1. 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)

2. SIP-ISUP
SIP overview:
SIP URLs
Format=
examples:
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

3. 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.

4. SIP-IP
PSTNIP  PSTN
Call flow:

5. 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

6. SIP-IP
PSTN IP
Call Flow:

7. 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

8. SIP-IP
IP PSTN

9. 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.

10. 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

11. 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

12. 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)

13. 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

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

15. 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.