Are the protocol implementations in TCP/IP same for all platforms or is there a specific requirement for each platform? I have this question when I read Windows and UNIX use different functions to communicate with same protocols so If i'm going to read just about the protocols i.e their header details, services, etc. Do I need worry about some sort of platform specific detail?
API's can and do vary between TCP/IP stack implementations, even on the same platform. Functionally they must satisfy the protocol specs so yes, if you read up on the protocol specifications themselves you'll be good. You should just need to read up on specific platform / implementation references if you're going to be actually coding to that implementation.
That said, different implementations will by nature create subtle differences and incompatibilities with each other. If you need to support an environment with mixed platforms then it's never a bad idea to go out and research known issues between platform implementations.
But again, for learning about TCP/IP itself start with material on the protocols themselves and wait for later to deal with peculiarities between platforms.