Media Gateway Control and the Softswitch … Architecture ... switching, signaling, routing, service...
Transcript of Media Gateway Control and the Softswitch … Architecture ... switching, signaling, routing, service...
2IP Telephony
Outline
IntroductionSoftswitch
Softswitch ArchitectureSoftswitch Operations
Media Gateway Control ProtocolsMGCPMEGACO
3IP Telephony
Next Generation Network
Internet Telecom & Wireless Communication
IP
MGCF
CSCF
SGW MGWMGW
WLAN
GPRS
CSCFSIP
Server
PSTN
InternetWireless App.Server
3rd Parties App.
4IP Telephony
Gateways in Next Generation Networks
CO
SCP
STP
PBX
H.323GK
SS7/IN
PSTN IP Networks
SG
TGW
H.323MG
MGC
MGC : Media Gateway ControllerSG : Signaling GatewayTGW : Trunking GatewayRGW : Residential Gateway
MGCP/MEGACOH.323/SIPSIGTRANRTP/RTCP
Analog Line
TrunkMGCP/MEGACO
PhonesRGW
H.323 Phones
5IP Telephony
H323/SIP VS. MGCP/MEGACO [1/2]
GWGK
MCU
GW : GatewayGK : GatekeeperTN : TerminalMCU : Multipoint Control Unit
TN
PSTN CA
TGW RGW
CA : Call AgentTGW : Trunking GatewayRGW : Residential GatewaySG : Singling Gateway
SS7
PSTN CO
SG
RTP
MGCP
H.323
TNTN
GWGK
MCU
TN
TNTN
6IP Telephony
H323/SIP VS. MGCP/MEGACO [2/2]
H.323 , SIPpeer-to-peerinternet orientedintelligent endpoint
optional GK decentralized
Problemsmaintenance
cost & scalability of large systems
signaling & media control are coupledinteroperability with SS7
MGCP/MEGACOclient-servertraditional telephonyintelligent server
“dumb” terminalcentralized
Conceptgateway decomposed
separate call control from media portsCA (MGC), MG, SG
interoperability with PSTN
7IP Telephony
Class 5 End Office Switch
The Telephone Network [1/2]
Circuit Switched Network
Intelligent Peripheral
Signal Transfer Point
Service Control Point
Class 4 Tandem Switch
Service Data Point
+
Transport Layer
Control Layer
SS7 SignalingISUP MessagesINAP/TCAP Messages
8IP Telephony
The Telephone Network [2/2]
5 Basic Components in Intelligent NetworksSSP/Service Switching Point
switching, signaling, routing, service invocation
STP/Service Transfer Pointsignaling, routing
SCP/Service Control Pointservice logic execution
SDP/Service Data Pointsubscriber data storage, access
IP/Intelligent Peripheralresources such as customized voice announcement, voice recognition, DTMF digit collection
SSPSSP
SCPSCP SDPSDP
STPSTPIPIP
SSPSSP
STPSTP
TCAP messages
ISUP messages
Voice
9IP Telephony
Softswitch
The switching functions are handled by software.International Softswitch Consortium (ISC)
www.softswitch.orgTo promote the softswitch concept and related technologies
Why the softswitch approach is popular?A distributed architectureFor network operators
It is possible to use different network components from different vendors.
For equipment vendorsIt is possible to focus on one area.
10IP Telephony
Abstract Softswitch Architecture
SIP is often used as the signaling protocol between the MGCs.
12IP Telephony
Softswitch Overview [1/3]
Softswitch: Emulating Circuit Switching in Software
IN/SCPPSTNLocal Switch
PSTNLocal Switch STP SS7 Network
IP Network
RTP Streams
MGCMGC MGCMGC
Trunk Trunk GatewayGateway
Trunk Trunk GatewayGateway
SIP-T
SGSGSGSG
MEGACO
IP PhoneIP Phone
90009000 Personalized VoIPService System
Application ServerApplication Server
13IP Telephony
Softswitch Overview [2/3]
Softswitch Provides Open Layered Architecture
• Solutions in a proprietary box• Expensive• Little room for innovation
Circuit-Switched
TransportHardware
Call Control & Switching
Services & Applications
PROPRIETARY
• Solutions are open standards-based• Customers choose best-in-class products • Open standards enable lower cost for
innovation
Soft-Switched
Transport Hardware
Softswitch Call Control
Services, Applications & Features (Management,
Provisioning and Back Office)
Open Protocols APIs
Open Protocols APIs
Open APIs for 3rd Party App develop.
Best-in-class Access Devices.
Scalable, Open Interfaces for Comm.
14IP Telephony
Softswitch Overview [3/3]
Softswitch Changes the Telecom LandscapeIntegration/Incorporation
Convergence of voice and dataCombination of telecom & internet technologiesReuse PSTN database & IN services in packet networks Multiple sources for app development & deploymentDecreased operating costs
StandardizationStandard interfaces (protocols) for communicationsOpen standards (APIs) for service creationCustomized services created by users themselvesBetter scalability
15IP Telephony
Softswitch Architecture
COSwitch
STP
SCP
COSwitch
STP
SCP
Signaling Layer
Transport Layer
IP
SIP-T
MediaServer
RTP
SIP-?/MGCP
SIP-TSI
Media Gateway
Controller
MGCP/MEGACOPhones
App.Server
Media Gateway
Controller
SIGTRANSSA/SCTP
MGCP/MEGACOTrunkingGateway
Signaling(SS7)
Gateway
SS7 TCAP
ISUP/TCAP
16IP Telephony
LocalSwitch
STP
SCP
STP STP STP
LocalSwitch
STP
LocalSwitch
TrunkingGateway
Signaling(SS7)
GatewayMedia
GatewayController
TrunkingGateway
Signaling(SS7)
Gateway
RoutingDirectory
Softswitch Operations [1/3]
Basic Call Control
12 ISUP ACM13 ISUP
ANM
ISUP ACMISUP ANM
ISUP IAM ISUP IAM
1
23
4 5
6 7
8
910
14
11
SIGTRAN
MGCP/MEGACOVoice Voice
RTP
17IP Telephony
Softswitch Operations [2/3]
Inter-Softswitch Communications
LocalSwitch
STP
TrunkingGateway
Signaling(SS7)
GatewayMedia
GatewayController
STP
TrunkingGateway
STP
MediaGateway
Controller
Signaling(SS7)
Gateway
STP STP
Domain A Domain B
LocalSwitch
RoutingDirectory
3
1
5
2
ISUP IAM
4
SIGTRAN
MGCP/MEGACO
6 SIP-T
7
9
16
Voice
RTP
8
ISUP IAM
12
13
Voice
10
11
14 ISUP ACM15 ISUP
ANM
ISUP ACMISUP ANM
18IP Telephony
Softswitch Operations [3/3]
IP-PSTN Interworking for IN Services
LocalSwitch
STP
SCP
STP STP STP
LocalSwitch
STP
LocalSwitch
TrunkingGateway
Signaling(SS7)
GatewayMedia
GatewayController
TrunkingGateway
Signaling(SS7)
Gateway
RoutingDirectory
ISUP IAM ISUP IAM
1
23
4
7
8 9
10
1112
13
SIGTRAN
MGCP/MEGACOVoice Voice
RTP
5
INAP/TCAP
16
6
14 ISUP ACM15 ISUP
ANM
ISUP ACMISUP ANM
19IP Telephony
Introduction
Voice over IPLower cost of network implementationIntegration of voice and data applicationsNew service featuresReduced bandwidth
Replacing all traditional circuit-switched networks is not feasible.VoIP and circuit-switching networks coexist
InteroperationSeamless interworking
20IP Telephony
Separation of Media and Call Control
GatewaysInterworkingTo 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 7The logical separation of signaling and media
21IP Telephony
Separation of Media and Call Control
A network gateway has two related but separate functions.
Signaling conversionThe call-control entities use signaling to communicate.
Media conversionA slave function (mastered by call-control entities)
Figure 6-1 illustrates the separation of call control and signaling from the media path.
22IP Telephony
Separation of Media and Call Control
Advantages of SeparationMedia conversion close to the traffic source and sinkThe 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 ProtocolIETF
MEGACO/H.248IETF and ITU-T Study Group 16
23IP Telephony
Requirements for Media Gateway Control [1/2]
RFC 2895Media Gateway Control Protocol Architecture and Requirements
RequirementThe creation, modification and deletion of media streams
Including the capability to negotiate the media formatsThe specification of the transformations applied to media streamsRequest the MG to report the occurrence of specified events within the media streams, and the corresponding actions
24IP Telephony
Requirements for Media Gateway Control [2/2]
Request the MG to apply tones or announcementsThe establishment of media streams according to certain QoS requirementsReporting QoS and billing/accounting statistics from an MG to an MGCThe management of associations between an MG and an MGC
In the case of failure of a primary MGCA flexible and scalable architecture in which an MGC can control different MGsFacilitate the independent upgrade of MGs and MGCs
25IP Telephony
Protocols for Media Gateway Control
The first protocol is MGCPRFC 2705, informationalTo be succeeded by MEGACO/H.248Has be included in several product developments
MEGACO/H.248A standards-track protocolRFC 3015 is now the official version.
IPDC
SGCP
MGCP
MDCP
MEGACO
Telcodia (Bellcore)
Level 3 Communication
Lucent (by ITU-T)
IETF RFC 3015ITU-T H.248November 2000
IETF RFC 2705October 1999
MGCP 1.0
IETF RFC 3435January 2003
27IP Telephony
MGCP/MEGACOPhones
TrunkingGateway
SignalingGateway
MGC
SIGTRANSSA/SCTP
RTP
MGCP/MEGACO
SS7 TCAP
ISUP/TCAP
Concept of MGCP/MEGACO
COSwitch
STP
SCP
PSTNPhones
Media Gateway
MGC
ConnectionCreateDeleteModify
Event NotificationRequest
StatusQuery
ResponseSuccessFailure
EventNotify
StatusReport
Dumb ClientStateless
Intelligent Server
28IP Telephony
MGCP
A master-slave protocol (A protocol for controlling media gateways)
Call agents (MGCs) control the operation of MGsCall-control intelligenceRelated call signaling
MGsDo what the CA instructsA line or trunk on circuit-switched side to an RTP port on the IP side
Types of Media GatewayTrunking Gateway to CO/SwitchesResidential Gateway to PSTN PhonesAccess Gateway to analog/digital PBX
Communication between call agentsLikely to be the SIP
29IP Telephony
The MGCP Model
EndpointsSources or sinks of mediaTrunk interfacesPOTS line interfacesAnnouncement endpoint
ConnectionsAllocation of IP resources to an endpointAn ad hoc relationship is established from a circuited-switched line and an RTP port on the IP side.A single endpoint can have several connections
30IP Telephony
GW’s Domain Name + Local Name Local Name
A hierarchical form: X/Y/Z
trunk4/12/[email protected] identify DS0 number 7 within DS1 number 12 on DS3 number 4 at gateway.somenetwork.net
Wild-cards$, any; *, alle.g., trunk1/5/[email protected]
CA wants to create a connection on an endpoint in a gateway and does not really care which endpoint is used.
e.g., trunk1/5/*@gateway.somenetwork.netCA requests statistical information related to all endpoints on a gateway.
Endpoint Identifier
31IP Telephony
MGCP Calls and Connections
A connectionRelationship established between a given endpoint and an RTP/IP session
A callA group of connections
The primary function of MGCP is to enableThe connections to be createdThe session descriptions to be exchanged between the connections
1 2 3
4 5 67 8 9
* 8 #
1 2 3
4 5 67 8 9
* 8 #
32IP Telephony
Call Identifier (Call ID)Created by CAUnique within CA Scope
Connection ID Created by GWUnique under Its GW
Calls and Connections
Endpoint Endpoint
CA1. CRCX3. MDCX
2. CRCX
IP, Port, Packetization
RTP
33IP Telephony
9 commands to handle Connection/EndpointsEndpointConfiguration (coding characteristics)NotificationRequest (requested events)Notify (GW: detected events)CreateConnectionModifyConnectionDeleteConnectionAuditEndpointAuditConnectionRestartInProgress (GW : taken in/out of service)
All commands are acknowledged.
EPCF RQNTNTFYCRCXMDCXDLCXAUEPAUCXRSIP
MGCP Commands