Computer Communication

1
Computer Communication Networks

• Lecture 1
• Introduction
• http//web.uettaxila.edu.pk/CMS/coeCCNbsSp09/index
  .asp

Waleed Ejaz waleed.ejaz_at_uettaxila.edu.pk
2
Overview

• Administrative
• Networking An Overview of Ideas and Issues

3
Whos 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
Web Resources

• Course web
• http//web.uettaxila.edu.pk/CMS/coeCCNbsSp09/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
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.

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
Required Skills

• The course does not assume prior knowledge of
  networking.

9
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 ?
Specialized to handle Keystrokes Voice Video

• Set of serial lines to attach terminals to
  mainframe ?
• Telephone network carrying voice traffic ?
• Cable network to disseminate video signals ?

13
What distinguishes a Computer network ?

• Generality
• Built from general purpose programmable hardware
• Supports wide range of applications

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
Networks

• Potential of networking
• move bits everywhere, cheaply, and with desired
  performance characteristics
• Network provides connectivity

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!

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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

19
Switched Networks

• A network can be defined recursively as...

• two or more nodes connected by a link
• white nodes (switches) implement the network
• colored nodes (hosts) use the network

20
Switched Networks

• A network can be defined recursively as...

• 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

• Circuit switching carry bit streams
• establishes a dedicated circuit
• links reserved for use by communication channel
• send/receive bit stream at constant rate
• example original telephone network

• Packet switching store-and-forward messages
• operates on discrete blocks of data
• utilizes resources according to traffic demand
• send/receive messages at variable rate
• example Internet

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
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

27
Multiplexing

• Physical links and nodes are shared among users
• (synchronous) Time-Division Multiplexing (TDM)
• Frequency-Division Multiplexing (FDM)

Multiple flows on a single link
Do you see any problem with TDM / FDM ?
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

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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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