Stallings, William. Data and computer communications/William Stallings.—Tenth edition. Data Communications and Networking for Today's Enterprise 9. William Stallings Data and Computer Communications 7th Edition. 83 Pages· · data communication and networking by behrouz a. forouzan 4th edition David Evans†, Paul Gruba, Justin Zobel · Download PDF Chapter. Page. pdf. Data and Communication Network by -william stallings 5th. Pages transparency masters of figures in the book in PDF (Adobe Acrobat) format, and.

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William Stallings. Upper Saddle River Copies of figures from the book in PDF format Data Communications and Networking for Today's Enterprise communications over long-distance networks. covers the material in the Computer Communication Networks course of the book in PDF (Adobe Acrobat ) format, and sign-up information for the book's . William Stallings. —Computer, terminal, phone, etc. • A collection of nodes and connections is a communications network. • Data routed by being switched from node to node.

Log In Sign Up. Hugo Silva. No part of this document may be reproduced, in any form or by any means, or posted on the Internet, without permission in writing from the author. Selected solutions may be shared with students, provided that they are not available, unsecured, on the Web. If you spot an error in a solution or in the wording of a problem, I would greatly appreciate it if you would forward the information via email to ws shore. An errata sheet for this manual, if needed, is available at ftp: Protocol Architecture Data Transmission Transmission Media Signal Encoding Techniques Digital Data Communications Techniques Data Link Control Protocols Spread Spectrum Circuit Switching and Packet Switching Asynchronous Transfer Mode Routing in Switched Networks Typically, the protocol architecture consists of a layered set of protocols, with one or more protocols at each layer.

The term is also used generically to refer to a more comprehensive collection of protocols developed by the U. Department of Defense and the Internet community. Some traffic uses no transport protocol, such as ICMP. The host communicates this order to the clerk, who places the order with the cook. The phone system provides the physical means for the order to be transported from host to clerk. The clerk boxes the pizza with the delivery address, and the delivery van encloses all of the orders to be delivered.

The road provides the physical path for delivery. However, the message is actually passed through two translators via the phone system. The French PM's translator translates his remarks into English and telephones these to the Chinese PM's translator, who translates these remarks into Chinese.

Note that the intermediate node handles the message only up to the second level; a minister's level is not needed. There is processing overhead because as many as seven modules OSI model are invoked to move data from the application through the communications software.

There is data overhead because of the appending of multiple headers to the data. Another possible disadvantage is that there must be at least one protocol standard per layer.

With so many layers, it takes a long time to develop and promulgate the standards. There is no way to be assured that the last message gets through, except by acknowledging it. Thus, either the acknowledgment process continues forever, or one army has to send the last message and then act with uncertainty.

First, look at the functions performed at the network layer to deal with the communications network hiding the details from the upper layers. The network layer is responsible for routing data through the network, but with a broadcast network, routing is not needed. Other functions, such as sequencing, flow control, error control between end systems, can be accomplished at layer 2, because the link layer will be a protocol directly between the two end systems, with no intervening switches.

So it would seem that a network layer is not needed.

Second, consider the network layer from the point of view of the upper layer using it. The upper layer sees itself attached to an access point into a network supporting communication with multiple devices.

The layer for assuring that data sent across a network is delivered to one of a number of other end systems is the network layer. This argues for inclusion of a network layer. The lower sublayer is concerned with medium access control MAC , assuring that only one end system at a time transmits; the MAC sublayer is also responsible for addressing other end systems across the LAN. LLC performs traditional link control functions.

This would violate the principle of separation of layers. It breaks that PDU into fragments and reassembles them in the proper order. Each N-level PDU must retain its own header, for the same reason given in a. Three network packets are needed. These functions would not normally be performed by protocols above the transport layer. Thus UDP provides a useful, though limited, service. TCP does guarantee delivery. However, the technique that is used is a timeout. If the source does not receive an acknowledgment to data within a given period of time, the source retransmits.

The header in TCP is of variable length. A resends packet k, which B acknowledges. From now on, 2 copies of every data packet and ACK will be sent. The maximum throughput is therefore bytes divided by the round- trip time.

This means that when the "netascii" transfer mode is employed, the file sizes of the local and the remote file may differ, without any implication of errors in the data transfer. This means that a given text file will usually occupy more space in a Windows host than in a UNIX system.

Suppose host A receives an error packet from host B, and responds it by sending an error packet back to host B. This packet could trigger another error packet from host B, which would again trigger an error packet at host A. Thus, error messages would bounce from one host to the other, indefinitely, congesting the network and consuming the resources of the participating systems.

For example, if both hosts are on the same local area network, a 5- second timeout is more than enough. On the other hand, if the transfer is taking place over a long delay satellite link, then a 5-second timeout might be too short, and could trigger unnecessary retransmissions. On the other hand, using a fixed value for the retransmission timer keeps the TFTP implementation simple, which is the objective the designers of TFTP had in mind.

Thus, reliability depends on the service provided by the underlying transport protocol UDP. While the UDP includes a checksum for detecting errors, its use is optional. Therefore, if UDP checksums are not enabled, data could be corrupted without being detected by the destination host. The internet protocol can be defined as a separate layer. The functions performed by IP are clearly distinct from those performed at a network layer and those performed at a transport layer, so this would make good sense.

The session and transport layer both are involved in providing an end-to-end service to the OSI user, and could easily be combined. If two devices transmit at the same time, their signals will be on the medium at the same time, interfering with each other; i. See discussion in Section A real signal therefore is bandlimited, with frequencies above a certain point absent.

However, most of the information is in the lower frequencies. This is not a problem if it is remembered that the object of the transmission is to send signals that represent binary 1s and 0s. Even though there will be some distortion because of the loss of higher frequencies, the shape of the original pulse is known by the specifications for the transmission system. Thus, the receiver will usually be able to distinguish a binary 0 from a binary 1. Several shift lock codes were defined in various versions of TTS shift, supershift, unshift.

These codes change the meaning of all codes that follow until a new shift lock code appears. The actual number is less, since some codes, such as space, are "don't-cares" with respect to shift locks. Retaining the vertical resolution of lines, each horizontal line occupies The scanning frequency is: We use the formula: Due to the fact there is a distortion level as well as other potentially detrimental impacts to the rated capacity, the actual maximum will be somewhat degraded from the theoretical maximum.

Data and Computer Communications 10th Edition William Stallings Test Bank

A discussion of these relevant impacts should be included and a qualitative value discussed. Shannon addressed the question of what signaling rate can be achieved over a channel with a given bandwidth, a given signal power, and in the presence of noise.

Output waveform: For example, it reduces crosstalk between wire pairs bundled into a cable. Shielded twisted pair STP surrounds the wire with a metallic braid or sheathing that reduces interference. The glass or plastic itself consists of two concentric columns. The inner column called the core has a higher index of refraction than the outer column called the cladding. It is affected by rainfall, however, especially above 10 GHz. It is also requires line of sight and is subject to interference from other microwave transmission, which can be intense in some places.

In practice, there will be some beam spread. Nevertheless, it produces a highly focused, directional beam. The edge in effect become a source and waves radiate in different directions from the edge, allowing a beam to bend around an obstacle.

If the size of an obstacle is on the order of the wavelength of the signal or less, scattering occurs. An incoming signal is scattered into several weaker outgoing signals in unpredictable directions. From Figure 4. If the outer conductor of a coaxial cable is everywhere held at ground potential, no external disturbance can reach the inner, signal-carrying, conductor.

Half of that is 5, km which is comparable to the east-to-west dimension of the continental U. While an antenna this size is impractical, the U. Defense Department has considered using large parts of Wisconsin and Michigan to make an antenna many kilometers in diameter.

The received power will increase by a factor of 4 4. Thus, the higher the frequency, the higher power is needed to obtain a given SNR. Power is much more readily available at earth stations than at satellites. Therefore, it makes more sense to put the higher power requirements on the earth stations than on the satellites. Using Equation 4. The available received signal power is 20 — A lack of high-frequency components means that less bandwidth is required for transmission.

In addition, lack of a direct-current dc component means that ac coupling via transformer is possible. The magnitude of the effects of signal distortion and interference depend on the spectral properties of the transmitted signal. Encoding can be used to synchronize the transmitter and receiver. Error detection: It is useful to have some error detection capability built into the physical signaling encoding scheme. Signal interference and noise immunity: Certain codes exhibit superior performance in the presence of noise.

Cost and complexity: The higher the signaling rate to achieve a given data rate, the greater the cost. Some codes require a signaling rate that is in fact greater than the actual data rate. The data themselves are encoded as the presence or absence of a signal transition at the beginning of the bit time. A transition low to high or high to low at the beginning of a bit time denotes a binary 1 for that bit time; no transition indicates a binary 0.

The binary 1 pulses must alternate in polarity. For pseudoternary, a binary 1 a is represented by the absence of a line signal, and a binary 0 by alternating positive and negative pulses. In the Manchester code, there is a transition at the middle of each bit period; a low-to-high transition represents a 1, and a high-to-low transition represents a 0.

In differential Manchester, the midbit transition is used only to provide clocking. The encoding of a 0 is represented by the presence of a transition at the beginning of a bit period, and a 1 is represented by the absence of a transition at the beginning of a bit period.

The filling sequence must be recognized by the receiver and replaced with the original data sequence. The filling sequence is the same length as the original sequence, so there is no data rate penalty. This approach is susceptible to sudden gain changes and is rather inefficient.

For PM, the phase is proportional to the modulating signal. For FM, the derivative of the phase is proportional to the modulating signal. Map this level as indicated by the definition for 1 and 0 for each of the other codes.

Second, under worst case, E-NRZ provides a minimum of one transition for every 14 bits, reducing the synchronization problem. Third, the parity bit provides an error check. The disadvantages of E-NRZ are added complexity and the overhead of the extra parity bit. Bipolar-AMI 5. For AMI, positive and negative pulses are used alternately for binary 1. The pulse in position 1 represents the third binary 1 in the data stream and should have a positive value.

First consider NRZ-L.

For the remaining codes, one must first determine the average number of pulses per bit. For example, for Biphase-M, there is an average of 1. These higher components cause the signal to change more rapidly over time. Hence, DM will suffer from a high level of slope overload noise.

The demodulator portion of a modem expects to receive a very specific type of waveform e. Thus, it would not function as the coder portion of a codec. The case against using a codec in place of a modem is less easily explained, but the following intuitive argument is offered. If the decoder portion of a codec is used in place of the modulator portion of a modem, it must accept an arbitrary bit pattern, interpret groups of bits as a sample, and produce an analog output.

Some very wide value swings are to be expected, resulting in a strange-looking waveform. Given the effects of noise and attenuation, the digital output produced at the receiving end by the coder portion of the codec will probably contain many errors. The actual step size, in volts, is: Thus the actual maximum quantized voltage is: The normalized step size is 2—8. The maximum error that can occur is one-half the step size.

Therefore, the normalized resolution is: For frequency deviation, recognize that the change in frequency is determined by the derivative of the phase: A stop binary one follows the character. One side transmitter or receiver pulses the line regularly with one short pulse per bit time. The other side uses these regular pulses as a clock. Another alternative is to embed the clocking information in the data signal.

For digital signals, this can be accomplished with Manchester or differential Manchester encoding.

Data & Computer Communications (6th Edition)

For analog signals, a number of techniques can be used; for example, the carrier frequency itself can be used to synchronize the receiver based on the phase of the carrier. That is, it provides more information that can be used to detect errors. You could design a code in which all codewords are at least a distance of 3 from all other codewords, allowing all single-bit errors to be corrected. Suppose that some but not all codewords in this code are at least a distance of 5 from all other codewords.

Then for those particular codewords, but not the others, a double- bit error could be corrected. For 10, characters, there are 20, extra bits. The file takes 10 frames or additional bits. Ten times as many extra bits and ten times as long for both.

Then the maximum effective data rate R is: There are 7 data bits, 1 start bit, 1. Write down a few dozen characters. Since some 1's will intervene before you find that zero, you will have moved the starting point of the framing process. Eventually, you will achieve proper framing.

Data and Computer Communications, 7th Edition, Solutions Manual

The stop bit is needed so that the start bit can be recognized as such. The start bit is the synchronization event, but it must be recognizable. The start bit is always a 0, and the stop bit is always a 1, which is also the idle state of the line.

When a start bit occurs, it is guaranteed to be different from the current state of the line. Then a frame is 12T long.

Let a clock period be T'. The last bit bit 12 is sampled at For a fast running clock, the condition to satisfy is T The resultant accuracy is 2 minutes in 1 year or: There are more bits that can be in error since the parity bit is now included. The parity bit may be in error when there are no errors in the corresponding data bits. Therefore, the inclusion of a parity bit with each character would change the probability of receiving a correct message. The modulo 2 scheme is easy to implement in circuitry.

It also yields a remainder one bit smaller than binary arithmetic.

We have: Each 1 bit will merge with a 1 bit exclusive-or to produce a 0; each 0 bit will merge with a 0 bit to produce a zero. The CRC bits are The string is sent. The errors are detected. The errors are not detected. The HDLC standard provides the following explanation. The addition of XK L X corresponds to a value of all ones.

This addition protects against the obliteration of leading flags, which may be non-detectable if the initial remainder is zero. The addition of L X to R X ensures that the received, error- free message will result in a unique, non-zero remainder at the receiver. The non-zero remainder protects against the potential non-detectability of the obliteration of trailing flags. The implementation is the same as that shown in Solution 6. At both transmitter and receiver, the initial content of the register is preset to all ones.

The final remainder, if there are no errors, will be For a codeword w to be decoded as another codeword w', the received sequence must be at least as close to w' as to w. Therefore all errors involving t or fewer digits are correctable.

Data transmitted by one side are received by the other. In order to operate a synchronous data link without a modem, clock signals need to be supplied. The Transmitter and Receive Timing leads are cross-connected for this purpose. The beginning and end of each frame must be recognizable. Flow control: The sending station must not send frames at a rate faster than the receiving station can absorb them.

Error control: Bit errors introduced by the transmission system should be corrected. On a multipoint line, such as a local area network LAN , the identity of the two stations involved in a transmission must be specified.

Control and data on same link: The receiver must be able to distinguish control information from the data being transmitted.

Link management: The initiation, maintenance, and termination of a sustained data exchange require a fair amount of coordination and cooperation among stations. Procedures for the management of this exchange are required. With smaller frames, errors are detected sooner, and a smaller amount of data needs to be retransmitted. The window changes dynamically to allow additional packets to be sent. The sliding window flow control technique can send multiple frames before waiting for an acknowledgment.

Efficiency can be greatly improved by allowing multiple frames to be in transit at the same time. Based on stop-and-wait flow control. A station retransmits on receipt of a duplicate acknowledgment or as a result of a timeout. Go-back-N ARQ: Based on sliding-window flow control. When an error is detected, the frame in question is retransmitted, as well as all subsequent frames that have been previously transmitted.

Selective-reject ARQ. When an error is detected, only the frame in question is retransmitted. Responsible for controlling the operation of the link. Frames issued by the primary are called commands. Secondary station: Operates under the control of the primary station. Frames issued by a secondary are called responses. The primary maintains a separate logical link with each secondary station on the line. Combined station: Combines the features of primary and secondary.

A combined station may issue both commands and responses. Used with an unbalanced configuration. The primary may initiate data transfer to a secondary, but a secondary may only transmit data in response to a command from the primary.

Asynchronous balanced mode ABM: Used with a balanced configuration. Either combined station may initiate transmission without receiving permission from the other combined station. Asynchronous response mode ARM: The secondary may initiate transmission without explicit permission of the primary. The primary still retains responsibility for the line, including initialization, error recovery, and logical disconnection.

This is achieved by bit stuffing. Additionally, flow and error control data, using the ARQ mechanism, are piggybacked on an information frame. Supervisory frames S-frames provide the ARQ mechanism when piggybacking is not used.

When using analog communications, channel capacity is measured in hertz Hz where 1 Hz equals oscillations per second. Common examples of data include text and numerical information. Raster graphics involves the use of binary codes to represent object type, size, and orientation.

Which of the following represents a digital form of information? Which of the following represents the most basic unit of digital information? Standard voice telephone lines, such as those found in residences, limit bandwidth to: A stereo compact disc typically requires the bandwidth for each channel to be: When using data communications with 8-bit codes, the number of alphabetic symbols A.

The time interval between when a user presses a key and when the result of that action arrives at his or her workstation is called the: In digital systems, the information rate and the capacity of a digital channel are measured in: Analog information sources include: UTF-8 B.

IRA C. Morse code D. The number of different characters that can be represented in the International Reference Alphabet text code is: IRA D.

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UCST RGB B. Color B. Black and white C. Pixilated D. Grayscale TIFF B. JPEG C.One side transmitter or receiver pulses the line regularly with one short pulse per bit time. Data Communications: Concerned primarily with the exchange of data between two directly connected devices. Thus, no further delimiters are needed.

Highlights include the following: xDSL: The term xDSL refers to a family of digital subscriber line technologies that provide high-speed access to ISDN and other wide area networks over ordinary twisted-pair lines from the network to a residential or business subscriber. The last bit bit 12 is sampled at Therefore, if UDP checksums are not enabled, data could be corrupted without being detected by the destination host.

It is not necessary for each host on a subnet to have an unique global internet address.

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