Introduction to Computer Networks

1
Introduction to Computer Networks Data
Communication

• ICS 31 Computer Networks Data Communications
• Lecture 1

2
A Communications Model

• Source
• generates data to be transmitted
• Transmitter
• Converts data into transmittable signals
• Transmission System
• Carries data
• Receiver
• Converts received signal into data
• Destination
• Takes incoming data

3
Simplified Communications Model - Diagram

4
Key Communications Tasks

• Transmission System Utilization
• Interfacing
• Signal Generation
• Synchronization
• Exchange Management
• Error detection and correction
• Addressing and routing
• Recovery
• Message formatting
• Security
• Network Management

5
Simplified Data Communications Model

6
Networking

• Why? - Point to Point Communication not Usually
  Practical
• Devices are too Far Apart
• Large Set of Devices would need Impractical
  Number of Connections
• Solution is a Communications Network
• Wide Area Network (WAN)
• Metropolitan Area Network (MAN)
• Local Area Network (LAN)

7
Simplified Network Model


8
Wide Area Networks

• Large geographical area
• Crossing public rights of way
• Rely in part on common carrier circuits
• Alternative technologies
• Circuit switching
• Packet switching
• Frame relay
• Asynchronous Transfer Mode (ATM)
• Integrated Services Digital Network (ISDN)

9
Metropolitan Area Networks

• Limited geographical area
• Crossing public rights of way
• Rely in part on common carrier circuits
• Alternative technologies
• Circuit switching
• Packet switching
• Frame relay
• Asynchronous Transfer Mode (ATM)
• Nomenclature is arbitrary - a MAN is technically
  similar to a WAN.

10
Local Area Networks

• Smaller scope
• Building or small campus
• Usually owned by same organization as attached
  devices
• Data rates much higher
• Usually broadcast systems
• IEEE 802.2 Logical Link Control
• IEEE 802.3 - Ethernet
• IEEE 802.4 - Token bus
• IEEE 802.5 - Token ring
• IEEE 802.11 Wireless
• GigE 10GigE
• Now some switched systems and ATM are being
  introduced

11
Uses of computer-based communication systems and
networks

• sharing of computing resources
• access to remote programs
• access to remote databases
• communication
• support net-centric, client/server and
  distributed computing

12
Whats the Internet a service view

• communication infrastructure enables distributed
  applications
• WWW, email, games, e-commerce, database., voting,
  
• more?
• communication services provided
• connectionless
• connection-oriented
• cyberspace Gibson
• a consensual hallucination experienced daily by
  billions of operators, in every nation, ...."

13
Net-centric computing (NCC)

• A distributed environment where applications and
  data are exchanged among peers across a network
  on as as-needed basis. NCC relies on portable
  applications running on multiple platforms,
  mobile code and data accessed via high-speed
  network connections, and low-cost appliances for
  local processing (from 3rd International Workshop
  on Net-Centric Computing May 14, 2001 Toronto,
  Canada)
• The traditional PC is history net-centric
  computing is the future. But what form will it
  take? Computing appliances, "connected PCs,"
  Web-enabled set-top boxes, Webphones,
  Internet-connected wireless communicators, or
  Java-based network computers? (from Emergence of
  Net-Centric Computing The Network Computers,
  InternetAppliances, and Connected PC's, Bernard
  Cole, 1999)

14
Client/server computing

• general software architecture (3-layered)
• presentation layer (user interface)
• application logic
• generalized services (e.g., file services, print
  services, communications services, and database
  services)
• one-tier, two-tier, three-tier, and n-tier
  client/server program architectures
• thin client and a fat client
• middleware

15
Distributed computing

• Distributed computing is a science which solves a
  large problem by giving small parts of the
  problem to many computers to solve and then
  combining the solutions for the parts into a
  solution for the problem. Recent distributed
  computing projects have been designed to use the
  computers of hundreds of thousands of volunteers
  all over the world, via the Internet, to look for
  extra-terrestrial radio signals, to look for
  prime numbers so large that they have more than
  one million digits, and to find more effective
  drugs to fight the AIDS virus. These projects are
  so large, and require so much computing power to
  solve, that they would be impossible for any one
  computer or person to solve in a reasonable
  amount of time. (from Internet-based Distributed
  Computing Project Web site http//www.aspenleaf.co
  m/distributed/)

16
Basic network hardware and software components

• Hardware
• Computers
• Network Interface cards
• Repeaters, Hubs
• Switches, Routers
• Transmission Media
• Software
• Applications and Services
• Network operating system
• Protocols and standards

17
Whats the Internet nuts and bolts view

• protocols control sending, receiving of msgs
• e.g., TCP, IP, HTTP, FTP, PPP
• Internet network of networks
• loosely hierarchical
• public Internet versus private intranet
• Internet standards
• RFC Request for comments
• IETF Internet Engineering Task Force

router
workstation
server
mobile
local ISP
regional ISP
company network
18
ICS 31 Computer Networks Data Communications

• Assignment 1
• 1. Approach a local organization that has a
  computer-based comm. system or network facility
  (e.g. LAN or campus network) and find out the
  following
• Uses of the facility
• Network software components
• Network hardware components
• Transmission media/telecommunication links
• Connection to the outside world (if any)
• Technical and management problems (if any)
• 2. Using a block diagram, describe the major
  components of a communication system. Show an
  example using a specific data communication
  scenario (e.g. dial-up Internet access via a
  local Internet Service Provider or a local area
  network). What are the things that you need in
  terms of hard ware and software?
• 3. Enumerate and describe the seven layers of the
  Open Systems Interconnect (OSI) Reference Model
  then describe the main layers of the Transmission
  Control Protocol/Internet Protocol (TCP/IP) and
  how it relates to the OSI reference model. Is
  there a one-to-one mapping between the TCP/IP and
  OSI layers? Show an example of layering by
  mapping the components of a network you are
  familiar with to the OSI RM or TCP/IP layers.
• Submit at least a 5 page write up of your
  answers (i.e., typed using size 12, Times New
  Roman font, single spaced)
• I will accept printed submissions only.
• Due June 26, 2003