GB2282510A

GB2282510A - A data network

Info

Publication number: GB2282510A
Application number: GB9318523A
Authority: GB
Inventors: Paul Dominic Baker; William Neil Robinson
Original assignee: Motorola Ltd
Current assignee: Motorola Solutions UK Ltd
Priority date: 1993-09-07
Filing date: 1993-09-07
Publication date: 1995-04-05
Anticipated expiration: 2013-09-07
Also published as: GB9318523D0; GB2282510B; DE4431355A1; FR2712130A1; FR2712130B1

Description

1) 2282510 1 A Data Network

Field of the Invention

This invention relates to a X.25 data nework, that is to say a data network which complies with CCITT standard X.25 as that standard is defined at the filing date of this patent application.

Background to the Invention

Within mobile radio networks, one of the main problems is keeping track of roaming radio users. This is normally referred to as "mobility management".

Within many mobile radio networks, the movement of radio units is monitored by the use of "registration" mechanisms. A "registration" mechanism is basically a method by which the roaming radio unit can tell the network infrastructure that it wishes to use that network services. The network infrastructure can then confirm 'or deny service depending upon the subscription status of the requesting radio unit, as well as determining the location of the radio user.

Registration mechanisms can also be used to provide information to a network infrastructure about equipment connected to a particular radio unit. For example, in TETRA (Trans European Trunked RAdio), a Connection Oriented Packet Switched data (CONP) protocol has been defined which uses a separate addressing domain (X.121) to that used to identify the individual radio units (ITSI's).

It has been proposed in the paper RES6.4 (93)125 of the European Telecommunications Standards Institute entitled "Addressing Issues" that a mobile terminal unit or Data Communications Unit (DCU) is informed of the binding between a TETRA ITSI address and a CONP X.121 address. When this feature is implemented and a Data Terminal Equipment (DTE) or a X.25 network is connected to a radio unit that wants to use the 1 2 CONP service, the radio unit will inform the network infrastructure of the binding between the X. 121 address and the radio unit's ITSI by including both addresses in a registration request. This will enable the network infrastructure, by means of a subscriber database (or some other similar mechanism), to route incoming CONP data packets to their X. 121 destinations via the connected radio units (ITSI's).

However, there is a limitation with fixed networks such as X.25 in that each X.121 address is preassigned to a fixed DCE from a central point, similar to a telephone network. In this fixed network case, all incoming X.25 packets can be routed to their destination by using the preassigned X. 121 allocation table. The X25 standard does not provide any mechanism for a DTE to inform a Data Communication Equipment (DCE) of it's X.121 address when it is connected or when it is disconnected. A DCE is only informed of the DTE address when a call request is made.

Accordingly there is a need for a protocol that will allow a radio unit to inform the network infrastructure of the binding between the X. 121 address and the radio unit's ITSI.

Summarv of the Invention According to a first aspect of the invention, an X.25 network is provided comprising a data terminal an infrastructure, wherein the data terminal is arranged to generate a data packet comprising a packet type identifier which is a registration type identifier, a terminal address field and a further field not specific to the network, characterized in that a unique code is included in the further field and that the infrastructure is arranged to recognise this code as a reconfiguration command and to Perform a reconfiguration of data routing for the terminal identified in the address field to route data for the terminal identified in the address field to that radio.

According to a second aspect of the invention, an X.25 35 network is provided comprising a data terminal and a switching 3 centre, wherein the data terminal is arranged to generate a data packet comprising a packet type identifier and a terminal address field, characterized in that the packet type identifier is a unique code and the switching center is arranged to recognise this unique 5 code as a reconfiguration command and to perform a reconfiguration of data routing to route data for that terminal to that radio.

The invention provides a mechanism by which, within a mobile radio network, a user can change the radio unit to which a piece of X.25 equipment is attached. The network infrastructure is immediately informed of the change and any incoming X.25 packets destined for that equipment are be routed to the new radio unit to which the X.25 piece of equipment is connected.

Brief Descri13tion of the Drawings Fig. 1 shows an overall view of a system in accordance with the invention.

Figs 2 and 3 show a registration request packet and a registration confirmation packet respectively in accordance with the first aspect of the invention.

Figs 4 and 5 show a registration request packet and a registration confirmation packet respectively in accordance with the second aspect of the invention; and Fig. 6 shows a sequence of events in the course of operation of a system in accordance with the invention.

Glossary of Abbreviations CCITT International Consultative Committee for Telegrahy and Telecommunications CONP Connection Orientated Packet Switched Data Protocol DCU Data Communication Unit DTE Data Terminal Equipment DXE Data Switch Equipment 1 4 ETSI ISO ITSI TETRA European Telecommunications Standards Institute International Standard Organisation Individual TETRA Subscriber Identity Trans European Trunked Radio, an ETSI standard for digital trunked radio Detailed description of the Preferred Embodiment

Referring to Fig. 1, a combined packet switched data network and trunked radio network is shown, that is to say a trunked TETRA radio network which supports X.25 data switching.

- By way of example the system is shown as having two items of data terminal equipment (DTEs) 10 and 11 physically connected to two data communication units (DCUs) 12 and 13 by means of standard connectors 14 and 15. The DCUs 12 and 13 have ITSI identification numbers A and B respectively and communicate over a radio interface either with each other via a base station 20 or through the base station 20 to a land line 21. In each case, communication is via a switching controller 22 which comprises I/0 interfaces 23 and 24, a central control unit 25 and a data base look-up memory 26. The data base 26 is shown in the enlarged view in dotted outline as correlating X. 121 addresses with ITSI registration numbers.

The operation is as follows. Considering, for example, the case where DTE 10 wishes to send a message to DTE 11. The message is presented to DCU 12 which has the ITSI identification number A. DCU 12 identifies itself with this identification number to the base station 20, which allocates a channel to DCU 12. DGU 12 forwards the message, together with its destination address, which in this case is X.121=2, to the base station 20, which presents the message and its address to the switching controller 22. Central controller unit 25 performs a look-up operation in data base 26 and identifies that the ITSI which corresponds to X. 121 address 2 is "B". Equally, the data base 26 could identify that the X.121 address corresponds to an address on 1 the land line 21. Switching controller 22 routes the packet back to base station 20 for retransmission to DCU 13, which receives the packet and forwards the contents to DTE 11. Thus the operation is complete.

Consider now the case where DTE 10 is disconnected from DCU 12 and connected to DCU 13 and DTE 11 is disconnected from DCU 13 and connected to DCU 12.

Each of the DTEs 10 and 11 performs a re-registration operation which involves sending a special control packet (described below) to switching controller 22. Central control unit 25 now reconfigures the data in database 26 such that ITSI B corresponds to X. 121 address I and ITIS A corresponds to X.121 address 2.

When DTE 10 now initiates the sending of a message, it is DCU 13 that requests the channel and forwards the message to base station 20 for routing by switching controller 22. Switching controller 22 now identifies that the destination address X.121=2 corresponds to DCU 12 having ITSI=A and accordingly switching controller 22 forwards the message via base station 20 to DCU 12 which forwards the message contents to DTE 11.

There now follows a description setting out two alternative ways for a DTE to inform a DCU to which it is connected, of its X.25 address. Each of these represents an enhancement to the CCITT X.25 standard (ISO 8208, ISO 8878, ISO 8348).

The first way for a DTE to inform a DCU to which it is connected, of its X.25 address is to use existing X.25 "registration request" and "registration confirmation" packets for sub-network registration/deregistration.

Within the X.25 (ISO 8208) standard, two registration packets have been defined ("registration request" and "registration confirmation"). These packets are an optional facility agreed to for a period of time by the DTE and DCU. If the on-line registration facility is agreed to, optional user facilities can be negotiated at any time between the DTE and DCU. However, in ISO 8208 (section 16) it states that a registration marker (contained within 1 6 the registration packets) is used to distinguish between X.25 registration facilities and non-X.25 registration facilities. A registration marker of 16 zero bits indicates a non-X.25 registration facility as defined in ISO 8208. 5 This proposal defines a non-X.25 registration facility for subnetwork registration. The format of the X.25 registration request and registration confirmation packets, which include a non-X.25 sub network registration/de-registration facility are shown in Figs. 2 and 3. This arrangement has the advantage of using an existing X. 25 packet type and making use of otherwise unused space in the packet. It does not require redefining the standard and does not use up any of the limited packet type identifiers reserved for future use.

As can be seen from Fig. 2, the registration request packet comprises a general format identifier 100 in the first 8-bit byte and twelve zeros completing the first and second bytes. The third byte 102 is a packet type identifier. This contains the identifier 11110011 and identifies the packet as a registration request. This is followed by fields 103 and 104 for the DTE address length and the length of a DXE address respectively. These are followed by a field 105 which contains the DTE and DXE addresses themselves and this is followed by a field 106 containing the total length of the packet. This field indicates that the packet extends to further bytes 107-109 ' these bytes may contain X.25 registration facilities 107 such as level of service indicators. Following field 107 is a registration marker 108 of sixteen zeros indicating the start of non X.25 registration facilities. Finally, and of significance regarding the present invention, there is a unique code 109 indicated as AAAAAAAA, which indicates that the registration request is a special registration request requesting reconfiguring of the network to update the recorded location of this particular DTE address.

Fig. 3 shows a corresponding confirmation packet having the packet type identifier 11110111 indicating confirmation of j 7 registration and having the same unique code AAAAAAAA in the non-X.25 facilities field.

As an alternative to the packets of Figs. 2 and 3, the packets of Figs. 4 and 5 can be used. In this arrangement, two new X.25 packets are defined specifically for the purpose of sub-network registration. In the packet of Fig. 4, the packet type identifier field 102 contains a unique code identifying the packet as a registration and reconfiguration packet (and confirmation thereof in the case of Fig. 5). Examples of suitable codes are 11100110 and 11100111.

The codes should be selected from the 256 possible alternatives, excluding the already assigned codes shown in Table 1.

Table 1

CALL REQUEST CALL ACCEPTED CLEAR REQUEST CLEAR CONFIRMATION PACKETTYPE OCTET 3 BITS:

FROM DTE TO DXE FROMI)XETODTE 87654321 Call setup and Call Clearing INCOMING CALL 00001011 CALL CONNECTED 00001111 CLEAR INDICATION 00010011 CLEAR CONFIRMATION Data and Interrupt DATA DATA INTERRUPT INTERRUPT INTERRUPT INTERRUPT CONFIRMATION CONFIRMATION Flow Control and Reset RECEIVE READY RECEIVE READY modulo 8 modulo 8 modulo 128 modulo 128 RECEIVE NOT RECEIVE NOT READY modulo 8 modulo 128 REJECT READY modulo 8 modulo 128 REJECT 00010111 XXXXXXX0 00100011 00100111 XXX00001 00000001 XXX00101 00000101 j 8 modulo 8 modulo 128 RESET REQUEST RESET CONFIRMATION modulo 8 XXX01001 modulo 128 00001001 RESET INDICATION 00011011 RESET CONFIRMATION 00011111 Restart RESTART REQUEST RESTART 11111011 INDICATION RESTART RESTART CONFIRMATION CONFIRMATION 11111111 Diagnoistic D1AGNOISTIC D1AGNOISTIC 11110001 Registration REGISTRATION REGISTRATION REQUEST REQUEST 11110011 REGISTRATION REGISTRATION CONFIRMATION CONFIRMATION 11110111 In Figs. 6 and 7 show two possible sub-network registration scenarios. Note that these senerios demonstrate that X.25 sub network registration will work with most types of sub network, whether it be a fixed or mobile radio network.

Referring to Fig. 6, X.25 DTE equipment is disconnected from one radio unit and connected to another (step 100). Upon connection to the new radio unit, the X.25 DTE equipment sends a "sub-network registration request" packet to that radio unit including it's address (step 101). In step 102, the radio unit (re)registers passing it's own identity and the address of the attached X.25 equipment, using its local registration procedures.

In step 104 the radio network confirms the local registration request and updates it's local subscriber database with the new X.25 equipment address. Finally (step 104) the radio unit sends a "sub-network registration confirmation" packet to the X.25 DTE equipment.

1 9 A similar sequence of events occurs in the case of using X.25 sub-network registration with a fixed network, except that a fixed DCU takes the place of the radio unit and a fixed network management unit takes the place of the radio network.

In the case of de-registration, the following steps occur. A user requests that the X.25 equipment be disconnected from his DCE. The X.25 equipment sends a "sub-network deregistration"packet to the DCE including its address. The DCE deregisters the X. 121 address binding with its own identity using its local de-registration procedures. The radio network management may then confirm the local de-registration request and update it's local subscriber database. The radio unit may then send a "subnetwork de- registration confirmation" packet to the X.25 DTE equipment, enabling the user to then disconnect the equipment. Note that the confirmation procedure could be optional.

The registration and deregistration method described can be initiated in a number of ways by appropriate means. Two examples of such means are as follows.

The user or application can initiate the process, either directly or indirectly initiating the above functions. For example, the user decides to switch off the registered terminal equipment, selects this function and the terminal equipment deregisters with the network prior to finally powering down. The user now disconnects the terminal equipment and moves it to a different gateway into the network where the terminal is connected. The user decides to switch on the terminal equipment and selects the registration and reconfiguration function. The terminal equipment registers with the network.

As an alternative (referring to Fig. 1), the terminal equipment 10 can be connected to the network equipment (DCU 12) via a physical connector 14. This connector has a control device 16 which can be in either of two states, TRUE or FALSE. It is only possible to perform the action of connecting or disconnecting the terminal equipment 10 to or from the network equipment 12 if the control device 16 is in the FALSE position. When the user 1 performs the action of connecting the terminal equipment 10 to the network equipment 12, the user connects the network equipment 12 to the terminal equipment using the connector 14 and sets the control device to TRUE. This change from FALSE to TRUE is detected by the terminal equipment 10 and the transition to TRUE is used to initiate the registration process. In order to disconnect the terminal equipment, the user first changes the control device 16 from the TRUE state to the FALSE state. This change from TRUE to FALSE is detected by the terminal equipment 10 and the transition to FALSE is used to initiate the deregistration process, which is completed before the user is able to perform the action of detaching the terminal equipment from the network.

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Claims

1. An X.25 network comprising a data terminal and infrastructure equipment, wherein the data terminal is arranged to generate a data packet comprising a packet type identifier which is a registration type identifier, a terminal address field and a further field not specific to the network, characterized in that a unique code is included in the further field and that the infrastructure equipment is arranged to recognise this code as a reconfiguration command and to perform a reconfiguration of data routing for the terminal identified in the address field to route data for the terminal identified in the address field to that terminal.

2. An X.25 network is provided comprising a data terminal and a switching centre, wherein the data terminal is arranged to generate a data packet comprising a packet type identifier and a terminal address field, characterized in that the packet type identifier is a unique code and the switching center is arranged to recognise this unique code as a reconfiguration command and to perform a reconfiguration of data routing to route data for the terminal identified in the address field to that terminal.

3. A method of reconfiguring an X.25 data network comprising a data terminal and infrastructure equipment, the method comprising the steps of generating, at a data terminal, a data packet comprising a registration packet type identifier, a terminal address field and a further field not specific to the network which comprises a unique code included in the further field; recognising this code within the infrastructure equipment as a reconfiguration command and performing a reconfiguration of the network for subsequent data routing for the terminal identified in the address field to route data for the terminal identified in the address field to that terminal.

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4. A method of reconfiguring an X.25 data network comprising a data terminal and infrastructure equipment, the method comprising the steps of generating, at a data terminal, a data packet comprising a packet type identifier which is a unique code and a terminal address field; recognising the unique code within the infrastructure equipment as a reconfiguration command and performing a reconfiguration of the network for subsequent data routing for the terminal identified in the address field to route data for the terminal identified in the address field to that terminal.

5. A combined mobile radio and packet switched data network comprising:

identification with base routing the data a packet data switching centre, a number of radio base stations connected to the switching centre; first and second mobile radios arranged for communication with the base stations, and a data terminal having means for disconnection from a the first radio and connection to the second radio: the switching centre comprising, means for receiving a data packet including an identifying a destination radio for the packet, look-up means for correlating radio identifications stations, switching means responsive to the look-up means for to the base station which correlates with the destination identification, and automatic reconfiguring means for routing data 35 destined for the data q 1 13 terminal to the first radio when the data terminal is connected to the terminal is connected first radio and to the second radio when the data to the second radio, characterised in that the second radio comprises connector means (16) for indicating new connection of the data terminal to the second radio the terminal comprises means responsive to the connector means for generating and sending to the switching centre a data packet including an identification and a connection command and the switching centre is arranged to perform the reconfiguring when the command is received.