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CS601 - Data Communication - Lecture Handout 02

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  • Link: connects adjacent nodes Wires, Cables, Any thing that physically connects two nodes
  • Path: end-to-end route within a network
  • Circuit: the conduit over which data travels
  • Packetizing: dividing messages into fixed-length packets prior to transmission over a network’s communication media
  • Routing: determining a message’s path from sending to receiving nodes

The transmission medium may itself be a network, so route needs to be specified


“A NETWORK is a set of devices (Nodes) connected by Communication Links”

Node: Can be a Computer, Printer or any other device capable of sending or receiving

  • The links connecting Nodes are called COMMUNICATION CHANNELS Networks- Why we need them?

Networks- Why we need them?

It is often impractical for devices to be directly connected for two major reasons:

  • The devices are very far apart. They are expensive to connect just two devices with one in Lahore and other in Islamabad
  • Large set of devices would need impractical number of connections e .g. Telephone Lines in the world and all the computers owned by a single organization

Solution to the Problem=Networks

  • Solution is to connect all devices to a central system known as a NETWORK in which all terminals or computers share the links.
  • Two Main Classifications of the Networks
    • LANS
    • WANS


  • Instead of a single large machine being responsible for all aspects of a process , each separate computer handles a subset of the task
    • Example – Project Given as a part of the Course
    • Example – Office Work

Advantages of Distributed Processing


A system designer can limit the kind of interaction that a given user can have with the entire system.

  • For example : Bank’s ATM

Distributed Data bases

No one system need to provide storage capacity for the entire database

  • For example WWW gives user access to pages stored anywhere on Internet

Faster Problem Solving

Multiple computers working on a problem can solve a problem faster than a computer working alone

Security through Redundancy

Multiple computers running the same program provide security through redundancy
If one computer hardware breaks down then others cover up.

Collaborative Processing

Both multiple computers and multiple users can interact for a task

Network Criteria

Network Criteria


Can be measured in many ways including Transit and Response Time

  • Depends on a no. of Factors:
    • Number of USERS
    • Type of Transmission Medium
    • Hardware
    • Software
    • Network Criteria


  • Number of USERS
    • Large Number of concurrent users slow network
    • Design of a network
    • Peak Load Periods
    • Network Criteria
  • Type of Transmission Medium
    • Medium defines speed at which data can travel
    • Fiber Optic Cable
    • 100Mbps and 10 Mbps
    • Hardware
    • Software
  • Hardware
    • Effect speed and the capacity of transmission
    • Fast computer with large storage capacity
    • Software
    • Network Criteria
  • Software
    • Software processes data at sender , receiver and intermediate nodes
    • All communication
    • Moving message from node to node
    • Transforming,
    • Processing at the sender and receiver
    • Error Free Delivery

Well designed software can speed up the process


  • Depends on a no. of Factors:
    • Frequency of Failure
    • Recovery Time of a Network after Failure
    • Catastrophe
    • Fire , Earthquake or Theft


  • Unauthorized Access
    • Sensitive data
    • Protection at multiple levels:
    • Lower level: Passwords and user ID codes
    • Upper Level: Encryption
  • Viruses

Network Applications

Marketing and Sales

  • Marketing
    • Collect, exchange and analyze data relating to the customers needs
    • Product development cycles
  • Sales
    • Tele shopping,
    • On line reservation systems

Financial Services

  • Online Banking
  • Foreign Exchange Transfers
  • Rates


  • Computer Aided Design
  • Computer Assisted Manufacturing
  • Network Applications

Electronic Messaging


  • Conferences to occur w/o participants at the same place
  • Chat
  • Voice Conferencing
  • Video Conferencing

Cable Television


  • Key Data Communication Terminology
  • Networks and why we need them?
  • Distributed Processing
  • Network Criteria
  • Network Applications

Reading Sections

  • Section 1.3, “Data Communications and Networking” 4th Edition by Behrouz A.Forouzan
  • Sections 1.3 “Data and Computer Communication” 6th Edition by William Stallings