The recharge fee is small. After a while, the recharge fee will be used up when making calls, so when making a call, a mobile phone reminder will appear that the balance is insufficient.

Authentication refers to verifying whether the user has the right to access the system. Traditional authentication is verified through passwords. The premise of this method is that each user who obtains the password has been authorized. When a user is created, a password is assigned to the user. The user's password can be specified by the administrator or applied by the user.

The weakness of this method is very obvious: once the password is stolen or the user loses the password, the situation will be very troublesome. The administrator needs to re-modify the user password, and the user must be manually verified before changing the password. legal status.

In order to overcome the shortcomings of this authentication method, a more reliable authentication method is needed. The mainstream authentication method uses authentication and authorization to verify the accuracy of digital signatures.

Logically, authorization occurs after authentication, but in fact, the two are often the same process.

If there is no authentication function, mobile users can access and use any wireless network at will, and the interests of operators will not be protected. At the same time, users' security will also be threatened.

At the beginning of the development of mobile communication networks, this problem was considered and solved:

Using user authentication to identify illegal users. User authentication is to authenticate users who are trying to access the network and check whether they have the right to access the network. User authentication can protect the network and prevent illegal theft; at the same time, it protects customers in the network by rejecting "intrusions" pretending to be legitimate customers.