1 Introduction Computer Networks Fall 2005

2 Computer Networks  Network: system for connecting computers using a single transmission technology  An internet: set of networks connected by routers that are configured to pass traffic among any computers attached to networks in the set  Data transmission - media, data encoding  Packet transmission - data exchange over a network  Internetworking - universal service over a collection of networks  Network applications - programs that use an internet

3 Networking Growth  New phenomenon - now, networks are an important part of everyday activities  Business  Home  Government  Education  Global Internet growing exponentially  Initially (2 decades ago) a research project with a few dozen sites  Today, millions of computers and hundreds of thousands of networks world-wide

4 Huge Impact  Societal –apparent in TV and Magazine advertisement  Economic –telecommuting, new large industry segments  Computer Science –Distributed computing –Data storage and computer architecture

5 Some History  Advanced Research Projects Agency initiated project to connect researchers with computers –Motivated by the need for remote access to expensive resources  Adopted new technology:  Packet switching »Data transmitted in small, independent pieces  Source divides outgoing messages into packets -- Destination recovers original data »Each packet travels independently  Includes enough information for delivery -- May follow different paths -- Can be retransmitted if lost  Internetworking »Internetworking glues together networks of dissimilar technologies with routers -- Result is virtual network whose details are invisible

6 Internet History  ARPANET began in late 1960s (not using TCP/IP)  TCP/IP developed in late 1970s  ARPANET switched to TCP/IP in early 80s  Start of public Internet (early 1990’s)  Few hundred computers  Few tens of networks

7 Internet Growth (Number of Computers Attached to the Internet)

8 Internet Growth (log scale) Number of connected hosts is approximately doubling every 18 months

9 Topic Complexity  Computer networking is complex –Many different hardware technologies »Ethernet, Token ring, ATM, Fibre Channel, etc. –Many different software technologies »TCP/IP, Apple talk, etc. –All can be interconnected in an internet  Terminology can be confusing –Abbreviations are very common –Industry redefines or changes terminology –New terms invented all the time  To unravel complexity, in the course, we will concentrate on concepts rather than details of specifics mechanisms

10 Simple Tools  Ping  Traceroute

11 Course Website/Syllabus