Network convergence analysis based on Softswitch technology (figure)

1. Introduction

As China becomes more open to the communication field, competition among telecom operators is becoming increasingly fierce. How to reduce network construction investment and reduce O & M costs becomes more and more important. Network convergence enables operators to provide various fixed and mobile access services on the same network. By sharing devices in the network, carriers can achieve unified services, management, and billing, ultimately, we can reduce investment and increase revenue. In terms of technology, the idea of the Next Generation Network's bearer and control separation, control and business separation coincide with the evolution of the third generation mobile communication network. Both adopt Softswitch technology at the core control layer, this provides a foundation for network convergence.

2. Application of Softswitch technology in fixed network and mobile network

The concept of Softswitch is proposed from the fixed network. It is a call and session control technology in the next generation network. It is generally divided into narrowband SoftSwitch and broadband SoftSwitch. Narrowband Softswitch is mainly used for narrowband voice services, and broadband Softswitch is mainly used for broadband multimedia services. In fixed networks, narrowband Softswitch technology means that a soft switch uses H.248 or MGCP protocol to control various gateways, including the relay Gateway TGTrunk Gateway) and Access Gateway AGAccess Gateway) and integrated Access Device IADintegrate Access Device), they are responsible for user Access and communication with the PSTN; In the WCDMA mobile network, the narrowband Softswitch technology refers to the MSC Server defined in R4 uses the extended H.248 to control the media gateway MGW. Broadband Softswitch technology in fixed networks refers to various SIPSession Initiated protocols, Session Initiation protocols) the technology of server call control based on the SIP Protocol.

In WCDMA mobile networks, broadband Softswitch refers to various CSCFCall Session Control functions of IMSIP Multimedia Subsystem and IP Multimedia Subsystem. Call Session Control functions) Implement core call Control functions based on the SIP protocol. CSCF types include P-CSCFProxy-CACF, proxy CSCF), I-CSCF (Interrogating CSCF, query CSCF) and S-CSCF (Serving CSCF, service CSCF), essentially they are all SIP servers, process SIP signaling. The service is carried by SGSNs (Serving GPRS Support Node), GGSNGateway GPRS Support Node, and Gateway GPRS Support Node) in the WCDMA grouping domain, and wireless access network.

Currently, both narrowband Softswitch technology and broadband Softswitch technology have commercial products and multiple commercial and experimental networks in fixed networks. In mobile networks, product maturity lags behind fixed networks, and there is no commercial network.

3. Comparison between fixed SoftSwitch and mobile Softswitch

The Softswitch technology in the fixed network and mobile network is basically the same in terms of technical ideas and basic principles. However, due to the different application environments in the fixed network and mobile network, there will be some corresponding changes in implementation. The following is a technical comparison between narrowband SoftSwitch and broadband SoftSwitch.

In terms of narrowband Softswitch, the Call Server in the fixed network and the MSC Server in the mobile network support the H.248 protocol to control the media gateway and complete the Call control function. Only the MSC Server uses H.248 to add some mobile-specific extended applications than the H.248 protocol of ITU, including BICCBearer Independent Call Control and bearer-Independent Call Control) the extension package and UMTS (Universal Mobile Telecommunication System, Universal Mobile Communication System) package are used to implement unique applications in the Mobile network. The difference between the Call Server in the fixed network and the MSC Server in the mobile network is mainly reflected in the different Supported Protocol systems. In terms of media gateway control protocol, the Call Server uses the H.248 protocol, MGCP (Media Gateway Control Protocol) Protocol is also used. MGCP is mainly used to Control small integrated access device IAD, while MSC Server does not use MGCP; in terms of Inter-board signaling, Call servers generally adopt SIP-T protocol and seldom use BICC Protocol. The Protocol between MSC servers is divided into Call-related protocol and Call-independent protocol, call-related Protocols use BICC. Call-independent protocols are called mobility management protocols use MAPMobile Application Part (Mobile Application Part) protocols. In terms of Intelligent Network-related protocols, the Call Server uses the INAPIntelligent Network Application Part. Communication with SCPService Control Point, business Control Point), MSC Server uses CAPCAMEL Application Part, CAMEL Application Part) Protocol to communicate with SCP, which is completely different from the two Protocols. In addition, MSC Server also supports the RANAP (Radio Access Network Application Part) protocol, which is used to establish Iu connections with RNC and build a channel between the Access Network and the core Network. In short, the functions of MSC Server are much more complex than those of Call Server. The two are only consistent in the support of H.248 basic protocols.

Compared with the control layer, the bearer device has relatively simple functions. AG and IAD in the fixed network are responsible for user access, TG is responsible for interworking with PSTN, and the fixed gateway supports H.248 and MGCP protocols in terms of protocols. In addition to the H.248 Protocol, media gateway also needs to support the Bearer Control Protocol. If the mgws are carried by IP addresses, mgws must support IPBCPIP Bearer Control Protocol and IP Bearer Control Protocol) protocol. If ATM is used, MGW must support the Q.2630 protocol to negotiate the address information and media stream features used between mgws. The interaction of this information is transmitted through the BICC tunnel between MSC Server and the interface between MSC Server and MGW. This is a unique function of the mobile media gateway, and the gateway in the fixed network does not have the bearer control function, the Call Server completes the corresponding functions, so the media gateways in the mobile network are more intelligent than those in the fixed network. In terms of speech coding, fixed Softswitch uses G.711, G.723, and G.729 voice encoding methods. In mobile Softswitch, MGW uses mobile-specific AMR voice encoding methods, MGW should support G.711, G.723, or G.729 when interworking with the fixed network.

In terms of broadband Softswitch, both fixed and mobile Softswitch, call control protocols adopt the SIP protocol. The SIP Protocol provides a unified end-to-end dialog mechanism for services running on IP addresses, regardless of the bearer network. Therefore, SIP-based applications can be used across networks. Although the various SIP servers of the fixed network and mobile network cannot completely correspond to each other, there are similarities in the various functions of implementing the SIP protocol. For example, the P-CSCF node function in the mobile network and the Proxy function of the fixed network SIP Proxy server and B2BUABack to Back User Agent, Back-to-Back User Agent) function is similar; the functions of S-CSCF nodes in mobile networks are similar to those of the Proxy and Registrar functions of the SIP registration server in fixed networks.

The SIP protocol is defined by IETF. The SIP protocol used in mobile networks directly references the IETF's SIP protocol. IETF adds mobile-related functions based on the original needs of mobile applications, for example, AKAAuthentication Key Agreement) the authentication process conforms to the authentication mechanism of mobile networks, and the SIP compression function is also added, because the air interface resources are very limited, we need to introduce a compression mechanism to save wireless resources. In addition, the media Resource server that implements the conferencing and television functions on the fixed network is similar to the MRFMultimedia Resource Function on the mobile network, and the Media Resource Function). It provides media control for applications such as ringtone provision, voice notification, and multi-party meetings. In short, in broadband Softswitch, the functions of fixed network and mobile network-related network elements are very similar, which also makes network convergence possible.

4. network convergence solution

The network convergence mentioned here refers to the network solution for achieving fixed and mobile services through the integration of devices, that is, the same core network serves both fixed users and mobile users. Obviously, this network convergence is based on the commonality of devices.

According to the previous comparison, although the functions of Call Server and MSC Server in narrowband Softswitch are similar, the differences between the two are more common, so it is not convenient for devices to share. In the access layer, the fixed network access gateway and the media gateway for access in the mobile network differ greatly in terms of interfaces, voice encoding, and support protocols, however, the TG in the fixed network and the gateway in the mobile network that is responsible for intercommunication with the PSTN are relatively less different. Therefore, it is easier to achieve the integration of the two than that of the Access Gateway. However, to share the fixed network and mobile network media gateways, the shared media gateway is required to support the functions of the virtual media gateway. That is to say, the same media gateway can be configured as two virtual media gateways, which are controlled by the Call Server and MSC Server respectively. Because two virtual media gateways share hardware and software resources, resource management and control become more complex. Therefore, the integration of fixed network and mobile network in narrowband Softswitch is difficult.

In broadband Softswitch, the functions of the fixed network and the SIP server in the mobile network are similar, and network convergence is relatively simple. The integrated network framework can be based on IMS in WCDMA. Mobile CSCF can be integrated with a fixed-network SIP server to complete processing of SIP signaling. MGCF completes signaling intercommunication with the circuit switching network and the bearer control separation network, that is, converting between the SIP signaling and ISUP or BICC, and controlling the IM-MGW through H.248. MGCF can be performed simultaneously by MSC Server and Call Server, or by a separate device. IM-MGW to complete the conversion of media formats, such as switching between AMR and G.711, can be done by fixed network and mobile network corresponding media gateway, can also be achieved by a separate media gateway. The mobile MRFCMultimedia Resource Function Controller and Media Resource Function Controller) work with the MRFPMultimedia Resource Function Processor and Media Resource Function Processor to implement Fixed Network Media Server Functions and multimedia services such as conference and television. HSSHome Subscriber Server of WCDMA, belonging to the user Server) can be integrated with the location Server in the fixed network to store the routing information of the fixed network and mobile network users, and the contracted business information, as shown in broadband network convergence solution 1.

The above network scheme can be used to connect a mobile user and a fixed user's SIP terminal, and can communicate with non-SIP terminals of other networks.

· Mobile SIP terminals access CSCF through access networks and core network grouping domains to obtain services provided by various application servers.

· Fixed SIP terminals can access CSCF over the Internet to obtain the same applications as mobile users.

· The communication between mobile SIP terminals and fixed SIP terminals is controlled by CSCF, and the communication is implemented through the IP bearer network.

· Voice communication between a fixed or mobile SIP terminal and a non-SIP terminal using the R99 circuit switching network. The control layer converts the SIP protocol and the ISUP protocol from MGCF, voice communication is completed through the intercommunication between the IM-MGW and GMSC. The interconnection between a fixed or mobile SIP terminal and a non-SIP terminal of other fixed and mobile circuit switching networks is similar, including interconnection with terminals such as PSTN and GSM.

· Voice communication between a fixed or mobile SIP terminal and a non-SIP terminal using the R4 circuit domain. The control layer converts the SIP protocol and BICC protocol from MGCF, voice communication is completed through the communication between the IM-MGW and the mgw controlled by GMSC Server in R4 network. The interconnection between a fixed or mobile SIP terminal and a non-SIP terminal of the fixed network narrowband Softswitch is similar.

Networks Based on Broadband Softswitch technology and various application servers can provide users with a variety of SIP applications, such as VoIP, POCPush to Talk over Cellular, and Cellular system key calls), Instant Messaging) and Prensence.

5. Conclusion

To sum up, it is technically feasible to integrate the fixed network and mobile network based on Broadband Softswitch, and from a qualitative perspective, because the sharing of equipment and network management resources can save network investment, reduces O & M costs and facilitates billing based on one account to provide unified bills. This may indeed have some advantages for a relatively small network, but when the network size is large enough, system Operation Efficiency and changes in the pressure of the network management system are all issues worth further research and discussion.