[Keyword] Mobile communication data communication networking technology IP mobile softswitch
Softswitch technology is the core technology for the evolution to the next generation network. The introduction of soft switching technology in the mobile core network can achieve the sharing and centralized control of resources in the core network, thereby improving the utilization rate of the entire network and reducing operating costs. The current softswitch technology has matured and the ability to provide services has been verified. Therefore, mobile softswitch equipment is widely used in mobile operators' 2G core networks. The current application models are mostly softswitch equipment, separate architecture, and TDM bearer. Voice softswitch networking. With the construction of the IP backbone network taking shape, in order to maximize the utilization rate of the backbone transmission network and the benefits of network investment, and further take advantage of the softswitch technology, VoIP (language) is implemented in the existing GSM core network IP) and signaling IP, wide and narrowband signaling interworking is the current development direction of 2G mobile core network. This article will mainly discuss the application scheme of IP-based mobile softswitch in 2G networks.
1. Mobile softswitch network structure
The mobile softswitch core network introduces mobile softswitch equipment on the basis of the original GSMTDM switching network, and reuses HLR, SCP, SMS and other network element equipment in the original GSM switching network, and is still 2GBSS access on the wireless side. TDM switching network equipment for interworking and integration. After the introduction of mobile softswitch in the 2GTDM switching network, the network structure of the mobile softswitch core network is shown in Figure 1.
Figure 1 Mobile softswitch core network structure
· MSCServer
The access control of 2GBSS is realized through the control plane of the A interface, the MGW is controlled through the Mc interface, and call control and mobility management functions are provided. In order to ensure the correct access of the softswitch system, the MSCServer should support the SCTP multi-homing mechanism.
· MGW
MGW completes the conversion and intercommunication between packet voice codecs under the control of softswitch, that is, the conversion between AMR coded voice and G.711 coded voice.
The MGW should have a built-in SG for transferring BSSAP and ISUP signaling interworking with the TDM exchange. The MGW built-in SG can use the M3UA proxy mode and the M3UA transfer mode to implement BSSAP communication between the BSC and MSCServer. When the MGW built-in SG also uses the M3UA transfer point method to transfer BSSAP signaling, and all BSCs of this MGW support multi-signaling point function, it can provide the basis for the network to introduce A-Flex function in the future, so transfer ISUP signaling It is generally used to work at the M3UA transfer point.
· GMSCServer and GMGW
Mainly responsible for dredging the interconnection and intercommunication between the end office and other operators and the intercommunication between the soft-switched end office and TDM end office carried by IP in the local network.
The GMGW also has a built-in signaling gateway SG to support the transfer of broadband and narrowband signaling when other TDM network elements communicate with the GMSCServer to which the GMGW belongs.
· CMN
The CMN is set up at the center of a province or a region, and is responsible for the analysis of the called number of the entire network and the aggregation of signaling links between inter-provincial soft switches. CMN does not need to support Mc interface and control MGW. The CMN node function can be upgraded through the existing softswitch tandem network TMSCSERVER.
2. Networking Solution
1. Network Organization
In an IP-based mobile softswitch network, the network service part and the signaling part are carried by the IP backbone network, and the entire network is flattened. But according to the physical location and maintenance interface of the network element equipment, it can be divided into three levels: the regional center set up TMSCServer / CMN is only responsible for the aggregation and transfer of long-distance traffic BICC signaling; the provincial center / regional center mainly sets up the end office MSCServer The TMG of the long-distance network is used to control the MGW of the end office and the access of long-distance traffic. At the same time, due to the upward movement of the MSCServer, the MGW of the end office, the softswitch gateway office, and the BSS part are mainly at the local network level. Specifically shown in Figure 2.
Figure 2 Mobile softswitch networking solution
Due to the large number of 2GTDM switching network equipment of mobile operators in the existing network, the actual network planning should focus on the interworking and integration of mobile softswitch and the original 2GTDM network. The following will discuss the traffic and signaling networking solutions of the IP-based mobile softswitch network in the existing TDM switching network.
2. Traffic network solution
After the introduction of soft switching equipment in the mobile local network, the organization of its traffic network is exactly the same as that of the existing 2G network, that is, the local network MGW and the TMSC2 and TMG (long-distance soft switch gateway) of their respective home gateways are set up to relay To clear its long-distance traffic; set up a direct relay between the MGW and other mobile end offices in the local network according to the current network situation, to clear the traffic in the local network, and set up a direct connection with the GW in the local network Circuits for dredging interconnection and intercommunication services. The access mode of the softswitch end office BSC is exactly the same as that of the TDM end office BSC. A direct TDM link is established between the MGW and the BSC. In order to make full use of the advantages of IP bearer, the routing of long-distance traffic adopts the principle of "incoming IP in the nearest place and outgoing IP in the nearest place".
The specific traffic interworking and routing in the mobile core network are as follows.
· Interworking between softswitch end offices
After the introduction of IP bearer in softswitch, flat networking will be adopted. The traffic between MGWs is directly cleared through the IP bearer network without going through the tandem connection. The MGW that is carried by IP adopts the flattened first-level networking mode of the entire network, and is directly cleared through the underlying IP dedicated bearer network, and uses RTP / RTCP / UDP / IP protocol stack communication.
· Interworking between Softswitch End Office and TDM End Office
In the same local network, when there is a switching relationship between the softswitch end office and the TDM end office, a TDM direct circuit will be established, and when there is no switching relationship, it will be transferred through the softswitch gateway office.
Across the local network, user voice is cleared by the IP bearer network and transferred from the TMG in the called area to TDM. On the TDM end office side, via TMSC / TMG transfer, it is consistent with the 2G existing network.
· Interworking between softswitch end office and other operators
The softswitch end office communicates with other local operators. The calling softswitch end office is routed to the local gateway office and communicates with the PSTN through the gateway office.
The softswitch end office communicates with other operators in different places. The called side is not a softswitch gateway office. The calling softswitch end office passes the IP bearer network to the TMG of the called area and then to the called office; the called side; It is a softswitch gateway office, which is directly transferred from the calling softswitch end office to the IP gateway office on the called side through the IP bearer network, and the softswitch gateway office and other operators can communicate with each other.
3. Signaling network solution
The softswitch signaling networking is shown in Figure 3. The softswitch MSCserver is set up independently from the local network and is responsible for signaling processing functions such as mobility management and call processing. The MGW does not process any signaling messages. Since MSCServer can control multiple MGWs, MSCserver, as a 2G network element, accesses the No. 7 signaling network of the existing 2G network, and should support multiple signaling points to logically divide the MSC server and the MGW under its jurisdiction into different mobiles Exchange the end office. Both MSC Server and MGW should support and set up the built-in SG. Through the MGW's built-in signaling gateway, the softswitch end office sets up direct signaling links with other MSCs, GWs, and TMSC2s in the local network, and is responsible for dredging ISUP messages. Since the two MGWs under the same MSC Server are virtually different switching end offices, a direct signaling chain must be set up to the network element. The BSSAP signaling between the MSC Server and the BSC is transferred by the MGW built-in SG, the IP bearer is used between the Server and the MGW, and the TDM bearer is used between the MGW and the BSC. Through the built-in SG in the MSC Server, the MSC Server can set up signaling links with HLR, SCP, SMS, etc., and transfer TDM signaling such as MAP / CAP.
Figure 3 Mobile Softswitch Signaling Network Solution
BICC signaling is adopted between MSC Servers, based on IP bearer, inter-provincial BICC signaling needs to be transferred through CMN.
GCP / ISUP / BSSAP signaling of Mc interface between MSCServer and MGW is based on IP bearer.
The MAP and CAP signaling between MSCServer and HLR, SCP, and SMS are carried by TDM. When the MSCServer is transferred via LSTP, the 2 Mbit / s signaling link carried by TDM is used between MSCserver and LSTP.
The ISUP signaling between the MSCServer and the TDM end office is transferred by the built-in SG of the MGW, and the IP bearer is used between the Server and MGW, and the TDM bearer is used between the MGW and the TDM end office.
When inter-local IP softswitch end office and TDM end office intercommunicate, on the softswitch end office side, the control plane BICC signaling is transferred to ISUP via TMSCServer. On the TDM end office side, via TMSC / TMG transfer, it is consistent with the 2G existing network.
4. Billing and network management
The connection method of the charging system is the same as that of the 2G switching network. The MSCServer generates detailed CDRs and performs preprocessing through the charging gateway before sending them to BOSS.
For billing across local networks, a softswitch system covers multiple local network areas, and MSCServer can allocate different MSCID and MSRN thousand segments to users according to their location. Softswitch fills the MSC number corresponding to the local network where the user (the calling user and the called user) is located in the bill (calling bill and called bill) of each communication, that is, the logical MSC ID. That is, the softswitch directly fills the logical MSC ID of the local network where the user is located in the MSC ID field in the existing bill format. The billing gateway dialogue pre-processes, sorts the bills of different business areas according to this field, and sends them to the BOSS system for post-processing such as batch price.
Due to the centralized placement of the softswitch equipment, the softswitch network management system is also set up accordingly. Softswitch network elements in various regions need to be connected to the network management system through the network management IP bearer network, and access to the system's OSS through the pull-back terminal Realize the management of local equipment. From the aspect of security and overall coordination, the bearer network of network element access network management should follow the following principles.
(1) For the cities where the network elements of the service network management system are installed, the local network management network should be divided into security zones, and a network element access area should be set up, which is specially used to access the network elements of each service network management.
(2) A firewall needs to be deployed at the boundary of the network element access zone for secure access control. The network elements of each service network management need to be set in the network element access zone, behind the firewall.
(3) For some important business network management systems and their network elements, a dedicated firewall has been configured during construction, which is specifically used for the security access control of the business network management system and its network elements. All such end firewalls should be retained to enhance the security of important business network management systems and their network elements.
(4) Due to the existence of multiple business network management systems and their network elements in various cities, the cost of configuring a dedicated firewall for each business network management system or network element is too high and the feasibility is low. In order to reduce the number of firewalls, an intrusion detection IDS device or a high-performance firewall can be added between the aggregation switch of each network management building and each professional network management network element to reduce the number of end firewalls.
(5) If each service network management system and its network elements are accessed by the same switch, VLANs need to be divided on the switch according to different service network management systems, and logically ensure that services cannot communicate with each other. The service network management system and its network elements can also be isolated by ACL at the end firewall.
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