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A low-pass channel has a bandwidth starting from zero; a band-pass channel has a bandwidth that does not start from zero? Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. See our User Agreement and Privacy Policy. See our Privacy Policy and User Agreement for details. Published on Sep 1, Solution manual for data communications and networking by behrouz forouzan 5th edition [complete].

In a controlled access method, end-to-end addressing is needed during the setup and teardown phase to create a connection for the whole data transfer phase. The data link layer needs to pack bits into frames. In a circuit-switched network, either a central authority in polling or other stations in reservation and 5tn passing control the access.

Labels: Engineering Books. In a virtual-circuit network, the VCIs are local. Nandkumar Khachane. QAM changes both the amplitude and the phase of the carrier. Introduction: 4 L B. So the bandwidth of both signals are the same. Flag for inappropriate content. It receives data from the Internet and passes them to the combiner, which sends them to the subscriber.

We except to get access to the site we are searching. Your email address will not be published. Computer Networks Forouzan Post a Comment. Home Contact. Monday, 19 June Engineering Books B. The book name is data communication and networking forouzan. This book presents highly technical subjects with more than figures from level 0 to level upper, without relying on complex formulations.

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. 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. 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. Algorithm We assume that a frame is made of an 8-bit flag , variable-length data possibly bit-stuffed , and an 8-bit ending flag ; we ignore header and trailer. Note that when the algorithm exits from the loop, there are six bits of the ending flag in the buffer, which need to be removed after the loop.

A five-bit sequence number can create sequence numbers from 0 to The sequence number in the Nth packet is N mod This means that the th packet has the sequence number mod 32 or 5.

See Algorithm Note that we have assumed that both events request and arrival have the same priority. Note that in this algorithm, we assume that the arrival of a frame by a site also means the acknowledgment of the previous frame sent by the same site. This is a very simple implementation in which we assume that both sites always have data to send. Event B: Receiver Site: Frame 1 received. Since there are no lost or damaged frames and the round trip time is less than the time-out, each frame is sent only once.

Here, we have a special situation. Although no frame is damaged or lost, the sender sends each frame twice. The reason is that the the acknowledgement for each frame reaches the sender after its timer expires. The sender thinks that the frame is lost. In this case, only the first frame is resent; the acknowledgment for other frames arrived on time. We need to send frames. We ignore the overhead due to the header and trailer. In the worst case, we send the a full window of size 7 and then wait for the We ignore the overhead due to the header and trailer.

In the worst case, we send the a full window of size 4 and then wait for the We ignore the overhead due to the header and trailer. The three categories of multiple access protocols discussed in this chapter are ran- dom access, controlled access, and channelization. In random access methods, no station is superior to another station and none is assigned the control over another.

Each station can transmit when it desires on the condition that it follows the predefined procedure. In controlled access methods, the stations consult one another to find which sta- tion has the right to send. A station cannot send unless it has been authorized by other stations. We discuss three popular controlled-access methods: reservation, polling, and token passing. Channelization is a multiple-access method in which the available bandwidth of a link is shared in time, frequency, or through code, between different stations.

In random access methods, there is no access control as there is in controlled access methods and there is no predefined channels as in channelization. Each station can transmit when it desires. This liberty may create collision. In a random access method, there is no control; access is based on contention. In a controlled access method, either a central authority in polling or other stations in reservation and token passing control the access.

Random access methods have less administration overhead. On the other hand, controlled access method are collision free. In a random access method, the whole available bandwidth belongs to the station that wins the contention; the other stations needs to wait. In a channelization method, the available bandwidth is divided between the stations. If a station does not have data to send, the allocated channel remains idle. In a controlled access method, the whole available bandwidth belongs to the sta- tion that is granted permission either by a central authority or by other stations.

If a station does not have data to send the allocated channel remains idle. We do not need a multiple access method in this case. The local loop provides a dedicated point-to-point connection to the telephone office.

We do need a multiple access, because a channel in the CATV band is normally shared between several neighboring customers. The cable company uses the ran- dom access method to share the bandwidth between neighbors. If we let ns to be the number of stations and nfs to be the number of frames a station can send per sec- ond. This means that either the data rate must be very high or the frames must be very small. If we let ns to be the number of stations and nfs to be the number of frames a station can send per second.

We can first calculate Tfr and G, and then the throughput. Let us find the relationship between the minimum frame size and the data rate. In Example Let us find the relationship between the collision domain maximum length of the network and the data rate. When the data rate is increased, the distance or maximum length of network or col- lision domain is decreased proportionally.

We calculate the maximum distance based on the above proportionality relationship. The reason is that with the Mbps, the minimum number of bits requirement is feasible only when the maxi- mum distance between stations is less than or equal to meters as we will see in Chapter See Figure The reason is that we need to send 16 extra polls. The preamble is a bit field that provides an alert and timing pulse.

It is added to the frame at the physical layer and is not formally part of the frame. SFD is a one- byte field that serves as a flag. An NIC provides an Ethernet station with a 6-byte physical address. Most of the physical and data-link layer duties are done by the NIC. A multicast address identifies a group of stations; a broadcast address identifies all stations on the network. A unicast address identifies one of the addresses in a group. A bridge can raise the bandwidth and separate collision domains.

A layer-2 switch is an N-port bridge with additional sophistication that allows faster handling of packets. In a full-duplex Ethernet, each station can send data without the need to sense the line. We interpret each four-bit pattern as a hexadecimal digit. We then group the hexa- decimal digits with a colon between the pairs: 5AAA:0F The bytes are sent from left to right.

However, the bits in each byte are sent from the least significant rightmost to the most significant leftmost. We have shown the bits with spaces between bytes for readability, but we should remember that that bits are sent without gaps. The arrow shows the direction of movement. The first byte in binary is The least significant bit is 1.

This means that the pattern defines a multicast address. A multicast address can be a destination address, but not a source address. Therefore, the receiver knows that there is an error, and discards the packet. The minimum data size in the Standard Ethernet is 46 bytes. The maximum data size in the Standard Ethernet is bytes.

The data of bytes, therefore, must be split between two frames. The standard dictates that the first frame must carry the maximum possible number of bytes ; the second frame then needs to carry only 10 bytes of data it requires padding. The follow- ing shows the breakdown: Data size for the first frame: bytes Data size for the second frame: 46 bytes with padding The smallest Ethernet frame is 64 bytes and carries 46 bytes of data and possible padding.

The largest Ethernet frame is bytes and carries bytes of data. The smallest frame is 64 bytes or bits. A station with no-transition mobility is either stationary or moving only inside a BSS. The orthogonal frequency-division multiplexing OFDM method for signal gen- eration in a 5-GHz ISM band is similar to frequency division multiplexing FDM , with one major difference: All the subbands are used by one source at a given time.

Sources contend with one another at the data link layer for access. Network Allocation Vector NAV forces other stations to defer sending their data if one station acquires access. In other words, it provides the collision avoidance aspect. When a station sends an RTS frame, it includes the duration of time that it needs to occupy the channel. The stations that are affected by this transmission create a timer called a NAV. A Bluetooth network is called a piconet. A scatternet is two or more piconets.

A Bluetooth primary and secondary can be connected by a synchronous connec- tion-oriented SCO link or an asynchronous connectionless ACL link. An ACL link is used when data integrity is more important than avoiding latency. The primary sends on the even-numbered slots; the secondary sends on the odd- numbered slots. If there is a collision, it will be detected, destroyed, and the frame will be resent. See Table Table An amplifier amplifies the signal, as well as noise that may come with the signal, whereas a repeater regenerates the signal, bit for bit, at the original strength.

Bridges have access to station physical addresses and can forward a packet to the appropriate segment of the network. In this way, they filter traffic and help control congestion. If a bridge is added or deleted from the system, reconfigura- tion of the stations is unnecessary.

A signal can only travel so far before it becomes corrupted. A repeater regenerates the original signal; the signal can continue to travel and the LAN length is thus extended.

A hub is a multiport repeater. A forwarding port forwards a frame that it receives; a blocking port does not. In a bus backbone, the topology of the backbone is a bus; in a star backbone, the topology is a star.

A VLAN saves time and money because reconfiguration is done through software. Physical reconfiguration is not necessary. Members of a VLAN can send broadcast messages with the assurance that users in other groups will not receive these messages. A VLAN creates virtual workgroups.

Each workgroup member can send broadcast messages to others in the workgroup. This eliminates the need for multicasting and all the overhead messages associated with it. Stations can be grouped by port number, MAC address, IP address, or by a com- bination of these characteristics. We have sorted the table based on the physical address to make the searching faster.

We made bridge B1 the root. Although any router is also a bridge, replacing bridges with routers has the follow- ing consequences: a. Routers are more expensive than bridges. Routers operate at the first three-layers; bridges operates at the first two layers. Routers are not designed to provide direct filtering the way the bridges do. A router needs to search a routing table which is normally longer and more time consuming than a filtering table. A router needs to decapsulate and encapsulate the frame and change physical addresses in the frame because the physical addresses in the arriving frame define the previous node and the current router; they must be changed to the physical addresses of the current router and the next hop.

A bridge does not change the physical addresses. Changing addresses, and other fields, in the frame means much unnecessary overhead. A filtering table is based on physical addresses; a routing table is based on the logical addresses. We have shown the network, the graph, the spanning tree, and the blocking ports. Network b. Spanning tree d. Blocking ports A router has more overhead than a bridge. A router process the packet at three layers; a bridge processes a frame at only two layers.

A router needs to search a routing table for finding the output port based on the best route to the final destina- tion; A bridge needs only to consult a filtering table based on the location of sta- tions in a local network.

A routing table is normally longer than a filtering table; searching a routing table needs more time than searching a filtering table. A router changes the physical addresses; a bridge does not. A bridge has more overhead than a repeater.

A bridge processes the packet at two layers; a repeater processes a frame at only one layer. A bridge needs to search a table and find the forwarding port as well as to regenerate the signal; a repeater only regenerates the signal. In other words, a bridge is also a repeater and more ; a repeater is not a bridge. A gateway has more overhead than a router. A gateway processes the packet at five layers; a router processes a packet at only three layers. A gateway needs to worry about the format of the packet at the transport and application layers; a router does not.

In other words, a gateway is also a router but more ; a router is not a gateway. A gateway may need to change the port addresses and application addresses if the gateway connects two different systems together; a router does not change these addresses. A mobile switching center coordinates communications between a base station and a telephone central office.

A mobile switching center connects cells, records call information, and is respon- sible for billing. A high reuse factor is better because the cells that use the same set of frequencies are farther apart separated by more cells.

In a hard handoff, a mobile station communicates with only one base station. In a soft handoff, a mobile station communicates with two base stations at the same time. GSM is a European standard that provides a common second-generation technol- ogy for all of Europe. CDMA encodes each traffic channel using one of the rows in the Walsh table. The three orbit types are equatorial, inclined, and polar.

A GEO satellite has an equatorial orbit since the satellite needs to remain fixed at a certain spot above the earth. A footprint is the area on earth at which the satellite aims its signal.

A satellite orbiting in a Van Allen belt would be destroyed by the charged parti- cles. Therefore, satellites need to orbit either above or below these belts. Transmission from the earth to the satellite is called the uplink. Transmission from the satellite to the earth is called the downlink. GPS is a satellite system that provides land and sea navigation data for vehicles and ships.

The system is also used for clock synchronization. The main difference between Iridium and Globalstar is the relaying mechanism. Iridium requires relaying between satellites. Globalstar requires relaying between satellites and earth stations. In AMPS, there are two separate bands for each direction in communication. In each band, we have analog channels. Out of this number, 21 channels are reserved for control. Since duplexing is pro- vided at the digital level, this means that analog channels are available in each cell assuming no control channels.

In GSM, separate bands are assigned for each direction in communication. This means analog channels are available in each cell assuming no control chan- nels. Each analog channel carries 1 multiframe. Each multiframe carries 26 frames 2 frames are for control. Each frame allows 8 calls. In IS, separate bands are assigned for each direction in communication.

This means 20 analog channels are available in each cell assuming no control chan- nels. Each analog channel carries 64 digital traffic channel 9 channels are for control.

In Exercise 19, we showed that the maximum simultaneous calls per cell for GSM is In Exercise 20, we showed that the maximum simultaneous calls per cell for IS is D-AMPS sends 25 frames per seconds in each channel. Each frame carries 6 slots. GPS satellites are orbiting at 18, km above the earth surface. Iridium satellites are orbiting at km above the earth surface. Globalstar satellites are orbiting at km above the earth surface.

The standards are nearly identical. An STS multiplexer multiplexes signals from multiple electrical sources and creates the corresponding optical signal. An STS demultiplexer demultiplexes an optical signal into corresponding electric signals.

OCs are the corresponding optical signals. Pointers are used to show the offset of the SPE in the frame or for justification. A single clock handles the timing of transmission and equipment across the entire network.