Chapter 1 - Introduction

How do Computer Networks and Internet operate?

Explosive growth

Internet

Economic impact

Complexity

Abstractions and concepts

How do Computer Networks and Internets Operate?

Network: system for connecting computer using a single transmission technologyInternet: 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

Explosive growth

•New phenomenon - now, networks are an important part of everyday activities

•Business •Home •Government •Education

•Global Internet growing exponentially •Initially a research project with a few dozen sites •Today, millions of computers and thousands of networks world-wide

Internet

•Roots in military network called Arpanet •Fundamental changes from centralized to distributed computing •Incorporated features for reliability and robustness

•Multiple links •Distributed routing

•Ethernet made local networking feasible •TCP/IP protocol made internetworking possible

•Developed after Arpanet •Switchover occurred in 1983

•Exponential growth - doubling every 18 months

Economic impact

•Large industry has grown around: •Networking hardware •Computers •Software

•Companies must integrate planning, implementation, management and upgrade

Complexity

•Computer networking is complex •Many different hardware technologies •Many different software technologies •All can be interconnected in an internet

•No underlying theory •Terminology can be confusing

•TLAs •Industry redefines or changes terminology from academia •New terms invented all the time

Chapter 2 - Motivation and Tools

Introduction Historic motivation ARPA Packet switching Internetworking History and growth Probing the Internet Ping Traceroute

Introduction

•Motivation •Service •Tools for exploration

Historic motivation

•Early computers were expensive •Large footprint •Centralized

•Programs took a long time to run •Couldn't afford to put computers everywhere

ARPA

•Advanced Research Projects Agency initiated project to connect researchers with computers •Adopted new technology:

•Packet switching •Internetworking

•Resulted in system for remote access to expensive resources

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

•Many (mutually incompatible) network technologies •No one technology appropriate for every situation •Internetworking glues together networks of dissimilar technologies with routers •Result is virtual network whose details are invisible

History and growth

•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 Internet

•Few hundred computers •Few tens of networks

Probing the Internet

•Two tools: •Ping - sends message that is echoed by remote computer •Traceroute - reports path to remote computer

Ping

•Sends packet to remote computer •Remote computer replies with echo packet •Local computer reports receipt of reply % ping www.ubalt.edu www.ubalt.edu is alive

Traceroute

•Sends series of packets along path to destination

•Each successive packet identifies next router along path •Uses expanding ring search

•Reports list of packets