Media Gateway Control And The Softswitch Architecture
Media Gateway Control and theSoftswitch Architecture
OutlinennIntroductionSoftswitchnnnSoftswitch ArchitectureSoftswitch OperationsMedia Gateway Control ProtocolsnnMGCPMEGACOIP Telephony2
Next Generation NetworknInternet Telecom & Wireless Communication3rd Parties tWLANMGCFMGWT-SGWMGWIPPSTNIP Telephony3
Gatewaysin Next Generation NetworksPSTNIP NetworksSCPSS7/INSGSTPMGCTGWCOTrunkAnalog MG: Media Gateway Controller: Signaling Gateway: Trunking Gateway: Residential GatewayMGCP/MEGACOH.323/SIPH.323 PhonesSIGTRANRTP/RTCPIP Telephony4
H323, SIP & MGCP, MCUGWGKTNMCUTNTNMCUTN: Gateway: Gatekeeper: Terminal: Multipoint Control UnitRTPTNCATGWRGWSG::::Call AgentTrunking GatewayResidential GatewaySingling GatewayIP Telephony5
H323, SIP & MGCP/MEGACOnH.323 , SIPnnnpeer-to-peerinternet orientedintelligent endpointnnnnnnnnmaintenanceSS7nn“dumb” terminalcentralizedConceptncost & scalability of largesystemssignaling & mediacontrol are coupledinteroperability withclient-servertraditional telephonyintelligent serverndecentralizednMGCP/MEGACOoptional GKProblemsnngateway decomposednnnseparate call control frommedia portsCA (MGC), MG, SGinteroperability withPSTNIP Telephony6
The Telephone Network [1/2]SS7 SignalingISUP MessagesServiceService ControlDataPointPointINAP/TCAP MessagesSignalTransferPointControl LayerIntelligentPeripheralTransport LayerClass 4Tandem SwitchClass 5End Office SwitchCircuit Switched NetworkIP Telephony7
The Telephone Network [2/2]n5 Basic Components in Intelligent NetworksnSSP/Service Switching PointnnSTP/Service Transfer Pointnnservice logic executionsubscriber data storage, accessIP/Intelligent PeripheralnSCPSCPTCAP messagesSDP/Service Data Pointnnsignaling, routingSCP/Service Control Pointnnswitching, signaling, routing, service invocationIPIPSTPSTPSSPSSPSDPSDPSTPSTPISUP messagesSSPSSPVoiceresources such as customized voice announcement,voice recognition, DTMF digit collectionIP Telephony8
SoftswitchnnThe switching functions are handled bysoftwareInternational Softswitch Consortium (ISC)nnnwww.softswitch.orgTo promote the softswitch concept and relatedtechnologiesWhy the softswitch approach is popular?nnA distributed architectureFor network operatorsnnIt is possible to use different network components fromdifferent vendors.For equipment vendorsnIt is possible to focus on one area.IP Telephony9
Abstract Softswitch ArchitectureIP Telephony 10
Softswitch/PSTN InterworkingnSIP is often used as the signaling protocol between the MGCs.Mo d em Ban kIP Telephony 11
Softswitch Overview [1/3]nSoftswitch: Emulating Circuit Switching in NetworkSGSGIP EGACORTP Streams9000Personalized VoIPService SystemIP PhoneApplication ServerIP Telephony 12
Softswitch Overview [2/3]nSoftswitch Provides Open ices &ApplicationsCall Control& SwitchingTransportHardwareSoft-SwitchedServices, Applications &Features (Management,Provisioning andBack Office)OpenProtocolsAPIsSoftswitch Call ControlOpenProtocolsAPIsTransport HardwareOpen APIs for3rd Party Appdevelop.Scalable,Open Interfacesfor Comm.Best-in-classAccess 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 innovationinnovationIP Telephony 13
Softswitch Overview [3/3]nSoftswitch Changes the Telecom ce of voice and dataCombination of telecom & internet technologiesReuse PSTN database & IN services in packet networksMultiple sources for app development & deploymentDecreased operating costsStandardizationnnnnStandard interfaces (protocols) for communicationsOpen standards (APIs) for service creationCustomized services created by users themselvesBetter scalabilityIP Telephony 14
Softswitch ArchitectureSCPApp.ServerSCPSS7 TCAPSTPIPSignaling(SS7)GatewaySTPSignaling LayerISUP/TCAPTransport ACOPhonesIP Telephony 15
Softswitch Operations [1/3]nBasic Call ControlSCPSTPISUP ACMISUP ANM2STPSTPISUP IAM3LocalSwitchRoutingDirectorySignaling nkingGatewayGatewayController8ISUP Gateway12 ISUP ACM13 ISUPANMLocalSwitch11Voice14 RTPIP Telephony 16
Softswitch Operations [2/3]nInter-Softswitch CommunicationsSTP2ISUP ACMISUP ANMSTPISUP IAM3LocalSwitch1STPDomain ADomain BRoutingDirectorySignaling ler7SIP-TTrunkingGateway MGCP/MEGACOMediaGatewayController10STPISUP IAM1112Signaling(SS7)Gateway9TrunkingGateway14 ISUP ACM15 ISUPANMLocalSwitch13Voice16 RTPIP Telephony 17
Softswitch Operations [3/3]nIP-PSTN Interworking for IN ServicesSCPSTPSTPISUP IAMISUP ACMISUP ling y1011ISUP er89MGCP/MEGACO16STPTrunkingGateway1214 ISUP ACM15 ISUPANMLocalSwitch13VoiceRTPIP Telephony 18
IntroductionnVoice over IPnnnnnnLower cost of network implementationIntegration of voice and data applicationsNew service featuresReduced bandwidthReplacing all traditional circuit-switchednetworks is not feasible.VoIP and circuit-switching networks coexistnnInteroperationSeamless interworkingIP Telephony 19
Separation of Media and Call ControlnGatewaysnnnSignaling path and media path are different inVoIP systems.nnnInterworkingTo make the VoIP network appear to the circuitswitched network as a native circuit-switchedsystem and vice versaMedia – directly (end-to-end)Signaling – through H.323 gatekeepers (or SIPproxies)SS7, Signaling System 7nThe logical separation of signaling and mediaIP Telephony 20
Separation of Media and Call ControlnA network gateway has two related but separatefunctions.nSignaling conversionnnMedia conversionnnThe call-control entities use signaling to communicate.A slave function (mastered by call-control entities)Figure 6-1 illustrates the separation of call controland signaling from the media path.IP Telephony 21
Separation of Media and Call ControlnAdvantages of SeparationnnnnnMGCP, Media Gateway Control ProtocolnnMedia conversion close to the traffic source andsinkThe call-handling functions is centralized.A call agent (media gateway controller - MGC) cancontrol multiple gateways.New features can be added more quickly.IETFMEGACO/H.248nIETF and ITU-T Study Group 16IP Telephony 22
Requirements for Media Gateway Control[1/2]nRFC 2895nnMedia Gateway Control Protocol Architecture andRequirementsRequirementnThe creation, modification and deletion of mediastreamsnnnIncluding the capability to negotiate the media formatsThe specification of the transformations applied tomedia streamsRequest the MG to report the occurrence ofspecified events within the media streams, andthe corresponding actionsIP Telephony 23
Requirements for Media Gateway Control[2/2]nnnnRequest the MG to apply tones or announcementsThe establishment of media streams according tocertain QoS requirementsReporting QoS and billing/accounting statisticsfrom an MG to an MGCThe management of associations between an MGand an MGCnnnIn the case of failure of a primary MGCA flexible and scalable architecture in which anMGC can control different MGsFacilitate the independent upgrade of MGs andMGCsIP Telephony 24
Protocols for Media Gateway ControlnThe first protocol is MGCPnnnnRFC 2705, informationalTo be succeeded by MEGACO/H.248Has be included in several product developmentsMEGACO/H.248nnA standards-track protocolRFC 3015 is now the official version.Telcodia (Bellcore)SGCPIETF RFC 2705October 1999Level 3 CommunicationMGCPIPDCIETF RFC 3435January 2003MGCP1.0IETF RFC 3015ITU-T H.248November 2000MEGACOLucent (by ITU-T)MDCPIP Telephony 25
Relation with H.323/SIP StandardsIP Telephony 26
Concept of ModifyEvent NotificationRequestStatusQuerySCPSS7 eEventNotifyStatusReportDumb ClientStatelessIP Telephony 27
MGCPnA master-slave protocol (A protocol for controllingmedia gateways)nCall agents (MGCs) control the operation of MGsnnnMGsnnnDo what the CA instructsA line or trunk on circuit-switched side to an RTP port on the IPsideTypes of Media GatewaynnnnCall-control intelligenceRelated call signalingTrunking Gateway to CO/SwitchesResidential Gateway to PSTN PhonesAccess Gateway to analog/digital PBXCommunication between call agentsnLikely to be the SIPIP Telephony 28
The MGCP ModelnEndpointsnnnnnSources or sinks of mediaTrunk interfacesPOTS line interfacesAnnouncement endpointConnectionsnnnAllocation of IP resources to an endpointAn ad hoc relationship is established from acircuited-switched line and an RTP port on the IPside.A single endpoint can have several connectionsIP Telephony 29
MGCP Endpoints [1/3]nDS0 channelnnnnA digital channel operates at 64kbps.Multiplexed within a larger transmission facilitysuch as DS1 (1.544 Mbps) or E1 (2.048 Mbps)G.711 (u-law or A-law)Analog linennnTo a standard telephone lineAn analog voice streamCould also be audio-encoded data from a modemnThe gateway shall be required to extract the data andforward it as IP packets.IP Telephony 30
MGCP Endpoints [2/3]nAnnouncement server access pointnnProvide access to a single announcementOne-waynnInteractive voice response (IVR) access pointnnProvide access to an IVR systemConference bridge access pointnnNo external circuit-switched channelsMedia streams from multiple callers can be mixedPacket relaynA firewall between an open and a protectednetworksIP Telephony 31
MGCP Endpoints [3/3]nWiretap access pointnnnFor listening to the media transmittedOne wayATM trunk-side interfacennThe termination of an ATM trunkMay be an ATM virtual circuitIP Telephony 32
Endpoint IdentifiernnGW’s Domain Name Local NameLocal Namenntrunk4/12/7@gateway.somenetwork.netnnA hierarchical form: X/Y/ZTo identify DS0 number 7 within DS1 number 12 on DS3number 4 at gateway.somenetwork.netWild-cardsnn , any; *, alle.g., trunk1/5/ @gateway.somenetwork.netnnCA wants to create a connection on an endpoint in a gatewayand does not really care which endpoint is used.e.g., trunk1/5/*@gateway.somenetwork.netnCA requests statistical information related to all endpoints ona gateway.IP Telephony 33
MGCP Calls and ConnectionsnA connectionnnA callnnRelationship established between a given endpoint and anRTP/IP sessionA group of connectionsThe primary function of MGCP is to enablennThe connections to be createdThe session descriptions to be exchanged between theconnections123456789*8#123456789*8#IP Telephony 34
Calls, Connections and Call AgentsnCall Identifier (Call ID)nnnConnection IDnnnCreated by CAUnique within CA ScopeCreated by GWUnique under Its GW1. CRCX3. MDCX2. CRCXCAIP, Port,PacketizationEndpointRTPEndpointCA Identifier (its domain name)nRedundant CAs with a domain name: reliabilityIP Telephony 35
MGCP Commandsn9 commands to handle Connection/EndpointsEPCF nRQNT nNTFY nCRCX nMDCX nDLCX nAUEP nAUCX nRSIP nnEndpointConfiguration (coding characteristics)NotificationRequest (requested events)Notify (GW: detected ctionAuditEndpointAuditConnectionRestartInProgress (GW : taken in/out of service)All commands are acknowledged.IP Telephony 36
MGCP Command FormatnA command linennnnnnA number of parameter linesAn optional session description (SDP)nnRequest verb (the name of the command)Transaction idEndpoint id (for which the command applies)Protocol versionSeparated by a single empty lineCommand EncapsulationnnnOne command can be included within anotherOnly one level of encapsulationE.g., when instructing a gateway to create a connection, CAcan simultaneously instruct the gateway to notify the CA ofcertain events.IP Telephony 37
MGCP Parameters [1/6]nBearInformation (B)nnnCallId (C)nnIn response to an auditConnectionId (I)nnComprised of hexadecimal digitsCapabilities (A)nnThe line-side encodingB:e:muComprised of hexadecimal digitsConnectionMode (M)nSend only, receive only and send-receiveIP Telephony 38
MGCP Parameters [2/6]nConnectionParameters (P)nnnnDetectEvents (T)nnnThat an endpoint should detect during quarantine periodE.g., off-hook, on-hook, hook-flash, DTMF digits LocalConnectionDescripter (LC)nnConnection-related statistical informationAverage latency, jitter, packets sent/received/lostGW - CAAn SDP session descriptionLocalConnectionOptions (L)nnBandwidth, packetization period, silence suppression, gaincontrol, echo cancellation L: e:off, s:onnTo turn echo cancellation off and to turn silence suppression onIP Telephony 39
MGCP Parameters [3/6]nEventStates (ES)nnnMaxMGCPDatagram (MD)nnnAn address for the CAObservedEvents (O)nnTo indicate the maximum size MGCP packet supported byan MGIncluded in the response to an AUEP commandNotifiedEntity (N)nnIn response to an audit commandA list of events associated with the current stateDetected by an endpointPackageList (PL)nnSupported by an endpointEvents and signals are grouped into packagesnAnalog line endpointIP Telephony 40
MGCP PackagesnnEvents & Signalspackage name(o)/event or signal name (insensitive)nnpackages: grouping of events & signals for aparticular type of endpointsnnnnnnnnnnnL/hu Hu (if L is the default package for the endpoint)Generic Media (G)DTMF (D)MF (M)Trunk (T)Line (L)Handset (H)RTP (R)ScriptNetwork Access Server (N)Announcement Server (A)GatewayTrunk GW (ISUP)Trunk GW (MF)Network Access ServerCombined NAS/VOIP GWAccess GW (VOIP)Access GW (VOIP NAS)Residential GWAnnouncement GWSupported packagesG, D, T, RG, M, D, T, RG, M, T, NG, M, D, T, N, RG, M, D, RG, M, D, N, RG, D, L, RA, RThe experimental packages have names beginningwith the two character “x-”.IP Telephony 41
MGCP Parameters [4/6]nQuarantineHandling (Q)nnnReasonCode (E)nnEvents that occur during theperiod in which the GW is waitingRequest Notify Responsefor a response to a NotifycommandTimeProcess the events or discardQuarantine PeriodthemWhen a GW deletes/restarts aconnectionRemoteConnectionDescripter(RC)nQ:Q: process/discardprocess/discardstep/loopstep/loop (notify)(notify)T:T: eventsevents toto detectdetectduringduring quarantinequarantineAn SDP session descriptionIP Telephony 42
MGCP Parameters [5/6]nRequestEvents (R)nnnnRequestInfo (F)nnnIn response to audit requestsThe current values of RequestEvents, DigitMap,NotifiedEntityRequestIdentifier (X)nnA list of events that an endpoint is to watch forAssociated with each event, the endpoint can be instructedto perform actionsE.g., collect digits, or apply a signalTo correlate a given notification from a GWRestartDelay (RD)nA number of seconds indicating when an endpoint will bebrought back into serviceIP Telephony 43
MGCP Parameters [6/6]nRestartMethod (RM)nnSecondConnectionId (I2)nnA connection between two endpoints on the sameGWSignalRequests (S)nnThe connection on a second endpointSecondEndpointID (Z2)nnGraceful or ForcedSignals to be applied by an endpointSpecificEndpointID (Z)nUsed to indicate a single endpointIP Telephony 44
Digit MapnCA ask GW to collect user dialed digitsnnCreated by CAUsagenGateways detect a set of digits.nnInter-digit Timere.g., (11x 080xxxxxx 03xxxxxxx 002x.T)Match accumulated digitsnnnunder-qualified, do nothing furthermatched, send the collected digits to CAover-qualified, send the digits to CAIP Telephony 45
MGCP ResponsenHeadernnnA response lineReturn code TransID CommentaryA set of parameter lines (optional)nnE.g., I: A3C47F21456789F0 (ConnectionId)Session DescriptionnnSession Description Protocolseparated from header by an empty lineIP Telephony 46
Return Coden100 199: provisional responsenn200 299: successful completionnnexecuted normally400 499: transient errornnncurrent being executedcould not be executed because of no sufficientresources at this timephone already off/on hook500 599: permanent errornnendpoint unknownprotocol errorIP Telephony 47
Protocol Description [1/2]nTransactions (simple text format)ncommandnnheadern a command line (case insensitive)nAction TransId Endpoint Versionn a set of parameter linesnparameter name (upper case): valuen ExamplenRQNT 1201 endpoint/1@rgw.net MGCP 1.0nX: 0123456789B1 (RequestIdentifier)nR: hd (requestedEvent: hang down)nS: rg (signalRequest: ring tone)session descriptionIP Telephony 48
Protocol Description [2/2]nTransactionsnresponsennheadern a response linenResponse code TransId Commentaryn a set of parameter lines (optional)n Examplen200 1201 OKnafter CRCX(/MDCX/DLCX/Audit/Restart)nI: A3C47F21456789F0 (ConnectionId)session descriptionn Session Description Protocol (RFC 2327)n separated from header by an empty lineIP Telephony 49
Call Setup Using MGCPi Ma cIP Telephony 50
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Softswitch Operations [2/3] n Inter-Softswitch Communications Local Switch STP Trunking Gateway Signaling (SS7) Gateway Media Gateway Controller STP Trunking Gateway STP Media Gateway Controller Signaling (SS7) Gateway STP STP Domain A Domain B Local Switch Routing Directory 3 1 5 2 ISUP IAM 4
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