1 computer communication & networks lecture 1 introduction waleed ejaz...
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Computer Communication & Networks
Lecture 1
Introduction
http://web.uettaxila.edu.pk/CMS/coeCCNbsSp09/index.asp
Waleed [email protected]
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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 messagesa. operates on discrete
blocks of datab. 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
R3Switch 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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