July, 2008

The fourth of seven layers of the ISO/OSI model.The transport layer defines protocols for message structure, and supervises  the validity of the transmission by performing some error checking.Transport Layer never actually transports the data but only prepares for transporting.The Transport Layer is also responsible for fragmentation and reassembly.

The primary function of this layer is to control the communications session between network nodes once a path has been established by the network control layer.

Responsible for the following : •Segmentation •End-to-end Communication •Flow Control •Error Control •Multiplexing of Applications

TCP, UDP work at this layer.

It is the Layer two, the second lowest layer in the OSI seven-layer model.It controls the transfer of information between nodes over the Physical layer.it splits data into frames for sending on the physical layer.

• It uniquely identifies each device in the Network.
• It translates data from Network Layer into bits for the Physical layer to transmit.
• It formats the messages into Data Frames
• Adds a customized header containing Source and Destination hardware address

Devices that works at this layer are -LAN Card -Switches -Bridges etc.

It is the third lowest layer in the OSI seven-layer model,It is the layer which is responsible for routing data across the network.The Network Layer is responsible for end-to-end (source to destination) packet delivery including any routing through intermediate hosts.

In other word, it is responsible for establishing paths for data transfer through the network.

• The Network Layer resides above the Data Link Layer and below the Transport Layer.
• It is responsible for communicating Networks.
• The Network Layer is also responsible for packet sequencing, congestion control, and error handling.
• It recognizes Networks with the help of Network Addresses
• Network Address is a logical address like IP Address or IPX Address
• Path determination or Routing is performed at this layer.
• Router works at this layer.

It is the fourth of seven layers of the ISO/OSI model.The transport layer defines protocols for message structure, and supervises  the validity of the transmission by performing some error checking.Transport Layer never actually transports the data but only prepares for transporting.

The Transport Layer is also responsible for fragmentation and reassembly.The primary function of this layer is to control the communications session between network nodes once a path has been established by the network control layer.

Responsible for the following : • Segmentation • End-to-end Communication • Flow Control • Error Control • Multiplexing of Applications

TCP, UDP work at this layer.

It is the fifth of seven layers of the ISO/OSI model concerned with network management functions including passwords and network monitoring and reporting.It coordinates communication between systems, and serves to organize their communication by offering three different modes: simplex, half duplex, and full duplex.

In other word, It is a set of rules for establishing and terminating data streams between nodes in a network. The services that this layer can provide include establishing and terminating node connections, message flow control, dialogue control and end-to-end data control.

• The Session layer is responsible for setting up, managing, and then tearing down sessions between Presentation layer entities.
• It coordinates communication between systems, and serves to organize their communication by offering three different modes: simplex, half duplex, and full duplex.
• The Session layer basically keeps different applications’ data separate from other applications’ data.
• Examples of Session Layer : RPC, SQL, NFS and NetBIOS .