Softswitch and Media Gateway (MGCP/MEGACO/SS7 over IP) 陳懷恩博士助理教授兼計算機中心資訊網路組組長國立宜蘭大學資工所 Email: wechen@niu.edu.tw TEL: 03-9357400 # 340
Outline Soft-switch Architecture MGCP (Media Gateway Control Protocol) MEGACO SS7 over IP 2
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) The following figure illustrates the separation of call control and signaling from the media path. 3
Softswitch Architecture [1/2] SIP MGCP MGCP RTP 4
Softswitch Architecture [2/2] 1 2 3 4 5 6 7 8 9 * 8 # 1 2 3 4 5 6 7 8 9 * 8 # 1 2 3 4 5 6 7 8 9 * 8 # 5
MGCP Calls and Connections A connection Relationship established between a given endpoint and an RTP/IP session A call A group of connections The primary function of MGCP is to enable The connections to be created The session descriptions to be exchanged between the connections 1 2 3 4 5 6 7 8 9 * 8 # 1 2 3 4 5 6 7 8 9 * 8 #
MGCP Connection Establishment imac 7
MGCP Commands 9 commands to handle Connection/Endpoints EPCF EndpointConfiguration (coding characteristics) RQNT NotificationRequest (requested events) NTFY Notify (GW: detected events) CRCX CreateConnection MDCX ModifyConnection DLCX DeleteConnection AUEP AuditEndpoint AUCX AuditConnection RSIP RestartInProgress (GW : taken in/out of service) All commands are acknowledged. 8
Call Setup Using MGCP imac 9
imac
Interworking between MGCP and SIP 11
Interworking between MGCP and SIP 12
MEGACO Command Naming MEGACO (1) Add (Termination to Context) (2) Modify (Termination-descriptor) (3) Subtract (Termination) (4) Move (Termination) (5) AuditValue (Termination-cur) (6) AuditCapability (Termination) (7) Notify (Termination) (8) ServiceChange (Termination) (NONE) Add, Modify, Move Add, Modify, Move Similar Commands in MGCP (1) CreateConnection (Endpoint) (2) ModifyConnection (Endpoint) (3) DeleteConnection (Endpoint) CreateConnection + DeleteConnection (4) AuditEndpoint (NONE) (5) Notify (Endpoint) (6) RestartInProgress (Endpoint) (7) AuditConnection (8) NotificationRequest (Endpoint) (9) EndpointConfiguration ti (Endpoint-encode) 13
MEGACO Connection Model 1 2 3 MGCP Endpoint Connection Call Agent (CA) MEGACO Termination Context Media Gateway Controller (MGC) 14
Concept of Context MGCP CA MEGACO MGC MGCP MEGACO RGW RTP RGW MG Context RTP MG IP Endpoint IP Endpoint Connection established after CRCX Termination Termination SCN Channel RTP Stream Add 2 Terminations into 1 context 15
Introduction to SS7 Channel Associated Signaling Still widely deployed today Considered as old telephony Common Channel Signaling Separation of signaling and call paths Signaling System 7 (SS7) To enable a wide range of services to be provided to the end-user Caller ID, toll-free calling, call screening, number portability, etc. SS7 is the foundation for Intelligent Network (IN) services. 17
The Telephone Network [2/2] 5 Basic Components in Intelligent Networks SSP (Service Switching Point) switching, service invocation STP (Service Transfer Point) signal routing SCP (Service Control Point) service logic execution SDP (Service Data Point) subscriber data storage, access IP (Intelligent Peripheral) TCAP messages IP SSP STP SCP STP ISUP messages Voice resources such as customized voice announcement, voice recognition, DTMF digit collection SDP SSP 18
SS7 Protocol Suite OSI Layers Application INAP MAP Presentation Session Transport Network Data Link Physical TCAP SCCP MTP Level 3 MTP Level 2 MTP Level 1 ISUP 19
MTP Levels 1 & 2 Message Transfer Part Level 1 Handling the issues related to the signals on the physical links between one signaling node and another Level 2 Dealing with the transfer of messages on a given link from one node to another Providing error detection/correction and sequenced delivery of the SS7 messages 20
MTP Level 3 Signaling gmessage handling Providing message routing between signaling points in the SS7 network Signaling network management Rerouting traffic to other SS7 signaling links in the case of link failure, congestion or node failure Load-sharing 21
ISUP ISUP: ISDN User Part Used as the protocol for setting up and tearing down phone calls between switches Initial Address Message (IAM) To initiate iti t a call between two switches Answer Message (ANM) To indicate that a call has been accepted by the called party Release Message (REL) To initiate call disconnection 22
SCCP SCCP: Signaling Connection Control Part Used as the transport layer for TCAP-based services freephone (800/888), calling card, wireless roaming Both connection-oriented and connectionless Mostly connectionless signaling Global title translation (GTT) capabilities The destination signaling gpoint and subsystem number is determined from the global title 23
TCAP, MAP and INAP TCAP: Transaction Capabilities Applications Part Supporting the exchange of non-circuit related information between signaling gpoints Queries and responses sent between SSPs and SCPs are carried in TCAP messages INAP (IN Application Part) MAP (Mobile Application Part) 24
ISUP Call Establishment and Release A given circuit between two switches is identified by OPC, DPC and CIC. IAM (Initial Address Message) ACM (Address Complete Message) CFG (Call ProGress) ANM (ANswer Message) REL (RELease) RLC (ReLease Complete)
Softswitch Architecture SS7 Network SCP STP Signaling (SS7) Gateway SIGTRAN MGCP/ MEGACO Internet Call Agent MGCP/ MEGACO CO Switch Trunking Gateway Trunking Gateway Trunking Gateway RTP Residential Gateway Residential Gateway Residential Gateway 26