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Content for  TS 23.205  Word version:  16.0.0

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1  ScopeWord‑p. 16
The present document defines the stage 2 description for the bearer independent CS core network. The stage 2 shall cover the information flow between the GMSC server, MSC server and media gateways. Note that nothing in the present document shall preclude an implementation of a combined MSC Server and MGW. The present document shall show the CS core network termination of the Iu interface in order to cover the information flow stimulus to the core network and describe the interaction with the supplementary and value added services and capabilities.
For the purposes of the present document, the protocol used over the Nc interface is an enhanced call control protocol supporting call bearer separation such as BICC (which is specified in [22]). The protocol used over the Mc interface is H.248 (which is specified in TS 29.232). Existing specifications and recommendations shall not be repeated, as such the relevant specification shall be referred to.
SIP-I based CS core network is further specified in TS 23.231.
Local Call Local Switch (LCLS) functionality is further specified in TS 23.284.
The present document is applicable only for ATM or IP transport in the CS core network.
[reproduction not planned]
Figure 1: CS core network logical architecture
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The CAP interfaces and the interfaces towards the HLR are outside the scope of the present document.
Details of Transcoder-Free Operation are outside the scope of the present document. Please see 3GPPTS 23.153 for more information.
The present document specifies functions, procedures and information which apply to GERAN Iu mode. However, functionality related to GERAN Iu mode is neither maintained nor enhanced.
2  References
The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
  • References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
  • For a specific reference, subsequent revisions do not apply.
  • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
[1]  TR 21.905   "Vocabulary for 3GPP Specifications".
[2]  TS 23.002   "Network architecture".
[3]  TS 23.153   "Out of Band Transcoder Control; Stage 2".
[4]  TS 24.008   "Mobile radio interface Layer 3 specification; Core network protocols; Stage 3".
[5]  ITU-T Recommendation H.248: "Gateway control protocol".
[6]  TS 29.232   "Media Gateway Controller (MGC) - Media Gateway (MGW) interface; Stage 3".
[7]  TS 29.415   " Core Network Nb Interface User Plane Protocols ".
[8]  TS 23.009   "Handover procedures".
[9]  TS 23.072   "Call Deflection Supplementary Service; Stage2".
[10]  TS 23.078   "Customized Applications for Mobile network Enhanced Logic (CAMEL); Stage 2".
[11]  TS 23.079   "Support of Optimal Routeing (SOR); Technical Realization; Stage2".
[12]  TS 23.082   "Call Forwarding (CF) Supplementary Services; Stage 2".
[13]  TS 23.083   "Call Waiting (CW) and Call Hold (HOLD) Supplementary Services; Stage 2".
[14]  TS 23.084   "MultiParty (MPTY) Supplementary Service; Stage 2".
[15]  TS 23.091   "Explicit Call Transfer (ECT) Supplementary Service; Stage 2".
[16]  TS 23.093   "Technical realization of Completion of Calls to Busy Subscriber (CCBS); Stage 2".
[17]  TS 23.135   "Multicall supplementary service; Stage 2".
[18]  TS 23.108   "Mobile radio interface layer 3 specification core network protocols; Stage 2".
[19]  3GPP TS 42.032: "Immediate Service Termination (IST); Service description; Stage 1".
[20]  TS 25.415   "UTRAN Iu interface user plane protocols".
[21]  TS 29.414   "Core Network Nb data transport and transport signalling".
[22]  TS 29.205   "Application of Q.1900 series to bearer independent circuit-switched core network architecture; Stage 3".
[23]  TS 29.010   "Information Element Mapping between Mobile Station - Base Station System (MS - BSS) and Base Station System - Mobile-services Switching Centre (BSS - MSC); Signalling Procedures and the Mobile Application Part (MAP)".
[24]  TS 43.045   "Technical Realization Of Facsimile Group 3 service - Transparent".
[25]  TS 23.146   "Technical realization of facsimile group 3 non-transparent".
[26]  TS 25.413   "UTRAN Iu Interface RANAP signalling"
[27]  TS 48.008   "Mobile Switching Centre - Base Station system (MSC - BSS) interface layer 3 Specification"
[28]  TS 23.226   "Global Text Telephony (GTT); Stage 2"
[29]  TS 43.051   "GSM/EDGE Radio Access Network (GERAN) overall description; Stage 2;"
[30]  TS 25.412   "UTRAN Iu interface signalling transport".
[31]  TS 25.410   "UTRAN Iu Interface: General Aspects and Principles".
[32]  TS 25.414   "UTRAN Iu interface data transport and transport signalling".
[33]  TS 23.014   "Technical Specification Group Core Network; Support of Dual Tone Multi-Frequency (DTMF) signalling".
[34]  TS 32.421   " Subscriber and equipment trace: Trace concepts and requirements".
[35]  TS 32.422   "Subscriber and equipment trace: Trace control and configuration management".
[36]  TS 32.423   "Subscriber and equipment trace: Trace data definition and management".
[37]  TS 29.007   "General requirements on interworking between the Public Land Mobile Network (PLMN) and the Integrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN)".
[38]  TS 23.172   "Technical Specification Group Core Network and Terminals;Technical realization of Circuit Switched (CS);multimedia service UDI/RDI fallback and service modification;Stage 2
[39]  TS 43.068   " Voice Group Call Service (VGCS)"
[40]  TS 43.069   " Voice Broadcast Service (VBS)"
[41]  RFC 2663:  "IP Network Address Translator (NAT) Terminology and Considerations ".
[42]  TS 23.231   "SIP-I based Circuit Switched Core Network ; Stage 2"
[43]  TS 29.002   "Mobile Application Part (MAP) specification".
[44]  TS 29.235   "Interworking between SIP-I based circuit-switched core network and other networks".
[45]  TS 23.284   "Local Call Local Switch; Stage 2".
[46]  TS 23.088   "Call Barring (CB) Supplementary Services; Stage 2".
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3  Symbols and abbreviationsWord‑p. 18
3.1  Symbols
For the purposes of the present document, the following symbols apply:
Iu
Interface between the RNS and the core network. It is also considered as a reference point.
Mc
Interface between the server and the media gateway.
Nb
Interface between media gateways.
Nc
The NNI call control interface between (G)MSC servers.
3.2  Abbreviations
For the purposes of the present document, the following abbreviations apply:
BCF
Bearer Control Function
BICC
Bearer Independent Call Control
CIC
Call Instance Code
CCF
Call Control Function
CS
Circuit Switched
GERAN
GSM/EDGE Radio Access Network
IAM
Initial Address Message
IETF
Internet Engineering Task Force
IP
Internet Protocol
IPv4
Internet Protocol version 4
IPv6
Internet Protocol version 6
LCLS
Local Call Local Switch
MGW
Media GateWay
MGC
Media Gateway Controller
MSC-S
MSC Server
MTP2
Message Transfer Part layer 2
MTP3
Message Transfer Part layer 3
NNI
Network-Network interface
RAB
Radio Access Bearer
RANAP
Radio Access Network Application Protocol
SBSS
Serving Base Station System
SRNS
Serving Radio Network Subsystem
TCAP
Transaction Capabilities Application Part
TFO
Tandem Free Operation
TRAU
Transcoder and Rate Adapter Unit
TrFO
Transcoder Free Operation
UDP
User Datagram Protocol
UTRAN
UMTS Terrestrial Radio Access Network
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3.3  Definitions |R5|Word‑p. 19
UE:
User Equipment. This specification makes no distinction between MS (mobile station) and UE.
A/Gb mode:
mode of operation of the UE when connected to the Core Network via GERAN and the A and/or Gb interfaces. Throughout this specification the term GSM refers to GERAN A/Gb mode.
Iu mode:
mode of operation of the UE when connected to the Core Network via GERAN or UTRAN and the Iu interface. Throughout this specification the term UMTS refers to UTRAN or GERAN Iu mode.
4  Main Concepts
4.1  General
The circuit switched core network enables the support of different transports (e.g. ATM or IP) in a bearer-independent fashion. For the ATM and IP transport, there is a strict separation between the call control level and the bearer control level. In the case of ATM or IP transport, the passage of compressed speech at variable bit rates is possible through the CS core network.
The CS core network shall employ the MSC server, GMSC server and media gateways. The GMSC server and MSC server shall provide the call control and mobility management functions, and the media gateway shall provide the bearer control and transmission resource functions. The media gateway shall contain the stream manipulating functions.
The GMSC server and MSC servers are connected to the media gateway via the Mc reference point. The MSC servers and GMSC servers are connected with the Nc reference point. There may be a number of call control transit nodes between the MSC server and GMSC server in the Nc reference point. The MGWs are connected with the Nb reference point.
The users connected to the CS core network shall not be aware whether a MSC server - media gateway combination is used, or a monolithic MSC is used.
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4.2  Bearer-Independent Call Control
The protocol used on the Nc interface shall be a call control protocol supporting IP and ATM transports in a bearer independent manner for the ISDN service set, allowing the physical separation of the call control entities from the bearer control entities.
An exception to this bearer independence concept is if Iu interface is on IP and the IP addresses are to be exchanged via call control plane signalling (known by the MSC due to configuration data). In this case the specific handling is described separately.
Another exception to the bearer independence concept is the case of A interface user plane over IP (AoIP). In that case the IP addresses/UDP port numbers are to be exchanged via call control plane signalling. Specific handling is also described separately for this case.
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4.3  H.248/MEGACOWord‑p. 20
H.248/MEGACO has been jointly developed within the ITU-T and the IETF, and supports a separation of call control entities from bearer control entities, and a separation of bearer control entities from transport entities. H.248 is used on the Mc interface between the (G)MSC servers and the media gateway.
5  General Circuit Switched Core Network Domain Architecture
5.1  Logical Architecture
The overall CS core network logical architecture is shown in figure 1.
5.1.1  CS Core Network Nodes
5.1.1.1  MSC Server
The MSC server mainly comprises the call control and mobility control parts of a GSM/UMTS MSC as described in TS 23.002. It is also integrated with a VLR to hold the mobile subscriber's service data and CAMEL related data.
The MSC server terminates the user-network signalling (see TS 24.008) and translates it into the signalling over the Nc interface. The MSC Server terminates the Iu control plane signalling and its transport bearer (see TS 25.413 and TS 25.412). It also terminates the signalling over the Mc interface with the Media Gateway.
The MSC server controls the parts of the call state model that pertain to connection control for media channels in an MGW. It also contains the "Call Control Function" in the BICC model.
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5.1.1.2  GMSC Server
The GMSC server mainly comprises the call control and mobility control parts of a GSM/UMTS GMSC as described in TS 23.002.
The GMSC server terminates the signalling over the Nc interface and the call control interfaces to the external networks. It also terminates the signalling over the Mc interface towards the Media Gateway.
The GMSC server controls the parts of the call state model that pertain to connection control for media channels in an MGW. It also contains the "Call Control Function" in the BICC model.
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5.1.1.3  Media Gateway
The Media Gateway terminates the signalling over the Mc interface from the (G)MSC servers. The Media Gateway terminates the Iu transport network control plane signalling with its transport bearer (see TS 25.410 and TS 25.414). The Media Gateway also terminates the Iu user plane protocol (see TS 25.415). It also terminates the bearer control signalling and the transport bearer over the Nb interface (see TS 29.414 and TS 29.415).
The Media Gateway contains bearer terminations and media manipulation equipment (e.g. transcoders, echo cancellers, or tone senders). It may perform media conversion and framing protocol conversion.
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5.1.2  CS Core Network Interfaces and Reference PointsWord‑p. 21
5.1.2.1  Mc Interface
The Mc reference point in the present document considers the aspects of the interface between the (G)MSC server and the MGW. The H.248 protocol [5] together with 3GPP specific extensions/packages shall be used over the Mc interface.
5.1.2.2  Nc Interface
The Network-Network based call control is used over the Nc interface. Any suitable call control protocol may be used over the Nc interface (e.g. BICC).
5.1.2.3  Nb Interface
The bearer control signalling and transport are carried over the Nb interface.
5.2  Network Interworking
5.2.1  Interworking on the Nc Reference Point
Interworking between the Nc reference point, call control protocols and ISUP is defined within the 3GPP stage 3 documentation for each protocol (or by references specified in stage 3 documentation [6]).
5.2.2  Interworking on the Nb Reference Point
The interworking is specified in TS 29.415 and TS 29.414.

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