1. Field of the Invention
The invention generally relates to handling abnormal interrupts during an attach procedure, and more particularly, to a system, apparatuses, and methods for handling abnormal interrupts, including tracking area updates, lower layer failures, and guard timer expiries, during an attach procedure in a mobile communication system.
2. Description of the Related Art
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In a typical mobile communication system, a mobile user equipment (UE) communicates with one or more service networks via radio access networks of the service networks. A UE comprises various types of equipment such as a mobile telephone (also known as cellular or cell phone), a laptop computer with wireless communications capability, a personal digital assistant (PDA) etc. UE may be portable, handheld, pocket-sized, or installed in a vehicle etc. . . . and communicate voice and/or data signals with a radio access network.
A universal mobile telecommunications system (UMTS) is a third generation mobile communication system that has evolved from the Global System for Mobile communications (GSM) system. The UMTS is a European standard which aims to provide better mobile communication services based on the GSM core network and wideband code division multiple access (W-CDMA) technology. Although UMTS delivers high data transfer rates, wireless data usage is expected to increase significantly over the next few years. For this reason, concepts for UMTS Long Term Evolution (LTE) have been proposed, with the objective to further improve UMTS to achieve high-data-rates, low-latency and packet-optimized radio access technology. The improved UMTS technology is called Evolved Universal Terrestrial Radio Access (E-UTRA) and the system employing the E-UTRA technology is called an Evolved Packet System (EPS).
Consider a wireless mobile device, generally referred to as a UE, which complies with the 3GPP specifications for the E-UTRA protocol. The 3GPP TS 24.301 specification, v.1.0.0, referred to herein as the 24.301 specification, addresses the subject of the Non-Access-Stratum (NAS) protocol requirements for the EPS and the UE. The 3GPP TS 36.304 specification, v.8.3.0, is referred to herein as the 36.304 specification.
After the UE is powered on and connects to the EPS, it will need to perform an attach procedure to register itself to the EPS so that it can start a packet data session over the EPS. As illustrated in FIG. 1, the attach procedure starts by the UE sending an ATTACH REQUEST message to the EPS (step S101). The ATTACH REQUEST message may be sent combined with a PDN CONNECTIVITY REQUEST message indicating that the UE wishes to start a packet data session with the EPS. When the EPS receives the ATTACH REQUEST message, it authenticates the UE, checks if the UE is authorized to have access to packet data services, and performs a security mode control procedure to activate the encryption on the subsequent messages in the connection (step S102). If none of the checks fails, the EPS accepts the attach request by sending an ATTACH ACCEPT message to the UE. The ATTACH ACCEPT message may be sent combined with an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message if the PDN CONNECTIVITY REQUEST message is found in the ATTACH REQUEST message (step S103). The ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message is used to activate the default bearer for the packet data session. When the UE receives the ATTACH ACCEPT message from the EPS, it corresponds to the EPS with an ATTACH COMPLETE message to acknowledge that it has received the ATTACH ACCEPT message (step S105). The ATTACH COMPLETE message may be sent combined with an ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message indicating that the UE has accepted the configuration of the default bearer from the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message. Lastly, the EPS waits for the ATTACH COMPLETE message combined with the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message. If the ATTACH COMPLETE message is received, the attach procedure ends successfully. Otherwise, the EPS will resend the ATTACH ACCEPT message to the UE.
However, in accordance with clause 5.5.1.2.7 of the 24.301 specification, when some abnormal interrupts occur (step 104), for instance, lower layer failure, the guard timer T3450 of the attach procedure expiring for 5 times, the tracking area of the UE is changed, etc., before the ATTACH COMPLETE message is received, the EPS does not resend the ATTACH ACCEPT message. That is to say, the ESM sub-layer in the UE is in the BEARER CONTEXT ACTIVE state while the ESM sub-layer in the EPS remains in the BEARER CONTEXT ACTIVE PENDING state. Thus, as the attach procedure is initiated for a packet data session, failing to receive the ATTACH COMPLETE message, combined with the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message, results in inconsistency between the EPS Session Management (ESM) sub-layer state in the UE and in the EPS. The inconsistency between the ESM sub-layer state in the UE and in the EPS may cause malfunction of the packet data session.