Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1998-09-25
2003-10-21
Marcelo, Melvin (Department: 2731)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S354000
Reexamination Certificate
active
06636502
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method, a switching device, a telecommunication system and a terminal station, in particular for a GSM-based General Packet Radio Service system (GPRS), that allow a subscriber station to select a predetermined network of several packet data networks (PDNs) connected to a gateway GPRS support node (GGSN). The packet data networks can be any kind of packet data networks or Internet Service Providers (ISPs).
BACKGROUND OF THE INVENTION
The standardization of the GSM General Packet Radio Service (GPRS) is currently in progress at the European Telecommunication Standards Institute (ETSI). GPRS is a new GSM-service that provides actual packet radio access for mobile GSM users. According to the GPRS system radio resources are reserved only when there is something to send (due to the packet nature of this system) and the same radio resource is shared by all mobile stations in a cell, providing effective use of the scarce resources. GPRS facilitates a variety of applications, such as telemetry, train control systems, interactive data access, charging systems and Internet browsing using WorldWideWeb.
Contrary to the circuit switched nature of the GSM network, the operation of GPRS is adapted to offer a connection to a standard data network (using protocols such as TCP/IP, X.25 and CLNP). By contrast, the conventional GSM network was originally designed to offer only circuit switched voice sessions. The packet-orientated GPRS network infrastructure introduces new functional elements which will hereinafter be briefly described with reference to FIG.
1
.
It should be noted that still some cooperation exists between elements of the current GSM services and the new GPRS network. On the physical layer, resources can be refused and some common signaling features exist. In the same radio carrier there can be time slots reserved simultaneously for circuit-switched and GPRS use. The most optimum resource utilization is obtained through dynamic sharing between circuit-switched and GPRS channels. During the establishment of a circuit switched call, there is still enough time to pre-empt the GPRS sources for circuit-switched cells that have higher priority.
Interaction of GSM Network and GPRS Network
FIG. 1
is a simple overview of the interaction of GSM circuit switched features and elements of the GPRS packet switched system. The GPRS Support Node GSN is the main element and provides connection and interworking with various data networks, mobility management by means of the GPRS registers and of course the delivery of data packets to mobile stations GPRS-MS independently of their location. Physically, the GSN can be integrated in the mobile switching center MSC of the PLMN (Public Land Mobile Network). Alternatively it can be a separate network based on the architecture of data network routers. The user data flows between the GSN and the base station sub-system (BSS) and a signaling is exchanged between the MSC and the GSN.
Thus, the GPRS provides a bearer service from the boundary of a data network to a GPRS MS. The users of the bearer service are the public network layer software packages (such as IP, OSI CLNP and X.25). Also, GPRS-specific applications will use the GPRS service.
GPRS uses a packet mode technique to transfer high-speed and low-speed data and signaling in an efficient manner. GPRS optimizes the use of the network resources and minimizes the load on the radios system. Strict separation between the radio subsystem and network subsystem is maintained allowing the network subsystem to be reused with other radio access technologies. GPRS as such does not mandate changes to an installed MSC base.
New GPRS radio channels are defined and the allocation of these channels is flexible: From 1 to 8 radio interface time slots can be allocated per TDMA frame and time slots are shared by the active users with the up-link and down-link allocated separately. The radio interface sources can be shared dynamically between speech and data services as a function of service load and operator preference. Various radio channel coding schemes are specified to allow bit rates from 9 to more than 150 Kbyte/s per user. It is even estimated that a raw data rate of up to 200 Kbyte/s can be obtained per user.
As explained above, applications based on standard data protocols are supported and interworking is defined with IP networks and X.25 networks. Specific point-to-point and point-to-multipoint services are supported for applications such as traffic telemetric and UIC train control. GPRS also allows a short message service (SMS) transfer over the GPRS radio channels.
GPRS is designed to support from intermittent and bursty data transfers through to occasional transmission of large volumes of data. Four different Quality of Service (QoS) levels (there QoS are set initially during a PDP-context activation procedure as explained below) are supported. GPRS is designed for fast reservation to begin a transmission of packets, to 0.5 to 1 seconds. Charging will typically be based on the amount of data transferred due to the packet nature of transmission.
Terminal Stations Supporting GPRS
In GPRS three different classes of GPRS mobile stations are supported: a class-A MS can operate GPRS and other GSM services simultaneously. A class-B MS can monitor control channels for GPRS and other GSM services simultaneously, but can only operate one set of services at one time. A class-C GPRS MS can exclusively operate GPRS services.
Data Packet Transmission
Having generally set up the GPRS support nodes GSN in
FIG. 1
, of course one of the main problems in GPRS network is the routing of data packets to/from a mobile station MS. This problem can be divided into two sub-problems, namely the data packet routing and the mobility management.
Data packet routing to a mobile station MS is a problem in the GPRS network, since the mobile station's data network address typically has a static routing mechanism, while the mobile station MS can roam from one network to another. One approach for a data packet routing in a mobile environment is the concept of mobile IP. (C. Perkins (editor): “IP Mobility Support, draft ietf-mobileip-protocol-11.txt”, July 1995, Work in progress in the Internet Engineering Task Force).
Mobile IP enables the routing of IP datagrams to mobile hosts, independent of the sub-network of point of attachment. Another approach is taken in the system for cellular digital packet data (CDPD) where the routing to mobile host is handled internally by the network (CDPD Industry Input Coordinator, “Cellular Digital Packet Data System Specification”, Release 1.0, July 1993).
The standard mobile IP concept does not fit exactly in the GPRS environment because of the requirement that network protocols other than IP must also be supported. Therefore, for the routing of the data packets the structure of the telecommunication network in
FIG. 1
(comprising general GPRS nodes GSN) is constructed in a concept similar to the mobile IP concept as is shown in FIG.
2
.
GPRS Support Nodes
In
FIG. 2
, GPRS introduces two new network nodes in the GSM PLMN: The serving GPRS support node (SGSN), which is at the same hierarchical level as the MSC (Mobile Switching Center) keeps track of the individual mobile stations' location and performs security functions and access control. The SGSN is connected to the base station system with frame relay. Thus, the main functions of the SGSN are to detect new GPRS MSs in its service area, to handle a process of registering the new MSs in the GPRS registers, to sent/receive data packets to/from the GPRS MS and keep a record of the location of MSs inside of its service area. The subscription information is stored in a GPRS register where the mapping between a mobile station's identity (such as MS-ISDN or IMSI: International Mobile Station Identity) and the PSPDN address is stored. The GPRS register acts as a data base from which the SGSNs can ask whether a new MS in its area is allowed to joint the GPRS network.
The gateway GSN (GGSN)
Essigmann Kurt
Lager Per
Marcelo Melvin
Telefonaktiebolaget LM Ericsson
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