Introductory Lecture-Data Communication and Computer Networks-Lecture Slides, Slides of Data Communication Systems and Computer Networks

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EEE

Data Communications and

Computer Networks

Lecture # 1

Introduction

7.2.

Course Objectives

In this course four major concepts will be discussed namely

• Data communications
• Networking
• Protocols and standards
• Networking models

Data Communications

• Communication is sharing of information
• Telecommunication is communication taking place over distance
• Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. - The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data.

Fundamental characteristics of Data

Communications

• Delivery: The system must deliver data to the correct destination
• Accuracy: The system must deliver the data accurately (unaltered, unchanged).
• Timeliness: The system must deliver data in a timely manner (without delay, synchronously).
• Jitter: Jitter refers to the variation in the packet arrival time(without uneven delay).

Data representation

Information today comes in forms

• Text
• Numbers
• Images
• Audio
• Video

Data Flow

(a) Simplex

(b) Half Duplex

(c) Full Duplex

Physical structures of network

• Dedicated link between two devices
• More then two devices sharing the link

Network physical Topologies

• The term physical topology refers to the way in which a network is laid out physically
• There are four basic topologies
  • Mesh
  • Star
  • Bus
  • Ring

Star topology

• Each device has a dedicated point-to-point link only to a central controller, usually called a hub or a switch.
• Advantages
  • No direct traffic between devices
  • Less expensive than mesh topology
  • Each device needs only one link and one I/O port
  • Easy to install and reconfigure
  • Far less cabling required
  • Easy fault isolation
• One big disadvantage of a star topology is the dependency of the whole topology on one single point, the hub. If the hub goes down, the whole system is dead.

Bus topology

• A multipoint topology in which Nodes are connected to the bus cable by drop lines
• The principal advantage of this topology are
  • Cost.
  • no hubs are required.
  • shorter lengths of cable can be used.
  • It is also easy to expand.
• Disadvantages include
  • Difficult reconnection and fault isolation.
  • Difficult to add new devices.
  • Signal reflection at the taps can cause degradation in quality.

Hybrid Topology

• A network can be hybrid. For example, we can have a main star topology with each branch connecting several stations in a bus topology

Network Models

• Computer networks are created by different entities.
• Standards are needed so that these heterogeneous networks can communicate with one another.
• The two best-known standards are the OSI model and the Internet model.

Local Area Network (LAN)

• LAN is usually privately owned and links the devices in a single office, building, or campus.
• LANs are designed to allow resources to be shared between personal computers or workstations.
• In addition to size, LANs are distinguished from other types of networks by their transmission media and topology.
• In general, a given LAN will use only one type of transmission medium. The most common LAN topologies are bus, ring, and star.

Wide Area Network

• A wide area network (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.
• The switched WAN connects the end systems, which usually comprise a router that connects to another LAN or WAN.
• 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.
• An early example of a switched WAN is X.25, a network designed to provide connectivity between end users.
• A good example of a switched WAN is the asynchronous transfer mode (ATM) network, which is a network with fixed-size data unit packets called cells.