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Contents: data communication and networking by behrouz a. Add to Wish List. The presentation begins with an explanation of the application layer, which makes it easier for students to understand how network devices work, and then moves on to discuss the other layers, ending with the physical layer. Out of stock. In this new first edition, well-known author Behrouz Forouzan uses his accessible writing style and visual approach to simplify the difficult concepts of cryptography and network security.
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The light ray travels along the interface. The incident angle 80 degrees is greater than the critical angle 60 degrees. We have reflection.
The light ray returns back to the more dense medium. Switching provides a practical solution to the problem of connecting multiple devices in a network. It is more practical than using a bus topology; it is more effi- cient than using a star topology and a central hub. Switches are devices capable of creating temporary connections between two or more devices linked to the switch.
The three traditional switching methods are circuit switching, packet switching, and message switching. The most common today are circuit switching and packet switching. There are two approaches to packet switching: datagram approach and virtual- circuit approach. In a circuit-switched network, data are not packetized; data flow is somehow a continuation of bits that travel the same channel during the data transfer phase.
In a packet-switched network data are packetized; each packet is somehow an indepen- dent entity with its local or global addressing information. The address field defines the end-to-end source to destination addressing.
The address field defines the virtual circuit number local addressing. In a space-division switch, the path from one device to another is spatially separate from other paths.
The inputs and the outputs are connected using a grid of elec- tronic microswitches. In a time-division switch, the inputs are divided in time using TDM. A control unit sends the input to the correct output device. TSI time-slot interchange is the most popular technology in a time-division switch. It used random access memory RAM with several memory locations. The RAM fills up with incoming data from time slots in the order received.
Slots are then sent out in an order based on the decisions of a control unit. In multistage switching, blocking refers to times when one input cannot be con- nected to an output because there is no path available between them—all the possi- ble intermediate switches are occupied.
One solution to blocking is to increase the number of intermediate switches based on the Clos criteria. A packet switch has four components: input ports, output ports, the routing pro- cessor, and the switching fabric.
An input port performs the physical and data link functions of the packet switch. The output port performs the same functions as the input port, but in the reverse order. The routing processor performs the function of table lookup in the network layer. The switching fabric is responsible for moving the packet from the input queue to the output queue. We assume that the setup phase is a two-way communication and the teardown phase is a one-way communication.
These two phases are common for all three cases. In case a, we have ms. The ratio for case c is the smallest because we use one setup and teardown phase to send more data. We assume that the transmission time is negligible in this case.
This means that we suppose all datagrams start at time 0. In a circuit-switched network, end-to-end addressing is needed during the setup and teardown phase to create a connection for the whole data transfer phase. After the connection is made, the data flow travels through the already-reserved resources. The switches remain connected for the entire duration of the data transfer; there is no need for further addressing.
In a datagram network, each packet is independent. The routing of a packet is done for each individual packet.
Each packet, therefore, needs to carry an end- to-end address. There is no setup and teardown phases in a datagram network connectionless transmission. The entries in the routing table are somehow permanent and made by other processes such as routing protocols.
In a virtual-circuit network, there is a need for end-to-end addressing during the setup and teardown phases to make the corresponding entry in the switching table. The entry is made for each request for connection.
During the data trans- fer phase, each packet needs to carry a virtual-circuit identifier to show which virtual-circuit that particular packet follows. A datagram or virtual-circuit network handles packetized data.
For each packet, the switch needs to consult its table to find the output port in the case of a datagram network, and to find the combination of the output port and the virtual circuit iden- tifier in the case of a virtual-circuit network. In a circuit-switched network, data are not packetized; no routing information is carried with the data.
The whole path is established during the setup phase. In circuit-switched and virtual-circuit networks, we are dealing with connections. A connection needs to be made before the data transfer can take place. In the case of a circuit-switched network, a physical connection is established during the setup phase and the is broken during the teardown phase.
In the case of a virtual-circuit network, a virtual connection is made during setup and is broken during the tear- down phase; the connection is virtual, because it is an entry in the table. These two types of networks are considered connection-oriented. In the case of a datagram network no connection is made. Any time a switch in this type of network receives a packet, it consults its table for routing information.
This type of network is con- sidered a connectionless network. The switching or routing in a datagram network is based on the final destination address, which is global. The minimum number of entries is two; one for the final destination and one for the output port.
Here the input port, from which the packet has arrived is irrelevant. The switching or routing in a virtual-circuit network is based on the virtual circuit identifier, which has a local jurisdiction. This means that two different input or output ports may use the same virtual circuit number. Therefore, four pieces of information are required: input port, input virtual circuit number, output port, and output virtual circuit number.
Packet 1: 2 Packet 2: 3 Packet 3: 3 Packet 4: 2 Packet 1: 2, 70 Packet 2: 1, 45 Packet 3: 3, 11 Packet 4: 4, 41 In a datagram network, the destination addresses are unique. They cannot be duplicated in the routing table. In a virtual-circuit network, the VCIs are local. A VCI is unique only in rela- tionship to a port. In other words, the port, VCI combination is unique. This means that we can have two entries with the same input or output ports.
However, we cannot have two entries with the same port, VCI pair. When a packet arrives at a router in a datagram network, the only information in the packet that can help the router in its routing is the destination address of the packet. The table then is sorted to make the searching faster. When a packet arrives at a switch in a virtual-circuit network, the pair input port, input VCI can uniquely determined how the packet is to be routed; the pair is the only two pieces of information in the packet that is used for routing.
The table in the virtual-circuit switch is sorted based on the this pair. However, since the number of port numbers is normally much smaller than the number of virtual circuits assigned to each port, sorting is done in two steps: first according to the input port number and second according to the input VCI. However, we need to know that a regular multiplexer discussed in Chapter b. However, we need to know that a regular demultiplexer discussed in See Figure 8.
Figure 8. Only four simultaneous connections are possible for each crossbar at the first stage. This means that the total number of simultaneous connections is Only six simultaneous connections are possible for each crossbar at the first stage.
The number of cross- can be left unused. Some of the input lines tion. We can see that there is no blocking involved because each 8 input line has 15 intermediate crossbars. With less than , cross- points we can design a three-stage switch.
The total number of crosspoints is , We give two solutions. We first solve the problem using only crossbars and then we replace the cross- bars at the first and the last stage with TSIs.
We can replace the crossbar at the first and third stages with TSIs as shown in Figure 8. In other words, the input frame has 10 slots and the output frame has only 4 slots. The data in the first slot of all input TSIs are directed to the first switch, the output in the second slot are directed to the sec- ond switch, and so on. We can see the inefficiency in the first solution.
Since the slots are separated in time, only one of the switches at the middle stage is active at each moment. This means that, instead of 4 crossbars, we could have used only one with the same result. In this case we still need memory locations but only crosspoints.
The telephone network is made of three major components: local loops, trunks, and switching offices. The telephone network has several levels of switching offices such as end offices, tandem offices, and regional offices. A LATA is a small or large metropolitan area that according to the divestiture of was under the control of a single telephone-service provider.
These car- riers, sometimes called long-distance companies, provide communication services between two customers in different LATAs. Signaling System Seven SS7 is the protocol used to provide signaling services in the telephone network. It is very similar to the five-layer Internet model.
Telephone companies provide two types of services: analog and digital. Dial-up modems use part of the bandwidth of the local loop to transfer data. The latest dial-up modems use the V-series standards such as V. Telephone companies developed digital subscriber line DSL technology to pro- vide higher-speed access to the Internet.
It uses a device called a digital sub- scriber line access multiplexer DSLAM at the telephone company site. The traditional cable networks use only coaxial cables to distribute video infor- mation to the customers. The hybrid fiber-coaxial HFC networks use a combi- nation of fiber-optic and coaxial cable to do so. To provide Internet access, the cable company has divided the available bandwidth of the coaxial cable into three bands: video, downstream data, and upstream data.
The downstream-only video band occupies frequencies from 54 to MHz. The downstream data occupies the upper band, from to MHz. The upstream data occupies the lower band, from 5 to 42 MHz. The cable modem CM is installed on the subscriber premises. The cable modem transmission system CMTS is installed inside the distribution hub by the cable company. It receives data from the Internet and passes them to the combiner, which sends them to the subscriber. Packet-switched networks are well suited for carrying data in packets.
The end-to- end addressing or local addressing VCI occupies a field in each packet. Tele- phone networks were designed to carry voice, which was not packetized. A cir- cuit-switched network, which dedicates resources for the whole duration of the conversation, is more suitable for this type of communication. The setup phase can be matched to the dialing process. After the callee responds, the data transfer phase here voice transfer phase starts. When any of the parties hangs up, the data transfer is terminated and the teardown phase starts.
It takes a while before all resources are released. In a telephone network, the telephone numbers of the caller and callee are serving as source and destination addresses. These are used only during the setup dialing and teardown hanging up phases. The delay can be attributed to the fact that some telephone companies use satellite networks for overseas communication.
In these case, the signals need to travel sev- eral thousands miles earth station to satellite and satellite to earth station.
See Figure 9. Figure 9. SDSL e. VDSL The DSL technology is based on star topology with the hub at the telephone office. The local loop connects each customer to the end office. This means that there is no sharing; the allocated bandwidth for each customer is not shared with neigh- bors. The data rate does not depend on how many people in the area are transfer- ring data at the same time.
The cable modem technology is based on the bus or rather tree topology. The cable is distributed in the area and customers have to share the available band- width.
This means if all neighbors try to transfer data, the effective data rate will be decreased. In a single bit error only one bit of a data unit is corrupted; in a burst error more than one bit is corrupted not necessarily contiguous.
Redundancy is a technique of adding extra bits to each data unit to determine the accuracy of transmission. In forward error correction, the receiver tries to correct the corrupted codeword; in error detection by retransmission, the corrupted message is discarded the sender needs to retransmit the message.
A linear block code is a block code in which the exclusive-or of any two code- words results in another codeword. A cyclic code is a linear block code in which the rotation of any codeword results in another codeword. The Hamming distance between two words of the same size is the number of differences between the corresponding bits. The Hamming distance can easily be found if we apply the XOR operation on the two words and count the number of 1s in the result.
The minimum Hamming distance is the smallest Hamming distance between all possible pairs in a set of words. The single parity check uses one redundant bit for the whole data unit. In a two- dimensional parity check, original data bits are organized in a table of rows and columns. The parity bit is then calculated for each column and each row. The remainder is always one bit smaller than the divisor.
The degree of the generator polynomial is one less than the size of the divisor. For example, the CRC generator with the polynomial of degree 32 uses a bit divisor. The degree of the generator polynomial is the same as the size of the remainder length of checkbits. For example, CRC with the polynomial of degree 32 creates a remainder of 32 bits. In this arithmetic, when a number needs more than n bits, the extra bits are wrapped and added to the number. In this arithmetic, the complement of a number is made by inverting all bits.
At least three types of error cannot be detected by the current checksum calcula- tion. First, if two data items are swapped during transmission, the sum and the checksum values will not change.
Third, if one or more data items is changed in such a way that the The value of a checksum can be all 0s in binary. This happens when the value of the sum after wrapping becomes all 1s in binary. It is almost impossible for the value of a checksum to be all 1s. For this to happen, the value of the sum after wrapping must be all 0s which means all data units must be 0s. First, the result of XORing two equal patterns is an all-zero pattern part b.
Second, the result of XORing of any pattern with an all-zero pattern is the original non-zero pattern part c. Third, the result of XORing of any pattern with an all-one pattern is the complement of the original non-one pattern. The codeword for dataword 10 is This codeword will be changed to if a 3-bit burst error occurs. This pattern is not one of the valid codewords, so the receiver detects the error and discards the received pattern.
This pattern is not one of the valid codewords, so the receiver discards the received pattern. The code is not linear. We check five random cases. All are in the code. We show the dataword, the codeword, the corrupted codeword, and the interpreta- tion of the receiver for each case: a.
Comment: The above result does not mean that the code can never detect three errors. The last two cases show that it may happen that three errors remain unde- tected.
We show the dataword, codeword, the corrupted codeword, the syndrome, and the interpretation of each case: a. C 7,4 cannot correct two errors. C 7,4 cannot correct three errors. If we rotate one bit, the result is , which is in the code. If we rotate two bits, the result is , which is in the code. And so on. We use trial and error to find the right answer: a. To detect single bit errors, a CRC generator must have at least two terms and the coefficient of x0 must be nonzero.
It has more than one term and the coefficient of x0 is 1. It can detect a single-bit error. It will detect all burst errors of size 8 or less. This means 8 out of burst errors of size 9 c. Burst errors of size 9 are detected most of the time, but they slip by with proba- are left undetected. This means 4 out of burst errors of size 15 d. Burst errors of size 15 are detected most of the time, but they slip by with prob- are left undetected. It detects all single-bit error. It will detect all burst errors of size 32 or less.
This means out of burst c. Burst errors of size 33 are detected most of the time, but they are slip by with errors of size 33 are left undetected. This means out of burst d. Burst errors of size 55 are detected most of the time, but they are slipped with errors of size 55 are left undetected. We need to add all bits modulo-2 XORing.
However, it is simpler to count the number of 1s and make them even by adding a 0 or a 1. We have shown the parity bit in the codeword in color and separate for emphasis. Figure Checksum at the sender site b. Checksum at the receiver site one caught error d. Checksum at the receiver site two errors. In part a, we calculate the checksum to be sent 0x2E32 b.
In part b, there is no error in transition. The receiver recalculates the checksum to be all 0x The receiver correctly assumes that there is no error. In part c, there is one single error in transition. The receiver calculates the checksum to be 0FFFD. The receiver correctly assumes that there is some error and discards the packet. In part d, there are two errors that cancel the effect of each other.
The receiver calculates the checksum to be 0x The receiver erroneously assumes that there is no error and accepts the packet. This is an example that shows that the checksum may slip in finding some types of errors. This example shows that the checksum can be all 0s. It can be all 1s only if all data items are all 0, which means no data at all.
The two main functions of the data link layer are data link control and media access control. Data link control deals with the design and procedures for commu- nication between two adjacent nodes: node-to-node communication. Media access control deals with procedures for sharing the link. The data link layer needs to pack bits into frames.
Framing divides a message into smaller entities to make flow and error control more manageable. In a byte-oriented protocol, data to be carried are 8-bit characters from a coding system. Character-oriented protocols were popular when only text was exchanged by the data link layers.
In a bit-oriented protocol, the data section of a frame is a sequence of bits. Bit-oriented protocols are more popular today because we need to send text, graphic, audio, and video which can be better represented by a bit pat- tern than a sequence of characters. Character-oriented protocols use byte-stuffing to be able to carry an 8-bit pattern that is the same as the flag.
Byte-stuffing adds an extra character to the data section of the frame to escape the flag-like pattern. Bit-oriented protocols use bit-stuffing to be able to carry patterns similar to the flag. Bit-stuffing adds an extra bit to the data section of the frame whenever a sequence of bits is similar to the flag.
Flow control refers to a set of procedures used to restrict the amount of data that the sender can send before waiting for acknowledgment. Error control refers to a set of procedures used to detect and correct errors. In this chapter, we discussed two protocols for noiseless channels: the Simplest and the Stop-and-Wait. The second uses pipelining, the first does not. In the first, we need to wait for an acknowledgment for each frame before sending the next one.
In the second we can send several frames before receiving an acknowledgment. If a frame is lost or damaged, all outstanding frames sent before that frame are resent. In the Selective- Repeat ARQ protocol we avoid unnecessary transmission by sending only the frames that are corrupted or missing. HDLC is a bit-oriented protocol for communication over point-to-point and multi- point links. PPP is a byte-oriented protocol used for point-to-point links.
Piggybacking is used to improve the efficiency of bidirectional transmission. When a frame is carrying data from A to B, it can also carry control information about frames from B; when a frame is carrying data from B to A, it can also carry control information about frames from A.
We give a very simple solution. We write two very simple algorithms. We assume that a frame is made of a one- byte beginning flag, variable-length data possibly byte-stuffed , and a one-byte ending flag; we ignore the header and trailer.
We also assume that there is no error during the transmission. Try the Kindle edition and experience these great reading features: Read more Read less. Data Communications and Networking. I had to buy this book for class. Only buy this book if you have to. Amazon Drive Cloud storage from Amazon. Would you like to tell forouaan about a lower price? Students are presented with the most up-to-date material currently available and are encouraged to view what they are learning in a real-world context.
Discover Prime Book Box for Kids. The content of the book is poorly written, dry, and poorly structured. See and discover other items: Alexa Mpsharraf Analytics for the Web. Ships from and sold by Amazon. About the Author Behrouz A. Showing of 6 reviews.
This book starts with the described content of the network model and provides the user with a perfect introduction to data transfer. File Name: forouzan computer networks 5th edition pdf. Shrikant Bhusalwad. We assume that a frame is made of an 8-bit flagand an 8-bit ending flag ; we ignore header and trailer. Start Free Trial 5tn anytime! Carousel Previous Carousel Next. We have shown the parity bit in the codeword in fotouzan and separate for emphasis.
Bit-oriented protocols are more popular today because we need to send text, each packet is independent, and video which can be better represented by a bit pat-tern than a sequence of characters. PPP is a byte-oriented protocol used for point-to-point links. In a datagram network. Technologies related to data communication and networking may be the fastest growing in today's culture. The appearance of some new social networking applications is a testimony to this claim.
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