This document provides an introduction and overview of a computer communication and networks course. It introduces the instructor, Engr. Waleed Ejaz, and lab engineer, Engr. Noshina Ishaq. It outlines the course website, grading policy, required skills, aim of the course to introduce computer networks, and discusses topics that will be covered like network design, addressing and routing, switching strategies, multiplexing, reliability issues, and research areas in networking. Required readings are listed from the textbook at the end.

1. 1
Computer Communication & Networks
Lecture 1
Introduction
http://web.uettaxila.edu.pk/CMS/coeCCNbsSp09/index.asp
Waleed Ejaz
waleed.ejaz@uettaxila.edu.pk

2. 2
Overview
 Administrative
 Networking: An Overview of Ideas and
Issues

3. 3
Who’s Who
 Instructor
 Engr. Waleed Ejaz
 2006 -2008 MS (Computer Engineering) from NUST
 Area of Specialization: Communication & Computer
Networks
 2003-2006 BE (Computer Engineering) from UET Taxila
 Lab Engineer
 Engr. Noshina Ishaq

4. 4
Web Resources
 Course web
• http://web.uettaxila.edu.pk/CMS/coeCCNbsS
p09/index.asp
• This website and email will serve as a
communication medium between you and me
besides the lecture timing.
 Do visit the course website regularly and see
Recent Announcements for updates.

5. 5
Grading Policy
 Final Exam: 100
 Grand Quiz 10
 Assignments 5
 Quizzes: 10
 Labs 25

6. 6
Answers to FAQs
 All home works are due at the beginning of the class
indicated on the course calendar
 After that 10% penalty: only if submitted before solutions
are posted.
 Exams are closed-book and extremely time limited.
 Exams consist of design questions, numerical,
maybe true-false and short answer questions.
 More about Exams you can see Past Exams from
WEB.

7. 7
Reading
 Text book:
 Data Communications and Networking, 4/e
 B.A. Forouzan,
McGraw-Hill, 2003,
ISBN 0-07-292354-7.
 Reference books:
 Computer Networking, a top-down approach
featuring the Internet (3rd edition),
 J.K.Kurose, K.W.Ross,
Addison-Wesley, 2005,
ISBN 0-321-26976-4.
 Computer Networks, A Systems Approach
L. Peterson & Davie

8. 8
Required Skills
 The course does not assume prior knowledge
of networking.

9. 9
My Requirement from YOU
 I require YOU to take active part during lectures
 Which means Lot of Questioning in the class –
(Interactive session)

10. 10
Aim of the Course
 Aim of the course is to introduce you to the
world of computer networks, so that you
could
 know the science being used in running this
network
 Use this knowledge in your professional field

11. 11
Network design
Before looking inside a computer
network, first agree on what a
computer network is

12. 12
Computer network ?
 Set of serial lines to attach
terminals to mainframe ?
 Telephone network carrying
voice traffic ?
 Cable network to disseminate
video signals ?
Specialized to
handle:
Keystrokes
Voice
Video

13. 13
What distinguishes a
Computer network ?
 Generality
 Built from general purpose
programmable hardware
 Supports wide range of applications

14. 14
Information, Computers, Networks
 Information: anything that is represented in bits
 Form (can be represented as bits) vs
 Substance (cannot be represented as bits)
 Properties:
 Infinitely replicable
 Computers can “manipulate” information
 Networks create “access” to information

15. 15
Networks
 Potential of networking:
 move bits everywhere, cheaply, and with desired
performance characteristics
 Network provides “connectivity”

16. 16
What is “Connectivity” ?
 Direct or indirect access to every other node in the
network
 Connectivity is the magic needed to communicate if
you do not have a direct pt-pt physical link.
 Tradeoff: Performance characteristics worse than true physical
link!

17. 17
Building Blocks
 Nodes: PC, special-purpose hardware…
 hosts
 switches
 Links: coax cable, optical fiber…
 point-to-point
 multiple access
…

18. 18
Why not connect each node
with every other node ?
 Number of computers that can be
connected becomes very limited
 Number of wires coming out of each
node becomes unmanageable
 Amount of physical hardware/devices
required becomes very expensive
 Solution: indirect connectivity using
intermediate data forwarding nodes

19. 19
Switched Networks
 two or more nodes
connected by a link
 white nodes
(switches)
implement the
network
 colored nodes
(hosts) use the
network
 A network can be defined recursively as...

20. 20
Switched Networks
 two or more networks
connected by one or more
nodes: internetworks
 white nodes (router or
gateway) interconnects
the networks
 a cloud denotes “any
type of independent
network”
 A network can be defined recursively as...

21. 21
A Network
A network can be defined recursively as
two or more nodes connected by a
physical link
Or
two or more networks connected by one or
more nodes

22. 22
Switching Strategies
 Circuit switching:
carry bit streams
a. establishes a dedicated
circuit
b. links reserved for use
by communication
channel
c. send/receive bit stream
at constant rate
d. example: original
telephone network
• Packet switching: store-
and-forward messages
a. operates on discrete
blocks of data
b. utilizes resources
according to traffic
demand
c. send/receive messages
at variable rate
d. example: Internet

23. 23
What next ?
 Hosts are directly or indirectly connected to
each other
 Can we now provide host-host connectivity ?
 Nodes must be able to say which host it
wants to communicate with

24. 24
Addressing and Routing
 Address: byte-string that identifies a node
 usually unique
 Routing: forwarding decisions
 process of determining how to forward messages
to the destination node based on its address
 Types of addresses
 unicast: node-specific
 broadcast: all nodes on the network
 multicast: some subset of nodes on the network

25. 25
Wrap-up
 A network can be constructed from
nesting of networks
 An address is required for each node
that is reachable on the network
 Address is used to route messages
toward appropriate destination

26. 26
What next ?
 Hosts know how to reach other hosts on
the network
 How should a node use the network for
its communication ?
 All pairs of hosts should have the ability
to exchange messages: cost-effective
resource sharing for efficiency

27. 27
Multiplexing
 Physical links and nodes are shared among users
 (synchronous) Time-Division Multiplexing (TDM)
 Frequency-Division Multiplexing (FDM)
L1
L2
L3
R1
R2
R3
Switch 1 Switch 2
Multiple flows
on a single link
Do you see any problem with TDM / FDM ?

28. 28
What Goes Wrong in the Network?
Reliability at stake
 Bit-level errors (electrical interference)
 Packet-level errors (congestion)
 distinction between lost and late packet
 Link and node failures
 distinction between broken and flaky link
 distinction between failed and slow node

29. 29
What Goes Undesirable in the
Network?
Required performance at stake
 Messages are delayed
 Messages are delivered out-of-order
 Third parties eavesdrop
 The challenge is to fill the gap between
application expectations and hardware
capabilities

30. 30
Research areas in Networking
 Routing
 Security
 Ad-hoc networks
 Wireless networks
 Protocols
 Quality of Service
 …

31. 31
Readings
 Chapter 1: 1.1, 1.2
 Computer Networks, A Systems Approach
L. Peterson & Davie

32. 32