session layer

hi everyone 



as you see into this picture , kr/keith bogart explaining application layer , presentation layer and session layer

he said that any application by itself is out of osi models (out of 7 layers), and there`s protocols into layer 7 that`s run with that application like ftp , dhcp , http , https , dns , snmp , ect 

into first box in the picture ( http data get there`s zeros and 1, that means layer 7 convert http protocol into 0&1 ? or what?

also into second green box (layer 6 application layer)that represent what? what is ascii? why he put another zeros and 1 that`s different than first black box?


  • Rarely will the Session Layer add its own, unique header.  If we take HTTPS as an example (Secure HTTP using TLS Encryption) then HTTP would create a stream of 1's and 0's at the Application layer.  Taking a simple webpage that is just text (no images or graphics) the "data" portion of the packet would contain 1's and 0's representing the actual letters/numbers that make up the text of the webpage as well as HTTP formatting messages (like new paragraph, bold, underline, etc). Then the HTTP protocol itself would add a Layer-7 (Application-layer) header would would have more 1s and 0s but THAT section of binary would be HTTP-specific information only (such as HTTP version, HTTP message type, etc).

    Because we're talking about HTTPS, then TLS would get involved adding another header.  That header (next set of 1s and 0s) would actually be both a Layer-6 (Presentation) and Layer-5 (Session) header all rolled into one.  It would indicate things such as type of cryptography used, key number, and other things necessary to encrypt/decrypt the packet.

    Off the top of my head, I can't think of a scenario where a grouping of 1's and 0's would JUST represent the Session Layer, although there probably are protocols out there that were written just for that purpose.

  • mr / keith bogart thank you


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