Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1999-09-29
2004-02-03
Chin, Wellington (Department: 2664)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S466000
Reexamination Certificate
active
06687243
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is a method and apparatus that provides for interconnection of private and public cellular networks, facilitating the exchange of subscriber profile and network data between systems.
Conventional Cellular Systems
Present day cellular mobile telephone systems provide for a large and increasing demand for mobile services. Cellular systems “reuse” frequency within a group of cells to provide wireless two-way radio frequency (RF) communication to large numbers of users. Each cell covers a small geographic area and collectively a group of adjacent cells covers a larger geographic region. Each cell has a fraction of the total amount of RF spectrum available to support cellular users. Cells are of different sizes (for example, macro-cell or micro-cell) and are generally fixed in capacity. The actual shapes and sizes of cells are complex functions of the terrain, the man-made environment, the quality of communication and the user capacity required. Cells are connected to each other via land lines or microwave links and to the public-switched telephone network (PSTN) through telephone switches that are adapted for mobile communication. The switches provide for the hand-off of users from cell to cell and thus typically from frequency to frequency as mobile users move between cells.
In conventional cellular systems, each cell has a base station with RF transmitters and RF receivers co-sited for transmitting and receiving communications to and from cellular users in the cell. The base station employs forward RF frequency bands (carriers) to transmit forward channel communications to users and employs reverse RF carriers to receive reverse channel communications from users in the cell.
The forward and reverse channel communications use separate frequency bands so that simultaneous transmissions in both directions are possible. This operation is referred to as frequency division duplex (FDD) signaling. In time division duplex (TDD) signaling, the forward and reverse channels take turns using the same frequency band.
The base station in addition to providing RF connectivity to users also provides connectivity to a Mobile Services Switching Center (MSC). In a typical cellular system, one or more MSCs will be used over the covered region. Each MSC can service a number of base stations and associated cells in the cellular system and supports switching operations for routing calls between other systems (such as the PSTN) and the cellular system or for routing calls within the cellular system.
Base stations are typically controlled from the MSC by means of a Base Station Controller (BSC). The BSC assigns RF carriers to support calls, coordinates the handoff of mobile users between base stations, and monitors and reports on the status of base stations. The number of base stations controlled by a single MSC depends upon the traffic at each base station, the cost of interconnection between the MSC and the base stations, the topology of the service area and other similar factors.
A handoff between base stations occurs, for example, when a mobile user travels from a first cell to an adjacent second cell. Handoffs also occur to relieve the load on a base station that has exhausted its traffic-carrying capacity or where poor quality communication is occurring. The handoff is a communication transfer for a particular user from the base station for the first cell to the base station for the second cell. During the handoff in conventional cellular systems, there may be a transfer period of time during which the forward and reverse communications to the mobile user are severed with the base station for the first cell and are not established with the second cell.
In time division multiple access (TDMA) systems, multiple channels are defined using the same carrier. The separate channels each transmit discontinuously in bursts which are timed so as not to interfere with the other channels on that carrier. Typically, TDMA implementations also employ FDMA techniques. Carriers are reused from cell to cell in an FDMA scheme, and on each carrier, several channels are defined using TDMA methods. The Global System for Mobile Communications (GSM), PCS 1900, IS-136, and PDC standards are examples of TDMA methods in current use.
The present specification uses a GSM system for purposes of explanation but the present invention applies to any wireless system protocol.
GSM Cellular Systems
The GSM system architecture is described, for example, in detail by M. Mouly and M. -B. Pautet, The GSM System for Mobile Communications, 1992 and Mouly and M. -B. Pautet, GSM Protocol Architecture: Radio Sub-system Signaling, IEEE 41st Vehicular Technology Conference, 1991. The following sections highlight some unique aspects of GSM systems.
The GSM system provides many advanced services, including: ISDN compatible supplementary services; Global roaming among GSM networks and other network types; advanced packet data services.
GSM System Architecture
There is a very comprehensive set of GSM Specifications which define the three major components of any GSM network, namely, the Mobile Station (MS), Base Station Sub-System (BSS) and the Network Sub-System CUSS).
Base Station Subsystem (BSS)
The Base Station Subsystem (BSS) is subdivided into two main entities, the Base Transceiver Station (BTS) and the Base Station Controller (BSC). The BTS includes the radio transceivers that define the radio cell and supports the radio (Um) interface link to the mobile station. The BTS further supports the defined channel coding, encryption and speech coding functions. The BTS interfaces to the BSC via the Abis-interface.
The Base Station Controller (BSC) manages the radio resources of multiple BTSs. The BSC controls all of the functions related to the radio network, including the allocation and release of radio resources and control of radio interface hand-overs. The BSC interfaces to the MSC via the A-interface.
Network Subsystem
The network subsystem (NSS) comprises four components these are, the Mobile services Switching Center (MSC), Home Location Register (HLR), Visitor Location Register (VLR), Authentication Centre (AuC) and the Equipment Identity Register (EIR).
The main part of the network subsystem (NSS) is provided by the Mobile services Switching Center (MSC). The MSC provides the ability to track the mobile user, switch calls to/from the user to the PSTN/ISDN/PLMN (public land mobile network) and maintain contact with the mobile user via radio handovers.
The GSM PLMN (GSM public land mobile network) contains two database functions related to the mobility of the user these are the Home Location Register (HLR) and the Visited Location Register (VLR).
The Home Location Register (HLR) is used by the operator to maintain data on all their subscribers. The subscriber data includes both fixed data, such as International Mobile Subscriber Identity (IMSI), subscriber MSISDN number and selected supplementary services, and dynamic data such as whereabouts of the mobile user and current settings for any supplementary services. Whenever a mobile users roams into a new Visitor Location Register (VLR) area the HLR downloads the subscriber data to the VLR. The HLR is also required to deal with mobile terminating calls by routing the call to the correct VLR for further processing.
The Visitor Location Register (VLR) is used as a local cache to store the subscriber data near the current location of the mobile user. Once the VLR has downloaded the subscriber data the mobile user can begin to use the services provided by the network. The process of downloading the user data and establishing a presence in a particular location is called roaming.
In order to prevent fraudulent use of the network the GSM PLMN also contains two further databases the Authentication Centre (AUC) and the Equipment Identity Register (EIR).
The Authentication Center (AUC) is a maintained in a secure environment since it contains the network authentication algorithms. The network uses this database to obtain data that is used to “challeng
Long Paul Jan
Sayers Ian Leslie
Chin Wellington
Cisco Technology Inc.
Hamilton Brook Smith & Reynolds P.C.
Pham Brenda
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