Core network;To put it simply, you canmovenetworkIt is divided into three parts: the base stationsystem, network subsystem, and system support, for examplesecurity management Wait for these.The core network is located in the network subsystem. The main function of the core network is to connect the call request or data request from the A port to different networks.
It mainly involves call connection, billing, mobility management, implementation of supplementary services, intelligent triggering, etcSwitch。as forSoftswitchThere are two obvious concepts: the separation of control and bearing, and the separation of control channel and data channel.
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According to the protocol, it plays the role of core switching or call routingNetwork elementThe 2G/3G core network is generally the same. In the R4 architecture, such as MSC SERVER, MGW, HLR, VLR, EIR and AUC, the main function is to control the whole call signaling and establish the bearer.
development direction
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The core network has entered the era of "IP"broadband, IntelligentDisaster recoveryAnd green environmental protection are its main characteristics.From the perspective of circuit domain, mobileSoftswitchIt has completely shifted from TDM transmission circuit to IP;From the grouping field,broadbandIts main characteristics are intellectualization;From the perspective of user data, the new HLR is widely accepted and gradually evolves to the future integrated data center.In addition,OperatorThey willDisaster recoveryAnd green environmental protection;Mobile networkIn the future development and evolution, the two camps of GSM and CDMA will move towards a common IMS+SAE+LTE architecture in the 4G era.
The function of the core network is mainly to provide user connection, user management and service carrying, as the interface of the carrying network to the external network.The establishment of user connections includes mobility management (MM), call management (CM), and switching/routeSound recording notice (combined withIntelligent networkThe service completes the connection relationship to the peripheral equipment of the intelligent network.User management includes user description, Qos (addedUser businessQos description), user communication record (Accounting), VHE (andIntelligent networkThe dialogue of the platform provides a virtual home environment), security (the authentication center provides corresponding security measures, including security management of mobile services and security processing of external network access).Access to includes PSTN, external circuit data network, packet data networkThe basic services that can be provided by core networks such as the Internet, intranets, and mobile SMS servers include mobile office, e-commerce, communications, entertainment services, travel and location-based services, remote sensing services - simple messaging services (monitoring and control), and so on.
Evolution and composition
The core network is divided into circuit switching domain andpacket switchingDomain.The functional parts required by the CS domain include TRAU, MSC, etc. The functional parts required by the PS domain include GGSN, SGSN, and other registers and servers.The specification stipulates that the Iu interface provided by the RNC is open, and the signaling and interfaces in the Iu CS domain and Iu PS domain are open.The signaling planes on the Iu CS domain and the Iu PS domain are both RANAP protocols, called RANAP-CS and RANAP-PS.The service plane of the CS domain corresponds to the voice, which needs to complete the rate adaptation of AMR and the code type conversion of TRAU, while the DATA service does not need code type conversion and is directly sent to the SGSN to complete the corresponding functions.Nortel introducedWireless gatewayWireless Gateway is actually the integration of equipmentnodeIn the R99 version, new functions need to be added to the TRAU part of the CS domain, and the MSC and SGSN do not need to change.The interface provided from the RNC is an optical fiber interface, which transmits ATM cells. Voice carries AAL2, and data carries AAL5.Through OC-3/STM-1card After the access, it is divided into two internal branches. AAL2 will send it to the TRAU to complete the code conversion and rate adaptation. It will adapt to the 64kbps TDM stream -- the synchronous stream of E1 circuit to transmit user information.For the packet domain, the service will be carried to the IP when it is converted from the SGSN to the IPbackbone networkGo to GGSN.The signaling on the Iu Cs interface is transparent to the TRAU, which onlyphysical layerSignaling messages will not be analyzed.So from the signaling perspective, the signaling on the Iu CS is a dialogue between the RNC and the MSC. It transparently passes through the TRAU to the MSC and is processed by the MSC CPU.As a PS domain, the Iu PS port exists between the RNC and the SGSN, and the direct protocol is still the RANAP-PS protocol, since rate adaptation and code conversion are not required in the middle.The SGSN to GGSN protocol will be directly converted to the GPRS protocol - GTP protocol, including GTP-C and GTP-U.The biggest difference from GSM is that for GPRS, the GTP-U is between SGSN and GGSN, while the GTP-U is still between SGSN and PCUFrame relayAgreement for.In WCDMA, GTP-U protocol on Gn interface will be extended to Iu Ps interface.That is, starting from the RNC, the service will assign a Tunnel ID to be used on the Iu Ps and Gn interfaces.
Will be introduced in both R4 and R5 versionsMulti-MediagatewayThe concept of MGW and Call Server.In R4, the circuit switching part of the MSC and theUser businessThe voice relay plane and relay module transferred are all cancelled, and only the signaling processing unit - CPU processing unit is retained.The two added control functions can be realized by software or throughcard It is called WGC and PSTN GC to complete the control of voice path establishment between the two MGWs.The CPU centralized processing center is called Call Server.The Call Server is still the original MSC platform at the beginning, and will eventually truly implement the server's processing platform.Voice will be built on the packet backbone network asynchronously through WGC and PSTN-GCdata streamThe mode of transmission.The type of packet backbone network selected depends on the development trend of the specification. According to the trend, it will be over IP.Therefore, as far as the backbone bearer is concerned, the R4 version first realizes the integration of voice and data transmission.In this case, when voice communication needs to be completed, signaling still realizes communication through Call Server. The voice channel only needs to establish connection relationship between different WGCs or between different WGCs and PSTN GCs.The introduction of PSTN GC is to provide 64kbps 2M voice circuit relay switching to PSTN.Mobile calls can only be made between WGCs. PSTN GC is set for PSTNgateway。After the R5 version, it will become a part of the packet backbone networknode, different function modules are no longer distinguished, and each node will be assigned an IP addressroutePlanaddressingAnd complete the establishment of the route.In the R4 version, changes in the CS domain are emphasized, and changes required for the access network are not emphasized.For example, when the mobile subscriber calls a fixed number, the signaling will be sent to the Call Server for corresponding processing, and the transfer and conversation of No. 7 signaling with the public network will be completed. The opposite end will ring, the user will be off hook, and the message will be replied to the Call Server. The Call Server will complete internal control, notify WGC and PSTN-GC to establish the MGCP protocol, and control the establishment of a Voice over IP path between WG and PSTN G,The user starts communication.Call Server will haverouteAnalyze the function to determine the pathway between different WGs and PSTNG.
After the domestic leading communication technology forum has realized the R4 version, it will useTFOandTrFOFunction of.TFOIt is called Tandem Free Operation,TrFOIt is called Trancoder Free Operation.TFOFunction refers to the process of code type conversion without completing the TRAU function, which is called TFO function.The precondition for realizing this function is to use the asynchronous stream transmission mode.TFOIt is optional. It means that whether code type conversion is required during mobile mobile is optional, depending on whether the two terminal rate is negotiated.For example, the rate selected by the user at one end is 12.2 kbps, while that at the opposite end is only 4.75 kbpsbackbone networkThe carrying rate is 64kbps.In this case, both ends need to pass through the TRAU.If one end fails to pass the TRAU, startTFOThe function enables one end not to pass through the TRAU.andTrFOThe communication rate of each other needs to be negotiated in advance.MSCBSC Mobile Communication Forum 2N9~, Z% S7f3j
The so-called R5 version is all IPbackbone network。Whether it is access network or corebackbone networkThe bottom layer is an IP based backbone network.IP efficiency is higher than ATM, and the underlyingEthernet technologyRapid development.So you can choose IPbackbone networkTo realize an integrated network.In R5, all exchanges areSoftswitch, that is, in the packet backbone networknodeBoth can be realized through the server.Server platform includes HLR (home location register) and SCP（Intelligent networkService control point platform) and UAS (Play Recording Notification Platform). These platforms are still connected through No.7 signaling, so a USP is required. The USP function is equivalent to the function of SIG in GPRS, that is, No.7 to IPgatewayProtocol translation server.
Evolution of protocol stack, in R99 versiondata service The bottom layer of the re IP is AAL5, which is carried by ATM, and AAL2, which is used for voice, is carried by ATM.In the R99+version, MPLS is selected for data, ATM is still used as the bearer at the bottom layer, and the voice remains unchanged.In the R4 version, there are two options for dialogue voice. The voice can be either over IP or AAL2 bearer.Finally, the R5 version achieves 100% Over IP,data link layerIt is still an ATM cell.
Protocol support
The signaling plane of the core network: In GSM, the BSS oriented protocol isBSSAPThe protocol for wireless access network in WCDMA is RANAP, which is completely equivalent to BSSAP and is the dialogue between core network and wireless access network.The RANAP protocol is also functionally divided into two parts, one is a direct conversation with the RNC, and the other is a transparent conversation with the mobile station.The protocol in the core network has no change compared with the GSM from the upper layer perspective. The signaling part still uses the MAP protocol. The protocols to the registers, such as MAP-B, MAP-C, MAP-D, MAP-E, and MAP-F, have not changed. They are still messages from the upper layer mobile application.The bottom layer of MAP is still TCAP (session layer capability application part), which addresses the upper subsystems (MAP-HLR, MAP-VLR, etc.).The SCCP of the service control part is an enhancement of the MTP3 network addressing of Layer 3.The only change is the underlying MTP3, MTP2 and MTP1. MTP1, MTP2 and MTP3 in GSM complete the No.7 complete carrier platform. In WCDMA, MTP3 can still be selected as the underlying carrier or IP address addressing.data link layerandphysical layerATM is selected.There are also CAP and INAP protocols on the upper layer of TCAP, which are exactly the same as GSM.INAP is mainly used in fixed networks, but no longer used in mobile networks.INAP can be calledIntelligent networkThe specifications in the first phase of the protocol are mainly used for fixed networks, but not for mobile networks.Used in GSM networkIntelligent networkCamel is adopted for the protocol, which is called CAP. It is based on the INAP protocol and proposes the features and functions of mobile network services.CAP2 has been completed. The R99 version of WCDMA may use CAP3 or CAP4.Core network and telephone user partcommunication protocolUP，Both TUP and ISUP protocols are selected.For GPRS, the signaling protocol plane of the packet core network on the Gn interface is still the GTP protocol,encapsulationEncapsulated in IP over UDP protocolnetwork layerThe underlying layer can still be ATM bearer or others.The underlying protocol depends on the implementation scheme.
In GPRS, the activation process of PDP Context is very important. The PDP scene is managed by SGSN, which will manage each user's PDP scene.The user and the external network need to activate a PDP scenario, which means that a GTP channel has been established between the SGSN and GGSN for the user.In the current GPRS network, each user can only activate one PDP scenario, and cannot activate multiple PDP scenarios at the same time.In the 3G specification, it is proposed that one user can activate multiple PDP scenarios, and SGSN has the ability to manage multiple PDP scenarios. For example, users can access the IP network through GGSN1, and it can also access its own intranet through GGSN2.
Intelligent networkThe platform consists of three main functional parts, namely SSP, SCP and IP.The SSP is called the service switching point, which is equivalent to each switch. It must be able to provide an interface to the SCP point.SCP is the wholeIntelligent networkBusiness logicControl platformIt exists with its environment. It is used to complete the call of the business logic of the intelligent network and the storage environment of this logic. It is a large database.IP is called intelligent peripheral, which plays intelligent recording notification under the control of SCP point.The IP implementation methods of different manufacturers are different.aboutIntelligent networkThe living environment of is called SMS - Business Management System.SMS and work terminals will form a business creation environment, that isIntelligent networkBuild platform for.The business creation environment can generate newIntelligent networkThe service is sent to the SCP database to complete the call of intelligent network logic.In 3G, using Camel3 and Camel4Intelligent networkThe functions are more refined, and theOperatorIf the function of generating business is given on the human-computer interface, the logical platform of the business will be automatically generated.Unlike the current business implementation, the equipment manufacturer is required to complete software writing and updating, such as prepaid business.
R99 services are classified into four categories according to the specification definition. Each service has different requirements for delay and block error rate according to the requirements of Qos.For interactive services, the delay requirement is 100ms, and the error rate can be higher than 5%, and so on. In fax services, the delay requirement can be 100s, but the error rate is less than 3%.So you can't have both.
billing system : Billing records can be provided from the MSC. Time based user records are available;It can also provide statistics on the time and byte size of each user from the SGSN;Records can be extracted from GGSNdata packetBilling of traffic.All billing records will be sent to the unified billing record center - CGF.CGF will integrate all the billing records and send them to the billing center, which will complete the bill generation.
