NT1210 Introduction to Networking Unit 2: Chapter 2, Introduction to Computer Networking 1
Objectives 2 • Identify the major needs and stakeholders for computer networks and network applications. • Identify the classifications of networks and how they are applied to various types of enterprises. • Explain the functionality and use of typical network protocols. • Use preferred techniques and necessary tools to troubleshoot common network problems.
Objectives 3 • Define a computer network. • Identify the primary needs for computer networks and network applications. • Draw the four major physical network topologies: bus, star, ring, and mesh.
Computer Networking 4 • Use large variety of components that must work together. • Move bits from one device to another. • Bit: Smallest unit of data, binary 1 or 0. • Focuses on copying bits on one device to another. • Computing devices include computers, gaming systems, televisions, phones, tablets, GPS navigation systems, watches, etc.
Defining a Network with User Applications 5 • Examples: Digital advertising, online/video games, text messages, websites, social media, and email. • Network diagrams often use cloud to identify what part of network to ignore for a particular discussion. • LAN vs WAN
Defining a Network with User Applications Computer Networks: Cloud Representing Hidden Parts of the Network Figure 2-1 6
An Informal General Definition of a Computer Network 7 • Telecom: Short for telephone communications • Primarily focuses on role of traditional telephone companies. • Datacom: Short for data communications • Older synonym for computer networking.
User Actions and the User Devices 8 • Users use network devices via applications (apps). • Application: Why we use networks. • Example: Would you use a phone that did not allow phone calls? Maybe, but what if it also did not allow texting? Or email? Or posting to social media? Or web surfing? Or anything that used a network? • Key common feature for many apps: Need to send bits. • Focus of this chapter: Email, voice calls, and video downloads.
Email 9 • Electronic Mail: One of oldest networking applications. • Sends mail electronically with bits. • Write (type) email. • Identify (type) sender’s and receiver’s email addresses. • Give messages to email service. • Email service delivers email to destination email address.
Email 10 • Users typically access email using email software or web browser. • Email software apps gives users way to create, send, and receive email. • Common email apps: • Microsoft Outlook • Microsoft Windows Mail • Mozilla Thunderbird • Apple Mail • Many built-in mail apps on phone/tablet
Email Sample Window on Email Software: Barney Types Email to Fred Figure 2-2 11 Example: Apple’s Mail application
Sending Email: Sender’s Computer Perspective 12 • Step 1: Start email application and click icon or menu item to cause “create message” window to open. • Step 2: Type destination’s email address and message. • Step 3: Behind the scenes: • Application stores and processes bits and bytes of message and addresses in RAM and (sometimes) on hard disk. • Application uses some kind of character set to represent text. • Application uses email addresses to identify sender and recipient of email. • Application works with other parts of computing device to send email.
Email General Process of Sending an Email on Barney’s Computer Figure 2-3 13 The Operating System (OS) on the computer typically plays a big role, because every modern OS includes lots of networking features, and the applications rely on the OS to do part of the work. The email client essentially asks the OS to send the email. However, the OS, being software, cannot physically send the bits. So the OS asks for help from theNIC. Figure 2-3 shows the general idea.
Sending Email: Network’s Perspective 14 • Network sits between user devices and physically moves bits between devices. • Networks must provide services that help clients (devices that use network) to do tasks they want to do. • Example: using “snail mail”: • To send mail, could go to different post office or drop. • When receiving mail, must go to particular place to pick it up. (e.g., box by house door, common area in apartment complex) • Each mailing address must be known by both post office and people who live at address.
Sending Email: Network’s Perspective Using an Outgoing Mail Drop/Box, and an Incoming Mail Box Figure 2-4 15 Example: Barney sends a letter to Fred’s postal address. Barney drops the letter in the mailbox for outgoing mail at his apartment complex (step 1). The postal service moves the letter towards Fred (step 2), and eventually, the postal service leaves the letter in Fred’s mailbox (step 3). Then the letter sits in Fred’s mailbox until he next checks his mail.
Sending Email: Network’s Perspective 16 • Works similar to snail mail but uses email servers. • Email servers (software running on computer in network) must be ready to receive, process, and hold emails for clients using SMTP (Simple Mail Transfer Protocol). • To send email: Email application sends mail to outgoing mail server using POP3 (Post Office Protocol, ver. 3). • Client must know location of outgoing mail server. • To receive mail: Email client must get mail from its incoming mail server also using POP3. • Email application must know location of incoming mail server.
Sending Email: Network’s Perspective Using Outgoing and Incoming Email Services Figure 2-5 17 Step 1: Barney sends an email to his outgoing email server. Step 2: Barney’s outgoing email server must know how to find the incoming email server used by Fred – more specifically, the incoming email server used by email address email@example.com. Step 3: Fred’s incoming email server holds the email for Fred, waiting until he next checks his email.
Voice Telephone Calls 18 • Modern telephony networks use bits to send telephone calls (voice calls). • Modern networks need to be ready to send bits, no matter whether those bits make up email or represent voice traffic.
Early Analog Voice Calls Big Picture View, Two Home Phones and the Telco Figure 2-6 • Majority of telephone services in USA for first 100 years grew from Bell’s original work and business ventures. • Local telephone company (Telco) ran cable to each home. • Inside Telco network, lots of other equipment connect to create telephone network.
Early Analog Voice Calls Example 20 • Barney picks up home phone in New York and dials Fred’s phone number in California. • To make Barney’s call work, Telco has to know all phone numbers and their matching phone lines. • Telco keeps a list of all phone numbers and knows which phone line connects to which phone using that phone number. • When new call occurs, Telco knows exactly where call physically needs to go.
Early Analog Voice Calls Electrical Circuit Between Two Phones to Carry the Voice Call Figure 2-7 21 To create the call, the Telco creates an electrical circuit all the way from one phone to the other. Once the Telco creates the call by creating an electrical circuit, the two people can talk.
Early Analog Voice Calls, Part 1 22 • Telco creates electrical circuit between phones. • Barney speaks, creating sound waves in air. • When graphed over time, sound waves go up and down just like waves in the ocean. • Microphone near mouth of speaker takes in sound waves and outputs electrical signal that looks very similar to graph of caller’s sound waves. (continued on next slide)
Early Analog Voice Calls, Part 2 23 • Fred’s phone converts analog electrical signal back to sound waves using speaker in part of phone near his ear. • Speaker takes in analog electrical signal and vibrates air, creating sound waves that look like analog electrical signal. • Result: What Barney speaks, Fred hears.
Digital Voice Calls, Part 1 24 • Telco had large networks to support analog voice calls long before computers became commonplace in businesses. • To take advantage of computers and related technology, Telco replaced analog telephone networks with digital ones. • Telco developed analog to digital (A to D—A/D) process to take electrical signal they already worked with (the analog signal) and convert it to digital signal (bits). • A/D paved way for VoIP (Voice over IP): Way to send digital voice signal over IP network.
Digital Voice Calls, Part 2 25 • Part of A/D process breaks voice into very small time intervals. • Voice in calls sampled voice 8000 times per second so each sound sample was .125 milliseconds long • Another part of A/D process assigns binary value to each unique short sound (similar to character map process). • Original AT&T A/D conversion process used 8-bit code. • To make use of networks for more efficient, lower cost, and better calls, Telcos added equipment to do A/D conversion process on each end of each call.
Digital Voice Calls Analog to the Phones, Digital in the Telco Figure 2-8 26 The two home phones create an electrical circuit into the Telco, but the analog circuit does not extend from phone-to-phone.
Digital Voice Calls 27 • Barney speaks, creating sound waves. • Phone creates analog signal representing voice and sends into Telco network. • Telco uses A/D device to convert analog voice to bits. • Telco sends bits across its network. • Telco converts bits back to analog electrical signal for transmission to Fred’s home phone. • Fred’s home phone uses speaker to convert electrical signal into sound waves. NOTE: Devices that perform A/D conversion called codecs (coders/ decoders). G.711—original AT&T codec—used 8,000 8-bit samples per second to create 64Kbps voice calls.
End-to-End Digital Voice with Business and Mobile Phones 28 • Modern business telephones and mobile phones only use digital voice. • Phone can connect to same network as PCs. • Send and receive digital signals (bits) directly; A/D converter built into phone. • Phones often have computer-like features built-in. • Display with simple web browser. • Some phones essentially have built-in tablet computers so they are mobile. • Look more like small computers with phone attached; voice calling feature just one of many features.
End-to-End Digital Voice with Business and Mobile Phones 29 • Mobile phones have some of same features as business phones, but no cables. • Mobile phones (cell phone) use wireless technologies to send and receive bits for voice calls and data applications (like text messaging). Summary: Voice traffic exists as common type of traffic in networks today. Networks typically support voice traffic as just one of many applications.
Recorded Video 30 • Networks may need to support live and recorded video. • Focus: Recorded video • Digital Video Recordings • Video Files • Video Compression
Recorded Video Video Camera Components and Moving the Video Files to a PC Figure 2-9 31 • Modern video cameras make digital recordingsand store them as bits. • Camera also has processors to take input and convert light and sound into bits to store as file on permanent storage. • Later, user can copy video to PC.
Video Files 32 • Digital video revolves around concept of single video frame (think animation cells). • Rectangle (width by height) of individual points of light of each video image as still image. • When played back, video player software shows one frame after another. • Computers cannot store video as points of light or as motions on screen, but as bits. • Computer thinks of video frame as pixel grid. • To represent color of pixel, computer uses table that lists all colors and matching binary code.
Video Files A Somewhat Extreme Example of Uncompressed Video Figure 2-10 33 • Videos files can become very large. • Example: High definition video with these specifications: • 3-byte code to represent color of each pixel • Frame size 1920 (wide) by 1080 (high) • Records 30 frames per second for smooth video
Video Compression 34 • Large video files cause problems: Take long time to download over network. • Compression: Stores video file as smaller file. • Compressed video file often looks just as good as original (depends on compression ratio used). • Example: Video originally recorded with frame size of 1920 x 1080 could be compressed by shortening width and height to 25% original size (480 by 270); only requires 1/16th original number of pixels. NOTE: To learn many aspects of video and video compression, use tools built into PC. Check out Real World Video Compression, by Andy Beach.
Video Compression Producing and Posting Smaller Compressed Video Files Figure 2-11 35 Example of the overall flow: The video producer – the person who recorded the video and decided what compressions to use – compressed and posted the file on a video server on the Internet (steps 1 through 3). Later, at step 4, video users might actually watch the video because it downloads in a reasonable amount of time.
Break Take 10 36
A Deeper Look at One Application: World Wide Web 37 • World Wide Web (the Web): Web browser software which allows users access to Web may be single most commonly used application in world. • Web works well for learning networking because uses basic client-server model. • User sits at computer and uses web browser (Web client). • “Client” indicates this software receives some type of service from another device (information from web server).
World Wide Web Web Browser Requesting and Receiving a Web Page from a Web Server Figure 2-12 38 The web browser (client) and web server cooperate so that the web browser can get a copy of the information from a web server. The server organizes information into pages called web pages. The web browser asks the web server for a web page, and the server sends the web page back to the web browser.
Web Browsers (Web Clients) Window Created by Apple Safari Web Browser Figure 2-13 39 • Web browser (first one came out in early 1990s): Software that allows user to get and display copy of web page from web server. • Once web server sends content back to browser, it displays information. • Example: Apple’s Safari browser.
Components on the Client Computer Photo of Network Interface Card (NIC) Figure 2-14 40 • Web browsers must follow same set of rules that tell browser how to request web page from server. • Browsers generally work same way in how they divide work: browser does some work but also relies on computer OS for some parts. • Client computer requires way to physically connect to network so bits that make up web page can move from server to client. • Client typically uses hardware called Network Interface Card (NIC) for network access.
Components on the Client Computer: NIC Each NIC has a circuit board with microchips and circuits (main part of the board) that is inside the computer case, as well as a port for the cable to connect to it on the outside of the case. Photo of Network Interface Card (NIC) Figure 2-14 41
Components on the Client Computer 42 • Some NICs exist as separate computer expansion cards. • Other devices put NIC functions onto some other part of device. • Tablet: Has wireless NIC function but doesn’t have NIC as separate physical card. • OS controls CPU, RAM, permanent storage, and other hardware, including NIC. • OS also manages all applications and provides services to them. • When user clicks or types something to load new web page, browser, OS, and NIC all play roles.
Components on the Client Computer Three Major Steps on Client Computer after the User Requests a Web Figure 2-15 43 Steps when user decides to load web page from www.example.com web server: • Browser creates message to request web page from server and gives request to OS for help. • OS does some work on request, including adding web server’s network address, then asks NIC to send request. • NIC physically sends request as bits into network.
Using Web Addresses (URLs) Protocol Web Server Web Page Example of Identifying a Web Page Using a Web Address (URL) Figure 2-16 44 • Web address: Identifies specific web page to display. • Formal name: Universal Resource Locator (URL). • Identifies web server and specific web page (file) on server: • Server name: Name listed between // and / • Web page: Name after / • Example: http://www.itt-tech.edu/information-technology
Using Web Addresses (URLs) 45 • Can also access web pages via hyperlinks. • Hyperlinks hide web addresses. • When hyperlinked item on web page is clicked, the browser loads web page for web address linked via that hyperlink. Note: When using web browsers to see hidden web address associated with hyperlink, hover over link, and right click mouse button. Browser will list menu that typically shows options to either display linked web address or copy.
Web Servers (Hardware and Software) 46 • Store information (text, graphics, video, and audio) that users see and hear. • Waits to receive requests for web pages, and sends page back to browser when requested. • Is software so must run on computer hardware which can support many kinds of applications.
Web Servers (Hardware and Software) 47 • Web server software allow web services to happen (e.g., storing web pages, listening for requests, and sending web pages in response to requests). • Hardware can be almost any computer that has OS that supports web server software. • Businesses must consider: • Number of users requesting same web page at same time. • Number of pages server must supply per second. • Speed of connection to network. • And many other factors.
Web Servers (Hardware and Software) Data Center with Servers in Racks Figure 2-17 48 • Many businesses build or lease space for their physical servers in a special type of room: Data Center (DC). • Server hardware sits in racks (see graphic). • DC also typically connects each server to network using cables.
Web Servers (Hardware and Software) Three Steps: Web Server Sends Web Page into Network Figure 2-18 49 What happens inside the server once it has decided to send a web page out into the network? • Server takes the web page in storage and asks the OS to send it out (via the network) to the web browser that requested the page. • The OS does some work (not shown) and asks the NIC for help. • The NIC sends the request physically into the network.
Web Sites, Pages, and Objects Conceptual View: Web Site, Web Page, Web Object Figure 2-19 50 • Web page: Collection of content (text, images, video, audio) that server supplies to web browsers. • Web objects: Parts of Web pagestored as separate files. • Web page includes links to objects’ locations on server. • Text in one Web object (file), and each graphic in as different object (file).