Jump Table Switch Case question

I am trying to understand some things about jump tables and its relationship between a switch case statement.

I was told that a jump table is a O(1) structure that the compiler generates which makes lookup of values essentially about as fast as you can get. However in some cases a Hashtable/Dictionary might be faster. I was also told this will only work if the switch case contains ordered data values.

Can someone please confirm or deny this and explain what a jump table is, it's importance and the time complexity versus using a dictionary or hashtable. Thanks.