Layered architecture
Basic aim of telecommunication is to transfer "information" from "one point" to "another point". These points may not be "connected" directly; rather there would be number of points or connections in between. The problem which is not apparent here is: though the points which are to be connected may speak same "protocol", in between points may speak different protocol.
Let us take an example.
Say point A need to be connected to point D, with points B and C connecting them as below:
A ------------ B ------------ C ------------ D
Say A speak protocol English, B speak English and French, C speak French and German, and D speak German. Now A wants to send parcel [secret code] to D. So here is what A would do, it would request B [to send parcel [secret code] to D] in English. B do not know where D is, but it "knows" that whatever comes for D need to given to C. It does that, but in French. C knows where D is, so it transfers package [secret code] to D thru their common protocol, German !
Let us draw layers for this example.
In above example, though points B and C did not understand what is inside information parcel [secret code], information was transferred !
Let us explore another similar example.
Let us say A and D are branches of a firm XYZ, A located in UK and D located in Germany. Manager M1 from branch A would like to ship an internal document to manager D1 in branch D.
So M1 gives the document to secretary S1, saying it need to go to D1. Secretary S1 puts the document in an envelope, addresses it to { D1, branch D }. S1 then hands over document to company courier department C1. Courier department puts the branch address of D and hands over the parcel to courier company U located in UK. U understanding that the document is for Germany, sends it to (partner) courier company G, located in Germany. Courier company G, sends the parcel to branch D located in Germany of firm XYZ.
Secretary S2 of manager M2 collects parcel from company courier department C2 and hands over parcel to M2.
Here would be what layered diagram would look like:
Varius protocols, layered architectures, and their interactions are basic to today's telecommunication networks. With above two examples in mind, let us look at OSI model.
7 layers of OSI
o OSI stand for "Open Systems Interconnection".
o Join effort of ISO and ITU-T
o Available on ITU site as X.200 document
Way to remember: Please Do Not Trust Sales People's Advice
© Copyright Samir Amberkar 2010
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