Design and Implementation of Short Message Service in Mobile Softswitch

At present, 3G and next-generation networks have become two hot topics in the communication field, both of which are constantly developing and evolving, and they are constantly integrated. Taking the implementation of short messages in softswitch as an example, this paper discusses the support of the Next Generation Network with Softswitch as the core for the UMTS network using WCDMA wireless technology in 3G, A solution for interworking with 3G wireless networks through Softswitch is provided.

1 Introduction

UMTS (Universal Mobile Tele communications System) is a third-Generation Mobile communication System that uses WCDMA in wireless technology. Its standardization work is organized by 3rd Generation Partnership Project, so far, four versions have been released, namely R99, R4, R5, and R6. The UMTS system defined by 3GPP, starting from the R4 version, has introduced the concept of softswitch in the circuit domain, which separates control and bearer, the original MSC is changed to MSC server and Media GateWay MGW (Media GateWay). Voice is transmitted through MGW by group domain.

As the core technology of the Next Generation Network (NGN), Softswitch provides Call Control and Connection Control functions for the Next Generation Network with real-time business requirements, it is the core of next generation network call and control. Mobile Softswitch is a new direction in the development of Softswitch technology.

Mobile Softswitch is an application of Softswitch technology in mobile communication networks and a new trend in the development of Softswitch technology. As one of mobile's main businesses, short message services bring huge economic benefits to operators and developers and convenience to consumers, it also becomes a service that must be supported in the implementation process of mobile SoftSwitch. The following uses the short message service as an example to describe how mobile Softswitch supports mobile networks.

2. Short Message Implementation Principle

2.1 business definition

There are two types of Short Messages: community broadcast short messages (CBS) and point-to-point short messages (SMS ). The short message service is usually referred to as a point-to-point short message. If it is not stated in this article, it is pointed to a point-to-point short message.

Short Messages are services that do not require end-to-end service paths in GSM/UMTS. You can transmit short messages even if the mobile device is in full circuit communication. Generally, short message communication is limited to one message. In other words, the transmission of a message constitutes a communication. Therefore, the business is not symmetric, generally think that the beginning of the Mobile Short message transmission (SM-MO) and mobile terminal Short Message (SM-MT) transmission is two different. This does not impede real-time dialog, but the system deems that different messages are independent from each other, and the transmission of messages is always relayed by the business center (SC) outside the GSM/UMTS. The message has a destination or origin, but is only related to the user and SC, and is not related to other GSM/UMTS infrastructure.

SMS uses SC to send short messages between GSM/UMTS MS and SME. SC is responsible for the interoperability and relay functions of message transmission between MS and SME.

2.2 Network Architecture

In the implementation of mobile communication networks, short message services mainly involve wireless access, MSC, and core network entities. Link 1 includes the wireless air interface and the Iu interface (the interface in GSM). The Iu interface uses the RANAP protocol. Link 2 and 3 belong to the mobile core network and use the MAP protocol. Link 4 is the interface between the mobile network and the short message center SC. The carrier determines the protocol used.

2.3 protocol system

(1) RANAP

The short message is transparently transmitted to the MSC Server (Softswitch entity) by RNC through the RANAP protocol ). RANAP is a Iu signaling protocol that contains all the control information required for the wireless network layer. RANAP functions are implemented through various basic RANAP processes (EP. Each RANAP function may require to run one or more Enis. Each EP may contain Request Response Message pairs (class 1 EP), or only request messages (Class 2 EP ), or include one request message and one or more response messages (three types of EP ). The Short Message PDU (Protocol Data Unit) transparently transmits from RNC to MSC through RANAP's UE-CN signaling.

(2) MAP

The MAP protocol is designed for mobile communication requirements. MAP corresponds to the Layer 7 of the OSI reference model on top of TCAP, and is the application layer protocol of the layer 7 signaling. MAP only uses the SCCP Connection-free mode. This protocol is used for communications between MSC, HLR, VLR, and EIR contacts: Location registration, location deletion, cancellation of registration, and processing, management, and retrieval of user services; management of user parameters (updating HLR and VLR), switching, transmission of confidential authentication data, and so on.

MAP is a TCAP user. It uses exchange protocol data and sessions to process the same layer of communication between different entities, such as MSC, HLR, and VLR. MAP contains a series of functional blocks called application context units, used for communication between two nodes at the same layer. Sometimes a system is associated with several systems at the same time. Switching is an example. With the MAP protocol, an object can communicate with several objects at the same time.

The support for short message services is also one of the functions of MAP. Through MAP message, short messages can be transmitted between servo MSC and IWMSC/GMSC.

(3) protocol structure in MSC Server

Since the MSC server is implemented by the Softswitch technology, the protocol system of the Short Message Service in MSC, that is, the protocol system in the softswitch entity. According to the 3GPP 24011 standard, the Internal Short Message Protocol system of Softswitch is divided into three layers: SM-TP, SM-RP and SM-CP. SM-TP-layer messages are encapsulated in user data of SM-RP-layer messages as TPDU, SM-RP-layer messages are encapsulated in user data of SM-CP-layer messages as RPDU, finally, the SM-CP layer message is used as the CPDU to transmit the underlying bearer signaling such as RANAP signaling between different entities. On the core network, because the messages in the SM-RP layer and the SM-CP layer have been processed by MSC, only the messages in the SM-TP layer are transmitted on the core network as the bearer signaling.

SM-TP is Short Message Transport Layer Protocol. The message parameters at this layer include the validity period, service center timestamp, protocol identifier, and target mobile phone user address, which must be processed by MS and SMC. Therefore, for MSC server, it is transparent transmission and does not need to be concerned. The task of MSC server is to correctly transmit the TPDU to SMC or MS.

SM-RP is the protocol of the short message relay layer. At this layer, message parameters mainly involve user data and destination SMS center addresses. Based on the message parameters at this layer, you can generate corresponding MAP messages and route the short messages on the core network. The following table lists related messages:

SM-CP is short message control layer protocol. The main function of messages at this layer is to control the short message process on the wireless interface to ensure the correct transmission of short messages on the wireless interface.

3 Implementation Scheme of Short Messages in Softswitch

3.1 system structure of Softswitch

The system diagram of the softswitch system, including Protocol Process, Call Control, Call Service, and VLR, service Adaptation and OAM subsystems. Among them, ML3 in the protocol processing subsystem represents the processing module of the mobile layer-3 signaling, including 2g bssap and 3g ranap Protocol adaptation.

The protocol processing subsystem communicates with the remote communication entity through the protocol stack (including signaling interaction and media interaction), and the upstream modules such as call control and call service shield protocol differences and maintain the status of online users. The system has corresponding sub-modules for different user access types, such as mobile devices, ISUP devices, and multimedia devices. Call Control communicates with the protocol processing sub-modules in the system to complete signaling control tasks, and communicates with the call service to obtain number analysis results, routing information, and other services. The call service communicates with the protocol processing sub-modules in the system to complete tasks such as resource management, location management, and user information management, and provides services such as number analysis and routing information. VLR is a user database associated with mobile devices and provides RP-Layer Control for short message transmission. Business adaptation is an external service interface of SoftSwitch. It provides service access functions for application servers and intelligent networks.

3.2 modules involved in Softswitch

Because MSC for Short Message Protocol processing is divided into SM-CP and SM-RP two layers, so combined with our Softswitch design scheme, we will Short Message Service Processing is also divided into two parts: SM-CP-layer messages are processed in ML3, and SM-RP-layer messages are processed in VLR. The role of VLR is very different from that of VLR in traditional mobile communication networks. In traditional mobile communication networks, VLR is only a database of MSC for handling MS outbound calls and retrieval information in the region to store data related to call processing. In the implementation of softswitch, in addition to the above functions, VLR has user data. To avoid too many internal communication flows, we will perform authentication, location update, and paging in mobile communication, control of call-independent business processes such as short messages is granted to VLR. Therefore, VLR has become a control entity for call-independent business processes.

SM is the short message protocol processing module in ml3. it implements the short message control entity (SMC) function. In the MO business mode, it is responsible for processing the SM-CP layer message, decoding the SM-RP layer parameter from it, forming the SM-RP layer message to send to VLR. In MT business, messages are encoded from the SM-RP layer received by VLR into RPDU, forming a SM-CP layer message sent to the underlying protocol stack. After the short message service process ends, it also notifies MM (mobility management) to release the wireless interface connection. The Alert Process status chart is the same as that of MO.

VLR completes the function of short message relay entity (SMR): The Interaction Between SM-RP messages and MAP messages. According to the received SM-RP layer message, constructs the corresponding with the MAP state machine intermediate message, MAP process, the opposite direction is according to the received MAP intermediate message, constructs the corresponding SM-RP layer message, for short message relay. In fact, VLR serves as a bridge between some wireless access protocols (RANAP or BSSAP) and the core network protocol (MAP) for short message service, so that SM and MAP state machines can be coordinated, send short messages together.

The MAP sub-module sends and receives short message services on the core network through MAP protocol messages. In the MO mode, the MAP sub-module starts the MAP conversation with the application context name shortMsgMO-RelayContext and sends a short message to IWMSC. During the Alert process, the MAP sub-module starts the MAP conversation with the application context name mwdMngtContext, send good news to HLR users. In MT mode, the MAP sub-module receives short messages from GMSC by receiving the MAP conversation in the application context named shortMsgMT-RelayContext. The above process is a standard process defined in the 3GPP 29002 specification and will not be repeated here.

3.3 Business Process

(1) SM-MO Process

This business process is triggered by a connection management message CM-SERVICE-REQUEST [5] And then established a MM connection; after the MM connection is established, the short message business process starts from the CP-DATA message sent by MS to the network side. After receiving the confirmation message returned by SC, the short message service process ends and the MM connection is released.

(2) SM-MT Process

The MT method is triggered by the MAP-MT-FORWARD-SHORT-MESSAGE received from GMSC, then VLR will issue PAGING message paging ms, establish a MM connection; after the MM connection is established, start the short message service process, send short messages to MS; after receiving confirmation from MS, release the MM connection.

4 Conclusion

This paper proposes a solution to implement Short Message Service Based on Softswitch, which is feasible and effective after practice. In addition to basic voice calls and short message services, it can adapt to the features of broadband, intelligent, and multi-media mobile networks in the future. 3GPP proposes high-speed multimedia services, such as location-based businesses, wireless Internet businesses, and on-demand videos. The support of softswitch for these enhanced mobile services will become a subject for further research and discussion.