Design of a Routing Mechanism to Provide Multiple Mobile Network Service on a Single SIM Card Boobalan. P, Krishna. P, Udhayakumar. P, Santhosh. A Abstract-The current scenario in mobile networks is that we make use of one network or utmost two networks at a particular point of time using a single mobile unit. The goal of this paper is to utilize the benefits of any number of networks (Airtel, BSNL, etc.,) using a single SIM card. This is achieved by storing the user details in all the subscribed mobile network provider s HLRs. Normally a user details will be stored only in the HLR of the subscribed network provider. Hence the mobile station can access this one and only network by scanning and accessing that particular frequency. But when this user detail is stored in more than one network provider s HLR, the mobile station can scan and access all the respective networks where the user details are being stored. This principle is used for providing multiple mobile services using a single SIM mobile system. 4-digit Personal Identification Number (PIN). In order to unlock a card, the user must enter the PIN. If a PIN is entered incorrectly three times in a row, the card blocks itself and cannot be used. It can only be unlocked with an 8-digit Personal Unblocking Key (PUK), which is also stored on the SIM card. Index Terms: BSC, GMSC, GSM, IMEI, MSC I. GSM NETWORK ARCHITECTURE A. Mobile Station (MS) The Mobile Station (MS) is made up of two components: Mobile Equipment (ME) refers to the physical phone itself. The phone must be able to operate on a GSM network. Older phones operated on a single band only. The new phones are dual-band, triple-band, and even quad-band capability. A quad-band phone has the technical capability to operate on any GSM network worldwide. Each phone is uniquely identified by the International Mobile Equipment Identity (IMEI) number. This number is burned into the phone by the manufacturer. The IMEI can usually be found by removing the battery of the phone and reading the panel in the battery well. It is possible to change the IMEI on a phone to reflect a different IMEI. This is known as IMEI spoofing or IMEI cloning. This is usually done on stolen phones. The average user does not have the technical ability to change a phone's IMEI. Subscriber Identity Module (SIM) - The SIM is a small smart card that is inserted into the phone and carries information specific to the subscriber, such as IMSI, TMSI, Ki (used for encryption), Service Provider Name (SPN), and Local Area Identity (LAI). The SIM can also store phone numbers (MSISDN) dialled and received, the KC (used for encryption), phone books, and data for other applications. A SIM card can be removed from one phone, inserted into another GSM capable phone and the subscriber will get the same service as always. Each SIM card is protected by a Fig. 1. Base Transceiver Station (BTS) [1] Base Transceiver Station (BTS) - The BTS is the Mobile Station's access point to the network. It is responsible for carrying out radio communications between the network and the MS. It handles speech encoding, encryption, multiplexing (TDMA), and modulation/demodulation of the radio signals. It is also capable of frequency hopping. A BTS will have between 1 and 16 Transceivers (TRX), depending on the geography and user demand of an area. Each TRX represents one ARFCN. One BTS usually cover a single 120 degree sector of an area. Usually a tower with 3 BTSs will accommodate all 360 degrees around the tower. However, depending on geography and user demand of an area, a cell may be divided up into one or two sectors, or a cell may be serviced by several BTSs with redundant sector coverage. A BTS is assigned a Cell Identity. The cell identity is 16-bit number (double octet) that identifies that cell in a particular Location Area. The cell identity is part of the Cell Global Identification (CGI), which is discussed in the section about the Visitor Location Register (VLR). Fig. 2 120 Sector [1] 99
Base Station Controller (BSC) - The BSC controls multiple BTSs. It handles allocation of radio channels, frequency administration, power and signal measurements from the MS, and handovers from one BTS to another (if both BTSs are controlled by the same BSC). A BSC also functions as a funneler. It reduces the number of connections to the Mobile Switching Center (MSC) and allows for higher capacity connections to the MSC. Fig. 5 Mobile Switching Center [1] The interface between the BSC and the MSC is known as the A Interface Gateway Mobile Switching Center (GMSC) There is another important type of MSC, called a Gateway Mobile Switching Center (GMSC). The GMSC functions as a gateway between two networks. If a mobile subscriber wants to place a call to a regular landline, then the call would have to go through a GMSC in order to switch to the Public Switched Telephone Network (PSTN). Fig. 3 Base Station Controller [1] A BSC may be collocated with a BTS or it may be geographically separate. It may even be collocated with the Mobile Switching Center (MSC). The Base Transceiver Station (BTS) and the Base Station Controller (BSC) together make up the Base Station System (BSS). Fig. 6 Gateway Mobile Switching Center [1] For example, if a subscriber on the Cingular network wants to call a subscriber on a T-Mobile network, the call would have to go through a GMSC. Fig. 4 Base Station System [1] Mobile Switching Center (MSC) - The MSC is the heart of the GSM network. It handles call routing, call setup, and basic switching functions. An MSC handles multiple BSCs and also interfaces with other MSC's and registers. It also handles inner-bsc handcuffs as well as coordinates with other MSC's for inter-msc handoffs. Fig. 7 Connections between Two Networks [1] Home Location Register (HLR) - The HLR is a large database that permanently stores data about subscribers. The HLR maintains subscriber-specific information such as the 100
MSISDN, IMSI, and current location of the MS, roaming restrictions, and subscriber supplemental features. There is logically only one HLR in any given network, but generally speaking each network has multiple physical HLRs spread out across its network. Cell Global Identification (CGI) The CGI is a number that uniquely identifies a specific cell within its location area, network, and country. The CGI is composed of the MCC, MNC, LAI, and Cell Identity (CI) Visitor Location Register (VLR) - The VLR is a database that contains a subset of the information located on the HLR. It contains similar information as the HLR, but only for subscribers currently in its Location Area. There is a VLR for every Location Area. The VLR reduces the overall number of queries to the HLR and thus reduces network traffic. VLRs are often identified by the Location Area Code (LAC) for the area they service. Fig. 8 Visitor Location Register [1] Table 2 cell Global Identity [1] The VLR also has one other very important function: the assignment of a Temporary Mobile Subscriber Identity (TMSI). TMSIs are assigned by the VLR to a MS as it comes into its Location Area. TMSIs are unique to a VLR. TMSIs are only allocated when in cipher mode. Equipment Identity Register (EIR) - The EIR is a database that keeps track of handsets on the network using the IMEI. There is only one EIR per network. It is composed of three lists: the white list, the gray list, and the blacklist. The blacklist is a list if IMEIs that are to be denied service by the network for some reason. Reasons include the IMEI being listed as stolen or cloned or if the handset is malfunctioning or doesn't have the technical capabilities to operate on the network. The gray list is a list of IMEIs that are to be monitored for suspicious activity. This could include handsets that are behaving oddly or not performing as the network expects it to. The white list is an unpopulated list. That means if an IMEI is not on the black list or on the gray list, then it is considered good and is "on the white list". The interface between the MSC and the EIR is called the F Interface. [1] Location Area Code (LAC) A LAC is a fixed-length code (two octets) that identifies a location area within the network. Each Location Area is serviced by a VLR, so we can think of a Location Area Code (LAC) being assigned to a VLR. Location Area Identity (LAI) An LAI is a globally unique number that identifies the country, network provider, and LAC of any given Location Area, which coincides with a VLR. It is composed of the Mobile Country Code (MCC), the Mobile Network Code (MNC), and the Location Area Code (LAC). The MCC and the MNC are the same numbers used when forming the IMSI. Table 1 Location Area Identities (LAI) [1] Fig. 9 Equipment Identity Register [1] The authentication Center (AuC) - The AuC handles the authentication and encryption tasks for the network. The Auc stores the Ki for each IMSI on the network. It also generates crypto variables such as the RAND, SRES, and KC. Although 101
it is not required, the AuC is normally physically collocated with the HLR. Fig. 10 Authentication Center [1] There is one last interface that we haven't discussed. The interface between the HLR and a GMSC is called the C Interface. You will see it in the full network diagram below. This completes the introduction to the network architecture of a GSM network. Below you will find a network diagram with all of the components as well as the names of all of the interfaces. Fig. 11 Full GSM Network [1] II. EXISTING SYSTEM A smart space, such as smart sensor rooms, an office, or simply an area, requires a smart telephony network for an effective voice communication between users. Nowadays, modern Private Branch Exchange (PBX) system does not only provide telephone exchange, but also supports many heterogeneous telephony networks and provides many other useful functions as well. Despite its powerfulness, PBX still cannot achieve a basic requirement for a smart space: It cannot adapt its surroundings automatically, i.e. people still need to make the call forwarding setting manually. They proposed a system with an algorithm named 2D location-aware for tracking a person in a smart space. According to the ever-changing environment, the system performs an on-the-fly configuration to provide a dynamic telephony network. In other words, they aimed to make all the telephones in the network available to every user in the smart space for receiving his phone calls without any manual call forwarding settings. Most people might have such kind of experience: try to get in touch with someone in a company by dialling its general phone number plus his extension number. After a few ring tones, the caller may only hear a voice message: Sorry, the person you are trying to reach is not available now. Please try again later or press 0 to leave a message. After a while, the caller may be lucky enough to reach the staff by calling again and again. This indeed requires too much time to find a person. No doubt, this problem can be easily resolved by providing every staff a wireless or cordless phone and the staff could be reached under most circumstances. Apparently, however, this solution brings out many other concerns as well, such as equipment costs, battery lifetime, interference and handover, etc. A smart space [3], such as smart sensor rooms, simply an office or even a whole building, is supposed to detect all the users in the space [4] and serve them. One of the important services they believe is the smart telephony network for an effective voice communication. Nowadays, modern Private Branch Exchange (PBX) [5] system does not only provide telephone exchange, but also supports many heterogeneous telephony networks and provides many other useful functions as well. Despite its powerfulness, PBX still cannot achieve a basic requirement for a smart space: It cannot adapt its surroundings automatically, i.e. people still need to make the call forwarding setting manually. Hence they proposed a different solution to serve the same purpose. With their solution, their user would no longer miss a single call simply because all the telephones in the system belong to him/her. Their proposed system will assign each employee in the company a unique extension number, say 168 for Employee A. Obviously, while he/she is working on his/her working station, its phone s extension number is "168". Yet, he/she may leave from his/her desk for a conference room to have a discussion with Employee B. Their system would then automatically instruct PBX or IP-PBX switch to reassign a new extension number 168 to the phone nearest to Employee A, i.e. the phone in the conference room. Similarly, their system would execute the same procedure for Employee B too. Thus, the system will forward all their incoming calls to the phone in the conference room and therefore, these 2 employees, even away from their working stations, will not miss a single call throughout their discussion. If no fixed phone is located around them, the system will forward their incoming calls to their cellular phones automatically. Their system has two advantages comparing with other call forwarding systems and those are: users do not need to know any telephone number or activate the call forwarding service; and their system can be installed in some particular places where mobile phone is forbidden, such as a hospital.[2] III. PROPOSED SYSTEM The basic concept of this paper is that we become the subscriber of a mobile network to which we want to communicate. That is if we want to call a BSNL mobile system then we become a BSNL subscriber for that point of time until the communication is completed. Later if we want 102
to communicate an Airtel mobile system then we become the subscriber of Airtel for that communication instant. At present, a mobile station (MS) can receive and scan all the frequencies of radio frequency spectrum allocated for cellular networks. The cellular frequencies (BSNL, Airtel, and other similar mobile networks) can be received and scanned by a mobile station but cannot access all the frequencies. A mobile station can access only the frequency of the network provider to which it is subscribed. That is, the subscribed network provider will have the user details in the HLR which is attached to the MSC, which will make the mobile station as a subscribed unit under that mobile network so that the mobile unit can access its frequency. So we propose that if the user detail of a particular mobile system is present in multiple HLRs of different mobile networks, then that particular mobile system can get access to the mobile networks where its details are stored in the respective HLRs. The below figure 3 shows an example of the proposed concept. At this point of time, we assume that the user detail of a mobile system is present in the HLRs of two network providers (BSNL and Airtel). number of mobile networks. The drawbacks of the existing system and benefits of this proposed concept are listed below. IV. DRAWBACKS OF EXISTING SYSTEM A. Customer s Side: Network coverage Cost of services (Call, SMS, data, etc.) Need for dual/triple SIM mobile phones B. Mobile phone manufacturer s Side: Huge investments in R&D for developing dual/triple SIM phones High end single SIM mobile (iphone 4s) is affordable, but not preferred by corporate people C. Network provider s Side: Loss of customers because of one of their bad service V. BENEFITS OF PROPOSED CONCEPT A. Customer s Side: In case of emergency Choosing the cheapest service Can use the existing single SIM mobile phone B. Mobile phone manufacturer s Side: Can invest a lot in developing the User Interface and other software areas C. Network provider s Side: Gain of customers because of one of their best service Fig. 12 Proposed Model Let us assume that a mobile system is in a cell which consists of BTS (towers) of both BSNL and Airtel mobile networks. Case 1: (If we want to communicate to BSNL customer) The mobile system is made to scan the frequency spectrum to find and get access to BSNL network as we are going to communicate to a BSNL customer. Now the mobile system will get access to the BSNL network as the user detail of this mobile unit (9943912041) exists in the HLR of BSNL s MSC. Now we can communicate with any BSNL customer at a considerably low cost compared to other network providers as this communication is considered to be within the BSNL s network. Case 2: (If we want to communicate to Airtel customer) The mobile system is made to scan the frequency spectrum to find and get access to Airtel network as we are going to communicate to an Airtel customer. Now the mobile system will get access to the Airtel network as the user detail of this mobile unit (9943912041) exists in the HLR of Airtel s MSC. Now we can communicate with any Airtel customer at a considerably low cost compared to other network providers as this communication is considered to be within the Airtel s network. This proposed concept can be extended to any REFERENCES [1] http://gnuradio.org/redmine/projects/gnuradio/wiki/openbtsne twork_architecture [2] Heng-Chih Huang, Yueh-Min Huang, And Kuan- Chieh Chiu, A Location-Aware Call Forwarding Manager System For A Smart Telephony Network Of The Smart Space, International Journal On Smart Sensing And Intelligent Systems, Vol. 2, No. 1, March 2009 [3] Gu, H.-L., Shi, Y.-C., Xu, G.-Y., He, W.-S., Zhang, B.-P., SLAP: a Location-aware Software Infrastructure for Smart Space, SEUS 2005. Third IEEE Workshop on (2005), 25-38 [4] Liyanage C De Silva, Audiovisual Sensing Of Human Movements For Home-Care And Security In A Smart Environment, International Journal On Smart Sensing and Intelligent Systems, Volume. 1, Issue 1, (2008), 220-245 [5] Du, A.T., Private PBX networks: Cost effective communications solutions, 3rd AFRICON Conference (1992). 637 640. AUTHOR S PROFILE Boobalan P B.Tech., M.Tech., MISTE, Ph.D Assistant Professor, Department of Information Technology, 103
Pondicherry Engineering College Publications: ISSN: 2277-3754 1. "Enhancement of Path-Based QoS Provisioning for Optical Burst Switching Networks", IJITE ISSN: 2229-7367, Vol 3, 2012 2. "Improving QoS Aware Active Queue Management Scheme for Multimedia Services", IJITE ISSN: 2229-7367, Vol 3, 2012 3. "Delayed Reservation Differential Service for Multimedia Traffic in Optical Burst Switched Networks", IJCSE ISSN : 0975-3397, Vol 3, 2011 4. "Controlling Burst Loss Ratio in OBS Using Feedback Control and Dynamic Techniques", IJCSE ISSN : 0975-3397, Vol 3, 2011 Research work: 1. "Modelling A Multimedia Traffic For Burst Assembly", 2009 2. "Improving Transmission Speed of Multimedia Data Traffic over Optical Burst Swiching Networks", 2010 3. "Improving QoS for Multimedia Traffic over Optical Burst Switching Networks", 2012 4. "Improving TCP Performance Over OBS Networks using Multi-Queue Burst Assembly Scheme", 2009 Krishna P Final year, B.Tech, Information Technology, Pondicherry Engineering College Udhayakumar P Final year, B.Tech, Information Technology, Pondicherry Engineering College Santhosh A Final year, B.Tech, Information Technology, Pondicherry Engineering College 104