We can approximately calculate the capacity as a. When the SNR is doubled, the data rate increases slightly. This means a bit occupies meters on a transmission medium. This means a bit occupies 20 meters on a transmission medium. This means a bit occupies 2 meters on a transmission medium. The three different techniques described in this chapter are line coding, block cod- ing, and scrambling. A data element is the smallest entity that can represent a piece of information a bit.
A signal element is the shortest unit of a digital signal. Data elements are what we need to send; signal elements are what we can send. Data elements are being carried; signal elements are the carriers. The data rate defines the number of data elements bits sent in 1s. The unit is bits per second bps. The signal rate is the number of signal elements sent in 1s.
The unit is the baud. In decoding a digital signal, the incoming signal power is evaluated against the baseline a running average of the received signal power. A long string of 0s or 1s can cause baseline wandering a drift in the baseline and make it difficult for the receiver to decode correctly.
When the voltage level in a digital signal is constant for a while, the spectrum cre- ates very low frequencies, called DC components, that present problems for a sys- tem that cannot pass low frequencies. A self-synchronizing digital signal includes timing information in the data being transmitted. This can be achieved if there are transitions in the signal that alert the receiver to the beginning, middle, or end of the pulse.
In this chapter, we introduced unipolar, polar, bipolar, multilevel, and multitran- sition coding. Block coding provides redundancy to ensure synchronization and to provide inher- ent error detecting.
In general, block coding changes a block of m bits into a block of n bits, where n is larger than m. Scrambling, as discussed in this chapter, is a technique that substitutes long zero- level pulses with a combination of other levels without increasing the number of bits.
PCM finds the value of the signal amplitude for each sample; DM finds the change between two consecutive samples. In parallel transmission we send data several bits at a time. In serial transmission we send data one bit at a time. We mentioned synchronous, asynchronous, and isochronous. In both synchro- nous and asynchronous transmissions, a bit stream is divided into independent frames. In synchronous transmission, the bytes inside each frame are synchro- nized; in asynchronous transmission, the bytes inside each frame are also indepen- dent.
In isochronous transmission, there is no independency at all. All bits in the whole stream must be synchronized. The number of bits is calculated as 0. See Figure 4. Figure 4. Bandwidth is proportional to 4.
Bandwidth is proportional to B is proportional to 5. The data stream can be found as a. NRZ-I: Differential Manchester: AMI: The data rate is Kbps. We then use Figure 4. All calculations are approximations. The output stream is The maximum length of consecutive 0s in the input stream is The maximum length of consecutive 0s in the output stream is 2. The number of unused code sequences is Since we specified that the last non-zero signal is positive, the first bit in our sequence is positive.
HDB3 In a low-pass signal, the minimum frequency 0. In a bandpass signal, the maximum frequency is equal to the minimum fre- quency plus the bandwidth. In a lowpass signal, the minimum frequency is 0. Note that we assume only one stop bit and one start bit.
Some systems send more start bits. For case b, we send extra for required bits. Normally, analog transmission refers to the transmission of analog signals using a band-pass channel. Baseband digital or analog signals are converted to a complex analog signal with a range of frequencies suitable for the channel. A carrier is a single-frequency signal that has one of its characteristics amplitude, frequency, or phase changed to represent the baseband signal.
The process of changing one of the characteristics of an analog signal based on the information in digital data is called digital-to-analog conversion. It is also called modulation of a digital signal. The baseband digital signal representing the digital data modulates the carrier to create a broadband analog signal. ASK changes the amplitude of the carrier. FSK changes the frequency of the carrier.
PSK changes the phase of the carrier. QAM changes both the amplitude and the phase of the carrier. We can say that the most susceptible technique is ASK because the amplitude is more affected by noise than the phase or frequency. A constellation diagram can help us define the amplitude and phase of a signal element, particularly when we are using two carriers.
In a constellation diagram, a signal element type is represented as a dot. The bit or combination of bits it can carry is often written next to it. The diagram has two axes. The horizontal X axis is related to the in-phase carrier; the vertical Y axis is related to the quadrature carrier.
The two components of a signal are called I and Q. The I component, called in- phase, is shown on the horizontal axis; the Q component, called quadrature, is shown on the vertical axis.
It is also called the modulation of an analog signal; the baseband analog signal modulates the carrier to create a broadband analog signal. AM changes the amplitude of the carrier b. FM changes the frequency of the carrier c. PM changes the phase of the carrier We can say that the most susceptible technique is AM because the amplitude is more affected by noise than the phase or frequency.
See Figure 5. We have two signal elements with peak amplitudes 1 and 3. The phase of both signal elements are the same, which we assume to be 0 degrees. We have two signal elements with the same peak amplitude of 2. However, there must be degrees difference between the two phases. We assume one phase to be 0 and the other degrees. We have four signal elements with the same peak amplitude of 3.
However, there must be 90 degrees difference between each phase. We assume the first phase to be at 45, the second at , the third at , and the fourth at degrees. Note that this is one out of many configurations. ASK b. QPSK d. As long as the differences are 90 degrees, the solution is satisfactory. We have four phases, which we select to be the same as the previous case.
For each phase, however, we have two amplitudes, 1 and 3 as shown in the figure. The phases can be at 0, 90, , and As long as the differences are 90 degrees, the solution is satisfac- tory. This is ASK. There are two peak amplitudes both with the same phase 0 degrees. The distance between each dot and the origin is 3. However, we have two phases, 0 and degrees. This is also BPSK. The peak amplitude is 2, but this time the phases are 90 and degrees.
The number of points define the number of levels, L. The number of bits per baud is the value of r. This means that that we need a QAM technique to achieve this data rate. We calculate the number of channels, not the number of coexisting stations. Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. In multiplexing, the word link refers to the physical path. The word channel refers to the portion of a link that carries a transmission between a given pair of lines.
One link can have many n channels. TDM is used to combine digital signals; the time is shared. To maximize the efficiency of their infrastructure, telephone companies have tradi- tionally multiplexed analog signals from lower-bandwidth lines onto higher-band- width lines. To maximize the efficiency of their infrastructure, telephone companies have tradi- tionally multiplexed digital signals from lower data rate lines onto higher data rate lines.
WDM is common for multiplexing optical signals because it allows the multiplex- ing of signals with a very high frequency. In multilevel TDM, some lower-rate lines are combined to make a new line with the same data rate as the other lines.
Multiple slot TDM, on the other hand, uses multiple slots for higher data rate lines to make them compatible with the lower data rate line. Pulse stuffing TDM is used when the data rates of some lines are not an integral multiple of other lines. In synchronous TDM, each input has a reserved slot in the output frame.
This can be inefficient if some input lines have no data to send. In spread spectrum, we spread the bandwidth of a signal into a larger bandwidth.
Spread spectrum techniques add redundancy; they spread the original spectrum needed for each station. The expanded bandwidth allows the source to wrap its message in a protective envelope for a more secure transmission. The frequency hopping spread spectrum FHSS technique uses M different car- rier frequencies that are modulated by the source signal.
At one moment, the signal modulates one carrier frequency; at the next moment, the signal modulates another carrier frequency. The direct sequence spread spectrum DSSS technique expands the bandwidth of the original signal. It replaces each data bit with n bits using a spreading code.
To multiplex 10 voice channels, we need nine guard bands. The required band- Each output frame carries 1 bit from each source plus one extra bit for synchro- b. Each frame carries 1 bit from each source. In each frame 20 bits out of 21 are useful. Each output frame carries 2 bits from each source plus one extra bit for syn- b. Each frame carries 2 bit from each source.
The output data rate here is slightly less than the one in Exercise In each frame 40 bits out of 41 are useful. Effi- ciency is better than the one in Exercise We can assume that we have only 6 input lines. Each frame needs to carry one character from each of these lines. We combine six kbps sources into three kbps. Now we have seven kbps channel. Each output frame carries 1 bit from each of the seven kbps line.
Frame b. Each frame carries 1 bit from each kbps source. We can also synchronizing bits. The frame carries 4 bits from each of the first two sources and 3 bits from each b. Each frame carries 4 bit from each kbps source or 3 bits from each kbps. We can also synchronization bits. Now we have two sources, each of Kbps. The frame carries 1 bit from each source. Here the output bit rate is greater than the sum of the input rates kbps because of extra bits added to the second source.
Each frame carries one extra bit. See Figure 6. Figure 6. This means that the The Barker chip is 11 bits, which means that it increases the bit rate 11 times. The transmission media is located beneath the physical layer and controlled by the physical layer.
The two major categories are guided and unguided media. Guided media have physical boundaries, while unguided media are unbounded. The three major categories of guided media are twisted-pair, coaxial, and fiber- optic cables. Twisting ensures that both wires are equally, but inversely, affected by external influences such as noise. Refraction and reflection are two phenomena that occur when a beam of light travels into a less dense medium.
When the angle of incidence is less than the crit- ical angle, refraction occurs. The beam crosses the interface into the less dense medium. When the angle of incidence is greater than the critical angle, reflection occurs.
The beam changes direction at the interface and goes back into the more dense medium. The inner core of an optical fiber is surrounded by cladding. The core is denser than the cladding, so a light beam traveling through the core is reflected at the boundary between the core and the cladding if the incident angle is more than the critical angle.
We can mention three advantages of optical fiber cable over twisted-pair and coax- ial cables: noise resistance, less signal attenuation, and higher bandwidth. In sky propagation radio waves radiate upward into the ionosphere and are then reflected back to earth. In line-of-sight propagation signals are transmitted in a straight line from antenna to antenna. Omnidirectional waves are propagated in all directions; unidirectional waves are propagated in one direction.
See Table 7. Table 7. As the Table 7. If we consider the bandwidth to start from zero, we can say that the bandwidth decreases with distance. For example, if we can tol- erate a maximum attenuation of 50 dB loss , then we can give the following list- ing of distance versus bandwidth.
We can use Table 7. As Table 7. This means all three figures represent the a. The wave length is the inverse of the frequency if the propagation speed is same thing.
We can change the wave length to frequency. For example, the value nm can be written as THz. The curve must be flipped horizontally. Therefore, we have: a. See Figure 7. Figure 7. The incident angle 40 degrees is smaller than the critical angle 60 degrees.
We have refraction. The light ray enters into the less dense medium. The incident angle 60 degrees is the same as the critical angle 60 degrees. 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. Explore Documents. Forouzan Solution. Uploaded by Ajay Pandey.
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Jump to Page. Search inside document. Documents Similar To forouzan solution. Md Saidur Rahman Kohinoor. Muhamad Ridzuan. Varun Jindal. Mona Sayed. At the application layer, the unit of data is a message. At the network layer, the unit of data is a datagram. At the data-link layer, the unit of data is a frame. A frame is a link-layer data unit. It encapsulates a data unit coming from the network layer.
In this case, the data unit is a datagram. A user datagram is a transport-layer data unit. It decapsulates a data unit going to the application layer.
In this case, the data unit is a message. The transport-layer packet needs to include two port numbers: source and destination port numbers. The transport-layer header needs to be at least 32 bits four bytes long, but we will see in Chapter 24 that the header size is normally much longer because we need to include other pieces of information.
At the application layer, we normally use a name to define the destinationcomputer name and the name of the file we need to access. An example is something somewhere. At the network layer, we use two logical addresses source and destination to define the source and destination computers.
These addresses are unique universally. At the data-link layer, we use two link-layer addresses source and destination to define the source and destination connections to the link. The answer is no. It only means that each of the transport-layer protocols such as TCP or UDP can carry a packet from any application-layer protocol that needs its service. However, a transport-layer packet can carry one, and only one, packet from an application-layer protocol.
We do not need a link-layer switch because the communication in this case is automatically one-to-one. A link-layer switch is needed when we need to change a one-to-many communication to a one-to-one. We do not need a router in this case because a router is needed when there is more than one path between the two hosts; the router is responsible for choosing the best path at each moment. Layer 1 takes the ciphertext from layer 2, inserts encapsulates it in an envelope and sends it.
Layer 1 receives the mail, removes decapsulates the ciphertext from the envelope and delivers it to layer 2. The services provided in part a and part b are the opposite of each other.
Layer 2 takes the plaintext from layer 3, encrypts it, and delivers it to layer 1. Layer 2 takes the ciphertext from layer 1, decrypts it, and delivers it to layer 3. In 10 years, the number of hosts becomes about six times 1.
This means the number of hosts connected to the Internet is more than three billion. The system transmits bytes for a byte message. The advantage of using large packets is less overhead. When using large packets, the number of packets to be sent for a huge file becomes small. Since we are adding three headers to each packet, we are sending fewer extra bytes than in the case in which the number of packets is large.
Report DMCA. Home current Explore. Words: 1, Pages: 5. To make the communication bidirectional, each layer needs to be able to provide two opposite tasks, one in each direction. The router is involved in: a. The identical objects are the two messages: one sent and one received. At the application layer, the unit of data is a message.
At the network layer, the unit of data is a datagram. At the data-link layer, the unit of data is a frame. A frame is a link-layer data unit. It encapsulates a data unit coming from the network layer. In this case, the data unit is a datagram. A user datagram is a transport-layer data unit. It decapsulates a data unit going to the application layer.
In this case, the data unit is a message. The data unit should belong to layer 4. In this case, it is a user datagram. The transport-layer packet needs to include two port numbers: source and destination port numbers.
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