What are the functions of VLR in mobile communication systems?

The Meaning of VLR

VLR is the abbreviation of "Visitors Location Register", which means "访客位置寄存器" in Chinese. It is an important component in mobile communication systems and is usually integrated with the Mobile Switching Center (MSC). The main function of VLR is to store and manage the location information of mobile users who are active within its jurisdiction. When users enter the service area of VLR, they need to perform location registration so that the system can find them and provide services. VLR is responsible for updating users' location information and deregistering this information when users leave the service area.

Technical Details of VLR

The data stored in VLR includes the International Mobile Subscriber Identity (IMSI), Mobile Directory Number (MDN), Electronic Serial Number (ESN), Calling Party's Category (CPC), Mobile Station Class Mark, Mobile Station Protocol Version, Slot Cycle Index, Service Profile, Bearer Service Information, User Terminal Service Information, Supplementary Service Information, Temporary Local Directory Number (TLDN), Home Location Register (HLR) number, the identification code of the last registered base station, the type of the last registration, the time of the last registration, and so on. These data enable VLR to effectively manage users' location information and support the normal operation of mobile communication systems.

Practical Applications of VLR

VLR (Visitor Location Register) has a wide range of practical applications in mobile communication networks, mainly including the following aspects:

1. Storage of User Data: VLR stores relevant information of registered mobile users who enter its control area, including parameters such as users' numbers, identification of the location area where they are located, and services provided to customers. This data is obtained from the users' Home Location Register (HLR) and then stored.

2. Retrieval of User Data: When a call is established, upon the request of the MSC (Mobile Switching Center), VLR can provide user information to the MSC based on the Temporary Mobile Subscriber Identity (TMSI) or the Mobile Station Roaming Number (MSRN). For example, when a mobile station initiates a call, it is based on TMSI; when a mobile station is called, it is based on MSRN.

3. Registration Function: When a mobile user appears in a new location area or receives registration, call establishment, or supplementary service operation messages from the mobile station, if necessary, VLR should be able to send a registration request notification to the HLR. Moreover, VLR should be able to complete the functions of registration and deregistration and retrieve user information from the HLR. According to the request of the HLR or when a user has not appeared in the MSC/VLR area within 24 hours, VLR should be able to ｄｅｌｅｔｅ the relevant information of this user.

4. Mobile Station Call Clearing: When VLR receives a call clearing notice of the mobile station sent by the MSC, VLR should be able to ｄｅｌｅｔｅ the data of this user and notify the corresponding HLR.

5. Authentication Function: VLR should be able to obtain and store authentication parameters from the Authentication Center (AUC). VLR requires the mobile station to perform authentication through the MSC and compares the authentication parameters returned by the mobile station with those stored by itself. When the comparison is inconsistent, it refuses the service request of the mobile station and gives a warning at the same time.

6. Provision of MSRN: When the location of the MS is updated, the local VLR should be able to request the MSC to allocate MSRN according to the request of the HLR and send MSRN to the requesting HLR, that is, support the allocation of MSRN whenever the MS is called.

7. Recovery of VLR: When a data error occurs in VLR, VLR should be able to notify the corresponding HLR and ｄｅｌｅｔｅ the corresponding data.

Functions of VLR in Mobile Communication Systems

VLR (Visitor Location Register) plays an important role in mobile communication systems and mainly undertakes the following key functions:

• Storage of User Information: As a dynamic database, VLR stores the information that needs to be retrieved for incoming and outgoing calls of MS (Mobile Station) in its jurisdiction area, as well as the information of users' subscribed services and additional services, such as parameters like customers' numbers, identification of the location area where they are located, and services provided to customers.

• Recording of Location Information: VLR records the location information of all active users within its jurisdiction area. This information is dynamically changing because users may be on the move. VLR manages this information through the Location Area Identity (LAI). Each MSCS manages multiple location areas, and VLR serves one MSCS to help it record the location information of all active users within its jurisdiction area.

• Support for Call Connection: VLR assists MSCS in recording the relevant information of all mobile users within the current coverage area and provides the necessary conditions for registered mobile users to establish call connections. When a mobile station appears in a certain location area, VLR will initiate the location update procedure to ensure that calls can be correctly routed to the user's current location.

• Roaming Management: For roaming users, VLR stores their user information, enabling the MSC to establish incoming and outgoing calls for mobile users who enter its coverage area. VLR obtains and stores necessary data from the users' Home Location Register (HLR). Once users leave the control area of VLR, they will register again in another VLR, and the original VLR will cancel the temporarily recorded user data.

• Data Synchronization: VLR obtains and saves user data from the users' HLR and provides necessary user data to the MSC when the MSC processes users' mobile services. This can ensure that even when users are in a roaming state, their service information can maintain consistency and accuracy.

In summary, the functions of VLR in mobile communication systems mainly focus on aspects such as user information management, location tracking, call routing, and roaming support. It is a key component to ensure the efficient operation of mobile communication systems.

Types of User Data Stored in VLR

VLR (Visitor Location Register) is an important component in mobile communication networks. It is mainly responsible for storing and managing the relevant information of mobile users who are active within its control area. The types of user data stored in VLR include:

• IMSI: International Mobile Subscriber Identity, which is used to uniquely identify mobile users.

• MDN: Mobile Directory Number of mobile users.

• ESN: Electronic Serial Number, which is used to identify mobile terminals.

• Calling Party's Category (CPC): It represents users' call permissions.

• Mobile Station Class Mark: It represents the technical level of mobile terminals.

• Mobile Station Protocol Version: The protocol standard used by mobile terminals.

• Slot Cycle Index: The usage situation of mobile terminals on wireless channels.

• Service Profile: It includes the types of services available to users and their restriction conditions.

• Roaming Restriction: Whether users can roam in specific areas or not.

• Bearer Service Information: The types of services that users are currently using.

• User Terminal Service Information: The service configuration information of user terminals.

• Supplementary Service Information: The information of additional services that users have subscribed to.

• MSC Number: The number of the Mobile Switching Center.

• MSC/VLR Manufacturer Type: The manufacturer information of the Mobile Switching Center.

• MS Deactivation Mark: The mark indicating whether the mobile terminal is in an inactive state.

• MS Deactivation Reason: The reason for the inactive state of the mobile terminal.

• Temporary Mobile Subscriber Identity (TMSI): It is used to protect users' privacy and avoid the direct transmission of IMSI on wireless channels.

• Mobile Station Roaming Number (MSRN): The temporary number when users are roaming.

• Location Area Identification Number: The identification of the location area where the user is located.

• Authentication Parameters: The parameters used to verify users' identities.

VLR is also responsible for functions such as retrieval of user data, registration, deactivation of mobile stations, authentication, and provision of MSRN to ensure the normal operation and service quality of mobile communication networks.

The Role of VLR in Mobile Communication Systems

VLR (Visiting Location Register) is a key component in mobile communication systems. It is responsible for storing the relevant information of registered mobile users who enter its control area. This information includes users' numbers, location area information, etc. The main function of VLR is to provide the necessary conditions for registered mobile users to establish call connections and update users' location information when they leave its control area.

Value-Added Services Supported by VLR

VLR supports a variety of value-added services in mobile communication systems, mainly including:

• Call Connection: VLR can provide call connection services for mobile users, ensuring that users can smoothly initiate and receive phone calls during the moving process.

• Location Update: When mobile users move from the control area of one VLR to that of another VLR, VLR will update users' location information to ensure that calls can be correctly forwarded to users' current locations.

• Roaming Support: VLR supports the roaming services of mobile users, enabling users to use mobile services in different geographical areas without losing contact with the outside world.

• Short Message Service (SMS): VLR supports short message service, allowing users to send and receive text messages. This is a popular value-added service in mobile communication.

• Multimedia Message Service (MMS): VLR also supports multimedia message service, allowing users to send messages containing pictures, audio, and video, further enriching the application scenarios of mobile communication.

• Mobile Internet Access: With the development of mobile Internet, VLR also supports users to access the Internet through mobile networks and enjoy various online services.

The Importance of VLR

VLR plays a vital role in mobile communication systems. It not only ensures the smooth communication of users but also supports the realization of a variety of value-added services. The efficient operation of VLR is crucial for improving user experience and service quality. With the continuous progress of technology, the functions and application scope of VLR are expected to be further expanded to provide users with richer and more convenient mobile communication services.

Summary

VLR, namely Visitor Location Register, is an important part of mobile communication systems. It can store and manage information such as users' locations and has multiple functions like data storage and retrieval, authentication, roaming management, etc. It supports call connection and value-added services and is of great significance for ensuring communication and improving user experience.