|Dear keshri ,|
It is too much to answer your question completely as I could write 20-30 pages on the subject, in fact you may want to read this document:
Generally categories of cable were developed over time to me the protocals in use at that time. Cat 3 was first developed for 10BaseT, Cat 5 for 100BaseT and cat 5e for 1000BaseT, Cat 6 is currently being developed for a 10 Gig system. There are two standards of color coding now known as T568A & T568B. The rease for the two was the large installed base of AT&T product using their wiring scheme known as 258A which became known as T568B. In reality the two schemes are electrically the same with only two pairs (Wht/or and Wht/Grn being interchanged. It does not matter which one you use as long as you stay consistant. Here in the US the T568B is the most popular for commercial structured cabling.
Joseph Golan, RCDD