The type of charging in LTE mobile network, may be Offline Charging or Online Charging.

The main difference between the two types, is whether the charging can affect the user data session in real time or not.

Offline Charging can not affect the user data session in real time. While the online charging can affect the user data session in real time.

Offline Charging

First let's discuss the offline charging.

• In offline charging, the node that is responsible for the charging is the Charging Gateway (CG).
• The SGW and the PGW creates records for the data session of every user. Those records are the Craging Data Records (CDRs).
• The CG collects the CDRs of every user, from the SGW and the PGW.
• Those CDRs contains all the details regarding the data session of the user.
• The CG uses those CDRs, in order to charge the users, after their data session ends.
• Therefore, this type of charging does not affect the user data session in real time.
• The CG connects to the SGW and the PGW through the Ga interface.
• Ga interface uses GTP' protocol in the communication between the nodes.

Online Charging

Now, let's discuss online charging.

• In Online Charging, the charging affects the user data session in rel time.
• This means when user balance of the user finishes, the data session may be blocked in real time.
• The node responsible for this type of charging, is the Online Charging System (OCS).
• The PGW provides all data regarding user consumption to the OCS, in real time.
• Therefore, the charging can affect user data session in real time.
• The PGW connects to the OCS through the Gy  interface.
• Gy interface uses Diameter protocol in the communication between the nodes.

Summary,

• The charging type may be Offline, in which the charging does not affect the data session in real time, and the node responsible for it is the CG.
• And Online, in which the charging affects the data session in real time, and the node responsible for it is the OCS.