CubanRican_NY
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OSI Reference Model
I need to explain the process that occurs between a client (browser) and Web server by describing the functionality of the OSI reference model.
What does it me, Diagram the interaction between the client and the server and illustrate the data flow.
How do I Discuss the importance of the OSI reference model for those who has responsible for network administration and network protocol development.
What does it me, Diagram the interaction between the client and the server and illustrate the data flow.
How do I Discuss the importance of the OSI reference model for those who has responsible for network administration and network protocol development.
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Thank you for your prompt answer. It saved my day.
Glen
Glen
So something you ought to realize is there's not actually such thing as a "Presentation layer protocol" or a "Session layer protocol" involved in browsing the web.
You will need to construct some sort of 'fiction' to describe some function of the web browsing process that takes the place of the 'presentation' and 'session' layer. I suppose, for example, you could describe the process of converting hypertext HTML into on-screen layout instructions, or translating to human-readable fonts as presentation: that is, whatever fits the OSI model's description of that layer.
Otherwise, you will probably want to start thinking of 'mapping' existing protocols and parts of application logic involved in browsers to OSI layers.
With the exception of Presentation Layer and Session layer, it should be pretty obvious...
E.g. map Browser Application, TCP, IP, Ethernet ("MAC protocol"),
Cabling, to their respective OSI layers.
Once you've mapped them, then an explanation should probably trace the path from peer A to peer B.
If you need a primary to understand OSI, I would suggest
Radia Perlman's book, Interconnections: Bridges, Routers, Switches, and Internetworking Protocols 2nd Ed.
Which discusses the OSI model, in slightly more detail than most introductory books on networking.
Key characteristics of OSI to remember are:
*It is a model comprised of 7 layers, that exist on communication peers.
* The Xth layer on one peer communicates with the Xth layer on the other peer, by sending PDUs (Protocol Data Units) through the other layers.
* The Xth layer's message on one peer to the next layer is called a *SDU Service Data Unit The * is replaced with the name of the Layer communicating.
An additional protocol header and layer of encapsulation is added in each *SDU when travelling -down- the stack one one of the hosts towards the physical layer.
The header is a message to the same layer on the other host, and the data encapsulated, is the message to the next layer on the other host.
After the message has crossed the physical layer, it is now travelling UP away from Layer 1. When Service Data Units are sent up, each layer strips off its own header.
For example, the "Application Layer" on one peer, encapsulates the PDU to the other peer's "Application Layer" in a PSDU (Presentation Layer Service Data Unit), and this process repeats at each layer, until the physical layer:
Where peer A's physical layer is in contact with peer B's physical layer.
When the datalink layer on host B receives the Service Data Unit from host B's physical layer, it strips off the datalink header (removes the 'datalink encapsulation'), and transmits the PDU to host B's network layer, with the network layer encapsulation intact.
Certain elements of a 'web browsing' session do fit nicely into the OSI model.
For example, IP packets really do get Encapsulated in Ethernet packets,
and you can map that association to the OSI model's Service Data Units at the proper layer..