United States Patent (19)
`Ahopelto et al.
`
`54) PACKET RADIOSYSTEM AND METHODS
`FOR A PROTOCOL-INDEPENDENT
`ROUTING OF A DATA PACKET IN PACKET
`RADIO NETWORKS
`
`75 Inventors: Juha-Pekka Ahopelto, Helsinki;
`Hannu Kari, Veikkola, both of Finland
`73 Assignee: Nokia Telecommunications Oy, Espoo,
`Finland
`21 Appl. No.:
`08/875,464
`22 PCT Filed:
`Jan. 8, 1996
`86 PCT No.:
`PCT/F96/00019
`S371 Date:
`Jul. 9, 1997
`S 102(e) Date: Jul. 9, 1997
`87 PCT Pub. No.: WO96/21983
`PCT Pub. Date:Jul.18, 1997
`Foreign Application Priority Data
`30
`Jan. 10, 1995
`FI
`Finland .................................... 95O116
`(51) Int. Cl." ........................................................ H04J 3/16
`52 U.S. Cl. ............................................. 370/338; 370/401
`58 Field of Search ..................................... 370/389, 401,
`370/402,403, 404, 464, 465, 466, 503,
`350, 338, 310, 312,352,392,397, 351,
`353; 379/90.01, 93.01, 93.33, 88.13, 88.2,
`88.24, 142, 210, 211, 214; 455/403, 432,
`517, 516, 524,525
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`USOO597OO59A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,970,059
`Oct. 19, 1999
`
`5,313,465 5/1994 Perlman et al. ........................ 370/401
`5,325,362 6/1994 Aziz ...................
`... 379/60
`5,590,133 12/1996 Billstrom et al.
`370/349
`5,717,689 2/1998 Ayanoglu ................................ 370/471
`5,793,762 8/1998 Panners et al. ......................... 370/389
`FOREIGN PATENT DOCUMENTS
`522 773 1/1993 European Pat. Off..
`692897 1/1996 European Pat. Off..
`Primary Examiner Dang Ton
`Attorney, Agent, or Firm- Pillsbury, Madison & Sutro, LLP
`57
`ABSTRACT
`The present invention relates to a protocol-independent
`routing of data packets between a mobile Station of a packet
`radio network and a party(Host) connected to an external
`network. In the invention, a data packet of an extraneous
`protocol (IPX) is transferred through a packet radio network
`using a Second protocol as encapsulated in a data packet
`according to the Second protocol. The transferring packet
`radio network does not thus need to understand the protocol
`of the transferred extraneous data packet or to be able to
`interpret the content of the data packet. A data packet
`network is connected to other packet radio networks, data
`networks or the backbone network between packet data
`networks via a gateway node(GPRS GSN), which uses the
`network-internal protocol towards the dedicated packet net
`work and the protocol of each network towards other
`networks. When a data packet is transferred via a gateway
`node from a network into another network, the data packet
`is encapsulated in a packet according to the protocol of the
`new network. When the encapsulated data packet arrives in
`a node which Supports the protocol of the encapsulated data
`packet, the encapsulation is stripped away and the data
`packet is routed forward according to the protocol of the data
`packet.
`
`4,755,992 7/1988 Albal ....................................... 370/389
`5,251,205 10/1993 Callon et al. ........................... 370/401
`
`11 Claims, 13 Drawing Sheets
`
`
`
`
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`GPRS
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`GPRS
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`GPRS GSN
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`WF
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`MscBSCBTs
`
`ROUTER
`-
`LOCAL
`NETWORK
`
`HOST -
`
`Ex.1005
`APPLE INC. / Page 1 of 21
`
`

`

`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 1 of 13
`
`5,970,059
`
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`Ex.1005
`APPLEINC./ Page 2 of 21
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`Ex.1005
`APPLE INC. / Page 2 of 21
`
`
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`

`

`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 2 of 13
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`5,970,059
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`Ex.1005
`APPLEINC./ Page 3 of 21
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`Ex.1005
`APPLE INC. / Page 3 of 21
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`

`

`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 3 of 13
`
`5,970,059
`
`APPLICATION IN
`MOBILE STATION
`
`MOBILE STATION - - -
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`Ex.1005
`APPLE INC. / Page 4 of 21
`
`

`

`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 4 of 13
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`5,970,059
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`Ex.1005
`APPLE INC. / Page 5 of 21
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`

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`U.S. Patent
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`Oct. 19, 1999
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`Ex.1005
`APPLE INC. / Page 6 of 21
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`

`

`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 6 of 13
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`5,970,059
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`Ex.1005
`APPLEINC./ Page 7 of 21
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`Ex.1005
`APPLE INC. / Page 7 of 21
`
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`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 7 of 13
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`5,970,059
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`Ex.1005
`APPLEINC./ Page 8 of 21
`
`Ex.1005
`APPLE INC. / Page 8 of 21
`
`

`

`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 8 of 13
`
`5,970,059
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`Ex.1005
`APPLEINC./ Page 9 of 21
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`Ex.1005
`APPLE INC. / Page 9 of 21
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`
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`

`

`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 9 of 13
`
`5,970,059
`
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`APPLICATION IN
`MOBILE STATION
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`MOBILE STATION
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`Ex.1005
`APPLE INC. / Page 10 of 21
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 10 of 13
`
`5,970,059
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`Ex.1005
`APPLEINC./ Page 11 of 21
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`Ex.1005
`APPLE INC. / Page 11 of 21
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`
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`

`

`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 11 of 13
`
`5,970,059
`
`Ex.1005
`APPLE INC. / Page 12 of 21
`
`

`

`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 12 of 13
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`5,970,059
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`Ex.1005
`APPLEINC./ Page 13 of 21
`
`Ex.1005
`APPLE INC. / Page 13 of 21
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`
`

`

`U.S. Patent
`
`Oct. 19, 1999
`
`Sheet 13 of 13
`
`5,970,059
`
`Ex.1005
`APPLE INC. / Page 14 of 21
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`

`

`5,970,059
`
`1
`PACKET RADIO SYSTEMAND METHODS
`FOR A PROTOCOL-INDEPENDENT
`ROUTING OF A DATA PACKET IN PACKET
`RADIO NETWORKS
`
`This application is the national phase of international
`application PCT/FI96/00019, filed Jan. 8, 1996 which des
`ignated the U.S.
`FIELD OF THE INVENTION
`The present invention relates to routing data packets
`independently of protocol between a mobile Station of a
`packet radio network and a party connected to an external
`network.
`
`15
`
`2
`SUMMARY OF THE INVENTION
`The object of the present invention is to route data packets
`of different protocols in a packet radio System.
`This is achieved with a packet radio network comprising
`a protocol-independent routing of data packets between a
`mobile Station and a party connected to an external network.
`In packet radio network of the invention in the internal
`routing of the packet radio network, a data packet received
`from a mobile Station or an external network is encapsulated
`according to the internal protocol of the packet radio net
`work.
`The present invention also relates to a method for a
`protocol-independent routing of packets in a packet radio
`network between a mobile Station and a party connected to
`an external network. The method by
`encapsulating data packets received from the mobile
`Station or from the external network, according to the
`protocol of the packet radio network,
`routing an encapsulated data packet in the packet radio
`network, according to the protocol of the packet radio
`network, and
`Stripping the encapsulation according to the protocol of
`the packet radio network away, when the data packet is
`transferred from the packet radio network to the external
`network having a different protocol than the packet radio
`network.
`The invention also relates to a method for routing a
`mobile terminated data packet from the Sending party via an
`external network when the mobile Station is located in its
`home packet radio network.
`The invention also relates to a method for routing a
`mobile originated data packet via an external data network
`to the receiving party when the mobile Subscriber is located
`in his home packet radio network or is visiting a packet radio
`network which Supports the protocol of the receiving party.
`The invention also relates to a method for routing a
`mobile terminated data packet when the mobile Station is
`located outside the home packet radio network, and routing
`between packet radio networks is required.
`The invention also relates to a method for routing a
`mobile originated data packet via an external data network
`to the receiving party when the mobile Station is located
`outside the home packet radio network in an extraneous
`packet radio network which does not Support the first
`protocol used by the mobile Station.
`The invention also relates to a method for routing a
`mobile originated data packet via a Second packet radio
`network and an external data network to the receiving party
`when the mobile Station is located outside the home packet
`radio network in an extraneous packet radio network which
`does not Support the first protocol used by the mobile Station.
`In the invention, a data packet of an extraneous protocol
`is transferred through a packet radio network using another
`protocol encapsulated in a data packet according to this
`other protocol. The transferring packet radio network does
`not need to understand the protocol of the transferred
`extraneous data packet or to be able to interpret the contents
`of the data packet. A data packet network is connected to
`other data packet networks, data networks, or the backbone
`network between packet data networkS via a gateway node,
`which uses the network-internal protocol towards the dedi
`cated packet network and the protocol of each network
`towards other networks. When a data packet is transferred
`via a gateway node from a network into another network, the
`data packet is encapsulated in a packet according to the
`
`25
`
`BACKGROUND OF THE INVENTION
`Mobile communication systems have been developed
`because there has been a need to allow people to move away
`from fixed telephone terminals without losing their ability to
`be reached. While the use of different data transmission
`Services in offices has increased, different data Services have
`also been introduced into mobile communication Systems.
`Portable computers enable efficient data processing
`whereever a user moves. Mobile communication networks,
`provide a user with efficient access network to actual data
`networks for mobile data transmission. In order to do this,
`different new data Services are designed for existing and
`future mobile communication networkS. Digital mobile
`communication Systems, Such as the pan-European mobile
`communication system GSM (Global System for Mobile
`Communication), Support particularly well mobile data
`transmission. General Packet Radio Service (GPRS) is a
`new service in the GSM System, and it is one the items of
`the standardization work of the GSM phase 2+ in ETSI
`(European Telecommunication Standard Institute). The
`GPRS operational environment consists of one or more
`Sub-network Service areas, which are interconnected by a
`GPRS backbone network. A sub-network comprises a num
`ber of packet data Service nodes, which are referred to as
`GPRS Support nodes (or agents) in this context, each packet
`40
`data service node being connected to a GSM mobile com
`munication network So that it is capable of providing packet
`data Service for mobile data terminal equipment via Several
`base Stations, i.e. cells. The intermediate mobile communi
`cation network provides circuit Switched or packet Switched
`data transmission between a Support node and mobile data
`terminal equipment. Different Sub-networks are connected
`to an external data network, Such as a public Switched packet
`data network (PSPDN). The GPRS service thus produces
`packet data transmission between mobile data terminal
`50
`equipment and external data networks with a, a GSM
`network acting as an access network. The GPRS service
`network operates almost independently of the GSM net
`work. One of the requirements of the GPRS service is that
`it must operate with external PSPDNs of different types, for
`instance, with Internet or X.25 networks. In other words, the
`GPRS service and a GSM network should be capable of
`Serving all users, irrespective of which type of data networks
`they want to register in via the GSM network. This means
`that the GSM network and the GPRS service have to support
`and handle different network addressing and data packet
`formats. This handling of data packets also compriseS rout
`ing in a packet radio network. In addition, users should be
`able to roam from a GPRS home network into an extraneous
`GPRS network, the backbone network of the operator of
`which may support a different protocol (for instance, CLNP)
`than the home network (for instance, X.25).
`
`35
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`45
`
`55
`
`60
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`Ex.1005
`APPLE INC. / Page 15 of 21
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`

`3
`protocol of the new network. If the data packet was encap
`Sulated also in the previous network, this previous encap
`Sulation is Stripped away before a new encapsulation. When
`the encapsulated data packet arrives in a node which Sup
`ports the protocol of the encapsulated data packet, the
`encapsulation is Stripped away and the data packet is routed
`forward according to the protocol of the data packet. The
`Support node or the home node which sends the encapsu
`lated packet to the gateway node does not need to know
`whether the gateway node Supports the protocol of the
`encapsulated packet or not.
`According to the invention, a mobile terminated or a
`mobile originated data packet can be routed through one or
`more packet radio networks or a network connecting them
`without any of the networks having to Support the protocol
`used by the mobile Station. The data packet is merely
`re-encapsulated in each network that uses an extraneous
`protocol. The invention enables the implementation of
`packet radio networks of different operators and that of
`networks connecting them by protocols differing from one
`another, without preventing, however, the roaming of a
`mobile station in networks of different operators and the
`routing of data packets.
`The home Support node of the home packet data network
`of a mobile Station is provided with a database, which maps
`together the network address of the mobile Station, for
`instance, in an IP network, X.25 network, CLNP network or
`in a number of these simultaneously, and the roaming
`number of the mobile Station. The roaming number may
`consist of the identifier of that Support node within the area
`of which the mobile Station is located, and of the temporary,
`link-level identifier of the mobile station, which is received
`from Said Support node in connection with the registration or
`location updating of the mobile Station. The roaming number
`is independent of the backbone network protocol used by the
`operator. The mobile Station may have Several protocols or
`Several addresses with the same protocol. The invention also
`enables So-called Virtual mobile Stations, one mobile Station
`is used by a number of users, each of which has a dedicated
`network address as mapped in the roaming number of the
`Same mobile Station, whereby the mobile Station “appears'
`as Several mobile Stations. Due to the encapsulation proce
`dure of the invention, a data packet arriving from an external
`network can always be routed, independently of the protocol
`of the packet, to the home Support node of the mobile
`station, from where it can then be forwarded to the mobile
`Station by means of the roaming number, which is found by
`means of the mobile Station network address contained by
`the data packet. The mapping between the mobile Station
`network address (for instance an IP address, X.25 address
`and/or CLNP address) and the mobile station roaming
`number is dynamic, because the roaming number changes
`every time the mobile Station moves from the area of one
`Support node into the area of another Support node.
`By the invention, it is also possible to Shorten the routing
`of data packets originating from a mobile Station which is
`located in an extraneous network.
`BRIEF DESCRIPTION OF THE FIGURES
`In the following, the invention will be described by means
`of preferred embodiments with reference to the accompa
`nying drawing, in which
`FIG. 1 shows two GPRS networks according to the
`invention and data networks associated with them;
`FIG. 2 is a block diagram and
`FIG. 3 is a signaling diagram which illustrate the routing
`of a mobile terminated packet according to the invention;
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`FIG. 4 is a block diagram and
`FIG. 5 is a signal diagram which illustrate the routing of
`a mobile originated packet according to the invention;
`FIG. 6 is a block diagram and
`FIG. 7 is a signaling diagram which illustrate the routing
`of a mobile terminated packet according to the invention
`when the mobile station is located in an extraneous GPRS
`network;
`FIG. 8 is a block diagram and
`FIG. 9 is a signaling diagram which illustrate the routing
`of a mobile originated packet according to the invention
`when the mobile station is located in an extraneous GPRS
`network which Supports the protocol of the mobile Station;
`FIG. 10 is a block diagram and
`FIG. 11 is a Signaling diagram which illustrate the routing
`of a mobile originated packet according to the invention
`when the mobile station is located in an extraneous GPRS
`network, and the packet is forwarded via the home network;
`FIG. 12 is a block diagram and
`FIG. 13 is a Signaling diagram which illustrate the routing
`of a mobile originated packet according to the invention
`when the mobile Station is located in an extraneous network,
`and the packet is routed via a third network.
`DETAILED DESCRIPTION OF THE
`CURRENTLY PREFERRED EMBODIMENTS
`The present invention can be used for routing data packets
`in packet radio Systems of different types. The invention is
`particularly well Suited to be used for implementing the
`general packet radio Service GPRS in the pan-European
`digital mobile communication system GSM (Global System
`for Mobile Communication) or in corresponding mobile
`communication systems, such as DCS1800 and PCN
`(Personal Communication Network). In the following, the
`preferred embodiments of the invention will be described by
`means of a GPRS packet radio network consisting of the
`GPRS service and the GSM system, without restricting the
`invention to Such a particular packet radio System, however.
`FIG. 1 illustrates a telecommunication system which
`includes GPRS packet radio networks, local networks, data
`networks, etc. FIG. 1 shows two GPRS operators, operator
`1 and operator 2, each of which has two GPRS Support nodes
`(GPRS SN), one GPRS home support node (GPRS HSN), a
`GPRS gateway support node (GPRS GSN) and interworking
`functions (IWF). These different support nodes GPRS SN,
`GPRS HSN, and GPRS GSN are interconnected by the
`intra-operator backbone network.
`Each support node GPRS SN controls a packet data
`Service within the area of one or more cells in a cellular
`packet radio network. For this, each support node GPRS SN
`is connected to a certain local part of the GSM mobile
`System. This connection is typically provided in a mobile
`eXchange, but in Some situations it may be advantageous to
`provide the connection directly in the base Station System
`BSS, i.e., in a base station controller BSC or one of the base
`stations BTS. The mobile station MS located in a cell
`communicates over the radio interface with a base Station
`BTS and further through the mobile communication network
`with the support node GPRSSN to the service area of which
`the cell belongs. In principle, the mobile communication
`network existing between the Support node GPRS SN and
`the mobile station MS merely delivers packets between
`these two. In order to do this, the mobile communication
`network may provide either a circuit Switched connection or
`packet Switched data packet transmission between the
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`mobile station MS and the serving support node GPRS SN.
`An example of a circuit Switched connection between a
`mobile Station MS and a Support node (agent) is provided in
`Finnish Patent Application 934115. An example of packet
`Switched data transmission between a mobile station MS and
`a Support node (agent) is provided in Finnish Patent Appli
`cation 940314. However, it should be noticed that the mobile
`communication network provides merely a physical connec
`tion between the mobile station MS and the support node
`GPRS SN, and the exact operation and structure thereof do
`not have essential significance as regards the invention. AS
`for more detailed description of the GSM system, reference
`is made, however, to ETSI/GSM specifications and to “The
`GSM System for Mobile Communications”, M. Mouly and
`M. Pautet, Palaiseau, France, 1992, ISBN:2-9507190-07-7.
`A typical mobile Station constituting a mobile data ter
`minal equipment consists of a mobile station 3 (MS) in a
`mobile communication network, and a portable computer 4
`connected to the data interface of said mobile station MS.
`The mobile station 3 may be, for instance, a Nokia 2110,
`which is manufactured by Nokia Mobile Phones Ltd., Fin
`land. By means of a PCMCIA-type Nokia Cellular Datacard,
`which is manufactured by Nokia Mobile Phones Ltd., the
`mobile station can be connected to any portable PC which is
`provided with a PCMCIA card location. The PCMCIA card
`thus provides the PC with an access point, which Supports
`the protocol of the telecommunication application used in
`the PC 4, for instance CCITT X.25 or Internet Protocol IP.
`Alternatively, the mobile Station may directly provide an
`access point which Supports the protocol used by the appli
`cation of the PC4. Furthermore, it is possible that the mobile
`station 3 and the PC 4 are integrated into one unit within
`which the application program is provided with an access
`point Supporting the protocol used by it.
`A home support node GPRS HSN is used for storing the
`location information of GPRS mobile stations and for
`authenticating GPRS mobile stations. The GPRS HSN also
`routes mobile terminated (MT) data packets. The GPRS
`HSN also includes a database, which maps together the
`network address of a mobile station, for instance in an IP
`network, X.25 network, CLNP network or in a number of
`these simultaneously, and the GPRS roaming number
`GPRS-MRNB of the mobile station. The GPRS roaming
`number may consist of the identifier of that GPRS support
`node GPRS SN within the area of which the mobile station
`is currently located, and of the temporary, link-level iden
`tifier TLLI of the mobile station, which is received from said
`support node GPRS SN in connection with the registration
`or location updating of the mobile Station. The mapping
`between the mobile station network address (for instance an
`IP address, X.25 address and/or CLNP address) and the
`mobile station roaming number GPRS-MRNB is dynamic,
`because the roaming number changes every time the mobile
`station moves from the area of one support node GPRS SN
`into the area of another support node. When the mobile
`55
`Station moves from one cell into another within the area of
`one support node GPRSSN, it is only necessary to perform
`a location updating in the support node GPRSSN, and there
`is no need to inform the home Support node GPRS HSN of
`the change in location. When the mobile station moves from
`a cell of one support node GPRS SN into a cell of another
`GPRSSN within the area of the same operator, an updating
`is also performed in the home support node GPRS HSN to
`store the identifier of the new visited support node and the
`new roaming number GPRS-MRNB of the mobile station.
`When the mobile station moves from a cell located within
`the area of one operator into a cell located within the area of
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`another operator, the new roaming number GPRS-MRNB of
`the mobile station and the new identifier of the visited
`support node are updated in the home support node GPRS
`HSN of the mobile station. The registration process of the
`mobile Station is thus in principle the same as within the area
`of one operator.
`The intra-operator backbone network, which intercon
`nects the equipments GPRS HSN, GPRS SN and GPRS
`GSN of the operator, may be implemented, for instance, with
`a local network. It should be noticed that it is also possible
`to implement a GPRS network of an operator without an
`intra-operator backbone network, for instance, by imple
`menting all aspects in a Single computer, but this modifica
`tion does not cause any changes in the manner the routing
`protocols of the invention behave.
`A GPRS gateway support node GPRS GSN connects the
`operator to the GPRS systems of the other operators of the
`GPRS network and to data networks, Such as an inter
`operator backbone network, IP network, or X.25 network.
`An interworking function IWF is provided between the
`gateway support node GPRS GSN and the other networks.
`It should be noticed that a GPRS network can be imple
`mented without the gateway support node GPRS GSN, but
`in such a case all support nodes GPRSSN and home support
`nodes GPRS HSN should use the same protocol towards the
`inter-operator backbone network as the gateway Support
`nodes GPRS GSN of the other operators.
`An inter-operator backbone network is a network via
`which the gateway support nodes GPRS GSN of different
`operators can communicate with one another. This commu
`nication is required to Support GPRS roaming between
`different GPRS networks. This inter-operator backbone net
`work can be implemented by using for instance X.25, IP,
`CLNP, or other networks, as long as the gateway Support
`nodes GPRS GSN of both parties use the same protocols
`towards the inter-operator backbone network.
`For instance, if the inter-operator backbone network is an
`IP network, the operator 1 may internally use an X.25
`network (in the intra-operator backbone network of the
`operator 1), and the operator 2 may internally use an CLNP
`network (in the intra-operator backbone network of the
`operator 2). The gateway support node GPRS GSN of the
`operator 1 should thus use the X.25 protocol locally and the
`IP protocol towards the inter-operator backbone network
`over the interworking function IWF. Correspondingly, the
`gateway Support node GPRS GSN of the operator 2 should
`use the CLNP protocol locally and the IP protocol over the
`interworking function IWF.
`FIG. 1 also shows a host computer Host, which is con
`nected to a local network, which is further connected via a
`router to an IPX network. A similar connection can also be
`constructed in other data networks, Such as an X.25 network.
`In the following, the present invention will be described
`by an example, assuming that the host computer Host desires
`to send messages to a GPRS mobile station and receive
`messages therefrom by using IPX protocols. IPX protocol is
`used only as an example in this context, and the routing
`events described below are implemented in the same manner
`also when IP, X.25, or CLNP protocols are used as end-to
`end protocols. In this example, it is also assumed that the
`intra-operator backbone network of the operator 1 is based
`on a X.25 network and that the intra-operator backbone
`network of the operator 2 is based on a CLNP network,
`whereas the inter-operator backbone network is based on the
`IP protocol. The purpose of this configuration is merely to
`illustrate how the routing of a message can be handled
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`despite the fact that different network protocols are used in
`different networks.
`Routing packets within the GPRS network of one operator
`The routing procedure of the invention when a mobile
`station is located in its GPRS home network, and inter
`operator routing is not required is described. In the routing
`example presented below, IPX data packets are used, but a
`Similar routing mechanism can also be used in connection
`with other protocols, such as IP, X.25, and CLNP.
`Mobile terminated (MT) packets
`FIG. 2 illustrates the routing of mobile terminated (MT)
`packets when the host computer Host sends an IPX packet
`to a mobile station of the operator 1 by using an IPX
`message. The routing event is also shown in FIG. 3 as a
`Signaling diagram. The numbering used in the following
`description corresponds to that used in FIGS. 2 and 3.
`1. The host computer Host sends a data packet, which
`contains the IPX address MS-IPX of the mobile station, the
`IPX address Host-IPX of the host computer and data, by
`using normal IPX message Structures. The data packet
`contains the IPX address of the mobile station. The data
`packet is forwarded via the local network, router, IPX data
`network, and interworking function IWF to the gateway
`support node GPRS GSN of the operator 1 by using normal
`IPX routing methods and the IPX address of the mobile
`Station.
`2. The GPRS GSN encapsulates the received IPX packet
`in an X.25 packet, which is used in the intra-operator
`backbone network of the operator 1. The X.25 packet is
`provided with the address GPRS-HSN1-X.25 of the home
`support node of the operator 1 and with the address GPRS
`GSN1-X.25 of the gateway support node. The GPRS GSN
`forwards the X.25 packet to the home Support node GPRS
`HSN via the intra-operator backbone network of the opera
`tor 1. The encapsulation format may be, for instance, the
`same as the one used in Point-to-Point Protocol PPP, which
`will be described in more detail below. (PPP) also contains
`an identification field, which can be used for determining the
`protocol type of the encapsulated data packet (IPX, in this
`case). The GPRS GSN forwards the X.25 packet to the home
`support node GPRS HSN via the intra-operator backbone
`network of the operator 1.
`3. The GPRS HSN receives the X.25 packet and checks
`the actual receiver, i.e., the IPX address MS-IPX of the
`mobile station. The GPRS HSN finds the GPRS roaming
`number GPRS-MRNB of the mobile Station in its internal
`database by means of the IPX address MS-IPX of the mobile
`Station. It