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 Post subject: Data at the Application/Session layers of the OSI model
 Post Posted: Thu May 08, 2008 4:30 am 
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Joined: Wed Jan 02, 2008 6:27 am
Posts: 16
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


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 Post Posted: Thu May 08, 2008 7:54 am 
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Joined: Thu Mar 08, 2007 11:32 pm
Posts: 587
Application Layer:

In the OSI model Application Layer, Data will be attached with an Application Header.

http://www.microsoft.com/technet/prodte ... x?mfr=true

http://support.microsoft.com/kb/103886

Protocols linked to Application layers: NCP, SMB, SMTP, FTP, SNMP, Telnet, Appletalk . For more Application Layer Protocols and what they do in relation to data:

http://en.wikipedia.org/wiki/Application_layer

Session Layer:

Accepts 2 applications to communicate on a network by opening a session and synchronizing the involved computers. The session layer handles connection establishment, data transfer and connection release.The name of this layer tells you much about what it is designed to do: to allow devices to establish and manage sessions.A session is a persistent logical linking of two software application processes, to allow them to exchange data over a prolonged period of time. In some case, these sessions are called dialogs. It provides dialog control between devices, or nodes. It coordinates communication between systems and serves to organize their communication by offering 3 different modes:

* Simple
* Half duplex
* Full-duplex

Protocols associated with the session layer:

* Network File System (NFS) - Allow access to remote resources
* Structured Query Languange (SQL) - Developed by IBM to provide users with a simpler way to define their information requirements on both local and remote systems.
* Remote Procedure Call (RPC) - broad client/Server redirection tool used for disparate service environments. It's procedure are created on clients and performed on servers.
* Apple-Talk Session Protocal (ASP) - establishes and maintains sessions between Apple Talk client and server machines.
* Digital Network Architecture session control Protocol (DNS SCP)- is DECnet session layer protocol.
* OSI protocol suite Session Layer Protocol, also known as X.225 or ISO 8327 - Recover data connection in case of data connection loss.

For more session layer protocols and what they do in relation to data:

http://en.wikipedia.org/wiki/Session_layer

http://www.microsoft.com/technet/prodte ... x?mfr=true

For details about application and session layer protocols and what they do with the data:

http://www.cisco.com/en/US/docs/interne ... #wp1020697

-- Kit


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