What are the functionalities of the session layer of the OSI model? How does it compare to the network layer?
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| What are the functionalities of the session layer of the OSI model? How does it compare to the network layer? |
Session layer:
Session layer is upper layer of OSI reference model, Its main aim is to establish, maintain and synchronize the interaction between communicating systems. Session layer manages and synchronize the conversation between two different applications. Transfer of data from one destination to another session layer streams of data are marked and are resynchronized properly, so that the ends of the messages are not cut prematurely and data loss is avoided.session layer also manege flow control, header size, time to leave(TTL).
1.Dialog Control : **This layer allows two systems to start communication with each other in half-duplex or full-duplex.
2.Synchronization : **This layer allows a process to add checkpoints which are considered as synchronization points into stream of data. Example: If a system is sending a file of 800 pages, adding checkpoints after every 50 pages is recommended. This ensures that 50 page unit is successfully received and acknowledged. This is beneficial at the time of crash as if a crash happens at page number 110; there is no need to retransmit 1 to100 pages.
Network layer:
- Network layer perform routing(selecting based root for data transmission is called routing).
- Subnet traffic control: routers (network layer intermediate systems) can instruct a sending station to "throttle back" its frame transmission when the router's buffer fills up.
- Frame fragmentation: if it determines that a downstream router's maximum transmission unit (MTU) size is less than the frame size, a router can fragment a frame for transmission and re-assembly at the destination station.
- Logical-physical address mapping: translates logical addresses, or names, into physical addresses.
- Subnet usage accounting: has accounting functions to keep track of frames forwarded by subnet intermediate systems, to produce billing information.