Transcript Data Communication & Network

Computer Communication & Networks
Lecture 1
Introduction
http://web.uettaxila.edu.pk/CMS/coeCCNbsSp09/index.asp
Waleed Ejaz
[email protected]
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Overview
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Administrative
Networking: An Overview of Ideas and
Issues
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Who’s Who
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Instructor
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Engr. Waleed Ejaz
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2006 -2008 MS (Computer Engineering) from NUST
 Area of Specialization: Communication & Computer
Networks
2003-2006 BE (Computer Engineering) from UET Taxila
Lab Engineer
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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.
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Do visit the course website regularly and see
Recent Announcements for updates.
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Grading Policy
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Final Exam:
Grand Quiz
Assignments
Quizzes:
Labs
100
10
5
10
25
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Answers to FAQs
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All home works are due at the beginning of the class
indicated on the course calendar
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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
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Text book:
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Data Communications and Networking, 4/e
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B.A. Forouzan,
McGraw-Hill, 2003,
ISBN 0-07-292354-7.
Reference books:
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Computer Networking, a top-down approach
featuring the Internet (3rd edition),
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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
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The course does not assume prior knowledge
of networking.
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My Requirement from YOU
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I require YOU to take active part during lectures
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Which means Lot of Questioning in the class –
(Interactive session)
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Aim of the Course
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Aim of the course is to introduce you to the
world of computer networks, so that you
could
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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 ?
Specialized to
handle:
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Set of serial lines to attach
terminals to mainframe ?
Telephone network carrying
voice traffic ?
Cable network to disseminate
video signals ?
Keystrokes
Voice
Video
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What distinguishes a
Computer network ?
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Generality
Built from general purpose
programmable hardware
Supports wide range of applications
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Information, Computers, Networks
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Information: anything that is represented in bits
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Form (can be represented as bits) vs
Substance (cannot be represented as bits)
Properties:
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Infinitely replicable
Computers can “manipulate” information
Networks create “access” to information
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Networks
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Potential of networking:
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move bits everywhere, cheaply, and with desired
performance characteristics
Network provides “connectivity”
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What is “Connectivity” ?
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Direct or indirect access to every other node in the
network
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Connectivity is the magic needed to communicate if
you do not have a direct pt-pt physical link.
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Tradeoff: Performance characteristics worse than true physical
link!
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Building Blocks
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Nodes: PC, special-purpose hardware…
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hosts
switches
Links: coax cable, optical fiber…
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point-to-point
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multiple access
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Why not connect each node
with every other node ?
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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
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A network can be defined recursively as...
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two or more nodes
connected by a link
white nodes
(switches)
implement the
network
colored nodes
(hosts) use the
network
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Switched Networks
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A network can be defined recursively as...
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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”
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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
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Circuit switching:
carry bit streams
a.
b.
c.
d.
establishes a dedicated
circuit
links reserved for use
by communication
channel
send/receive bit stream
at constant rate
example: original
telephone network
• Packet switching: storeand-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 ?
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Hosts are directly or indirectly connected to
each other
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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
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Address: byte-string that identifies a node
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Routing: forwarding decisions
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usually unique
process of determining how to forward messages
to the destination node based on its address
Types of addresses
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unicast: node-specific
broadcast: all nodes on the network
multicast: some subset of nodes on the network
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Wrap-up
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A network can be constructed from
nesting of networks
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An address is required for each node
that is reachable on the network
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Address is used to route messages
toward appropriate destination
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What next ?
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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
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Physical links and nodes are shared among users
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(synchronous) Time-Division Multiplexing (TDM)
Frequency-Division Multiplexing (FDM)
L1
R1
L2
L3
Switch 1
Multiple flows
on a single link
Switch 2
R2
R3
Do you see any problem with TDM / FDM ?
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What Goes Wrong in the Network?
Reliability at stake
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Bit-level errors (electrical interference)
Packet-level errors (congestion)
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distinction between lost and late packet
Link and node failures
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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
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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
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Routing
Security
Ad-hoc networks
Wireless networks
Protocols
Quality of Service
…
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Readings
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Chapter 1: 1.1, 1.2
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Computer Networks, A Systems Approach
L. Peterson & Davie
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