Regarding transfer of priority level information between networks, it is useful to highlight the case of networks having different degrees of service support and different phases of service implementation, such as "a new network supporting both Priority Service and eMLPP", "a new network supporting Priority Service only" and "an old network supporting eMLPP only" respectively. The following parameters are used in use cases. Types of subscribers

1. Priority Service subscribers (i.e., Service Users)
2. eMLPP subscribers
3. "Normal subscribers", having none of those services

Degrees of service support in networks

1. Priority Service only networks
2. eMLPP only networks
3. Priority Service + eMLPP networks
4. Networks supporting none of these services

Phases of network implementation

1. "New" networks supporting the 3GPP standards release where Priority Service + eMLPP is specified
2. "Old" networks not supporting the 3GPP standards release where Priority Service + eMLPP is specified

Networks involved

1. Calls within one network
2. Calls between neighbouring 3GPP networks
3. Calls passing through intermediate 3GPP networks
4. Calls passing through intermediate non-3GPP networks

Roaming

1. Subscribers being in the home network
2. Subscribers roaming in a visited network

In the following uses cases, to differentiate between Priority Service priority levels and eMLPP priority (precedence) levels respectively, these priority levels are called Priority Service1 - Priority Service5 and eMLPP1 - eMLPP7.