✔ ISO (International Standard Organisation) gives the name of OSI.
✔ OSI is a collection of rules.
✔ Open means all the rules in OSI are open for all type of computer.
✔ It decide which rule are necessary for communication.
✔ It take module for similar type of rules.
✔ They divide all rules in several layers.
✔ Each layer can communicate with its our upper layer and our lower layer.
✔ OSI is a collection of rules.
✔ Open means all the rules in OSI are open for all type of computer.
✔ It decide which rule are necessary for communication.
✔ It take module for similar type of rules.
✔ They divide all rules in several layers.
✔ Each layer can communicate with its our upper layer and our lower layer.
Example: Application layer can communicate with user ( which is upper one ) and presentation layer which is in lower one and same.
There are seven layers in OSI model such as:
- Application Layer (seventh layer)
- Presentation Layer (sixth layer)
- Session Layer (fifth layer)
- Transport Layer (fourth layer)
- Network Layer (third layer)
- Data Link Layer (second layer)
- Physical Layer (first layer)
Each layer has their own responsibilities such as:
1. Application layer:
Application layer manage application level protocol.for example, suppose four application S/W are kept in application layer and some code are provide for each S/W such as:
If system A make some doc.in word star and mail it to the system B but we know that if doc. made in word star than it will open in word star and if system B have no such knowledge than it create a problem ,So for overcome this problem system A & B make some agreement that they provide code for particular S/W as given in above table.When they send some data than with this data one header is also mention which show the type of S/W.
Application layer manage application level protocol.for example, suppose four application S/W are kept in application layer and some code are provide for each S/W such as:
If system A make some doc.in word star and mail it to the system B but we know that if doc. made in word star than it will open in word star and if system B have no such knowledge than it create a problem ,So for overcome this problem system A & B make some agreement that they provide code for particular S/W as given in above table.When they send some data than with this data one header is also mention which show the type of S/W.
Here A application layer send Hello message to B application layer with some header such as 01 by which B application recognise that Hello message is written in which S/W ( Suppose here is Page Maker) and B application layer open that message in Page Maker.
Application layer is a application level protocol.It is in HOST.
2. Presentation Layer: It has following duties such as:
Data Encryption:
It mean change the code into another code.By we can provide security of our message or data that no one can understand message.Here for this purpose system A and B both make some agreement about data encryption. such as:
It mean change the code into another code.By we can provide security of our message or data that no one can understand message.Here for this purpose system A and B both make some agreement about data encryption. such as:
CODE ENCRYPTED CODE
00 - No Encryption
01 - Encrypt shift-1
10 - Encrypt shift-2
11 - Encrypt shift-3
At the receiver end like system B again Decrypted and transform the message block to its original form.
Data Compression:
Data compression reduce number of bits to be transmitted.Data compression become practically important in transmission of multimedia such as text,audio,video etc.
Character Encoding:
We know that two system usually exchange information in the form of character,string,number and so on.Here also system A and B both make same agreement such as:
Data compression reduce number of bits to be transmitted.Data compression become practically important in transmission of multimedia such as text,audio,video etc.
Character Encoding:
We know that two system usually exchange information in the form of character,string,number and so on.Here also system A and B both make same agreement such as:
CODE ENCODING
00 - ASCII,
01 - EBCD,
10 - BCD
11 - BCD.
3.Session Layer: It ha following duties such as:
Agreement such as:
Transport layer is responsible for error control.This layer performed end to end error control.Suppose A is one end and B is another end.B has one mechanism through which it can identify the receiving message is error free or not. Error may be Damage of Frame,Lost of frame and Duplication of frame etc
3.Session Layer: It ha following duties such as:
- Establishment of session
- To provide synchronous points (check points)
- Remote procedure call (RPC).
Establishment of Session:
It allows the communication between two process to take place either in Simplex/Half duplex/Full duplex.
It allows the communication between two process to take place either in Simplex/Half duplex/Full duplex.
Data in a simplex channel is always one way.An example of simplex is Television, or Radio.
A half-duplex channel can send and receive, but not at the same time.Only one end transmits at a time, the other end receives.example of half-duplex is talk-back radio, and CB Radio (Citizens Band).
In full-duplex data can travel in both directions simultaneously. Full duplex allows both way communication simultaneously.Example can be a consumer which uses a cable connection to not only receive TV channels, but also the same cable to support their phone and Internet surfing.
Agreement such as:
Code Operation
00 Simplex
01 Half Duplex
11 Full Duplex
To provide synchronous point(check point):
The session layer allow a process to add check point (synchronous points) into a stream of data.
The session layer allow a process to add check point (synchronous points) into a stream of data.
If a system is sending a file of 2000 pages it is advisable to insert check point after every 100 pages to ensure that each 100 pages unit is received and acknowledged independently.In this case if crash happen during the transmission of page 523, re transmission begin at 501 page, page 1 to 500 need not be transmitted.
4.Transport layer:
It is responsible for end-to-end delivery.It has following duties.
It is responsible for end-to-end delivery.It has following duties.
- Connection establish and release.
- Divide the message into fixed size data block known as TPDU (Transport protocol data unit).
- End to end error control.
- End to end flow control.
- To provide quality of service (QOS).
Connection establish and release:
For adding security the transport layer may create a connection between to en ports.A connection is single logical path between source and destination that is associated with all the packets in a message.Creating connection involve three steps
For adding security the transport layer may create a connection between to en ports.A connection is single logical path between source and destination that is associated with all the packets in a message.Creating connection involve three steps
- Connection Establishment
- Data Transfer
- Connection Release.
By conforming transmission of all packets to a single pathway, the transport layer has more control over sequencing,flow and error detection and correction.
Divide the message into fixed size data block known as TPDU:
Transport layer breaks the incoming message into segments(parts) or (packets).The size of each packets are same.Suppose it is of 1KB each packet are (TPDU).Here breaking of message into packet has importance in network.By this we can send different packet through different path, when any path is busy.The main concept is the size of packets.Actually when we send any packet then it first store in first coming router.Router has buffer,the size of buffer is decided on the basis of size of packet that is a reason the size of packet is constant.If the line is free than router sent the stored packet on the line (path).
Transport layer breaks the incoming message into segments(parts) or (packets).The size of each packets are same.Suppose it is of 1KB each packet are (TPDU).Here breaking of message into packet has importance in network.By this we can send different packet through different path, when any path is busy.The main concept is the size of packets.Actually when we send any packet then it first store in first coming router.Router has buffer,the size of buffer is decided on the basis of size of packet that is a reason the size of packet is constant.If the line is free than router sent the stored packet on the line (path).
End to End Error Control:
Transport layer is responsible for error control.This layer performed end to end error control.Suppose A is one end and B is another end.B has one mechanism through which it can identify the receiving message is error free or not. Error may be Damage of Frame,Lost of frame and Duplication of frame etc
End to End Flow control:
Problem arise when sending speed of sender is greater than receiving speed of receiver.In transport layer flow control is performed end to end .Here sending speed of any packet of message is more than receiving speed at the receiving end due to which a packet overhead is takes place at receiving end, this create a problem for removing this problem this layer provide a flow control mechanism.
To provide quality of service(QOS):
This layer provide quality full service because the receiving message will error free.
5.Network Layer:
The network layer is responsible for the source to destination delivery of a packet.Possibly across multiple network links.The network layer ensure that each packet gets from its points of origin to its final destination.If two system are connected to the sane link there is usually no need for a network layer.However if the two system are attached to different network with connecting devices between the network,there is often need for the network layer to accomplish source to destination delivery.
It has following duties:
This layer provide quality full service because the receiving message will error free.
5.Network Layer:
The network layer is responsible for the source to destination delivery of a packet.Possibly across multiple network links.The network layer ensure that each packet gets from its points of origin to its final destination.If two system are connected to the sane link there is usually no need for a network layer.However if the two system are attached to different network with connecting devices between the network,there is often need for the network layer to accomplish source to destination delivery.
It has following duties:
- Routing
- Congestion Control
- Inter-networking
Routing:
When two system are attached to different network with connecting device (such as Routers /Gateways) than the route or path are decide for passing the message to destination.That means router can decide the path through which the message will send by some algorithm.
Congestion Control:
If each node send message with maximum rate and subnet are not able to carry message and generate congestion (traffic problem). Example if subnet has capacity to carry only 100 messages.But the incoming message will be more than 100 than congestion control will needed.
Inter-networking:
Independent network are connected together to create a inter networking.It is a network of network.More than one network to form a network is called inter network.
6. Data link layer:
Data link layer transforms the physical layer a raw transmission facility, to a reliable link and is responsible for node to node delivery.
It has following duties:
When two system are attached to different network with connecting device (such as Routers /Gateways) than the route or path are decide for passing the message to destination.That means router can decide the path through which the message will send by some algorithm.
Congestion Control:
If each node send message with maximum rate and subnet are not able to carry message and generate congestion (traffic problem). Example if subnet has capacity to carry only 100 messages.But the incoming message will be more than 100 than congestion control will needed.
Inter-networking:
Independent network are connected together to create a inter networking.It is a network of network.More than one network to form a network is called inter network.
6. Data link layer:
Data link layer transforms the physical layer a raw transmission facility, to a reliable link and is responsible for node to node delivery.
It has following duties:
- Framing
- Error control between two consecutive sections. (Same as in transport layer)
- Flow control between two consecutive sections. (Same as in transport layer)
- Link management.
- Physical addressing.
Framing:
The data link layer divide the stream of bits received from the network layer into manageable data units called Frame.
The data link layer divide the stream of bits received from the network layer into manageable data units called Frame.
Link management:
When two or more device are connected to the same link,Data link layer protocol are necessary to determine which device has control over the link at any given time.
7. Physical addressing:
When two or more device are connected to the same link,Data link layer protocol are necessary to determine which device has control over the link at any given time.
7. Physical addressing:
If frames are to be distributed to different system on the network the data link layer add a header to the frame to define the physical address of sender (source) and receiver (destination).
Physical Layer:The physical layer coordinate the functions required to transmit a bit stream over a transmission media.
It has following duties:
- Electrical property of signal transmitted.
- Mechanical property of transmission.
Electrical property of signal transmitted:
Electrical property of signal means all property of signal which is in the form of 0&1 (low & high) ,what is the shape of the signal ,which modulation technique is used such ASK,PSK etc all these contain electrical signals.
Electrical property of signal means all property of signal which is in the form of 0&1 (low & high) ,what is the shape of the signal ,which modulation technique is used such ASK,PSK etc all these contain electrical signals.
Mechanical property of signal:
Mechanical property is a description of physical media is used such as.same colour of wire between two (agreement) which type of connector is used (router/socket)(agreement) and physical property of wire etc.
Mechanical property is a description of physical media is used such as.same colour of wire between two (agreement) which type of connector is used (router/socket)(agreement) and physical property of wire etc.
