BCIS 5304 - Data Communications - Midterm

Briefly define noise. Describe five types of noise and the underlying causes of this noise. Which type of noise is likely to pose the greatest problem to network managers? What does error look like in a data network?

-Line noise is undesirable electrical signals in twisted-pair wire and coaxial cable and undesirable light in firber-optic cable. - In general, errors are more likely to occur in wireless, microwave, or satellite transmission than in transmission through cables. Therefore, error detection is more important when using radiated media than guided media. Impulse noise is the most frequent cause of errors in today's networks. Unfortunately, as the next section describes, it could be very difficult to determine what caused this type of error. -White/Gaussian noise, a hiss or static background sound, is caused by the thermal agitation of electrons, which is unavoidable even if the equipment were perfect and wires were perfectly insulated. Usually not a problem unless it becomes so strong that it obliterates the transmission. -Impulse noise or spike is the primary source of error in data communications. It is heard as a click or a crackling noise and can last as long as 1/100 of a second. Such a click does not really affect voice communications, but it can obliterate a group of data, causing a burst error. At 1.5 Mbps, 15,000 bits would be changed by a spike of 1/100 of a second. Some of the sources of impulse noise are voltage changes in adjacent lines, lightning flashes during thunderstorms, fluorescent lights, and poor connections in circuits. -Cross-talk occurs when one circuit picks up signals in another. A person experiences cross-talk during telephone calls when she or he hears other conversations in the background. It occurs between pairs of wires that are carrying separate signals, in multiplexed links carrying many discrete signals, or in microwave links in which one antenna picks up a minute reflection from another antenna. Cross-talk between lines increases with increased communication distance increased proximity of the two wires, increased signal strength, and higher-frequency signals. Wet or damp weather can also increase cross-talk. Like white noise, cross-talk has such a low signal strength that it normally is not bothersome. -Echoes are the result of poor connections that cause the signal to reflect back to the transmitting equipment. If the strength of the echo is strong enough to be detected, it causes errors. Echoes, like cross-talk and white noise, have such a low signal strength that they normally are not bothersome. Echoes can also occur in fiber-optic cables when connections between cables are not properly aligned. -Attenuation is the loss of power a signal suffers as it travels from the transmitting computer to the receiving computer. Some power is absorbed by the medium or is lost before it reaches the receiver. As the medium absorbs power, the signal becomes weaker, and the receiving equipment has less and less chance of correctly interpreting the data. This power loss is a function of the transmission method and circuit medium. High frequencies lose power more rapidly than do low frequencies during transmission, so the received signal can thus be distorted by unequal loss of its component frequencies. Attenuation increases as frequency increases or as the diameter of the wire decreases. -Intermodulation noise is a special type of cross-talk. The signals from two circuits combine to form a new signal that falls into a frequency band reserved for another signal. This type of noise is similar to harmonics in music. On a multiplexed line, many different signals are amplified together, and slight variations in the adjustment of the equipment can cause intermodulation noise. A maladjusted modem may transmit a strong frequency tone when not transmitting data, thus producing this type of noise.

Explain how the client computer in the LAN figure in the book (Figure 5.15) would obtain the data link layer address of its subnet gateway.

A computer with TCP/IP knows the IP address of its subnet gateway. This information is provided by a configuration file or DHCP server. However, the computer does not know the subnet gateway's Ethernet address. Because of this, TCP would broadcast an ARP request to all computers on its subnet, request that the computer whose IP address is 128.192.98.1 to respond with its ethernet address. From here, that computer would obtain the data link layer address of its subnet gateway.

Describe the process of MAC address spoofing

A software-enabled technique that can change the hardcoded MAC address to any MAC address and thus overcome MAC address filtering.

Describe the difference between a two tier and three tier email message transfer, using diagrams and discussing how this approach differs from the two layer email transfer. Do users always require the same architecture for email? Why or why not? Discuss.

A two tier email transfer involves client computer that runs an application layer software package called a mail user agent (email client, example would be Outlook). A three tier email transfer uses a Web server and Web browser to provide access to your email. Two-tier: User creates an email message, which is formatted into a SMTP packet by the client. The email client then sends the SMTP packet to a mail transfer agent (mail server software). The server reads the packet to find the destination address and sends the packet through the network from mail server to mail server until it reaches the specified destination. The mail server on the destination address stores the message in the receivers mailbox. Three tier: User uses browser and writes an email message using a form. The Web browser sends the form to the Web server inside an HTTP request. The Web server runs a program that takes the information from the HTTP request and builds a SMTP packet which contains the email message. The Web server sends the SMTP packet to the mail server, which processes it. Then the SMTP packet flows through the network in the same manner as before. Lastly when it arrives at the destination mail server it is placed in the receiver's mailbox. The sender and receiver do not have to use the same architecture for email because all communication is standardized using SMTP between the different mail servers.

Discuss the functions of a web browser. Describe two web browsers. What was the first graphical Web browser? What are three search engines that you might use to find information on the Internet?

A web browser is used by the client to connect to a website page stored on a Web server. Web browsers and servers communicate with each other using a standard called HTTP. The browser sends a request to the server, and once the server responds, the web browser can display the Web page or an error message. The first graphical Web browser was called Mosaic, and it was created by a team of students at the University of Illinois. By 1993, Mosaic was available on UNIX, Windows, and Macintosh. 3 search engines one might use to find information on the Intent are Google, Bing, and Microsoft Edge.

What is coding? Briefly describe the two most important coding schemes

All computer systems produce binary data. For these data to be understood by both the sender and receiver, both must agree on a standard system for representing the letters, numbers, and. Symbols that compose messages. The coding scheme is the language that computers use to represent data. A pair of special devices called codecs(code/decode) are used to translate the incoming analog voice signal into a digital signal for transmission across the digital circuit. There are three predominant coding schemes in use today. ASCII - The most popular code for data communications and is the standard code on most microcomputers. Document1 18 of 51 There are two types of ASCII; one is a 7-bit code that has 128 valid character combinations, and the other is an 8 bit code that has 256 combinations. ISO 8859- A second commonly used coding scheme is iso 8859, which includes the ASCII codes plus nonEnglish letters used by many European languages. Unicode - the other commonly used coding scheme. UTF-8 is an 8-bit version, which is very similar to ASCII. UTF-16 uses 16 bits per character, by using more bits, UTF-16 can represent many more characters beyond the usual English or Latin characters, such as Cyrillic or Chinese.

What are the three important characteristics of a sound wave?

Amplitude - the Height of the wave- Amplitude is measured in decibels. Our ears detect amplitude as the loudness or volume of sound. Every sound wave has two parts, half above the zero amplitude point and half below. Both halves are always the same height. Frequency - The length of the wave, usually expressed as the number of waves per second. Frequency is measured in Hertz. Our ears detect frequency as the pitch of the sound. High frequency-> many short waves in a 1 second interval. Low Frequency- Fewer, but longer waves in 1 second. Phase - Refers to the direction in which the wave begins. The phase is measured in the number of degrees.

Clearly explain the differences between analog data, analog transmission, digital data, and digital transmission.

An analog signal is a continuous signal that represents physical measurements. Digital signals are time separated signals which are generated using digital modulation.

Define analog, and then describe the conversion from analog to digital using a four step method (sampling, measuring, quantizing and coding), and present a detailed diagram like the one which in the slides. What is quantizing error and ho w can it be lessened in some situations? Draw a sketch of quantizing error in your model.

Analog transmission occurs when the signal sent over the transmission media continuously varies from one state to another in a wave-like pattern much like the human voice. Modems translate the digital binary data produced bby computers into the analog signals required by voice transmission circuits. Sampling - Analog data must first be translated into a series of binary digits before they can be transmitted over a digital circuit. This is done by sampling the amplitude of the sound wave at regular intervals and translating it into a binary number. Reduce quantizing error. - voice transmissions using digitized signals that have a great deal of quantizing error sound metallic or machinelike to the ear. There are two ways to reduce quantizing error and improve the quality of the digitized signal Document1 16 of 51 Increase the number of amplitude levels, or sample more frequently(oversampling). Coding - All computer systems produce binary data. For these data to be understood by both the sender and receiver, both must agree on a standard system for representing the letters, numbers, and. Symbols that compose messages. The coding scheme is the language that computers use to represent data. A pair of special devices called codecs(code/decode) are used to translate the incoming analog voice signal into a digital signal for transmission across the digital circuit. Measuring- Pulse code modulation (PCM) is the most used technique for transmitting analog data to digital. PCM samples the amplitude of the incoming voice signal 8,000 times per second and uses 8 bits to represent the signal.

Internet Model

Application Transport Network Data Link Physical

how is a web request filled?

Application Layer First, the user creates a message at the application layer using a Web browser by clicking on a link (e.g., get the home page at www.somebody.com). The browser translates the user's message (the click on the Web link) into HTTP. The rules of HTTP define a specific PDU—called an HTTP packet—that all Web browsers must use when they request a Web page. For now, you can think of the HTTP packet as an envelope into which the user's message (get the Web page) is placed. In the same way that an envelope placed in the mail needs certain information written in certain places (e.g., return address, destination address), so too does the HTTP packet. The Web browser fills in the necessary information in the HTTP packet, drops the user's request inside the packet, then passes the HTTP packet (containing the Web page request) to the transport layer. Transport Layer The transport layer on the Internet uses a protocol called TCP (transmission control protocol), and it, too, has its own rules and its own PDUs. TCP is responsible for breaking large files into smaller packets and for opening a connection to the server for the transfer of a large set of packets. The transport layer places the HTTP packet inside a TCP PDU (which is called a TCP segment), fills in the information needed by the TCP segment, and passes the TCP segment (which contains the HTTP packet, which, in turn, contains the message) to the network layer. Network Layer The network layer on the Internet uses a protocol called IP (Internet Protocol), which has its rules and PDUs. IP selects the next stop on the message's route through the network. It places the TCP segment inside an IP PDU, which is called an IP packet, and passes the IP packet, which contains the TCP segment, which, in turn, contains the HTTP packet, which, in turn, contains the message, to the data link layer. Data Link Layer If you are connecting to the Internet using a LAN, your data link layer may use a protocol called Ethernet, which also has its own rules and PDUs. The data link layer formats the message with start and stop markers, adds error checks information, places the IP packet inside an Ethernet PDU, which is called an Ethernet frame, and Document1 3 of 51 instructs the physical hardware to transmit the Ethernet frame, which contains the IP packet, which contains the TCP segment, which contains the HTTP packet, which contains the message. Physical Layer The physical layer in this case is network cable connecting your computer to the rest of the network. The computer will take the Ethernet frame (complete with the IP packet, the TCP segment, the HTTP packet, and the message) and send it as a series of electrical pulses through your cable to the server. When the server gets the message, this process is performed in reverse. The physical hardware translates the electrical pulses into computer data and passes the message to the data link layer. The data link layer uses the start and stop markers in the Ethernet frame to identify the message. The data link layer checks for errors and, if it discovers one, requests that the message be resent. If a message is received without error, the data link layer will strip off the Ethernet frame and pass the IP packet (which contains the TCP segment, the HTTP packet, and the message) to the network layer. The network layer checks the IP address and, if it is destined for this computer, strips off the IP packet and passes the TCP segment, which contains the HTTP packet and the message, to the transport layer. The transport layer processes the message, strips off the TCP segment, and passes the HTTP packet to the application layer for processing. The application layer (i.e., the Web server) reads the HTTP packet and the message it contains (the request for the Web page) and processes it by generating an HTTP packet containing the Web page you requested. Then the process starts again as the page is sent back to you.

What are the seven layers of the OSI model

Application, Presentation, Session, Transport, Network, Data Link, Physical

What is asynchronous transmission v. synchronous transmission? Describe one protocol of each type.

Asynchronous transmission is often referred to as start-stop transmission because the transmitting computer can transmit a character whenever it is convenient, and the receiving Document1 26 of 51 computer will accept that character. With asynchronous transmission each character is transmitted independently of all other characters. With synchronous transmission all the letters or data in one group of data are transmitted at one time as a block of data. The block of data is called a frame. In summary, asynchronous data transmission means each character is transmitted as a totally independent entity with its own start and stop bits to inform the receiving computer that the character is beginning and ending. Synchronous transmission means that whole blocks of data are transmitted as frames after the sender and receiver have been synchronized. Synchronous Data Link Control Synchronous data link control (SDLC) is a mainframe protocol developed by IBM in 1972 that is still in use today. It uses a controlled-access media access protocol. If you use a 3270 protocol, you're using SDLC. Ethernet is a very popular LAN protocol, conceived by Bob Metcalfe in 1973 and developed jointly by Digital, Intel, and Xerox in the 1970s. Since then, Ethernet has been further refined and developed into a formal standard called IEEE 802. 3ac.Thereare several versions of Ethernet in use today. Ethernet uses a contention media access protocol. There are several standard versions of Ethernet.

Is the bit rate the same as the symbol rate? Explain.

Bit rate - the number of bits transmitted per second - A bit is a unit of information Symbol rate- a unit of signaling speed used to indicate the number of times per second the signal on the communication circuit changes. The bit rate and the symbol rate are the same only when 1 bit is sent on each symbol.

Compare and contrast data rate (i.e., bits per second) and symbol rate (also called baud rate) by giving two concrete, different examples

Bit rate is the number of bits per second transmitted. Baud rate is the number of times per second the signal on the communication circuit changes. The bit rate and the symbol rate (or baud rate) are the same only when 1 bit is sent on each symbol. For example, if we use AM with two amplitudes, we send 1 bit on one symbol. Here, the bit rate equals the symbol rate. However, if we use QAM, we can send 4 bits on every symbol; the bit rate would be four times the symbol rate.

Three Trends in Communications and Networking

Bring Your Own Device (BYOD) is when employees use their personal devices, such as smartphones and tablets, at work to access their work email. -This potentially saves the company money on the purchase of employee smartphones and tablets. -Employer may need to expand the Wireless Local Area Network, adding expense and maintenance. -Employer must manage how employees access company applications -Create a Native app for each application that allows employees to connect to a particular application -Require/allow employees to access applications using a web browser -Employer must manage device security if the device is lost or stolen. Internet of Things (IoT) is a reletavly low-powered device connected to the internet to exchange information with other devices and systems. -As IoT becomes more common, it can create a Network of Things (NoT) where all the interactions between the IoT devices happen seamlessly without any human interaction. -Alexa and Siri are able to control locks and thermostats without human intervention -Google has developed self-driving cars capable of passing driving tests and having fewer collisions than human-driven cars Document1 4 of 51 -A mall in Boston has a semi-autonomous security robot Massive Online is the connection and availability of massive amounts of information to an enormous audience. -Online gaming such as World of Warcraft -Edx, Hhan Academy, Lynda.com and Code Academy offer education modules for children and adults in a variety of fields -Universitys such as Standord, UC Berkely, MIT offer Massive Open Online Courses (MOOC) for free -President Obama used Facebook,

Describe the six subsystems of TIA/EIA 568-B.

Building entrance: the point where external cabling and wireless connects to the internal building wiring and equipment room. Equipment room: the room where network servers and telephone equipment are stored. Telecommunications closet: the room that contains the cable termination points and distribution frames. Backbone cabling: the calling that interconnects the telecommunications closet, equipment rooms, and building entrances within a building. This also refers to the cabling between buildings. Horizontal cabling: the cabling that runs from the telecommunications closer to each LAN. Work area: the cabling where computers, printers, patch cables, jacks, etc are located.

What is cloud computing and how is it useful?

Cloud computing is outsourcing all or part of an organization's infrastructure to a company specializing in managing infrastructure. As a result, it can be quickly and cheap to implement an organization's infrastructure without ordering and purchasing lots of software and hardware. Software as a Service (SaaS) is when the vendor provides the client the entire application, operating system, and infrastructure. Platform as a Service (PaaS) enables the client to write the code to build its application on hardware and operating system provided by the vendor. Infrastructure as a Service (IaaS) is when the vendor provides the client just the hardware

Describe how data could be transmitted using a combination of modulation techniques.

Combine AM with four defined amplitudes (capable of sending 2 bits) with FM with four defined frequencies (capable of sending 2 bits) to enable us to send 4 bits on the same symbol.

How does analog data differ from digital data?

Computers produce digital data that are binary, either on or off. In contrast, telephones produce analog data whose electrical signals are shaped like the sound waves they transfer. Analog data are signals that vary continuously within a range of values (e.g., temperature is analog).

Define digital data. Explain why most networks are now digital. Why is digital transmission superior to analog? Give five reasons.

Digital transmission is the transmission of binary electrical or light pulses in that it only has two possible states, a 1 or a 0. Digital transmission is preferred to analog transmission because it produces fewer errors It permits higher maximum transmission rates Is more secure Simplifies the integration of voice, video, and data on the same circuit.

Describe how data could be transmitted using frequency modulation.

Each 0 or 1 is represented by a number of waves per second (i.e., a different frequency). The amplitude (height) does not vary. One frequency (certain number of waves per second) is the symbol defined to be a 1, and a different frequency (a different number of waves per second) is the symbol defined to be a 0. For an example, if a higher frequency wave symbol represents a (binary) 1, and a lower frequency wave symbol represents a (binary) 0, when a device wants to transmit a 1, it would send a high-frequency wave.

Explain two reasons why the use of twisted pair cable is becoming more common than the use of coax cable?

Ease of installation and cost.

Errors normally appear in ______________________________, which is when more than one data bit is changed by the error-causing condition. Is there any difference in the error rates of lower speed lines and of higher speed lines? What kinds of lines are more prone to errors?

Errors normally appear in bursts. Normally errors appear in bursts.In a burst error, more than one bit is changed by the error-causing condition. The difference in the error rates of lower speed lines when compared to higher speed lines is slower speed lines have a lower error rate than high speed lines because higher transmission speeds are more error prone. Because they have additional shielding provided by their multiple layers of material, coaxial cables are less prone to interference and errors than basic low-cost twisted pair wires. Coaxial cables cost about three times as much as twisted pair wires but offer few additional benefits other than better shielding.One can also buy specially shielded twisted pair wire that provides the same level of quality as coaxial cable but at half its cost. For this reason, few companies are installing coaxial cable today, although some continue to use existing coaxial cable that was installed years ago. (pg. 65)

Under what circumstances would you use a microwave circuit rather than a satellite circuit?

For moderate distances (several hundred miles). Cheaper than satellite.

de jure standards

Formalized by an industry or government body e.g. HTTP, IEEE 802.3, 802.11n

Compare and contrast Frequency Division Multiplexing (FDM) and Wavelength Division Multiplexing (WDM).

Frequency division multiplexing(Fdm) - Can be described as dividing the circuit horizontally so that many signals can travel a single communication circuit simultaneously. The circuit is divided into a series of separate channels, each transmitting on a different frequency, much like a series of different radio or tv stations. All signals exist in the media at the same time, but because they are on different frequencies, they do not interfere with each other. Wavelength division multiplexing(WDM) - WDM is a version of FDM used in fiber-optic cables. When fiber-optic cables were first developed, the devices attached to them were designed to use only one color of light generated by a laser or LED. By attaching different devices that can transmit in the full spectrum of light rather than just one frequency, the capacity of the existing fiber-optic cables could be dramatically increased, with no change to the physical cables themselves.

For what is HTML used? What are its major parts? Are all required?

HTML stands for: Hypertext Markup Language. Most Web pages are written in HTML, but there are other formats as well. HTML is a structural language that stores information. HTML allows the author to use different styles and sizes of texts, titles, and headings. HTML also allows the author to define links to other pages that may be stores on the same web server or on any web server. The major parts of HTML are: • HTML o Contains HTML version information • Head o Used to contain page HTML metadata o Title of document (will not appear on actual page) o The author • Title o Page title (this title will appear) • Body o Hold content of HTML o Information and other visible contents on the page All four parts are required.

For what is HTTP used? What are its major parts? Are all required?

HTTP is the standard protocol for communication between a web browser and a web server. To get a page from a web server, the web browser issues a special packet called an HTTP request that contains the URL and other information about the web page requested. Once the server receives the HTTP request, it processes it and sends back and HTTP response (the requested page or error message) • HTTP request: Asks the server for information o HTTP request has three parts. The first 2 parts are required, while the last part is optional. The parts are: ▪ Request line • Starts with a command (get) • Provides the web page • Ends with HTTP version number that the browser understands • The version number is included as part of the packet because it ensures that the web server does not attempt to use a more advanced or newer version of the HTTP standard that the browser does not understand ▪ Request header • Contains a variety of optional information such as the web browser being used (Internet explorer) and the date ▪ Request body Document1 10 of 51 • Contains information sent to the server (information that the user has typed into a form for example) • HTTP response: sends information presentation or the drawing of information on the screen o Similar to HTTP request format o Three parts, first part is required, second two are optional ▪ Response status: • Contains the HTTP version number the server has used, a status code (example: 404, not found), and a reason phrase that describes the status code ▪ Response header • Contains a variety of optional information such as the web server being used, the date, and the exact url of the page in response ▪ Response body • Web page itself

What are the three major parts of an HTTP request and what information does each part contain? Why does HTTP include a version number as part of the packet?

HTTP request has three parts. The first 2 parts are required, while the last part is optional. The parts are: • Request line o Starts with a command (get) o Provides the web page o Ends with HTTP version number that the browser understands ▪ The version number is included as part of the packet because it ensures that the web server does not attempt to use a more advanced or newer version of the HTTP standard that the browser does not understand • Request header o Contains a variety of optional information such as the web browser being used (Internet explorer) and the date • Request body o Contains information sent to the server (information that the user has typed into a form for example)

What are the advantages and disadvantages of host-based networks versus client-server networks? Explain two major benefits and/or limitations of client-server networks compared to host-based networks.

Host-based networks are an older architecture that centralizes all computer resources onto a mainfraim. The client or terminal was essentially a keyboard and monitor used to sent and received messages to and from the centralized mainframe. They were thought to be economical at that time. However, prioritizing users and upgrading networks became difficult and costly as the workload increased on the mainframe and its response time decreased. Client-server based networks attempt to spread the network load between the client and server. Both the client and the server will process various parts of the application logic. This architecture enables software and hardware from different vendors to work together using middleware. Middleware provides a standard communication method between different vendors and it manages messages sent between the client and server. Updating application logic on a server is easier to manage. The more application logic that is placed on the client, the harder it becomes to keep it updated.

How does forward error correction work? How is it different from other error correction methods? Under what circumstances is forward error correction desirable? What is one type of forward error correction by

How does forward error correction work? - Uses codes containing sufficient redundancy to prevent errors by detecting and correcting them at the receiving end without retransmission of the original message. How is it different from other error correction methods? - The error-detecting bits are roughly equal to the number of data bits, rnaging from a small percentage of extra bits to 100% redundancy. Document1 21 of 51 Under what circumstances is forward error correction desirable? - In circumstance in which conditions (such as weather) make it impossible to transmit without some errors and where there is a significant delay in transmission which would make error rates fluctuate. What is one type of forward error correction by name? - Hamming code, Reed-Solomon Given a diagram like that in the text of forward error correction, be able to explain how the system works.

What is IM? How does it work?

IM stands for instant messaging. IM allows exchange of real time messages or chats. IM works in a similar way to the Web. The client computer needs an IM client software package, which communicates with an IM server software package that runs on a server. When the user connects to the internet, the IM client software package sends an IM request packet to the IM server informing it that the user is now online. The IM client software package continues to communicate with the IM server to monitor what other users have connected to the IM server. When a friend connects to the IM server, the IM server sends an IM packet to your client computer so that you can see your friend is connected to the internet. The friend also receives a packet to their client computer so that they know you are online as well.

If you were buying a multiplexer, why would you choose either TDM or FDM?

If all of the signals on the circuit use different frequencies, then FDM is best because all the signals can exist on the media at the same time, but they do not interfere with each other. If you were sending signals that use the same frequencies, then TDM is best because the signaling devices take turns.

Describe how MAC address filtering works.

If you want to allow only certain computers to connect to your network, you can use MAC address filtering. MAC address filtering will create a list of MAC addresses that are allowed to connect to a Wi-Fi network or to a switch in corporate networks. This feature allows for some degree of security. (107) With MAC address filtering, the AP permits the owner to provide a list of MAC addresses (i.e., layer 2 addresses). The AP only processes frames sent by computers whose MAC address is in the address list; if a computer with a MAC address not in the list sends a frame, the AP ignores it. (199)

Describe continuous ARQ (Automatic Repeat reQuest).

In the OSI (Open Systems Interconnection) model error control is defined to be a layer 2 function - it is the responsibility of the data link layer. However, in practice we have moved away from this. Most network cables - especially LAN cables - are very reliable and errors are far less common that they were in the 1980's. Therefore, most data link layer software used in LANs (i.e., Ethernet) are configured to detect errors but not correct them. Anytime a packet with an error is discovered it is dimply discarded. Wireless LAN's and some Wide Area Networks (WAN's) where errors are more likely still perform both error detection and error correction. The implication from this is that error correction must be performed at higher layer. This commonly done be the transport layer using continuous automatic repeat request (ARQ), as we shall see in the next chapter. The transport layer must be able to detect lost packets (i.e., those that have been discarded) and request the sender to retransmit them. (pg.99) With continuous ARQ the sender does not wait for an acknowledgement after sending the message: it immediately sends the next one. Although the messages are being transmitted, the sender examines the stream of returning acknowledgements. If it receives a NAK (negative acknowledgement the sender retransmits the needed messages. Continuous ARQ is a full duplex transmission technique because both the sender and receiver are transmitting simultaneously. Continuous ARQ is also important in providing flow control, which means that the computer sending the message is not transmitting to quickly for the receiver.

Transmission Control Protocol (TCP)

Is a transport layer protocol and is responsible for breaking large files into smaller packets called segments. TCP ensures each segment is reliably delivered and puts the segments back into the proper order when received. It is also responsible for opening a connection to the server for the transfer of a large set of packets.

List and describe five reasons why TCP/IP has become the predominant protocol for Internet level transport applications. What do you think is the future market share potential for proprietary standards? What are some limitations of TCP/IP in terms of future Internet growth capabilities?

It is an industry-standard model that can be effectively deployed in practical networking problems. 2. It is interoperable, i.e., it allows cross-platform communications among heterogeneous networks. 3. It is an open protocol suite. It is not owned by any particular institute and so can be used by any individual or organization. 4. It is a scalable, client-server architecture. This allows networks to be added without disrupting the current services. 5. It assigns an IP address to each computer on the network, thus making each device to be identifiable over the network. It assigns each site a domain name. It provides name and address resolution services. 6. Guarantee of deliveries via attempts to retransmit errored or lost packets and consequent error reports when connectivity fails. Although TCP/IP is more popular than UDP, UDP IP protocol, along with other ad hoc protocols are still being used 30-40 years after their introduction. UDP is faster than TCP although it does not offer retransmission of lost data packets. Nevertheless, drawbacks of TCP/IP indicates that its popularity may be surpassed by a better IP protocol in the future. Limitations: • It does not clearly separate the concepts of services, interfaces, and protocols. So, it is not suitable to describe new technologies in new networks. • It is not generic in nature. So, it fails to represent any protocol stack other than the TCP/IP suite. For example, it cannot describe the Bluetooth connection. Document1 33 of 51 • It does not distinguish between the data link and the physical layers, which has very different functionalities.

What do a user agent and message transfer agent do in an SMTP/IMAP email system? What are some examples of user agent packages?

Mail User Agent is a special application layer software package used by the client computers to format the email into SMTP packets. Eudora and Outlook are examples of user agent packages Mail Transfer Agent is a special application layer software that receives and stores the message in the recipient's mailbox on the server until the email is read.

What is media access control and why is it important? What are two examples of controlled access methods and contention based media access methods? When might one access method be preferred over another in a network, and why? Under what conditions do contention-based media access control techniques outperform controlled-access techniques (i.e., have lower response time)? Explain.

Media Access Control (MAC) controls when computers communicate on a network. MAC is important on a network when several computers share the same communication circuit. MAC tries to ensure that no more than one computer attempts to transmit data at the same time but provides a way to recover if multiple transmissions do occur at the same time. -Contention is when a computer waits until the circuit is free and then sends its data. It is commonly used with LAN ethernet. Ethernet. -Controlled Access is when one device controls the circuit and determines which clients can transmit at what time. Access request and polling are two common controlled access techniques. - Access request - The computer that wants to transmit sends a "request to transmit" to the device that is controlling the circuit, such as a wireless access point. The controlling device grants permission for one computer to transmit, and all other computers wait until that computer has finished before they listen for the circuit to be free and send an access request. - Polling is the process of sending a signal to a client computer that permits it to transmit. The client computer stores all messages that need to be transmitted, and the polling device (WAP) polls the client computer if it has data to send. The client computer then sends its data or responds negatively, so the controller can poll another device if it has data to send. - - Roll-call polling is a type of polling where the controller works consecutively through a list of clients (can set priorities) until all are polled. It can take time for the controller to poll through each device before getting back to the first device. The controller waits for a message being sent, a negavice response (no message to send), or a time-out period if the client is out of service. Additionally, a fail-safe time-out rule is needed to prevent the controller from locking up on an out-of-service client. - -Hub polling (token passing) is when 1 device starts the poll and passes it to the next computer on the multipoint circuit. It sends a message and passes the poll to the next device, which repeats the process. - Contention approach is better for smaller networks (no more than about 20 computers) with low usage (minimize the chance of collisions) where clients can transmit without waiting for permission. - Controlled access is better for large (more than 20 computerson 1 shared cirucit) networks (chances of collisions are high) where many clients need to transmit because the clients must wait for the poll to transmit. Collisions waste circuit capacity when they occur, and both computers are required to retransmit later

What is middleware and what does it do?

Middleware is software that sits between the application software on the client and the application software on the server. It provides a standard way of communicating that can translate between softwares provided by different vendors. It also manages the message transfers between clients and servers, so that a client does not need to know which server contains the needed data. The middleware will forward the message to the correct server.

What is a modem? How does a modem send digital data on an analog network, explaining the process step by step?

Modem - (Modulator/Demodulator) takes the digital data from a computer in the form of electrical pulses and converts the m into the analog signal that is needed for transmission over an analog voice-grade circuit.

What is the difference between multiplexing and modulation? Why are each important?

Multiplexing means to break one high speed physical communication circuit into several lower-speed logical circuits so that many different devices can simultaneously use it but still think that they have their own separate circuits. Primary benefit of multiplexing is to save money by reducing the amount of cable or the number of network circuits that must be installed. Modulation- Uses the shape of the sound waves (Amplitude, Frequency, and Phase) to represent different data values. Modulation is done by transmitting a simple sound wave through the circuit and then changing its shape in different ways to represent a 1 or a 0. The sender and receiver must agree on what symbols will be used (What amplitude, frequency and phase will represent a 1 or a 0) and on the symbol rate (how many symbols will be sent per second. This is important because modems use modulation and demodulation to transmit between digital and analog data.

What is transparency? (I search the PDF of the book and did not find the word transparency used.)

Network transparency, in its most general sense, refers to the ability of a protocol to transmit data over the network in a manner which is transparent (invisible) to those using the applications that are using the protocol. In this way, users of a particular application may access remote resources in the same manner in which they would access their own local resources. An example of this is cloud storage, where remote files are presented as being locally accessible, and cloud computing where the resource in question is processing. (Wikipedia) Multiplexing means to break one high-speed physical communication circuit into several lowerspeed logical circuits so that many different devices can simultaneously use it but still think they have their own separate circuit. (The multiplexer is transparent.) (pg. 62-63) So, I think the idea "transparency" is trying to communicate is that network resources are used in a way that divides the resources among the computers, each computer thinks it has its own resource. For example, physical hard drives are divided into logical drives. The multiplexer Document1 24 of 51 divides one circuit among many devices.This is done so that the division of the resources (hard drives, circuits, and other network resources) is transparent to the devices and users. This division saves money but also may not be the most efficient use of the network. However, it may be a cost savings worth having if the network was not used for mission critical applications.

Data Link Layer

The second layer in the OSI model. This layer bridges the networking media with the Network layer. Its primary function is to divide the data it receives from the Network layer into frames that can then be transmitted by the Physical layer.

What is transmission efficiency? How do information bits differ from overhead bits? What are three issues which might affect packet throughput rates? Which is better for file transfer, large packet sizes or small packet sizes?

One objective of a data communication network is to move the highest possible volume of accurate information through the network. The higher the volume, the greater the resulting networks efficiency and the lower the cost. (pg. 105) Every protocol adds additional bits to the user's message before sending it (e.g., for error detection) These bits are called overhead bits because they add no value to the user; they simply ensure correct data transfer. The efficiency of a transmission protocol is the number of information bits sent by the user divided by the total number of bits transferred (information bits plus overhead bits). (pg. 107) Network efficiency is affected by the characteristics of the circuits such as: Error rates and maximum transmission speed The speed of the receiving equipment The error and detection control methodology The protocol used by the data link layer (pg. 104) The general rule is that the larger the message field, the more efficient the protocol. So why not have 10,000-byte or even 100,000-byte packets to really increase the efficiency? The answer is that anytime a frame is received containing an error, the entire frame must be retransmitted. Thus, if an entire file is sent as one large packet (e.g., 100 K) and 1 bit is received in error, all 100,000 bytes must be sent again. Clearly, this is a waste of capacity. Furthermore, the probability that a frame contains an error increase with the size of the frame; larger frames are more likely to contain errors than are smaller ones, simply because of the laws of probability. Thus, in designing a protocol, there is a trade-off between large and small frames. Small frames are less efficient but are less likely to contain errors and cost less (in terms of circuit capacity) to retransmit if there is an error. (pg. 105) It sounds like there is a tradeoff between large packets and small packets. Large packets may be more efficient but may use more band width if there is an error that needs to be retransmitted. Larger packets may have a greater probability of an error. Smallerpackets are less prone to error and smaller and less costly to transmit.

How is data transmitted in parallel? What feature distinguishes serial mode from parallel mode?

Parallel transmission is the way the internal transfer of binary data takes place inside a computer. If the internal structure of the computer is 8 bit, then all 8 bits of the data element are transferred between the main memory and the central processing unit simultaneously on 8 separate connections. In other words, the circuit will have 8 separate wires wrapped in one outer coating, and each wire is used to send 1 bit of the 8 bit character. The same is true of computers that use a 32-bit structure; all 32 bits are transferred simultaneously on 32 connections. This differs from serial mode, since serial mode only requires one wire and all data is transmitted over that one wire. This makes serial mode slower than parallel as it sends one bit at a time.

Describe three approaches to detecting errors, including how they work, the probability of detecting an error, and any other benefits or limitations.

Parity Checking - One additional bit is added to each byte in the message. The value of this additional parity bit is based on the number of 1s in each byte transmitted. This parity bit is set to make the toal number of 1s in the byte (including the parity bit) either an even number or an odd number. (example is figure 4-3 at top of page 98) A single error (switching of a bit from 1 to a 0 or vice versa) will be detected by parity, but it cannot determine which bit was in error. You will know an error occurred, but not what the error was. But if two bits are switched, the parity check will not detect any error. Parity detects errors only when an odd number bits have been switched, any even number of errors cancels one another out. The probability of detecting an error, given that one has occurred, is only abut 50%. Many networks today do not use parity because of its low error-detection rate. Checksum - A checksum (typically 1 byte) is added to the end of the message. The checksum is calculated by adding the decimal value of each character in the message, dividing the sum by 255, and using the remainder as the checksum. The receiver calculates its own checksum in the same way and compares it with he transmitted checksum. If the two values are equal, the message is presumed to contain no errors. The use of checksum detects close to 95% of the errors for multiple-bit burst errors. Cyclic Redundancy Check (CRC) - Adds 8, 16, 24, or 32 bits to the message. With CRC, a message is treated as one long binary number, which is divided by a preset number, and the remainder is used as the CRC code. The preset number is chosen so that the remainder will be either 8 bits, 16 bits, 24 bits, or 32 bits. The receiving hardware divides the received message by the same preset number, which generates a remainder. The receiving hardware checks if the received CRC matches the locally generated remainder. If it does not, the message is assumed to be in error. In practice, the CRC algorithm is implemented using binary logic on a bit-by-bit basis to simplify memory requirements. It is one of the most popular and performs quite well. The most commonly used CRC codes are CRC-16 and CRC-CCITT (both 16 bit versions) and CRC-32 (32 bit version). The probability of detecting an error is Document1 22 of 51 100% for all errors of the same length as the CRC or less. For example, CRC-16 is guaranteed to detect errors if 16 or fewer bits are affected. IF the burst error is longer than the CRC, then CRC is not perfect but is close to it. CRC-16 will detect about 99.998% of all burst errors longer than 16 bits, whereas CRC-32 will detect about 99.99999998% of all burst erros longer than 32 bits.

Briefly describe how even parity and odd parity work. Give an example of even parity with a 7-bit ASCII code, for the following: 0110110, using a 0 start bit and a 1 stop bit.

Party bits is a single bit added to the end of each message, based on an odd or even count of each 1 in the message. An even number of 1 in the message will result in a 0 at the end of the message and an odd number of 1 in the message will Document1 28 of 51 result in a 1 at the end of the message. Party checking can detect errors if a single bit changes in the message but not if 2 bits changed because the even # cancels the other error out.

Describe how data could be transmitted using phase modulation

Phase refers to the direction in which the wave begins. Waves can can start by moving up and to the right (phase of 0 degrees), or start by moving down and to the right (phase of 180 degrees). With phase modulation, one phase symbol is defined to be a 0 and the other phase symbol is defined to be a 1. In other words, a phase of 0 degrees can be defined to be a binary 0, while a phase of 180 degrees can be defined to be a binary 1.

Compare private, public, and community cloud architectures

Private cloud o Created for the exclusive use of a single private organization o The cloud's hardware and software is hosted in a private data center o This model allows for the highest levels of control, privacy and security o Used in financial and health-care industries • Public cloud o This deployment model is used by multiple organizations that share the same cloud resources o Level of control and security is lower than private clouds o This deployment model doesn't require any upfront capital investment o Cloud can be up and running in a few days o Public cloud good choice when a lot of people in the organization are using the same application o Used in universities • Community cloud Document1 8 of 51 o Subset of public cloud o Used by organizations that have a common purpose ▪ Limited number of companies have access to it o Realize the benefits of public clouds (fast deployment) and added level of privacy and security o Used in government, healthcare and finance industries

Describe four types of radiated media. Give an example, describe what it looks like and how it works, and why it might be used in a scenario of a network.

Radio transmissions: When you connect your laptop into the network wirelessly, you are using radio transmission. Each device has a radio receiver/transmitter that uses specific frequency range. It is designed to work only for short distances, and is often used by portable computers, phones, personal digital assistants. Infrared transmission: uses low frequency light waves to carry the data through the air in a direct line-of-sight path between two points. Infrared lights are invisible the human eye. An example would be a TV remote control. Microwave transmission: is an extremely high-frequency radio communication beam that is transmitted over a direct line-of-sight path between any two points. It is typically used for long distance data or voice transmission. No cables are required. Microwaves transmissions use antennas. Satellite transmission: is similar to microwave transmission, but instead of antennas, it uses a satellite floating in space. This type of transmission has propagation delay and is affected by heavy rain.

Compare and contrast roll call polling, hub polling (or token passing), and contention. Which is better, hub polling or contention? Explain.

Roll Call Polling - The controller works consecutively through a list of clients, first polling client 1, then client 2 and so on, until all are polled. Roll-call polling can be modified to select clients in priority so that some get polled more often than others. Hub Polling (token passing) - One device starts the poll and passes it to the next computer on the multipoint circuit, which sends its message and passes the poll to the next. That computer then passes the poll to the next, and so on, until it reaches the first computer, which restarts the process again. Contention - Computers wait until the circuit is free (no other computers are transmitting) and then transmit whenever they have data to send. Contention is commonly used in Ethernet - Local Area Networks (LANs). Which is better? - Key consideration is throughput - which approach will permit the most amount of user data to be transmitted through the network. Contention generally works better for small networks that have low usage. Controlled access (polling) works better for large network with high usage.

Describe from a high-level perspective the packet layout for SDLC(Synchronous Data Link Control), Ethernet, and PPP (Point to point protocol).

SDLC and PPP the data can be of variable sizes. Ethernet has a defined data size of 46-1500 bytes. Ethernet frames are longer than SDLC and PPP. That would seem to indicate a higher data overhead for data transmission across a network. Also SDLC and PPP frames are bit orientated protocols whereas Ethernet is a byte orientated protocol.

What are the major parts of an email message?

SMTP is the most commonly used email standard because it is the email standard used on the internet. SMTP defines how message transfer agents operate and how they format messages sent to other message transfer agents. An SMTP packet has 2 parts: • Header o Lists source and destination email addresses (name) as well as the address itself (email address), date, subject • Body o The word DATA followed by the message itself

Describe two ways in which Statistical Time Division Multiplexing (STDM) differs from Time Division Multiplexing (TDM).

STDM allows more terminals or computers to be connected to a circuit than TDM. STDM is the exception to the rule that the capacity of the multiplexed circuit must equal the sum of the circuits it combines. Also, unlike TDM which has computers taking turns communicating, STDM allows computers to transmit at the same time. In TDM, devices have equal turns, but STDM uses statistical analysis to manage transmissions.

Describe the three types of data flows, and discuss why some are applicable in some situations and vice versa

Simplex Transmission - a one-way transmission such as that with radios and tvs Half duplex transmission - a two-way transmission, but you can transmit in only one direction at a time ie a walkie talkie. Full-duplex transmission- You can transmit in both directions simultaneously, with no turnaround time

What is the typical sampling network in telephony? Why is a higher sampling rate more effective for sound quality?

Symbol rate for telephony uses PCM. The input voice signal is sampled 800 times per second. Each time the signal is signaled, 8 bits are generated. Therefore the transmission speed on the digital circuit must be 64,000 bps, (8 bits per sample X 8000 bits per second) or 64kbps. The north American telephone network is built using millions of 64kbps Document1 19 of 51 digital circuits that

What are the parts of TCP/IP and what do they do? Who is the primary user of TCP/IP?

TCP is like the transport layer, IP is like the network layer. Sender uses TCP while both parties use IP. Detailed explaination: TCP/IP has two parts. TCP is the transport layer protocol that links the application layer to the network layer. It performs segmenting: breaking the data into smaller PDUs called segments, numbering them, ensuring each segment is reliably delivered, and putting them in the proper order at the destination. IP is the network layer protocol and performs addressing and routing. IP software is used at each of the intervening computers through which the message passes; it is IP that routes the message to the final destination. The TCP software needs to be active only at the sender and the receiver, because TCP is involved only when data comes from or goes to the application layer. TCP/IP is the transport/network layer protocol used on the Internet. It is the world's most popular protocol set, used by almost all BNs, MANs, and WAN

What is Telnet and why is it useful?

Telnet o Enables users on one computer to log in to other computers on the Internet o It is useful because it allows network administrators to log in to servers and routers to make configuration changes

How are Internet standards developed?

The Internet Engineering Task Force (IETF; www.ietf.org) sets the standards that govern how much of the Internet will operate. Developing a standard usually takes 1-2 years. Usually, a standard begins as a protocol developed by a vendor. When a protocol is proposed for standardization, IETF forms a working group of technical experts to study it. The working group examines the protocol to identify potential problems and possible extensions and improvements, and then issues a report to IETF. If the report is favorable, the IETF issues a Request for Comment (RFC) that describes the proposed standard and solicits comments from the entire world. Once no additional changes have been identified, it becomes a Proposed Standard. Once at least two vendors have developed software based on it, and it has proven successful in operation, the Proposed Standard is changed to a Draft Standard. This is usually the final specification, although some protocols have been elevated to Internet Standards, which usually signifies a mature standard not likely to change. There is a correlation of IETF RFCs to ISO standards.

Describe the history of the Internet and the Web (part of this is in Chapter 1, part in Chapter 2). Where do you forsee the future evolution of the Internet heading, and why?

The Web was first conceived in 1989 by Sir Tim Berners-Lee while working at CERN. His idea was to create a hypertext network of information. A few years later several browsers had been created for UNIX computers by CERN and some universities, and there were about 30 Web servers in the entire world. In 1993, Mosaic, the first graphical Web browser, was available for UNIX, Windows, and Macintosh computers, and there were about 200 Web servers in the world. Today, there are more than 250 million websites and an unknown amount of web servers. No one owns the Internet, but the Internet Society is an open-membership society that focus on issues and improvements regarding the Internet. In the future, Internet will move from from being a Web of computers to also being the Internet of Things. This is due to computers and networks being built into everyday objects, such as kitchen appliances. Also, smart devices becoming more common. More and more people will be connected to the Internet and using it for games, politics, education, and more. Many organizations are working on a new, faster internet, such as Internet2.

and data link layer addresses in the network, except those for the web server itself. Describe how the client would obtain the IP address for the web server

The client could send a DNS request to one of the DNS root servers that it knows. The root server would respond to the resolving name server with a DNS response that said "I don't know the IP address you need, but ask this DNS server," and it would include the IP address of the top-level domain (TLD) server for the requested website. The resolving name server would then send a DNS request to a TLD server. The TLD domain server would respond with a DNS response that tells the resolving name server to ask the authoritative name server and provides its IP address. The resolving name server would send a DNS request to the authoritative name server. The authoritative name server would then respond to the resolving name server with the needed IP address, and the resolving name server would send a DNS response to the client computer with the IP address.

What does the data link layer do? What are its primary responsibilities? Where does the data link layer sit in terms of the simplified five layer network model?

The data link layer is divided into 2 sub-layers that connect to the layer above and below it. 1. The logical link control (LLC) sublayer connects to the network layer. LLC is responsible for adding (sending PC) or removing (receiving PC) a data link layer Protocol Data Unit (PDU) (usually an Ethernet Frame) to the network layer Protocol Data Unit (PDU) (usually an IP packet). 2. (Sending PC)The media access control (MAC) sublayer takes the data link layer PDU from the LLC sublayer and converts it into a stream of bits and controls when the physical layer transmits the bits over the circuit. (Receiving PC) The MAC sublayer translates the stream of bits from the physical layer into the data link layer PDU, ensures that no errors have occurred during transmission, and passes it to toe LLC sublayer. - The data link layer (also called layer 2) is responsible for moving a message from one computer or network device to the next computer or network device in the overall path from the sender or receiver. It controls the way messages are sent on the physical media. Both the sender and receiver have to agree on the rules, or protocols, that govern how they will communicate with each other. A data link protocol determines who can transmit at what time, where a message begins and ends, and how a receiver recognizes and corrects a transmission error. The data link layer is responsible for sending and receiving messages to and from other computers. Its job is to reliably move a message from one computer over one circuit to the next computer where the message needs to go. 91 - The data link layer sits between the physical layer and the network layer

Session Layer

The fifth layer in the OSI model. This layer establishes and maintains communication between two nodes on the network. It can be considered the "traffic cop" for network communications.

Transport Layer

The fourth layer of the OSI model. In this layer protocols ensure that data are transferred from point A to point B reliably and without errors. this layer services include flow control, acknowledgment, error correction, segmentation, reassembly, and sequencing.

How can the Internet be used for competitive advantage in business? Describe three firms which are using the Internet for conducting business and speculate as to the underlying technologies which might be in use in these firms. Will the Internet become an essential business tool like the telephone or will it go the way of the dinosaurs? What do you envision the Internet and web becoming in the future for businesses? Discuss.

The internet can be used to gain a competitive advantage by making it easier for businesses to understand their competitive forces, what product/services are in the market, by being able to compete globally and my improving overall processes and quality of products or services that are offered. Three major firms that are using the internet for conducting business are Walmart, Amazon and Google. They are successful users of data communications which allow them to have access to the buying habits of their customers. The more insight a company has on their customers, the more they can cater to them. The Internet has become, and will continue to be an essential business tool. More and more companies rely on the vastness of the Internet. The world is becoming an increasingly virtual place, and trends such as BYOD and the increase of IoT is proof of that.

Physical Layer

The lowest, or first, layer of the OSI model. Protocols in this layer generate and detect signals so as to transmit and receive data over a network medium. These protocols also set the data transmission rate and monitor data error rates, but do not provide error correction.

What does the network layer do? Where does it sit in relationship to the other four layers of our simplified network model?

The network layer performs three important functions: addressing, routing, and breaking long messages into smaller packets for transmission by the data link layer. The network layer sits between the application layer and the data link layer. The network layer accepts messages from the application layer and formats and addresses them for transmission by the data link layer. The network layer also accepts individual messages from the data link layer and organizes them into coherent messages that it passes to the application layer.

Describe some of the cyber security implications related to the application layer.

The network must provide a worry-free and secure environment for applications on the application layer to run on. The application itself must have application security coded within the application or receive security code updates from the vendor. Users must install application updates immediately to avoid the application or other systems from being compromised. SQL injection is an attack on a website that allows SQL code to be inserted and executed on the webpage form, enabling a hacker to steal data from the database. The webpage must be designed to prevent SQL code from being executed inside the webpage form. Email spoofing is when a hacker impersonates the sender's address on an email so that the receiver believes the communication is coming from a legitimate source.

Describe how Domain Name Server works and is hierarchically organized. What happens if a URL is not in a local DNS server?

The process of DNS resolution involves converting a hostname (such as www.example.com) into a computer-friendly IP address (such as 192.168.1.1). An IP address is given to each device on the Internet, and that address is necessary to find the appropriate Internet device(like a street address is used to find a particular home). When a user wants to load a webpage, a translation must occur between what a user types into their web browser (example.com) and the machinefriendly address necessary to locate the example.com webpage. DNS uses a hierarchy to manage its distributed database system. The DNS hierarchy is an inverted tree structure. The hierarchy is comprised of root-level, top-level domains, Second-level domains, sub-domains and host. If the queried DNS server does not have a match for the query name, it will return a referral to a DNS server authoritative for a lower level of the domain namespace. The DNS client will then make a query to the referral address. Document1 31 of 51 Ultimately the name servers will keep forwarding until they reach an SOA(Start of Authority) name server for that domain or a root level name server. This process continues with additional DNS servers down the query chain until either an error(e.g HTTP 404 or domain not found) or timeout occurs.

What is the purpose of a data and network communication standard? Give five examples of various standards and describe what that standard is (e.g., RS 232, HTTP, etc.)

The purpose of data communication standards is to standardize the rules on how different communication protocols should work together to transmit and receive data. Communication starts at the top layer, where rules identify and define the communication type. Then, as the message travels through the communication layers, predefined protocols guide the communication down and up the layers from one layer to the next until the message reaches its destination.

Application Layer

The seventh layer of the OSI model. Application layer protocols enable software programs to negotiate formatting, procedural, security, synchronization, and other requirements with the network.

Presentation Layer

The sixth layer of the OSI model. Protocols in the Presentation layer translate between the application and the network. Here, data are formatted in a schema that the network can understand, with the format varying according to the type of network used. The Presentation layer also manages data encryption and decryption, such as the scrambling of system passwords.

What is the term used to describe the placing of two or more signals on a single circuit?

The term used to describe the placing of two or more signals on a single circuit is called multiplexing. Multiplexing allows devices to simultaneously use a circuit, while thinking that they have their own separate circuits. Multiplexing is important for the Internet, and the primary benefit of multiplexing is that it recedes the amount of cable or network circuits needed, which saves money. There are 4 different types of multiplexing. DSL uses multiplexing.

Network Layer

The third layer in the OSI model. Protocols in this layer translate network addresses into their physical counterparts and decide how to route data from the sender to the receiver.

What do the following tools enable you to do: the Web, email, Telnet, IM?

The web o With the help of a web browser, it enables users to be able to access web servers which allows access to different websites • Email o Users create and send messages to other users o Enables users to send text messages and attach files from word processors, spreadsheets, graphic programs and more o Email packages allow users to filter and organize messages by priority • Telnet o Enables users to log in to servers or other clients o Requires an application layer program on both the client and host computer ▪ Once Telnet makes the connection from client to server, use account name and password of an authorized user to log in • IM o Allows the exchange of real time typed messages or chats with friends o Enables you to verbally talk with friends in the same way as telephone or the use of cameras to exchange real rime video in the same way as a videoconferencing system

Describe a two-tier, three-tier and n-tier architecture. What is a network architecture? Compare and contrast two-tiered, three-tiered, and n-tiered client server architectures. What are the technical differences and what advantages and disadvantages do each offer? How does a two-tier client server network differ from an n-tier client server network. Describe one advantage and one disadvantage that a three-tier architecture has compared to a two-tier architecture.

There are many ways in which the application logic can be partitioned between the client and the server • Two-tier o 2 sets of computers ▪ Server is responsible for data storage ▪ Client is responsible for presentation logic, application logic, and data access logic o Advantage: enables software and hardware from different vendors to be used together o Disadvantage: difficult to get software from different vendors to work together • Three-tier o 3 sets of computers ▪ Client computer is responsible for presentation logic ▪ Application server is responsible for the services logic and application logic ▪ A database server is responsible for the data access logic and data storage • N-tier o More than 3 sets of computers ▪ Example: Document1 9 of 51 • the client is responsible for presentation logic • A database server is responsible for the data access logic and data storage • The services logic and application logic are spread across two or more different sets of servers o Advantage (this is the primary advantage of an n-teir client-server architecture compared with a two-tier architecture as well as a 3-tier compared with 2-tier): ▪ separates the processing that occurs to better balance the load on different servers ▪ More scalable o Disadvantage: ▪ Greater load on network ▪ Harder to program and test software

List and describe the three ways that a network manager can connect to a router and configure and maintain it.

There are three ways that a network manager can connect to a router and configure and maintain it: (1) console port, (2) network interface port, and (3) auxiliary port (see Figure 5-16). When the router is turned on for the very first time, it does not have an IP address assigned, so it cannot communicate on the network. Because of this, the console port, also called the management port, is used to configure it. A network manager would use a blue rollover cable (not the Ethernet cable) to connect the router's console port to a computer that has terminal emulation software on it. The network manager would use this software to communicate with the router and perform the basic setup (e.g., IP address assignment, routing protocol selection). Once the basic setup is done, the network manager can log in to the router from any computer using the network interface using TCP/IP and Telnet with Secure Shell (SSH). Although routers come with an auxiliary port that allows an administrator to log via a direct, nonnetwork connection (e.g., using modems), this connection is rarely used today

Describe three types of guided media. Give an example, describe what it looks like and how it works, and why it might be used in a scenario of a network.

Twisted pair cables are one type of guided media. Twisted pair cables are isolated pairs of wires that are twisted to minimize electromagnetic interference. Twisted pairs can be used in LANs and to connect a telephone. Examples of twisted pair cables include Cat 5e and Cat 6. Coaxial cables have a copper core (inner conductor), insulator, second conductor, and outer shield for insulation. With multiple layers and additional shielding, these cables are less prone to interface and error than basic twisted pairs. However, they are more expensive. Fiber optic cables send telecommunication signals in high-speed streams of light pulses from lasers or LEDs instead of the traditional electrical form. There are multimode and single mode fiber optic cables. They can carry huge amounts of information very fast, making it ideal for the simultaneous of voice, data, and image signals. They also work better in harsh environments and is more resistant to damage.

How does dynamic addressing work? What benefits and problems does dynamic addressing provide?

With dynamic addressing, a server is designated to supply a network layer address to a computer each time the computer connects to the network. Instead of providing a network layer address in a configuration file, a software package installed on the clients computer instructs it to contact bootp or DHCP servers using data link layer address. This message asks the server to assign the client a unique network layer address. Some of the benefits are that users get leased an amount of time to have that address which simplifies the network. The downside is that users have to request a new address each time their lease is up.

How does bipolar signaling differ from unipolar signaling? Why is Manchester encoding more popular than either? Wh at kind of signaling is used in Ethernet?

Unipolar signaling- The voltage is always positive or negative (Like a DC Current) Bipolar signaling- the ones and zeros vary from a plus voltage to a minus voltage (Like an AC Current) In general, bipolar signaling experiences fewer errors than unipolar signaling because the symbols are more distinct. Noise or interference on the transmission circuit is less likely to cause the bipolar's +5 volts to be misread as a -5 volts than it is to cause the unipolar's 0 volts to be misread a a +5 volts. This is because changing the polarity of a current (From positive to negative) is more difficult than changing its magnitude. Ethernet & Manchester encoding - Ethernet uses manchester encoding, which is a special type of bipolar signaling in which the signal is changed from high to low or from low to high in the middle of the signal. Manchester encoding is less susceptible to having errors go undetected because if there is no transition In midsignal, the receiver knows that an error must have occurred.

Describe two common modem standards

V.44 is the ISO standard for data compression used by modems. V.44 uses Lempel-Ziv encoding to build a dictionary of character combinations that can occur in a message. Anytime the same character pattern reoccurs in a message, the index to the dictionary entry is transmitted instead of the actual data. This allows about six times more data to be sent per second. V.32 is the standard for modems in high speed networks that transmit a lot of data. Modems with this standard will work anywhere in the world. It is full duplex.

VoIP

Voice Over Internet Protocol (VoIP) (pronounced as "voyp") is commonly used to transmit phone conversations over digital networks. VoIP is a relatively new standard that uses digital telephones with built-in codecs to convert analog voice data into digital data (see Figure 3-21). Because the codec is built into the telephone, the telephone transmits digital data and therefore can be connected directly into a local area network, in much the same manner as a typical computer. Because VoIP phones operate on the same networks as computers, we can reduce the amount of wiring needed; with VoIP, we need to operate and maintain only one network throughout our offices, rather than two separate networks—one for voice and one for data. However, this also means that data networks with VoIP phones must be designed to operate in emergencies (to enable 911 calls) even when the power fails; they must have uninterruptable power supplies (UPS) for all network circuits. One commonly used VoIP standard is G.722 wideband audio, which is a version of ADPCM that operates at 64 kbps. It samples 8,000 times per second and produces 8 bits per sample. Because VoIP phones are digital, they can also contain additional capabilities. For example, high-end VoIP phones often contain computer chips to enable them to download and install small software applications so that they can function in many ways like computers.

What is the purpose of multiplexing? How does it work? Multiplexing usually is done in multiples of _______? Of the different types of multiplexing, what distinguishes a. Frequency division multiplexing (FDM)? (describe and draw a sketch of this) b. Time division multiplexing (TDM)? (describe and draw a sketch of this) c. Statistical time division multiplexing (STDM)? (describe

What is the purpose of multiplexing? - Primary benefit is saving money by reducing the amount of cable or network circuits. How does it work? - Break one high-speed physical communication circuit into several lower-speed logical circuits so that many different devices can simultaneously use it but still "think' they have their won separate circuits. Multiplexing usually is done in multiples of _______? - 4 (e.g., 8, 16) Of the different types of multiplexing, what distinguishes a. Frequency division multiplexing (FDM)? (describe and draw a sketch of this) - Frequency division multiplexing is best described as dividing the circuit 'horizontally' so that many signals can travel a single communication circuit simultaneously. The circuit is divided into a series of separate channels, each transmitting on a different frequency. All signals exist in the media at the same time, but because they are on different frequencies, they do not interfere with each other. b. Time division multiplexing (TDM)? (describe and draw a sketch of this) - Time division multiplexing shares a communication circuit among two or more computers by having them take turns, and can be described as dividing the circuit 'vertically'. c. Statistical time division multiplexing (STDM)? (describe and draw a sketch of this) - Statistical time division multiplexing does not follow the rule that the capacity of the multiplexed circuit must equal the sum of the Document1 20 of 51 circuits it combines. More terminals or computer can be connected to the circuit with statistical time division multiplexing then frequency division multiplexing or time division multiplexing. STDM is called statistical because the selection of transmission speed for the multiplexed circuit is based on a statistical analysis of the usage requirements of the circuits to be multiplexed. Example: 4 computers connected to a multiplexer and each can transmit at 64kbps, then you should have a circuit capable of transmitting 256kbps (4x64kbps). Since all computers will not be transmitting continuously at max transmission, then you don't need the full 256kbps circuit. d. Wavelength division multiplexing (WDM)? (describe) - Wavelength division multiplexing is a version of frequency division multiplexing used in fiber-optic cables. Light can have different frequencies (colors), therefore attaching different devices that could transmit in the full spectrum of light rather than just one color, allows for an increase in the capacity of fiber optic cables with no changes to the physical cabling.

Describe some of the physical security concerns described in this chapter

With data being stored on hard drives and USB drives, these could be stolen and security measures such as firewalls would be rendered useless in protecting that data. It is easy to copy data from laptops, USB drives, and mobile devices. An employee may also lose their USB drive. Data should always be encrypted, and unfamiliar USB drives should never be used, as they might contain malware. All organizations should have a physical security plan and have measures to protect their data, routers, servers, and devices.

What is ARP and how and why does it work? What is MAC address resolution and how does it work?

When a client in a building does not know its router's Ethernet address, it broadcast an ARP request to all computers on its subnet, requesting the router to respond with its Ethernet address. This request is processed by all computers on the subnet, but only the router responds with an ARP packet giving its Ethernet address. The network layer software on the client stores this address in its data link layer address table (called ARP cache). Then the client computer could send the message. 142 This same ARP request/response process can occur at any point as a message moves through the network. For example, suppose that the router in the data center (128.192.254.96) did not know the Ethernet address of the DNS server (128.192.50.4). The DNS request would flow through the network in exactly the same way as described earlier (because no computer knows whether the router knows or doesn't know the Ethernet address) until the DNS request arrived at the data center router. This router would try to address the message to the DNS server and would realize that it did not have the server's Ethernet address, so it would issue an ARP request. The DNS server would respond with an ARP response containing its Ethernet address, and the router would put that address on the message and send it to the server. 142 - Address Resolution Address resolution is the process of translating an application layer address into a network layer address or translating a network layer address into a data link layer address. On the Internet, network layer resolution is done by sending a special message to a DNS server (also called a name server) that asks for the IP address (e.g., 128.192.98.5) for a given Internet address (e.g., www.kelley.indiana.edu). If a DNS server does not have an entry for the requested Internet address, it will forward the request to another DNS server that it thinks is likely to have the address. That server will either respond or forward the request to another DNS server, and so on until the address is found or it becomes clear that the address is unknown. Resolving data link layer addresses is done by sending an ARP request in a broadcast message to all computers on the same subnet that asks the computer with the requested IP address to respond with its data link layer address.

Describe how a Web browser and Web server work together to send a web page to a user

When a user enters a uniform resource locator (URL) into the web browser address bar or clicks on a URL link, it creates a Hypertext Transfer Protocol (HTTP) request at the application layer. A request line containing a get command and HTTP version number, a request header containing various information, and a request body containing the information being sent to the server are added to the HTTP request. Request lines and request headers are required, but request bodies are not required. The HTTP is processed by the transport, network, data link, and physical layers as it travels from the user's computer through the network to the web server. When the web server reads the received HTTP request, it prepares an HTTP response, which contains a response status, a response header, and a response body. The required response status contains the HTTP version number, a message status code (200 for "ok" and 404 for "not found"), and a reason phrase. The response header is optional and contains a variety of information about the HTTP response. The response body is optional and contains the information that makes up the webpage.

de facto standards

Widely accepted, but not formalized e.g. Microsoft Windows Often become de jure standards eventually

Describe how data could be transmitted using amplitude modulation.

With AM, the amplitude, or height of the wave is changed. One amplitude is the symbol defined to be 0, and another amplitude is the symbol defined to be a 1. For an example, if the highest amplitude symbol represents a (binary) 1 and the lowest amplitude symbol represents a (binary) 0, when the sending device wants to transmit a 1, it would send a high-amplitude wave.

What is the difference between centralized routing and decentralized routing? What is the difference between static routing and dynamic routing? What is a distance vector algorithm and what is a link state algorithm? What is interior routing and what is exterior routing? Define and describe RIP, OSPF, EIGRP, BGP protocols using these terms.

With centralized routing, all routing decisions are made by one central computer or router. All computers are connected to the central computer, so any message that needs to be routed is simply sent to the central computer. With decentralized routing, multiple independent machines are connected and provide a pool of resources. Since each node within the network retains independent control, every one of them can set their own rules regarding data and workload availability. Static routing is decentralized, which means that all computers or routers in the network make their own routing decisions following a formal routing protocol. With static routing, routing decisions are made in a fixed manner by individual computers or routers. Dynamic routing is used when there are multiple routes through a network, and it is important to select the best route. The Distance vector algorithm is mainly used in ARPANET and RIP. The Link state routing algorithm is used to find the shortest path from one node to every other node in the network. Interior gateway protocols are used inside an organization's network and are limited to the border router. Exterior gateway protocols are used to connect the different Autonomous Systems. RIP- dynamic distance vector interior routing protocol that is commonly used in smaller networks, such as those operated by one organization. OSPF - dynamic hybrid interior routing protocol that uses number of computers in a route as well as network traffic and error rates to select the best route. EIGRP- dynamic hybrid interior routing protocol developed by Cisco. Hybrid means that it has some features that act like distance vector protocols and some other features that act like link state protocols. Document1 32 of 51 BGP- dynamic distance vector exterior routing protocol used on the Internet to exchange routing information between autonomous systems

What is X.400 and CMC?

X.400 and Common Messaging Calls (CMC) are email standards used for email that work essentially the same ways as SMTP.

Ethernet

frames the packet from the network layer. The frame contains the destination and source MAC address, which are removed and replaced as the frame travels through a network

Internet protocol (IP)

is a network layer protocol and has 2 version, IPv4 and IPv6. IP creates a packet from the transportation layer segment containing the sending and destination devices IP address. The packet can be routed many times through different network devices that add and remove IP addresses until the packet reaches its final destination. The protocol then removes the IP addresses and send the underlying segment to the transportation layer.

Hypertext Transfer Protocol (HTTP)

operates at the application layer and is used to manage communication between a web browser and a web server. The web browser initiates communication to the web server by sending a packet called an HTTP request containing URL and other information concerning the web page request. Once the web server receives the request, it will process it and send an HTTP response contining the web page content or an error

Simple Mail Transfer Protocol (SMTP)

operates at the application layer and manages email transmission (text only) on the internet between mail servers to mail server or between sending email client and the mail server, which is why it is the most commonly used email protocol.

Post Office Protocol (POP)

operates at the application layer and manages email transmission on the internet between the mail server and the receiving email client. The email is downloaded to the receiving client's hard drive and deleted on the mail server hard drive

Internet Message Access Protocol (IMAP)

operates at the application layer and manages email transmission on the internet between the mail server and the receiving email client. The email remains on the mail server after the being received by the receiving email client.

Multipurpose Internet Mail Extension (MIME)

used to convert non-text files, such as a Power Point file, into a special text-like code that can be embedded into the SMTP. The receiving email client identifies the MIME coding and uses MIME software to convert the text back to the non-text file.