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Week 1 Lecture Review

Week 1 Lecture Review

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Week 1 Lecture Review

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  1. Week 1 Lecture Review Do you remember? • Definition of The Internet • “internet” vs “The Internet” • 3 types of networks • Why was the “internetworking project” at ARPA funded by the US DoD ? • What was the role of Bush, Taylor, Cerf, Berners-Lee, Andreeson? Week2 - May 16, 2005

  2. Week 1 Lecture Review The Internet • a specific worldwide network of interconnected networks • communication protocols are used to specify a common language so that these different computers can exchange messages Week2 - May 16, 2005

  3. Week 1 Lecture Review Networks That Became The Internet Week2 - May 16, 2005 source: http://www.course.com/

  4. Week 1 Lecture Review Did you.... • Do the required reading? • Do lab 1b at home? Week2 - May 16, 2005

  5. Week 1 Lab Review Do you remember? • Your learn ID • Your matrix ID and Password • How to get help with your accounts Week2 - May 16, 2005

  6. Week 1 Lab Review Do you remember? • Have you accessed your “matrix” account from home using telnet? • The answers to the questions at the end of lab1 Week2 - May 16, 2005

  7. This Week • Intro to the Internet continued • Some basic UNIX commands Week2 - May 16, 2005

  8. Protocols Definition: Communication protocol • an agreement that specifies a common language that two computers use to exchange messages. A protocol is a set of agreed upon rules ex. a “lecture protocol” – raise your hand to ask a question Week2 - May 16, 2005

  9. Definition: TCP/IPTransmission Control Protocol/Internet ProtocolThe communications protocols used to connect hosts on the Internet. • TCP/IP: • uses several protocols - the two main ones are TCP and IP. • TCP/IP is built into the UNIX operating system and is used by the Internet • It is the standard for transmitting data over networks. Week2 - May 16, 2005

  10. Definition: TCP “The part of the TCP/IP set of rules for sending data over a network that includes the rules that computers on a network use to establish and break connections” source:The Internet, Perry & Schneider • The TCP protocol • is a “connection-oriented” service that enables two hosts to establish a connection and exchange streams of data. • guarantees delivery of data • guarantees that packets will be reassembled in the same order in which they were sent. Week2 - May 16, 2005 source: www.webopedia.com

  11. Definition: The Internet Protocol (IP) The part of the TCP/IP set of rules for sending data over a network that includes the rules for routing of individual data packets The IP protocol specifies how a packet is created specifies how a router must forward each packet to its destination IP is “connectionless” – it does not try to establish a connection with its peer before sending data Week2 - May 16, 2005

  12. Definition: packet or datagram “A unit of data sent across a network”. • When a large block of data is to be sent over a network, it is broken up into several packets, sent, and the reassembled at the other end... • The exact layout of an individual packet is determined by the protocol being used. Week2 - May 16, 2005 source: www.netdictionary.com

  13. IP Address • Each host in the Internet is assigned to a unique number for identification. • Such a number is called the IP address of the host. • To improve readability, IP addresses are split up into four numbers. The range of each number falls into 0-255, inclusive. • For example, the host robin.cse.cuhk.edu.hk has an IP address of 137.189.90.184. Week2 - May 16, 2005 source: John Hunter

  14. Network Number/Host number • IP addresses are split into a network number, and a host number. • For example, 137.189 is the network number of CUHK, while 90.184 is the host number of the host robin.cse.cuhk.edu.hk. • Network numbers are assigned by a central authority, the The Internet Corporation for Assigned Names and Numbers (ICANN). Week2 - May 16, 2005 source: John Hunter

  15. Class Networks • Class Acomprises networks 1.0.0.0 through 127.0.0.0. The network number is contained in the first quad. It allows roughly 16 million hosts per network. • Class Bcontains networks 128.0.0.0 through 191.255.0.0. The network number is in the first two quads. This class allows for 16,320 nets with 65,024 hosts each. Week2 - May 16, 2005 source: John Hunter

  16. Class Networks • Class Cnetworks range from 192.0.0.0 through 223.255.255.0, with the network number contained in the first three octets. This class allows for nearly 2 million networks with up to 254 hosts. • Classes D, E, and F Addresses falling into the range of 224.0.0.0 through 254.0.0.0 are either experimental or are reserved for special purpose use. Week2 - May 16, 2005 source: John Hunter

  17. Subnet • The Internet is structured hierarchically. For example, CUHK consists of many academic departments and administrative bodies, each maintaining their own network. • IP allows you to subdivide a network into several subnets. For example, CSE and CSC are two subnets inside CUHK. • Each subnet is identified by a subnet number. Week2 - May 16, 2005 source: John Hunter

  18. Subnet • For example, we have a different way to interpret the IP address 137.189.90.184, • 137.189 refers to the network number of CUHK; • 90 refers to the subnet number of CSE; and • 184 refers to the host number of robin. Week2 - May 16, 2005 source: John Hunter

  19. Example: The Chinese University of Hong Kong Week2 - May 16, 2005 source: John Hunter

  20. IP Routing Remember? The Internet is a packet switching network. • The process of transmitting a data packet from the source to the destination via a series of intermediate stations is called routing. source: John Hunter Week2 - May 16, 2005

  21. IP Routing IP routing works as follows: • Each data packet is labeled with the IP address of the destination host. • When a packet is being delivered, the IP address of the destination attached is examined. Week2 - May 16, 2005 source: John Hunter

  22. IP Routing For example: When a packet is destined to: robin.cse.cuhk.edu.hk (137.189.90.184) Week2 - May 16, 2005 source: John Hunter

  23. IP Routing • First - the network number is extracted as 137.189, which is the network number of CUHK. The packet is thus sent to Hong Kong and then to CUHK. 137.189.90.184 1500 bytes Data here Week2 - May 16, 2005 source: John Hunter

  24. IP Routing • Inside CUHK, the subnet number is examined and is found to be 90, which is the subnet number of CSE. The packet is thus sent to CSE. 137.189.90.184 1500 bytes Data here Week2 - May 16, 2005 source: John Hunter

  25. Inside CSE, the host number is examined and is found to be 184, which is the host number of robin. Finally, the packet is sent to robin, the destination. IP Routing 1500 bytes Data here 137.189.90.184 Week2 - May 16, 2005 source: John Hunter

  26. Making it more human • Humans have trouble remembering IP addresses. • Therefore URLs, Domain Names, and Host Names were created. Week2 - May 16, 2005 source: Inge McLaurin

  27. Domain and Domain Name • A domain is a logical grouping of computers on a network. It may include multiple networks. It may also just be a subset of a network of computers. • Just like people, domains need to have names. Week2 - May 16, 2005 source: Inge McLaurin

  28. Top Level Domain • Some top level domains (TLD) of the Internet • com: for commercial entities • edu: for four-year educational institutions • gov: for non-military, US federal gov. institutions • net: for network operations and Internet Service Providers (ISP) • org: for non-profit organizations • There are also domain names for each country Week2 - May 16, 2005 source: Inge McLaurin

  29. Top Level Domain • There are also domain names for each country • ca: Canada • cn: China • uk: United Kingdom Week2 - May 16, 2005 source: Ling Zhu

  30. Host and Host Name • A host is a computer that is enabled to function on a network. • To be a host on the Internet, a computer must meet 4 requirements: • Use the Internet Protocol (IP) • Be assigned a unique IP address; eg., 206.96.248.226 • Have a network connection that provides a route to the Internet • Have a domain name (optional) Week2 - May 16, 2005 source: Inge McLaurin

  31. Domain and Host Names • A given domain can, potentially, contain millions of host names as long as they are all unique within that domain. www.senecac.on.ca cns.senecac.on.ca cs.senecac.on.ca learn.senecac.on.ca phobos.senecac.on.ca 142.204.1.1 142.204.119.46 142.204.57.12 142.204.1.21 142.204.57.136 Week2 - May 16, 2005 source: Inge McLaurin

  32. cns.senecac.on.ca/ siris.senecac.on.ca/ Domain Name TLD Host Name Qualified Domain Name • The host name, and domain name combine to give a qualified domain name Qualified Domain Name Qualified Domain Name Week2 - May 16, 2005 source: Inge McLaurin

  33. Top Level Domain (TLD) Host Name Domain Name Qualified Domain Name Examples http://www.yahoo.com/ http://www.howstuffworks.com/ http://cns.senecac.on.ca/~fac/ http://htmlgoodies.earthweb.com/ Week2 - May 16, 2005 source: Inge McLaurin

  34. Domain Name to IP address • All of the machines use names called IP Addresses to refer to one another. • For example, • the machine that humans refer to as www.howstuffworks.com • has an IP address of 216.27.61.137. • Every time you use a domain name, you use the Internet's domain name servers (DNS) to translate the human-readable domain name into the machine-readable IP address. Week2 - May 16, 2005 source: Inge McLaurin

  35. The DNS does a lot of work Domain name servers translate domain names to IP addresses. That sounds simple and it would be except for 5 things: • There are billions of IP addresses currently in use, and most have a human readable name as well. • There are many billions of requests made from domain name servers every day. • Domain names and IP addresses change daily. • New domain names get created daily. • Millions of people do the work to change and add domain names and IP addresses every day. Week2 - May 16, 2005 source: Inge McLaurin

  36. The DNS database • The DNS system is a database • No other database on the planet gets this many requests. • No other database has millions of people changing it every day either. • That is what makes the DNS system so unique! www.senecac.on.ca A machine running a DNS 142.204.1.1 Week2 - May 16, 2005 source: Inge McLaurin

  37. DNS system-throughout the world • Every domain has a domain name server somewhere that handles its requests, and there is a person maintaining the records in that DNS. • This is one of the most amazing parts of the DNS system -- it is completely distributed throughout the world on millions of machines administered by millions of people, yet it behaves like a single, integrated database! Week2 - May 16, 2005 source: Inge McLaurin

  38. ISP (Internet Service Provider) • Companies that provide access to the Internet • the ISP provides your computer with a different IP address each time you connect • this way the ISP only needs enough IP addresses for all the users that are connected simultaneously. Week2 - May 16, 2005

  39. ISP’s (Internet Service Providers) Network Access Providers (NAPS) Sell Access to: Internet Service Providers (ISP’s) Sell Access to: Large Firms Small ISP’s Sell Access to: Small Firms Individuals Week2 - May 16, 2005 source: The Internet, Perry & Schneider

  40. Internet Accounts – PPP & SLIP Definition: Point-to-Point Protocol (PPP) “a method of connecting a computer to the Internet that: is more stable than the older SLIP protocol provides error checking features. sends the computer's TCP/IP packets to a server that puts them onto the Internet Week2 - May 16, 2005 source: www.webopedia.com

  41. Internet Accounts – PPP & SLIP Definition: SLIP (PPP) “a method of connecting a computer to the Internet that: source: www.webopedia.com a protocol used to connect to an ISP using a dial-up telephone line is older and simpler than PPP is not much different from connecting to the Internet via PPP from a practical perspective Week2 - May 16, 2005

  42. Internet Accounts In general, service providers offer only one protocol.... • Which does yours offer? • What about Seneca dial-up? • Once connected does PPP “give you more” of the Internet than SLIP? Additional Reading (Optional) http://www.ccsi.com/survival-kit/slip-vs-ppp.html Week2 - May 16, 2005

  43. Internet Services • World Wide Web (WWW) • Email • Newsgroups (Usenet) • Internet Relay Chats (IRC) • File Transfer Week2 - May 16, 2005

  44. Internet Services • World Wide Web (WWW) • Email • Newsgroups • Internet Relay Chats (IRC) • File Transfer Week2 - May 16, 2005

  45. 1. The World Wide Web X Isn’t the definition of “The World Wide Web” the same as the definition of the Internet? Definition: Wait a minute!!!!! Wrong! Week2 - May 16, 2005

  46. The Web is just one of the ways that information can be sent over the Internet. • The Web uses the HTTP protocol, only one of the languages spoken over the Internet, to transmit data. • The Internet, not the Web, is also used for e-mail, which relies on SMTP, Usenet news groups, instant messaging and FTP. The WebThe Internet Week2 - May 16, 2005 source: www.webopedia.com

  47. Internet Services1. The World Wide Web Definition: “A system of Internet servers that support documents formatted in a script called HTML (HyperText Markup Language). These documents support links to other documents, as well as graphics, audio, and video files.” • Not all Internet servers are part of the World Wide Web • HTTP (Hypertext Transfer protocol) defines how messages are formatted and transmitted and what actions Web servers and browsers take Week2 - May 16, 2005 source: www.webopedia.com

  48. Web Pages Definition: a web page is a file written in HTML (Hyper Text Mark-Up Language) • HTML is the computer language used to specify the contents and format of documents in the WWW • to access a web page you need the URL (Uniform Resource Locator) which specifies its location Week2 - May 16, 2005

  49. Internet Services • World Wide Web (WWW) • Email • Newsgroups • Internet Relay Chats (IRC) • File Transfer Week2 - May 16, 2005

  50. Internet Services2. Email Definition: the transmission of text messages over communications networks Interesting Note – According to “How Stuff Works”... • The first e-mail message was sent in 1971 by an engineer named Ray Tomlinson. • before this, you could only send messages to users on a single machine. • Tomlinson's breakthrough was the ability to send messages to other machines on the Internet, using the @ sign to designate the receiving machine. Week2 - May 16, 2005