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What is the purpose of Twinax cables and how does it differ from straight through and cross over cables for the connection of unlike and like devices?
I want to know whether there is any difference between them.
Also, Kindly tell me what type of cabling is used for various connections in the network?
Twinax cables are very high-frequency yet bulky cables that most often serve either of two purposes:
Their reach is usually very low - there's no horizontal or vertical cabling standard for twinax. Structured cabling uses fiber for high performance or high reach.
Twinax has much higher performance (=signal fidelity) than cheap twisted pair cabling - several GHz instead of hundreds of MHz - but it's also more bulky and of much higher cost. Due to the expected low-price nature and better reach of Ethernet, it is only used for early PHYs when a new speed grade is developed or in "niche applications" like short-reach interconnects and stacking.
Twisted pair needs much more complex encoding due to its comparatively inferior frequency performance, so it's only available somewhat later on with a new speed grade - check gigabit or 10 gigabit Ethernet for reference.
The reason why twisted-pair Ethernet came up with the straight-through and crossover variants is that Cat-3 straight cabling already existed when 10BASE-T came up (or StarLAN even earlier) and Ethernet had to find a solution to work with that: nearly all devices use one variant of transmitter and receiver contacts (MDI), except for hubs (and subsequently switches) which use the opposite MDI-X pinout. It doesn't work in all situation, so you'd need crossover cables for connecting like devices.
Twinax (or fiber for that matter) didn't ever have this problem, so there's a signal crossover in every cable, creating an odd number of crossovers in nearly any situation.
Note that the twisted-pair crossover vs straight confusion is mostly a thing of the past as nearly all devices from 1999 on (or so) support Auto MDI-X.
