软交换技术

专题V数据网新业务及生成技术软交换技术Sotswitch Technologiesyears a steady transition from a circuit -刘继明1 Introductionswitched to a packet - based infrastructureLiu Jimingecent technology advances contin-among the service providers and switchingRue to drive the shift towards con-vendors worldwide.verged IP networks. Networking hardwareEconomic forces are behind the shiftand software are simultaneously gettingaway from traditional circuit - basedbetter, faster, and cheaper. Packet -switching and towards packet - basedbased technology has finally matched theswitching which takes voice signals, digi-circuit - based in terms of reliability. Thetizes them, breaks them into packets, andexplosive growth of P networks providessends the packets over a standard IP basedample bandwidth to accommodate voicedata network, or is commonly referred as tocll.s We have witnessed in the last fewVoIP. Compared to the traditional PSTNnetworks, IP networks offer several distinct摘要:duction on Softswitch technologiesadvantages. An IP network can carry calls文章简要介绍了软交换技and provides an overview on thewith less bandwidth, integrate voice with术,并在概括软交换体系结构的Sottswitch architecture. Key com-data and video, and deliver new telecom-基础上，进一步阐述了软交换技ponents of Softswitch technologiesmunications services with ease. It uses the术的关键组成部分。从市场和技are further elaborated. Market andlow cost Intermet infrastructure, rather than术两方面论证了软交换技术将会technical aspects that contribute tothe traditional PSTIN propretary circuit成为下一代网络基础设施的核place Softswitch technologies at thenetworks. Finally， P networks allow心。heart of the next generation networktelecommunications service providers to in-infrastructure are examined.troduce new services less expensively than关键词:using proprietary methods, often by just软交换技术基于IP的语音KEY WORDS:adding a new server and integrating it with下一代网络增强型业务会聚型Softswitch technologies VoIPthe existing network.业务Next generation network En-An IP network is especially well suit-hanced service Converged ser-ed to handle the convergence of voice, da-ABSTRACT:■ta, fax, and video. There is already moreThis article gives a brief intro-data taffc than voice in the United States_owing over ten文章编号: 1009 - 6868(2001 )02 -0010-06文献标识码: A中图分类号 : TN915. 9中国煤化工MHCNMHCutie.Some10 2001年第2期《中兴通讯技术》C: \MAGrs. PUB一-7PPS/P1专题数据网新业务及生成技术analysts predict that more than 30% ofof technologies that perform the functionsSignaling Gateway and Media Server com-voice trffic worldwide will be over IP net-of (a) swithing-- establishing connec-ponents from the Access Plane and Appli-works by 2004. In addition to driving In-tions for end - to - end communications,cation Servers from the Service Plane. Aernet growth, consumers are demandingnd (b) converged service一providingsoftswitch alone usually refers to thenore and more converged services thatcombined service of voice, data, fax,Softswitch component in the Control Plane.combine voice, data and video services tovideo, and new services that could be of-The Media Gateway Contoller is themanage their increasingly complexfered in the future via Softswitch openkey component in the Control Plane. Irtelecommunications needs and new solu-API. Softwitch solutions can coexist withfact, the most popular word used in the in-tions are required to satisfy these. Onetraditional circuit - based switch and pro-dustry for this component is the termsuch solution is the Softswitch technolo-vide similar services using packet - basedSoftswitch. It mainly performs the callgies. Softswitch technologies are a collec-switch technology. The end user devicesontrol function providing connection andtion of products and services to enablemay include regular POIS phones, Icall control, translations and routing, me-telecommunications services to run on thephones, Multimedia Computers, Beepers,dia gateway management, bandwidth man-data network, notably, the Internet. It canPagers，Video Conferencing Terminals,agement, signaling, provisioning, securi-integrate voice, data, and video, and han-etc. Softswitch technologies may extendty, and call detail record generation.dle protocol translatons between separatebeyond IP networks to other forms ofThe switch plane consists of standardnetworks such as wireline, wireless andwired, wireless or broadband networks.IP routers and/ or ATM switches. Unlikecable systems. Softswitch technologies en-Softwitch technologies as implement-the traditional PSTN networks where tele-able cost - efective VoIP implementationsed by ZTE lgcall break into 4 functionalphone switches use their switching fabric toand give service providers the flexibility toplanes as seen in figure one. Componentsperform the function of switching, the newadd value while adhering to legacy switch-that reside in each of these functionalSoftswitch based network uses the networking standards like SS7. Although the ma-planes will be briefly descrbed here. Noteitself as the switching fabric.jority deployment of Softswitch solutionsthat Sftswitch technologies usually refer toThe Access Plane consists of Signal-today is to replace the traditional PSTNa set of technologies accomplished by net-ing Gateway, Media Gateway, and MediaClass 4 and/ or Class 5 switches, the keywork components from several functionalerver. A Signaling Gateway provides con-of these solutions is their ability to efec-planes, i. e, the Softswitch component inversion between the SS7 signaling networktively integrate the circuit and packet net-he Control Plane, the Media Gateway,(SS7 links) and the packet network, in-works and to deliver converged service.Service PlaneApplication Servers, Open APl(Parlay) Service Creation EnvironmentThis article gives a brief intoductionon the emerging Softswitch technologies .SIP, LDAPthat refer to a set of technologies that per-Control PlaneSotswitch/ Media Gateway Cntollerform the functions of switching and con-vergeservice. In the fllowing SectionSwitch PlaneIP Router/ ATM swichwe shall provide an overview on theH. 323, MGCP/H.248, Q.2931, Q Sig, SIPSoftswitch architecture and discuss some ofAccess PlaneSignaling Gateway, Media Gateway, Media Serverthe major architecture considerations in thedesign of ZTE Softswitch solution.SS7 yw'包PSTI/IONVirels( NetvBroadband ACcessTT向团国2 Softswitch TechnologiesOverview中国煤化工Softswitch technologies refer to a set| Figure 1 Softswitch ArchitectureTYHCNMHG2001年第2期《中兴通讯技术》11C: \MAG西方数据rs. PUB一-7PPS/P2专题数据网新业务及生成技术cluding protocols such as ISUP and TCAP.architecture is so designed that there iscalled a media gateway controller or a callIt is a key unit within the Softswitch archi-no single point of failure in the system. .agent, is responsible for bridging the tradi-tecture. A Media Gateway connects to the●Failure Recovery. A highly efectivetional wireline and wireless, SS7 signalingtelephone switch side and deals with thefailover schemenust be built in suchand P networks together. This " bridging"payload voice media data. It provides con-that the system is able to recover fromfunction involves establishing phone callversion between circuit - switched re-any type of failures quickly enough to ;and managing voice and data tafficsources(lines, trunks) and the packetachieve the high availability comparable(media) throughout the various networks.network (IP, ATM), including voice com-to those (99. 9% ) curently seenThe Softswitch is the controlling elementpression, fax relay, echo canellation, .with the PSTN switches. At the veryand the call control engine of the Softswitchand digit detection. In the near future theleast stable calls must be recoverable insolution architecture.video media data may also apply. A Mediafailure.The major functions of a SoftswitchServer provides for specialized media re-●Interoperability. To achieve interoper-are as fllws:sources, such as IVR, conferencing, fac-ability with media gatewaysnd●Perform the call control functionsimile, announcements, speech recogni-softswitches made from other vendors,●Control media gateways using industrialtion, and handles the bearer interface tomultiple device protocols and their vari-standard media gateway control proto-nedia gateways. An announcement serverants are implemented.cols such as MGCP and Megaco/H. 248can be a type of media server.●Service Extensibility. The ability of●Support voice call establishment proto-Application Servers reside on the Ser-rapidly creating and providing innova-cols such as H. 323 and SIPvice Plane and are another kind of keytive new services is one of the strengthSupport Class features such as Class 4components that provide for the executionof the architeture. Realizing the im-features and/ or Class 5 featuresand managerment of enhanced services andportance of time to market of new ser-●Provide Class of service/ quality of ser-blling, and handle the signaling interfacevices to the service providers today, thevice controlto softswitches. It also provides Applica-system supports open standard service●Interface with SS7 network via SIC-tion Programming Interface (API) for cre-creation API such as JAIN/PARLAYTRAN (SS7 over IP)ating and deploying services. Examples ofwhich are best suited for creating new●Support various forms of routing andenhanced services are Internet Call Wait-generation convergence services. Ser-numbering planing, Multiparty Conferencing, etc.vices built on these standard API are not- E.164 numbering planThe major architecture considerationsconstrained by Softswitch solution ven-- digit analysis overlap and/ or chan-in the design of ZTE Softswitch solution aredors.nel associated signalingthe flowing aspect:- digit translation support for IP, FR●Performance. It should achieve high3 Key Components of theand ATMBusy Hour Call Attempt (BHCA) for aSoftswitch Technologies●Call Detail Records (CDR) for bllinggiven CPU type and speed.In this section we shall elaborate on●Provisioning●Scalability. The architecture must bethose key components that are collectively- for media gateway controlled:flexible enough so that it can grow toknown as the Softswitch technologies. De-米DSO channel assignmentssupport many millions of BHCA as wellscriptions of the major functions provided米asignment and real time configura-as potentially many millions of sub-by these components are given here.tion of DSP resourcesscribers.米media transmission (voice coding,●Redundancy. The state persistence and3. 1 Softswitch(Media Gatewaycompression and packetization)database replication are some of theContoller)p SS7 cimaline nateway: .中国煤化工main architectural considerations. TheThe Softswitch component, sometimesMYCNMH G12 2001年第2期《中兴通讯技术》C: \MAG西方数据rs. PUB一-7PPS/P3专题数据网新业务及生成技术米point code/ routing configurationa result of MGCP/H.248 messages●Provide physical connectivity to the SS7米SS7 variants such as ANSI or ITU●Manage DSP resources to provide voicenetwork via T1/E1/V. 35 physical* timersand packet servicesconnection●Optionally support Gatekeeper function-●Support for legacy protocols such as●Transport SS7 informnation between SGlityLoop- Start, Ground -Start, E & M,and Softwitch via packet network●Optionally support bandwidh manage-CAS, Q. SIG and TR -303●Support of TI clear channel configuration3. 4 Application ServerA Sofswitch tpically runs on com-for taferring voice taffic payload inAn Application Server is an applica-mercially available servers such as SUNSS7 networkstion level server that provides for the exe-Netra workstations. A few vendors includ-●Manage TDM resources and linkcution and management of advanced ser-ing ZTE have chosen to have it run on morevices. It typically has a signaling interfacefault tolerant machines than commercial3.3 Signaling Gatewayto a call control function entity such asworkstations to increase the reliability andA Signaling Gateway (SG) bridgesSoftswitch. It also provides APIs for creat-shorten the time required for the componentthe SS7 network with the PSTN and ATM/ing and deploying services.failure recovery.IP networks for the Softswitch and estab-Advanced services provided by Appli-lishes the protocol, timing and messagecation Servers generally include several3. 2 Media Gatewayframing requirement of the SS7 networkservices such as:The Media Gateway provides a way toand the functional equivalents in the●Virtual Call Centertransport the media (voice/ data/fax/ATM/IP network. It makes the Softswitch●Unified Messagingvideo) between the ATM/IP packet net-look like another SSP in the SS7 network.●IP centrexwork and the legacy PSTN network. In theThe SG only handles the SS7 signaling,●Internet Call W aitingPSTN network, toll quality voice payload iswhile the media gateway will handle the●Pre - paid Clling cardsriding in a DSO. For the purpose of trans-voice circuits established by means of the●Calling Card applicationsporting in the packet network, samples ofSS7 signaling. If SIGTRAN is used as thethis toll quality voice are compressed andprotocol between the SG and Softswitch,3. 5 Media Serverpacketized. Typically Digital Signal Pro-then only MTP1, and MTP2 and SIGTRANA Media Server provides for special-cessors perform the functions such as ana-will rside on the SG. MTP3 and the aboveized media resources (IVR, conferencin,log to digital conversion (Mu-Law, A-will reside on the Softswitch. SIGTRANfacsimile, announcements, speech recog-aw)， voice - audio code compressiondefines a suite of protocols and user adap-nition), and handles the bearer interface to(G.723.1, C. 729a, C.711, etc. ), echotation layers for transporting signaling in-media gateways. An announcement servercancellation, presence of voice detection,formation over P - based networks. It usescan be a type of media server. Media Serv-silence detection and compression, comfortSCTP for reliable signaling transpor,er is not strictly required as part of the me-noise generation, out of band DTMF signalstreaming, congestion avoidance and con-dia gateway functions. However, in manytransport, etc. The DSPs control the play-trol, and M3UA for the tansfer of SS7implementations the media server function-out of voice into the IP network.MTP3 user part messages for ISUP, SCCP,ality is also built into the media gateways.Some of the key functional require-and TUP. If another protocol such as SIP isMGCP is now often used as the contollingments of a media gateway are as fllws: .used between the SG and Softswitch, thenprotocol for media servers.●Transmission of voice - data (media)the entire SS7 protocol will reside on theTypically, media servers provide the .using transmission protocol RTPG.fllowing functions:●DSP resource and TDM timeslot alaThe major functional requirements ofrannrded. nnnrements, IVR,中国煤化工tion contolled by the Media Gateway as ;SG are:fYHCNMHG2001年第2期《中兴通讯技术》13C: \MAG西方数据rs. PUB一-7PPS/P4专题数据网新业务及生成技术●n - way station conferenceing the PSTN while migrating to IP - basedlonger need to purchase an expensive Class●DTMF/MF tone detection/ generationnetworks.4 or Class 5 phone switch. They can also●Fax supportThe market acceptance of Softswitchpurchase only the capacity they need,technologies has been overwhelming. Manystarting with as few as several hundred4 Softswitch Technologiesservice providers in North America andports or customers, and add more as theyAre the Heart to theEurope have started or planed to deployexpand their customer base.Next Generation NetworkSoftswitch technologies. For example,The Softswitch is easier to manage andThe following combination of marketGlobal Crossing Ltd, which is buildingoperate than the traditional circuit - basedand technical forces contribute to placeand operating the world' 8 most extensiveswitch. As the control function is per-Softswitch technologies at the heart of theglobal IP - based fiber optic network, an-formed in the software based softswitches,next generation network infrastructure.nounced on September 27, 2000 that it hadthe upgrade and configuration changes arelit up its VoIP backbone in its domesticmuch more manageable than the traditional4.1 The market place and acceptanceproduction network using Sftswitch tech-PSTN switches. All these can help sericeof Softswitch technologiesnologies. The company completed the firstproviders bring down the maintenance costAny company that provides telecom-phase of its U. S. VoIP network by the endof their network dramatically.munications services, whether voice, In-of 2000, alowing it to originate and termi-ternet Access, wireless, or a bundle ofnate calls on its own core network in the4. 3 Softswitch technologies improvethese, can use Softswitch technologies toUS. Global Crossing plans to transfer itsservice deliveryprovide advanced functions to its customerntire voice traffic from the circuit -The key to the rapid acceptance ofbase. Long distance and local phone com-switched network to the packet - basedSoftswitch technologies in the telecommu-panies can use Sftswitch technologies tonetwork by 2002.nications industry is their ability to deliverreplace Class 4 and Class 5 telephonenew service. In the new architecture, ser-switches, add capacity, increase services4. 2 Cost reduction by Softswitchvices are progranned through open APIsoffered, or boost capabilities to handletechnologiesand this is one of the crucial elements imultimedia service.Internet serviceSoftswitch technologies allow telecom-enhanced service delivery. Basic servicesproviders and Internet telephony servicemunication companies to reduce the coststhat already exist in today' s Class switchesproviders can broaden the range of servicesof handling taffic, especially the explod-are typically done in softswitches while en-they ofer beyond basic Internet connectivi-ing volumes of data that their networkshanced services that may be far too com-ty. Emerging next generation carriers whomust carry. It is known that IP transportplex for traditional Class switches are of-sell bandwidth to others can use the privateand switching cost less than circuit switch-fered by separate application servers. Dif-fiber optic networks they built to cary con-ing. Softwitches in PSTN networks can offferent services may be provided by separateverged data, including voice, fax, anload dial - up data calls and intercept faxapplication servers and this architecture al-video, over their own lines with the help ofdata and route them to lower cost IP net-lows carriers to maintain a robust infras-Softswitch technologies. Softswitch tech-works. They can also be used to shifttructure for completing calls independent ofnologies provide service providers the ca-high - priced international long distancethe additional features they provide to indi-pability to seamlessly link to the PSTN tocalls to less expensive data networks.vidual customers.reach new customers not served by theirService providers can use SoftwitchBy adding new serices either as anfiber optic backbones. We believe that alltechnologies to replace existing Class 4upgrade to the software based softswitches,companies that deploy Softswitch technolo-and/or Class 5 telephone switches moreor as a replacement of an application serv-gies will gain the benefits of cost reduc-cost efectivele. New service providersewvice nmridore ran deploy new ser-中国煤化工tion, service iferentiation, and leverag-have lower barriers to entry since they noYHCNMHGower cost than14 2001年第2期《中兴通讯技术》C: \MAGrs. PUB一-7PPS/PS专题数据网新业务及生成技术with traditional methods. New value -simply adding new device control protocoltechnologies. Most early players in thadded offerings or service bundles repre-adaptors in the softswitches, serviceVoIP market have focused primarily 0sent an excellent way for companies to dif-providers can easily incorporated new typesH. 323 for voice and video call setup. Re-ferentiate themselves from their competi-of devices into the networks and expandcently, packet voice protocols, such astion.their networks and services.MGCP and Megaco/H. 248 for mediaExamples of basic services includegateway control, SIP for session initiationcall waiting and forwarding, call blocking,4.5 Open architecture and interoper-and management, SIP -T and BICC for800 numbers, and caller ID. Instances ofabilty of Softswitch technologiesSoftswitch peer -to - peer communica-enbanced services are such as UnifiedOne of the most important aspects oftions, SICTRAN for SS7 Over IP, have e-Communications, P Conferencing, Localthe Softswitch technologies is that theymerged. These protocols allow seamlessNumber Portability, and IP Centrex. Manybreak apart the linkages between the soft-traffic exchange within or between serviceof the existing Softswitch implementationsware and the itelligence, and the hard-provider networks and improve the interop-support customer self - configuration whichware, transport and switching layers. Urerability among components from diferentmeans that individual customers can go to alike traditional PSTN switches, wherevendors.specific web site provided by the servicethere were few manufacturers, and modify-Note that several of the protocols,provider to self - configure the services .ing an existing switch was dfficult and ex-such as H 323, SIP and MCCP/H. 248,pensive, many vendors compete to providecan work interchangeably. For example, a4. 4 Softswitch technologies are thehardware, software, and application com-softswitch using the H. 323 protocol cankey to the seamless migrationponents for Softswitch based solutions. Nottalk to and pass messages to a SIP - basedto IP Networksonly does this keep pricing competitive, itsoftswitch or a MGCP based softswitch.The migration of the traditional cir~also allows service providers or phone com-This interoperability among protocols addscuit - based PSTN networks to all P net-panies to select the best solution for theirto the Softswitch flexibility and ease of de-works will take years to complete and untilspecific needs, mixing and matchingployment. Standard based sofware comp0-then, PSTN and IP networks will coexist.ieces from different vendors and combin-nents of Softswitch solutions can be dis-The Softswitch technologies offer interoper-ing them using standard open interfaces.ributed across hardware elements butability across these two types of networks asSoftwitch solutions from dfferentfunction as a single unit, and standardthey transfer from circuit to packet basedvendors have begun to demonstrate inter-based media gateways can be easily inte-switching and are the key to facilitate car-operability recently. The Internationalgrated with legacy systems via SS7 inter-riers to seamlessly migrate their networks toSoftswitch Consortium (ISC) was formned inface, bringing new services to an existingall IP networks.999 to promote the interoperability ofsubscriber base. Service providers can ex-The distibuted architecture ofSoftswitch components from different ven-ploit Softswitch technologies modular ar-Sofiswitch technologies is well suited to al-dors and several interoperability test labo-chitecture and expand their systems to ac-low the phone networks to continue to eratories have been established that arecommodate new market needs.0volve by allowing service providers to addopen to Softswitch vendors. ISC currentlycapacity or services when and where theyhas more than 200 members.are needed. By implementing various pro-tocol adaptors, softswitches can leverage4. 6 Standards related to Softswitch(收稿日期: 2001 -03-11)existing resources such as directory andtechnologies刘继明， 中兴通讯美国分公司副总裁、博士。network SCP databases currently availableThere have been major efrts going真在美公尔实验室作司，2000年进入中兴通t。在国in PSTN network, allowing new services toon in ITU -T and ETF to standardize the中国煤化工年来致力于下一代interoperate with legacy databases. Byprotocols and architecture in SoftswitchYHCNM HG2001年第2期《中兴通讯技术》15C: \MAG西亦数据rs. PUB一-7PPS/P6