This invention relates to electronic communication systems and more particularly to packet-data communication systems.
Electronic communication systems include time-division multiple access (TDMA) systems, such as cellular radio telephone systems that comply with the GSM telecommunication standard and its enhancements, such as General Packet Radio Service (GPRS) and Enhanced Data Rates for GSM Evolution (EDGE), and code-division multiple access (CDMA) systems, such as cellular radio telephone systems that comply with the IS-95, cdma2000, and wideband CDMA (WCDMA) telecommunication standards. Electronic communication systems also include “blended” TDMA and CDMA systems, such as cellular radio telephone systems that comply with the universal mobile telecommunications system (UMTS) standard, which specifies a third generation (3G) mobile system being developed by the European Telecommunications Standards Institute (ETSI) within the International Telecommunication Union's (ITU's) IMT-2000 framework. The Third Generation Partnership Project (3GPP) promulgates specifications for UMTS, WCDMA, and GSM communication systems.
FIG. 1 depicts a cellular radio telephone system 10. A base station controller (BSC) 12 and a radio network controller (RNC) 14 control various radio network functions, including for example radio access bearer setup, diversity handover, etc. More generally, the BSC and RNC direct connections to/from mobile stations (MSs) 16 and user equipments (UEs) 18, which may be mobile telephones or other remote terminals, via the appropriate base transceiver station(s) (BTSs) and Node Bs, which communicate with each MS and UE through downlink (i.e., BTS/Node B to MS/UE) and uplink (i.e., MS/UE to BTS/Node B) channels. BSC 12 is shown coupled to BTSs 20, 22, and RNC 14 is shown coupled to Node Bs 24, 26. Each BTS/Node B serves a geographical area that can be divided into one or more cell(s). The BTSs/Node Bs are coupled to their corresponding BSC/RNC by dedicated telephone lines, optical fiber links, microwave links, etc. A BSC and its connected BTSs generally comprise a base station system (BSS), as indicated by the dashed lines in FIG. 1.
The BSC 12 and RNC 14 are connected to external networks such as the public switched telephone network (PSTN), the Internet, etc. through one or more nodes in a core network 28. As depicted in FIG. 1, the core network 28 includes a mobile switching center (MSC) 30, and packet radio service nodes, such as serving GPRS support nodes (SGSNs) 32, 34, and a gateway GPRS support node 36. Also shown in FIG. 1 is a domain name system (DNS) server 38 that is provided for internet protocol (IP) address resolution.
It will be appreciated of course that various names can be used for the devices depicted in FIG. 1, and for simplicity, the terminals 16, 18 will be commonly called UEs in this application. In general, the signal and data interface between a BSS and an MSC, which may have a co-located visitor location register (VLR), is called the “A interface”, and signal and data interface between a BSS and an SGSN is called the “Gb interface”. It will be recognized that the A interface connects the BSS to circuit-switched core network nodes and that the Gb interface connects the BSS to packet-switched core network nodes.
Today, the 3GPP standard requires a UE to derive various identifiers and other parameters from the International Mobile Subscriber Identity (IMSI), which is unique to the UE. For example, generic access to the A/Gb interfaces (GAN) and interworking wireless local area network (I-WLAN) use such identifiers and parameters. In particular, Sections 14.2, 17.2, and 17.3 of 3GPP Technical Specification (TS) 23.003 V6.14.0, Numbering, Addressing, and Identification (Release 6) (September 2007), specifies that a WLAN UE or an MS with WLAN capabilities derives from the IMSI such parameters as the home network realm for I-WLAN, the home network domain name for GAN, the provisioning GANC-SEGW identifier, and the provisioning GANC identifier. “GANC” is short for generic access network controller, and “SEGW” is short for security gateway.
The identifiers and parameters are derived by a procedure that involves examining an IMSI and identifying the digits of the Mobile Country Code (MCC) and Mobile Network Code (MNC) in order to determine the network to which the IMSI belongs. As explained in Section 2.2 of 3GPP TS 23.003 and as depicted in FIG. 2, an IMSI is not more than fifteen digits and has three parts: a 3-digit MCC that identifies uniquely the country of domicile of the mobile subscriber; a 2- or 3-digit MNC that identifies the home public land mobile network (HPLMN) of the mobile subscriber; and a mobile subscriber identification number (MSIN) that identifies the mobile subscriber within a PLMN. The MNC and MSIN constitute a national mobile subscriber identity (NMSI). As depicted in FIG. 2, the first three digits of an IMSI are always the MCC, and either the next two or the next three digits are the MNC.
Under ITU-T Recommendation E.212, The International Identification Plan for Mobile Terminals and Mobile Users, an MNC is allowed to be up to three digits, but the original GSM standard specified two-digit MNCs. Currently, some countries and regions (i.e., MCCs) use a combination of 2-digit MNCs and 3-digit MNCs. In the past, only the United States and a few other countries have used 3-digit MNCs, but that situation has changed as many other countries have decided to use 3-digit MNCs. Furthermore, looking at the 1 Nov. 2006 version of the ITU-T Recommendation E.212, the trend seems to favor 3-digit MNCs for new countries and networks.
The derivation procedure specified in 3GPP TS 23.003 for the I-WLAN and GAN identifiers uses the fact that the UE knows whether a 2- or 3-digit MNC is used in its IMSI. This is implied by the reference to 3GPP TS 31.102, Characteristics of the Universal Subscriber Identity Module (USIM) Application, in Sections 14.2; 17.2.1; and 17.3.1 of TS 23.003. According to those sections of TS 23.003, one simply takes an IMSI's first five or six digits, depending on whether a 2- or 3-digit MNC is used, and separates those digits into an MCC and an MNC. If the MNC is two digits, then a zero is added at the beginning to make it three digits.
Nevertheless, a UE does not always know whether a 2- or 3-digit MNC is used in its IMSI. The reference to TS 31.102 in the procedure specified by TS 23.003 is appropriate for UEs having universal subscriber identity modules (USIMs), but not for UEs having subscriber identity modules (SIMs). A SIM may not have information on whether a 2- or 3-digit MNC is used in the IMSI, and yet UEs having SIMs can be used for both I-WLAN and GAN. Indicating whether a 2- or 3-digit MNC is used is only an option for SIMs compliant with versions of the 3GPP specifications that are Release 99 or later.
Because such MNC information is just an option, and one that was introduced relatively recently, the fact is that many SIM implementations currently on the market do not provide this information. Many users still have the SIM that they received with their first mobile network subscriptions, and many users do not change SIMs when they get new mobile phones. Even if a user does change SIM, the new SIM provided may still not provide the necessary information, because it is just optional. Furthermore, it is important to remember that during at least the first few years of operation of both I-WLAN and GAN deployments, it can be expected that the number of SIMs would be larger than the number of USIMs.
By applying HPLMN matching criteria as described in Annex A of 3GPP TS 23.122 V6.5.0, Non-Access-Stratum Functions Related to Mobile Station (MS) in Idle Mode (Release 6) (June 2005), a UE having a SIM can determine whether a 2- or 3-digit MNC is used in its IMSI if the PLMN indicates the MCC and MNC in its broadcast channel messages. The UE first compares the MCC stored in its SIM with the broadcast MCC and determines whether they match (which indicates that the UE is under home country coverage). If so, the UE reads the third digit of the broadcast MNC. If the third digit has the hexadecimal value F, then the MNC used by the PLMN is a 2-digit MNC. Finally, the UE compares just the first two digits or three digits of the MNC stored in its SIM with the broadcast MNC. If the values match, then the HPLMN match succeeds; otherwise, the HPLMN match fails. In this way, the UE learns whether a 2- or 3-digit MNC is used in its IMSI.
European Patent Application Publication EP 1 496 716 A1 states that it describes a method of communicating a variable length MNC from a network to a mobile station. The method includes transmitting a message having first and second fields, in which the first field indicates whether the MNC is greater than a fixed length and whether the second field is included in the message.
U.S. Pat. No. 7,079,834 to Kyung et al. states that it describes a method for identifying a mobile device in a communication network by determining an identifier for the device. The identifier has one or more fields that include an MCC and an MNC.
Nevertheless, without help from a PLMN's broadcast channel messages, a UE having a SIM still cannot always know which digits of the IMSI belong to the MNC. Moreover, even if a HPLMN provides the necessary broadcast messages, the I-WLAN and GAN features allow improving indoor coverage such that it is increasingly likely that a UE does not have the possibility of receiving service from its HPLMN in the usual way. Thus, a UE having a SIM will not, in many cases, be able to determine whether a 2- or 3-digit MNC is used in its IMSI, and so such a UE will not be able to derive the identifiers/parameters needed for GAN and I-WLAN features as specified by 3GPP TS 23.003 and for enabling the UE to get network service.