Are hub and repeaters the same? And the same applies for switched and bridges? Since I am finding hub/repeaters and switch/bridge in some books while hubs/switch in others. Also in which layers do they operate?
A Ethernet Repeater extends the usable range of ethernet cabling so it is not the same as a hub. This is a layer 1 device. You might be getting confused with the name "Repeater" and the function of a hub. Or you could be referring to Multiport Repeater which is just another name for a Hub function.
A Hub is also a layer 1 device. It repeats data out from a source port out every other port. Collision is heavy on a hub.
Bridges are layer 2 devices. They exist to physically seperate LAN segments. One of the only decisions a bridge makes is whether to forward or drop a frame. They are different than a switch as a switch can separate LAN segments on the same hardware using VLANs.Switches generally consist of a multitude of ports, while a bridge may only have one.