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