1 / 47

Networking And The Internet

Networking And The Internet. Lectures 17,18 Dr. Adam P. Anthony. Overview. Tuesday: Computer Network Basics Physical Layer of the Internet Network Security Basics Next Week: Data layer of the internet (World Wide Web) Types of internet data Technical Internet Protocols.

hosea
Download Presentation

Networking And The Internet

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Networking And The Internet Lectures 17,18 Dr. Adam P. Anthony

  2. Overview • Tuesday: • Computer Network Basics • Physical Layer of the Internet • Network Security Basics • Next Week: • Data layer of the internet (World Wide Web) • Types of internet data • Technical Internet Protocols

  3. In the Beginning… • A typical computation setup involved one computer and one or more users • Then, computers dropped in price • Sharing data is important • Shouldn’t have to pass around disks • Put wires between the computers that let them share data • Combination of computers + wires (or some other communication medium) = NETWORK

  4. About Abbreviations • Networking Systems require long phrases to describe components and protocols: • “Carrier Sense, Multiple Access with Collision Detection” • Professionals grew tired of repeating these tongue twisters constantly • Most people resort to abbreviations: • CSMA/CD • You WILL be tested on whether you know these abbreviations!

  5. Types of Networks • Local Area Network (LAN) • Buildings, homes • Metropolitan Area Network (MAN) • Larger areas, such as whole cities • Wide Area Network (WAN) • Massive networking efforts connecting computers across entire countries or the world

  6. Network Topologies • Topology: sort of like a bird’s eye view of a network • Two parts to topology: nodes and edges • In a network: • Nodes = computers, connection equipment • Edges = connections between computers and/or equipment • Topology is not always determined by how the layout ‘looks’ but by how the nodes connect to edges

  7. Bus Network Topology • Similar to the bus inside a computer • All messages are relayed across the bus. • Every computer gets to read every message • Each message includes an address so that computers can ignore messages intended for others • Security Issues? A network Hub is a piece of equipment that acts as a very short bus. It has little internal circuitry.

  8. Star Network Topology • Center computer: has the task of relaying messages from one computer to another • Called an Access Point • Neighbors don’t get to ‘listen in’ on conversations • Difference between Bus/Star? • Advantages/ Disadvantages?

  9. Communication Protocols • No matter the topology, we have multiple computers talking at the same time • How do they keep messages straight? • Only send a message when the line is quiet • If two computers send at same time, message is ruined • Ethernet uses Carrier Sense, Multiple Access with Collision Detection (CSMA/CD): • Each computer waits a random amount of time, then re-sends if the line is quiet • WiFi uses Carrier Sense, Multiple Access with Collision Avoidance (CSMA/CA) • Simplest approach: ask the Access Point if it’s OK to transmit (request/permit strategy)

  10. Combining Homogeneous Networks • Repeater • Does not discriminate as to where the message is going • Takes two small busses, creates one big bus • Bridge • Same as repeater, but blocks messages if they aren’t addressed to anyone in the adjacent bus • Lets 2 separate but compatible bus networks talk to each other • Switch • Same as bridge, but can connect multiple busses together • Analogy to a switch between several train tracks

  11. Building a large bus network from smaller ones

  12. Routers and internets • BW has Ethernet connections (CSMA/CD), as well as WiFi (CSMA/CA) connections • Different protocols can’t talk to each other! • Router • Used to distribute messages between incompatible and/or separate networks • Each separate network gets its own router • internet (Lower-case i) • Multiple incompatible or separate networks that are able to pass messages to each other • Routers know how to: • Communicate with their home network • Communicate with other routers • Locate an outside network, given an appropriate address for a single computer

  13. Routers connecting two WiFi networks and an Ethernet network to form an internet

  14. Process Communication Methods • Client/Server Model • Two distinct programs that work together • Client: what users at home use. Connects to the server. • Server: provides data and services to the client • Most of the work is done on the server • Peer-to-Peer • Also two (or more) programs working together • Different from client/server • Both programs are identical but know how to work together • Examples: Skype, AIM, BitTorrent • Distributed Systems • Multiple programs working collaboratively to solve a single problem

  15. The client/server model compared to the peer-to-peer model

  16. What is the Internet? • A proper noun (always an uppercase I) • Al Gore invented it (not really!) • Initiated by the U.S. Military for infrastructural reasons • Universities also involved for research purposes • Later expanded, commercialized • It is an internet (lowercase i) on a really large scale—world wide.

  17. The Internet: Physically Big, less well-known companies establish rough, world-wide network (each bubble a router). Same (or similar) companies establish regional networks; lease connections from Tier 1. Road-runner, Baldwin-Wallace, WOW!, AT&T, Comcast, etc. lease connections from Tier 2 You and I lease connections from Access ISP’s.

  18. Internet Addressing • Any internet (including the Internet) needs an explicit addressing system • Each and every computer needs a unique and undisputable address • Managed by the Internet Corporation for Assigned Names and Numbers (ICANN) • Independent, but internationally cooperative not-for-profit company • IP Address numbering system • Domain Name registration

  19. IP Addresses • Every computer that has internet access—large or small—has been assigned unique number (or Address), given by their ISP • Current Version IPv4: • 32-bit binary addressing system • Dotted Notation: • 192.168.1.1 • Number represents one byte of the total binary address

  20. The Internet: What Routers Do 100.X.X.X – 199.X.X.X 600.X.X.X – 699.X.X.X • US user’s IP is 138.492.345.691 • Makes request for connection to 645.204.183.221. How do we find it? • Extra connections: • Economic Advantage • Speed Advantage • Reliability Factor 645.X.X.X 645.204.X.X US China 645.204.183.221

  21. What is a Domain? • Once a computer is given an address, no other computer can have the same address • Example: AT&T might “own” all IP addresses that start with 100, up to addresses that start with 199 • They then sell them to lower-level customers • The set of numbers an entity owns are called the entity’s domain • All communication with computers whose address starts with 100 up to 199 are controlled, directly or indirectly, by AT&T 100.X.X.X – 199.X.X.X AT&T

  22. What is a Domain Name? • Text-Based replacement for an IP address • Simple to implement: • keep a list of all known domain names (millions of them!) • Maintain a server (Domain Name Server, or DNS) that will give you an IP address if you give it a name • Sub-Domains • Some companies will name portions of their domain, even just single computers (servers) • http://bb.bw.edu Top-Level Domain (can also be .com, .gov, country-specific, among others) Sub-Domain Name Main Domain Name

  23. Domain Name Servers DNS ?? http://www.zhaodaola.com.cn/ US China !! 645.204.183.221

  24. Network Security Basics • Virus: • Lives “inside” another legitimate program • Won’t do anything until that program is executed by a user • Once executed, will cause damage, then try to spread • Worm • Like a virus, but it is a standalone program that exploits operating systems to get installed and executed automatically • Trojan Horse • Program that looks legitimate, but has a virus or a worm included in its code • Spyware • Phishing • Denial of Service • Making 1000’s of requests to a server until it crashes so nobody gets to use it

  25. Network Protection Measures • Firewall • Block connections based on certain rules: • Software used • Service requested • Sophisticated pattern matching • Can be placed at the router (entry point to network) or on each individual computer • Proxy Servers • “Middle Man” strategy—all messages go through one computer, keep that computer secure • May also act as a firewall • Encryption • Use mathematics to make messages unreadable unless you have the correct ‘key’ to decipher the message • Legislation • Difficult to enforce because Internet is world-wide and actions may be legal in other countries.

  26. The World-Wide Web Lecture 18

  27. What is the World Wide Web? • It is just a _single_ application that runs on the Internet • Other applications that run on the Internet include: • Email • Instant Message • File Transfer Protocol (FTP) • It is the most popular • Built on the idea of sharing, linking documents • “Surfing the Internet” vs. “Surfing the web” • Commonly taken to have same meaning • Technically speaking, more is done on the Internet than just ‘surfing’

  28. Hypertext • Anyone familiar with the internet is familiar with hypertext • Simple concept: within one document, allow for a method of referencing and accessing other documents • Called a hyperlink • Clearly, not limited to just the WWW • WWW = huge collection of inter-connected hypertext documents that are all accessible from the Internet • Hypermedia: term that recognizes that much of the web is no longer text but still has hyperlinks

  29. Implementing Hypertext on the Internet • Remember, the Internet is just a network; a way for computers to communicate • Nothing happens on the internet unless someone writes and distributes a program that makes it happen • Tim Berniers-Lee • Did not invent the Internet! • Did invent the WWW • Two components make WWW possible: • Hyper Text Transfer Protocol (HTTP) • Hyper Text Markup Language (HTML)

  30. Hyper Text Transfer Protocol • Client/Server protocol for finding, retrieving hypertext documents: • Client: requests document from server • Most common client = web browsers • Server: responds to requests, initiates data transfer to client • Client: displays the downloaded data on the screen • Uniform Resource Locator (URL): • Method for finding/linking to documents on WWW (next slide)

  31. Uniform Resource Locators Optional: defaults may be used.

  32. More on URL’s • URL’s can be used to locate any file/service on the Internet, using any protocol • Most common is HTTP • Many browsers don’t require you to type http:// at the beginning, assuming that is what you wanted • Others include: • FTP (File Transfer Protocol) • SCP (Secure Copy Protocol) • AFP (Apple Filing Protocol) • SSH (Secure Shell) • More on this later!

  33. The Other Half: Hyper Text Markup Language • Hyper text Markup Language (HTML) has two purposes: • Provide a method for linking to other documents • Provide a simple method for giving a web page rich formatting capabilities • Is a type of ‘code’ that we can write using a basic text editor • HTTP client has a third job: read hypertext and display the resulting document on the screen • Sometimes called rendering

  34. Internet Protocols • The Internet is a world-wide phenomenon, allowing people in different cultures with different computers communicate and share information with each other freely • This is only possible because of the wide-spread adoption of common communication and data protocols (sort of like languages) • Without these protocols, the Internet is not nearly as fascinating • Rare example where world-wide cooperation yields an amazing benefit

  35. Process Layers

  36. Internet Process Layers • Application: Constructs message with address • Transport: Chops message into packets • Network: Handles routing through the Internet • Link: Handles actual transmission of packets

  37. Following a Message Through the Internet Computers Routers

  38. About Ports • Bottom 3 layers don’t care what is being transferred • Top Layer (Application) does care • WMP doesn’t want HTTP data, IE doesn’t want video data • Data can be given a port number • Each application gets its own port number • Anything with a different port number is ignored • Some port numbers are unofficially standardized: • HTTP browsers ‘listen’ to port 80 • FTP: port 20 or 21 • SSH: 22 • Email: 25 • Port numbers can be changed, blocked for security reasons • URL’s can include a port: http://www.domain.com:1245

  39. Process Layer (Internet) Protocols • Link: CSMA/CD (ethernet) or CSMA/CA (wireless) • Application: written by individual software developers, but must be compatible with transport layer protocol • Transport: next slide • Has to be compatible with the installed network layer protocol (done as a package deal) • Network: next slide • Has to be compatible with the installed link layer protocol (usually trivial—done on networking equipment)

  40. TCP/IP Protocol Suite • TCP: Transmission Control Protocol • One implementation of the transport layer • Verifies connection to destination before sending data • Verifies receipt of each packet • Offers flow and congestion control • If these seem like a waste of time, use UDP, another protocol which skips all of that • IP: Internet Protocol • Defines the language routers use to talk to each other • Biggest job: finding the fastest path between two addresses • Takes into consideration traffic and equipment malfunction • TCP/IP identifies the whole suite, but there are many protocols in the package besides TCP and IP!

  41. Getting Started With HTML • No installation required! • Create a new file with a .html extension • Edit with notepad! • Or, download a better text editor. Many CSC students like notepad++ • Once finished, just find the file and double click it to view it in a web browser • If you’re not happy with the result, go back to notepad and make changes • Once 100% happy, you can upload it to a web server and put it on the WWW

  42. HTML and Tags • A ‘Tag’ is a bit of text inside ‘<‘ ‘>’ • Every tag has a start-tag and an end tag: • <body> • </body> • All non-tag text in between a start tag and an end tag is ‘affected’ by that tag when rendered: • The code: <b>This text is bold-faced.</b> This text is not. • Is rendered as: This text is bold-faced. This text is not. end tag has same text as start tag, but with a forward slash in front

  43. Non-Displaying Tags • Some tags are for organizational purposes: • <html>: indicates that this file is using the hypertext markup language. </html> should be the last line in the code • <head>…</head>: section for non-displayed header information such as Title, author, keywords, style information, etc. • <body>…<body>: indicates the portion of the file that will actually be displayed by the browser

  44. Text-Augmenting Tags: • Already learned about bold-font (<b>) • Others: • <H1>, <H2>, <H3>, <H4>: decreasing levels for header text (titles, chapters, sections, etc.) • Mostly affects size of text, but can have other effects • <i>, <u>: italic, underline • <p>: start a new paragraph (skips a line) • <small>, <big>: temporarily resize text • For more information: • http://www.w3.org/html/wiki/Learn

  45. Hyperlink and Image Tags • <a>: hyperlink tag • Requires additional information, href: • <a href=“www.bw.edu”>Go to BW’s home page</a> • Renders as: Go to BW’s home page • <img>: image tag • Has no end-tag (one of a few exceptions) • Example: <imgsrc = “myPic.jpg”> • myPic.jpg needs to either: • Be in the same folder as the file • Have a path included from the server’s top-level: • Src = “/images/random/myPic.jpg”

  46. Lists • <UL>: Unordered list (bullet points) • <OL>: Ordered list (numbered points) • <li>: list item for both types of list <UL> <li> 4 C. Flour</li> <li>1 C. Milk</li> <li>3 Eggs</li> <li>4 Tbs Sugar</li> </UL> <OL> <li>Combine Flour, sugar</li> <li>Beat together Milk, Eggs</li> <li>Gradually stir milk mixture into flour mixture</li> </OL> • 4 C. Flour • 1 C. Milk • 3 Eggs • 4 Tbs Sugar Combine Flour, sugar Beat together Milk, Eggs Gradually stir milk mixture into flour mixture

  47. Common, but advanced features • Know what these are for now; in Web programming you’ll learn how to use them: • Tables: organizing data into blocks of cells • XML: eXtensible Markup Language • Make up your own tags, write programs that interpret/render tags in any way you like • Very popular for data representation, storage • Cascading Style Sheets (CSS): • Set up ‘default’ styles including backgrounds, colors, fonts, etc. • Used to create a uniform, site-wide template for all pages

More Related