4G Stands For Fourth Generation, And It Is The Standard That Promises High Bit Rates, And Low End To End Network Delay.
3GPP is the standardization organization that develops and manages the different releases of the 4G standard, and 4G is called as Long Term Evolution (LTE) in the 3GPP documents, which is the official name for 4G.
4G/LTE network consists of specific network components;
1- eNodeB: This is the evolved version of the NodeB (3G) base station, and it is responsible for resource management, scheduling, link adaptation, mobility management, bearer management, error checking, modulation, and demodulation.
2- MME: This is the Mobility Management Entity. MME is responsible for initial user terminal context setup, authentication, initial QoS template management, and location management.
3- HSS: Home Subscriber Server is responsible for keeping the subscriber profile information, initial QoS templates for initial bearer setup, and location information.
4- SGW: Serving Gateway is handling the user data transmission between eNodeB and PGW. It is responsible to initiate the connection with PGW during the initial UE attachment process. SGW is the mobility anchor for UE.
5- PGW: Packet gateway assigns IP address to the UE, and responsible for bearer establishment, and QoS enforcement with the help of PCRF. PGW receives the QoS information for each bearer from PCRF and enforces these QoS rules in order to make sure that every traffic is getting its fair share of the network resources.
6- PCRF: Policy Control Rules Function, is the QoS database for users. When user connects to the network, specific QoS rules have to be applied to the user traffic (bearer), and PCRF communicates required QoS profiles with PGW. There are 2 ways of these communication, either PGW might request this information (pull), and PCFR might push the QoS profile to the PGW.
I mentioned bearer concept in the text. Think of bearer as a data pipe, that has specific attributes for successful delivery of particular traffic type. If you are watching YouTube video, LTE network will establish a high QoS bearer (dedicated bearer) to you so that you can watch your video without any interruption in service quality levels.