In wireless communication networks the User Equipment (UE) attaches to the wireless network for services. During use, the UE can have to re-attach to the network for a variety of reasons, one reason is that the UE can receive a reject message from the network. When re-attachment is required, the user equipment issues an attach request to the wireless network.
In the 3GPP Long Term Evolution (LTE) system, attach requests are issued by the Non-Access Stratum (NAS). The NAS is the highest stratum of the control plane between the UE and the Mobility Management Entity (MME) which functions as a network control apparatus. Operation of the NAS in a LTE system is described in 3GPP TS 24.301 Version 11.4.0 (October 2012), incorporated herein by reference.
3GPP TS 24.301 allows two modes of operation for both the UE and the MME. In a first mode a Radio Resource Control (RRC) connection which is already open can be used for subsequent NAS transactions, including attach requests. In a second mode, a new RRC connection is required for each NAS transaction. However, there is no mechanism for the UE to determine whether the MME will operate in the first mode, and re-use an existing RRC connection, or the second mode, and require a new RRC connection.
Providing the UE makes the correct assumption about the mode used by the MME no problems occur. However, it has been found that when the UE makes an incorrect assumption about the mode used by the network a delay of around 10 seconds can be incurred in some circumstances.