Media Gateway Control and the Softswitch Architecture Outline n Introduction n Softswitch n Softswitch Architecture n Softswitch Operations n Media Gateway Control Protocols n MGCP n MEGACO IP Telephony 2 Next Generation Network n Internet Telecom & Wireless Communication 3rd Parties App. GPRS CSCF Wireless App. SIP Internet Server Server CSCF WLAN MGCF MGW T-SGW MGW IP PSTN IP Telephony 3 Gateways in Next Generation Networks PSTN IP Networks SCP SS7/IN SG STP MGC TGW Trunk CO MGCP/MEGACO RGW Phones Analog Line H.323 GK H.323 PBX MG H.323 Phones MGC : Media Gateway Controller MGCP/MEGACO SG : Signaling Gateway H.323/SIP TGW : Trunking Gateway SIGTRAN RGW : Residential Gateway RTP/RTCP IP Telephony 4 H323, SIP & MGCP, MEGACO SS7 PSTN CA SG MGCP GK GW TN GK GW TN PSTN CO TGW RGW H.323 RTP MCU TN TN MCU TN TN GW : Gateway CA : Call Agent GK : Gatekeeper TGW : Trunking Gateway TN : Terminal RGW : Residential Gateway MCU : Multipoint Control Unit SG : Singling Gateway IP Telephony 5 H323, SIP & MGCP/MEGACO n H.323 , SIP n MGCP/MEGACO n peer-to-peer n client-server n internet oriented n traditional telephony n intelligent endpoint n intelligent server n optional GK n “dumb” terminal n decentralized n centralized n Problems n Concept n maintenance n gateway decomposed n cost & scalability of large n separate call control from systems media ports n signaling & media n CA (MGC), MG, SG control are coupled n interoperability with n interoperability with PSTN SS7 IP Telephony 6 The Telephone Network [1/2] SS7 Signaling Service Service + ISUP Messages Control Data INAP/TCAP Messages Point Point Signal Transfer Control Layer Point Intelligent Transport Layer Peripheral Class 4 Class 5 Tandem Switch End Office Switch Circuit Switched Network IP Telephony 7 The Telephone Network [2/2] n 5 Basic Components in Intelligent Networks n SSP/Service Switching Point n switching, signaling, routing, service invocation n STP/Service Transfer Point n signaling, routing SCPSCP SDPSDP TCAP messages n SCP/Service Control Point IP IP STP STP n service logic execution STP STP n SDP/Service Data Point SSP SSP ISUP messages SSPSSP n subscriber data storage, access Voice n IP/Intelligent Peripheral n resources such as customized voice announcement, voice recognition, DTMF digit collection IP Telephony 8 Softswitch n The switching functions are handled by software n International Softswitch Consortium (ISC) n www.softswitch.org n To promote the softswitch concept and related technologies n Why the softswitch approach is popular? n A distributed architecture n For network operators n It is possible to use different network components from different vendors. n For equipment vendors n It is possible to focus on one area. IP Telephony 9 Abstract Softswitch Architecture IP Telephony 10 Softswitch/PSTN Interworking n SIP is often used as the signaling protocol between the MGCs. Modem Bank IP Telephony 11 Softswitch Overview [1/3] n Softswitch: Emulating Circuit Switching in Software IN/SCP PSTN STP SS7 PSTN Local Network Local Switch Switch SG IP Network SG SIGTRAN MGC MGC SIP-T Trunk MEGACO Trunk Gateway Gateway RTP Streams 9000 Personalized VoIP Service System IP Phone Application Server IP Telephony 12 Softswitch Overview [2/3] n Softswitch Provides Open Layered Architecture Circuit-Switched Soft-Switched Services, Applications & Open APIs for P Services & Features (Management, R Applications Provisioning and 3rd Party App O develop. P Back Office) Open Protocols APIs R Call Control Scalable, I & Switching E Softswitch Call Control Open Interfaces T for Comm. A Transport Open Protocols APIs R Y Hardware Best-in-class Transport Hardware Access Devices. • Solutions in a proprietary box• Solutions are open standards-based • Customers choose best-in-class products • Expensive • Open standards enable lower cost for • Little room for innovation innovation IP Telephony 13 Softswitch Overview [3/3] n Softswitch Changes the Telecom Landscape n Integration/Incorporation n Convergence of voice and data n Combination of telecom & internet technologies n Reuse PSTN database & IN services in packet networks n Multiple sources for app development & deployment n Decreased operating costs n Standardization n Standard interfaces (protocols) for communications n Open standards (APIs) for service creation n Customized services created by users themselves n Better scalability IP Telephony 14 Softswitch Architecture App. SCP SCP SIP-?/ Server MGCP SS7 TCAP SIGTRAN Signaling SSA/SCTP SIP-TSI Media STP STP (SS7) Server IP Gateway Signaling Layer ISUP/TCAP Media Media Gateway Gateway Transport Layer Controller SIP-T Controller MGCP/MEGACO CO CO Trunking RTP Switch Switch Gateway MGCP/ MEGACO Phones IP Telephony 15 Softswitch Operations [1/3] n Basic Call Control SCP STP STP STP STP STP ISUP IAM ISUP IAM 3 9 2 Routing 10 ISUP ACM Directory 12 ISUP ACM SIGTRAN ISUP ANM Signaling Signaling 13 ISUP (SS7) 4 5 8 (SS7) ANM Local Gateway Local Gateway Local Switch SwitchMedia Switch Gateway 1 Controller 11 6 7 Voice Trunking MGCP/MEGACO Trunking Voice Gateway Gateway 14 RTP IP Telephony 16 Softswitch Operations [2/3] n Inter-Softswitch Communications STP STP STP STP STP ISUP IAM Domain A Domain B ISUP IAM 3 11 2 Routing 12 ISUP ACM Directory 14 ISUP ACM ISUP ANM SignalingSIGTRAN Signaling 15 ISUP (SS7) 5 8 (SS7) ANM Local Gateway Gateway Local 4 10 Switch Media 7 Media Switch 1 Gateway Gateway 13 Controller SIP-T Controller 6 9 Voice Trunking Trunking Voice GatewayMGCP/MEGACO Gateway 16 RTP IP Telephony 17 Softswitch Operations [3/3] n IP-PSTN Interworking for IN Services SCP STP STP STP STP STP ISUP IAM INAP/TCAP ISUP IAM 3 6 11 2 Routing 12 ISUP ACM Directory 14 ISUP ACM Signaling SIGTRAN Signaling ISUP ANM 15 ISUP (SS7) 7 (SS7) 5 10 ANM Local Gateway Local Gateway Local Switch 4 SwitchMedia Switch Gateway 1 Controller 13 8 9 Voice Trunking MGCP/MEGACO Trunking Voice Gateway Gateway RTP 16 IP Telephony 18 Introduction n Voice over IP n Lower cost of network implementation n Integration of voice and data applications n New service features n Reduced bandwidth n Replacing all traditional circuit-switched networks is not feasible. n VoIP and circuit-switching networks coexist n Interoperation n Seamless interworking IP Telephony 19 Separation of Media and Call Control n Gateways n Interworking n To make the VoIP network appear to the circuit switched network as a native circuit-switched system and vice versa n Signaling path and media path are different in VoIP systems. n Media – directly (end-to-end) n Signaling – through H.323 gatekeepers (or SIP proxies) n SS7, Signaling System 7 n The logical separation of signaling and media IP Telephony 20 Separation of Media and Call Control n A network gateway has two related but separate functions. n Signaling conversion n The call-control entities use signaling to communicate. n Media conversion n A slave function (mastered by call-control entities) n Figure 6-1 illustrates the separation of call control and signaling from the media path. IP Telephony 21 Separation of Media and Call Control n Advantages of Separation n Media conversion close to the traffic source and sink n The call-handling functions is centralized. n A call agent (media gateway controller - MGC) can control multiple gateways. n New features can be added more quickly. n MGCP, Media Gateway Control Protocol n IETF n MEGACO/H.248 n IETF and ITU-T Study Group 16 IP Telephony 22 Requirements for Media Gateway Control [1/2] n RFC 2895 n Media Gateway Control Protocol Architecture and Requirements n Requirement n The creation, modification and deletion of media streams n Including the capability to negotiate the media formats n The specification of the transformations applied to media streams n Request the MG to report the occurrence of specified events within the media streams, and the corresponding actions IP Telephony 23 Requirements for Media Gateway Control [2/2] n Request the MG to apply tones or announcements n The establishment of media streams according to certain QoS requirements n Reporting QoS and billing/accounting statistics from an MG to an MGC n The management of associations between an MG and an MGC n In the case of failure of a primary MGC n A flexible and scalable architecture in which an MGC can control different MGs n Facilitate the independent upgrade of MGs and MGCs IP Telephony 24 Protocols for Media Gateway Control n The first protocol is MGCP n RFC 2705, informational n To be succeeded by MEGACO/H.248 n Has be included in several product developments n MEGACO/H.248 n A standards-track protocol IETF RFC 3435 n RFC 3015 is now the official version. January 2003 Telcodia (Bellcore) MGCP SGCP IETF RFC 2705 1.0 October 1999 IETF RFC 3015 MGCP ITU-T H.248 Level 3 Communication November 2000 IPDC MEGACO Lucent (by ITU-T) MDCP IP Telephony 25 Relation with H.323/SIP Standards IP Telephony 26 Concept of MGCP/MEGACO Intelligent Connection Server Create Delete SCP Modify MGC SS7 TCAP Event Notification Request SIGTRAN SignalingSSA/SCTP Status STP Gateway Query ISUP/TCAP MGC Response Success Failure MGCP/MEGACO Event CO Trunking Media Notify Switch Gateway Gateway Status Report RTP Dumb Client PSTN MGCP/ MEGACO Stateless Phones Phones IP Telephony 27 MGCP n A master-slave protocol (A protocol for controlling media gateways) n Call agents (MGCs) control the operation of MGs n Call-control intelligence n Related call signaling n MGs n Do what the CA instructs n A line or trunk on circuit-switched side to an RTP port on the IP side n Types of Media Gateway n Trunking Gateway to CO/Switches n Residential Gateway to PSTN Phones n Access Gateway to analog/digital PBX n Communication between call agents n Likely to be the SIP IP Telephony 28 The MGCP Model n Endpoints n Sources or sinks of media n Trunk interfaces n POTS line interfaces n Announcement endpoint n Connections n Allocation of IP resources to an endpoint n An ad hoc relationship is established from a circuited-switched line and an RTP port on the IP side.