Data At The Application/session Layers Of The Osi Model

[Olafiranye]

Dear sir,
In the OSI layers of the Network, I learnt that during encapsuation the physical layer consist of bit stream i.e 0s and 1s.the datalink layer encapsulate the packet with the source and destination mac addresses, etherfield,fcs etc. the network layer encapsulate the segment with the source and destination ip address, protocol field etc.the transport layer encapsulate the data with the source and destination port numbers, etc.
I also learnt that at the presentation layer the data is either encrypted/decprited, coded/decoded, formatted etc. What happens to the data at the application and session layers of the OSI model?what does protocols at the the application and session layers of the OSI model have to do with the data.Pls sir include much explanation in your reply.Thanks

Kunle

[sherman]

Dear sir,
In the OSI layers of the Network, I learnt that during encapsuation the physical layer consist of bit stream i.e 0s and 1s.the datalink layer encapsulate the packet with the source and destination mac addresses, etherfield,fcs etc. the network layer encapsulate the segment with the source and destination ip address, protocol field etc.the transport layer encapsulate the data with the source and destination port numbers, etc.
I also learnt that at the presentation layer the data is either encrypted/decprited, coded/decoded, formatted etc. What happens to the data at the application and session layers of the OSI model?what does protocols at the the application and session layers of the OSI model have to do with the data.Pls sir include much explanation in your reply.Thanks

Kunle


I have the same question with Kunle.your book don't say much about application and session layers.thanks a lot.

[even_zhang]

In my opinion,there are some mistakes in your description,(if my opinion is wrong,please correct me,^_^)
Layer Description
------------------------------
Physical use Bits('0' or '1')
Datalink use Frame(Including Mac address and Upper layer's data)
Network use Packets(Including IP address and others)
Transport use Segment(Including UDP/TCP,Port and others)
Presentation encrypted/decprited, coded/decoded
Session mainly help upper layer to establish/maintain/break the session between source and destination
Application service for users,encapsulate/inencapsulate the users's data,and send them to the lower layer

Regards,HTH.

[rosen]

hey guys if u remember the tcp/ip model (DOD model) it jus has 4 layers.
Application
host 2 host (transport)
internet (n/w layer)
internet access(physical layer + data layer).

in the osi model u jus have expanded the application layer in to the following

application layer( this is the guy who produces the data )

presentation( u encode the data here so that the application on the other side i.e. destination can understand it after decoding example like u used radix64 encoding in pgp(pretty good privacy) for mails )

session layer ( rarely used forget it SIP (session initiation protocols used in IM n streaming etc .) ).

it is these 3 layers that provide u with the data that u r later gonna add ports to in transport layer ..
next u move to ip layer n add ip address .. next mac address at data link layer ..

ultimately 0 ,1 in wires ..

so this is how the story ends on sender side .

[lammle]

Since there was two posts in here saying that I didn't discuss the upper layer (session, presentation and applicaiton), that is because our job doesn't go there. Are you an application developer? If not, then those layer are not as important to us as the middle and lower layers.

I do mention this in the chapter....

However, as I mention in chapter 2, the application/process layer programs are important to understand how they were develped. Telnet, FTP, etc....and how they work with port numbers and the Transport layer.

Hope this helps....
Re-read chapter 2.

Cheers!
Todd