a
                                    by a public              MAN to connect
                                    company, such as         the LANs in all
                                    a local telephone        offices
                                    company.                 throughout the
                                                             city
      JUNE 2005                    DATA COMMUNICATION AND NETWORING
      Categories of Networks

                  Size             Ownership            Distance it
                                                        covers

WAN               Unlimited # of   Public leased        Large          Data, voice,
                  miles            through AT&T,        geographical   image & video
                                   MCI, SPRINT          areas          information.
                                   or private           (country,
                                   communication        continent,
                                   devices or           whole world
                                   combination




      JUNE 2005                DATA COMMUNICATION AND NETWORING
The Internet – A Brief
History

An internet (note the lowercase
letter i) is two or more networks
that can communicate with each
other. The most notable internet is
called   the  Internet   (uppercase
letter I), a collaboration of more
than    hundreds    of    thousands
interconnected networks.


JUNE 2005   DATA COMMUNICATION AND NETWORING
  Milestones
Mid-1960s
       Mainframe computers in research organizations
        were stand-alone devices.
       ARPA in the DOD
1967
       ACM meeting ARPA presented its ideas for
        ARPANET
       interface message processor (IMP).
1969
       ARPANET was a reality.
       Four nodes: UCLA, UCSB, SRI, University of
        Utah
       Network Control Protocol (NCP)


  JUNE 2005          DATA COMMUNICATION AND NETWORING
  Milestones
1972
       Vint Cerf and Bob Kahn collaborated on
        Internetting Project
       1973 paper outlined the protocols to achieve
        end-to-end delivery of packets.
       Paper on TCP included concepts such as
        encapsulation, the datagram, and the functions
        of a gateway.
TCP split into two protocols: TCP and IP
       IP would handle datagram routing
       TCP would be responsible for higher-level
        functions such as segmentation, reassembly,
        and error detection. The internetworking
        protocol became known as TCP/IP.


  JUNE 2005          DATA COMMUNICATION AND NETWORING
 PROTOCOLS AND STANDARDS
Protocol
Is a set of rules that govern data
communication. For communication to
occur they must agree on a protocol.
A protocol defines what, how, when it
is communicated. The key elements of
a protocol are syntax, semantics, and
timing.




 JUNE 2005   DATA COMMUNICATION AND NETWORING
     Key Elements of a Protocol

1.    Syntax refers to the structure or
      format of the data, meaning the
      order in which they are presented.
2.    Semantics refers to the meaning of
      each section of bits. How a
      particular pattern to be
      interpreted, and what action is to
      be taken based on that
      interpretation?
     JUNE 2005   DATA COMMUNICATION AND NETWORING
     Key Elements of a Protocol

3.    Timing refers to two
      characteristics: when data
      should be sent and how fast
      they can be sent.




     JUNE 2005   DATA COMMUNICATION AND NETWORING
 Standards
Standards   are    essential   in
creating and maintaining an open
and competitive market.
They   provide    guidelines   to
manufacturers,           vendors,
government agencies, and other
service providers to ensure the
kind of interconnectivity.


 JUNE 2005   DATA COMMUNICATION AND NETWORING
     Categories of Standards

1.    De facto (by fact). Standards
      that have not been approved by
      an organized body but have been
      adopted as standards through
      widespread use.
2.    De jure (by law). Those that
      have been legislated by an
      officially recognized body.
     JUNE 2005   DATA COMMUNICATION AND NETWORING
 Standard Organizations

Standards are develop through
the cooperation of standards
creation committees, forums, and
government regulatory agencies.




 JUNE 2005   DATA COMMUNICATION AND NETWORING
      Standard Creation Committees
International Organization for
Standardization (ISO)
        Multinational body
        Created in 1947
        OSI
International Telecommunication Union-
Telecommunication Standards (ITU-T)
        Consultative Committee for International
         Telegraphy and Telephony (CCITT)
        Best known standards are V series: define
         transmission over public digital networks, and X
         series: define transmission over public digital
         networks.


      JUNE 2005         DATA COMMUNICATION AND NETWORING
     Standard Creation Committees
American National Standards Institute (ANSI)
     U.S. voting representative to both ISO and ITU-T.
     Members include professional societies, industry
     associations, governmental and regulatory bodies,
     and consumer groups.
Institute of Electrical and Electronics
Engineers (IEEE)
    Largest national professional group involved in
     developing standards for computing, communication,
     electrical engineering, and electronics.
    Sponsored an important standard for LAN called
     Project 802 (e.g. 802.3, 802.4, 802.5)



     JUNE 2005       DATA COMMUNICATION AND NETWORING
     Standard Creation Committees

Electronic Industries Association (EIA)
    An association of electronic manufacturers in the
     U.S.
    Responsible for developing the EIA-232-D, EIA-449,
     and EIA-530 define serial transmission between
     two digital devices (e.g. computer to modem)




     JUNE 2005       DATA COMMUNICATION AND NETWORING
 Forums
Telecommunications technology
development is moving faster than
the ability of standard
committees to ratify standards.
Forums consist of representatives
from corporations, they work with
universities, and users that
test, evaluate, and standardize
new technologies.
 JUNE 2005   DATA COMMUNICATION AND NETWORING
 Regulatory Agencies
All communications technology is
subject to regulation by government
agencies such as the Federal
Communications Commission (FCC) in the
United States. The purpose of these
agencies is to protect the public
interest by regulating radio,
television, and wire/cable
communications.


 JUNE 2005   DATA COMMUNICATION AND NETWORING

				
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Description: My documents about school up to my 4th year College. Hope some of them will be useful to you.