COMMUNICATION NETWORK

COMMUNICATION NETWORK

A communication network, consists of a set of equipment and facilities that provide a service, the transfer of information between users located at various geographical points. For example telephone networks provides telephone service, computer networks, television broadcast networks, cellular networks and Internet.

Communication network and transportation networks have become essential infrastructure in every society.

The capacity to transfer high volume of data for a long distance almost immediately are the features of network-based services. For example Internet provides e-mail, information search and retrieval, various forms of electronic service.

EVOLUTION OF NETWORK ARCHITECTURE AND SERVICES

A communication service which is used of transfer of information. Different services differ in the details of how and in what form information is transferred.

Let us consider three example networks
i) Telegraph networks
ii) Telephone networks
iii) Computer networks

TELEGRAPH NETWORKS AND MESSAGE SWITCHING

In the year 1987 Samuel B. Morse demonstrated a practical telegraph that provided the basis for telegram service, the transmission of text message over long distance. Here the text was encoded into sequence of dots and dashes. Each dot and dash which is used to be represented by short and long pulses of electrical current over a copper wire. By relying on two signals, telegraphy made use of digital transmission system. In Morse code the pause between letter was 3 dots and for word is 5 dots.

In store-and-forward process, the message is completely received and stored at an intermediate point and then forward to the next node depending on the availability of link. The process of selecting an appropriate link is known as routing. If the information is message, then it is known as message switching. In simpler terms, message switching is a switching method that sends data from point-to-point with each intermediate node storing the data , waiting for a free transmission channel and forwarding the data to the next point until the destination is reached.

In the beginning communication channel used to carry information sent by one person. Naturally transmission rate (in bits/second) was less. To increase the transmission rate multiplexing was developed. Multiplexing is a technique used to place multiple signals on a single communication channel. Multiplexing partitions a channel into many separate channels, each capable of transmitting its own independent signal, thereby enabling many different transmission over a single medium.

One approach of multiplexing involves modulation. Binary symbols can be transmitted by sending a sinusoidal signal of a given frequency for a given period of time. Multiple sequence of binary symbols could be transmitted simultaneously by using multiple pairs of frequencies for the different telegraphy signals. This concept is used in Modems.

We know characters can be represented by ASCII ( American Standard Code for Information Interchange) , is a 7 bit code. The equipments can communicate with ASCII code.

The telegraph service involves the transmission of text messages between geographically far places. To provide the service , the architecture of the telegraph network contains the following key elements or functions.

i) Digital transmission takes in the network that is information is represented either 0 or 1. It can make use of ASCII code also. The transmission medium can be copper wire and radio.
ii) To identify the messages exactly, messages are covered by beginning and ending by sequence of characters. This is known as framing.
iii) There should be destination address that is to whom it want to deliver. Routing procedure determines the path that a message follows across a network of telegraph stations interconnected by digital lines

TELEPHONE NETWORKS AND CIRCUIT SWITCHING

In 1876 Alexander Graham Bell developed a device that can transmit voice signals. The device that is known as Telephone. The telephone network provides a two-way, real-time transmission of voice signals across a network.

Telephone service became popular due to its voice service and expert operator with knowledge of Morse code is not required like in the case of telegraph. Here voice signals are converted into equivalent electrical signal and passed through cable.

COMMUNICATION FUNDAMENTALS

COMMUNICATION FUNDAMENTALS

Communication concepts

Communication is the process of transmitting information. It’s a big, vague, fuzzy word and broadly applied. The “Communications Department “ at a university may include speech teachers, public relations specialists, writers and broadcasters, who have nothing to do with hardware. By that definition , a writer is in the communication business.

Evolution of communications

We the human beings are communicating from early days that is by drawing the pictures on cave walls. It can be how to attack the animal or how to the save the life from the threats or it may be a route to go to another cave.

The earlier long-distance communications was by signal fires that relayed simple information. The signal used to represent “yes” or “no” – the question being asked had to be known beforehand. It’s only a single bit information, not a detailed message.

A written letter or a human messenger could carry more information. The first systems we might call telecommunications were series of hilltop towers, built by French engineer Claude Chappe in the 1790s. The towers had to be in sight of each other, with an operator in each one. The operator relayed a message by moving arms on top of the tower. The operator of the next tower looked through a telescope to watch the arms move, reading the message, recording it, then moving the arms of his tower to relay it to the next tower. Chappe invented a code that used arm position to indicate letters or certain common words. His system was called an optical telegraph.

Samuel Morse’s electrical telegraph eventually replaced Chappe’s optical one. It also required operators, but they used keys that completed an electrical circuit, sending bursts of currents through a wire. The Morse code was a series of dots an dashes ( short and long pulses) that represented letters.

The electrical telegraph spread across the continents and in 1866 across the Atlantic. Its wires formed a network running between major cities. Telegraphers received signals and either sent them for local delivery or relayed them to more distant stations. We can think of each dot and dash of the telegraph as a bit of information.

Later Alexander Graham Bell developed telephone. He borrowed some principles from the telegraph , but instead of transmitting dots and dashes, it sent a continuously changing electrical current that represented a speaker’s voice. The telephone network was bigger and more complex than the telegraph network.

After that radio waves are used to carry signals through air. Radio first carried telegraph signals. Wires worked fine on land, but only radio could send telegrams to ships at sea and relay urgent messages such as request for help. It was radio rescue calls that sent ships to help the survivors of the sinking of the Titanic. Radio communications started for ships and airplanes in the world war II.

Radio communication started at low frequencies, but gradually moved to higher ad higher frequencies as electronics improved. The higher the frequency the more information the signal can carry. Pictures need more transmission capacity than sound alone, so television are broadcast at higher frequencies than audio radio.

By the 1970s , satellites were beaming radio signals around the globe. The telephone system had become global and known popularly “telecommunication network” . We could make phone calls to anywhere in the world.

After that fiber optics arrived. Fiber provides high bandwidth. It carries high capacity information at faster rate. Now it is a integral part of telecommunication network.

Protocols and standards

Protocols and standards

The Communication occurs between entities in different systems. An entity is anything capable of sending or receiving information. But two entities cannot just send bit streams to each other and expect to be understood. For communication to occur the entities must agree on a protocol. The key elements of a protocol are syntax, semantics and timing.

Syntax : Syntax refers to the structure or format of the data, meaning the order in which they are presented. For example , a simple protocol might expect the first eight bits of data to be the address of the sender , the second eight bits to be the address of receiver and rest of the stream to be the message itself.

Semantics : Semantics refers to the meaning of each section of bits. How is a particular pattern to be interpreted and what action is to be taken based on that information.

Timing : Timing refers to two characteristics. When data should be sent and how fast it can be sent. For example , if a sender produces data at 100 Mbps but the receiver can process data at only 1 Mbps, the transmission will overload and receiver and data will be largely lost.

Standards

Standards are essential in creating and maintaining an open and competitive market fro equipment manufacturers and in guaranteeing national and international operational ability of data and telecommunication technology and processes. They provide guidelines to manufacturers, vendors, government agencies and other service providers to ensure the king of interconnectivity necessary in today’s marketplace and in international communications.

Data communications standards fall into two categories

1. de facto ( by fact)
2. de jure ( by law)

De jure standards are those that have been legislated by an officially recognized body.

De facto standards are often established originally by manufacturers seeking the functionality of a new product or technology.

Standards organization

Standards are developed by cooperation among standard creation committees forums and government regulatory agencies.

i) The International Standards Organization (ISO)
ii) The International Telecommunication Union (ITU-T)
iii) ANSI (American National Standards Institute)
iv) The Institute of Electrical and Electronics Engineer (IEEE)
v) The Electronic Industries Association (EIA)

The ISO is an organization dedicated to worldwide agreement on international standards in variety of fields. ITU-T is an international standards organization related to the United Nations that develops standards for telecommunications. Two popular standards developed by ITU-T are the V series and X series. ANSI , a nonprofit organization is the United States, voting representative to both the ISO and ITU-T. The IEEE is the largest national professional group involved in developing standards for computing , communication, electrical engineering and electronics. It sponsored an important standard for Local Area Network (LAN) called project 802. EIA is an association of electronics manufacturers in the United States. It is responsible for developing the EIA-232-D and EIA-530 standards.

System Functions

System Functions

Communications systems serve many functions. It is possible to divide into four categories on functions.
a) Point-to-point
b) Broadcasting
c) Switched
d) Networked

Point-to-point

A point-to-point configuration provides a dedicated link between two devices. The entire capacity of the channel is reserved for transmission between those two devices. Most point-to-point line configuration use an actual length of wire or cable to connect the two ends.

Broadcasting

A broadcast system send the same signal to everyone who receives it. In its usual form , transmission is one way, from the signal source to the individual. Local radio and television transmission are good examples of pure one-way broadcast systems.

Switched systems

A switched system makes temporary connections between terminals so they can exchange information. The telephone is a good example.

Networking

A network connects many terminals that can communicate with each other. For example Local Area Network is belongs to this category.

Services

Services

We know the operation of modern communication networks is a very complex process that involves the interaction of many systems. A communication network , is a set of equipment and facilities that provides a service, the transfer of information between users located at various geographical points. The ability of communication networks to transfer communication at extremely high speeds, allows users to gather information in large volumes almost instantly with the help of computers for long distances.

Radio and television broadcasting are probably the most common communication services. Various stations transmit an ensemble of signals simultaneously over radio or cable distribution networks.

Telephone service is the most common real-time service provided by a network. Two people are able to communicate by transmitting their voices across the network. The service is considered as connection-oriented in the sense that users must first interact with the network to set up a connection

Telephone networks provide a broad class of call management services that use the originating number or the destination number to determine the handling of a call. For example , in call return the last originating number is retained to allow it to be automatically called by the destination user at a later point in time. Caller ID allows the originating number and sometimes name, of the originating call to be displayed to the destination user when the receiving device is display capable. Voice mail allows a destination user to have calls forwarded to a message receiving device when the destination user is not available.

Cellular telephone service extends the normal telephone service to mobile users who are free to move within a regional area covered by an interconnected array of smaller geographical areas called cells. Each cell has a radio transmission system that allows it to communicate with users in its area. Cellular system should handle “handoff” when user moves from one area to another area.

Electronic mail (e-mail) is another popular network service. The user provides a text message and a name and/or address to a mail application. The application interacts with a local mail server, which in turn transmits the message to a destination server across a computer network. The destination user retrieves the message by using a mail application. E-mail is not a real-time service , where large delays can be tolerated. Here security and privacy is matter of concern.

Many applications that involve an interaction between processes running in two computers may be characterized by client/server interaction. Internet is an example of distributed system. The World Wide Web (WWW) is accessed through a browser program that displays the document and allows the user to access other documents by clicking the links. Each link provides the browser with a uniform resource locator (URL) that specifies the name of the machine where the document is located as well as the name of the file that contains the requested document.

Video on demand characterization another type of interactive service. The objective of the service is to provide access to a video library. The user initiates the service by accessing a menu from which a selection is made. Video which requires lot of bandwidth to pass from source computer to the destination.

Streamed audiovisual services over the internet provide an example of a service with some of the feature of video on demand. An application like “real player “ can be used to access a channel that provides an audio visual stream to the client machine.

Another class of service is audio-visual conferencing. Here both audio and video are transmitted over a distance. This service requires real-time response requirement. This service is being used by many companies for training, client interaction from a site, group discussion etc.

modern-communication-networks

Computing environments

Computing environments

Introduction

We know, in information technology era, sharing of resources and easy communication are acting as a backbone of any network. Popular example is our Internet. With the help of internet we are able to exchange information and share resources. Hence in this chapter we study different advantages of the network and different forms of the network and their features.

The learning objectives of this chapter are to know
What is a computer network ?
How network is advantageous ?
What are different forms of networks ?
What is a e-mail ?

Networking of computers and its advantages.

Computer network is defined as an interconnection of autonomous computer. Here autonomous means, there is no master and slave relationship. All computers are equal. Computer network enables to share the resources. Computer networking also refers to connecting computers to share data, application software and hardware devices. Networks allow sharing of information among various computers and permit users to share files. For example a students accesses compilers sitting at one place, where compiler may be stored on the other machine. The students takes printout with the help of one printer connected to the network. The printer can be shared among many students.

Network offers the opportunity to communicate more efficiently with others through electronic mail. Networks allow companies to share software and peripherals such as printers, plotters, scanners and so on. With networking all the computers in an office can be connected to a single printer and scanner. It also helps in using storage devices efficiently.

Computer network acts as a very powerful communication medium. It means people exchange their information. When compared to mainframe computers, network of computers saves money.

Types of networks

Depending the nature of the distances, protocols ( the set of rules used for communication) the network can be classified into LAN (Local Area Network ), MAN (Metropolitan Area Network ) and WAN ( Wide Area Network).

Local Area Network (LAN)
A LAN (local area network) is a group of computers and network devices connected together, usually within the same building. By definition, the connections must be high-speed and relatively inexpensive (e.g., token ring or Ethernet). They function to link computers together and provide shared access to printers, file servers, and other services.

Any individual computer connected to a network is called workstation. A workstation may not need a floppy disk or hard disk. A LAN or local area network connects computers and peripherals in a limited area. LAN requires cables to connect workstations. For example LAN is used in a hall or within a building. Figure 5.1 shows Local Area Network , where various departments are connected.

Metropolitan Area Network (MAN)

A MAN ( Metropolitan Area Network) is used to connect computers to cover the city or town. The range may be approximately 50 Kilometers. Normally cables and fiber optic cables are used to connect computers. The routing of the messages are fast. Normally central library in a city may be connected by a MAN, so users can access the information. Figure 5.2 shows a typical view of Metropolitan Area Network.

Wide Area Network (WAN)
A WAN (Wide Area Network) covers large distance like state, country or continents. The WAN uses the fiber optics, cables and even satellites also. Here communication circuits are connected with the help of hardware device called routers. Routers forward small pieces of information called packets from one to another. Internet is the popular one comes under WAN. Some of the examples makes use of internet are reservation of airplane tickets, railway tickets and even cinema tickets. Another facility called e-commerce, where business is carried out through internet. Here people can buy books, articles and so on through registering their wants through the internet. Figure 5.3 shows a typical view of Wide Area Network.

Internet
The internet is a massive wide area network ,connecting thousands of computer networks around the world. The internet is a world wide “network of networks”. It is a collection of thousands of smaller networks in different countries around the world. It links thousands of academic government, military and public computers, enabling millions of people to share information and other resources.

Internet pathways are used to exchange digitized computer data. The basic services that form the foundation of the internet are e-mail , telnet and FTP. With internet we can easily exchange electronic mail with friends and family anywhere in the world.

Telnet allows you to connect to a remote computer. We can access any of the public services or tools and library databases at the remote site. FTP(File Transfer Protocol) provides for transferring files from one computer to another across the internet.

Internet has many uses. For individuals, the most important uses of internet are e-mail and surfing the Web. One can read the topics of interest like sports, a hobby, a country or any place of interest.

E-mail:
The e-mail stands for electronic mail. One of the major features of computer networking is that messages can be sent electronically to various terminals on the network. The messages are sent very quickly and accurately. E-mail uses the concept of Storing and forwarding messages. It saves a lot of money for the users. Here user registers his/her account with one of the providers. The e-mail account normally contains username and the provider name. For example abc @ yahoo.com , represents abc is the name of the user , who is registered in yahoo provider.

Summary:
• Computer network is defined as a interconnection of autonomous computers.
• Computer networking enables us to connect computers to share data, application software and hardware devices.
• Networks allow sharing of information among various computers and permit users to share files.
• A LAN or local area network connects computers and peripherals in a limited area.
• A MAN covers the city or town.
• A Wide Area Network covers a large area.
• The internet is a massive wide area network, connecting thousands of computer networks around the world.
• E-mail is a cost effective communication

Quiz questions

1. Computer network defined as a interconnection of ———- computers
2. Computer network allows user to —– the resources
3. ——– network confined to hall or building.
4. ——- is one example of WAN.
5. —— business is carried our through internet.
6. Small piece of information called —- are forwarded by router in Internet.

Answers
1. Autonomous
2. share
3. Local area
4. Internet
5. E-commerce
6. packets

Applications and Layered architecture

Applications and Layered architecture

Communication network must support wide range of services. Normally people use networks to communicate, send e-mails, transfer of files and so on. Industry people use communication network for transfer of funds, update information about the product and so on. Hence, to provide support for current service and future services, a complete plan is required. This necessitates developing a complete flexibility in network architecture.

communications functions are grouped into the following tasks
• The transport across a network of data from a process in one machine to the process at another machine.
• The routing and forwarding of packets across multiple hops in a network
• The transfer of a frame of data from one physical interface to another.

To reduce their design complexity, most networks are organized as a series of layers or levels, each one built upon its predecessor. The number of layers, the name of the each layer, the contents of each layer and the function of each layer differ from network to network.

Interaction between the layers must be defined precisely. Interaction is done with definition of the service provided by each layer and to the layer above. Interface between layers through which a service is requested and through which results are conveyed. New services that build on existing services can be introduced even at the later stage. The layered approach accommodates incremental changes readily.


We know , in all networks, the purpose of each layer is to offer certain services to the higher layers. The entities comprising the corresponding layers on different machines are called peer processes. Between each pair of adjacent layers there is an interface. The interface defines which primitive operations and services the lower layer offers to the upper one. The set of layers and protocols is called the network architecture.

A protocol is a set of rules that governs how two or more communicating devices are to interact. HTTP protocol enables retrieval of web pages and TCP protocol enables the reliable transfer of streams of information between computers.

HTTP

Let us consider a client/server architecture, a server process in a computer waits for incoming requests by listening to a port. Port is an address that identifies which process is to receive a message that is delivered to a given machine. The server provide response to the requests. The server process always runs a process in the background called daemon. httpd refers to server daemon for HTTP. The documents are prepared using Hyper Text Markup Language (HTML) which consists of text, graphics and other media are interconnected by links that appear within the documents. The www is accessed through a browser program that displays the documents and allows the user to access other documents by clicking one of these links. Each link provides the browser with a uniform resource Locator (URL) that specifies the name of the machine where the document is located and the name of the file that contains the requested document. The HTTP ( Hyper Text Transfer Protocol ) specifies rules by which the client and server interacts so as to retrieve a document.


In HTTP, we use two-way connection that transfer a stream of bytes in correct sequential order and without errors. The TCP protocol provides this type of communication service between two processes in two machines connected to a network. Each HTTP inserts its messages into a buffer and TCP transmits the contents of the buffer to the other TCP in blocks of information called segments. Each segment contains port number information in addition to the HTTP message information. The following figure shows how communication is carried between HTTP client and HTTP server.

data-communication-networks-http1

Introduction to CAN (Controlled Area Network)

Introduction to CAN (Controlled Area Network)

OVERVIEW

CAN was originally developed by the German company, Robert Bosch, for use in cars, to provide a cost-effective communications bus for in-car electronics and as alternative to expensive, cumbersome and unreliable wiring looms and connectors. The car industry continues to use CAN for an increasing number of applications, but because of its proven reliability and robustness, CAN is now also being used in many other control applications.
Intra-vehicular communication:

A typical vehicle has a large number of electronic control systems

The growth of automotive electronics is a result of:
Customers wish for better comfort and better safety.
Government requirements for improved emission control
Reduced fuel consumption

Some of such control systems
Engine timing
Gearbox and carburetor throttle control
Anti-block systems (ABS)
Acceleration skid control (ASC)

The complexity of the functions implemented by these electronic control systems necessitates communication between them.
In addition, a number of systems are being developed which will cover more than one device. For example
ASC requires the interplay of the engine timing and carburetor control in order to reduce torque when drive wheel slippage occurs.
In the electronic gearbox control, the ease of gear changing can be improved by a brief adjustment to ignition timing

How do we connect these control devices?

With conventional systems, data is exchanged by means of dedicated signal lines.

But this is becoming increasingly difficult and expensive as control functions become ever more complex.

In the case of complex control systems in particular, the number of connections cannot be increased much further.

Solution: Use Field bus networks for connecting the control devices

FIELD BUS NETWORKS


Field buses are communication technologies and products used in vehicular, automation and process control industries.

Proprietary Field buses
Proprietary Field buses are an intellectual property of a particular company or body.

Open Field buses
For a Field bus to be Open, it must satisfy the following criteria.
The full Field bus Specification must be published and available at a reasonable price.
Critical ASIC components must be available, also at a reasonable price.
Well defined validation process, open to all of the Field bus users.


Field bus Advantages:

I.Reduces the complexity of the control system in terms of hardware outlay.

II.Resulting in the reduced complexity of the control system, project design engineering is made simpler, more efficient and conversely less expensive.

III.By selecting a recognized and well established system, this will make the Fieldbus equipment in you plant or plants interchangeable between suppliers.

IV.The need to be concerned about connections, compatibility and other potential problems is eradicated.

What constitutes a Field bus?
The specification of a Field bus should ideally cover all of the seven layers of the OSI model as shown below,.

FEATURES OF CAN
CAN features are as follows:-

CAN is a robust protocol – essential for automotive applications
SO 11898 and SAE/J2411 are open standards
Well documented and fully supported worldwide
Choice of three CAN physical layer options
High-speed (HS)for high data rates
Fault-tolerant (FT)for additional robustness
Single-wire (SW)for minimum wiring
Any node can access the bus when the bus is quiet.
Non- destructive bit-wise arbitration to allow 100% use of bandwidth without loss of data.
Variable message priority based on 11-bit (or 29 bit) packet identifier.
Peer- to-Peer and multi-cast reception
Automatic error detection, signaling and retries.
Data packets 8 bytes long

BENEFITS OF CAN

Can is a fast serial Bus that designed to provide
An efficient
Reliable and
Very economical link between sensors & actuators
Can uses a twisted pair cables to communicate at speed up to 1 Mbit/s up to 40 devices.
Originally CAN is developed to simplify the wiring in automobiles.
CAN field buses are now used in machine and factory automation products as well.

CAN  HISTORY
In the early 1980s, engineers at Bosch were evaluating existing serial bus systems regarding their possible use in passenger cars. Because none of the available network protocols were able to fulfill the requirements of the automotive engineers, Uwe Kiencke started the development of a new serial bus system in 1983. The new bus protocol was mainly supposed to add new functionality – the reduction of wiring harnesses was just a by-product, but not the driving force behind the development of CAN. Engineers from Mercedes-Benz got involved early on in the specification phase of the new serial bus system, and so did Intel as the potential main semiconductor vendor. Professor Dr. Wolfhard Lawrenz from the University of Applied Science in Braunschweig-Wolfenbüttel, Germany, who had been hired as a consultant, gave the new network protocol the name ‘Controller Area Network’. Professor Dr. Horst Wettstein from the University of Karlsruhe also provided academic assistance. In February of 1986, CAN was born: at the SAE congress in Detroit, the new bus system developed by Bosch was introduced as ‘Automotive Serial Controller Area Network’. Uwe Kiencke, Siegfried Dais and Martin Litschel introduced the multi-master network protocol. It was based on a non-destructive arbitration mechanism, which would grant bus access to the message with the highest priority without any delays. There was no central bus master. Furthermore, the fathers of CAN – the individuals mentioned above plus Bosch employees Wolfgang Borst, Wolfgang Botzenhard, Otto Karl, Helmut Schilling, and Jan Unruh – had implemented several error detection mechanisms. The error handling also included the automatic disconnection of faulty bus nodes in order to keep up the communication between the remaining nodes. The transmitted messages were not identified by the node address of the transmitter or the receiver of the message (as in almost all other bus systems), but rather by their content. The identifier representing the content of the message also had the function of specifying the priority of the message within the system.

A lot of presentations and publications describing this innovative communication protocol followed, until in mid 1987 – two months ahead of schedule – Intel delivered the first CAN controller chip, the 82526. It was the very first hardware implementation of the CAN protocol. In only four years, an idea had become reality. Shortly thereafter, Philips Semiconductors introduced the 82C200. These two earliest ancestors of the CAN controllers were quite different concerning acceptance filtering and message handling. On one hand, the FullCAN concept favored by Intel required less CPU load from the connected micro-controller than the BasicCAN implementation chosen by Philips. On the other hand, the FullCAN device was limited regarding the number of messages that could be received. The BasicCAN controller also required less silicon. In today’s CAN controllers, the ‘grandchildren’, very often different concepts of acceptance filtering and message handling have been implemented in the same module, making the misleading terms BasicCAN and FullCAN obsolete.


IMPLEMENTATION OF CAN

Communication is identical for all implementations of CAN. However, there are two principal hardware implementations. The two implementations are known as Basic CAN and Full CAN.

Basic CAN
In Basic CAN configurations there is a tight link between the CAN controller and the associated microcontroller. The microcontroller, which will have other system related functions to administer, will be interrupted to deal with every CAN message.

Full CAN
Full CAN devices contain additional hardware to provide a message “server” that automatically receives and transmits CAN messages without interrupting the associated microcontroller. Full CAN devices carry out extensive acceptance filtering on incoming messages, service simultaneous requests, and generally reduce the load on the microcontroller.

Network Sizes
The number of nodes that can exist on a single network is, theoretically, limited only by the number of available identifiers. However, the drive capabilities of currently available devices impose greater restrictions. Depending on the device types, up to 32 or 64 nodes per network is normal, but at least one manufacturer now provides devices that will allow networks of 110 nodes.

HOW CAN  WORKS ?

Principle

Data messages transmitted from any node on a CAN bus do not contain addresses of either the transmitting node, or of any intended receiving node.
Instead, the content of the message (e.g. Revolutions per Minute, Hopper Full, X-ray Dosage, etc.) is labeled by an identifier that is unique throughout the network. All other nodes on the network receive the message and each performs an acceptance test on the identifier to determine if the message, and thus its content, is relevant to that particular node. If the message is relevant, it will be processed; otherwise it is ignored. The unique identifier also determines the priority of the message. The lower the numerical value of the identifier, the higher the priority.
In situations where two or more nodes attempt to transmit at the same time, a non-destructive arbitration technique guarantees that messages are sent in order of priority and that no messages are lost.

Bit encoding
CAN use Non Return to Zero (NRZ) encoding (with bit-stuffing) for data communication on a differential two wire bus. The use of NRZ encoding ensures compact messages with a minimum number of transitions and high resilience to external disturbance.

The physical bus
The two wire bus is usually a twisted pair (shielded or unshielded). Flat pair (telephone type) cable also performs well but generates more noise itself, and may be more susceptible to external sources of noise.

The CAN protocol is an international standard defined in the ISO 11898. Beside the CAN protocol itself the conformance test for the CAN protocol is defined in the ISO 16845, which guarantees the interchangeability of the CAN chips.


CAN is based on the “broadcast communication mechanism”, which is based on a message-oriented transmission protocol. It defines message contents rather than stations and station addresses. Every message has a message identifier, which is unique within the whole network since it defines content and also the priority of the message. This is important when several stations compete for bus access (bus arbitration), as a result of the content-oriented addressing. This allows for a modular concept and also permits the reception of multiple data and the synchronization of distributed processes. Also, data transmission is not based on the availability of specific types of stations, which allows simple servicing and upgrading of the network.

Message formats

CAN distinguishes four message formats: data, remote, error, and overload frames. Here we limit the discussion to the data frame, shown in Fig. 5. A data frame begins with the start-of-frame (SOF) bit. It is followed by an eleven-bit identifier and the remote transmission request (RTR) bit. The identifier and the RTR bit form the arbitration field. The control field consists of six bits and indicates how many bytes of data follow in the data field. The data field can be zero to eight bytes. The data field is followed by the cyclic redundancy checksum (CRC) field, which enables the receiver to check if the received bit sequence was corrupted. The two-bit acknowledgment (ACK) field is used by the transmitter to receive an acknowledgment of a valid frame from any receiver. The end of a message frame is signalled through a seven-bit end-offrame (EOF). There is also an extended data frame with a twenty-nine-bit identifier (instead of eleven bits).
The CAN protocol was internationally standardized in 1993 as ISO 11898-1. The development of CAN was mainly motivated by the need for new functionality, but it also reduced the need for wiring. The use of CAN in the automotive industry has caused mass production of CAN controllers. Today, CAN controllers are integrated on many microcontrollers and available at a low cost.

CAN ARCHITECTURE

Any node can access the bus when the bus is quiet

Non-destructive bit-wise arbitration to allow 100% use of the bandwidth without loss of data

Variable message priority based on 11-bit (or 29 bit) packet identifier

Peer-to-peer and multi-cast reception

Automatic error detection, signalling and retries

Data packets 8 bytes long


ERROR HANDLING PERFORMANCE OF CAN

Error detection and error handling are important for the performance of CAN. Because of complementary error detection mechanisms, the probability of having an undetected error is very small. Error detection is done in five different Vehicle Applications of Controller Area Network 7 ways in CAN: bit monitoring and bit stuffing, as well as frame check, ACK check, and CRC. Bit monitoring simply means that each transmitter monitors the bus level, and signals a bit error if the level does not agree with the transmitted signal. (Bit monitoring is not done during the arbitration phase.) After having transmitted five identical bits, a node will always transmit the opposite bit. This extra bit is neglected by the receiver. The procedure is called bit stuffing, and it can be used to detect errors. The frame check consists of checking that the fixed bits of the frame have the values they are supposed to have, e.g., EOF consists of seven recessive bits. During the ACK in the message frame, all receivers are supposed to send a dominant level. If the transmitter, which transmits a recessive level, does not detect the dominant level, then an error is signalled by the ACK check mechanism. Finally, the CRC is that every receiver calculates a checksum based on the message and compares it with the CRC field of the message. Every receiver node obviously tries to detect errors within each message. If an error is detected, it leads to an immediate and automatic retransmission of the incorrect message. In comparison to other network protocols, this mechanism leads to high data integrity and a short error recovery time. CAN thus provides elaborate procedure for error handling, including retransmission and reinitialization. The procedures have to be studied carefully for each application to ensure that the automated error handling is in line with the system requirements.

APPLICATIONS

CAN networks can be used as an embedded communication system for microcontrollers as well as an open communication system for intelligent devices. The CAN serial bus system, originally developed for use in automobiles, is increasingly being used in industrial field bus systems, the similarities are remarkable. In both cases some of the major requirements are: low cost, the ability to function in a difficult electrical environment, a high degree of real-time capability and ease of use.
Some users, for example in the field of medical engineering, opted for CAN because they have to meet particularly stringent safety requirements. Similar problems are faced by manufacturers of other equipment with very high safety or reliability requirements (e. g. robots, lifts and transportation systems).  CAN controllers and interface chips are physically small. They are available as low-cost, off-the-shelf components. They will operate at high, real-time speeds, and in harsh environments. All these properties have led to CAN also being used in a wide range of applications other than the car industry. The benefits of reduced cost and improved reliability that the car industry gains by using CAN are now available to manufacturers of a wide range of products.

For example:

•  Marine control and navigation systems
•     Elevator control systems
•     Agricultural machinery
•     Production line control systems
•     Machine tools
•     large optical telescopes
•     Photo copiers
•     Medical systems
•     Paper making and processing machinery

VEHICLE APPLICATIONS OF CAN

The Controller Area Network (CAN) is a serial bus communications protocol developed by Bosch in the early 1980s. It defines a standard for efficient and reliable communication between sensor, actuator, controller, and other nodes in real-time applications. CAN is the de facto standard in a large variety of networked embedded control systems. The early CAN development was mainly supported by the vehicle industry: CAN is found in a variety of passenger cars, trucks, boats, spacecraft, and other types of vehicles. The protocol is also widely used today in industrial automation and other areas of networked embedded control, with applications in diverse products such as production machinery, medical equipment, building automation, weaving machines & wheelchairs.
In the automotive industry, embedded control has grown from stand-alone systems to highly integrated and networked control systems. By networking electro-mechanical subsystems, it becomes possible to modularize functionalities and hardware, which facilitates reuse and adds capabilities. Fig. 1 shows an example of an electronic control unit (ECU) mounted on a diesel engine of a Scania truck. The ECU handles the control of engine, turbofan, etc. but also the CAN communication. Combining networks and mechatronic modules makes it possible to reduce both the cabling and the number. The work of K. H. Johansson was partially supported by the European Commission through the ARTIST2 Network of Excellence on Embedded Systems Design, by the Swedish Research Council, and by the Swedish Foundation for Strategic Research through an Individual Grant for the Advancement of Research Leaders.


The work of M. T¨orngren was partially supported by the European Commission through ARTIST2 and by the Swedish Foundation for Strategic Research through the project SAVE of connectors, which facilitates production and increases reliability. Introducing networks in vehicles also makes it possible to more efficiently carry out diagnostics and to coordinate the operation of the separate subsystems.

Heavy Vehicles

Most existing vehicle model libraries are designed primarily for cars. Heavy vehicles have a number of sub-systems which are not present in passenger cars. Particularly the engine/transmission system includes de-vices like an exhaust brake and possibly a retarder. Further, the cooling system also has a more prominent role than in cars, and coolant is often used both by the engine and the transmission.

Signalling Bus

A key issue in an architecture which contains both physical plant and controller models is the handling of electrical signals. The controllers need to exchange data among themselves and they need to exchange signals with sensors and actuators. For our applications the actual signalling behaviour is not that important, an ideal communications model is sufficient. For the communication between a plant and its controller, standard library in-ports and out-ports are used. The communication between the controllers was a tougher case. Two implementations of the same controller may not have the same signalling needs, thus it must be possible to change the set of signals sent between control units. Separate input and output ports for all links between control units in the vehicle would create an un-decipherable graphical mess. Some type of signalling bus is needed. Both the standard library bus connectors and the type of bus used in the vehicle modelling architecture proposal by Tiller Etal were evaluated. We did not find enough information about the inter-controller communication in the Tiller paper to implement that system. Our main problem was to find a way of having compatible connectors in all controllers, without modifying the code of every controller when a signal was added to the bus. The standard library bus does not solve that problem, since it requires all signals to be declared in the connector. Eventually we chose a simpler solution based on a common connector called ”CAN” with a replace-able variable, called ”protocol”, which contains all the signals. The protocol variable can easily be redeclared into a type which contains exactly the signals broad-cast on the bus in a particular model. Different implementations of the CAN connector are used for different signal buses in the vehicle.

Most of our control units are implemented through external function calls, thus the drawback of having no convenient graphical way of converting a signal from inport/ outport to bus format is minor.

RESUME

RESUME

Resume is the first step of marketing program for an educated person. Resume is a French word which means ‘To summarise. It is the same as the bio-data, curriculum vitae. It represents a qualified person with all the details. Although you are well qualified and intelligent enough, if your resume in weak, you may not face an interview.

Therefore a good resume is a powerful tool to secure a job. Resume should portray you in the best possible manner. Resume is an important contact with an employer. Usually, a resume consists of two-three typed pages about the candidate.

Contents of Resume:
Resume should contain the most important and a lot of different information, as given here under
1. Personal data (Including Name, Address, Phone no., e-Mail ID, etc.)
2. Educational qualification.
3. Caste and sub caste.
4. Work experience, if any.
5. Other qualifications (Awards, Honours and publications etc.)
6. Sports and other interests.
7. Languages known.
8. Marital status.

Types of Resumes:
There are three kinds of resumes, namely:
1. A Traditional resume.
2. A Functional resume.
3. A Skills Emphasis resume.


1.A Traditional Resume:

This gives the clear list of the candidate’s educational qualification and work experience in the chronological order. It gives the clear information of the job titles, name of the company, school or colleges, dates of enrolment and employment etc., which are essentially needed for the employers. Some professions, viz Law, Finance and IT require such traditional resumes.

The traditional resume should contain the following points
• Continuity in work history
• If you are looking for a job, related to your cost experience
• A gap in past service
• Emphasis on no professional jobs

This traditional resume is not meant for class IV and below grade appointments.

2.A Functional Resume:

This resume contains even minor observations which are not preferable in traditional resume. It highlights your education and job experience and arranges them in a concise manner. It gives more importance to description of functions instead of employment, job titles, names of the company and dates of the employment. This contains the description about the functions which gives the satisfaction and your research. It also contains the way you interact and manage the people and solve the problems.

A functional resume must be existing and personal. Here you can mention abot sports and other extracurricular activities.
A functional resume is preferred in the following context.
1. Change in career
2. With other job oriented experiences, entering the job market with no work history.
3. Returning to the job market after a long gap.
4. Seeking a position unrelated to your previous employment.
5. Promotion from one position to another


3. A Skills Emphasis Resume
In format, this resembles a functional resume. It gives importance to identification. E.g.: Desired: Experience as a sales representative, leadership quality, communication skills, financial analysis and creativity etc.

ORAL COMMUNICATION ACTIVITIES

ORAL COMMUNICATION ACTIVITIES

Dyadic Communication
The term “dyadic communication” is general reference to an interaction between two persons. Even if more than two persons are present in a situation, it is only two communications that play fundamental role. The formal dyadic communication with which we are concerned demands artistry that can be acquired through practice, dyadic communication may take a number of forms but we shall discuss only the following file, face to face conversation, telephonic conversation, interview, inspection and dictation.

Face to face conversation:
Conversation is the most common form of dyadic communication. It links people together to be in social or personal life. Conversation may be defined as oral and usual informal or friendly exchange of views, ideas etc. In a conversation the participants has to play the role of a speaker or a listener interchangeable the role that the best practice for conversation itself holds true.

Helpful hints for successful face to face conversation
1. The conversation should be of interest to the participant and may being with a topic in which both have some interest. As it flow into new channels adjusts yourself to be comments and new point of view this needs not bother you because often during this spells new thoughts are generated.
2. Be alert to the attitudes that others may have and don’t be surprised when you realise that the attitudes are likely to change.
3. Occasionally call the person by name  and look at him while speaking, if you speak the name aloud you would be generating a more friendly feeling to cop it all take care of a language and oral demeanour.
4. Be always courteous and cheerful. Feel interested in what is being said.
5. Being dogmatic and argumentative may spoil your conversation. But it is useful to have a point of view.
6. Avoid pet and superfluous words and phrases

Telephonic Conversation:
One form of dyadic conversation is interaction between two persons on a telephone. In this form the advantage of using body language and eye contact is lost. But it is one of the common and fastest ways of contacting persons. It is simple handy in the long run economically, therefore it is termed as prices less means of communication.

Guidelines for telephonic conversation:
1. Cultivate a cheerful and friendly tone.
2. Modulate your voice.
3. Never sound hurried, flustered or impotence.
4. Pronunciate your words clearly.
5. Do not use slang.
6. Speak distinctly if you use a word which is likely to be misunderstood, spell it out.
7. Listen attentively to the caller.
8. Be courteous in all the circumstances.
9. Don’t engage your telephone longer than necessary.

While receiving and making calls bare the following points in mind:

Lift the receiver promptly.
Reveal your identity
Obtain the caller’s name and designation
Give the required information accurately
Keep a job pad and pencil, Handy to note message
While calling keep all the materials ready before you dial the number

Telephone is the best answer to transact with an officer busy interacting with others.

Interviews
The word “Interview” is derived from interview meaning sight between. It is a meeting between two persons with a specific purpose. An interview demands direct and dynamic interaction. One of the purposes of interview is to elicit information, which is not available from written records or other sources.

Therefore various steps of interviews ranging from the one conducted by a journalist for a newspaper reporting to that by a psychiatrists with a patient. The purpose defines the type of interview. Here we are interested in the following two types of interviews :

1. Employment interviews
2. Data collection interviews

The term employment interview refers to interviews of a candidate for a job in a particular organisation. Promotional interview and annual interviews are conducted in respect of the employees who are already in service.

Employment Interview:
The main purpose of the employer is to judge the stability of applicant to the job and that of the applicant to find out whether the needs and requirements of the job wood suit him also whether the environment to his professional growth and intellectual or social pursuits.

Disposition:
A vital piece of information that the employer would like to have is whether the candidate has the ability to work with others.

Circumstances:
A peep into the interview’s previous environment and family circumstances may give some clue to the candidate capacity to work.

Data Collection Interview:
Very often one would be called upon to collect data for specific purpose and present it in the form of a letter, memo, report etc. This information may either be available with your officers in your own organisation or other organisation.

Instructions:
Directing others to perform a particular function of a profession infant giving instructions in an art can be cultivated. While giving instructions to sub-ordinates and junior officers the following things must be keep in mind:
1. The background knowledge of the recipient.
2. His physiological recipient.
3. His capacity to group.
4. His ability to act upon your instruction.

Dictation:
Dictation is another type of communication very frequently used in professional organisation. It is an art in which every profess prospective employers main aim is to judge your sense of values, your attitude towards the work.

Each applicant must plan to be successful. Failure in interview certainly injures the ego of a person temporarily. So to be successful must pay the close attention to the following:
1. Physical appearance creates the first impression and tells something about the personality of the individual.
2. Good department and good manners generates a proper atmosphere and put you at ease, nothing should appear to be artificial and imitative.
3. Care should be taken not to in judge in certain mannerism in speech and behaviour.
4. Does not use long and highly colloquial long wage the tone should be friendly but not imitative.
5. One must be careful not be in the habit of making add gestures while taking.
6. Listening is an art one should create an impression that he is a good listener.
7. Speech must be cultivated by listening to recordings one’s own voice to get job and to move up on the ladder of career.
8. Most important of all these is to be clear doubts and those thoughts must be expressed in plain language.
9. Avoid giving uncomplimentary references to your former employers.

Employer’s expectations:
We may classify the information which an employer seeks while considering a person for job into the following sub-headings.

State of Health:
Every organisation desires its employees to be in a healthy state. A part from judge at the interview the organisation requires a new entrant to undergo a medical examination the standards of which differ from profession to profession.

Attainments:
A probe is made through searching question to verify what the candidate in the bio-data writes and to asset nature and quality of his achievements.

Intelligence:
A close observation is made of the reflex and response of the interview to discover the extent of his grasp and confidence.

Attitude:
Certain questions are directed merely to find out the candidate’s attitude for the job he has applied for.

Interests:
An attempt is made to understand the other dimensions of the responsibility of the candidate by encouraging him to speak about his day today business. Some of the hints given below would prove helpful to you in learning the art of dictation.
1. Tell the steno the form of communication you are going to use and the situation promoting it.
2. Picture the entire composition i.e. the total matter to be dictated in verbal terms.
3. Take care in dictating homonyms. E.g., pale, pail, ascent compliment, etc.
4. Dictating all the punctuation marks.
5. Match the speech of dictation to the speed of your steno.
6. If you dictate into a machine listen to the material recoded before asking your steno to type it. This should be also with a steno new to the job.

Meetings:
The word meeting is used in two sense; one to refer to a small group meeting committee, meeting of board of directors, cabinet meeting, meeting of sectional heads etc. And the second to refer to any meet of two or more persons, what ever be the label application to such a group, the meeting is perhaps the most commonly used form of discussion in a professional organisation. The person who chairs the meeting act is the leader of the groups and usually has a higher status or enjoys authority over other members. Every meeting is result oriented and therefore the discussion is directed towards a specific end.

Purpose:
There are number of purpose for which meeting are held, some of the following are typical of most situations.
1. To save time and communication.
2. To convey information to a group at one time.
3. To brief members on plans already made or work already done.
4. To give and get new ideas.
5. To get immediate reactions, a new ideas, proposals and pans.
6. To exchange ideas and experience.
7. To discuss and solve problems.
8. To resolve conflict confusions and disagreements.
9. To arrive at widely acceptable decisions persons in power to take decisions.

Chairmanship:
The chairman generally concerns a meeting of the member of a committee or any other constituted body or a member authorised by him. In other cases an authorised official calls it whose wishes to use it for any other purpose mentioned earlier.
In this case he acts as the chairman and he may name a member of group to act as a secretary of a particular meeting. The following points should be born in mind by the person who calls the meeting:
1. The announcement for any meeting must be made in written at least a week before the fixed date.
2. The notice should be sent to all members, even if it were known that some of them would not attend.
3. The notice should clearly state the agenda.

Chairmanship:
Chairing a meeting requires a lot of patience, a sense of humour and sound knowledge of the technique of making people discuss a meeting intelligently and arrive at well reasoned conclusion, when you are called upon to conduct a meeting read through the agenda carefully and prepare a discussion plan. Before the meeting begins ensure that the proper physical arrangement has been made and aids and materials to be used are available at the venue.

A discussion plan is nothing but a guide prepared by you reflecting your own thinking and the subject to be discussed. A logical sequence of the ideas is expected to be presented. The questions likely to be raised to the members and the conclusions that might be reached you should also estimate the time you should like to be devoted to each item in the agenda.

In every meeting the beginning is crucial; don’t wait for those who are not present, think of those who are present. After you have set the discussion in motion invited response but don’t get unnerved if there is silence for some time.  Do not rush the group at arrive at a discussion. Let the meeting problem entered and discussion oriented. Give a fair chance to every member to speak and don’t take sides. Be especially alert about problem participant, the commenter and monopolizes and the reticent.

The conclusion of the meeting put special responsibility on the chairman. As chairman’s duty is to take a position of the authority and to state firmly, the result of the discussion are namely to obtain the maximum benefits, the summary and closing of the meeting are of equal importance.
To sum up the chairman performs the following functions which are necessary:
1. He draws preliminary plans and makes the arrangements for the meeting.
2. He invites, directs and controls the discussion.
3. He facilitates or directs the plan of action for implementing the conclusions.

Participation:
The role of participant is an equally important aspect of a meeting which very much depends upon the kind and quality of contribution made by the participants, when you are asked to attend a meeting and to go through the agenda, carefully collect the useful information and develop a tentative point of view with an open mind.
Be a good listener and try to read the thoughts behind the expression, whether relevant or not to listen to every speaker attentively. Don’t hesitate to volunteer and relevant information you may have on the topic under discussion and with confidence. Sincere participation should be your goal. Note down the important points briefly at the meeting for reference in future physical arrangements.

A good physical arrangement contribution to the success of the meeting is the most favourable seating arrangement is around a large table.

In case of rectangular table is used the chairman should seat himself at a position from where he can face everyone.

Group Discussion:
The term group discussion is used to refer to a situation in which a small number of persons meet face to face and through free oral interaction among themselves, exchange information or attempt to reach a decision on shared problem if it is difficult to specify the number of participants that would make the group discussion useful. Research indicates that if the number is kept between 5 to 9, fruitful discussion can take place. It is also observed that group of even numbers of participants tend to be less stable and rewarding the groups. As the discussion precedes one of the participants emerged as a leader. One of the advantages of this type of discussion is that there is a self imposed discipline on the discussion and greater responsibility on the participants for making it useful to keep the discussion on the track it may be worthwhile for a participant to summarise the point.

Occasionally when the group discussion takes place some persons may be invited as observer that may be done for two purposes.
1. To let the observer learn the process of group discussion and
2. To evaluate the contribution by members purpose.

Very often group discussion is used in addition to written test/interviews for employment. Therefore a representative of the prospective will judge each individual’s personality traits such as intellectual ability, creativity approach to solve problems, qualities of leadership, tolerance and group behaviour. In this process he would also note the clarity of thought and felicity of expression of each member.

Sometimes a group discussion is also an instrument to develop and judge the student personality trails mentioned above. It trails the student to function in the professional world efficiently.

Organisation:
There are two ways of organising a group discussion.
1. The topic is announced before hand and participant is expected their homework before coming to the discussion table.
2. The topic is announced after the members have assembled and five to ten minutes are given to them for collecting their thoughts.

The room where the group discussion takes place should have proper   ventilation and sufficient height. The chairs should be arranged in a circle so that a member’s expression can be seeing all by others.

Case-study:
Case –study means analysing a case subject to a problem. Every now and then in a day to day life we come across crisis, problem, etc which might have multi dimensional solution which might vary from one person’s perception to another person’s perception. Choosing the ability of the person analysing the case the detailed study performed would only make it possible to find the most feasible solution.