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

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

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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

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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.

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

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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.

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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

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

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

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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

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

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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

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

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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

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

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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!

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

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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

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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...

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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...

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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

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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

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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

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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

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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

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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

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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 ?

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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

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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

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

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

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