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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
http://www.hill2dot0.com/wiki/index.php?title=X.25http://www.hill2dot0.com/wiki/index.php?title=X.25http://www.hill2dot0.com/wiki/index.php?title=Packet_Layer_Protocol&action=edithttp://www.hill2dot0.com/wiki/index.php?title=Packet_Layer_Protocol&action=edithttp://www.hill2dot0.com/wiki/index.php?title=Path_Control_Layer&action=edithttp://www.hill2dot0.com/wiki/index.php?title=Path_Control_Layer&action=edithttp://www.hill2dot0.com/wiki/index.php?title=Path_Control_Layer&action=edithttp://www.hill2dot0.com/wiki/index.php?title=Internet_Protocolhttp://www.hill2dot0.com/wiki/index.php?title=Internet_Protocolhttp://www.hill2dot0.com/wiki/index.php?title=The_Internetwork_Packet_Exchange&action=edithttp://www.hill2dot0.com/wiki/index.php?title=The_Internetwork_Packet_Exchange&action=edithttp://www.hill2dot0.com/wiki/index.php?title=Datagram_Delivery_Protocol&action=edithttp://www.hill2dot0.com/wiki/index.php?title=Datagram_Delivery_Protocol&action=edithttp://www.hill2dot0.com/wiki/index.php?title=VINES_Internet_Protocol&action=edithttp://www.hill2dot0.com/wiki/index.php?title=VINES_Internet_Protocol&action=edithttp://www.hill2dot0.com/wiki/index.php?title=IPX&action=edithttp://www.hill2dot0.com/wiki/index.php?title=IPX&action=edithttp://www.hill2dot0.com/wiki/index.php?title=IPX&action=edithttp://www.hill2dot0.com/wiki/index.php?title=PCL&action=edithttp://www.hill2dot0.com/wiki/index.php?title=PCL&action=edithttp://www.hill2dot0.com/wiki/index.php?title=PCL&action=edithttp://www.hill2dot0.com/wiki/index.php?title=DDP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=DDP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=DDP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=VIP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=VIP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=VIP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=PLP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=PLP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=PLP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=PLP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=VIP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=DDP&action=edithttp://www.hill2dot0.com/wiki/index.php?title=PCL&action=edithttp://www.hill2dot0.com/wiki/index.php?title=IPX&action=edithttp://www.hill2dot0.com/wiki/index.php?title=VINES_Internet_Protocol&action=edithttp://www.hill2dot0.com/wiki/index.php?title=Datagram_Delivery_Protocol&action=edithttp://www.hill2dot0.com/wiki/index.php?title=The_Internetwork_Packet_Exchange&action=edithttp://www.hill2dot0.com/wiki/index.php?title=Internet_Protocolhttp://www.hill2dot0.com/wiki/index.php?title=Path_Control_Layer&action=edithttp://www.hill2dot0.com/wiki/index.php?title=Packet_Layer_Protocol&action=edithttp://www.hill2dot0.com/wiki/index.php?title=X.25 -
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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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SAJID SIDDIQUE MEWATI (MSCIT-S11-M13)
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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