Presentation on

Communication Protocol

• B. Tech Part-III Examination 2008 in Computer Science & Engineering

• Registration No — 0047009 of 2002-03• Roll No — 91/CSE/060019

Data communication Data : It refers to the information presented in whatever form is

agreed upon by the parties creating and using the data. Data communication : It is the exchange of data between two

devices via some form of transmission medium such as a wire cable.

Characteristics : Delivery : The system must deliver data to the correct

destination. Accuracy : The system must deliver data accurately. Timeliness : The system must deliver data in a timely

manner. Data delivered late are useless. Jitter : It is the uneven delay in the delivery of the audio or

video data.

Components of Data communication

Message : It is the data to be communicated. Ex-Text, number, picture, audio, video.

Sender : It is the device that sends the data message.Receiver : It is the device that receives the data

message.Transmission medium : It is the physical path by

which a message travels from sender to receiver.Protocol : It is the set of rules that govern data

communication.

Communication protocol

• Definition : Communication protocol is a set of

rules that govern data communication . It represents an agreement between the communicating devices. Without a protocol two devices can only be connected but not communicated ,just as a person speaking French cannot be understood by a person who speaks only Japanese. So here Harry and Gary can communicate if they agree on the language English.

Difference between the entity and system

Entity : An entity is anything capable of sending or receiving information. Examples -- user application programs, file transfer packages, data base management systems, electronic mail facilities.

System : A system is a physically distinct object that contains one or more entities. Examples --- computers, terminals, and remote sensors.

For two entities to successfully communicate, they must agree on some protocol. The set of conventions which may be defined as a set of rules governing the exchange of data between two entities is called the communication protocol.

What should the protocol define?

What is communicated ? How it is communicated ? When it is communicated ? How is data transmitted on the transmission

media ? How do the hosts on the network know when to

transmit data ? How does each host know how much data can be

transmitted at a time ? How can hosts using different operating systems

communicate ? How can a host check the data received for

transmissions ?

Key elements of protocol

• Syntax : It refers to the format or structure of the data. Ex—first 8 bit represents the sender address and the next 8 bit represents the receiver address and the rest is the data.

• Semantic : It refers to the meaning of each section of the bits. It represents how a particular pattern is to be interpreted and what action is to be taken based on this interpretation?

• Timing : It refers to two characteristics ---• When data should be sent?• How fast they can be sent?

What is protocol suite?• Protocol suite : A single protocol addresses one particular

issue that helps to enable communication. When combined with other protocols, the protocol group that results is called a protocol suite. TCP/IP, for example, is a protocol suite.

• protocol suite : A combination of protocols.• Some of the popular protocol suites in today's network

communications include:• IPX/SPX : This is the protocol suite that Novell

has implemented with its operating system.

• AppleTalk : This is the protocol suite that Apple has implemented with its operating system.

• TCP/IP : This is the protocol suite that has been made a standard of the Internet Anyone who would like to use the Internet must use the TCP/IP suite.

Important characteristics of protocol

• Direct Protocol: If two systems share a point-to-point link, data and control information pass directly between entities with no intervening active agent. This protocol is called direct protocol.

• Indirect Protocol : If systems connect through a switched communication network, it is called indirect protocol .The two entities must depend on the functioning of other entities to exchange data.

• Monolithic Protocol : To be truly monolithic, the package would need to include all of the rules in a single layer. A change in any aspect means that this huge package must be modified. This type of protocol is called monolithic protocol.

• Structured Protocol : Instead of a single protocol, there is a set of protocols that exhibit a hierarchical or layered structure. This type of protocol is called structured protocol.

• Symmetric Protocol : Most of the protocols are symmetric; that is, they involve communication between peer entities. The peer entities have the same protocol. This type of protocol is called symmetric protocol.

• Asymmetric Protocol : Asymmetry may be dictated by the desire to keep the logic of one of the entities or systems as simple as possible. An example of the latter situation is the normal response mode of HDLC. Typically, this involves a computer that polls and selects a number of terminals. The logic on the terminal end is quite straightforward but the logic on the server side is too complex. This type of protocol is called asymmetric protocol.

• Non-Standard Protocol : A nonstandard protocol is one built for a specific communications situation or, at most, a particular model of a computer . Thus, if K different kinds of information sources have to communicate with L types of information receivers, (KL) different protocols are needed without standards and a total of (2KL) implementations are required

• Standard Protocol : If all systems share a common protocol, only (K+L) implementations would be needed . The increasing use of distributed processing and the decreasing inclination of customers to remain locked into a single vendor dictate that all vendors implement protocols that conform to an agreed-upon standard.

Protocol functions

• Segmentation : The transfer can be characterized as consisting of a sequence of blocks of data of some bounded size. At the application level, we refer to a logical unit of data transfer as a message. Now, whether the application entity sends data in messages or in a continuous stream, lower-level protocols may need to break the data up into blocks of some smaller bounded size: this process is called segmentation.

• Protocol data unit (PDU) : A block of data exchanged between two entities via a protocol as a protocol data unit (PDU).

A protocol specification is consists of three parts:a) Definition of Protocol Control Information (PCI) format

which forms the PDU header .b) Definition of procedures for transmitting and receiving

PDUs.c) Definition of services provided by the protocol layers.

The PDUs have two parts: (1) A header (also known as the Protocol Control Information (PCI)) (2) A payload (also known as a Service Data Unit (SDU)).

The protocol does not define or constrainthe data carried in the payload part. It does specify the format of the PCI, defining the fields which are present and the way in which the patterns of bits are to be interpreted. A protocol also defines the procedures which determine how the PDU will be processed at the transmit and receive ends.

• Advantages of segmentation The communication network may only accept blocks of data up to a

certain size. Error control may be more efficient with a smaller PDU size. More equitable access to shared transmission facilities, with shorter

delay, can be provided. A smaller PDU size may mean that receiving entities can allocate

smaller buffers. An entity may require that data transfer comes to some sort of closure

from time to time, for checkpoint and recovery operations.

disadvantages of segmentation Each PDU contains a fixed minimum amount of control

information. Hence, the smaller the block, the greater the percentage overhead.

PDU arrival may generate an interrupt that must be serviced. Smaller blocks result in more interrupts.

More time is spent processing smaller, more numerous PDUs.

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Reassembly : If PDUs arrive out of order, the task is to sort them in actual order. This is called reassembly.

Encapsulation • Encapsulation: Each PDU contains not only data but control

information. Indeed, some PDUs consist solely of control information and no data. The control information falls into three general categories:

• Address: The address of the sender and/or receiver may be indicated.

• Error-detecting code: Some sort of frame check sequence is often included for error detection.

• Protocol control: Additional information is included to implement the protocol functions

• The addition of control information to data is referred to as encapsulation.

• Data are accepted or generated by an entity and encapsulated into a PDU containing that data plus control information

Connection control• Connection less data control : An entity may transmit

data to another entity in such a way that each PDU is treated independently of all prior PDUs. This process is known as connectionless data transfer; an example is the use of the datagram.

• Connection oriented data control : Connection-oriented data transfer is to be preferred (even required) if stations anticipate a lengthy exchange of data and/or certain details of their protocol must be worked out dynamically. A logical association, or connection, is established between the entities. Three phases occur

• Connection establishment• Data transfer• Connection termination

• Flow control : In essence, flow control is a function performed by a receiving entity to limit the amount or rate of data that is sent by a transmitting entity.

• Error control : Techniques are needed to guard against loss or damage of data and control information. Most techniques involve error detection, based on a frame check sequence, and PDU retransmission. Retransmission is often activated by a timer. If a sending entity fails to receive an acknowledgment to a PDU within a specified period of time, it will retransmit.

Application of Communication Protocol:TCP/IP protocol suite (Layers):

Functions of Each layer :• Physical layer :

• Physical characteristics of interfaces and media.• Representation of bits.• Data rate• Synchronization of bits

• Data link layer :• Framing.• Physical addressing.• Flow control.• Error control.• Access control.

• Network layer:• Logical addressing.• Routing.

• Transport layer:• Port addressing.• Segmentation and reassembly.• Connection control.• Flow control.

• Application layer:• Mail services.• File transfer and access.• Remote log-in.• Accessing the WWW.

Functions of Each layer in brief

References:1) en.wikipedia.org 2) www.protocols.com 3) www.w3schools.com

4) Books.google.com