Mobile Technology 

Obviously this is for the people who has never experienced with any type of protocol .. like me when I got into this area around 15 years ago. You may hear about many words everybody around you use them as if they have known them since elementry school but only you don't have any clue on it. Unless you are working at the level of electrical circuit of communication system, working in the field of a communication technology mean working on some type of protocol.

As in many of operating system or wired communication system, the cellular communication protocol is constructed in multiple levels. Each level has a set of predefined goal(a set of functions) to achieve. This 'level' is called as a 'layer'. So we can say the cellular protocol is made up of multiple layers. Depending on situation, we classify these layers as PHY, MAC, RLC, PDCP, RRC , NAS or call it as L1, L2, L3 layers as illustrated above. Usually in protocol stack development, an engineer tend to work with only one specific layers since each of the layers requires different skillset. However in test and verification process, an engineer is required to have a certain level of knowledges for all the layers.