WO2014206251A1

WO2014206251A1 - Inter-system handover method, apparatus, and network system

Info

Publication number: WO2014206251A1
Application number: PCT/CN2014/080474
Authority: WO
Inventors: 武绍芸; 任厚平; 姜志健
Original assignee: 华为技术有限公司
Priority date: 2013-06-27
Filing date: 2014-06-23
Publication date: 2014-12-31
Also published as: CN103338489A; CN103338489B

Abstract

Embodiments of the present invention provide an inter-system handover method, apparatus, and network system. The method comprises: a first core network element in a first system obtaining subscription information of a user equipment (UE) in a second system; and the first core network element sending a forward relocation request message to a second core network element in the second system, so that the second core network element determines subscription information corresponding to a context identifier according to the context identifier, the forward relocation request message comprising the context identifier, and a value of the context identifier being a value of a context identifier in the subscription information of the UE in the second system. The technical solutions of the present invention can improve a success rate of handover of the UE between the first system and the second system.

Description

Inter-system switching method, device and network system

TECHNICAL FIELD Embodiments of the present invention relate to communication technologies, and in particular, to an inter-system handover method, apparatus, and network system. Background technique

Before the long-term evolution (LTE) technology matures, a large number of general packet radio services (GPRS) networks have been deployed around the world, including GSM/EDG.E radio access networks (GSM). / EDGE Radio Access Network (GERAN), GERAN uses Global System of Mobile Communication (GSM) access technology (ie 2G), UMTS Universal Terrestrial Radio Access Network (UTRAN) For wireless networks, UTRAN uses the Universal Mobile Telecommunications System (UMTS) access technology (g卩3G) and the GPRS core network. The introduction of the LTE-EPS network is a gradual process, including the evolved UMTS terrestrial radio access network (Evolved Universal Terrestrial Radio Access Network) wireless network (using LTE access technology, ie 4G) ) and the Evolved Packet System (EPS) core network. Operators cannot build a pure, isolated EPS network at a glance. So 2/3G and 4G networks will exist for a long time. Accordingly, end user switching between 2/3G and 4G networks will become frequent.

In the case where UMTS (3G) and LTE (4G) coexist, the UE performs services on the LTE network, when the coverage (signal) of the UMTS network is superior to the LTE network, or the eNodeB (eNodeB) is heavily loaded. If the UE moves from the LTE coverage area to the UMTS coverage area, the eNodeB triggers the UE to switch to the UMTS network.

However, the user equipment (User Equipment, referred to as the user equipment acquired by the core network element of the second system exists in the handover process between the first system (for example, the 4G system) and the second system (for example, the 2/3G system). UE) The problem of inaccurate subscription information in the second system. SUMMARY OF THE INVENTION Embodiments of the present invention provide an inter-system handover method, apparatus, and network system, which are used to implement accurate acquisition of a core network element of a second system by a UE when the UE switches between the first system and the second system. The subscription information of the APN in the second system, thereby improving the success rate of the UE switching between the first system and the second system.

A first aspect of the present invention provides an inter-system handover method, including:

The first core network element in the first system acquires the subscription information of the user equipment UE in the second system;

The first core network element sends a forward relocation request message to the second core network element in the second system, where the forward relocation request message includes a context identifier, and the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system, so that the second core network element determines the subscription information corresponding to the context identifier according to the context identifier.

In a first possible implementation manner of the first aspect, the first core network element in the first system obtains the subscription information of the user equipment UE in the second system, including:

The first core network element sends a location update request message to the second subscription information storage network element, where the second subscription information storage network element is a network element that stores the UE subscription information in the second system;

Receiving, by the first core network element, the first insertion subscription data message sent by the second subscription information storage network element, where the first insertion subscription data message includes the subscription information of the UE in the second system .

According to a first possible implementation of the first aspect, in a second possible implementation of the first aspect,

After the first core network element receives the insertion subscription data message sent by the second subscription information storage network element, the method further includes:

Transmitting, by the first core network element, the first insertion subscription data response message to the second subscription information storage network element;

The first core network element receives the location update response message sent by the second subscription information storage network element.

With reference to the first aspect or the first or second possible implementation manner of the first aspect, in a third possible implementation manner of the first aspect, the first core network element receives the second subscription information After the first insertion subscription data message sent by the storage network element, the method further includes:

Receiving, by the first core network element, a second insertion subscription data message sent by the second subscription information storage network element;

Updating, by the first core network element, the UE stored in the first core network element according to the subscription information of the UE in the second system in the second insertion subscription data message The contract information in the second system;

The first core network element sends a second insertion subscription data response message to the second subscription information storage network element.

With reference to the first aspect or the first to third possible implementation manners of the first aspect, in a fourth possible implementation manner of the first aspect, the first system is a 2G system or a 3G system, where the The second system is a 4G system; or the first system is a 4G system, and the second system is a 2G system or a 3G system.

A second aspect of the present invention provides an inter-system handover method, including:

The second subscription information storage network element receives the location update request message sent by the first core network element in the first system, where the second subscription information storage network element is a network element that stores the user equipment UE subscription information in the second system;

The second subscription information storage network element sends a first insertion subscription data message to the first core network element, where the first insertion subscription data message includes the subscription information of the UE in the second system, so that The first core network element sends a forward relocation request message to the second core network element in the second system, where the forward relocation request message includes a context identifier, and the value of the context identifier is a value of a context identifier in the subscription information of the UE in the second system.

In a first possible implementation manner of the second aspect, after the sending, by the second subscription information storage network element, the first insertion subscription data message to the first core network element, the method further includes:

Receiving, by the second subscription information storage network element, a first insertion subscription data response message sent by the first core network element;

The second subscription information storage network element sends a location update response message to the first core network element.

With reference to the second aspect, or any one of the first possible implementation manners of the second aspect, in a second possible implementation manner of the second aspect, the second subscription information storage network element is to the first core After the network element sends the first insertion subscription data message, the network element further includes: The second subscription information storage network element sends a second insertion subscription data message to the first core network element, so that the first core network element is configured according to the second insertion subscription data message.

The subscription information of the UE in the second system is updated, and the subscription information of the UE in the second system stored in the first core network element is updated;

The second subscription information storage network element receives the second insertion subscription data response message sent by the first core network element.

With reference to the second aspect, or any one of the first or second possible implementation manners of the second aspect, in a third possible implementation manner of the second aspect, the second subscription information storage network element receives the first After the location update request message sent by a core network element, the method further includes:

The second subscription information storage network element sends a cancel location registration message to the third core network network element, where the third core network element is attached to the UE in the second system, except the second core. a core network element other than the network element, so that the third core network element deletes the locally stored context information of the UE;

The second subscription information storage network element receives the cancel location registration response message sent by the third core network element.

With reference to the second aspect, or any one of the first to the third possible implementation manners of the second aspect, in a fourth possible implementation manner of the second aspect, the first system is a 2G system or a 3G system The second system is a 4G system; or the first system is a 4G system, and the second system is a 2G system or a 3G system.

A third aspect of the present invention provides an inter-system handover method, including:

The second core network element in the second system receives the forward relocation request message sent by the first core network element in the first system, where the forward relocation request message includes a context identifier, where the context identifier is a value of a value of a context identifier in the subscription information of the user equipment UE in the second system;

The second core network element determines the subscription information corresponding to the context identifier according to the context identifier.

A fourth aspect of the present invention provides an inter-system switching apparatus, including:

An obtaining module, configured to acquire subscription information of the user equipment UE in the second system;

a sending module, configured to send a forward relocation request message to the second core network element in the second system, where the forward relocation request message includes a context identifier, and the value of the context identifier And a value of the context identifier in the subscription information of the UE in the second system, where the second core network element determines the subscription information corresponding to the context identifier according to the context identifier.

In a first possible implementation manner of the fourth aspect, the acquiring module is specifically configured to: send a location update request message to the second subscription information storage network element, where the second subscription information storage network element is a second system a network element that stores UE subscription information;

Receiving a first insertion subscription data message sent by the second subscription information storage network element, where the first insertion subscription data message includes subscription information of the UE in the second system.

According to the first possible implementation manner of the fourth aspect, in a second possible implementation manner of the fourth aspect, the acquiring module is further configured to receive an insertion subscription sent by the second subscription information storage network element After the data message, sending a first insertion subscription data response message to the second subscription information storage network element;

Receiving a location update response message sent by the second subscription information storage network element.

With reference to the fourth aspect or the first or second possible implementation manner of the fourth aspect, in a third possible implementation manner of the fourth aspect, the acquiring module is further configured to receive the second subscription After receiving the first insertion subscription data message sent by the information storage network element, receiving the second insertion subscription data message sent by the second subscription information storage network element;

Updating, according to the subscription information of the UE in the second system in the second insertion subscription data message, the subscription of the UE stored in the first core network element in the second system .

Sending a second insertion subscription data response message to the second subscription information storage network element.

With reference to the fourth aspect or the first to third possible implementation manners of the fourth aspect, in a fourth possible implementation manner of the fourth aspect, the first system is a 2G system or a 3G system, where the The second system is a 4G system; or the first system is a 4G system, and the second system is a 2G system or a 3G system.

A fifth aspect of the present invention provides an inter-system switching apparatus, including:

a receiving module, configured to receive a location update request message sent by the first core network element in the first system, where the second subscription information storage network element is a network element that stores user equipment UE subscription information in the second system;

a sending module, configured to send a first insertion subscription data message to the first core network element, where the first insertion subscription data message includes the subscription information of the UE in the second system, so that The first core network element sends a forward relocation request message to the second core network element in the second system, where the forward relocation request message includes a context identifier, where the value of the context identifier is The value of the context identifier in the subscription information of the UE in the second system.

In a first possible implementation manner of the fifth aspect, the receiving module is further configured to: after sending the first insertion subscription data message to the first core network element, receive the first core network element The first inserted subscription data response message sent;

The sending module is further configured to send a location update response message to the first core network element. With the fifth aspect or the first possible implementation manner of the fifth aspect, in a second possible implementation manner of the fifth aspect, the sending module is further used in the second subscription information storage network. After the first insertion subscription data message is sent to the first core network element, the second insertion subscription data message is sent to the first core network element, so that the first core network element is according to the And signing the subscription information of the UE in the second system in the second subscription network data message, and updating the subscription information of the UE in the second system stored in the first core network element;

The receiving module is further configured to receive a second insertion subscription data response message sent by the first core network element.

With reference to the fifth aspect, or any one of the first or second possible implementation manners of the fifth aspect, in a third possible implementation manner of the fifth aspect, the sending module is further configured to receive After the location update request message sent by the core network element, the canceled location registration message is sent to the third core network element, where the third core network element is the attached to the UE in the second system. a core network element other than the second core network element, so that the third core network element deletes the locally stored context information of the UE;

The receiving module is further configured to receive a cancel location registration response message sent by the third core network element.

With reference to the fifth aspect, or any one of the first to the third possible implementation manners of the fifth aspect, in a fourth possible implementation manner of the fifth aspect, the first system is a 2G system or a 3G system The second system is a 4G system; or the first system is a 4G system, and the second system is a 2G system or a 3G system.

According to a sixth aspect of the present invention, an inter-system switching apparatus is provided, including:

a receiving module, configured to receive a forward relocation request message sent by the first core network element in the first system, where the forward relocation request message includes a context identifier, and the value of the context identifier a value of a context identifier in the subscription information of the user equipment UE in the second system; a processing module, configured to determine, according to the context identifier, a subscription corresponding to the context identifier? from

A seventh aspect of the present invention provides a network system, comprising: the inter-system switching device according to any one of the possible implementations of the fourth aspect or the fourth aspect, the fifth aspect or the fifth aspect An intersystem switching device as described in a possible implementation and an intersystem switching device as described in the sixth aspect.

The inter-system switching method, device, and network system provided by the embodiment of the present invention first obtain the subscription information of the UE in the second system by using the first core network element in the first system, and the first core network element is further forwarded to the second The second core network element in the system sends a forward relocation request message, where the forward relocation request message includes a context identifier, where the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system, The second core network element determines the subscription information corresponding to the context identifier according to the context identifier, so that when the UE switches between the first system and the second system, the core network element of the second system accurately obtains the APN used by the UE. The subscription information in the second system further improves the success rate of the UE switching between the first system and the second system. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief description of the drawings used in the embodiments or the prior art description will be briefly described below. The drawings are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive labor.

1 is a flowchart of Embodiment 1 of an inter-system handover method according to the present invention;

2 is a schematic diagram of a SGSN searching for APN subscription information from an HLR according to a context identifier in the prior art;

3 is a flowchart of Embodiment 2 of an inter-system handover method provided by the present invention;

4 is a flowchart of Embodiment 3 of an inter-system handover method according to the present invention;

FIG. 5 is a flowchart of Embodiment 4 of an inter-system handover method according to the present invention;

6 is a flowchart of Embodiment 5 of an inter-system handover method according to the present invention;

7 is a flowchart of Embodiment 6 of an inter-system handover method according to the present invention;

8 is a flowchart of Embodiment 7 of an inter-system handover method according to the present invention; FIG. 9 is a schematic structural diagram of Embodiment 1 of an inter-system switching device according to the present invention; FIG. 10 is a schematic structural diagram of Embodiment 2 of an inter-system switching device according to the present invention;

11 is a schematic structural diagram of Embodiment 3 of an inter-system switching device according to the present invention;

FIG. 12 is a schematic structural diagram of Embodiment 4 of an inter-system switching apparatus according to the present invention; FIG.

13 is a schematic structural diagram of Embodiment 5 of an inter-system switching device according to the present invention;

14 is a schematic structural diagram of Embodiment 6 of an inter-system switching device according to the present invention;

FIG. 15 is a schematic structural diagram of Embodiment 1 of a network system according to the present invention. The technical solutions in the embodiments of the present invention are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present invention. The embodiments are a part of the embodiments of the invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

FIG. 1 is a flowchart of Embodiment 1 of an inter-system handover method according to the present invention. As shown in FIG. 1, the inter-system handover method in this embodiment includes:

5101. The first core network element in the first system acquires subscription information of the UE in the second system.

The first core network element sends a forward relocation request message to the second core network element in the second system, where the forward relocation request message includes a context identifier, and the value of the context identifier is the UE in the second system. The value of the context identifier in the subscription information, so that the second core network element determines the subscription information corresponding to the context identifier according to the context identifier.

Optionally, the first system is a 2G system or a 3G system, and the second system is a 4G system; or the first system is a 4G system, and the second system is a 2G system or a 3G system.

Specifically, the GPRS Service Support Node (SGSN) and the Mobility Management Entity (MME) are the Packet Switch (PS) signaling messages in the GPRS and EPS networks, respectively. The core network element, it should be noted that the SGSN in this embodiment refers to the GnGp-SGSN (that is, the SGSN in the 2/3G system). The Home Location Register (HLR) is a network element that stores user subscription information on a 2/3G network. The Home Subscriber Server (HSS) is a network element that stores user subscription information on a 4G network. For example, if the first system is a 2G system or a 3G system, and the second system is a 4G system, the first core network element is the SGSN, the second core network element is the ΜΜΕ, and the second subscription information storage network element is the HSS. If the first system is a 4G system, and the second system is a 2G system or a 3G system, the first core network element is ΜΜΕ, the second core network element is SGSN, and the second subscription information storage network element is HLR.

The handover process of the UE from 4G to 3G may include: the eNodeB initiates a handover request to the MME,

The MME notifies the SGSN to perform a Forward Relocation Request; the SGSN notifies the target Radio Network Controller (RNC) to establish a radio resource, and sends a relocation response to the MME; if there is no straight between the eNodeB and the target RNC The MME needs to notify the Serving Gateway (S-GW) to establish a non-direct transmission link; the MME sends a handover command to the UE through the eNodeB; the eNodeB performs data forwarding: if there is a direct transmission link, the eNodeB directly directly transmits the data. Forwarding to the target RNC; if there is no direct transmission link, the eNodeB first forwards the data to the S-GW, and then the S-GW forwards the data to the target RNC; the UE completes the handover and sends the radio resource control to the target RNC (Radio Resource Control, Referred to as RRC) Reconfiguration Complete message. After the UE completes the RRC reconfiguration, the routing area identifier (RAI) is changed, and the routing area update (RAU) process of the 4G to 3G is performed. The SGSN notifies the MME that the target side has completed the relocation. The MME responds to the relocation completion; the SGSN notifies the GGSN to update the context information; the MME notifies the S-GW to delete the session, and notifies the eNodeB to release the resource.

During the 4G to 2/3G handover, the SGSN as the target side acquires the mobility management context and Packet Data Protocol (PDP) context information of the UE from the source MME. The PDP context information includes other information such as an Access Point Name (APN) that the UE is using, and an APN Context-Identifier. After obtaining the APN or APN context identifier, the SGSN can obtain the 2/3G service subscription information of the APN from the HLR.

The process of the UE switching from LTE to GREAN/UTRAN is clearly defined in 3GPP 23401. In the preparation phase of the handover, the MME on the source side sends a PDP Context (PDP Context) and other information to the target side SGSN through a "Forward Relocation Request" message. .

The "Forward Relocation Request" message between the MME and the SGSN is defined in 3GPP 29060. The message carries the PDP Context cell, and the source MME fills the APN used by the 4G service and the PDP Context Identifier in the PDP Context cell to the target side. SGSN, After obtaining the APN information, the target SGSN obtains 2/3G subscription data from the HLR through the Update Location Request message in the subsequent RAU process.

The prior art does not explicitly require the SGSN to query the HLR from the HLR whether the APN is used as an index or the Context Identifier as an index, which causes different vendors to implement differently.

When the SGSN queries the APN subscription information from the HLR with the Context Identifier as an index, since the Context Identifier is obtained from the MME, and the MME is obtained from the HSS query when the user 4G accesses, the scenario implemented by the HLR and the HSS is separated. The 2/3G subscription data and the 4G subscription data are separately managed. That is, for the same APN, the Context Identifier assigned to the HLR and the HSS cannot be guaranteed to be the same.

2 is a schematic diagram of the SGSN searching for APN subscription information from the HLR according to the context identifier in the prior art. As shown in FIG. 2, the SGSN obtains an APN value of a from the MME, and the context identifier C1 is 1. When the SGSN requests from the HLR according to the C1, The subscription information of APN a actually obtains the subscription information of APN b, which causes the subscription information obtained by the SGSN from the HLR to be inaccurate.

The MME will initiate an update to the HSS after the 4G user accesses the MME through the Attachment or Tracking Area Update (TAU), as in the example of the 4G to 2/3G handover process. The process obtains the subscription information of the user and notifies the HSS of the dynamic information of the user. In this embodiment, when the MME attaches or TAUs, in addition to performing an Update Location process to the HSS, an MME needs to go to the HLR's Update Location process to obtain the 2/3G subscription information of the user, including the APN Context Identifier. When the 4G user is in the 2/3G handover, the MME fills the PDP Context ldentifier with the value in the 2/3G subscription information in the Forward Relocation Request message sent to the SGSN. Thus, the SGSN on the target side is based on the APN. The Context Identifier can query the 2/3G subscription data from the HLR and obtain it accurately.

In the inter-system handover method provided by the embodiment, the first core network element in the first system first obtains the subscription information of the UE in the second system, and the first core network element is redirected to the second core in the second system. The network element sends a forward relocation request message, where the forward relocation request message includes a context identifier, and the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system, for the second core network. The element determines the subscription information corresponding to the context identifier according to the context identifier, and can implement the core network element of the second system when the UE switches between the first system and the second system. Obtaining the subscription information of the APN used by the UE in the second system, thereby improving the success rate of the UE switching between the first system and the second system.

Further, S101 may include:

The first core network element receives the first insertion subscription data message sent by the second subscription information storage network element, and the first insertion subscription data message includes the subscription information of the UE in the second system.

Specifically, the first core network element may obtain the subscription information of the UE in the second system included in the first insertion subscription data message by receiving the first insertion subscription data message sent by the second subscription information storage network element.

Further, after the first core network element receives the insertion subscription data message sent by the second subscription information storage network element, the first core network element further includes:

The first core network element receives the location update response message sent by the second subscription information storage network element. Further, after the first core network element receives the first insertion subscription data message sent by the second subscription information storage network element, the first core network element further includes:

The first core network element updates the subscription information of the UE stored in the second system in the second core network element according to the subscription information of the UE in the second system in the second insertion subscription data message;

Specifically, when the subscription information of the UE in the second subscription information storage network element is changed, the second subscription information storage network element notifies the first core network element by sending a second insertion subscription data message. After receiving the message, the first core network element updates the subscription information of the locally saved UE in the second system.

FIG. 3 is a flowchart of Embodiment 2 of the method for switching between systems according to the present invention. As shown in FIG. 3, the method for switching between systems in this embodiment includes:

S201. The second subscription information storage network element receives the first core network element sent by the first system. a location update request message, where the second subscription information storage network element is a network element that stores UE subscription information in the second system;

S202, the second subscription information storage network element sends a first insertion subscription data message to the first core network element, where the first insertion subscription data message includes the subscription information of the UE in the second system, so that the first core network element Sending a forward relocation request message to the second core network element in the second system, where the forward relocation request message includes a context identifier, where the value of the context identifier is a context identifier of the UE in the subscription information in the second system. value.

Specifically, after receiving the forward relocation request message sent by the first core network element, the second core network element sends a forward relocation request message, and determines the context identifier according to the context identifier in the forward relocation request message. Corresponding signing information.

In the inter-system handover method provided by the embodiment, the second subscription information storage network element receives the location update request message sent by the first core network element in the first system, and sends the first insertion subscription to the first core network element. a data message, so that the first core network element sends a forward relocation request message to the second core network element in the second system, where the forward relocation request message includes a context identifier, and the value of the context identifier is the UE. The value of the context identifier in the subscription information in the second system may be implemented. When the UE switches between the first system and the second system, the core network element of the second system accurately acquires the APN used by the UE in the second system. The subscription information, thereby improving the success rate of the UE switching between the first system and the second system.

Further, after S202, it also includes:

The second subscription information storage network element receives the first insertion subscription data response message sent by the first core network element;

Further, after S202, it also includes:

The second subscription information storage network element sends a second insertion subscription data message to the first core network element, so that the first core network element updates the subscription information of the UE in the second system according to the second insertion subscription data message. The subscription information of the UE stored in the second system in the first core network element;

The second subscription information storage network element receives the second insertion subscription data response message sent by the first core network element. Further, after S201, it also includes:

The second subscription information storage network element sends a cancel location registration message to the third core network network element, where the third core network element is a core network element that is attached by the UE in the second system except the second core network element. So that the third core network element deletes the context information of the locally stored UE;

FIG. 4 is a flowchart of Embodiment 3 of the method for switching between systems according to the present invention. As shown in FIG. 4, the method for switching between systems in this embodiment includes:

S301: The second core network element in the second system receives the forward relocation request message sent by the first core network element in the first system, where the forward relocation request message includes a context identifier, and the value of the context identifier is The value of the context identifier in the subscription information of the UE in the second system.

S302. The second core network element determines the subscription information corresponding to the context identifier according to the context identifier.

The inter-system handover method provided by the embodiment, the second core network element in the second system receives the forward relocation request message sent by the first core network element in the first system, in the forward relocation request message. Include a context identifier, where the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system, and then determining the subscription information corresponding to the context identifier according to the context identifier, so that the UE may be implemented in the first system and the second system. During the inter-switch, the core network element of the second system accurately obtains the subscription information of the APN used by the UE in the second system, thereby improving the success rate of the UE switching between the first system and the second system.

The interaction process between the first core network element, the second subscription information storage network element, and the second core network element is taken as an example for the UE to switch between the first system and the second system. The switching method is described in detail.

FIG. 5 is a flowchart of Embodiment 4 of an inter-system handover method according to the present invention. As shown in FIG. 5, the inter-system handover method in this embodiment is a UE switching from 4G to 2/3G, and the first core network element is in the UE. After the first core network element is accessed by the attaching process, the information about the subscription information of the UE in the second system is obtained as an example, including:

S401-S405 is attached to the LTE-EPS network by the UE through security, location update, and default bearer creation. This process is defined in the 3GPP 23401 protocol and will not be described in detail here.

S406. After the standard attach procedure ends, the MME (via the Gr+ interface) sends a bit to the HLR. Set Update Request Request message.

5407. If the HLR also records other SGSN information that the user has attached, the HLR sends a cancel location registration (Cancel Location) message to the old SGSN.

5408. The old side SGSN deletes the locally cached context information of the user, and returns a Cancel Location Ack message to the HLR.

5409. The HLR sends the user's 2/3G subscription information to the MME by using an Insert Subscriber Data message.

5410. The MME locally saves the 2/3G subscription information of the user, and returns an Insert Subscriber Data Ack message to the HLR.

S411. The HLR returns a Location Update Answer (Update Location Ack) message to the MME.

5412. The HLR sends an Insert Subscriber Data message to the MME.

5413. The MME updates the locally saved 2/3G subscription information, and returns an Insert Subscriber Data Ack message to the HLR.

When the UE switches from 4G to 2/3G, the MME takes the Context Identifier in the "Forward Relocation Request" message from the 2/3G subscription data. Other processing is the same as the definition of 3GPP 23401.

Specifically, in the embodiment scenario where the UE switches from the 4G network to the 2/3G (because the processing of the core network element is the same regardless of the 2G or 3G wireless access for the present invention, the 2G wireless access is not performed. Expand). The UE originally performs services in the LTE network (4G) coverage area, and switches to the UMTS network (2/3G) coverage area for service through the handover process.

In the inter-system handover method provided by the embodiment, after the UE accesses the first core network element through the attaching process, the first core network element acquires the subscription information of the UE in the second system, and then goes to the second system. The second core network element sends a forward relocation request message, where the forward relocation request message includes a context identifier, and the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system, so that the second The network element of the core network determines the subscription information corresponding to the context identifier according to the context identifier, and when the UE switches between the first system and the second system, the core network element of the second system accurately obtains the APN used by the UE in the second The subscription information in the system further improves the success rate of the UE switching between the first system and the second system.

FIG. 6 is a flowchart of Embodiment 5 of the method for switching between systems according to the present invention. As shown in FIG. 6, the inter-system handover method in this embodiment is performed by the UE switching from 4G to 2/3G, and the first core network element is in the UE. After the TAU process is used to access the first core network element, the information about the subscription information of the UE in the second system is obtained as an example, including:

S501-S506 is a process for the UE to access the EPS network through the TAU process. The TAU process is defined in the 3GPP 23401 protocol, and will not be described in detail herein.

S507: After returning the TAU Accept message to the UE, the MME sends an Update Location Request message to the HLR (via the Gr+ interface).

5508. The HLR sends the 2/3G subscription information of the user to the MME by using an "Insert Subscriber Data" message.

5509. The MME locally saves the 2/3G subscription information of the user, and returns an "Insert Subscriber Data Ack" message to the HLR.

5510. The HLR returns an "Update Location Ack" message to the MME.

It can be understood that, in this embodiment, when the 2/3G subscription information in the HLR changes, the HLR notifies the MME by using an "Insert Subscriber Data" message; after receiving the message, the MME updates the locally saved 2/3G subscription information. And return the "Insert Subscriber Data Ack" message to the HLR.

The inter-system handover method provided by the embodiment, after the UE accesses the first core network element through the TAU process by the first core network element, obtains the subscription information of the UE in the second system, and then goes to the second system. The second core network element sends a forward relocation request message, where the forward relocation request message includes a context identifier, and the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system, so that the second The network element of the core network determines the subscription information corresponding to the context identifier according to the context identifier, and when the UE switches between the first system and the second system, the core network element of the second system accurately obtains the APN used by the UE in the second The subscription information in the system further improves the success rate of the UE switching between the first system and the second system.

FIG. 7 is a flowchart of Embodiment 6 of the method for switching between systems according to the present invention. As shown in FIG. 7, the inter-system handover method in this embodiment is performed by the UE switching from 2/3G to 4G, and the first core network element is in the UE. After the first core network element is accessed by the attaching process, the information about the subscription information of the UE in the second system is obtained as an example, including: S601-S604 is attached to the GPRS network for the UE through security, location update, default bearer creation, etc. This process is defined in the 3GPP 23060 protocol, and will not be described in detail herein.

S605: After receiving the Attach Complete message from the UE, the SGSN sends an Update Location Request message to the HSS (through the S6d interface) (this message is defined in 3GPP 29272).

S606. If the MME information of the user is also recorded in the HSS, send a Cancel Location message to the MME on the old side.

5607. The old MME replies to the HSS with a Cancel Location Ack message.

5608. The HSS sends the 4G subscription information of the user to the SGSN through the "Insert Subscriber Data" message.

S609, SGSN locally saves the user's 4G subscription information, and returns "Insert" to HSS.

Subscriber Data Ack "message.

5610. The HSS returns an "Update Location Ack" message to the SGSN.

5611. The HSS sends an Insert Subscriber Data message to the SGSN.

5612. The SGSN updates the locally saved 4G subscription information, and returns an Insert Subscriber Data Ack message to the HSS.

When the UE switches from 2/3G to 4G, the SGSN takes the Context Identifier in the "Forward Relocation Request" message from the 4G subscription data. Other processing is the same as the definition of 3GPP 23401.

FIG. 8 is a flowchart of Embodiment 7 of the method for switching between systems according to the present invention. As shown in FIG. 8, the inter-system handover method in this embodiment is performed by the UE switching from 2/3G to 4G, and the first core network element is in the UE. After the RAU process is accessed to the first core network element, the information about the subscription information of the UE in the second system is obtained as an example, including: S701-S706 is that the UE accesses the GPRS network through the RAU process, and the RAU process is defined in the 3GPP 23060 protocol, and will not be described in detail herein.

S707. After returning the RAU Accept message to the UE, the SGSN sends an Update Location Request message to the HSS (through the S6d interface) (this message is defined in 3GPP 29272).

S708, HSS sends the user's 4G subscription information to "Insert Subscriber Data"

SGSN.

5709. The SGSN locally saves the user's 4G subscription information, and returns "Insert Subscriber Data Ack" to the HSS.

5710. The HSS returns "Update Location Ack" to the SGSN.

It can be understood that, in this embodiment, when the 4G subscription information in the HSS changes, the HSS notifies the SGSN by using an "Insert Subscriber Data" message; after receiving the message, the SGSN updates the locally saved 4G subscription information to the HSS. Returns the "Insert Subscriber Data Ack" message.

The inter-system handover method provided by the embodiment, after the UE accesses the first core network element through the RAU process, obtains the subscription information of the UE in the second system, and then goes to the second system. The second core network element sends a forward relocation request message, where the forward relocation request message includes a context identifier, and the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system, so that the second The network element of the core network determines the subscription information corresponding to the context identifier according to the context identifier, and when the UE switches between the first system and the second system, the core network element of the second system accurately obtains the APN used by the UE in the second The subscription information in the system further improves the success rate of the UE switching between the first system and the second system.

FIG. 9 is a schematic structural diagram of Embodiment 1 of an inter-system switching apparatus according to the present invention. As shown in FIG. 9, the inter-system switching apparatus in this embodiment may be a first core network element, including: an obtaining module 91 and a sending module. 92, the obtaining module 91 is configured to acquire the subscription information of the UE in the second system, and the sending module 92 is configured to send the forward relocation request message, the forward relocation request, to the second core network element in the second system. The message includes a context identifier, where the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system, so that the second core network element determines the subscription information corresponding to the context identifier according to the context identifier. Optionally, the first system is a 2G system or a 3G system, and the second system is a 4G system; or the first system is a 4G system, and the second system is a 2G system or a 3G system.

The device in this embodiment can be used to implement the technical solution of the method embodiment shown in FIG. 1. The principle and the technical effect are similar, and details are not described herein again.

Further, the acquisition module 91 is specifically used to:

Sending a location update request message to the second subscription information storage network element, where the second subscription information storage network element is a network element storing the UE subscription information in the second system;

Receiving a first insertion subscription data message sent by the second subscription information storage network element, where the first insertion subscription data message includes the subscription information of the UE in the second system.

Further, the obtaining module 91 is further configured to: after receiving the insert subscription data message sent by the second subscription information storage network element, send the first insertion subscription data response message to the second subscription information storage network element;

Further, the obtaining module 91 is further configured to: after receiving the first insertion subscription data message sent by the second subscription information storage network element, receive the second insertion subscription data message sent by the second subscription information storage network element;

And updating the subscription information of the UE stored in the second system in the first core network element according to the subscription information of the UE in the second system in the second insertion subscription data message;

The device in this embodiment may be used to implement the technical solution of the first core network element in the method embodiment shown in FIG. 1 and FIG. 5, and the implementation principle and the technical effect are similar, and details are not described herein again.

10 is a schematic structural diagram of Embodiment 2 of an inter-system switching device according to the present invention. As shown in FIG. 10, the inter-system switching device in this embodiment may be a first core network element, including a transmitter 11 and a receiver 12. And a memory 13 and a processor 14 connected to the transmitter 11, the receiver 12 and the memory 13, respectively. Of course, the inter-system switching device may also include a common component such as an antenna, a baseband processing component, a medium-frequency processing component, and an input/output device. The embodiment of the present invention is not limited herein.

The memory 13 stores a set of program codes, and the processor 14 is configured to call the program code stored in the memory 13 for performing the following operations:

Obtaining subscription information of the UE in the second system;

Sending a forward relocation request message to the second core network element in the second system, forward relocation The request message includes a context identifier, where the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system, so that the second core network element determines the subscription information corresponding to the context identifier according to the context identifier.

The device in this embodiment may be used to perform the technical solution of the first core network element in the method embodiment shown in FIG. 1 or FIG. 5 to FIG. 8. The implementation principle and the technical effect are similar, and details are not described herein again.

FIG. 11 is a schematic structural diagram of Embodiment 3 of an inter-system switching device according to the present invention. As shown in FIG. 11, the inter-system switching device in this embodiment may be a second subscription information storage network element, including: a receiving module 111 and a sending The module 112, where the receiving module 111 is configured to receive a location update request message sent by the first core network element in the first system, where the second subscription information storage network element is a network element that stores the UE subscription information in the second system; The module 112 is configured to send a first insertion subscription data message to the first core network element, where the first insertion subscription data message includes the subscription information of the UE in the second system, so that the first core network element is in the second system. The second core network element sends a forward relocation request message, where the forward relocation request message includes a context identifier, and the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system.

The device in this embodiment can be used to implement the technical solution of the method embodiment shown in FIG. 3, and the principle and the technical effect are similar, and details are not described herein again.

Further, the receiving module 111 is further configured to: after sending the first insertion subscription data message to the first core network element, receive the first insertion subscription data response message sent by the first core network element; the sending module 112 is further configured to: A location update response message is sent to the first core network element.

Further, the sending module 112 is further configured to: after the second subscription information storage network element sends the first insertion subscription data message to the first core network element, send the second insertion subscription data message to the first core network element, And causing the first core network element to update the subscription of the UE stored in the second core network element in the second system according to the subscription information of the UE in the second system in the second insertion subscription data message? From .

The receiving module 111 is further configured to receive a second insertion subscription data response message sent by the first core network element.

Further, the sending module 112 is further configured to: after receiving the location update request message sent by the first core network element, send a cancel location registration message to the third core network element, the third core network element a core network element that is attached to the UE in the second system except the second core network element, so that the third core network element deletes the context information of the locally stored UE;

The receiving module 111 is further configured to receive a cancel location registration response message sent by the third core network element.

The device in this embodiment may be used to implement the technical solution of the second subscription information storage network element in the method embodiment shown in FIG. 3 and FIG. 5, and the implementation principle and the technical effect are similar, and details are not described herein again.

FIG. 12 is a schematic structural diagram of Embodiment 4 of the inter-system switching device according to the present invention. As shown in FIG. 12, the inter-system switching device in this embodiment may be a second subscription information storage network element, including a transmitter 121 and a receiver. 122. A memory 123 and a processor 124 coupled to the transmitter 121, the receiver 122, and the memory 123, respectively. Of course, the inter-system switching device may also include a common component such as an antenna, a baseband processing component, a medium-frequency processing component, and an input/output device, and the embodiment of the present invention is not limited thereto.

The memory 123 stores a set of program codes, and the processor 124 is configured to call the program code stored in the memory 13 for performing the following operations:

Receiving a location update request message sent by the first core network element in the first system, where the second subscription information storage network element is a network element storing the user equipment UE subscription information in the second system;

Sending a first insertion subscription data message to the first core network element, where the first insertion subscription data message includes the subscription information of the UE in the second system, so that the first core network element is directed to the second core in the second system. The network element sends a forward relocation request message, where the forward relocation request message includes a context identifier, and the value of the context identifier is a value of the context identifier in the subscription information of the UE in the second system.

FIG. 13 is a schematic structural diagram of Embodiment 5 of the inter-system switching device according to the present invention. As shown in FIG. 12, the inter-system switching device in this embodiment may be a second core network element, including: a receiving module 131 and a processing module. The receiving module 131 is configured to receive a forward relocation request message sent by the first core network element in the first system, where the forward relocation request message includes a context identifier, and the value of the context identifier is the second in the UE. The value of the context identifier in the subscription information in the system; The processing module 132 is configured to determine subscription information corresponding to the context identifier according to the context identifier.

The device in this embodiment may be used to implement the technical solution of the method embodiment shown in FIG. 4, and the principle and the technical effect are similar, and details are not described herein again.

FIG. 14 is a schematic structural diagram of Embodiment 6 of the inter-system switching device according to the present invention. As shown in FIG. 14, the inter-system switching device in this embodiment may be a second core network element, including a transmitter 141 and a receiver 142. A memory 143 and a processor 144 coupled to the transmitter 141, the receiver 142, and the memory 143, respectively. Of course, the inter-system switching device may also include a common component such as an antenna, a baseband processing component, a medium-frequency processing component, and an input/output device, and the embodiment of the present invention is not limited thereto.

Wherein, a set of program codes is stored in the memory 143, and the processor 144 is configured to call the memory.

The program code stored in 13 is used to perform the following operations:

Receiving a forward relocation request message sent by the first core network element in the first system, where the forward relocation request message includes a context identifier, where the value of the context identifier is in the subscription information of the user equipment UE in the second system. The value of the context identifier;

The subscription information corresponding to the context identifier is determined according to the context identifier.

The device in this embodiment may be used to implement the technical solution of the second core network element in the method embodiment shown in FIG. 4 and FIG. 5, and the implementation principle and the technical effect are similar, and details are not described herein again.

FIG. 15 is a schematic structural diagram of Embodiment 1 of a network system according to the present invention. As shown in FIG. 15, the network system in this embodiment may include: The network system in this embodiment may include: The embodiment shown in FIG. 9 or FIG. Any one of the first core network element 100, any of the second subscription information storage network elements 200 of the embodiment shown in FIG. 11 or FIG. 12, and any one of the embodiments shown in FIG. 13 or FIG. The second core network element 300.

It should be noted that the corresponding structural diagrams of the above embodiments are only one schematic, and the connection relationship of each part or module is not limited to the form shown in the figure, and may be subject to the actual application.

In the several embodiments provided by the present invention, it should be understood that the disclosed apparatus and method may be implemented in other manners. For example, the device embodiments described above are merely illustrative. For example, the division of the unit is only a logical function division. In actual implementation, there may be another division manner, for example, multiple units or components may be combined or Can be integrated into another system, or some features can be ignored, or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed may be through some interface, indirect coupling or communication of the device or unit. It can be electrical, mechanical or other form.

The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solution of the embodiment.

In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above integrated unit can be implemented in the form of hardware or in the form of hardware plus software functional units.

The above-described integrated unit implemented in the form of a software functional unit can be stored in a computer readable storage medium. The software functional unit is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) or a processor to perform the method of various embodiments of the present invention. Partially. The foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, and the like, which can store program codes. .

A person skilled in the art can clearly understand that for the convenience and brevity of the description, only the division of each functional module described above is exemplified. In practical applications, the above function assignment can be completed by different functional modules as needed, that is, the device is installed. The internal structure is divided into different functional modules to perform all or part of the functions described above. For the specific working process of the device described above, refer to the corresponding process in the foregoing method embodiment, and details are not described herein again.

Finally, it should be noted that the above embodiments are only for explaining the technical solutions of the present invention, and are not intended to be limiting thereof; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will understand that The technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and the modifications or substitutions do not deviate from the technical solutions of the embodiments of the present invention. range.

Claims

claims

1. An inter-system switching method, characterized by including:

The first core network element in the first system obtains the subscription information of the user equipment UE in the second system;

The first core network element sends a forward relocation request message to the second core network element in the second system. The forward relocation request message includes a context identifier, and the value of the context identifier is The value of the context identifier in the subscription information of the UE in the second system is used by the second core network element to determine the subscription information corresponding to the context identifier based on the context identifier.

2. The method according to claim 1, characterized in that the first core network element in the first system obtains the subscription information of the user equipment UE in the second system, including:

The first core network element sends a location update request message to a second subscription information storage network element, and the second subscription information storage network element is a network element in the second system that stores UE subscription information;

The first core network element receives the first insertion subscription data message sent by the second subscription information storage network element, and the first insertion subscription data message contains the subscription information of the UE in the second system. .

3. The method according to claim 2, characterized in that, after the first core network element receives the insert subscription data message sent by the second subscription information storage network element, it further includes:

The first core network element sends a first insertion subscription data response message to the second subscription information storage network element;

4. The method according to claim 2 or 3, characterized in that, after the first core network element receives the first insertion subscription data message sent by the second subscription information storage network element, it further includes: The first core network element receives the second insert subscription data message sent by the second subscription information storage network element;

The first core network element updates the subscription information of the UE in the second system stored in the first core network element according to the subscription information of the UE in the second inserted subscription data message. Describe the contract information in the second system;

The first core network element sends a second inserted subscription number to the second subscription information storage network element. According to the response message.

5. The method according to any one of claims 1 to 4, characterized in that, the first system is a 2G system or a 3G system, the second system is a 4G system; or, the first system is 4G system, the second system is a 2G system or a 3G system.

6. An inter-system switching method, characterized by including:

The second subscription information storage network element receives the location update request message sent by the first core network element in the first system, and the second subscription information storage network element is a network element in the second system that stores user equipment UE subscription information;

The second subscription information storage network element sends a first insertion subscription data message to the first core network element, and the first insertion subscription data message contains the UE's subscription information in the second system, so that The first core network element sends a forward relocation request message to the second core network element in the second system. The forward relocation request message includes a context identifier, and the value of the context identifier is The value of the context identifier in the subscription information of the UE in the second system.

7. The method according to claim 6, characterized in that, after the second subscription information storage network element sends the first insertion subscription data message to the first core network network element, it further includes:

The second subscription information storage network element receives the first insertion contract data response message sent by the first core network element;

8. The method according to claim 6 or 7, characterized in that, after the second subscription information storage network element sends the first insertion subscription data message to the first core network network element, the method further includes: The second subscription information storage network element sends a second insertion subscription data message to the first core network network element, so that the first core network element sends the second subscription data insertion message to the first core network element according to the UE in the second insertion subscription data message. The subscription information in the second system, updating the subscription information of the UE in the second system stored in the first core network element;

9. The method according to any one of claims 6 to 8, characterized in that, after the second subscription information storage network element receives the location update request message sent by the first core network network element, it further includes: The second contract information storage network element sends a location registration cancellation message to the third core network element, The third core network element is a core network element other than the second core network element to which the UE has been attached in the second system, so that the third core network element deletes the local The stored context information of the UE;

The second subscription information storage network element receives the location registration cancellation response message sent by the third core network element.

10. The method according to any one of claims 6 to 9, characterized in that, the first system is a 2G system or a 3G system, the second system is a 4G system; or, the first system is 4G system, the second system is a 2G system or a 3G system.

11. An inter-system switching method, characterized by including:

The second core network element in the second system receives the forward relocation request message sent by the first core network element in the first system. The forward relocation request message includes a context identifier, and the context identifier The value is the value of the context identifier of the user equipment UE in the subscription information in the second system;

The second core network element determines the subscription information corresponding to the context identifier based on the context identifier.

12. An inter-system switching device, characterized in that it includes:

An acquisition module, used to acquire the subscription information of the user equipment UE in the second system;

A sending module, configured to send a forward relocation request message to the second core network element in the second system, where the forward relocation request message contains a context identifier, and the value of the context identifier is the UE The value of the context identifier in the subscription information in the second system is used by the second core network element to determine the subscription information corresponding to the context identifier based on the context identifier.

13. The device according to claim 12, characterized in that the acquisition module is specifically used for:

Send a location update request message to a second subscription information storage network element, which is a network element in the second system that stores the UE subscription information;

Receive a first insertion subscription data message sent by the second subscription information storage network element, where the first insertion subscription data message contains the subscription information of the UE in the second system.

14. The device according to claim 13, characterized in that, the acquisition module is further configured to, after receiving the insert subscription data message sent by the second subscription information storage network element, add the data to the second subscription information storage network element. The network element sends the first insertion subscription data response message; Receive a location update response message sent by the second subscription information storage network element.

15. The device according to claim 12 or 13, characterized in that, the acquisition module is further configured to receive the first insertion subscription data message sent by the second subscription information storage network element. The second subscription information stores the second inserted subscription data message sent by the network element;

According to the subscription information of the UE in the second system in the second inserted subscription data message, update the subscription information of the UE in the second system stored in the first core network element. .

Send a second insertion subscription data response message to the second subscription information storage network element.

16. The device according to any one of claims 12 to 15, wherein the first system is a 2G system or a 3G system, the second system is a 4G system; or, the first system is a 4G system. 4G system, the second system is a 2G system or a 3G system.

17. An inter-system switching device, characterized by including:

A sending module, configured to send a first insertion subscription data message to the first core network element, where the first insertion subscription data message contains the UE's subscription information in the second system, so that the first insertion data message The core network element sends a forward relocation request message to the second core network element in the second system. The forward relocation request message includes a context identifier, and the value of the context identifier is the value of the UE in the second system. The value of the context identifier in the subscription information in the second system.

18. The device according to claim 17, wherein the receiving module is further configured to receive the first core network element after sending the first insertion subscription data message to the first core network element. The first insert subscription data response message sent by the element;

The sending module is also configured to send a location update response message to the first core network element.

19. The device according to claim 17 or 18, characterized in that, the sending module is further configured to send the first insertion subscription data message after the second subscription information storage network element sends the first insertion subscription data message to the first core network network element. , sending a second insertion subscription data message to the first core network element, so that the first core network element can insert the subscription data in the second system according to the information of the UE in the second insertion subscription data message. Subscription information: update the subscription information of the UE in the second system stored in the first core network element; The receiving module is also configured to receive the second insertion subscription data response message sent by the first core network element.

20. The device according to any one of claims 17 to 19, wherein the sending module is further configured to send a request message to the third core network after receiving the location update request message sent by the first core network element. The network element sends a cancel location registration message, and the third core network element is a core network element to which the UE has been attached in the second system, except for the second core network element, so that the The third core network element deletes the locally stored context information of the UE;

The receiving module is also configured to receive a location registration cancellation response message sent by the third core network element.

21. The device according to any one of claims 17 to 20, wherein the first system is a 2G system or a 3G system, the second system is a 4G system; or, the first system is a 4G system. 4G system, the second system is a 2G system or a 3G system.

22. An inter-system switching device, characterized in that it includes:

A receiving module, configured to receive a forward relocation request message sent by the first core network element in the first system, where the forward relocation request message contains a context identifier, and the value of the context identifier is the user equipment UE in The value of the context identifier in the contract information in the second system;

A processing module, configured to determine the contract corresponding to the context identifier according to the context identifier? since

23. A network system, characterized in that it includes: the inter-system switching device according to any one of claims 12-16, the inter-system switching device according to any one of claims 17-21, and the inter-system switching device according to any one of claims 17-21. The inter-system switching device described in 22.