uqe dcn paper with solution

7/30/2019 Uqe Dcn Paper With Solution

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SAJID SIDDIQUE MEWATI (MSCIT-S11-M13)

DCN (IMPORTANT QUESTION) 40 MARKS

Short question (4/5) 3*4=121. Define Analog signal & digital signal?

Data and Signals

Data must be transformed to electromagnetic signals

Data are entities that convey meaning

Analog & Digital data

Analog Data refers to information that is continuous

Digital Data refers to information that has discrete states

Examples:

Analog Clock - gives information in continuous form.

Digital clock - will change suddenly from 08:05 to 8:06

Continuous or Analog signal

Various in a smooth way over time. e.g., speech

Infinity many levels of intensity over a period of time

Analog signals can have an infinite number of values in a range

Discrete or Digital signal

Maintains a constant level then changes to another constant level. e.g., binary 1s and 0s.

Digital signals can have only a limited number of values.

2. Why cables are twisted in unshielded twisted pair? Explain?Twisted-pair cable is a type of cabling that is used for telephone communications and most modern

Ethernet networks. A pair of wires forms a circuit that can transmit data. The pairs are twisted to


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provide protection against crosstalk, the noise generated by adjacent pairs. When electrical current

flows through a wire, it creates a small, circular magnetic field around the wire. When two wires in an

electrical circuit are placed close together, their magnetic fields are the exact opposite of each other.

Thus, the two magnetic fields cancel each other out. They also cancel out any outside magnetic fields.

Twisting the wires can enhance this cancellation effect. Using cancellation together with twisting the

wires, cable designers can effectively provide self-shielding for wire pairs within the network media.

3. Define TCP UDP & DNS?TCP(Transmission control protocol) UDP(User Datagram Protocol)

Reliability: TCP is connection-oriented protocol. When

a file or message send it will get delivered unless

connections fails. If connection lost, the server will

request the lost part. There is no corruption while

transferring a message.

Reliability: UDP is connectionless protocol. When

you a send a data or message, you don't know if

it'll get there, it could get lost on the way. There

may be corruption while transferring a message.

Ordered: If you send two messages along a

connection, one after the other, you know the first

message will get there first. You don't have to worry

about data arriving in the wrong order.

Ordered: If you send two messages out, you don't

know what order they'll arrive in i.e. no ordered

Heavyweight: - when the low level parts of the TCP

"stream" arrive in the wrong order, resend requests

have to be sent, and all the out of sequence parts

have to be put back together, so requires a bit of

work to piece together.

Lightweight: No ordering of messages, no

tracking connections, etc. It's just fire and forget!

This means it's a lot quicker, and the network

card / OS have to do very little work to translate

the data back from the packets.Streaming: Data is read as a "stream," with nothing

distinguishing where one packet ends and another

begins. There may be multiple packets per read call.

Datagrams: Packets are sent individually and are

guaranteed to be whole if they arrive. One packet

per one read call.

Examples: World Wide Web (Apache TCP port 80), e-

mail (SMTP TCP port 25 Postfix MTA), File Transfer

Protocol (FTP port 21) and Secure Shell (OpenSSH

port 22) etc.

Examples: Domain Name System (DNS UDP port

53), streaming media applications such as IPTV or

movies, Voice over IP (VoIP), Trivial File Transfer

Protocol (TFTP) and online multiplayer games etc

Domain Name System (or Service or Server), an Internet service that translates domain names into IP

addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is

really based on IP addresses. Every time you use a domain name, therefore, a DNS service must

translate the name into the corresponding IP address. For example, the domain name

www.example.com might translate to 198.105.232.4.


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The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular

domain name, it asks another one, and so on, until the correct IP address is returned.

4. Define IP (Internet Protocol) and layer and class of IP?Every machine on a network has a unique identifier. Just as you would address a letter to send in the

mail, computers use the unique identifier to send data to specific computers on a network. Most

networks today, including all computers on the Internet, use the TCP/IP protocol as the standard for

how to communicate on the network. In the TCP/IP protocol, the unique identifier for a computer is

called its IP address.

There are two standards for IP addresses: IP Version 4 (IPv4) and IP Version 6 (IPv6). All computers with

IP addresses have an IPv4 address, and many are starting to use the new IPv6 address system as well.

The most significant protocol at layer 3 (also called the network layer) is the Internet Protocol, or IP.

Class Leftmost bits Start address Finish address

A 0xxx 0.0.0.0 127.255.255.255

B 10xx 128.0.0.0 191.255.255.255

C 110x 192.0.0.0 223.255.255.255

D 1110 224.0.0.0 239.255.255.255

E 1111 240.0.0.0 255.255.255.255

5. Difference b/w bus topology and star topology?Bus topology

Bus networks (not to be confused with the system bus of a computer) use a common backbone to

connect all devices. A single cable, the backbone functions as a shared communication medium that

devices attach or tap into with an interface connector. A device wanting to communicate with another

device on the network sends a broadcast message onto the wire that all other devices see, but only the

intended recipient actually accepts and processes the message.

Star topology

Many home networks use the star topology. A star network features a central connection point called a

"hub node" that may be a network hub, switch or router. Devices typically connect to the hub with

Unshielded Twisted Pair (UTP) Ethernet.

Summary


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Compared to the bus topology, a star network generally requires more cable, but a failure in any star

network cable will only take down one computer's network access and not the entire LAN. (If the hub

fails, however, the entire network also fails).

6. What is the difference between datagram and circuit switching?

datagram circuit switching

1. each packet is on its own and may follow

its own path

2. Each packet treated independently

3. Packets can take any practical route

4. Packets may arrive out of order

5. Packets may go missing

6. Up to receiver to re-order packets and

recover from missing packets

1. dedicated path

2. Reserved Resources

3. The entire information is to be transmitted

at a constant data rate

4. Example telephone

5. The connection is dedicated until one

party or another terminates the

connection

6. Guaranteed the full bandwidth for the

duration of the call

7. What is mesh topology?

Mesh topology work on the concept of routes. In Mesh topology, message sent to thedestination can take any possible shortest, easiest route to reach its destination.

Internet employs the Mesh topology and the message finds its route for its destination. Router

works in find the routes for the messages and in reaching them to their destinations. The

topology in which every devices connects to every other device is called a full Mesh topology

unlike in the partial mesh in which every device is indirectly connected to the other devices.


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8. Define Spread Spectrum Modulation?

9. What is a Sample?In statistics, a sample is a subset of a population that is used to represent the entire group as awhole. When doing research, it is often impractical to survey every member of a particular

population because the sheer number of people is simply too large. In order to make inferences

about characteristics of a population, researchers can use arandom sample

10.What is difference between Half-Duplex and Full-Duplex transmission?Half-Duplex In half-duplex mode, each station can both transmit and receive, but not at the same time.

When one device is sending, the other can only receive, and vice versa. In a half-duplex transmission,

the entire capacity of a channel is taken over by whichever of the two devices is transmitting at the

time. Walkie-Talkies is an example of half-duplex.

Full-Duplex In full-duplex mode (also called duplex), both stations can transmit and receive

simultaneously. In full-duplex mode, signals going in one direction share the capacity of the link with

signals going in the other direction. This sharing can occur in two ways: Either the link must contain two

physically separate transmission paths, one for sending and the other for receiving; or the capacity of

the channel is divided between signals travelling in both directions. One common example of full-

duplex communication is the telephone network.
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LONG QUESTION (2/3) 2*14=24

1. What is packet switching? Write three application of packet switching? What is the differencebetween datagram and virtual switching?

Packet switching

Data sent out of sequence

Small chunks (packets) of data at a time

Packets passed from node to node between source and destination

Used for terminal to computer and computer to computer communications

Three application of packet switching

X.25

Frame relay

ATM

TCP/IP

datagram virtual switching

7. each packet is on its own and may follow

its own path

8. Each packet treated independently

9. Packets can take any practical route

10.Packets may arrive out of order

11.Packets may go missing

12.Up to receiver to re-order packets and

recover from missing packets

1. Create a logical path through the subnet

and all packets from one connection

follow this path.

2. Preplanned route established before any

packets sent

3. Call request and call accept packets

establish connection (handshake)

4. Each packet contains a virtual circuit

identifier instead of destination address

5. No routing decisions required for each

packet

6. Not a dedicated path


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2. Define TCP/IP layer in sequence and OSI model?TCP/IP has five layers, which are described below in table 2:

Name Description

Application Layer Provides a direct interface for

applications to communicate with

Transport Layer Provides a data transfer service that

appears to be a point to point link

Internet Layer Handles routing the data through one or

more networks

Network Access Layer Handles the logical interface between

points in the network

Physical Layer Handles the communication at the most

primitive level (medium, encoding, etc)

OSI Model

The Open System Interconnection (OSI) Model is used to describe networks and network application.

There are Seven Layers of OSI Model

Layers of the OSI Model

1. Physical (Bits)2. Data Link (Frames)3. Network (Packets)4. Transport (Segment)5. Session (Dialog units)6. Presentation (Raw Data)7. Application (Text, Numbers)

The easiest way to remember the different layers of OSI Model is to use the mnemonic

"All people seem to need Data Processing":

PleaseDo not Touch Steves Pet Alligator

Physical Layer


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The physical layer data consists of a stream of bits (sequence of 1s and 0s)

Physical interface between devices.

The physical layer defines the hardware items such as cables, cards,voltage levels, connectors,

media choice etc.

Choice of Wired / wireless medium.

Data is converted into signals

Includes voltage levels, connectors, media choice

Examples

V.24 V.35 EIA/TIA-232 EIA/TIA-449 FDDI

802.3 802.5 Ethernet RJ45 NRZ

NRZI

Data Link Layer

Data link layer is responsible for

Framing, divides the streams of bits into frames

Physical Addressing

Frames need to be transmitted to different systems on a network

Data Link layer adds a HEADER to Frame

Header defines the physical address of sender(Source address) and/or receiver address

(Destination address)

If frame is intended for a device outside the network, the receiver address is the address of the

device that connects one network to the other

Error Control, Data link layer adds reliability to physical layer by adding mechanisms

to detect and retransmit lost or damaged frames

Flow Control Data Link layer imposes Flow Control mechanisms to prevent

overwhelming the receiver

Examples

IEEE 802.2 IEEE 802.3 802.5 - Token Ring

HDLC Frame Relay FDDI

ATM PPP


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Network Layer

Transfers a data packet from node to node within the network.

One of the functions of Network layer is to define this route

Translating the logical network address and names into their physical address ( MAC address).

Responsible for Source-to-Destination delivery

Examples

DECnet X.25's

Packet Layer Protocol(PLP),

IBM'sPath Control Layer(PCL), Multiprotocol Label Switching (MPLS).

Internet Protocol(IP), The Internetwork Packet Exchange(IPX),

Datagram Delivery Protocol(DDP), VINES Internet Protocol(VIP).

Internetwork Packet Exchange Protocol (IPX): Path Control Layer (PCL):

Datagram Delivery Protocol (DDP): VINES Internet Protocol (VIP):

Packet Layer Protocol (PLP):

Transport Layer

This layer is responsible for

Service point addressing / Port addressing.

Connection Control, connection oriented / connectionless

Segmentation & Reassembling, It first divides the streams of data into chunks or packetsbefore transmission and then the receiving computer re-assembles the packets.

Error Control, It also guarantees error free data delivery without loss or duplications.

Flow Control on end systems

Examples
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ATP,AppleTalk Transaction Protocol CUDP,Cyclic UDP

DCCP,Datagram Congestion Control Protocol TP,Micro Transport Protocol

FCP,Fiber Channel Protocol NBF,NetBIOS Frames protocol

RDP,Reliable Datagram Protocol SCTP,Stream Control Transmission Protocol

SPX,Sequenced Packet Exchange SST,Structured Stream Transport

TCP,Transmission Control Protocol UDP,User Datagram Protocol

Session Layer

This layer is responsible for

Synchronization Points

Dialog Control, it allows the communication between 2 processes to take place in either half

duplex or full duplex

Establishing the process-to-process communication between the host in the network.

Establishing and ending the sessions across the network.

The interactive login is an example of services provided by this layer in which the connective are re-

connected in case of any interruption

Example

RPC SQL NetBIOS names Appletalk ASP

DECnet SCP
http://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/Cyclic_UDPhttp://en.wikipedia.org/wiki/Cyclic_UDPhttp://en.wikipedia.org/wiki/Cyclic_UDPhttp://en.wikipedia.org/wiki/Datagram_Congestion_Control_Protocolhttp://en.wikipedia.org/wiki/Datagram_Congestion_Control_Protocolhttp://en.wikipedia.org/wiki/Datagram_Congestion_Control_Protocolhttp://en.wikipedia.org/wiki/Micro_Transport_Protocolhttp://en.wikipedia.org/wiki/Micro_Transport_Protocolhttp://en.wikipedia.org/wiki/Micro_Transport_Protocolhttp://en.wikipedia.org/wiki/Fibre_Channelhttp://en.wikipedia.org/wiki/Fibre_Channelhttp://en.wikipedia.org/wiki/Fibre_Channelhttp://en.wikipedia.org/wiki/NetBIOS_Frames_protocolhttp://en.wikipedia.org/wiki/NetBIOS_Frames_protocolhttp://en.wikipedia.org/wiki/NetBIOS_Frames_protocolhttp://en.wikipedia.org/wiki/Reliable_Datagram_Protocolhttp://en.wikipedia.org/wiki/Reliable_Datagram_Protocolhttp://en.wikipedia.org/wiki/Reliable_Datagram_Protocolhttp://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocolhttp://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocolhttp://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocolhttp://en.wikipedia.org/wiki/IPX/SPXhttp://en.wikipedia.org/wiki/IPX/SPXhttp://en.wikipedia.org/wiki/IPX/SPXhttp://en.wikipedia.org/wiki/Structured_Stream_Transporthttp://en.wikipedia.org/wiki/Structured_Stream_Transporthttp://en.wikipedia.org/wiki/Structured_Stream_Transporthttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/Structured_Stream_Transporthttp://en.wikipedia.org/wiki/IPX/SPXhttp://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocolhttp://en.wikipedia.org/wiki/Reliable_Datagram_Protocolhttp://en.wikipedia.org/wiki/NetBIOS_Frames_protocolhttp://en.wikipedia.org/wiki/Fibre_Channelhttp://en.wikipedia.org/wiki/Micro_Transport_Protocolhttp://en.wikipedia.org/wiki/Datagram_Congestion_Control_Protocolhttp://en.wikipedia.org/wiki/Cyclic_UDPhttp://en.wikipedia.org/wiki/AppleTalk


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3. Define protocol? Name protocol of application layer? TCP AND UDP IN DETAIL ?

Protocol

A standard set of regulations and requirements that allow two electronic items to connect to and

exchange information with one another. Protocols regulate data transmission among devices as well

as within a network of linked devices through both error control and specifying which data

compression method to use. In particular, protocols decide: the method of error checking, how to

compact data (if required), how the transmitting device signals that it has concluded sending data,

and how the receiving device signals that it has completed receiving data.

Among the most common Internet protocols are FTP (File Transfer Protocol), HTTP (Hypertext

Transfer Protocol), TCP/IP (Transfer Control Protocol/Internet Protocol), and SMTP (Simple Mail

Transfer Protocol).

A uniform set of rules that enable two devices to connect and transmit data to one another.

Protocols determine how data are transmitted between computing devices and over networks. Theydefine issues such as error control and data compression methods. The protocol determines the

following: type of error checking to be used, data compression method (if any), how the sending

device will indicate that it has finished a message and how the receiving device will indicate that it

has received the message. Internet protocols include TCP/IP (Transfer Control Protocol/Internet

Protocol), HTTP (Hypertext Transfer Protocol), FTP (File Transfer Protocol), and SMTP (Simple Mail

Transfer Protocol).

Name protocol of application layer

FTP DNS SMTP gateways

Web browser Network File System (NFS) Telnet and Remote Login (rlogin)

X.400 FTAM Database software

Print Server Software SNMP

User Datagram Protocol

UDP packets, called user datagram, have a fixed-size header of 8 bytes. Figure shows the format of a

user datagram.

The fields are as follows:


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1. Source port number. This is the port number used by the process running on the source host. It

is 16 bits long, which means that the port number can range from 0 to 65,535. If the source host

is the client (a client sending a request), the port number, in most cases, is an ephemeral port

number requested by the process and chosen by the UDP software running on the source host.

If the source host is the server (a server sending a response), the port number, in most cases, is

a well-known port number.

2. Destination port number. This is the port number used by the process running on the

destination host. It is also 16 bits long. If the destination host is the server (a client sending a

request), the port number, in most cases, is a well-known port number. If the destination host is

the client (a server sending a response), the port number, in most cases, is an ephemeral port

number. In this case, the server copies the ephemeral port number it has received in the request

packet.

3. Length. This is a 16-bit field that defines the total length of the user datagram, header plus data.

The 16 bits can define a total length of 0 to 65,535 bytes. However, the total length needs to be

much less because a UDP user datagram is stored in an IP datagram with a total length of 65,535

bytes.

The length field in a UDP user datagram is actually not necessary. A user datagram is encapsulated in an

IP datagram. There is a field in the IP datagram that defines the total length. There is another field in the

IP datagram that defines the length of the header. So if we subtract the value of the second field from

the first, we can deduce the length of a UDP datagram that is encapsulated in an IP datagram.

UDP length = IP length - IP header's length

However, the designers of the UDP protocol felt that it was more efficient for the destination UDP to

calculate the length of the data from the information provided in the UDP user datagram rather than ask

the IP software to supply this information.


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We should remember that when the IP software delivers the UDP user datagram to the UDP layer, it has

already dropped the IP header.

4. Checksum. This field is used to detect errors over the entire user datagram (header plus data).

TCP Header Format

The format of a segment is shown in Figure.

The segment consists of a 20- to 60-byte header, followed by data from the application program. The

header is 20 bytes if there are no options and up to 60 bytes if it contains options.

Source port address. This is a 16-bit field that defines the port number of the application program in

the host that is sending the segment. This serves the same purpose as the source port address in the

UDP header.

Destination port address. This is a 16-bit field that defines the port number of the applicationprogram in the host that is receiving the segment. This serves the same purpose as the destination

port address in the UDP header.

Sequence number. This 32-bit field defines the number assigned to the first byte of data contained

in this segment. As we said before, TCP is a stream transport protocol. To ensure connectivity, each

byte to be transmitted is numbered. The sequence number tells the destination which byte in this


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sequence comprises the first byte in the segment. During connection establishment, each party uses

a random number generator to create an initial sequence number (ISN), which is usually different in

each direction.

Acknowledgment number. This 32-bit field defines the byte number that the receiver of the

segment is expecting to receive from the other party. If the receiver of the segment has successfully

received byte number x from the other party, it defines x + I as the acknowledgment number.

Acknowledgment and data can be piggybacked together.

Header length. This 4-bit field indicates the number of 4-byte words in the TCP header. The length of

the header can be between 20 and 60 bytes. Therefore, the value of this field can be between 5 (5 x

4 =20) and 15 (15 x 4 =60).

Reserved. This is a 6-bit field reserved for future use.

Control. This field defines 6 different control bits or flags as shown in Figure. One or more of these

bits can be set at a time.

These bits enable flow control, connection establishment and termination, connection abortion, and

the mode of data transfer in TCP. A brief description of each bit is shown in

Flag Description

URG The value of the urgent pointer field is valid.

ACK The value of the acknowledgment field is valid.

PSH Push the data.

RST Reset the connection.

SYN Synchronize sequence numbers during connection.

FIN Terminate the connection.

Window size. This field defines the size of the window, in bytes, that the other party must maintain.Note that the length of this field is 16 bits, which means that the maximum size of the window is

65,535 bytes. This value is normally referred to as the receiving window and is determined by the

receiver. The sender must obey the dictation of the receiver in this case.

Checksum. This 16-bit field contains the checksum. The calculation of the checksum for TCP follows

the same procedure as the one described for UDP. However, the inclusion of the checksum in the


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UDP datagram is optional, whereas the inclusion of the checksum for TCP is mandatory. The same

pseudo-header, serving the same purpose, is added to the segment. For the TCP pseudo-header, the

value for the protocol field is 6.

Urgent pointer. This l6-bit field, which is valid, only if the urgent flag is set, is used when the

segment contains urgent data. It defines the number that must be added to the sequence number

to obtain the number of the last urgent byte in the data section of the segment.

Options. There can be up to 40 bytes of optional information in the TCP header.

5. What is FDM, TDM and QAM with example?Time Division Multiplexing

Time Division Multiplexing works by the multiplexor collecting and storing the incoming transmissions

from all of the slow lines connected to it and allocating a time slice on the fast link to each in turn. The

messages are sent down the high speed link one after the other. Each transmission when received can

be separated according to the time slice allocated.

Theoretically, the available speed of the fast link should at least be equal to the total of all of the slow

speeds coming into the multiplexor so that its maximum capacity is not exceeded.

Two ways of implementing TDM are:

Synchronous TDM

Asynchronous TDM

Frequency Division Multiplexing
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Frequency Division Multiplexing (FDM) works by transmitting all of the signals along the same high

speed link simultaneously with each signal set at a different frequency. For FDM to work properly

frequency overlap must be avoided. Therefore, the link must have sufficient bandwidth to be able to

carry the wide range of frequencies required. The demultiplexor at the receiving end works by dividing

the signals by tuning into the appropriate frequency.

FDM operates in a similar way to radio broadcasting where a number of different stations will broadcast

simultaneously but on different frequencies. Listeners can then "tune" their radio so that it captures the

frequency or station they want.

FDM gives a total bandwidth greater than the combined bandwidth of the signals to be transmitted. In

order to prevent signal overlap there are strips of frequency that separate the signals. These are called

guard bands.

Wave Division Multiplexing

Wave or Wavelength Division Multiplexing (WDM) is used with fibre optic cables. WDM is a technology

that closely resembles frequency division multiplexing, but is specifically used to combine lots of OpticalCarrier signals into a single optical fibre.

The WDM technique relies on a laser that is designed to emit single colours of light. Each of the signals

that is to be transmitted is then attached to a laser that will emit a different coloured light beam. All

these individual light beams are then sent at the same time. At the receiving end, a device splits the

combined colours back into the original individual colours again.

QAM (quadrature amplitude modulation) is a method of combining two amplitude-modulated (AM)

signals into a single channel, thereby doubling the effective bandwidth. QAM is used with pulse

amplitude modulation (PAM) in digital systems, especially inwirelessapplications.

In a QAM signal, there are two carriers, each having the same frequency but differing in phase by 90

degrees (one quarter of a cycle, from which the term quadrature arises). One signal is called the I signal,

and the other is called the Q signal. Mathematically, one of the signals can be represented by a sine

wave, and the other by a cosine wave. The two modulated carriers are combined at the source for

transmission. At the destination, the carriers are separated, the data is extracted from each, and then

the data is combined into the original modulating information.
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uqe dcn paper with solution

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