CA2381622C - Implementation of call setup procedures with separation of call control and bearer control - Google Patents

Implementation of call setup procedures with separation of call control and bearer control Download PDF

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Publication number
CA2381622C
CA2381622C CA002381622A CA2381622A CA2381622C CA 2381622 C CA2381622 C CA 2381622C CA 002381622 A CA002381622 A CA 002381622A CA 2381622 A CA2381622 A CA 2381622A CA 2381622 C CA2381622 C CA 2381622C
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Prior art keywords
call
media gateway
control
switching centre
gateway
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CA2381622A1 (en
Inventor
Martin Stumpert
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IDTP Holdings Inc
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Telefonaktiebolaget LM Ericsson AB
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
    • H04L65/1066—Session management
    • H04L65/1069—Session establishment or de-establishment
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W76/00—Connection management
    • H04W76/10—Connection setup
    • H04W76/12—Setup of transport tunnels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
    • H04L65/10—Architectures or entities
    • H04L65/102—Gateways
    • H04L65/1023—Media gateways
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
    • H04L65/10—Architectures or entities
    • H04L65/102—Gateways
    • H04L65/1033—Signalling gateways

Abstract

The invention herein relates to implementation of basic call set-up for GSM/UMTS core networks, including supplementary services CFU, CFB, CFNREA, CFNRY, CW, HOLD
and MPTY, with transporting Media Gateway address and logical point coding and framing information in a forward direction in cellular networks with separation of call control and bearer control. Call set-up is described in various traffic cases.

Description

IMPLEMENTATION OF CALL SETUP PROCEDURES WITH SEPARATION OF
CALL CONTROL AND BEARER CONTROL
BACKGROUND OF THE INVENTION
A conventional GSM (Global System for Mobile Communications) or UMTS (Universal Mobile Telecommunications Service) core network uses bearer control and call control. The bearer control is the aspect of signaling related to the control of the selection of a path through the transmission network and utilizing (reserving, releasing and setting up) the required resources. The call control is the aspect of signaling related to the subscriber and service control, taking, e.
g., the subscriber state into consideration.
In the existing implementations of N-ISDN (Integrated Services Digital Network) the call control and the bearer control arc integral with one another. A user plane is associated directly with the control servers, such as MSCs( Mobile Services switching Centers) and GMSCs (Gateway MSCs). Thus, the control nodes implement both, application logic for signaling and the user plane.
Knight R. R. and Law B. describe in "The call control protocol in a separated call and bearer environment", published in BT Technical Journal, volume 16 Number 2 published April 1998, a system and a protocol with separated call and bearer control.
However, the described system does not separate the control nodes from nodes for the transmission of payload. Thus, the control nodes perform both, call control and bearer control, separated only in time. By that, optimised routing of payload is not possible.

A._ __- J_ J Ct i_ __ a UUJ4y~/4-Cf'Ul)Ub8y PATENT
1282.00001 la The present invention is directed to separation of the call control and the bearer control.

Summarv of the Invention s For impleinentation of GSM and jJMTS core networks there is a new approach to separate call control and bearer control.

P12172 15. Oct 2001 2 Emvfang AMENDED SHEET 16-10-2001 In accordance with the invention, with the implementation of separation between call and bearer control, the following features are described:

Transfer the media gateway address, a termination and possibly the chosen transcoder in a forward direction. With transfen:ing the transcoder in the forward direction TFO (tandem free operation) or TrFO (transcoder free operation) is possible.

The application software is independent from the used transmission technology, e.
g. STM, ATM, IP.

Changes to call control and bearer control signaling to achieve the optimized user plane set up.

Usage of logical points in the media gateway to allow different control servers to control one media gateway.

Giving a MSC, TSC server the possibility to control several media gateways by allocating one PC per media gateway in the control node.

The user plane routing for call set-up is optimized significantly.

The user plane routing for supplementary services CFNREA, CFB, CFNRY, CFU
is optimized significantly.

The user plane routing for supplementary services CW, HOLD is optimized significantly.
Only one media gateway is used if the call stays inside one network or goes over one network border. If the call goes over two network boarders, then two MGWs are involved, each at the edge to the network.

The user plane pipe size is optimized by transferring coded (compressed) user plane to the edge of the network or between two MGWs, e. g. for MPTY calls Allowing of pooling of conference call devices in MGWs.
Combining different coded speech streams to one MPTY.

Further features and advantages of the invention will be readily apparent from the following specification and the drawings.

Brief Description of the Drawin .gs Figure 1 is a block diagram illustrating basic call set-up for a call from UE
to UE, media gateway address being transported in the forward direction;

Figure 2 is a block diagram illustrating basic call set-up for a call to UE, media gateway address being transported in the forward direction;

Figure 3 is a block diagram illustrating basic call set-up for call forwarding in GMSC
to an ISDN no., media gateway address being transported in the forward direction;

Figure 4 is a block diagram illustrating basic call set-up for call forwarding in GMSC
to UE no., media gateway address being transported in the forward direction;
Figure 5 is a block diagram illustrating basic call set-up for a call from UE
with call forwarding in GMSC to UE, media gateway address being transported in the forward direction;
Figure 6 is a block diagram illustrating basic call set-up for call forwarding in MSC
to an ISDN number, media gateway address being transported in the forward direction;

Figure 7 is a block diagram illustrating basic call set-up for call waiting and accepting the waiting call in different MGWs, media gateway address being transported in the forward direction;

Figure 8 is a block diagram illustrating basic call set-up for call waiting and accepting the waiting call in one MGW, media gateway address being transported in the forward direction;
Figure 9 is a block diagram illustrating basic call set-up for a MPTY call, media gateway address being transported in the forward direction;

Figure 10 is a block diagram illustrating basic call set-up for call forwarding in MSC
to an ISDN number, the MSC setting the connection between MGW 1 and media gateway MGW2;
Figure 11 is a block diagram illustrating basic call set-up for call waiting and hold;
and Figure 12 is a block diagram illustrating basic call set-up for a MPTY call with CCDs only in MGW3.

Description The present invention relates to enabling and optimizing call set-up in a telecommunication network with separated call control and bearer control, i.e., set up of a payload connection. The separation of call control and payload transmission means that the signaling between control nodes like MSCs, GMSCs and TSCs takes a different way through the network than the payload. This enables the telecommunication network to perform an optimal routing for the payload, using a minimum of resources. Depending on the call case, originating call, terminating call, internal call or transit call, there are only one or maximally two media gateway necessary.

The invention particularly relates to a method comprising the transmission of an identification of a selected media gateway in a forward direction. That is, the first control node or the second control node selects the media gateway depending on:
- the call origin;

- the call destination (important for the selection of the terminating control node transit switch or MSC, and for the coding decoding); or - the required service (voice, fax or else), for all call cases. In some call cases, further information can be relevant for the selection of a MGW, such as:

- the invoked service, e.g. CFB;

- the coding of the payload (in the case of compressed voice it is sensible to keep the voice data compressed throughout the network to save transmission capacity);
or - the framing of the calls.

The invention herein relates to implementation of basic call setup, GSM/UMTS
supplementary services CFU, CFB, CFNREA, CFNRY, CW, HOLD and MPTY with transporting a media gateway address, a logical point, the chosen coding type and the chosen framing type in a forward direction in networks with separation of call control and bearer control. Call set-up is described in various traffic cases, each illustrated in one of the figures.
Each of the figures is a block diagram of a wireless communication system, such as a GSM or UMTS core network, with directional arrows illustrating control signaling between control servers and with MGWs during call set-up for the different traffic cases. The written description herein describes information conveyed in each signal. The particular signal is identified herein and in the drawing with a reference numeral.

Many of the calls in the traffic cases described herein involve a mobile terminal or a fixed terminal, for example a fax, a PC, or a phone that is located within the network. Such a mobile terminal is referred to herein as User Equipment (UE). The UE
communicates with the network via an RNC (Radio Network Controller) using Radio Resource Control (RRC) protocol.

A logical point is a reference locally generated by a media gateway and only with the media gateway address valid to identify a connection in the control servers e.
g. MSC/VLR

(MSC/Visitor Location Register), GMSC, TSC and in the RNC. For this purpose a logical point P
in a first MGW 1 is reserved. This reserved point is sent back in a DCP
resource response message to the control server and passed on from this control server to another media gateway MGW2 or RNC, which shall set up an AAL2 connection. In this set up the logical point P
is included to identify to which reserved resource in a MGW 1 the connection shall be set up. The logical point is equivalent to a termination used in the H.GCP protocol standardized by TTU.

A control node, such as one of the control servers, discussed above, provides the application logic. The strict separation of the application logic from the user plane handling allows intensive application development and execution. In the described system the control nodes GMSC, MSC, TSC and home location register HLR (only signaling) exist. The interfaces of the control nodes are, e.g., N-ISUP, for call control signaling, DCP signaling for media gateway control and MAP for transferring connectionless signaling between control servers.

A media gateway (MGW) modifies or switches the user plane. It performs operations such as announcement generation, tone generation, echo cancellation, modem handling for data calls, frame handling and CODEC (transcoder) handling for speech calls.

A signaling gateway (GW) performs bearer conversion of signaling messages. In UMTS with an ATM core network and ISDN network interworking a conversion from to MTP is done in the signaling gateway. The signaling GW relays the N-ISUP
signaling and exchanges the lower transport layer which is carrying the signaling. Therefore the signaling GW is always collocated with e. g. a GMSC or TSC server.

The backbone network transfers the user plane and the control signaling and can, e.g., be based on STM, ATM or IP. The media gateway is the edge node of the backbone network.
The following mnemonics, in addition to others which are well known, are used herein:

AAL2 ATM Adaption Layer Type 2 ATM Asynchronous Transfer Mode BICC Bearer Independent Call Control CCD Conference Call Device CIC Circuit Identity Code CFB Call Forwarding Busy CFNREA Call Forwarding Not REAchable CFNRY Call Forwarding No ReplY

CFU Call Forwarding Unconditional CM Connection Management CW Call Waiting Supplementary Service DCP Device Control Protocol, e. g. X-CP
DPC Destination Point Code DTAP Direct Transfer Application Part GMSC Gateway MSC

HLR Home Location Register HOLD Call Hold Supplementary Service IP Internet Protocol ISDN Integrated Services Digital Network ISUP ISDN User Part MAP Mobile Application Part MGW Media Gateway MSC Mobile Services Switching Center MPTY MultiparTY Supplementary Service OPC Originating Point Code PC Point Code P Logical Point RANAP Radio Access Network Application Part RNC Radio Network Controller SigGW Signaling Gateway STM Synchronous Transfer Mode TSC Transit Switching Center UE User Equipment (mobile) In the new network architecture described herein, N-ISDN is used for call control, while STM, AAL2 or IP are used for bearer control and usage of the user plane.

The generation of control tones are omitted in this description and shall be handled in other known manners.

The media gateway address can be transported on BICC, ISDN e. g., as a sublayer transport address. To find the TSC and/or the media gateway address, some IN
service, the routing analyse or the B-number analyse are used. The TSC is then chosen for an outgoing call to the ISDN.
The media gateway is chosen based on capabilities required for handling the call, e. g. which devices such as CODECs, coding, compression, framing scheme, announcement machines, tone senders, or modems are required. In the examples, for simplification, only the B-number analyse is mentioned.
The selection depends mainly on the destination. Depending on the destination a group of MGWs with different capabilities can be found. Then a media gateway with the needed capabilities, e. g.
CCDs, modem support, Internet connectivity is chosen.

All resources which have been reserved by a server have to be released by that server.
For simplifying the message flows, described below relative to the Figures, the release of media gateway resources is omitted.

In the examples, a one-to-one relation is assumed between the first control node GMSC/TSC server inside the core network and the first media gateway inside the CN.

To be able to receive incoming calls over different MGWs, but with the control signaling (IAM) to the same GMSC, the GMSC needs to have one point code per MGW, where the ISDN user plane can terminate. Out of the DPC, to which the IAM was sent, the GMSC can derive the media gateway to which the ISDN user plane was set up.

To allow that a TSC controls more than one media gateway for outgoing (incoming) traffic the TSC needs one point code per controlled media gateway. For a chosen media gateway the TSC has to use a certain OPC. Depending on the chosen OPC the transit switch can distinguish the ISDN user planes received from different MGWs.

Another alternative solution to receive or send user plane to different MGWs is that different signaling routes are used between servers, if the user plane is routed via different MGWs.
A third alternative to receive or send user plane to different MGWs from/to a transit switch and control signaling from/to one server is that different CICs are used for different MGWs, if the user plane is routed via different MGWs.

The concept of identifying the originating media gateway by OPC used in the IAM
message instead of transporting the media gateway address in the IAM message, is also possible through the whole CN, but it requires, for a network of m MGWs, m different point codes in each of the the control servers, which can control the MGWs.

Another alternative solution to transfer the knowledge of an media gateway from one server to the other is to use different routes for signaling, if the user plane was routed to different MGWs. If a TSC can receive calls from m MGWs, then m different signaling routes towards the RNC are required.

In the following description of the various drawings, various signal names are used.
Some of these signals are conventional in nature. The DTAP messages are defined in GSM 04.08 V8Ø0 and UMTS 24.08 V3Ø0. The RANAP messages are defined in UMTS 25.413 V1Ø2. The MAP messages are defined in GSM 09.02 V 6.3.0 and UMTS 29.002 V 3.3.2. The AAL2 messages are used for bearer control in accordance with the invention. The DCP
messages, which are particularly described below, are used for communications between control nodes and the MGWs in connection with resource requests and assignments. The ISDN messages are used for signaling between network control nodes and external ISDN networks. An updated ISDN set of messages is to be used between core network servers. Updated is, for example, the IAM
message.

Figure 1 shows a call from one UE to another UE within the network, with an media gateway address being transported in a forward direction. In this alternative the originating exchange selects the media gateway MGW1, e. g. on traffic and because of location, and transports the media gateway MGW 1 address in the forward direction with the ISUP IAM message to the gateway mobile services switching centre GMSC1 and then to the mobile services switching centre MSC2.

In this case only one media gateway is used, which can be used by all control servers to influence the user plane.

A transcoder is linked in by the originating MSC as the termination is not known. On the radio network controller RNC1 side, the coding negotiated with the user equipment UE1 is used and on the outgoing side a default coding is used. The terminating mobile services switching centre mobile services switching centre MSC2 chooses the default coding on the one side and the coding, which it negotiated with the user equipment UE2 on the side of the radio network controller RNC2.
The following steps in the basic call setup, as with the other examples, below, describe the control signaling in each step and are numbered corresponding to reference numbers in the described figure.
The description includes signal protocol, followed by the type of signal.

1. DTAP, CM service request 2. DTAP, Set-up 3. DTAP, Call Proceeding 4. DCP, resource request (MGW1) 5. DCP, resource response (Pi 1, Pv 11) 6. DCP, Through connect (Pv 11, Pi 1) The mobile services switching centre MSC 1 commands the media gateway MGW 1 to backward through connect the incoming point Pil and the virtual point Pvl1.
7. RANAP, Assignment Request 8. AAL2, Establish Request 9. AAL2, Establish Confirm 10. RANAP, Assignment Response 11. ISDN, Initial Address Message IAM (MGW1, Pvl l, OPC, DPC, CIC) Call set-up is requested from the originating mobile services switching centre MSC1.
The media gateway MGW1 address and Pvl l or optional the OPC, DPC, CIC can be used for identifying the incoming connection in the gateway mobile services switching centre GMSC 1.
12. DCP, resource request (MGW1, Pvl1) 13. DCP, resource response (Pv12) A virtual point Pv12 is returned from the media gateway MGW1.
14. Optional DCP, Through connect (Pv 12, Pv 11) The gateway mobile services switching centre GMSC1 commands the media gateway MGW1 to through connect the incoming point Pv12 and the virtual point Pvll.
Optionally the whole media gateway MGW 1 connection can be through connected with one DCP, Through connect (Pi 1, Po 1) message.
15. MAP, SendRouting information request The gateway mobile services switching centre GMSC1 interrogates the home location register HLR for routing information.
16. MAP, SendRouting information response The gateway mobile services switching centre GMSC1 receives the forwarding to number and an indication, if a notification shall be given to the calling party.
17. Optional ISDN, Address Complete Message ACM

The ACM message is sent from the gateway mobile services switching centre GMSC1 to the mobile services switching centre MSC1.
18. ISDN, Initial Address Message IAM (MGW1, Pv12, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre to the mobile services switching centre mobile services switching centre MSC2.
The media gateway MGW1 address and Pv12 or optional the OPC, DPC, CIC can be used for identifying the incoming connection in the mobile services switching centre mobile services switching centre MSC2.
19. DCP, resource request (MGW1, Pv12) Resources are requested for the call identified by its CIC.
20. DCP, resource response (Pol) An outgoing point Pol is returned from the media gateway MGW1.
21. DCP, Through connect (Pol, Pv12) The mobile services switching centre mobile services switching centre MSC2 commands the media gateway MGW1 to through connect the virtual point Pv12 and the outgoing point Pol. Optionally, the media gateway MGW1 connection can be through connected with one DCP, through connect (Pv 11, Po 1) message.
22. RANAP, Paging 23. DTAP, Paging Response 24. DTAP, Set-up 25. DTAP, Call confirmed 26. RANAP, Assignment Request 27. AAL2, Establish Request 28. AAL2, Establish confirm 29. RANAP, Assignment Response 30. DTAP, Alert 31. ISDN, Address Complete Message ACM
32. ISDN, Call Proceeding CPG
33. DTAP, Connect 34. DTAP, Connect ack 35. ISUP, Answer Message ANM
36. ISUP, Answer Message ANM
37. DCP, Through connect (Pv 11, Pi 1) The mobile services switching centre MSC1 commands the media gateway MGWI
to through connect the incoming point Pil and the virtual point Pv11.
38. DTAP, Connect 39. DTAP, Connect ACK.

Figure 2 illustrates a call to UE originating outside of the network. The media gateway address is again transported in the forward direction. Here a subscriber is calling a served user equipment UE1. In this case only one media gateway is used, which can be used by all control servers to influence the user plane.

A transcoder is linked in by the terminating mobile services switching centre MSC.
On the incoming side, e. g. PCM coding is used and on the outgoing side the coding, negotiated with the user equipment UE1 by the radio network controller RNC, is used.

1. ISDN, Initial Address Message IAM (OPC, DPC, CIC) Call set-up is requested from an extetnal ISDN network for a mobile terminated call attempt. In this example the gateway mobile services switching centre/transit switching centre GMSC1/TSC and the Signaling Gateway 1 are collocated.

2. DCP, resource request (MGW 1, CIC) Resources are requested for the call identified by its CIC, which were chosen by the transit switch of the ISDN network.

3. DCP, resource response (Pil, Pvl1) An incoming point Pil and a virtual point Pvl1 are returned from the media gateway MGW 1.

4. MAP, SendRouting Information request The gateway mobile services switching centre GMSCI interrogates the home location register HLR for routing information.

5. MAP, SendRouting Information response The gateway mobile services switching centre GMSC1 receives the mobile services switching centre MSC address.

6. ISDN, Address Complete Message ACM

The ACM message is sent from the gateway mobile services switching centre/transit switching centre GMSC1/TSC to the transit switch 1.

7. Optional DCP, Through connect (Pil, Pvl1) The gateway mobile services switching centre/transit switching centre commands the media gateway MGW 1 to through connect the incoming point Pi 1 and the virtual point Pvl 1. Optionally, the whole media gateway MGW1 connection can be through connected with one DCP, Through connect (Pil, Po1) message.

8. ISDN, Initial Address Message IAM (MGW1, Pvl1, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre/transit switching centre GMSC1/TSC to the mobile services switching centre MSC. The media gateway MGW1 address and Pvll or optional the OPC, DPC, CIC can be used for identifying the incoming connection in the mobile services switching centre MSC.

9. DCP, resource request (MGW1, Pvl1) Resources are requested for the call identified by its CIC.
10. DCP, resource response (Pol) An outgoing point Pol is returned from the media gateway MGW1.
11. DCP, Through connect (Pvl1, Po1) The mobile services switching centre MSC commands the media gateway MGW1 to through connect the virtual point Pv11 and the outgoing point Po 1.
Optionally, the whole media gateway MGW 1 connection can be through connected with one DCP, Through connect (Pil, Pol) message.

12. RANAP, Paging 13. DTAP, Paging Response 14. DTAP, Set-up 15. DTAP, Call confirmed 16. RANAP, Assignment Request 17. AAL2, Establish Request 18. AAL2, Establish confirm 19. RANAP, Assignment Response 20. DTAP, Alert 21. ISDN, Address Complete Message ACM
22. ISDN, Call Proceeding CPG

23. DTAP, Connect 24. DTAP, Connect ack 25. ISUP, Answer Message ANM
26. ISUP, Answer Message ANM

Figure 3 shows a call forwarding in a GMSC to an ISDN subscriber identified by an ISDN no. outside of the network. The media gateway address is transported in the forward direction.
For CFNREA in mobile services switching centre MSC the same handling applies as for CFNREA in GMSC. Therefore only the signaling for CFNREA in GMSC are described below.

Alternatively of transit switching centre TSC2 controlling the set-up from media gateway MGW 1 to media gateway MGW2, GMSC can control the set-up as the analyse performed in GMSC optional to transit switching centre TSC2 can also deliver the media gateway MGW2 address as a one-to-one relation exists between both.

In this case only two MGWs are used, each at the edge of the network.

A transcoder is optionally linked in by the transit switching centre TSC2 in both media gateways, media gateway MGW 1 and media gateway MGW2 to compress the transferred user data. On the STM side, e. g. PCM coding is used and on the other side CN
default coding is used.
1. ISDN, Initial Address Message IAM (OPC, CPC, CIC) Call set-up is requested from an external ISDN network for a mobile terminated call attempt. In this example the GMSC and the Signaling Gateway 1 are collocated.

2. DCP, resource request (MGW 1, CIC) Resources are requested for the call identified by its CIC, which were chosen by the transit switch 1 of the ISDN network.

3. DCP, resource response (Pil, Pvll) An incoming point Pil and a virtual point Pv 11 are returned from the media gateway MGW 1.

4. MAP, SendRouting Information request The GMSC interrogates the home location register HLR for routing information.
5. MAP, SendRouting Information response The GMSC receives the forwarding to number and an indication, if a notification shall be given to the calling party. The forwarded-to number received fromhome location register HLR is analysed and a transit switching centre TSC2 and optional media gateway MGW2 address are received from the B-number analysis.

6. ISDN, Address Complete Message ACM

The ACM message is sent from the GMSC to the transit switch 1. An outband notification can be included in the AM message. This saves signaling, in and out linking of announcement machine and user plane transmission.

7. Optional DCP, Connect announcement machine (Pil) Optional the announcement machine is connected, if inband notification is required.
8. Optional DCP, Disconnect announcement machine (Pi 1) After the announcement the announcement machine is disconnected.
9. Optional DCP, Through connect (Pil, Pvll) The GMSC commands the media gateway MGW 1 to through connect the incoming point Pi 1 and the virtual point Pv11. Optionally, the whole media gateway MGW

connection can be through connected with one DCP, Through connect (Pil, Pol) message. This is in line with ITU N-ISDN specifications.

10. ISDN, Initial Address Message IAM (MGW 1, PV 11, OPC, DPC, CIC) The IAM message is sent from the GMSC to the transit switching centre TSC2, which is controlling the media gateway MGW2. The media gateway MGW 1 address and PV 11 or optional the OPC, DPC, CIC can be used for identifying the incoming connection in the transit switching centre TSC2.

11. DCP, resource request (MGW2) Resources are requested for the call identified by its CIC.
12. DCP, resource response (Pi2, Pv21) An incoming point Pi2 and a virtual point Pv21 are returned from the media gateway MGW2.

13. DCP, Set-up connection (MGW1, MGW2, Pvl1, Pi2) The transit switching centre TSC2 requests resources for an outgoing call identified by its virtual CIC and commands the media gateway MGW 1 to set up a connection towards Pi2 in media gateway MGW2.

14. AAL2, Establish Request 15. AAL2, Establish confirm 16. DCP, Set-up connection response (Pol) The media gateway MGWI signals back that the outgoing connection has been set up successfully and returns an outgoing point Pol.

17. DCP, Through connect (Pol, Pvll) The transit switching centre TSC2 commands the media gateway MGW1 to through connect the outgoing point Pol and the virtual point Pvll. Optionally, the whole media gateway MGW 1 connection can be through connected with one DCP, Through connect (Pi 1, Po 1) message.

18. Optional DCP, Through connect (Pol, Pv2) The transit switching centre TSC2 commands the media gateway MGW2 to through connect the incoming point Pi2 and the virtual point Pv21.

19. DCP, Set-up connection (MGW2, Pv21) The transit switching centre TSC2 requests resources for an outgoing call identified by its virtual CIC and commands the media gateway MGW2 to set up a connection toward the transit switch 2.

20. DCP, Set-up connection response (Po2, CIC) The media gateway MGW2 signals back that the outgoing connection has been set up successfully and returns an outgoing point Po2.

21. DCP, Through connect (Po2, Pv21) The transit switching centre TSC2 commands the media gateway MGW2 to through connect the outgoing point Po2 and the virtual point Pv21.

22. ISDN, Initial Address Message IAM (OPC, DPC, CIC) The IAM message is sent from the transit switching centre TSC2 to the transit switch 2.

23. ISDN, Address Complete Message ACM
24. ISDN, Call Proceeding CPG

25. ISDN, Call Proceeding CPG
26. ISDN, Answer Message ANM
27. ISDN, Answer Message ANM

The ANM message is passed on by the transit switching centre TSC2.
28. ISDN, Answer ANM

The ANM message is passed on by the GMSC.

Figure 4 illustrates call forwarding in GMSC to a UE subscriber identified by a UE
no. in the network. The media gateway address is transported in the forward direction.

For subsequent forwarding to UE in GMSC instead of gateway mobile services switching centre GMSC2 several GMSCs have to be included. In this case only one media gateway is used, which can be used by all control servers to influence the user plane.
A transcoder is linked in by the terminating mobile services switching centre MSC. On the incoming side, e. g. PCM
coding is used and on the outgoing side the coding, negotiated with the user equipment UE1, is used.
1. ISDN, Initial Address Message IAM (OPC, DPC, CIC) Call set-up is requested from an external ISDN network for a mobile terminated call attempt. In this example the gateway mobile services switching centre/transit switching centre GMSC1/TSC1 and the Signaling Gateway 1 are collocated.

2. DCP, resource request (MGW1, CIC) Resources are requested for the call identified by its CIC, which were chosen by the transit switch of the ISDN network.

3. DCP, resource response (Pi 1, Pv 11) An incoming point Pi 1 and a virtual point Pv 11 are returned from the media gateway MGW 1.

4. MAP, SendRouting Information request The GSMC interrogates the home location register HLR for routing information.
5. MAP, SendRouting Information response The gateway mobile services switching centre GMSC1 receives the forwarding to number and an indication, if a notification shall be given to the calling party.

6. ISDN, Address Complete Message ACM

The ACM message is sent from the gateway mobile services switching centre/transit switching centre GMSC1/TSCI to the transit switch 1. An outband notification can be included in the ACM message. This saves signaling, in and out linking of announcement machine and user plane transmission.

7. Optional DCP, Connect announcement machine (Pi2) Optionally the announcement machine is connected, if inband notification is required.

8. Optional DCP, Disconnect announcement machine (Pi1) After the announcement the announcement machine is disconnected.
9. Optional DCP, Through connect (Pil, Pv11) The gateway mobile services switching centre/transit switching centre connnands the media gateway MGW 1 to through connect the incoming point Pi 1 and the virtual point Pv 11. Optionally, the whole media gateway MGW1 connection can be through connected with one DCP, Through connect (Pil, Pol) message.

10. ISDN, Initial Address Message IAM (MGW1, PV11, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre/transit switching centre GMSC1/TSC1 to the gateway mobile services switching centre GMSC2. The media gateway MGW 1 address and Pv 11 or optional the OPC, DPC, CIC can be used for identifying the incoming connection in the gateway mobile services switching centre GMSC2.

11. DCP, resource request (MGW 1, Pv 11) Resources are requested for the call identified by its CIC.
12. DCP, resource response (Pv12) A virtual point Pv12 is returned from the media gateway MGWI.

13. Optional DCP, Through connect (Pvl1, Pv12) The gateway mobile services switching centre GMSC2 commands the media gateway MGWI to through connect the virtual point Pv 11 and the virtual point Pv12.
Optionally, the whole media gateway MGW 1 connection can be through connected with one DCP, Through connect (Pil, Po1) message.

14. MAP, SendRouting Information request The gateway mobile services switching centre GMSC2 receives the mobile services switching centre MSC address from HLR.

15. MAP, SendRouting Information request The gateway mobile services switching centre GMSC2 receives the mobile services switching centre MSC address from HLR.

16. ISDN, Initial Address Message IAM (MGW1, PV12, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre to the mobile services switching centre MSC.

17. DCP, resource request (MGW1, Pv12) Resources are requested for the call identified by its CIC.
18. DCP, resource response (Pol) An outgoing point Pol is returned from the media gateway MGWI.

19. DCP, Through connect (Pol, Pv12) The mobile services switching centre MSC commands the media gateway MGW1 to through connect the virtual point Pv12 and the outgoing point Pol.
Optionally, the whole media gateway MGW 1 connection can be through connected with one DCP, Through connect (Pil, Pol) message.

20. RANAP, Paging 21. DTAP, Paging Response 22. DTAP, Set-up 23. DTAP, Call confirmed 24. RANAP, Assignment Request 25. AAL2, Establish Request 26. AAL2, Establish confirm 27. RANAP, Assignment Response 28. DTAP, Alert 29. ISDN, Address Complete Message ACM
30. ISDN, Call Proceeding CPG

31. ISDN, Call Proceeding CPG
32. DTAP, Connect 33. DTAP, Connect ack 34. ISUP, Answer Message ANM

35. ISUP, Answer Message ANM
36. ISUP, Answer Message ANM

Figure 5 illustrates a call from UE with Call forwarding in GMSC to a UE
subscriber identified by a UE no. in the network. The media gateway address is transported in the forward direction.

There are three alternatives for assuring user plane optimised routing. In the first alternative the media gateway MGW 1 is chosen in the mobile services switching centre mobile services switching centre MSC2. Then the media gateway MGW1 address is transferred in the backward direction with ISUP ACM/CPG or some new message to the originating mobile services switching centre MSC1. The mobile services switching centre MSC1 then commands radio network controller RNC1 to set-up the user plane connection towards media gateway MGW
1 and commands media gateway MGW1 to through connect. Then mobile services switching centre mobile services switching centre MSC2 commands radio network controller RNC2 to set up the user plane connection towards media gateway MGW I.

The second alternative commands the radio network controllers to connect without in linking of an media gateway and only possible for the mobile to mobile case.

The third alternative is that the originating exchange selects the media gateway MGW 1 and transports the media gateway MGW 1 address in the forward direction with the ISUP
IAM message to the mobile services switching centre mobile services switching centre MSC2. This alternative can be optimised by combining it with the first alternative. So if a media gateway address is received in the backward direction, then the mobile services switching centre MSC1 can perform a subsequent assignment towards radio network controller RNC1. Below the third alternative without optimisation is described.

For subsequent forwarding to UE in GMSC instead of gateway mobile services switching centre GMSC2 several GMSCs have to be included. In this case only one media gateway is used, which can be used only by all control servers to influence the user plane. A transcoder is linked in by the originating MSC as the termination is not known. On the radio network controller RNC1 side, the coding is negotiated with the user equipment UE1 is used and on the outgoing side a default coding is used. The terminating mobile services switching centre mobile services switching centre MSC2 chooses the default coding on the one side and the coding, which it negotiated with the user equipment UE2 on the side of radio network controller RNC2. If only media gateway is used that comprises both linked in CODECs, the media gateway can decide to link out both CODECs if the coding towards user equipment UEl and user equipment UE2 is of the same type.

1. DTAP, CM service request 2. DTAP, Set-up 3. DTAP, Call Proceeding 4. DCP, resource request (MGW 1) 5. DCP, resource response (Pi 1, Pv 11) An incoming point Pi 1 and a virtual point Pv 11 are returned from the media gateway MGW1.

6. DCP, Through connect (Pv 11, Pi 1) The mobile services switching centre MSC 1 commands the media gateway MGW 1 to backward through connect the incoming point Pi1 and the virtual point Pvl1.

7. RANAP, Assignment Request 8. AAL2, Establish Request 9. AAL2, Establish Confirm 10. RANAP, Assignment Response 11. ISDN, Initial Address Message IAM (MGW1, Pvl1, OPC, DPC, CIC) Call set-up is requested from the originating mobile services switching centre MSC1.
The media gateway MGW 1 address and Pv 11 or optionally the OPC, DPC, CIC can be used for identifying the incoming connection in the gateway mobile services switching centre/transit switching centre GMSC1/TSC.

12. DCP, resource request (MGW l, Pv 11) 13. DCP, resource response (Pv12) A virtual point Pv12 is returned from the media gateway MGWI.
14. Optional DCP, Through connect (Pv12, Pvl1) The gateway mobile services switching centre GMSC1 commands the media gateway MGW 1 to through connect the incoming point Pv 12 and the virtual point Pv 11.
Optionally, the whole media gateway MGW 1 connection can be through connected with one DCP, Through connect (Pi 1, Po 1) message.

15. MAP, SendRouting Information request The gateway mobile services switching centre GMSC1 interrogates the home location register HLR for routing information.

16. MAP, SendRouting Information response The gateway mobile services switching centre GMSC 1 receives the forwarding to number and an indication, if a notification shall be given to the calling party.

17, Optional ISDN, Address Complete Message ACM

The ACM message is send from the gateway mobile services switching centre GMSC1 to the MSC.

18. ISDN, Initial Address Message IAM (MGW1, Pv12, OPC, DPC, CIC) The IAM message is send from the gateway mobile services switching centre GMSC1 to the gateway mobile services switching centre GMSC2. The media gateway MGW1 address and Pv12 or optionally the OPC, DPC, CIC can be used for identifying the incoming connection in the gateway mobile services switching centre GMSC2.

19. DCP, resource request (MGW1, Pv12) Resources are requested for the call identified by its CIC.
20. DCP, resource response (Pv13) A virtual point Pv13 is returned from the media gateway MGW1.
21. Optional DCP, Through connect (Pv13, Pv12) The gateway mobile services switching centre GMSC2 commands the media gateway MGW1 to through connect the virtual point Pv13 and the virtual point Pv12.
Optionally, the media gateway MGW 1 connection can be through connected with one DCP, Through connect (Pvl l, Pol) message.

22. MAP, SendRouting Information request The gateway mobile services switching centre GMSC2 interrogates the home location register HLR for routing information.

23. MAP, SendRouting Information response The gateway mobile services switching centre GMSC2 receives the MSC address from HLR.

24. ISDN, Initial Address Message IAM (MGW 1, Pv13, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre to the MSC.

25. DCP, resource request (MGWl, Pv13) Resources are requested for the call identified by its CIC.
26. DCP, resource response (Pol) An outgoing point Pol is returned from the media gateway MGW1.
27. DCP, Through connect (Po 1, Pv13) The mobile services switching centre mobile services switching centre MSC2 commands the media gateway MGWI to through connect the virtual point Pv13 and the outgoing point Pol. Optionally, the media gateway MGW1 connection can be through connected with one DCP, Through connect (Pvl1, Pol) message.

28. RANAP, Paging 29. DTAP, Paging Response 30. DTAP, Set-up 31. DTAP, Call confirmed 32. RANAP, Assignment Request 33. AAL2, Establish Request 34. AAL2, Establish confirm 35. RANAP, Assignment Response 36. DTAP, Alert 37. ISDN, Address Complete Message ACM
38. ISDN, Call Proceeding CPG

39. ISDN, Call Proceeding CPG
40. ISDN, Call Proceeding CPG
41. DTAP, Connect 42. DTAP, Connect ack 43. ISUP, Address Complete Message ANM
44. ISUP, Address Complete Message ANM
45. ISUP, Address Complete Message ANM
46. DCP, Through connect (Pv 11, Pi 1) The mobile services switching centre MSC 1 commands the media gateway MGW 1 to through connect the incoming point Pi 1 and the virtual point Pv 11.
47. DTAP, Connect 48. DTAP, Connect ACK

Figure 6 illustrates call forwarding in mobile services switching centre MSC
to an ISDN subscriber identified by an ISDN no. The media gateway address is transported in the forward direction.

In this example the conditional call forwarding in mobile services switching centre MSC is described. The case describes CFNRY, if the UE user does not answer the call, and the call has to be forwarded to an ISDN no. In case of CFNREA, if the UE does not answer the paging, steps 12 to 22 are to be omitted. In the current example only two MGWs are used, each at the edge of the network. A transcoder is optionally linked in by the TSC in both media gateways to compress the transferred user data. On the STM side, e. g., PCM coding is used and on the other side CN default coding is used.

1. ISDN, Initial Address Message IAM (OPC, DPC, CIC) Call set-up is requested from an external ISDN network for a mobile terminated call attempt. In this example the gateway mobile services switching centre/transit switching centre GMSC1/TSC1 and the Signaling Gateway 1 are collocated.

2. DCP, resource request (MGW1, CIC) Resources are requested for the call identified by its CIC, which were chosen by the transit switch of the ISDN network.

3. DCP, resource response (Pil, Pvl1) An incoming point Pil and a virtual point Pv 11 are returned from the media gateway MGW 1.

4. MAP, SendRouting Information request The gateway mobile services switching centre GMSC1 interrogates the home location register HLR for routing information.

5. MAP, SendRouting Information response The gateway mobile services switching centre GMSC1 receives the mobile services switching centre MSC address.

6. ISDN, Address Complete Message ACM

The ACM message is sent from the GMSC to the transit switch 1.
7. Optional DCP, Through connect (Pil, Pvl1) The GMSC commands the media gateway MGW 1 to through connect the incoming point Pi 1 and the virtual point Pv 11. Optionally, the whole media gateway connection can be through connected with one DCP, Through connect (Pil, Pol) message.

8. ISDN, Initial Address Message IAM (MGW1, Pvl1, OPC, DPC, CIC) The IAM message is sent from the GMSC to the mobile services switching centre MSC. The media gateway MGW1 address and Pvl l or optional the OPC, DPC, CIC
can be used for identifying the incoming connection in the mobile services switching centre MSC.

9. DCP, resource request (MGW1, Pvl1) Resources are requested for the call identified by its CIC.

10. DCP, resource response (Pol) An outgoing point Pol is returned from the media gateway MGWI.
11. DCP, Through connect (Pvl l, Pol) The mobile services switching centre MSC commands the media gateway MGW 1 to through connect the virtual point Pv 11 and the outgoing point Po 1.
Optionally the whole media gateway MGW1 connection can be through connected with one DCP, Through connect (Pi 1, Po 1) message.

12. RANAP, Paging 13. DTAP, Paging Response 14. DTAP, Set-up 15. DTAP, Call confirmed 16. RANAP, Assignment Request 17. AAL2, Establish Request 18. AAL2, Establish confirm 19. RANAP, Assignment Response 20. DTAP, Alert 21. ISDN, Address Complete Message ACM
22. ISDN, Call Proceeding CPG

23. RANAP, lu release command 24. AAL2, Release request 25. AAL2, Release confirm 26. RANAP, lu release complete 27. Optional DCP, Connect announcement machine (Pvl1) Optionally, the announcement machine is connected, if inband notification is required.

28. Optional DCP, Disconnect announcement machine (Pvl 1) After the announcement the announcement machine is disconnected.
29. ISDN, Initial Address Message IAM (MGW1, Pol, OPC, DPC, CIC) The IAM message is send from the mobile services switching centre MSC to the transit switching centre TSC2. The media gateway MGW1 address and Pvll or optionally the OPC, DPC, CIC can be used for identifying the incoming connection in the mobile services switching centre MSC.

30. DCP, resource request (MGW2) Resources are requested for the call identified by its CIC.
31. DCP, resource response (Pi2, Pv21) An incoming point Pi2 and a virtual point Pv21 are returned from the media gateway MGW2.

32. DCP, Set-up connection (MGW1, media gateway MGW2, Pol, Pi2) The transit switching centre TSC2 requests the already reserved resources for an outgoing call identified by its virtual CIC and commands the media gateway MGW

to set up a connection towards Pi2 in media gateway MGW2.

33. AAL2, Establish Request 34. AAL2, Establish confirm 35. DCP, Set-up connection response (Pol) The media gateway MGW 1 signals back that the outgoing connection has been set up successful and returns an outgoing point Pol.

36. DCP, Through connect (Po 1, Pv 11) The transit switching centre TSC2 commands the media gateway MGW1 to through connect the outgoing point Pol and the virtual point Pvl1. If optional DCP, Through connect (Pi2, Pvl 1) is omitted, instead of Pvl l Pil must be used.

37. Optional DCP, Through connect (Pi2, Pv21) The transit switching centre TSC2 commands the media gateway MGW2 to through connect the incoming point Pi2 and the virtual point Pv21.

38. DCP, Set-up connection (MGW2, Pv21) The transit switching centre TSC2 requests resources for an outgoing call identified by its virtual CIC and commands the media gateway MGW2 to set up a connection towards the transit switch 2.

39. DCP, Set-up connection response (Po2, CIC) The media gateway MGW2 signals back that the outgoing connection has been set up successfully and returns an outgoing point Po2.

40. DCP, Through connection (Po2, Pv21) The transit switching centre TSC2 commands the media gateway MGW2 to through connect the outgoing point Po2 and the virtual point Pv21.

41. ISDN, Initial Address Message IAM (OPC, DPC, CIC) The IAM message is send from the transit switching centre TSC2 to the transit switch 2.

42. ISDN, Address Complete Message ACM
43. ISDN, Call Proceeding CPG

44. ISDN, Call Proceeding CPG
45. ISDN, Call Proceeding CPG
46. ISDN, Answer Message ANM
47. ISDN, Answer Message ANM
48. ISDN, Answer Message ANM
49. ISDN, Answer Message ANM

Figure 7 illustrates call waiting and accepting the waiting call in different MGWs.

The media gateway address is transported in the forward direction.

Here a subscriber B is calling a served user equipment A, who has the supplementary services CW and HOI.D. After the call from B to A is active another terminating call from a subscriber C to A is received. Subscriber A accepts the waiting call from C
and therefore has to put the call to B on hold. The user plane is routed directly to the media gateway of the active call. This is the optimal way for the transmission, but it requires subsequent assignment over the Iu interface.

In this case only one media gateway is used for each call, which can be used by all control servers to influence the user plane. No user plane connection is needed between the MGWs.
1. ISDN, Initial Address Message IAM (OPC, DPC, CIC) Call set-up is requested from an external ISDN network for a mobile terminated call attempt. In this example the gateway mobile services switching centre/transit switching centre GMSC1/TSC and the Signaling Gateway 1 are collocated.

2. DCP, resource request (MGW1, CIC) Resources are requested for the call identified by its CIC, which were chosen by the transit switch of the ISDN network.

3. DCP, resource response (Pil, Pvll) An incoming point Pi 1 and a virtual point Pv 11 are returned from the media gateway MGW l .

4. MAP, SendRouting Information request The gateway mobile services switching centre GMSC1 interrogates the home location register HLR for routing information.

5. MAP, SendRouting Information response The gateway mobile services switching centre GMSC1 receives the mobile services switching centre MSC address.

6. ISDN, Address Complete Message ACM

The ACM message is sent from the gateway mobile services switching centre/transit switching centre GMSC1/TSC to the transit switch 1.

7. Optional DCP, Through connect (Pil, Pvll) The gateway mobile services switching centre/transit switching centre conunands the media gateway MGW 1 to through connect the incoming point Pi 1 and the virtual point Pvl1. Optionally, the whole media gateway MGW1 connection can be through connected with one DCP, Through connect (Pil, Pol) message.

8. ISDN, Initial Address Message IAM (MGW1, Pvll, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre/transit switching centre GMSC1/TSC to the mobile services switching centre MSC. The media gateway MGW1 address and Pvl1 or optionally the OPC, DPC, CIC can be used for identifying the incoming connection in the mobile services switching centre MSC.

9. DCP, resource request (MGW1, Pv11) Resources are requested for the call identified by its CIC.
10. DCP, resource response (Pol) An outgoing point Pol is returned from the media gateway MGW1.
11. DCP, Through connect (Pvl1, Pol) The mobile services switching centre MSC commands the media gateway MGW 1 to through connect the virtual point Pv11 and the outgoing point Pol.
Optionally the whole media gateway MGW1 connection can be through connected with one DCP, Through connect (Pil, Pol) message.

12. RANAP, Paging 13. DTAP, Paging Response 14. DTAP, Set-up 15. DTAP, Call confirmed 16. RANAP, Assignment Request 17. AAL2, Establish Request 18. AAL2, Establish confirm 19. RANAP, Assignment Response 20. DTAP, Alert 21. ISDN, Address Complete Message ACM
22. ISDN, Call Proceeding CPG

23. DTAP, Connect 24. DTAP, Connect ack 25. ISUP, Answer Message ANM
26. ISUP, Answer Message ANM

27. ISDN, Initial Address Message IAM (OPC, DPC, CIC) Call set-up is requested from an external ISDN network for a mobile terminated call attempt. In this example the gateway mobile services switching centre GMSC2 and the Signaling Gateway 2 are collocated.

28. DCP, resource request (MGW2, CIC) Resources are requested for the call identified by its CIC, which were chosen by the transit switch 2 of the ISDN network.

29. DCP, resource response (Pi2, Pv 11) An incoming point Pi2 and a virtual point Pv21 are returned from the media gateway MGW2.

30. MAP, SendRouting Information request The gateway mobile services switching centre GMSC2 interrogates the home location register HLR for routing information.

31. MAP, SendRouting Information response The gateway mobile services switching centre GMSC2 receives the mobile services switching centre MSC address.

32. ISDN, Address Complete Message ACM

The ACM message is send from the gateway mobile services switching centre GMSC2 to the transit switch 2.

33. Optional DCP, Through connect (Pi2, Pv21) The gateway mobile services switching centre GMSC2 commands the media gateway MGW2 to through connect the incoming point Pi2 and the virtual point Pv21.
Optionally, the whole media gateway MGW2 connection can be through connected with one DCP, Through connect (Pi2, Po2) message.

34. ISDN, Initial Address Message IAM (MGW2, Pv21, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre to the mobile services switching centre MSC. The media gateway MGW2 address and Pv21 or optionally the OPC, DPC, CIC can be used for identifying the incoming connection in the mobile services switching centre MSC.

35. DCP, resource request (MGW2, Pv21) Resources are requested for the call identified by its CIC.
36. DCP, resource response (Po2) An outgoing point Po2 is returned from the media gateway MGW2.
37. DCP, Through connect (Pv21, Po1) The mobile services switching centre MSC commands the media gateway MGW2 to through connect the virtual point Pv21 and the outgoing point Po2.
Optionally, the whole media gateway MGW2 connection can be through connected with one DCP, Through connect (Pi2, Po2) message.

38. RANAP, Paging 39. DTAP, Paging Response 40. DTAP, Set-up 41. DTAP, Call confirmed 42. DTAP, Alert 43. ISDN, Address Complete Message ACM
44. ISDN, Call Proceeding CPG

45. DTAP, HOLD (B) 46. DTAP, HOLD ACK

47. ISUP, Call Proceeding Message CPG (B held) 48. ISUP, Call Proceeding Message CPG (B held) 49. RANAP, Assignment Request 50. AAL2, Release Request 51. AAL2, Release Confirm 52. AAL2, Establish Request 53. AAL2, Establish confirm 54. RANAP, Assignment Response 55. DTAP, Connect 56. DTAP, Connect ack 57. ISUP, Answer Message ANM
58. ISUP, Answer Message ANM

Figure 8 illustrates call waiting and accepting the waiting call in one media gateway.
The media gateway address is transported in the forward direction.

Here a subscriber B is calling a served mobile subscriber A, who has the supplementary services CW and HOLD. After the call from B to A is active another terminating call from a subscriber C over media gateway MGW2 to A is received. Subscriber A
accepts the waiting call from C and therefore has to put the call to B on hold. The user plane is routed from media gateway MGW2 to the media gateway MGWI of the first active call. The active call becomes then the held call. It is assumed that both the active and the waiting call use the same service, e. g., speech, so that the AAL2 connection between radio network controller RNC and media gateway MGW1 can be reused. This allows fast switches between the active and the held call and if a multiparty is required later on, only a conference call device has to be linked in the media gateway MGW 1.

In this case only one media gateway is used for each call, which can be used by all control servers to influence the user plane. The user plane connections are gathered at one media gateway. This allows faster switches between the calls from B and C. A
transcoder is linked in by the terminating mobile services switching centre MSC for each call. On the incoming side, e. g., PCM coding is used and on the outgoing side the coding, negotiated with the UEs, is used.

1. ISDN, Initial Address Message IAM (OPC, DPC, CIC) Call set-up is requested from an external ISDN network for a mobile terminal call attempt. In this example the gateway mobile services switching centre/transit switching centre GMSC1/TSC and the Signaling Gateway 1 are collocated.

2. DCP, resource request (MGW1, CIC) Resources are requested for the call identified by its CIC, which were chosen by the transit switch of the ISDN network.

3. DCP, resource response (Pi2, Pvl1) An incoming point Pi 1 and a virtual point Pv 11 are returned from the media gateway MGW 1.

4. MAP, SendRouting Information request The gateway mobile services switching centre GMSCI interrogates the home location register HLR for routing information.

5. MAP, SendRouting Information response The gateway mobile services switching centre GMSCI receives the mobile services switching centre MSC address.

6. ISDN, Address Complete Message ACM

The ACM message is send from the gateway mobile services switching centre/transit switching centre GMSC1/TSC to the transit switch 1.

7. Optional DCP, Through connect (Pi 1, Pv 11) The gateway mobile services switching centre/transit switching centre commands the media gateway MGW 1 to through connect the incoming point Pi 1 and the virtual point Pvl 1. Optionally, the whole media gateway MGW1 connection can be through connected with one DCP, Through connect (Pi2, Po2) message.

8. ISDN, Initial Address Message IAM (MGW1, Pvl l, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre/transit switching centre GMSC1/TSC to the mobile services switching centre MSC. The media gateway MGW1 address and Pvl l or optional the OPC, DPC, CIC can be used for identifying the incoming connection in the mobile services switching centre MSC.

9. DCP, resource request (MGW 1, Pv 11) Resources are requested for the call identified by its CIC.
10. DCP, resource response (Po1) An outgoing point Pol is returned from the media gateway MGW1.
11. DCP, Through connect (Pv 11, Po1) The mobile services switching centre MSC commands the media gateway MGW1 to through connect the virtual point Pvl 1 and the outgoing point Pol.
Optionally, the whole media gateway MGW1 connection can be through connected with one DCP, Through connect (Pil, Po1) message.

12. RANAP, Paging 13. DTAP, Paging Response 14. DTAP, Set-up 15. DTAP, Call confirmed 16. RANAP, Assignment Request 17. AAL2, Establish Request 18. AAL2, Establish confirm 19. RANAP, Assignment Response 20. DTAP, Alert 21. ISDN, Address Complete Message ACM
22. ISDN, Call Proceeding CPG

23. DTAP, Connect 24. DTAP, Connect ack 25. ISUP, Answer Message ANM
26. ISUP, Answer Message ANM

27. ISDN, Initial Address Message IAM (OPC, DPC, CIC) Call set-up is requested from an external ISDN network for a mobile terminated call attempt. In this example the gateway mobile services switching centre GMSC2 and the Signaling Gateway 2 are collocated.

28. DCP, resource request (MGW2, CIC) Resources are requested for the call identified by its CIC, which were chosen by the transit switch 2 of the ISDN network.

29. DCP, resource response (Pi2, Pvl l) An incoming point Pi2 and a virtual point Pv21 are returned from the media gateway MGW2.

30. MAP, SendRouting Information request The gateway mobile services switching centre GMSC2 interrogates the home location register HLR for routing information.

31. MAP, SendRouting Information response The gateway mobile services switching centre GMSC2 receives the mobile services switching centre MSC address.

32. ISDN, Address complete Message ACM

The ACM message is send from the gateway mobile services switching centre GMSC2 to the transit switch 2.

33. Optional DCP, Through connect (Pi2, Pv21) The gateway mobile services switching centre GMSC2 commands the media gateway MGW2 to through connect the incoming point Pi2 and the virtual point Pv21.
Optionally, the whole media gateway MGW2 connection can be through connected with one DCP, Through connect (Pi2, Po2) message.

34. ISDN, Initial Address Message IAM (MGW2, Pv21, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre to the mobile services switching centre MSC. The media gateway MGW2 address and Pv21 or optionally the OPC, DPC, CIC can be used for identifying the incoming connection in the mobile services switching centre MSC.

35. DCP, resource request (MGW1) Resources are requested for incoming AAL2 connection.
36. DCP, resource response (Pv 12, Pi 11) An incoming point Pi 11 is returned from the media gateway MGW 1.
37. Optional DCP, Through connect (Pv12, Pill) The mobile services switching centre MSC commands the media gateway MGW1 to through connect the virtual point Pv 12 and the incoming point Pi 11.
Optionally, the whole media gateway MGW 1 connection can be through connected with one DCP, Through connect (Pil l, Po2) message.

38. RANAP, Paging 39. DTAP, Paging Response 40. DTAP, Set-up 41. DTAP, Call confirmed 42. DTAP, Alert 43. ISDN, Address Complete Message ACM
44. ISDN, Call Proceeding CPG

45. DTAP, HOLD (B) 46. DTAP, HOLD ACK

47. ISUP, Call Proceeding Message CPG (B held) 48. ISUP, Call Proceeding Message CPG (B held) 49. DCP, Set-up connection (MGW1, media gateway MGW2, Pv21, Pill) MSC requests resources for an outgoing AAL2 connection and commands the media gateway MGW 1 to set up a connection towards Pi 11 in media gateway MGW 1.
50. AAL2, Establish Request 51. AAL2, Establish confirm 52. DCP, Set-up connection response (Po2) The media gateway MGW2 signals back that the outgoing connection has been set up and returns an outgoing point Po2.

53. DCP, Through connect (Pv21, Po2) The mobile services switching centre MSC commands the media gateway MGW2 to through connect the virtual point Pv21 and the outgoing point M.
Optionally, the whole media gateway MGW2 connection can be through connected with one DCP, Through connect (Pi2, Po2) message.

54. DCP, Disconnect (Po1, Pv11) 55. DCP, Through connect (Pv12, Po2) The mobile services switching centre MSC commands the media gateway MGW 1 to through connect the virtual point Pv12 and the outgoing point Po2.
Optionally, the whole media gateway MGW2 connection can be through connected with one DCP, Through connect (Pi2, Po2) message. This connects the existing user plane between radio network controller RNC and media gateway MGW 1 with the user plane of subscriber C.

56. DTAP, Connect 57. DTAP, Connect ack 58. ISUP, Answer Message ANM
59. ISUP, Answer Message ANM

Figure 9 illustrates a MPTY call. The media gateway address is transported in the forward direction.

Here a subscriber B is calling a served user equipment A, who has the supplementary services CW, HOLD and MPTY. After the call from B to A is active another terminating call from a subscriber C over media gateway MGW2 to A is received. Subscriber A accepts the waiting call from C and therefore has to put the call to B on hold. The user plane of the second call is routed from media gateway MGW2 to the media gateway MGW 1 of the first active call. Then mobile services switching centre MSC commands media gateway MGW1 to switch from the former active call to the waiting call. The active call becomes then the held call. It is assumed that both the active and the waiting call use the same service, e. g., speech, so that the AAL2 connection between radio network controller RNC and media gateway MGW 1 can be reused. Now a multiparty is invoked by subscriber A. Therefore the mobile services switching centre MSC links in a conference call device (CCD). Before the user planes can be connected, the user planes all must be in the same format, e.
g., PCM 64 kbit/s.

In this case only one media gateway is used for each call, which can be used by all control servers to influence the user plane. The user plane connections are gathered at one media gateway. This allows faster switches between the calls from B and C.

A transcoder is linked in by the terminating mobile services switching centre MSC
for each call. On the incoming side, e. g., PCM coding is used and on the outgoing side the coding, negotiated with the UEs, is used. The linked in conference bridge is assumed to be a PCM
conference bridge, therefore at each leg coding from the received coding to PCM coding applies.
This allows gathering of different coded data streams.

1. ISDN, Initial Address Message IAM (OPC, DPC, CIC) Call set-up is requested from an external ISDN network for a mobile terminated call attempt. In this example the gateway mobile services switching centre/transit switching centre GMSC1/TSC and the Signaling Gateway 1 are collocated.

2. DCP, resource request (MGW1, CIC) Resources are requested for the call identified by its CIC, which were chosen by the transit switch of the ISDN network.

3. DCP, resource response (Pil, Pvl l) An incoming point Pil and a virtual point Pvl l are returned from the media gateway MGW 1.

4. MAP, SendRouting Information request The gateway mobile services switching centre GMSCI interrogates the home location register HLR for routing information.

5. MAP, SendRouting Information response The gateway mobile services switching centre GMSC1 receives the mobile services switching centre MSC address.

6. ISDN, Address Complete Message ACM

The ACM message is send from the gateway mobile services switching centre/transit switching centre GMSC1/TSC to the transit switch 1.

7. Optional DCP, Through connect (Pi 1, Pv 11) The gateway mobile services switching centre/transit switching centre commands the media gateway MGW 1 to through connect the incoming point Pi 1 and the virtual point Pv 11. Optionally, the whole media gateway MGW 1 connection can be through connected with one DCP, Through connect (Pi 1, Po 1) message.

8. ISDN, Initial Address Message IAM (MGW1, Pv11, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre/transit switching centre GMSC1/TSC to the mobile services switching centre MSC. The media gateway MGW1 address and Pv11 or optionally the OPC, DPC, CIC can be used for identifying the incoming connection in the mobile services switching centre MSC.

9. DCP, resource request (MGW1, Pvl1) Resources are requested for the call identified by its CIC.
10. DCP, resource response (Po1) An outgoing point Pol is returned from the media gateway MGW 1.
11. DCP, Through connect (Pv 11, Po 1) The mobile services switching centre MSC commands the media gateway MGW lto link in a transcoder and to through connect the virtual point Pvl and the outgoing point Po I. Optionally, the whole media gateway MGW1 connection can be through connected with one DCP, Through connect (Pi 1, Po l) message.

12. RANAP, Paging 13. DTAP, Paging Response 14. DTAP, Set-up 15. DTAP, Call confirmed 16. RANAP, Assignment Request 17. AAL2, Establish Request 18. AAL2, Establish confirm 19. RANAP, Assignment Response 20. DTAP, Alert 21. ISDN, Address Complete Message ACM
22. ISDN, Call Proceeding CPG

23. DTAP, Connect 24. DTAP, Connect ack 25. ISUP, Answer Message ANM
26. ISUP, Answer Message ANM

27. ISDN, Initial Address Message IAM (OPC, DPC, CIC) Call set-up is requested from an external ISDN network for a mobile terminated call attempt. In this example the gateway mobile services switching centre GMSC2 and the Signaling Gateway 2 are collocated.

28. DCP, resource request (MGW2, CIC) Resources are requested for the call identified by its CIC, which were chosen by the transit switch 2 of the ISDN network.

29. DCP, resource response (Pi2, Pvl1) An incoming point Pi2 and a virtual point Pv21 are returned from the media gateway MGW2.

30. MAP, SendRouting Information request The gateway mobile services switching centre GMSC2 interrogates the home location register HLR for routing information.

31. MAP, SendRouting Information response The gateway mobile services switching centre GMSC2 receives the mobile services switching centre MSC address.

32. ISDN, Address Complete Message ACM

The ACM message is send from the gateway mobile services switching centre GMSC2 to the transit switch 2.

33. Optional DCP, Through connect (Pi2, Pv21) The gateway mobile services switching centre GMSC2 commands the media gateway MGW2 to through connect the incoming point Pi2 and the virtual point Pv21.
Optionally, the whole media gateway MGW2 connection can be through connected with one DCP, Through connect (Pi2, Po2) message.

34. ISDN, Initial Address Message IAM (MGW2, Pv21, OPC, DPC, CIC) The IAM message is sent from the gateway mobile services switching centre to the mobile services switching centre MSC. The media gateway MGW2 address and Pv21 or optional the OPC, DPC, CIC can be used for identifying the incoming connection in the mobile services switching centre MSC.

35. DCP, resource request (MGW1) Resources are requested for incoming AAL2 connection.

36. DCP, resource response (Pv 12, Pi 11) An incoming point Pi 11 is returned from the media gateway MGW 1.
37. Optional DCP, Through connect (Pv12, Pil l) The mobile services switching centre MSC commands the media gateway MGW1 to through connect the virtual point Pv12 and the incoming point Pil l.
Optionally, the whole media gateway MGW1 connection can be through connected with one DCP, Through connect (Pi 11, Po2) message.

38. RANAP, Paging 39. DTAP, Paging Response 40. DTAP, Set-up 41. DTAP, Call confirmed 42. DTAP, Alert 43. ISDN, Address Complete Message ACM
44. ISDN, Call Proceeding CPG

45. DTAP, HOLD (B) 46. DTAP, HOLD ACK

47. ISUP, Call Proceeding Message CPG (B held) 48. ISUP, Call Proceeding Message CPG (B held) 49. DCP, Set-up connection (MGW1, media gateway MGW2, Pv21, Pill) MSC requests resources for an outgoing AAL2 connection, links in a transcoder and commands the media gateway MGW2 to set up a connection towards Pi 11 in media gateway MGW I.

50. AAL2, Establish Request 51. AAL2, Establish confirm 52. DCP, Set-up connection response (Po2) The media gateway MGW2 signals back that the outgoing connection has been set up and returns an outgoing point Po2.

53. DCP, Through connect (Pv21, Po2) The mobile services switching centre MSC commands the media gateway MGW2 to through connect the virtual point Pv21 and the outgoing point Po2. Optional the whole media gateway MGW2 connection can be through connected with one DCP, Through connect (Pi2, Po2) message.

54. DCP, Disconnect (Po2, Pv22) 55. DCP, Through connect (Pv12, Po2) The mobile services switching centre MSC commands the media gateway MGW1 to through connect the virtual point Pv12 and the outgoing point Po2.
Optionally, the whole media gateway MGW2 connection can be through connected with one DCP, Through connect (Pi2, Po2) message. This connects the existing user plane between the radio network controller RNC and media gateway MGW1 with the user plane of subscriber C.

56. DTAP, Connect 57. DTAP, Connect ack 58. ISUP, Answer Message ANM
59. ISLTP, Answer Message ANM
60. DTAP, Build Multiparty 61. DCP, Link in CCD (MGW1, Po11, Pv11) A PCM 64 kbit/s CCD is linked in the path where the user plane is 64 kbit/s.
62. DCP, Disconnect (Pol, Pv12) 63. DCP, Link in transcoder (MGW 1, Pi 11, Pv 12) To convert speech to PCM.
64. DCP, Through connect (Pv 12) Through connect Pv 12 and conference bridge.
65. ISUP, Call Proceeding CPG (Retrieve) 66. ISUP, Call Proceeding CPG (Retrieve) 67. ISUP, Call Proceeding CPG (MPTY) 68. ISUP, Call Proceeding CPG (MPTY) 69. ISUP, Call Proceeding CPG (MPTY) 70. DTAP, Build MPTY ack Figure 10 illustrates call forwarding in the mobile services switching centre MSC to an ISDN subscriber identified by an ISDN no. The mobile services switching centre MSC sets up the connection between media gateway MGW 1 and media gateway MGW2.

In this scenario a subscriber A has set up a call over the ISUP to a user equipment B.
For this purpose the TSC1 has set up the context between the terminations Pil and Pvl 1 in media gateway MGW 1 and the mobile services switching centre MSC has set up the context including a transcoder between the terminations Pol and Pv 11. An assignment request has been sent over the lu interface, which has set up the user plane between the UE and the media gateway MGW 1. The mobile services switching centre MSC deducts the transit switching centre TSC2 address and the media gateway MGW2 address out of the forwarded to number. Then the mobile services switching centre MSC forwards the user plane from media gateway MGW1 to media gateway MGW2.

Figure 11 illustrates an example involving the CW and HOLD functions. In this scenario, a subscriber A has set up a call over ISUP to a user equipment B.
For this purpose the TSC 1 has set up the context between the terminations Pi 1 and Pv 11 in media gateway MGW 1 and the mobile services switching centre MSC has set up the context including a transcoder between the terminations Pol and Pvl l. An assignment request has been sent over the lu interface, which has set up the user plane between the UE and the media gateway MGW 1. Then a subscriber C sets up a call over ISUP to user equipment B. For this purpose the transit switching centre TSC2 has set up the context between the terminations Pi2 and Pv21 in media gateway MGW2. If the active call is to be put on hold, the user plane has to be disconnected at media gateway MGW l.
If the waiting call is to be accepted the mobile services switching centre MSC sets up the context including a transcoder between the terminations Po2 and Pv21 in media gateway MGW2.

Figure 12 illustrates MPTY calls, using CCDs only in media gateway MGW3. In this scenario, a subscriber A has set up a call over ISUP to a user equipment B.
Then a subscriber C has set up a call over ISUP to user equipment B. The user equipment B has accepted the waiting call from subscriber C and put the active call on hold. If a built MPTY message is received from the UE, then the mobile services switching centre MSC selects a media gateway with CCD
capabilities. The capabilities are requested by the mobile services switching centre MSC, whenever a new media gateway is introduced to the MSC server or when a previously introduced media gateway comes back into service again. The media gateway selection is done according to the following priorities:
an media gateway with the active call on (this saves a subsequent set-up from RNC towards the MGW); an media gateway with the call on hold call; or any media gateway with CCD capabilities, chosen depending on the current load situation.

The above described examples illustrate the new approach to separation of call control and bearer control for implementation of GSM and UMTS core networks.
This implementation provides the features summarized above and set forth in the following claims.

Claims (27)

1. A method of setting up a call in a wireless communication network with separation of call control and bearer control, wherein the following steps are performed by at least one control node (MSC1, GMSC, MSC2; GMSCI, MSC;
TSC2; GMSC2; TSCI):
receiving a service request for a call, the service request originating internal to the wireless communication network or external to the wireless communication network, the call being intended for a select destination;
analyzing the service request and the call origin;
selecting at least one media gateway (MGW1, MGW2) to switch a user plane for handling the call dependent on the result of said analysis;
sending an address of the selected media gateway in a forward direction, that is towards the intended destination, to a succeeding control node if the succeeding control node is needed for setting up the call; and communicating with the selected media gateway to set-up bearer control for the call.
2. The method of claim 1 wherein the call is from a mobile terminal in the network to a mobile terminal in the network and the selecting step comprises selecting a single media gateway for handling the call.
3. The method of claim 1 wherein the call is from an external ISDN network to a mobile terminal in the network and the selecting step comprises selecting a single media gateway for handling the call.
4. The method of claim 1 wherein the call is from an external ISDN network and the select destination is external to the network and the selecting step comprises selecting a first media gateway and a second media gateway for handling the call.
5. A method according to any of the claims 1 to 4, wherein the media gateway is selected from among a plurality of media gateways dependent on media gateway capabilities required for handling the call.
6. A method according to any of the claims 1 to 5, wherein the media gateway is selected, from among a plurality of media gateways dependent on a selected destination for the call.
7. A method according to any of the claims 1 to 6, wherein the call is from a mobile terminal in the network to the external ISDN network and the selecting step comprises selecting a single media gateway for handling the call.
8. A method according to any of the claims 1 to 7, wherein the selecting step comprises selecting a group of media gateways according to the select destination of the call and the at least one media gateway is selected from the group of media gateways according to capabilities of the at least one media gateway.
9. The method of claim 8 wherein the at least one media gateway is further selected based on traffic load of the at least one media gateway.
10. A method according to any of the claims 1 to 9, wherein a multiparty call is established by selecting a media gateway preferring the media gateway serving the active call, and if said media gateway serving the active call cannot be used, the media gateway serving the held call, and if the media gateway serving the held call cannot be used, a media gateway with multiparty capabilities selected based on traffic conditions.
11. A method of setting up a call in a wireless communication network with separation of call control and bearer control comprising:
a) initiating call set-up over one control node (RNC1 GMSC1; GMSC; TSCl),the one control node determining a media gateway (MGW1, MGW2) for routing a user plane of the call, wherein the determination of the media gateway (MGW1, MGW2) is made depending on one of: origin of the call, destination of the call or the required services of the call;
b) the one control node requesting resources from the media gateway for handling the call;
c) the one control node transferring an address for the media gateway in a forward direction to a further control node (MSC1, GMSC, MSC2, RNC2; GMSC1, MSC, RNC; TSC2;
GMSC2; TSCI);
d) the further control node implementing steps b) and c) until either a call destination or an external network is reached, the call being carried through the network, whereby call control is implemented in the control nodes and bearer control is implemented in the media gateway.
12. A method according to claim 11 wherein the one control node selects the media gateway for handling the bearer control of the call.
13. A method according to claim 11 or 12, wherein the further control node is one of a gateway mobile services switching centre.
14. A method according to claim 11 or 12, wherein the further control node is a gateway mobile services switching centre and a second mobile services switching centre.
15. A method according to claim 11 or 12 wherein the one control node is a Transit Switching Centre.
16. A method according to any of the claims 11 to 15, wherein the media gateway reserves a logical point identifying reserved resources in the media gateway for handling the call in response to a request for resources.
17. The method of claim 16 wherein the step c), the one control node transferring an address for the media gateway in a forward direction to a further control node, further comprises transferring an identification of the logical point in the forward direction to the further control node.
18. A wireless communication network comprising:
plural control nodes (MSC1, GMSC, MSC2; GMSCl, MSC;
TSC2; GMSC2; TSCI), the control nodes receiving information about a call, the control nodes requesting resources from at least one media gateway (MGWI, MGW2) for handling a user plane of the call; wherein the determination of the at least one media gateway (MGW1, MGW2)is made depending on one of: origin of the call, destination of the call or the required services of the call; and the at least one media gateway including plural logical points (Pol, Pv12, Pvll, Pil; Pi2, Pv21, Po2; Pv13;
Pol1; Po22, Pi32, Pv32, Po3) for connecting plural media gateway resources for handling the user plane of the call, the at least one media gateway being adapted to identify one of the logical points to one of the control nodes in response to a request for resources from the one of the control nodes, whereby the plural control nodes use the at least one media gateway for handling the user plane of the call and at least one control node is adapted to transmit in a forward direction an identification of a media gateway used for the handling of user plane to a further control node.
19. A wireless communication network according to claim 18, wherein application logic implemented for call control in a control node is adapted to requesting media gateway resources from the at least one media gateway for handling a call to allow pooling of media gateway resources under control of the application logic.
20. A wireless communication network according to claim 18 or 19, wherein the communication between control nodes and the at least one media gateway regarding the control and reservation of resources in said at least one media gateway is performed using a Device Control Protocol.
21. A wireless communication network according to claim 18, 19, or 20, wherein the Device Control Protocol is the international telecommunication union Gateway Control Protocol.
22. A wireless communication network according to any of the claims 18 to 21, wherein the control nodes request resources from one of the media gateways in response to the information being a service request for the call.
23. A wireless communication network according to any of the claims 18 to 22, wherein each media gateway includes plural logical points for connecting plural media gateway resources for handling the call, the media gateway being adapted to identify one of the logical points to one of the control nodes in response to a request for resources from the one of the control nodes.
24. A wireless communication network according to any of the claims 18 to 23, wherein the identified logical point identifies a reserved resource and is returned to the control server using the international telecommunication union Gateway Control Protocol.
25. A wireless communication network according to any of the claims 18 to 24, wherein the network uses N-ISUP interface between the control nodes for call control signaling.
26. A wireless communication network according to any of the claims 18 to 25, wherein the user plane is transferred compressed within and between media gateways.
27. A wireless communication network according to any of the claims 18 or 26 wherein at least one of the plural media gateway resources is one of a transcoder, a conference call device, a modem, a tone generator, a framing device or an announcement device.
CA002381622A 1999-08-16 2000-07-19 Implementation of call setup procedures with separation of call control and bearer control Expired - Fee Related CA2381622C (en)

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