Hon Wai Leong, NUS (UIT2201, Networks) Page 1 Copyright © 2007 by Leong Hon Wai Networks, Internet & WWW  Reading Materials:  Ch 7 of [SG3]  Additional Notes: (from web-site)  Contents:  Motivation for Networks  Types of Networks and Their Structure  Communication Protocols – routing info  Network Services / Applications  Internet and WWW

Hon Wai Leong, NUS (UIT2201, Networks) Page 2 Copyright © 2007 by Leong Hon Wai Objectives In this chapter, you will learn about  Basic networking concepts  Communication protocols  Network services and benefits  A brief history of the Internet and the WWW

Outline What is the Internet? What is the Internet? Where did it come from? Where did it come from? What are we going to discuss in cs193i? What are we going to discuss in cs193i? Break Break Networking basics Networking basics Physical Infrastructure Physical Infrastructure

The Ever-changing Internet Different colors based on IP address

What is the Internet? WWW WWW Video conferencing Video conferencing ftp ftp telnet telnet Instant messaging Instant messaging …

What is the Internet? WWW WWW Video conferencing Video conferencing ftp ftp telnet telnet Instant messaging Instant messaging … A communication infrastructure Usefulness is in exchanging information

“On-line interactive communities... will be communities not of common location, but of common interest.... the total number of users...will be large enough to support extensive general purpose [computers]. All of these will be interconnected by telecommunications channels... [to] constitute a labile network of networks--ever changing in both content and configuration.” J. C. R. Licklider

Where Did It Come From? It was invented by Al Gore. JUST KIDDING! It was invented by Al Gore. JUST KIDDING! Early 1960’s - DARPA (ARPA in 1960’s) project headed by Licklider Early 1960’s - DARPA (ARPA in 1960’s) project headed by Licklider Late 1960’s - ARPANET & research on packet switching by Roberts Late 1960’s - ARPANET & research on packet switching by Roberts First node installed by BBN at UCLA in September 1969 First node installed by BBN at UCLA in September Four host computers (UCLA, SRI, UCSB, University of Utah) Four host computers (UCLA, SRI, UCSB, University of Utah) Get more info at:

ARPANET,

History of the Internet RFCs begun by S. Crocker ( RFCs begun by S. Crocker ( by Ray Tomlinson & Larry Roberts by Ray Tomlinson & Larry Roberts 1970’s - TCP by Vint Cerf & Bob Kahn 1970’s - TCP by Vint Cerf & Bob Kahn Evolved into TCP/IP, and UDP Evolved into TCP/IP, and UDP 1980s – Hardware Explosion (LANs, PCs, and workstations) 1980s – Hardware Explosion (LANs, PCs, and workstations) 1983 – Ethernet by Metcalfe 1983 – Ethernet by Metcalfe DNS – Distributed and scalable mechanism for resolving host names into IP addresses DNS – Distributed and scalable mechanism for resolving host names into IP addresses UC Berkeley implements TCP/IP into Unix BSD UC Berkeley implements TCP/IP into Unix BSD 1985 – Internet used by researchers and developers 1985 – Internet used by researchers and developers

History of the Internet Tim Berners-Lee at CERN in 1989 Tim Berners-Lee at CERN in 1989 Proposal for WWW in 1990 Proposal for WWW in 1990 First web page on November 13, 1990 First web page on November 13, 1990 Hypertext - Text that contains links to other text. Hypertext - Text that contains links to other text. Ted Nelson’s Xanadu Ted Nelson’s Xanadu Vannevar Bush’s Memex Vannevar Bush’s Memex( W3C W3C Get more info at:

Communicating Via the Internet

Bits and Bytes Computer Data is stored in Binary Computer Data is stored in Binary Binary Digits (bits) Base 2 representation Binary Digits (bits) Base 2 representation Every 8 bits == 1 Byte Every 8 bits == 1 Byte (2 bytes (once known as octet)) Hexadecimal == Base 16 representation Hexadecimal == Base 16 representation B 8 6 A B 8 6 A Decimal == Base 10 (we have 10 fingers) Decimal == Base 10 (we have 10 fingers) 0...9, A = 10, B= 11, C = 12, D = 13, E = 14, F = 15

Bits and Bytes Kilobyte (2^10=1024 Bytes, 10^3=1000 Bytes in networking) Kilobyte (2^10=1024 Bytes, 10^3=1000 Bytes in networking) Megabyte (2^20 Bytes, 10^6 in Networking) Megabyte (2^20 Bytes, 10^6 in Networking) Gigabyte (2^30 Bytes, 10^9 in Networking) Gigabyte (2^30 Bytes, 10^9 in Networking) Terabyte (2^40, 10^12) Terabyte (2^40, 10^12) Petabyte (2^50, 10^15) Petabyte (2^50, 10^15)

Latency Latency How long minimum communication takes in seconds (s) How long minimum communication takes in seconds (s) Round trip vs. single trip Round trip vs. single trip More difficult to overcome than bandwidth More difficult to overcome than bandwidth Bandwidth Bandwidth Number of bits per time unit usually seconds (bps) Number of bits per time unit usually seconds (bps) Performance: Latency and Bandwidth bandwidth latency link

Any-to-Any Communication n 2 Network Effect (Metcalfe’s Law) n 2 Network Effect (Metcalfe’s Law) Total utility of system proportional to n 2 Total utility of system proportional to n 2 Think about Orkut, MSN Messenger Think about Orkut, MSN Messenger

Babel Internet consists of many different types of networks Ethernet Token ring Different types of operating systems and other software How do they work together? Standards

Divide Work into Layers b a physically encode bits on “wire” physically encode bits on “wire” connect segments, address (locating points on graph) and route (navigating graph) connect segments, address (locating points on graph) and route (navigating graph) make network simple and reliable make network simple and reliable

Sending Data Along Wires Connection-oriented Connection-oriented Circuit switched Circuit switched Persistent connection set up between sender and receiver Persistent connection set up between sender and receiver Example: telephone system Example: telephone system Connectionless Connectionless Packet switched Packet switched Data partitioned into packets and Data partitioned into packets and sent individually from sender to receiver sent individually from sender to receiver Reassembled at receiver Reassembled at receiver

Comparison of Switching Technologies Circuit switched Advantages Advantages Only route once Only route once Latency and bandwidth constant Latency and bandwidth constant Disadvantages Disadvantages Idle resources unavailable for other connections Idle resources unavailable for other connections Large setup time Large setup time Single point of failure Single point of failure Distributed state Distributed state Packet switched Advantages Efficient use of wires Small startup overhead Disadvantages Route each packet Per packet overhead Bursty

Ethernet Bob Metcalfe at Xerox PARC Bob Metcalfe at Xerox PARC Used for local area networks (LANs) Used for local area networks (LANs) Physically near one another Physically near one another 200 computers within 100 meters 200 computers within 100 meters Broadcast medium Broadcast medium Single wire connects all computers Single wire connects all computers Each computer has unique 48-bit MAC address Each computer has unique 48-bit MAC address All computers constantly listen All computers constantly listen “Carrier Sense, Multiple Access with Collision Detect” “Carrier Sense, Multiple Access with Collision Detect” Sender waits until wire unused before sending Sender waits until wire unused before sending If hears collision, stops, waits random time, retransmits If hears collision, stops, waits random time, retransmits

Ethernet

Ethernet Variations

Ethernet Properties Shared Shared Distributed (not Centralized) Distributed (not Centralized) Insecure Insecure Unpredictable Latency & Bandwidth Unpredictable Latency & Bandwidth But it works! But it works! Under light load (<30%), appears to be point-to- point Under light load (<30%), appears to be point-to- point

Alternative to Ethernet: Token Ring Alternative introduced by IBM (1980s) Alternative introduced by IBM (1980s) “Passing the Conch Shell” “Passing the Conch Shell”

Hon Wai Leong, NUS (UIT2201, Networks) Page 26 Copyright © 2007 by Leong Hon Wai Thank you.