LAU Reject: No Suitable Cells in Location Area Explained

This scenario occurs when the network sends a message to the mobile station (MS) indicating an LAU (Location Area Update) reject with the cause being “no suitable cells in Location Area.”

Image alt: LAU Reject-no suitable cells in Location Area

This reject cause is transmitted by the network to the MS with the intention of the MS camping on the same PLMN (Public Land Mobile Network), but in a different LA or with a different RAT (Radio Access Technology).

This cause is sent by the network (either the HPLMN - Home PLMN or VPLMN - Visited PLMN) to the Mobile Subscriber (MS). When the mobile receives this message, it will not search for another PLMN; instead, it will search for another location area (LA) of the same PLMN.

It’s like the network saying to the MS: “I will not be able to provide services in this LA; please try another LA in this PLMN.”

Example Scenario

Imagine two networks: a GSM (2G) network and a WCDMA (3G) network. The WCDMA network has LA5 and LA6 regions providing 3G service. The other location areas, LA1, LA2, LA3, and LA4, provide 2G service. Both the 2G and 3G service regions are overlapping.

Suppose Subscriber-Z has subscribed only to 2G services and not 3G services. Now, Subscriber-Z moves to the overlapping region where both 2G and 3G services are available and attempts to access the 3G service. In this case, the network will send the aforementioned reject cause: “no suitable cells are found in this location area.”

This reject cause from the network tells the MS that it may register with LA3, which provides 2G services, but not with LA5/LA6, which provide 3G services. Therefore, the mobile will register with LA3.

Important Note: The network sends this message only when other LAs are available to provide service to the mobile station.

Other LAU Reject Causes

• PLMN Not Found
• PLMN Not Allowed
• Location Area (LA) Not Allowed
• Roaming Not Allowed
• No Suitable Cells in this LA