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ULR Update Location Request

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Update Location Request (ULR):

Update Location Request (ULR) is a signaling message used in the mobile telecommunications network to request the update of a mobile subscriber's location. It is part of the Signaling System 7 (SS7) protocol suite, specifically designed for use in GSM (Global System for Mobile Communications), UMTS (Universal Mobile Telecommunications System), and LTE (Long-Term Evolution) networks.

Background:

In mobile telecommunications, the location of a subscriber's mobile device (often referred to as the Mobile Station or User Equipment) is essential for routing voice calls, SMS messages, and data traffic to the correct serving network element, such as the Mobile Switching Center (MSC) or the Serving GPRS Support Node (SGSN). To maintain accurate location information, the network needs to be aware of the subscriber's current location and the network element serving the subscriber at any given time. This information is managed by the Home Location Register (HLR) or the Home Subscriber Server (HSS) in LTE networks.

Purpose of Update Location Request (ULR):

The ULR message is used to update the location of a mobile subscriber in the HLR or HSS when the subscriber moves from one location area or tracking area to another. The location update is essential to ensure that incoming calls, messages, and data sessions can be correctly routed to the subscriber's current location.

ULR Flow and Procedure:

The ULR message is typically initiated by the Serving GPRS Support Node (SGSN) in UMTS or the Mobility Management Entity (MME) in LTE when it detects that the mobile subscriber has moved to a new tracking area or an LTE serving area. The steps involved in the ULR procedure are as follows:

  1. Initiation: When the mobile subscriber moves to a new tracking area or LTE serving area, the SGSN or MME detects the location change and decides to initiate a location update.
  2. Sending the ULR Message: The SGSN or MME sends a ULR message to the subscriber's Home Location Register (HLR) or Home Subscriber Server (HSS) through the Signaling System 7 (SS7) signaling network or Diameter protocol in LTE.
  3. Authentication and Subscriber Data Retrieval: Upon receiving the ULR message, the HLR or HSS performs authentication to ensure the subscriber's identity and retrieves the subscriber's profile, including the new serving network element (MSC/VLR or SGSN/MME).
  4. Location Update in HLR/HSS: The HLR or HSS updates the subscriber's location information to reflect the new serving network element.
  5. Acknowledge (ULA): After updating the subscriber's location, the HLR or HSS sends an Acknowledge message (ULA - Update Location Acknowledge) to the SGSN or MME, confirming the successful update.
  6. Call and Data Routing: With the updated location information, incoming calls, SMS messages, and data sessions can be correctly routed to the subscriber's current serving network element.

Periodic Location Updates:

In addition to location updates triggered by subscriber movements, mobile networks also perform periodic location updates to keep track of subscribers' location even when they are not actively moving. Periodic updates help ensure that the network always has up-to-date location information for each subscriber.

Conclusion:

The Update Location Request (ULR) is a critical signaling message in mobile telecommunications networks like GSM, UMTS, and LTE. It is used to update the location of a mobile subscriber in the Home Location Register (HLR) or Home Subscriber Server (HSS) when the subscriber moves to a new location area or tracking area. The accurate and timely updating of subscriber location information enables efficient call and data routing in the mobile network, ensuring a seamless and reliable communication experience for mobile subscribers.