Computer Networks:

Physical Layers
Data link Layer(DLL)
☚ Computer Network
TCP /IP ☛

OSI Model

The operating system interconnection model (OSI Model) is earlier frame for the design of network system. That allows communication across all types of computer system.

it consists of 7 separate but related layer each of which define the segment of the process of moving information across and network. The OSI Model is a product of the open system interconnection effort at the international organization for standardization.

 

 
Layered architecture: 

 

The OSI model is built of 7 order physical (layer 1), data link (layer 2), network (layer 3), transport (layer 4), session (layer 5), presentation (layer 6), and application (layer 7). 

 

OSI Model

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Physical layer (layer 1): 

 

The lowest layer of the OSI reference model is near one the physical layer. it is commonly “PHY”, physical layer is special compared to the other layer of the model because it is only one were data is physically moved across the network interface. 

 

  • Physical year converts that logic 1’s and 0’s into electrical signal. 
  • Data encoding is also done here 
  • Examples : hub, repeater, modem , cables are physically are devices.
 
OSI Model
Function of physical layer: 
 

The following are the main responsibility of the physical layer in the OSI reference model. 

1) Definition of hardware specification: 

The detail of operation of cable connections Wireless, radio transmission, network interface card, in other hardware devices are generally the function of the physical layer. 

 

 

2) Bit synchronization: 

Physical layer provide synchronization of Bit by providing clock, this clock control both sender and receiver bits. 

 

 

3) Topology and physical network design: 

The physical year is also considers the domain of many hardware related network design issues such as LAN WAN,MAN and topology. 

 

 

4) Transmission mode: 

Network layer define the way in which the data flows the between two connected device via simplix, Half duplex and full duplex. 

 

Are one that are at very lowest level and deals with the actual one and zero that are sent over the network. 

Data link layer (layer 2):

  • Data Link Layer is responsible for node to node delivery of message. 
  • Data link layer make the physical layer to appear error free to the upper layer. 
  • Packet receive from network layer are divided into frames size of network interface card NIC. 
  • Device use in data link layer are switch and bridges. 

Data link layer are divided into two sub layers: 

 1) logical link control 

Network for transferring the packet to network layer. It identify the address of network layer. 

 

2) Media access control: 

Media access control is a link between logical link and network physical layer

To the procedures used by device to control access to the network medium since many network use share medium(such as cable or any series of cable) it is necessary to have rule for managing the medium to avoid conflict. 

 

OSI Model
Function of data link layer:
 

1)Data framing; 

The data link layer divide the stream of Bits receive from the network layer into manageable data units called frames. 

 

 

2) Physical addressing: 

Data link layer add physical address of sender and receiver in the header of each frame. 

 

 

3) Error controlling: 

The data link layer provides a medium of error control in which it detect an Retransmit damage or lost frame. 

 

 

4) Flow control: 

If the rate at which the data are received is less than the rate at which data is sent, then it’s control the data flow. 

 

 

5) Access control: 

Went to or more devices are connected to the same link data link layer protocols unnecessary to determine which device has control over the link at any given time. 

Network layer (layer 3):

It responsible for the source to destination delivery of a packet possible the across multiple networks. The IP address has place in network layer device. 

 

Network layer OSI Model
Function of network layer 

 

1)Router: 

Network layer determine the best optimum path for data transmission. 

 

2)Logical addressing: 

The network layer is a header to the packet coming from the upper layer that among other things in indicates the logical address of the sender and receiver. 

 

3)Encapsulation /Packet: 

Normally and capsulate message receive from higher level by placing them into datagram called packets with a network layer header. 

 

Transport layer (Layer 4): 

  • Transport layer also known as the heart of the OSI model the transfer dear is responsible for source to destination and to and delivery of the entire message. 
  • Transport decide if data transmission should be parallel or single path. 
  • The data from upper layer are converted into small unit known as segments. 
Transport layer OSI Model
 
Function of transport layer: 

 

1)Segmentation and reassembly: 

Transport layer received message into segments and each segment is assigned with sequence number that uniquely identify each segment. When the message has arrived at destination then transport layer reassemble according to sequence number. 

 

2) Flow and error control: 

Flow control: 

Like the data link layer the transport layer is also responsible for flow control however flow control at this layer is perform into end rather than across a single link. 

 

Error control: 

Light the data link layer the transport layer is also responsible for error control however error control at this layer is perform n to end rather than across a single link. 

Service provided by transport layer 

 

Connection oriented: 

A connectionless transport layer treats each segment as an independent packet and deliver it to the transport layer at the destination machine. 

Connection oriented:

Are connection oriented transport layer makes connection with the transport layer at the destination machine fast before delivering the packet 

Session layer (Layer 5): 

The session layer is the network dialogue controller it established maintains and synchronize the interaction between communication system. 

 

Function of session layer: 
  • Session established maintain and termination. 
  • Dialogue control either have duplex or full duplex. 
  • Synchronization; 

Presentation layer (Layer 6): 

 

The presentation layer is concerned with the Syntex and semantic of the information exchange between two system presentation layer also known as translation layer.

 

 
OSI Model
Function of presentation layer; 

Translation: 

The presentation layer at the centre change the information from its sender dependent format into a common format. The presentation layer at the receiving machine change the common format into a receiver dependent format. This is also known as and coding and decoding. 

 

Encryption: 

To carry sensitive information assistant message in the form of same court over the network description reverse the original process to transfer the message back to its original form. 

Compression: 

Data compression reduce the number of bits to our transmitted. 

Application layer (Layer 7): 

The application layer enables the user whether human or software to access the network it provides user interface and support for service such as email remote file accessing and transfer 

 

Function of application layer: 
  • Identify communication. 
  • Determine resources. 
  • Synchronizing communication.
 
Services of application layer:
  • Network virtual terminal. 
  • File transfer access and Management. 
  • Male service. 
  • Directory services. 
☚ Computer Network
TCP /IP ☛

Computer Networks:

Physical Layers
Data link Layer(DLL)
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