Review: Networking

CS100: Introduction to n Networks q Linked computer systems Computer Science q Share information and resources n Network Classifications q LAN, MAN, WAN Lecture 11: Internet, WWW and HTML q Open vs. Closed q Ring, Bus or Stars n Protocols

q Token ring, CSMA/CD

Figure 4.2 Communication over a Figure 4.3 Communication over a ring network A bus network

A B C

B E

D E

• Each message is broadcast to all the machines on the bus. D C • Each machine monitors all the messages but only keep those addressed to itself • Token: a unique bit pattern. • A machine can send a message if the bus is silent, at the same time it keeps • A machine can transmit its own message when holding the token, otherwise monitor the bus forward messages • If it detects a collision, wait for a random period and transmit again. • Forward the token to next machine when it receives its own message.

Review: Combining Networks The Internet n Repeater n The Internet: An internet that spans the world n Bridge q Original goal was to develop a means of connecting networks that would not be disrupted n Switch by local disasters. n Router

q Today it has shifted from an academic research project to a commercial undertaking. n A combination of LANs, MANs and WANs. n Millions of computers

1 Internet Architecture How to Establish a Domain on the Internet? n Internet: can be viewed as a collection of domains. n A domain A domain must first be registered via a registrar, delegated by ICANN n Domain: A portion of the Internet, controlled by a single authority q Connected to the rest of the Internet (the cloud) by a router n A domain is connected to the Internet by a called a gateway router. n Naming of domains and assignment of Internet addresses n Gateway: The particular router that connects q Internet Corporation for Assigned Names & Numbers (ICANN): Oversees the registration of domains a domain to the Internet.

Figure 4.7 A typical approach to Strategies for connecting to the connecting to the Internet Internet n Internet Service Provider (ISP): Provides connectivity to the Internet n Popular means of connecting:

q Traditional telephone (dial up connection, 56Kbps) q Cable connections (30 Mbps) q DSL (256Kb/s – 24Mbps) q Wireless (11Mps – 54 Mbps)

Internet Addressing: IP Addresses Internet Addressing: Host Names

n IP address: 32 bit identifier for a machine n Mnemonic address made up of two parts: q IP : Internet Protocol q Domain name n Assigned by a registrar q Network identifier: identifies the domain. (Assigned by ICANN) n Example: aw.com q Host address: Identifies a particular computer within a domain. n Top level domain: Classification of domain owner (Assigned by domain administrator) q By usage – Example: .com = commercial q By country – Example: .au = Australia n Dotted decimal notation: Common notation for displaying IP q Subdomains and individual host names addresses n Assigned by domain owner n Example: r2d2.compsci.nowhereu.edu q Example: 192.207.177.133

q First three bytes (192.207.177) is the network identifier, n Translation between mnemonic addresses and IP addresses identifying the Addison-Wesley domain handled by name servers q The last byte (133) is the host address, identifying a partivular q Each domain has a name server. computer within the Addison-Wesley’s domain. q Domain name system (DNS) is used to convert a n=mnemonic address into its equivalent IP address.

2 Traditional Internet Applications World Wide Web: an Internet Application n Electronic Mail (email) n Hypertext q Hypertext: documents that contain links to other documents q Transfer messages among Internet users n It can encompass images, audio and video. n World Wide Web (WWW): n File Transfer Protocol (FTP) q The collection of hypertext documents residing on machines in the Internet q Transfer files across the Internet n It forms an intertwined web of related information. n Web Page: a hypertext document on the WWW. n Telnet and SSH n Website: a collection of closely related Web pages. q Access computers remotely

How to Access Hypertext on the Internet Figure 4.8 A typical URL n Software packages q Web Browser: a client package resides on the user’s computer n It obtains materials requested by a user and presents the these materials to the user. n Internet Explorer, q Web Server: resides on a computer containing hypertext documents to be accessed. n It provides access to the documents on its machine as requested by users. n HTTP: Hypertext Transfer Protocol q A protocol for transferring hypertext documents between browsers and web servers n URL (Uniform Resource Locator) q A unique address for a document on the Web.

Questions: Hypertext Markup Language (HTML)

n The predominant markup language for creation of web pages. n q (markup languages combine text and extra information about the 1. What is a URL? text) n 2. What is the difference between a network n Provides a means to describe the structure of text-based information identifier and a host address? in a document q denoting certain text as headings, paragraphs, lists, etc. n 3. What bit pattern is represented by 3.4.5 in q supplementing the text with interactive forms, embedded images, and dotted decimal notation? other objects

n HTML is written in the form of labels (known as tags), created by less- than signs (<) and greater-than signs (>). n 4. Express the bit pattern 0001001100010000 use dotted decimal notation? n Can include embedded scripting programming language code which can affect the behavior of web browsers.

3 Hypertext Document Format Figure 4.9 A simple Web page

n Entire document is printable characters n Contains tags to communicate with browser

q Appearance n

Wednesday (7 – 9pm) n Next Lecture: More about HTML n Reading assignments: q Lab1’s material on the course web site q HTML (search related information on the Web)
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