Bus Data Comm Mdtrm 1

Front 1

1.1 What three kinds of basic organizational difficulties can communications technology help companies overcome?

Back 1

1-overcoming the challenges of a geographically dispersed companies through the use of good networks in order to make such companies more manageable by helping bridge the distance and communication gap.
2-help top-heavy companies trim down middle management in order to save money.
3-helps companies break down barriers between divisions by making information available as needed and to those that would benefit from access to such information.

Front 2

1.2 Name four types of information that are found on networks?

Back 2

voice, video, data & image

Front 3

1.3 Briefly describe convergence and unified communications.

Back 3

Convergence basically refers to the merger of technologies such as voice, data, and video that were previously separate technologies. The three benefits of convergence include efficiency, effectiveness and transformation.

Unified communications refers to the user’s perspective of the convergence of voice, data, and video technology as it applies to its uses in business applications. Real-time communications services merged with non-real-time applications is merged through the use of unified communications. Personal unified communications, workgroup unified communications, and enterprise unified communications are three important functional levels of the integration of unified communications in business applications.

Front 4

1.4 How has the technology of the compact disc used in the music industry been used in image communications

Back 4

The optical disc, which is similar to the compact disc, enables the storage of immense amounts of information that can be stored inexpensively as well as it being easily distributable in an office setting.

Front 5

1.5 Why are the burdens on the manager greater today than in previous years when it comes to using new technology efficiently?

Back 5

-keeping up with emerging technology & finding ways to incorporate it in their businesses at a reasonable cost.
-finding ways to incorporate technology into networks as well as making them secure and reliable.
-faced with the difficult task of smartdevices & using these devices efficiently, cost effectively, and securely via their networks.

Front 6

1.6 Why has the optical fiber transmission become popular in the past few years?

Back 6

-high data transmission capacity as well as the drop in cost of this resource in the last ten years.
-security characteristics of optical fiber transmission makes this resource a much sought after tool
-only issue with this mode of transmission is the bottleneck created by switching.

Front 7

1.7 What types of communications can be carried by satellite transmission?

Back 7

Satellite transmission enables the user to have a portable terminal such as a smartphone from which the user can access the web, chat, and do other transactions over the satellite transmission. Satellite transmission is a huge factor in the rise of portable computing.

Front 8

1.8 Name two approaches that can be used for increasing the efficiency of transmission services.

Back 8

multiplexing and compression

Front 9

1.9 Contrast the function of application software with that of interconnection software.

Back 9

Application software could be described as the end product of a certain application offered to users. An example of an application software is multimedia messaging in which the user has access to a variety of sources by which to communicate such a e-mail and voice mail. Interconnection software is the software that makes it possible for the end user to be able to see the final product such as the interface for using emails. Interconnection software makes it possible for computers in a network to work together by communicating in the same language.

Front 10

A company’s telephone exchange digitizes telephone channels at 8,000 samples per second; each sample requires 8 bits for adequate quantization. This telephone exchange must transmit simultaneously 24 of these telephone channels over a communications link. What is the required data rate (expressed in bits per second)?

Back 10

8,000 smp/s * 24 channels = 192,000 smp/s

192,000 smp/s * 8 b/smp = 1,536,000 bps

The required data rate is 1,536,000 bits per second.

Front 11

Problem 2.4(e)
How many bits will it take to represent the following sets of outcomes?
e. Population of the world (about 6 billion)

Back 11

2^32.5 = 6.074001 × 10^9

It will take approximately 33 bits to represent the population of the world.

Front 12

What are the two different interpretations of the prefixes kilo, mega, and giga? Define a context in which each interpretation is used.

Back 12

In data transmission, the prefixes kilo, mega and giga are used to define the rate of data transmission as powers of 10, i.e. kilo = 10^3, mega = 10^6, and giga = 10^9. It is common to see internet download speeds of 18 Mbps(megabits per second). In terms of computer storage, memory is expressed by binary addresses and memory size is in powers of 2, i.e. kilo = 2^10, mega = 2^20, and giga = 2^30. A good computer system usually has a memory size of at least 8 GB(gigabytes).

Front 13

What is the bandwidth of telephone voice?

Back 13

The bandwidth of telephone voice is approximately 3400 Hz

Front 14

The process that takes advantage of redundancy to reduce the number of bits sent for a given piece of data is called what?

Back 14

compression

Front 15

2.4 What is the difference between Centrex and PBX?

Back 15

The difference between Centrex and PBX is that PBX is an on-premise switching facility whereas Centrex provides a similar switching service but is located in the telephone company’s central office.

Front 16

2.5 What is the difference between a printable character and a control character?

Back 16

The difference between a printable character and a control character is that a printable character is able to be printed as output whereas a control character is not printable and is used for things such as error detection and function control.

Front 17

2.6 Explain the basic principles of vector graphics and raster graphics.

Back 17

Vector graphics basically involves the representation of an image as curved and straight line segments which can be grouped together to form complex shapes. Vector graphics use binary codes to represent details of an image such as size, type and orientation which can later be used to be transmitted digitally. Raster graphics represent images as pixels, which are two-dimensional array of spots. The most used form of raster graphics is for facsimile transmissions over fax machines.

Front 18

2.7 List two common image formats.

Back 18

Two common image formats are Joint Photographic Experts Group (JPEG) and Graphic Interchange Format (GIF).

Front 19

2.8 List two common document formats.

Back 19

common document formats are Portable Document Format (PDF) and postscript.

Front 20

2.9 Describe the process used to prevent flicker in a video screen.

Back 20

Interlacing is the process used to prevent flicker in a video screen while at the same time it prevents having to increase bandwidth. Interlacing basically involves the use of scanning odd-numbered lines and even-number lines separately in order to refresh the screen 60 times per second versus 30 times per second in order to prevent a flicker in the screen.

Front 21

2.10 Define response time.

Back 21

Response time refers to the reaction time taken by a system after an input has been given, such as hitting a letter on the keyboard and that letter appearing on the screen. Statistics show that the less time it takes to respond to a command, the more likely it is that the user will continue engaging in that particular application and the more productive the interaction will be. Response time involves a computer's processing power as well as competing requirements such as processing two applications at a time that might take up each other's response time rate.

Front 22

2.11 What is considered an acceptable system response time for interactive applications
and how does this response time relate to acceptable response times for Web sites?

Back 22

A system response time of less than two seconds would be an acceptable system response time for interactive applications. Ideally, a subsecond response time or decisecond response time would be the goal so that the user's attention, interest, and productivity is maintained at optimal levels. Having an acceptable rapid response time is especially crucial for Web sites given that potential clients will be discouraged if they have to wait long periods for a company Web page to load. An acceptable response time of less than three seconds would be ideal in order to maintain user attention on Web systems.

Front 23

5.1 What is the major function of the network access layer?

Back 23

-ensure the exchange of data between a computer and a network so that the data can be passed through the transport layer.
-network access layer makes sure that the network has the address of the appropriate destination computer who is requesting data from the network.

Front 24

5.2 What tasks are performed by the transport layer?

Back 24

-assures that there is a reliable exchange of data between applications. -ensures that the data sent arrives at the destination application in the order that it was sent as well as checking for errors.

Front 25

5.3 What is a protocol?

Back 25

A protocol is a set of rules that preside over the exchange of data between two entities. Syntax, semantics and timing are key elements of a protocol that answer the what, how, and when of communication respectively.

Front 26

5.4 What is a protocol data unit (PDU)?

Back 26

A PDU is a combination of data from the next higher layer and control information. It is a unit of data in a the protocol of a given layer, such as the transport layer, that contains important information such as the source port, destination port, sequence number, and error-detection code.

Front 27

5.5 What is a protocol architecture?

Back 27

A protocol architecture is a structured set of modules that implement the communications functions in a network. The modular approach of a protocol architecture allows for easier program development as well as easier adaptation to changes in the network.

Front 28

Problem 2.14(a)

Commonly, medical digital radiology ultrasound studies consist of about 25 images extracted from a full-motion ultrasound examination. Each image consists of 512 by 512 pixels, each with 8 b of intensity information.

Back 28

a. How many bits are there in the 25 images?

512 * 512 * 8 = 2,097,152 bits per image

2,097,152 * 25 = 52,428,800 bits

Front 29

Problem 2.14(b)

b. Ideally, however, doctors would like to use 512 × 512 × 8 bit frames at 30 fps (frames per second). Ignoring possible compression and overhead factors, what is the minimum channel capacity required to sustain this full-motion ultrasound?

Back 29

2,097,152 * 30 = 62,914,560 bits per second

Front 30

c. Suppose each full-motion study consists of 25 s of frames. How many such studies could fit on a 600-MB CD-ROM?

Back 30

62,914,560 b/sec x 25 sec = 1,572,864,000 b
=196,608,000 B per study

=600,000,000 / 196,608,000 = 3.05
holds 3 studies

Front 31

5.6 What is TCP/IP?

Back 31

TCP/IP is a protocol suite developed by the Defense Advanced Research Projects Agency (DARPA) that consists of a large collection of protocols issued as Internet standards by the Internet Activities Board (IAB). TCP/IP was a product of protocol research and development on ARPANET, an experimental packet-switched network. It identifies five layers, which consists of: application layer, transport layer, internet layer, network access layer, and the physical layer.

Front 32

5.7 There are several protocol models that have been developed. Examples of these include SNA,Appletalk, OSI, and TCP/IP as well as more general models such as three layer models.What model is actually used for communications that travel over the Internet?

Back 32

The model used for communications to travel over the Internet is the TCP/IP.

Front 33

5.8 What are some advantages of layering as seen in the TCP/IP architecture?

Back 33

-ease of developing standards simultaneously for protocol at each layer of the architecture.
-layering allows for individual focus on each layer when developing protocols for each and thus breaks down the task.
-allows for specific focus on each layer's function in terms of understanding the function of each as well as making it easier to design and implement.

Front 34

5.9 Which version of IP is the most prevalent today?

Back 34

The most prevalent IP version used today is the IPv4, which provides for 32-bit source and destination addresses. This allows for an approximately 4.3 billion theoretical addresses.

Front 35

5.10 Does all traffic running on the Internet use TCP?

Back 35

Although TCP/IP is commonly used on the internet, it is not mandatory for it to be used. Some applications might not need the use of TCP and might request the services of a specific layer in TCP/IP or altogether use IP directly.

Front 36

5.11 Compare the address space between IPv4 and IPv6. How many bits are used in each?

Back 36

IPv4 provides for 32-bit source and destination addresses. This allows for an approximately 4.3 billion theoretical addresses. IPv6 allows for 128-bit addresses, which amount to approximately 3.4 x 1038 theoretical addresses.

Front 37

5.12 Large files sent over the network must be broken up into smaller packets. How does
the IP layer keep the packets from getting misplaced or collected out of order?

Back 37

The IP layer keeps the packets from getting misplaced or collected out of order by appending a header of control information to each segment and thus forming an IP datagram. The header in the IP datagrams contain important information such as the destination address, source address, identifier, total length and a header checksum. This control information allows the receiving source to put the files in the correct order and allows for error detection such as missing packets through the use of the header checksum.

Front 38

5.13 What is a router?

Back 38

A router is a type of intermediate system (ISs) that connects subnetworks. Its prime function is to provide a link between networks through which routing and delivery of data can be exchanged without requiring modification of the networking architecture of the attached networks. A router operates at layer 3 of the OSI layer.

Front 39

5.14 Does a router require that all attached layer 2 protocols are the same?

Back 39

A router does not require that all attached layer 2 protocols are the same. A router provides routing and delivery of data between end systems attached to different networks without requiring the modification of the attached networks; therefore layer 2 protocols do not have to be the same.

Front 40

5.3 List the major disadvantages of the layered approach to protocols.

Back 40

-there are too many layers it adds unnecessary complexity as in the case of the OSI protocol architecture versus the TCP/IP protocols. The OSI employs seven layers while the TCP/IP contains five.
-if something goes wrong in one
layer it might affect the whole architecture and error source detection in terms of finding where the error originated might become an issue in the layered approach.

Front 41

Problem 5.8
5.8 Why does the TCP header have a header length field while the UDP header does not?

Back 41

The UDP header does not have a header length field because it has a fixed length size of 8 bytes while the TCP header length can vary.

Front 42

A TCP segment consisting of 1500 bits of data and 160 bits of header is sent to the IP layer, which appends another 160 bits of header. The IP segment is then passed to the data link control layer which uses a 24-bit header. Assuming there is no fragmentation, what is the transmission efficiency? (Hint: Transmission Efficiency = (number of original data bits) / (total number of transmitted bits.)

Back 42

Transmission Efficiency = number of original data bits / total number of transmitted bits

= 1500 / 1500+160+160+24

= 1500 / 1844

= .813 = 81.3%

Front 43

17.1 Define flow control.

Back 43

Flow control is a technique used between two entities, transmitter and receiver, to make sure that the data being transferred does not overwhelm a receiver. This technique is deemed necessary when the amount of data being sent by the transmitter is faster that the rate by which it can be processed by a receiver. The sequential frame numbering and acknowledgement of receipt so that more data is sent once received is the basis of flow control.

Front 44

17.2 Define error control.

Back 44

Error control provides the transmitter and receiver of data with mechanisms by which to detect and correct errors in the data sent. The two types of errors in the transmission of data are lost frames and damaged frames. The technique most commonly used for error control is referred to as automatic repeat request (ARQ). ARQ consists of error detection, positive acknowledgment, retransmission after timeout, and negative acknowledgment and retransmission.

Front 45

17.3 List common ingredients for error control for a link control protocol.

Back 45

The most common ingredients for error control for a link control protocol are error detection, positive acknowledgment, retransmission after timeout, and negative acknowledgment and retransmission.

Front 46

17.4 What is the purpose of the flag field in HDLC?

Back 46

The purpose of the flag field in HDLC is to provide synchronization. A flag appears at the beginning and end of the frame so that it marks the beginning of data contained in the frame as well as the end of data contained in the frame. This way the receiver knows and that the frame is complete and synchronized with the sender.

Front 47

17.5 What type of error detection is used in the HDLC frame check sequence field?

Back 47

Cyclic redundancy check is used for error detection in the HDLC frame check sequence field.

Front 48

17.6 What are the three frame types supported by HDLC? Describe each.

Back 48

The three frame types supported by HDLC are information frames, supervisory frames, and unnumbered frames. Information frames contain the user data to be transmitted. Supervisory frames provide flow and error control. Unnumbered frames provide supplemental link control functions.

Front 49

17.7 What is multiplexing?

Back 49

Multiplexing allows for the shared use of communication capacity and is typically used in long-haul communications on microwave, high-capacity fiber, and coaxial links. Multiplexing involves the use of a multiplexer and a demultiplexer. The multiplexer combines data from a certain n number of lines and transmit over a high-capacity link. The data is received, separated and delivered by a demultiplexer to the appropriate outlines lines.

Front 50

17.8 The set of time slots or the frequency allocated to a single source is called what?

Back 50

The set of time slots or the frequency allocated to a single source is called a channel.

Front 51

17.9 Why is multiplexing so cost-effective?

Back 51

Multiplexing is cost-effective because as the data rate of the transmission facility increases, the cost per kpbs declines. In addition, with an increasing data rate the cost of transmission and receiving equipment per kpbs declines.

Front 52

17.10 How is interference avoided by using frequency division multiplexing?

Back 52

In frequency division mulitplexing (FDM), interference is avoided by using guard bands to separate the channels. Guard bands are unused portions of the spectrum.

Front 53

17.11 What is echo cancellation?

Back 53

Echo cancellation involves a transmitter subtracting the echo in its own transmission from the incoming signal to recover the signal sent by the other side. Echo cancellation is a signal processing technique that when used allows the entire frequency band for the upstream channel to overlap the lower portion of the downstream channel. This technique is good in that the higher the frequency, the greater the attenuation. The disadvantage of this technique is that both ends of the line need echo cancellation logic.

Front 54

17.12 Define upstream and downstream with respect to subscriber lines.

Back 54

With respect to subscriber lines, upstream can be defined as the capacity from the customer to the carrier. An example of upstream can be in the form of keyboard strokes or transmission of short e-mail messages. Downstream can be defined as the capacity from the carrier's central office to the customer's site. An example of downstream can be downloading large amounts of data or video from the Web.

Front 55

17.13 Explain how synchronous time division multiplexing (TDM) works.

Back 55

Synchronous time division (TDM) works by having signals take turns over a medium. It requires that the data rate of the medium exceeds the data rate of the signals being transmitted. The data from various sources are carried in repetitive frames. Each frame is made up of a set of time slots that is assigned one or more time slots per frame. An example of where synchronous TDM is used is in today's digital telephone system. The most popular form of synchronous TDM is T-1.

Front 56

17.14 What are some of the major uses of T-1 lines?

Back 56

Some of the major used of T-1 lines include private voice networks, private data network, video teleconferencing, high-speed digital facsimile, and internet access.

Front 57

17.15 Why is the use of private T-1 lines attractive to companies?

Back 57

The use of private T-1 lines is attractive to companies because it can allow a company to construct a private network within geographically dispersed organizations. T-1 lines allow for simpler configuration and their transmission services are less expensive. It is also attractive to companies because it is used to provide business-user access to public telephone networks.

Front 58

Problem 17.8 (a)
17.8 To get some indication of the relative demands of voice and data traffic, consider the following:

a. Calculate the number of bits used to send a 3-minute telephone call using standard PCM.

(Hint: Standard PCM has a data rate of 64 kbps)

Back 58

64 kbps * (3*60 s) = 64 kbps * 180 s = 11,520 kb

Front 59

17.8 (c)
c. How many pages of facsimile at standard resolution, that is, 200 dpi (dots per inch) horizontally and 100 dpi vertically, correspond to one 3-minute phone call? Assume that the effective page is 8 inches wide and 10.5 inches long. Moreover, assume an effective compression ratio of 10 to 1.

(Hint: For coding, assume an 8-bit gray scale which means that each pixel or dot requires 8 bits of data)

Back 59

200 dpi * 100 dpi = 20,000 dpi

8 in * 10.5 in = 84 in

20,000 dpi * 84 in * 8 bits per dot = 13,440,000 bits

With a 10 to 1 compression: 13,440,000 bits / 10 = 1,344,000 bits

PCM data rate: 64,000 bits / 1,344,000 bits = .048 pages / second

.048 pages * ((60*3) seconds) = 8.64 pages

Front 60

17.9 Recently a new scanner was announced that provided 1200 dpi resolution and over 1 billion colors.

a. How much memory in bytes would it take to store a bit map of an 8 × 10 inch monochrome picture at 1200 dpi with a 10-bit gray scale?

(Hint: If a scanner scans at 300 dpi, then there are a total of 300x300=90,000 dots per square inch of area; if a scanner scans at 600 dpi, then there are a total of 600x600=360,000 dots per square inch of area)

Back 60

1200 * 1200 = 1,440,000 dots per square inch of area

8 in * 10 in = 80 square inch

1,440,000 dots per square in * 80 square in * 10 b = 115,200,000 dots

115,200,000 bits / 8 = 144,000,000 bytes

Front 61

Problem 17.9 (c)

c. How long would it take to send a gray scale representation of an 8 × 10 inch picture at 1200 dpi over a T-1 line (1.544 Mbps)?

Back 61

1,152,000,000 bits / 1,544,000 bits = 746 sec

Front 62

16.1 Distinguish among analog data, analog signaling, and analog transmission.

Back 62

Analog data take on continuous values on some interval such as temperature and pressure, are continuous valued. An analog signal is a continuously varying electromagnetic wave that may be transmitted over a variety of media, depending on frequency. Analog transmission is a means of transmitting analog signals without regard to their content; the signals may represent analog data (such as voice) or digital data (such as data that pass through a modem).

Front 63

16.2 Distinguish among digital data, digital signaling, and digital transmission.

Back 63

Digital data take on discrete
values; examples are text, integers, and binary data. A digital signal is a sequence of voltage pulses that may be transmitted over a wire medium; for example, a constant positive voltage may represent binary 0, and
a constant negative value may represent binary 1. Digital transmission, in contrast, is concerned with the content of the signal. We have mentioned that a digital signal can be propagated only a limited distance before attenuation endangers the integrity of the data. To achieve greater distances, repeaters are used. A repeater receives the digital signal, recovers the pattern of ones and zeros, and retransmits a new signal. Thus the attenuation is overcome.