If You're an Educator Download instructor resources Additional order info. Description Two-time winner of the best Computer Science and Engineering textbook of the year award from the Textbook and Academic Authors Association, including the current edition. With a focus on the most current technology and a convenient modular format, this best-selling text offers a clear and comprehensive survey of the entire data and computer communications field. Emphasizing both the fundamental principles as well as the critical role of performance in driving protocol and network design, it explores in detail all the critical technical areas in data communications, wide-area networking, local area networking, and protocol design.
Preface Preface is available for download in PDF format. This text features: Solutions Manual - Solutions to all the homework problems and review questions in the book. New to This Edition. Data Communications, Data Networking, and the Internet 1. Data Transmission 3. Guided and Wireless Transmission 4.
Signal Encoding Techniques 5. Digital Data Communication Techniques 6. Data Link Control 7. Multiplexing 8. Spread Spectrum 9. Circuit Switching and Packet Switching Southern Polytechnic State University. Includes PPT slides. CIS Data Communications. Programming assignments, exercises. EL Principles of Communications Networks. Polytechnic U.
Includes PPT slides and audio notes. CSE Network Technology. Monash U. Includes PDF slides. EG Communications Engineering. Includes lecture notes, an number of useful supplement pages. Taylor Eric J. Simon Jean L. Berk, J. Crowe, Donald F. Elger, John A. Meriam, L. Stickney Paul Brown James M. Lial, Raymond N. Greenwell, and Nathan P. Hoyle, , andTimothy S.
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Block Geoffrey A. Choi Gary K. 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. 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. Addressing: 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.
A station retransmits on receipt of a duplicate acknowledgment or as a result of a timeout. 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. Based on sliding-window flow control. When an error is detected, only the frame in question is retransmitted. 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. 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 : Used with an unbalanced configuration. 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. 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. The REJ 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.
This would contradict the intent of the SREJ frame or frames. However, for simplicity, bit stuffing is used on this field. When a flag is used as both an ending and starting flag that is, one 8-bit pattern serves to mark the end of one frame and the beginning of the next , then a single-bit error in that flag alters the bit pattern so that the receiver does not recognize the flag. Accordingly, the received assumes that this is a single frame.
If a bit error somewhere in a frame between its two flags results in the pattern , then this octet is recognized as a flag that delimits the end of one frame and the start of the next frame. Any discrepancies result in discarding the frame. 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 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, the entire 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.
The character is delimited by the bounds of the time slot, which are defined by the synchronous transmission scheme. Thus, no further delimiters are needed. When the character arrives at its destination, the start and stop bits can be added back if the receiver requires these. TDM's focus is on the medium rather than the information that travels on the medium.
Its services should be transparent to the user. It offers no flow or error control. These must be provided on an individual-channel basis by a link control protocol. The actual bit pattern is If a receiver gets out of synchronization it can scan for this pattern and resynchronize. This pattern would be unlikely to occur in digital data. Analog sources cannot generate this pattern. It corresponds to a sine wave at 4, Hz and would be filtered out from a voice channel that is band limited.
One SYN character, followed by 20 bit terminal characters, followed by stuff bits. The available capacity is 1. This is a practical limit based on the performance characteristics of a statistical multiplexer.
If the receiver is on the framing pattern no searching , the minimum reframe time is 12 frame times the algorithm takes 12 frames to decide it is "in frame".
Hence it must search the maximum number of bits 55 to find it. Each search takes 12T f. Assuming the system is random, the reframing is equally to start on any bit position. Hence on the average it starts in the middle or halfway between the best and worst cases. Therefore, the channel cost will be only one-fourth, since one channel rather than four is now needed.
The same reasoning applies to termination charges. The present solution requires eight low speed modems four pairs of modems.
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