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William Stallings Data and Computer Communications 7th Edition lesforgesdessalles.info Never Split the Difference. Computer System Architecture-Morris Mano third edition. Pages·· MB·60, William Stallings Data and Computer Communications 7th Edition. Data and Computer Communications, 7th Edition, Solutions Manual. Home · Data and Computer downloads Views 3MB Size Report. DOWNLOAD PDF.
A scheme such as depicted in Figure 8. Data and Computer Communications. A user of a VCC is provided with a Quality of Service specified by parameters such as cell loss ratio ratio of cells lost to cells transmitted and cell delay variation. Data Communications and Networking Solution Manual. The cook gives the pizza to the clerk with the order form acting as a "header" to the pizza. The implementation is the same as that shown in Solution 6.
It is available at a discount for courses using this textbook. Data Link Simulator: This tool enables students to write connection oriented data link protocols and have them tested on a simulated communication channel. On-line Simulation: Ann Burroughs, an Associate Professor at Humboldt State University has created two simulations that may help you visualize some of the concepts in the book.
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Instructors might find these web sites for courses taught using this book useful. I would appreciate hearing about web sites for other courses. PDF slides. Includes PPT slides. CIS Data Communications. Programming assignments, exercises. EL Principles of Communications Networks. Polytechnic U. Includes PPT slides and audio notes. IS Telecommunications Systems. CSE Network Technology. Monash U. The session and transport layer both are involved in providing an end-to-end service to the OSI user, and could easily be combined.
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. 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 roundtrip time. 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 The period of cos 2t is p and therefore the period of f t is p.
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: 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.
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. PCM, on the other hand, does not estimate changes in signals, but rather the absolute value of the signal, and is less affected than DM. 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.
An other alternative is to embed the clocking information in the data signal. For digital signals, this can be accomplished with Manchester or differential Manchester encoding. 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 doublebit 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. 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 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, errorfree 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 Data transmitted by one side is 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. Unnumbered frames U-frames provide supplemental link control functions.
Because only one frame can be sent at a time, and transmission must stop until an acknowledgment is received, there is little effect in increasing the size of the message if the frame size remains the same.
All that this would affect is connect and disconnect time. This would lower line efficiency, because the propagation time is unchanged but more acknowledgments would be needed. For a given message size, increasing the frame size decreases the number of frames. This is the reverse of b. Then, using Equation 7. The first frame takes 10 msec to transmit; the last bit of the first frame arrives at B 20 msec after it was transmitted, and therefore 30 msec after the frame transmission began.
It will take an additional 20 msec for B's acknowledgment to return to A. Thus, A can transmit 3 frames in 50 msec. B can transmit one frame to C at a time. Thus, the total number of frames transmitted without an ACK is: The NAK improves efficiency by informing the sender of a bad frame as early as possible.
Station A sends frames 0, 1, 2 to station B. Station B receives all three frames and cumulatively acknowledges with RR 3. Because of a noise burst, the RR 3 is lost. A times out and retransmits frame 0. B has already advanced its receive window to accept frames 3, 0, 1, 2. Thus it assumes that frame 3 has been lost and that this is a new frame 0, which it accepts. The sender never knows that the frame was not received, unless the receiver times out and retransmits the SREJ.
Also from the standard: This would contradict the intent of the SREJ frame or frames. From the beginning of the transmission of the first frame, the time to receive the acknowledgment of that frame is: Any discrepancies result in discarding the frame. The last three enhancements allow the rejection of frames when the closing flag has been destroyed. Bit-stuffing at least eliminates the possibility of a long string of 1's. This is the number of the next frame that the secondary station expects to receive.
The same frame format as for LAPB is used, with one additional field: The LAPB control field includes, as usual, a sequence number unique to that link.
The MLC field performs two functions. First, LAPB frames sent out over different links may arrive in a different order from that in which they were first constructed by the sending MLP. Second, if repeated attempts to transmit a frame over one link fails, the DTE or DCE will send the frame over one or more other links.
The MLP sequence number is needed for duplicate detection in this case. In essence, a transmitter must subtract the echo of its own transmission from the incoming signal to recover the signal sent by the other side. This explains the basic difference between the 1. A scheme such as depicted in Figure 8. Each Hz signal can be sampled at a rate of 1 kHz. If 4-bit samples are used, then each signal requires 4 kbps, for a total data rate of 16 kbps.
This scheme will work only if the line can support a data rate of 16 kbps in a bandwidth of Hz. In time-division multiplexing, all of the channel is assigned to the source for a fraction of the time.
If there is spare bandwidth, then the incremental cost of the transmission can be negligible. The new station pair is simply added to an unused subchannel. If there is no unused subchannel it may be possible to redivide the existing subchannels creating more subchannels with less bandwidth.
If, on the other hand, a new pair causes a complete new line to be added, then the incremental cost is large indeed. What the multiplexer receives from attached stations are several bit streams from different sources.
What the multiplexer sends over the multiplexed transmission line is a bit stream from the multiplexer. As long as the multiplexer sends what can be interpreted as a bit stream to the demultiplexer at the other end, the system will work. The multiplexer, for example, may use a self-clocking signal. The incoming stream may be, on the other hand, encoded in some other format. The multiplexer receives and understands the incoming bits and sends out its equivalent set of multiplexed bits.
In synchronous TDM, using character interleaving, the character is placed in a time slot that is one character wide.