Wireless transmission uses electromagnetic signals broadcast through the air without conductors, dividing the electromagnetic spectrum from 3kHz to 900 THz into radio waves, microwaves, and infrared for communication; radio waves can travel long distances making them suitable for broadcasting, while microwaves and infrared have shorter ranges due to line of sight and inability to penetrate walls respectively.

1. Unguided Media –wireless
• It transports electromagnetic signal without using a conductor
• Signals broadcast through air and the electromagnetic spectrum,
ranging from 3kHz to 900 THz is used for wireless communication
• We can divide wireless transmission in three groups
Radio wave
Microwave
Infrared
1.1

2.  Radio wave:-
 Electromagnetic wave ranging from 3KHz to 1 GHz
 They are Omni directional means when antenna transmits radio
wave they propagate in all directions
 So that sending and receiving antenna do not have to be aligned
 Radio waves of low and medium frequency can penetrate walls
 They are used for radio and television, cordless phones system
 They can travel long distance so they are good for long distance
broadcasting
1.2

3. • Microwave:-
• Electromagnetic wave having frequency between 1GHz to 300GHz
• They are unidirectional so sending and receiving antenna need to
be aligned
• Microwave propagation is line of sight so towers with antenna need
to be in direct sight of eachother.towers which are far apart need to
be tall
• They are used in satellite networks, wireless LAN,
• The parabolic dish and horn antenna are used for transmission and
reception of microwave
1.3

4. • Infrared:-
• These signals having frequencies ranging from 300GHz to 400THz
can be used for short distance communication
• They cannot penetrate walls
• So when we use Infrared remote control, we do not interfere with
the help of remote by our neighbors
• The recent data rates are 4 Mbps
• Application:-
• They are used with communication between keyboards,PCs and
printers
• Some manufacturers provide IrDA port that allows wireless
keyboard to communicate with a PC
1.4

5. Specification of cable
• There are several different specifications used to classify cable.
• One of the oldest is the AWG (American Wire Gauge) rating.
• This rating measures the thickness or gauge of the wire with the size
being inverse to the rating.
• For example, a 22 AWG cable is thicker than a 24 AWG cable.
• 22 AWG wire is typically used in telephone wire and UTP

6. Cable categories
• UTP cabling is not recommended for distances greater than 100 meters without the
use of a repeater.
• Category one is used for traditional phone lines. It carries only voice
communication.
• Cat2 is capable of carrying data but only at rates up to 4 Mb/second. Cat2 cables
consist of four twisted pairs.
• Cat3 contains four twisted pairs at a rate of three twists per foot. Data transmission
speeds are up to 10Mb/second.
• Cat4 cables consist of four twisted pairs of copper wire. Cat4 is capable of speeds
up to 16Mb/second.
• Cat5 contains four twisted copper pairs and maxes out at 100Mb/second.
• Cat5e was developed to handle speeds up to 1000Mb/second (1Gb/second).

7. Cable characteristics
• characteristics of UTP (unshielded twisted pair)
• Transmission rate of 10-100 Mbps
• Most susceptible to electrical interference or ‘crosstalk’ but
shielding may lessen the impact)
Less expensive than coax or fiber-optic.
• Very flexible and easy to work with
• Wire type is 22-26AWG
• Uses an RJ-45 connector
• Ethernet designation is 10baseT
• Shielded twisted pair
• (STP) is similar to UTP except it contains a copper braid jacket to ‘shield’
the wires from electrical interference.
• It can support transmissions over greater distances than UTP.

8. • Cat5 UTP cable is a popular choice for network cable because it meets the
European standard for allowing data transfer speeds of 100Mbps.
• 100BaseT stands for:
• Data Transmission Rate of 100Mbps, i.e. 100
• Uses baseband transmission, i.e. Base
• The media is twisted pair, i.e. the T.

9. • Co-axial cable
• Thinnet cable (10Base2)
• Thicknet cable (10Base5)
• 10Base2 stands for:
• Data Transmission Rate of 10Mbps, i.e. 10
• Uses baseband transmission, i.e. Base
• Used in Ethernet networks it has a maximum cable length of 185 metres, i.e. the 2
for approximately 200 meters
• 10base5 stands for:
• Data Transmission Rate of 10Mbps, i.e. 10
• Uses baseband transmission, i.e. Base
• Used in Ethernet networks it has a maximum cable length of 500 metres, i.e. the 5
is for 500 meters

10. Characteristics of co-axial cable
• Transmission rate of about 10 Mbps
• Maximum cable length of 185 meters for Thinnet, 500 meters for
Thicknet
• Good resistance to electrical interference
• Less expensive than fiber-optics but more expensive than
twisted pair.
• Flexible and easy to work with (Thinnet)
• Wire type is 20 AWG for Thinnet (R-58) and 12 AWG for Thicknet.

11. Characteristics if Fiber optic cable
• Transmission rate of 100 Mbps
• Cable length of 2 kilometers or more
• Not affected by electrical interference
• Supports voice, video, and data
• Provides the most secure media
• Most expensive cable
• Not very flexible; difficult to work with

12. Advantages and Disadvantages
• UTP
• PRO: Most flexible; cheapest cable ,easy to install;
· CON: Shortest usable cable length; susceptible to electrical
interference; unsecured;
• Coaxial Cable
• · PRO: Flexible and easy to install; relatively
• good resistance to electronic interference; electronic support components are
relatively inexpensive
• · CON: Short cable length; more expensive than UTP; unsecured; hard
to change;
• Fiber-Optic
• · PRO: Fastest transmission rate; not susceptible to electrical
interference; secure;
• · CON: Most expensive; relatively difficult to work with

13. Criteria for Selection of cable
• Size - How many nodes (computers) and what are the total distances between
them?
• Cost - What is the budget and how much can be spent on cabling?
• Reliability - How dependent are your organization’s operations on the network?
• Speed - How many concurrent users are there be and how critical is response time?
• Security - How important is it to protect data from possible interception?
• Growth - What are the organization’s plans for growth?
• Administration - How will the network be administered?
• Electrical Interference - What is the physical environment in which the network
will operate?

14. Connecting LAN
• Two or more devices connected together for the purpose of sharing
resources or data can form a network
• To increase coverable distance a device is inserted which is
repeater or regenerator
• Then for traffic management a device called bridge is inserted
• Linking number of LANs, and to create internet, routers and
gateways are inserted
• These four devices interacts with protocol at different layers of OSI
model

15. Connecting LAN
• Repeaters act on electrical component of signal and active at
physical layer
• Bridge can affect flow control of single LAN, active at Data Link
Layer
• Routers provide links between two separate LAN,active at Network
layer
• Gateway provides translation services between incompatible LAN or
application and active in all layers

16. Connecting Devices

17. Network Components
• Repeaters or regenerator is electronic device operate on physical
layer
• Signals carry information within a network can travel a fixed
distance before attenuation
• So a repeater is installed on a link that receives a signal before it
becomes weak or corrupted and regenerate original bit pattern onto
link
• It allows us to extend length of network and it does not change any
function of network
• Repeater is not an amplifier: It regenerates the signal
• Whenever it receives a weakened or corrupted signal,It creates a
copy for that bit

18. Repeaters
 Here station A sends a frame to station B,all stations including (C
and D) receive it
 So repeater does not have intelligence to keep track of frame from
passing to right when it is meant for left side


19. Bridge

20. Bridge
 It operates in Physical and data link layer
 It divides large network in small segment or network
 It contains logic to relay frame to intended receiver
 It keeps the traffic for each segment separate, so it filter the traffic,
control congestion and provide security
 Bridges do not modify the content of packet therefore it can be
used between segments that use same protocol
 When a frame enters a bridge, It checks the address of
destination ,compares address with a table of all stations
 When it finds a match, It relays a packet to that segment

21. Routers

22. Routers
• It operates in physical,datalink and network layer
• They have access to network layer addresses and contain software
that enables them to determine which path is best for particular
transmission
• A packet sent from a station on a neighbouring network goes first to
jointheld router, which switches it to destination network
• If there is no router connected to sending and receiving device,the
sending router transfer packet across one of its network to next
router in direction of destination

23. Gateways
• It operates in all seven layers of OSI model
• It is a protocol converter
• A gateway can accept a packet formatted for one protocol
(Appletalk) and convert it to packet formatted for another
protocol (TCP/IP) before forwarding it
• It is a software installed within a router
• It understands a protocol used by each network, linked into the
router and able to translate from one to another

24. Gateways

25. Data communication

26. Addressing
• In computer networking addressing is classified into three
catagories
• Physial Addressing
• Logical Addressing/ Network Addressing
• Port Addressing
• Through logical address the system identify a network (source
to destination).
• After identifying the network physical address is used to
identify the host on that network.
• The port address is used to identify the particular application
running on the destination machine.

27. • Logical Address:
• An IP address of the system is called logical address.
• This address is the combination of Net ID and Host ID.
• This address is used by network layer to identify a particular network
(source to destination) among the networks.
• This address can be changed by changing the host position on the network.
So it is called logical address.
• Physical address:
• Each system having a NIC(Network Interface Card) through which two
systems physically connected with each other with cables.
• The address of the NIC is called Physical address or mac address.
• This is specified by the manficture company of the card. This address is
used by data link layer.

28. • Port Address:
• There are many application running on the computer.
• Each application run with a port no.(logically) on the computer. This port no.
for application is decided by the Karnal of the OS. This port no. is called port
address.
• Port numbers are most commonly used with TCP/IP connections..
• These port numbers allow different applications on the same computer to
share network resources simultaneously.
• How Port Numbers Work
• Port numbers are associated with network addresses. For example, in TCP/
IP networking, bothTCP and UDP utilize their own set of ports that work
together with IP addresses.
• In both TCP and UDP, port numbers start at 0 and go up to 65535.

29. • Network Addressing
• A network address serves as a unique identifier for a computer on a
network.
• When set up correctly, computers can determine the addresses of other
computers on the network and use these addresses to send messages to
each other.
• One of the best known form of network addressing is the
Internet Protocol (IP) address.
• IP addresses consist of four bytes (32 bits) that uniquely identify all
computers on the public Internet.
• Internet address define three fields: class, net id,host id

30. • One portion of address indicates network,(netid) and other
indicates host or router on network(host id)
• That means that to reach a host on internet we must first reach to
the network using first portion of the address then we must reach
host using host id

31. IP address classes

32. • Class A addresses, indicated by a 0 bit in the first bit of the address
• It has an 8 bit NETID and a 24 bit HOSTID.
• Class A addresses are intended for use in very large networks since
the 24 bit HOSTID can uniquely identify over 16 million hosts.
• Class B addresses, indicated by a 1 bit followed by a 0 bit in the
first two bits of the address,
• Have a 16 bit NETID and a 16 bit HOSTID. Subnetworks can
support up to 65,534 hosts and there are 16,382 possible network
addresses .

33. • class C addresses, indicated by two 1s followed by a 0 in the first
three bits of the address,
• Class C addresses have a 24 bit NETID and an 8 bit HOSTID,
permitting over two million possible network addresses. each
subnetwork can support up to 254 hosts
• Class D addresses begin with a digit between 224 and 239, and are
used for multicast applications
• Class E addresses begin with a number between 240 and 255 and
are used for experimental purposes.

34. • multicast is the delivery of a message or information to a group of
destination computers simultaneously in a single transmission
• unicast transmission is the sending of messages to a single network
destination identified by a unique address

35. Industry open standard
• Because parallel communication is not prevalent in
industrial network,this discussion focusing on serial
standards
• EIA(Electronic Industry Assoiation) has developed
several recommended standards(RS-xxx) to aid in ease
of connection
• The Electronics Industry Association (EIA) has produced
standards for RS485, RS422, RS232, and RS423 that
deal with data communications

36. RS-232
• Architecturally RS-232 is a bi-
directional point to point link
• RS-232 is a standard by which (serial port - PC side)
two serial devices communicate.
 Two independent channels
are established for two-way
(full-duplex)
communications.
 RS-232 can also carry
additional signals used for
flow control (RTS, CTS) and
modem control (DCD, DTR,
DSR, RI).

37. RS-232 settings
• One byte of async data has:
 Stop bits = 1 (or 2)
– Start Bit = 1 (always)  Parity = NONE (or EVEN or
– Data Bits = 8 (or 7) ODD)
+ 25
- 25

38. DB-25 connectors and its pin
DB-25M Function Abbreviation
Pin #1 Chassis/Frame Ground GND
Pin #2 Transmitted Data TD
Pin #3 Receive Data RD
Pin #4 Request To Send RTS
Pin #5 Clear To Send CTS
Pin #6 Data Set Ready DSR
Pin #7 Signal Ground GND
Pin #8 Data Carrier Detect DCD or CD
Pin #9 Transmit + (Current Loop) TD+
Pin #11 Transmit - (Current Loop) TD-
Pin #18 Receive + (Current Loop) RD+
Pin #20 Data Terminal Ready DTR
Pin #22 Ring Indicator RI
Pin #25 Receive - (Current Loop) RD-

39. DB-9 connectors and pins
DB-9M Function Abbreviation
Pin #1 Data Carrier Detect CD
Pin #2 Receive Data RD or RX or RXD
Pin #3 Transmitted Data TD or TX or TXD
Pin #4 Data Terminal Ready DTR
Pin #5 Signal Ground GND
Pin #6 Data Set Ready DSR
Pin #7 Request To Send RTS
Pin #8 Clear To Send CTS
Pin #9 Ring Indicator RI

40. RS-232 Signals
• Common 25 pin D-shell connector pinout used for
asynchronous data communications.
Pin Signal
1 PGND Protective
Ground
2 TXD Transmit Data
3 RXD Receive Data
4 RTS Ready To Send
5 CTS Clear To Send
6 DSR Data Set Ready
7 SG Signal Ground (serial port - PC side)
8 CD Carrier Detect
20 DTR Data Terminal
Ready
22 RI Ring Indicator

41. Handshaking
• DTE (Data Terminal
• Process of using signals Equipment)
to establish conditional – Terminal or Computer
communication
• DCE (Data
• Process Communications
– Transmitter activate RTS Equipment)
– Receiver senses CTS by – Modem or Printer
interrupt or Polling
– Receiver activate RTS
– Transmitter senses CTS
• Transmitter waits until
CTS input is activated
– Transmitter send Data

42. • RS-232 Signal Descriptions
• DTR: Data Terminal Ready--Used by a DTE to signal
that it is plugged in and available to begin
communication.
• DSR: Data Set Ready--Sister signal to DTR, it is used by
the DCE to indicate it is ready to begin communication.
• CTS: Clear to Send--Used by DCE to signal it is
available to send data, and used in response to a RTS
request for data.
• RTS: Request to Send--Used by a DTE to indicate that it
wants to send data.

43. • DCD: Data Carrier Detect--Used by a DCE to indicate to the DTE
that it has received a carrier signal from the modem and that real
data is being transmitted.
• RI: Ring Indicator--Used by DCE modem to tell the DTE that the
phone is ringing and that data will be forthcoming.
• TxD: Transmit Data--This wire is used for sending data.
• RxD: Receive Data--This line is used for receiving data.
• GND: Signal Ground--This pin is the same for DTE and DCE
devices, and it provides the return path for both data and hand-
shake signals.

44. Line drivers and receivers
• Line drivers and receivers are commonly used to
exchange data between two or more points (nodes) on a
network.
• Reliable data communications can be difficult in the
presence of induced noise, ground level differences,
impedance mismatches,
• EIA standards where previously marked with the prefix
"RS" to indicate recommended standard; however, the
standards are now generally indicated as "EIA"
standards to identify the standards organization.

45. • Simplex & Duplex
One of the most fundamental concepts of communications technology is the
difference between Simplex and Duplex.
• Simplex can be viewed as a communications "one-way street".
• Data only flows in one direction. That is to say, a device can be a receiver or
a transmitter exclusively. A simplex device is not a transceiver.
• A good example of simplex communications is an FM radio station and your
car radio.
• Information flows only in one direction where the radio station is the
transmitter and the receiver is your car radio.
• Simplex is not often used in computer communications because there is no
way to verify when or if data is received.
• However, simplex communications is a very efficient way to distributed vast
amounts of information to a large number of receivers.

46. • Half Duplex
• devices have the dubious honor of allowing both transmission and
receiving, but not at the same time.
• Essentially only one device can transmit at a time while all other
half duplex devices receive.
• Devices operate as transceivers, but not simultaneous transmit and
receive.
• RS485 operates in a half duplex manner.

47. • Duplex communications overcome the limits of Simplex
communications by allowing the devices to act as transceivers.
• Duplex communication data flow in both directions thereby allowing
verification and control of data reception/transmission.
• Exactly when data flows bi-directionally further defines Duplex
communications.
• Full Duplex devices can transmit and receive data at the same
time.
• RS232 is a fine example of Full Duplex communications. There are
separate transmit and receive signal lines that allow data to flow in
both directions simultaneously.
• RS422 devices also operate Full Duplex.

48. • RS-232 SERIAL COMMUNICATION
OVERVIEW
• Data is typically transmitted between two points either
asynchronously or synchronously.
• It is simple, inexpensive to implement, and though relatively slow, it
is more than adequate for most simple serial communication
devices such as keyboards and mice.
• RS-232 is a single-ended data transmission system, which means
that it uses a single wire for data transmission.
• (Since useful communication is generally two way, a two-wire
system is employed, one to transmit and one to receive.)

49. Unbalanced Serial Communications
• Signals are processed by determining whether they are positive or
negative when compared with a ground.
• Because signals traveling this single wire are vulnerable to
degradation,
• RS-232 systems are recommended for communication over short
distances 15m (up to 50 feet) and at relatively slow data rates (up to
20 kbps).

50. • Unbalanced Serial Communications
• Unbalanced connections use single connectors for each
signal and a common ground.
• The signal level is relative to the common GROUND.
• Cheap (fewer pins) but susceptible to 'noise' and hence is
almost always lower in speed
• RS-232, V.10 etc are all unbalanced serial connections.

51. • Unbalanced Line Drivers
For example, the transmitted data (TD) from a DTE device appears on pin 2
with respect to pin 7 (signal ground) on a DB-25 connector.
• This voltage will be negative if the line is idle and alternate between that
negative level and a positive level when data is sent with a magnitude of ±5
to ±15 volts.
• The RS-232 receiver typically operates within the voltage range of
+3 to +12 and -3 to -12 volts as shown in Figure 1.1.

52. • Balanced Line Drivers
• In a balanced differential system the voltage produced by the driver appears
across a pair of signal lines that transmit only one signal.
• A balanced line driver can also have an input signal called an "Enable" signal.
• This signal is to connect the driver to its output terminals, A and B. If the
"Enable" signal is OFF, one can consider the driver as disconnected from the
transmission line.
• An RS-485 driver must have the "Enable" control signal.
• An RS-422 driver may have this signal, but it is not always required.
• The disconnected or "disabled" condition of the line driver usually is referred to
as the "tristate" condition of the driver.
• The term "tristate" comes from the fact that there is a third output state of an
RS-485 driver, in addition to the output states of "1" and "0".
•

54. Industry open standard
• Because parallel communication is not prevalent in
industrial network,this discussion focusing on serial
standards
• EIA(Electronic Industry Assoiation) has developed
several recommended standards(RS-xxx) to help in ease
of connection
• The Electronics Industry Association (EIA) has produced
standards for RS485, RS422, RS232, and RS423 that
deal with data communications

55. • RS-232 SERIAL COMMUNICATION
OVERVIEW
• RS-232 is a standard by which two serial devices communicate.
• It is simple, inexpensive to implement, and though relatively slow, it
is more than adequate for most simple serial communication
devices such as keyboards and mice.
• RS-232 is a single-ended data transmission system, which means
that it uses a single wire for data transmission.
• RS-232 systems are recommended for communication over short
distances 15m (up to 50 feet) and at relatively slow data rates (up to
20 kbps).

56. RS-422
• An RS-232 based system allows only two devices to communicate.
• With RS-422 a master can use one communication line to connect
up to 10 slaves.
• It provides a mechanism by which serial data can be transmitted
over great distances (to 4,000 ft) and at very high speeds (to 10
Mbps).
• It is a balanced and differential system and It makes system
immune to noise and interference
• This is accomplished by splitting each signal across two separate
wires in opposite states -- one inverted; the other not inverted.

57. Balance system
• The difference in voltage between the two lines is compared by the
receiver to determine the logical state of the signal.
• It can have multiple receivers but one line driver per twisted pairs of
wires
• For full duplex communication two separate channels are used(four
wires)

58. RS-485
• It is a balance system It uses tri-state line driver
• RS-485 driver has always the “Enable” direction control signal.
• This signal is to connect the driver to its output terminals, A and B. If the "Enable"
signal is OFF, one can consider the driver as disconnected from the transmission
line.
• Differential system provides noise immunity, because much of the common
mode signal can be rejected by the receiver.
• The term "tristate" comes from the fact that there is a third output state of an
RS-485 driver, in addition to the output states of "1" and "0".

59. RS 485
• The standard specifies up to 32 drivers and 32 receivers can share a
network
• The third state-high impedence state allows inactive device to sit quietly on
network making multiple drops
• With high-impedance drivers / receivers this "limitation" can be extended to
hundreds (or even thousands) of nodes on a network.
• When the device is not working ,it goes to high impedence state and does
not interfere in transmission
• It provides transmission rates upto 100kbps at
4000ft(1219 m)

60. EIA-485 Half Duplex
• This system links multiple drivers and receivers on same single path
• So EIA-485 must have ENABLE pins which enable only one driver
to send data at a time
• It allows data transmission in both direction but not at same time
• It uses two wires for half duplex system

61. EIA-485 full Duplex
• It is known as four wire network connected in master/slave
configuration
• It allows communication in both direction at same time between
master and slave nodes

62. Manchester encoding
• None of ethernet(cable) virsion uses binary encoding with 0 volt for
0 bit and 5 volt for1 bit because it leads to ambiguities
• To solve it by 1 volt for 1 bit and -1 volt for 0 bit
• But there is problem of sampling occurs
• It causes transmitter and receiver to get out of synchronization
• So way is needed for receiver to determine start,end,middle without
any reference to external clock

63. Manchester encoding
0 1 0 0 1 1 0 0 0 1 1
• Always transition in middle of bit period:
0 = low-to-high transition
1 = high-to-low transition
• Transition at beginning of bit period making ease for receiver to
synchronize with sender
• used for 10Mbps ethernet over coax and twisted pair
• good clock recovery, good signal recovery
• inefficient use of bandwidth: 10Mbps ethernet uses a 20Mbps
signaling rate!

64. Differential Manchester
0 1 0 0 1 1 0 0 0 1 1
• 0 = transition at beginning of bit period (low-to-high or high-to-
low, depending on previous output level)
1 = no transition at beginning of bit period
• same properties as Manchester encoding, but better signal
detection and better signal recovery
• inefficient use of bandwidth: 2B signaling for a data rate B

65. protocol
• It is a set of rules that governs the communication system
• Segmentation (fragmentation) and re-assembly
• Each protocol has to deal with the limitations of the PDU (protocol data unit)
or packet size associated with the protocol below it.
• For example, the Internet protocol (IP) (layer 3) can only handle 65 536
bytes of data, hence the transmission control protocol (TCP) (layer 4) has to
segment the data received from layer 5 into pieces no bigger than that.
• IP (layer 3), on the other hand, has to be aware that Ethernet (layer 2)
cannot accept more than 1500 bytes of data at a time and has to fragment
the data accordingly.
• Obviously, the data stream fragmented by a protocol on
the transmitting side has to be re-assembled by its corresponding peer on
the receiving side

66. • Encapsulation:
• Each protocol has to handle the information received from the layer
above it
• For example, the information passed on to IP (layer 3) could contain
a TCP header (layer 4) plus an FTP header (layers 5, 6, 7) plus data
from an FTP client (e.g. Cute FTP).
• IP simply regards this as a package of information to be forwarded,
adds its own header with the necessary control information, and
passes it down to the next layer

67. protocol
• It is a set of rules that governs the communication system
• Segmentation (fragmentation) and re-assembly
• Each protocol has to deal with the limitations of the PDU (protocol
data unit) or packet size associated with the protocol below it. For
example, the Internet protocol (IP) (layer 3) can only handle 65 536
bytes of data, hence the transmission control protocol (TCP) (layer
4) has to segment the data received from layer 5 into pieces no
bigger than that.
• IP (layer 3), on the other hand, has to be aware that Ethernet
• (layer 2) cannot accept more than 1500 bytes of data at a time and
has to fragment the data accordingly. The term ‘fragmentation’ is
normally associated with layer 3, whereas the term ‘segmentation’ is
normally associated with layer 4.
• Obviously, the data stream fragmented by a protocol on
the transmitting side has to be re-assembled by its corresponding
peer on the receiving side

68. • Connection control:
• Some layer protocols such as TCP create logical
connections with their peers on the other side.
• For example, when browsing the Internet, TCP on the
client (user) side has to establish a connection with TCP
on the server side before a web site can be accessed.
• there are mechanisms for terminating the connection as
well.

69. • Ordered delivery:
• Large messages have to be cut into smaller fragments,
but on a packet switching network,
• the different fragments can theoretically travel via
different paths to their destination.
• This results in fragments arriving at their destination out
of sequence, which creates problems in rebuilding the
original message.
• protocols use different mechanisms, including sequence
numbers and fragment offsets.

70. • Flow control
• In simple protocols, this is accomplished by a lock-step mechanism
(i.e. each packet sent needs to be acknowledged before the next
one can be sent) or XON/XOFF
• mechanisms where the receiver sends an XOFF message to the
sender to pause transmission,
• then sends an XON message to resume transmission.
• More sophisticated protocols use ‘sliding windows’.

71. • Error control:-
• The sender needs some mechanism by which it can
confirm if the data received is the same as the data sent.
• This is accomplished by performing some form of
checksum on the data to be transmitted, including the
checksum in the header or in a trailer after the data.
• Types of checksum include CRC

72. • Addressing
• Protocols at various levels need to identify the physical
or logical recipient on the other side.
• Layer 4 protocols such as TCP and UDP use port
numbers.
• Layer 3 protocols use a protocol address (such as the
IP address for the Internet protocol) and
• Layer 2 protocols use a hardware (or ‘media’) address
such as a station number or MAC address.

73. • Routing:
• In an internetwork, i.e. a larger network consisting of two
or more smaller networks interconnected by routers,
• the routers have to communicate with each other in
order to know the best path to a given destination on the
network.
• This is achieved by routing protocols (RIP, OSPF, etc.)
residing on the routers. RIP – routing information
protocol,OSPF – open shortest path first

74. • Ingress protection
• It describes the degree of protection offered by an enclosure.
• This enclosure can be of any description, including a cable, cable
assembly, connector body, the casing of a network hub, or a large
cabinet used to enclose electronic equipment.
• Enclosures are rated in the format ‘IP xy’ or ‘IP xyz’.
• (x) describes the degree of protection against access to hazardous
parts
• (y) designates the degree of protection against water.
• (z) describes the degree of protection against mechanical impacts
and is often omitted. It does, e.g. apply to metal enclosures but not
to cables or cable assemblies.
• Here follows a list of meanings attributed to the digits of the IP
rating.

76. • For example, a marking of IP 68 would indicate a dust
tight (first digit = 6) piece of equipment that is protected
against submersion in water (second digit = 8).

77. MODBUS
• MODBUS Serial Line protocol is a Master-Slave protocol. This
protocol takes place at level 2 of the OSI model.
• A master-slave type system has one node (the master node) that
issues commands to one of the "slave" nodes and processes
responses.
• Slave nodes will not typically transmit data without a request from
the master node, and do not communicate with other slaves.
• MODBUS application layer messaging protocol, positioned at level 7
of the OSI model, provides client/server communication between
devices connected on buses or networks.
• On MODBUS serial line the client role is provided by the Master of
the serial bus and the Slaves nodes act as servers.
• slave is any peripheral device (I/O transducer, valve, network drive,
or other measuring device),

78. • Client server Architecture
• The client (on the master device) initiates a request.
• The MODBUS messaging protocol (layer 7) then generates a protocol data
unit or PDU, consisting of a function code and a data request.
• At layer 2, this PDU is converted to an application data unit (ADU) by the
addition of some bus or network related fields, such as a slave address and
a checksum for error detection purposes
• The server (on the slave device) then performs the required action and
initiates a response

79. • ADDRESS field
• On MODBUS Serial Line, the Address field only contains the slave
address which are in the range of 1 – 247.
• A master addresses a slave by placing the slave address in the
address field of the message.
• When the slave returns its response, it places its own address in the
response address field to let the master know which slave is
responding.
• Function code
• Indicates to the server what kind of action to perform. The function
code can be followed by a data field that contains request and
response parameters.

80. Transmission Mode
• Transmission mode defines bit definitions of message
bytes & method of packing & decoding the message
information into message stream
• ASCII transmission mode :
• RTU transmission mode (Remote terminal unit)

81. • The format for each byte ( 11 bits ) in RTU mode is :
• Coding System: 8–bit binary
• Bits per Byte: 1 start bit
• 8 data bits, least significant bit sent first
• 1 bit for parity completion
• 1 stop bit
• each 8–bit byte in a message is sent as two ASCII characters. The
main advantage of this mode is that it allows time intervals of up to
one second to occur between characters without causing an error.

83. • A MODBUS message is placed by the transmitting device with
starting and Ending point.
• In RTU mode, message frames are separated by a silent interval of
at least 3.5 character times.
• If a silent interval of more than 1.5 character times occurs between
two characters, the message frame is declared incomplete and
should be discarded by the receiver.

84. • MODBUS ERROR CHECKING
• MODBUS networks employ two methods of error checking:
• 1. Parity checking of the data character frame (even, odd, or no
parity)
• 2. Frame checking within the message frame (Cyclical Redundancy
Check in RTU Mode, or Longitudinal Redundancy Check in ASCII
Mode).
• Parity Checking
• A MODBUS device can be configured for even or odd parity, or for
no parity checking.
• If even or odd parity checking is selected, the number of 1 bits in the
data portion of each character frame is counted.
• Each character in RTU mode contains 8 bits.
• The parity bit will then be set to a 0 or a 1, to result in an even (even
parity), or odd (odd parity) total number of 1 bits.

85. CRC Error Checking (RTU Mode Only)
• The CRC value is calculated by the transmitting device, which
appends the CRC to the message.
• The receiving device recalculates a CRC during receipt of the message,
and compares the calculated value to the actual value it received in the
CRC field.
• If the two values are not equal, an error results.
• Placing the CRC into the Message
• When the 16–bit CRC (two 8–bit bytes) is transmitted in the message, the
low-order byte will be transmitted first, followed by the high-order byte.
• For example, if the CRC value is 1241 hex (0001 0010 0100 0001):

86. ASCII MODE
• Remark : this mode is less efficient than RTU since each
byte needs two characters.
• Example : The byte 0X5B is encoded as two
characters : 0x35 and 0x42 ( 0x35 ="5", and 0x42 ="B" in
ASCII ).
• The format for each byte ( 10 bits) in ASCII mode is :
• Coding System: Hexadecimal, ASCII characters 0–9, A–
F
• Bits per Byte: 1 start bit
• 7 data bits, least significant bit sent first
• 1 bit for parity completion;
• 1 stop bit

87. • The address field of a message frame contains two characters.
• In ASCII mode, a message is delimited by specific characters as
Start-of-frames and End-of-frames.
• A message must start with a ‘colon’ ( : ) character (ASCII 3A hex),
and end with a ‘carriage return – line feed’ (CRLF) pair (ASCII 0D
and 0A hex).
• The devices monitor the bus continuously for the ‘colon’ character.
When this character is received, each device decodes the next
character until it detects the End-Of-Frame.

88. LRC Longitudinal Redundancy Check
• The Longitudinal Redundancy Check (LRC) field is one
byte, containing an 8–bit binary value.
• The LRC value is calculated by the transmitting device,
which appends the LRC to the message.
• The receiving device recalculates an LRC during receipt
of the message, and compares the calculated value to
the actual value it received in the LRC field.
• If the two values are not equal, an error results.

89. LRC Longitudinal Redundancy Check (ASCII Mode Only)
• Placing the LRC into the Message
• When the the 8–bit LRC (2 ASCII characters) is transmitted in the
message, the high–order character will be transmitted first, followed
by the low–order character.
• For example, if the LRC value is 61 hex (0110 0001):

92. Data Addresses in Modbus Messages
• All data addresses in Modbus messages are referenced to zero.
• The coil known as ‘coil 1’ in a programmable controller is addressed
as coil 0000 in the data address field of a Modbus message.
• Coils are addressed starting at zero: coils 1–16 are addressed as
0–15.
• Holding register 40001 is addressed as register 0000 Holding
register 40108 is addressed as register 006B hex (107 decimal).

93. • When a message is sent from a master to a slave device the
function code field tells the slave what kind of action to perform.
• Examples are to read the ON/OFF states of a group of discrete coils
or inputs; to read the data contents of a group of registers; to allow
loading, recording, or verifying the program within the slave.
• When the slave responds to the master, it uses the function code
field to indicate either a normal (error–free) response or that some
kind of error occurred.
• For a normal response, the slave simply echoes the original
function code. For an exception response, the slave returns a code
that is equivalent to the original function code with its most–
significant bit set to a logic 1.

94. • For example, a message from master to slave to read a group of
holding registers would have the following function code:
• 0000 0011 (Hexadecimal 03)
• If the slave device takes the requested action without error, it
returns the same code in its response. If an exception occurs, it
returns:
• 1000 0011 (Hexadecimal 83)

95. • The data field of messages sent from a master to slave devices
contains additional information which the slave must use to take the
action defined by the function code.
• To Read coil(function code 01) the data field of the request
consists of the relative address of the first coil followed by the
number of coils to be read.
• The data field of the response frame consists of a count of the coil
bytes followed by that many bytes of coil data.

96. 01 Read Coil Status (query and Response)
• Query
• The query message specifies the starting coil and quantity of coils to
be read.
• Coils are addressed starting at zero: coils 1–16 are addressed as
0–15.
• Here is an example of a request to read coils 20–56(37 decimal)
from slave device 17:

97. • Response
• Status is indicated as: 1 = ON; 0 = OFF.
• The LSB of the first data byte contains the coil addressed in the query. The
other coils follow from ‘low order to high order’ in subsequent bytes.
• If the returned coil quantity is not a multiple of eight, the remaining bits in the
final data byte will be padded with zeros (toward the high order end of the
byte).

98. • The status of coils 27–20 is shown as the byte value CD hex, or binary 1100 1101.
• Coil 27 is the MSB of this byte, and coil 20 is the LSB. Left to right, the status of
coils 27 through 20 is: ON–ON–OFF–OFF–ON–ON–OFF–ON.
• In the last data byte, the status of coils 56–52 is shown as the byte value
1B hex,or binary 0001 1011. Coil 56 is in the fourth bit position from the
left, and coil 52 is the LSB of this byte.
• The status of coils 56 through 52 is: ON–ON–OFF–ON–ON.
• Note how the three remaining bits (toward the high order end) are zero–
filled.

99. Modbus Plus Protocol
• Modbus Plus protocol was developed to overcome the ‘single-
master’ limitation prevalent in the Modbus Protocol.
• Modbus Plus is a local area network system for industrial control
applications.
• Networked devices can exchange messages for the control and
monitoring of processes at remote locations in the industrial plant.
• The Modbus Plus protocol topography allows for up to 64 devices
on a network segment.
• Multiple networks segments may be bridged together to form wide
network

100. Network Terminology
• Network:- It is a grouping of nodes connecting on a common
path and is accessed by passing a token

101. • Section:-A section is a series of nodes that are joined only by
cable segments.
• Here the repeater joins two sections. Each section can be up to1500 ft
(450 m) long and can contain up to 32 physical node connections .
• Cable segment:- A cable segment is a single length of trunk
cable between two taps.
• Token: A token is a grouping of bits that is passed in sequence
from one device to another on a single network, to grant access for
sending messages.
• If 2 networks are joined by a bridge plus, each network has its own
token that is passed only among the devices on that network.

102. • Node:-
• A node is any device that is physically connected to the
Modbus Plus cable.
• Some nodes, like programmable controllers, have
addresses and can serve as sources or destinations for
messages.
• The repeater is a node on each of 2 sections, but has no
address, serving only to extend the length of cable

103. • Physical Network
• Each network supports up to 64 addressable node
devices.
• The network bus consists of twisted-pair shielded cable that is run in
a direct path between successive nodes.
• The network consists of one or more cable sections, with any
section supporting up to 32 nodes at a maximum cable distance of
1500 ft (450 m).
• Repeaters can extend the cable distance to its maximum of 6000 ft
(1800 meters) and the node count to its maximum of 64.
• Fiber optic repeaters are available for longer distances.

104. Physical Network
• The minimum cable length between any pair of nodes must be at
least 10 ft (3 m).
• The maximum cable length between two nodes is the same as the
maximum section length of 1500 ft (450 m).
• On dual-cable networks, the cables are known as cable A & cable B.
Each cable can be up to 1500 ft (450 m) long, measured between the
two extreme end devices on a cable section.
• The difference in length between cables A and B must not exceed
500 ft (150 m),measured between any pair of nodes on the cable
section.
• Nodes are connected to the cable by means of a tap device

106. Logical Network
• The token is a grouping of bits that is passed in a rotating address
sequence from one node to another.
• While holding the token, a node initiates message transactions with
other nodes.
• Each message contains routing fields that define its source and
destination,including its routing path through bridges to a node on a
remote network

107. • While a node holds the token, it sends its application messages if it
has any to transmit.The other nodes monitor the network for
incoming messages.
• When a node receives a message, it sends an immediate
acknowledgment to the originating node.
• If the message is a request for data, the receiving node will begin
assembling the requested data into a reply message.
• When the message is ready, it will be transmitted to the requestor
when the node receives a subsequent token granting it access to
transmit.
• After a node sends all of its messages, it passes the token on to the
next node. Protocols for token passing and messaging are
transparent to the user application.

108. GPIB(General purpose interface bus)
• The GPIB bus was invented by Hewlett-Packard Corporation in 1974
to simplify the interconnection of measuring instruments with
computers.
• the GPIB standard was adopted by theInstitute
for Electrical and Electronic Engineers (IEEE) and is referred as the
IEEE 488 bus .
• The devices that are connected to this bus fall into three categories:
controller, listener and talker
• Controller manages the flow of information over the bus
• A GPIB Digital Voltmeter is acting as a Listener as its input
configurations and ranges are set, and then as a Talker when it
actually sends its readings to the computer.
• A printer will act as listener only because it will only need to accept
data to print out on the paper

109. GPIB
General Purpose Interface Bus (GPIB)
GPIB-USB GPIB-RS232 GPIB-PCI

110. Instrument Control Overview
Control any instrument if you know the following:
– Type of connector on the instrument − Type of cables needed
– Electrical properties involved − Communication protocols used
– Software drivers available
Instruments Computer

111. GPIB Communication
GPIB Interface
GPIB Instruments
GPIB
Cable

112. GPIB Hardware Specifications
It is 24 conductor parallel bus
The GPIB uses an eight-bit parallel, byte-serial, asynchronous data transfer scheme.
• Max cable length
DIO1 DIO5 between devices = 2
DIO2 1 13 DIO6
DIO3
DIO4
DIO7 m
DIO8
EOI
DAV
REN
GND (TW PAIR W/DAV) • Max cable length =
NRFD
NDAC
GND (TW PAIR W/NRFD)
GND (TW PAIR W/NDAC) 20 m
IFC GND (TW PAIR W/IFC)
SRQ
ATN 12 24
GND (TW PAIR W/SRQ)
GND (TW PAIR W/ATN)
• Max number of
SHIELD SIGNAL GROUND devices = 15

113. • DATA LINES
• DIO1 through DIO8 are the data transfer bits. Most GPIB systems
send 7-bit data and use the eight bit as a parity
• HANDSHAKING LINES
• NRFD (Not Ready For Data): this is used to indicate the readiness
(or lack thereof) of a device to accept data
• DAV (Data Valid): This is used to indicate to receiving devices that
data has been placed on the bus and is available to read.
• NDAC (Not Data Accepted): is asserted by the receiving device to
indicate that data has been read and may now be removed from the
bus

114. IEEE488 Data Bus Transfer Timing

115. • SYSTEM MANAGEMENT LINES
• ATN (Attention): is used by the controller to specify how data on the
DIO lines is interpreted and which devices must respond to the data
• IFC (Interface Clear): is used by the system controller to reset the
bus . This is used when system needs resetting
• REN (Remote Enable): is used by the controller in conjunction with
other messages to place a device on the bus into either remote or
local mode
• SRQ (Service Request): is used by a device on the bus to indicate
the need for attention so when this line goes low it indicates the
device wants to interrupt current activity
• EOI (End or Identify): Is used by Talkers to indicate the end of a
message string, or is used by the Controller to command a polling
sequence.

116. GPIB configuration

118. • Advantages
• Simple hardware interface
• Ease of connecting multiple device to a single host
• Allows mixing of slow and fast devices
• Well-established and mature, widely supported
• Disadvantages
• Mechanically bulky connectors and cables
• Limited speed and expansion
• implementation options (e.g. end of transmission handling) can
complicate interoperability in pre-IEEE-488.2 devices
• High cost (compared to RS-232/USB/Firewire/Ethernet)
• Limited availability (again compared to
RS-232/USB/Firewire/Ethernet)