Communication protocols like any other technology arrive on the scene to solve a particular problem. Some protocols endure while many perish. The last 60 years or so have seen a true proliferation of protocols in various domains.
So what is a protocol?
In my opinion a protocol is any pre-defined set of communication rules. For e.g. consider the exchange between you and me.
Me: “Thank You”
You: “You’re welcome”.
A more complex exchange could be
You: “How are you doing today?”
Me:” Fine. And yourself?”
You: “Great”
These are “protocols of courtesy or decorum”. There are many such protocols in daily use so there is little wonder that the technological world is full of protocols.
So then what is a protocol stack?
Let us take this hypothetical example. Assume that the CEO of company ABC Inc. wants to talk to CEO of XYZ Inc. This is how this would work in the context of an organizational protocol stack.
CEO (ABC Inc.) to secretary: “Can you arrange for a call with CEO (XYZ Inc.)?”
Secretary (ABC Inc.): “Sure.”
Next the secretary of ABC Inc. will make a call to secretary of XYZ Inc. The exchange would go like this.
Secretary (ABC Inc.): “My CEO would like to have a talk with your CEO”.
Secretary (XYZ Inc.) looks up her CEOs calendar and says
Secretary (XYZ Inc.): My CEO will be free between 3.00 pm – 3.30 pm
So at 3.15 pm
CEO (ABC Inc.) calls CEO (XYZ Inc.): “Can we have a round of golf this weekend?”
CEO (XYZ Inc.): “Absolutely!”
This is typically what also happens in communication protocol stacks. The lower layers provide functions to upper layers (for e.g. the secretary to CEO). Once the lower layers establish the communication channels the upper layers (CEOs) can communicate.
Now is that all there is protocols and protocol stack? In a way, yes. However if we return to our 2nd exchange we could have received any of the following responses
You: “How are you doing today?”
Me:” Will you shut up?”
Or
You: “How are you doing today?”
Me: Sigh.
In other words the protocol suite must take into account all the moods of the communicating parties at either end. So there will be what is known as “sunny day” scenarios and “error scenarios”
This is essentially the basics of any communication protocol whether it is in the internet domain, telecom (SS7 domain), IEEE or any other domain.
Giga thoughts ... 
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