Roaming SIM card with network operator preference (steered SIM).

With roaming SIM cards with network operator preference (steered SIM), several mobile networks in Germany are supported, but a specific mobile network is preferred. The provider controls this by first consistently rejecting authentications via "undesired" mobile networks. An "undesired" mobile network is only admitted if no authentication attempt is made via a preferred network even after several rejections.

Example 1: The preferred mobile network Network-C is available, but it is the weakest network:

1. The modem determines Network-A as mobile network with best signal strenght at the location and initiates an authentication attempt over it.
   However, the provider rejects authentication via Network-A several times because it is not the preferred mobile network.
   
   
2. The modem searches for other mobile networks and finds Network-B as another network and triggers an authentication attempt over it.
   However, the provider also rejects the authentication via Network-B because it is not the preferred mobile network.
   
   
3. The modem searches for other mobile networks, finds Network-C and now triggers an authentication attempt via it.
   Authentication via Network-C is immediately allowed by the provider because this is the preferred mobile network.
   
   

Example 2: The preferred mobile network Network-C is not available:

1. The modem determines the mobile network Network-A as best network and triggers authentication attempts over it.
   However, the provider rejects authentication via Network-A several times, because it is not the preferred mobile network (Network-C).
   
   
2. The modem finds the mobile network Network-B and triggers authorisation attempts over it.
   However, the provider rejects the authentication via Network-B several times again, because it is not the preferred mobile network (Network-C).
   
   
3. As no other mobile networks are found, the modem again triggers an authentication attempt via the mobile network Network-A .
   Authentication via Network-A is now allowed by the provider because no authorisation attempts are made via the preferred mobile network (Network-C).
   

These roaming SIM cards therefore always use the provider's preferred mobile network, although according to the criteria in the modem or router another mobile network with a better signal strenght is maybe available at the location. Only if the modem or router does not trigger any authentication attempts via the preferred mobile network, the other mobile networks are used.

Roaming SIM card without network operator preference (unsteered SIM).

In the case of roaming SIM cards without network operator preference (unsteered SIM), the selection of the mobile network is not influenced by the provider, but all mobile networks are equally permitted. The actual network selection is therefore made exclusively according to the criteria defined in the modem or router.

Example: All mobile networks are admitted with equal weighting:

1. The modem determines Network-A as best mobile network at the location and triggers an authentication attempt via it.
   The provider accepts the authentication via Network-A immediately.
   
   
2. The modem determines Network-B as best mobile network at the location and triggers an authentication attempt over it.
   The provider accepts the authentication via Network-B immediately.
   
   
3. The modem determines Network-C as best mobile network at the location and triggers an authentication attempt over it.
   The provider accepts the authentication via Network-C immediately.

These roaming SIM cards therefore offer all the prerequisites that the mobile data connection is always established via the available mobile network with best signal strenght. However, the prerequisite for this is that the criteria in the modem or router also search for and use the best mobile network.