# Telephony Communication Control

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## Lecture 1
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## Lecture 2
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## Lecture 3
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## Lecture 4
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## Lecture 5
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## Lecture 6
- [Msg. format of ISUP](https://what-when-how.com/roaming-in-wireless-networks/isdn-user-part-ccs7-in-wireless-networks/)
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## Lecture 7
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## Lecture 8
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## Lecture 9
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## Lecture 10
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## Lecture 11
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- the basic syntax used for Dial application

exten => <extension>,<priority>,Dial(<technology/resource>,<timeout>,<options>)

- the example of `extensions.conf`

[general]
static=yes
writeprotect=no

[default]
exten => 1001,1,Answer()
exten => 1001,2,Dial(SIP/1001,20)
exten => 1001,3,Voicemail(1001,u)
exten => 1001,4,Hangup()

exten => 1002,1,Answer()
exten => 1002,2,Dial(SIP/1002,20)
exten => 1002,3,Voicemail(1002,u)
exten => 1002,4,Hangup()

exten => 2000,1,Answer()
exten => 2000,2,Playback(demo-thanks)
exten => 2000,3,Hangup()

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## Lecture 12
- [Ref.](https://cafetele.com/volte-architecture/)
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- MME(Mobility Management Entity): UE registration, and UE tracking and paging procedures
- PCRF(Policy and Charging Rule Function): flow-based policy control and flow-based charging controls
- SGW(Serving Gateway): routes and forwards user data packets
- PGW(Packet Data Network Gateway): provides connectivity between the UE and external packet data networks
- IMS Core(IP Multimedia Subsystem Core): handle the delivery of multimedia services
- P-CSCF(Proxy Call Session Control Function): the first point of contact for the user’s device in the IMS network, responsible for routing signaling messages
- I/S-CSCF(Interrogating/Serving Call Session Control Function)
- I-CSCF: Handles session routing and interacts with the HSS for user authentication and authorization
- S-CSCF: The central node of the IMS core, managing session control and service invocation
- HSS(Home Subscriber Server): a database that contains user profiles, authentication information, and service permissions
- TAS(Telephony Application Server): provides a platform for deploying a wide range of voice and multimedia applications
- CS Core: circuit-switched infrastructure used in 2G and 3G
- HLR: 4G is HSS, 3G is HLR
- MGCF-MSS: control the conversion of singaling and management of voice calls between the circuit-switched and packet-switched domains
- MRFP-MGW: handle media processing functions, such as transcoding, voice compression/decompression