The Interworking of IP Telephony with Legacy Networks ISUP is used in PSTN, ISDN, MSC/GMSC of GSM and the gateway of IS-41. ISUP is the 'almighty' signaling for inter-connecting the different telephony networks In IP Telephony networks, the signaling is SIP, H.323 or MGCP/MEGACO. The signaling of Interworking: 1, SIP-ISUP 2, H.323-ISUP 3, MGCP/MEGACO-ISUP(also TCAP)

SIP-ISUP SIP overview: SIP URLs Format= User@host examples: root@metro.edu 4193701@cs.ucl.ac.uk Locating a SIP Server: Client request( E.g. INVITE) is sent to SIP server Either default local proxy SIP server Or SIP server for called party

The signaling is the ISUP MGC1 calls MGC2 The signaling is the SIP SIP-ISUP PSTNIP  PSTN PSTN1 calls MGC1 The signaling is the ISUP MGC1 calls MGC2 The signaling is the SIP MGC2 calls PSTN2 SIP looks like a transparent media for ISUP.

SIP-IP PSTNIP  PSTN Call flow:

MGC calls the SIP server and SIP phone The signaling is SIP Note: SIP-ISUP PSTN IP PSTN calls the MGC The signaling is ISUP MGC calls the SIP server and SIP phone The signaling is SIP Note: The SIP phone should already register to a SIP server. SIP server could be a proxy or a redirect server

SIP-IP PSTN IP Call Flow:

IP PSTN SIP phone calls the MGC The signaling is SIP SIP-ISUP IP PSTN SIP phone calls the MGC The signaling is SIP MGC calls the PSTN The signaling is ISUP

SIP-IP IP PSTN

H.225.0: Call Signaling and media packetisation H.323-ISUP H.323: H.225.0: Call Signaling and media packetisation Specifies call setup message which are based on Q.931 H.245: Call control MGC: Map the ISUP signaling to H.225 signaling and H.225 signaling to ISUP for call setup. Map the ISUP signaling to H.245 signaling and H.245 signaling to ISUP for call control.

Carries call setup messages to set up H.245 H.323-ISUP Q.931 channel Carries call setup messages to set up H.245 Can be closed as soon as H.245 Channel set up H.245 channel Exchange audio/video capabilities Master/slave determination initiate setup of RTP sessions Terminate call

Gateway Decomposition Scalability Seamless PSTN Integration MGCP/MEGACO-ISUP Gateway Decomposition Scalability Seamless PSTN Integration SS7/C7 connectivity Availability 2 kind of Gateway Trunk(TGW) Connects PSTN to IP network Residential(RGW) Connects residential telephone an IP network

Controls TGW and RGW using MGCP/MEGACO MGCP/MEGACO-ISUP Call agent Controls TGW and RGW using MGCP/MEGACO Handles SS7/C7 signaling for trunks that interconnect PSTN with IP network Interacts with SCPs over SS7 networking support of various services May support SIP/H.323 signaling In UMTS All-IP Core Network, the Call agent is ' Call Processing Server' (CPS)

Here is a example of MGCP-ISUP MGCP/MEGACO-ISUP Here is a example of MGCP-ISUP MGCP/MEGACO also support the mapping of TCAP

Call Flow of the MGCP-ISUP MGCP/MEGACO-ISUP Call Flow of the MGCP-ISUP

UMTS All-IP Core Network Here is The UMTS All-IP Core Network . In UMTS All-IP Core Network , R-SGW is used for the MAP connection to the Legacy 2G Network for Roaming.