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Computer Science 1611 Internet & Web Technology Infrastructure Internet and the Web.

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1 Computer Science 1611 Internet & Web Technology Infrastructure Internet and the Web

2 Computer Science 1611 Internet & Web Learning Objectives In this section, we will learn about: The origin, growth, and current structure of the Internet How packet-switched networks combined to form the Internet Internet protocols and Internet addressing

3 Computer Science 1611 Internet & Web Technology Overview Computer networks and the Internet form the basic technology structure for what is now the WWW. The computers in these networks run such software as: Operating systems, database managers, encryption software, multimedia creation and viewing software, and the graphical user interface

4 Computer Science 1611 Internet & Web Technology Overview The Internet includes: The hardware that connects the computers together the hardware that connects the networks together Rapid change in these technologies requires businesses to be flexible

5 Computer Science 1611 Internet & Web Packet-Switched Networks A local area network (LAN) is a network of computers close together. A wide area network (WAN) is a network of computers connected over a great distance. Circuit switching is used in telephone communication. The Internet uses packet switching Files are broken down into small pieces (called packets) that are labeled with their origin, sequence, and destination addresses.

6 Computer Science 1611 Internet & Web Internet Protocols Wide Web mailto: address ftp://File Transfer Protocol telnet:Telnet

7 Computer Science 1611 Internet & Web Top Level Domain Names.edu Educational Institution (in US).ca Country Codes ( two letters such as.ca,.de,.mx,.jp).gov Governmental Agency.mil Military Entity.com Commercial Entity.net Internet Service Provider.org Non-Profit Organization

8 Computer Science 1611 Internet & Web When Computers Communicate When two or more computers communicate, they must have a common way in which to communicate. To do this computers use protocols A protocol is an agreement by which two or more computers can communicate. Transfer Control Protocol/Internet Protocol (TCP/IP) is the underlying protocol for the Internet.

9 Computer Science 1611 Internet & Web How TCP/IP Works 1) Transfer Control Protocol (TCP) breaks data into small pieces of no bigger than 1500 characters each. These “pieces” are called packets

10 Computer Science 1611 Internet & Web How TCP/IP Works(II) 2) Each packet is inserted into different Internet Protocol (IP) “envelopes.” Each contains the address of the intended recipient and has the exact same header as all other envelopes

11 Computer Science 1611 Internet & Web How TCP/IP Works A router receives the packets and then determines the most efficient way to send the packets to the recipient. After traveling along a series of routers, the packets arrive at their destination. Packet Router 1 Router 2 Router 3 Router 4 Packet

12 Computer Science 1611 Internet & Web Packets Everything you do on the Internet involves packets. For example, every Web page that you receive comes as a series of packets, and every you send leaves as a series of packets. Networks that ship data around in small packets are called packet switched networks. On the Internet, the network breaks an message into parts of a certain size in bytes. These collections of bytes are the packets. Each packet carries the information that will help it get to its destination – –the sender's IP address, –the intended receiver's IP address, –something that tells the network how many packets this message has been broken into and –the sequence number of this particular packet.

13 Computer Science 1611 Internet & Web Packets Purpose The packets carry the data in the protocols that the Internet uses: Transmission Control Protocol/Internet Protocol (TCP/IP). Each packet contains part of the body of your message. A typical packet contains perhaps 1,000 or 1,500 bytes. Each packet is then sent off to its destination by the best available route -- a route that might be taken by all the other packets in the message or by none of the other packets in the message. This makes the network more efficient. First, the network can balance the load across various pieces of equipment on a millisecond-by-millisecond basis. Second, if there is a problem with one piece of equipment in the network while a message is being transferred, packets can be routed around the problem, ensuring the delivery of the entire message.

14 Computer Science 1611 Internet & Web Packet Design Most packets are split into three parts: Header - The header contains instructions about the data carried by the packet. These instructions may include: Body - Also called the payload or data of a packet. This is the actual data that the packet is delivering to the destination. If a packet is fixed-length, then the payload may be padded with blank information to make it the right size. Footer - sometimes called the trailer, typically contains a couple of bits that tell the receiving device that it has reached the end of the packet. It may also have some type of error checking.

15 Computer Science 1611 Internet & Web How are Packets Used If a message is sent over the internet, it will be broken into packets. Each packet's header will contain the proper protocols, the originating address (the IP address of your computer), the destination address (the IP address of the computer where you are sending the ) and the packet number (1, 2, 3 or 4 since there are 4 packets). Routers in the network will look at the destination address in the header and compare it to their lookup table to find out where to send the packet. Once the packet arrives at its destination, the receiving computer will strip the header and footer off each packet and reassemble the message based on the numbered sequence of the packets.Routers

16 Computer Science 1611 Internet & Web Packet Header Header (contains instructions about the data carried by the packet) –Length of packet –Synchronization (a few bits that help the packet match up to the network) –Packet number (which packet this is in a sequence of packets) –Protocol (on networks that carry multiple types of information, the protocol defines what type of packet is being transmitted: , Web page, streaming video) –Destination address –Originating address

17 Computer Science 1611 Internet & Web Packet Body and Footer Body - Also called the payload or data of a packet. This is the actual data that the packet is delivering to the destination. If a packet is fixed- length, then the payload may be padded with blank information to make it the right size. Footer - sometimes called the trailer, typically contains a couple of bits that tell the receiving device that it has reached the end of the packet. It may also have some type of error checking.

18 Computer Science 1611 Internet & Web Error Checking The most common error checking used in packets is Cyclic Redundancy Check (CRC). CRC takes the sum of all the 1s in the payload and adds them together. The result is stored as a hexadecimal value in the footer (trailer). The receiving device adds up the 1s in the payload and compares the result to the value stored in the trailer. If the values match, the packet is good. But if the values do not match, the receiving device sends a request to the originating device to resend the packet.

19 Computer Science 1611 Internet & Web Error checking example (CRC) Suppose you have 4 bytes of data of the form –The sum of all the 1’s in this data is 17. This value can be represented in binary form as The value 17 ( ) is the CRC value which is inserted into the footer (trailer)

20 Computer Science 1611 Internet & Web Packet Construction Suppose you send an to a friend, that the is about 3,500 bits (3.5 kbits) in size, and that the network you send it over uses fixed- length packets of 1,024 bits (1 kilobit). The header of each packet is 96 bits long and the footer is 32 bits long, leaving 896 bits for the payload. To break the 3,500 bits of message into packets, you will need four packets (divide 3,500 by 896). Three packets will contain 896 bits of data and the fourth will have 812 bits.

21 Computer Science 1611 Internet & Web Routing Packets The computers that decide how best to forward each packet in a packet-switched network are called ‘routers’. The programs on these routers use ‘routing algorithms’ that call upon their ‘routing tables’ to determine the best path to send each packet. When packets leave a network to travel on the Internet, they are translated into a standard format by the router. These routers and the telecommunication lines connecting them are referred to as ‘the Internet backbone’.

22 Computer Science 1611 Internet & Web How TCP/IP Works Upon arrival at their destination, TCP checks the data for corruption against the header included in each packet. If TCP finds a bad packet, it sends a request that the packet be re-transmitted.

23 Computer Science 1611 Internet & Web IP Addresses Since computers process numbers more efficiently and quickly than characters, each machine directly connected to the Internet is given an IP Address An IP address is a 32-bit address comprised of four 8- bit numbers (2 8 ) separated by periods. Each of the four numbers has a value between 0 and 255 Normally, an IP address is is given in “dotted decimal” form

24 Computer Science 1611 Internet & Web IP Addresses Example of an IP Address: The IP Address of the MtA Web Server

25 Computer Science 1611 Internet & Web IP Addresses vs. URLs While numeric IP addresses work very well for computers, most humans find it difficult to remember long patterns of numbers. Instead, humans identify computers using Uniform Resource Locators (URLs), a.k.a. “Web Addresses”. When a human types a URL into a browser, the request is sent to a Domain Name Server (DNS), which then translates the URL to an IP address understood by computers. The DNS acts like a phonebook.

26 Computer Science 1611 Internet & Web Anatomy of a URL http protocol wwwmachine name mtasubdomain catop level domain name

27 Computer Science 1611 Internet & Web Internet Protocols A protocol is a collection of rules for formatting, ordering, and error-checking data sent across a network. ARPANET is the earliest packet-switched network. (ARPA = Advanced Research Projects Agency)ARPANET The open architecture of this experimental network used Network Control Protocol (NCP) which later was modified to become TCP/IP, the core of the Internet.

28 Computer Science 1611 Internet & Web Internet Protocols This open architecture has four key rules that have contributed to the success of the Internet. –Independent networks should not require any internal changes to be connected to the network. –Packets that do not arrive at their destinations must be retransmitted from their source network. –Router computers act as receive-and-forward devices; they do not retain information about the packets that they handle. –No global control exists over the network.

29 Computer Science 1611 Internet & Web Internet Protocols The Transmission Control Protocol (TCP) and the Internet Protocol (IP) are the two protocols that support the Internet operation (commonly referred to as TCP/IP). The TCP controls the disassembly of a message into packets before it is transmitted over the Internet and the reassembly of those packets when they reach their destination. The IP specifies the addressing details for each packet being transmitted.

30 Computer Science 1611 Internet & Web IP Addresses IP addresses are based on a 32-bit binary number that allows over 4 billion unique addresses for computers to connect to the Internet. ( is Art Miller’s office machine) –Ping Ping IP addresses appear in ‘dotted decimal’ notation (four numbers separated by periods). –Each number is in the range 0…255 –Hex notation (aside) –IP Addresses in decimal formIP Addresses IP addresses are assigned by three not-for-profit organizations (ARIN, RIPE, and APNIC). –Organization of IP numbersOrganization of IP numbers

31 Computer Science 1611 Internet & Web IP Addresses Approximately two billion IP addresses are either in use or unavailable for use. Private IP addresses are a series of IP numbers that have been set aside for subnet use and are not permitted on the Internet. IPv6 is a possible solution that uses a 128-bit hexadecimal number for addresses. –A number written using 128 bits can be in the range from 1…2 128 –Since 2 10 is approximately 10 3 = 1,000, it follows that –2 128 ~ (2 10 ) 12 ~ (10 3 ) 12 ~ ~ –1,000,000,000,000,000,000,000,000,000,000,000,000

32 Computer Science 1611 Internet & Web Domain Names To make the numbering system easier to use, an alternative addressing method that uses words was created. An address, such as is called a domain name. = The last part of a domain name (i.e., ‘.com’) is the most general identifier in the name and is called a ‘top-level domain’ (TLD).

33 Computer Science 1611 Internet & Web Top-level Domain Names

34 Computer Science 1611 Internet & Web History: Before the Web History of the Internet Before the creation of the World Wide Web (when, whom?) there was a set of technologies which constituted the internet –telnettelnet –ftpftp –GopherGopher History of the Web Early browsers for the Web were not as capable as those of todaybrowsers

35 Computer Science 1611 Internet & Web Web Page Delivery Hypertext Transfer Protocol (HTTP) is the set of rules for delivering Web pages over the Internet.HTTP HTTP uses the client/server modelclient/server A user’s Web browser opens an HTTP session and sends a request for a Web page to a remote server. In response, the server creates an HTTP response message that is sent back to the client’s Web browser. In particular, this same action can be accomplished without a browser by using the (DOS command prompt) TELNET 80 TELNET 80 (port 80) and once connected using the case sensitive command GET / (followed by two carriage returns) This will return the same thing that is returned by your web browser when you enter The combination of the protocol name and the domain name is called a uniform resource locator (URL).

36 Computer Science 1611 Internet & Web SMTP, POP, MIME, and IMAP sent across the Internet must also be formatted to a common set of rules, otherwise created by one company (or Web site) could not be read by a person at another company. Simple Mail Transfer Protocol (SMTP) specifies the exact format of a mail message and describes how mail is to be administered at the Internet and network level.

37 Computer Science 1611 Internet & Web SMTP, POP, MIME, and IMAP An program running on a user’s computer can request mail from the company’s main computer using the Post Office Protocol (POP). Multipurpose Internet Mail Extensions (MIME) allow the user to attach binary files to . The Interactive Mail Access Protocol (IMAP) performs the same basic functions as POP, but includes additional features.

38 Computer Science 1611 Internet & Web Markup Languages and the Web Web pages are marked with tags to indicate the display and formatting of page elements. SGML is a meta language (a language that can be used to define other languages) and historically is the first markup language HTML and XML are both derivatives of SGML.

39 Computer Science 1611 Internet & Web HTML Tags An HTML document contains both document text and elements. Tags are codes that are used to define where an HTML element starts and (if necessary) where it ends. In an HTML document, each tag is enclosed in brackets (<>). A two-sided tag set has an opening tag and a closing tag.

40 Computer Science 1611 Internet & Web Document Tags Document tags are those divide up a Web page into its basic sections, such as the header information and the part of the page which contains the displayed text and graphics. HTML –The first and last tags in a document should always be the HTML tags. These are the tags that tell a Web browser where the HTML in your document begins and ends. The absolute most basic of all possible Web documents is: – –If we load such a page into a Web browser, it will give us a blank screen, but it is technically a valid Web page.blank screen

41 Computer Science 1611 Internet & Web HTML Links Hypertext documents differ from regular docuements by offering hyperlinks Hyperlinks are bits of text that connect the current document to: another location in the same document another document on the same host machine another document anywhere on the Internet

42 Computer Science 1611 Internet & Web Internet Connection Options The Internet is a set of interconnected networks. Large firms that provide Internet access to other businesses are called Internet Service Providers (ISPs).

43 Computer Science 1611 Internet & Web Connectivity Overview The most common connection options that ISPs offer to the Internet are telephone, broadband, leased-line, and wireless. The internet grew quickly in North America because local telephone calls were free, as opposed to Europe, where local calls were charged by the time unit Bandwidth is the amount of data that can travel through a communication line per unit of time.

44 Computer Science 1611 Internet & Web Voice-Grade Telephone Connections The most common way to connect to an ISP is through a modem connected to your local telephone service provider. POTS uses existing telephone lines and an analog modem to provide a bandwidth of Kbps. DSL protocol offers high speed bandwidth over standard phone lines.

45 Computer Science 1611 Internet & Web Broadband Connections Connections that operate at speeds of greater than 200 Kbps are called broadband services. ADSL uses the DSL (Digital Subscriber Line) protocol to provide bandwidths (over standard phone lines) of between Kbps upstream and Mbps downstream. Cable modems provide transmission speeds between 300 Kbps-1 Mbps from the client to the server and a downstream rate as high as 10 Mbps. Satellite microwave transmissions handle Internet downloads at speeds around 500 Kbps.

46 Computer Science 1611 Internet & Web Networks: Local area and Wide area Connections Large firms can connect to an ISP using higher- bandwidth connections that they can lease from telecommunications carriers. A ‘T1’ line operates at Mbps A ‘T3’ line operates at Mbps. Ethernet (local) currently operates at 10 Mbps or 100 Mbps, and there are emerging standards for 10Gbps and 100 Gbps ethernet.Ethernet

47 Computer Science 1611 Internet & Web WirelessWireless Connections Many researchers and business managers see great potential for wireless networks and the devices connected to them. The term m-commerce (mobile commerce) is used to describe the kinds of resources people might want to access using devices that have wireless connections.

48 Computer Science 1611 Internet & Web Internet2 Internet2 is an experimental test bed for new networking technologies that is separate from the original Internet.Internet2 200 universities and a number of corporations joined together to create this network. It has achieved bandwidths of 10 Gbps. Internet2 promises to be the proving ground for new technologies and applications of those technologies that will eventually find their way to the Internet.


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