GB2418796A

GB2418796A - Internet Protocol Media Gateway (IPMG)

Info

Publication number: GB2418796A
Application number: GB0421822A
Authority: GB
Inventors: Percy Lau; Peter Tarle; Cuthbert Cheung; Zhiguo Chen; Ivan Novakovic; Wendy Eng; Gwen Clarke
Original assignee: Nortel Networks Ltd
Current assignee: Nortel Networks Ltd
Priority date: 2004-10-01
Filing date: 2004-10-01
Publication date: 2006-04-05
Also published as: GB2418796A8; GB0421822D0

Abstract

When the IPMG registers with the central call server, some IPMG configuration data in the call server are downloaded to the IPMG. These elements of configuration data are used to map the configured resources or devices in the call server to the hardware in the IPMG and vice versa. This mapping is utilised to identify the source and destination hardware during call processing. This process will enable the call to be made from any type of phone to any other type of phone. In order to set up a speech path between two traditional phones in the same IPMG the central call server sends a speech path setup message to the IPMG switches on a two way speech path between the originating telephone and the terminating telephone. To clear down the speech path, the central call server sends a speech path clear down message to the IPMG. The IPMG clears down the speech path between the two telephones thereby effecting disconnection between the phones. Invention can be used when migrating from a POTS network to an IP based network.

Description

24 1 8796 - 1 IMPROVEMENTS IN OR RELATING TO VOICE OVER IP (VolP) NETWORKS

This invention relates to voice over IP (VolP) networks and improvements relating thereto.

One of the advantages of VolP is the ability to set up audio media streams directly between the source terminal to a destination terminal. This capacity eliminates the requirements of central switching devices. However, this characteristic becomes an obstacle to large businesses and networks who are intending to change to an IP environment because the change makes their investment in existing legacy hardware worthless. In addition, substantial capital expenditure is required to replace them with their IP counterparts. Accordingly, it would be convenient for enterprises and networks to have the ability to make a gradual transition from traditional TDM media switching to IP type networks.

This in itself is not straight forward. In a traditional POX environment speech paths are connected via a central switching matrix. If IP telephones are used, digital signal processing (DSP) resources are provided to convert audio TDM media streams to audio IP media streams and vice versa. To set up a call between a traditional TDM telephone and an IP telephone, a DSP resource is allocated to the IP telephone. Direct audio IP media stream is then set up between the IP phone and the DSP resource and then a two way TDM speech path is set up between the DSP resource and traditional telephone to complete the two way speech set up. This requires that a DSP resource is provided for every traditional device for every IP telephone. This would both be costly and tedious for anyone to adopt.

One object of the present invention is to provide a system which allows gradual transition from the TDM domain to the IP domain without encountering the disadvantages of currently proposed solutions.

According to one aspect of the present invention there is provided a media gateway in a telephone network for connecting a call from a first type terminal to a second type terminal comprising: a detector for identifying a characteristic of the first type - 2 terminal; determining means for determining the destination of a call; route planning means for determining the route to connect the first and second type terminals using both first and second type call formats and thereby effecting the connection.

This provides a cost effective solution for migrating towards IP format from TDM format and allows for disaster recovery when the determination of the call destination can be made using a redundancy element distributed in a different place to the list element that determines call destination. Also the invention allows reuse of the TDM devices and resources in a distributed IP network environment.

Reference will now be made by way of example to the accompanying drawings in 1 0 which: FIGURE 1 is a known diagram showing a traditional TDM PBX; FIGURE 2 is a known diagram showing an IP PBX; FIGURE 3 is a network diagram for a combined IP TDM PBX network according to the present invention; FIGURE 4 is a block diagram of the IP media gateway (IPMG) of figure 3; FIGURE 5 is a drawing for showing an example of a call between two TDM sets using the system of the present invention; FIGURE 6 is a second example of a call between two TDM sets using the system of the present invention; FIGURE 7 is an example of connecting a TDM to an IP phone using the present invention; and FIGURE 8 is an example of how to make a conference call using the present invention.

Referring to Figure 1, two Time Division Multiplex (TDM) phones 10 and 12 are shown connected to a locally located piece of hardware 14. The locally located piece of hardware Is a typical PBX and includes such elements as a call processor 16, switching hardware 18 and line cards 20 of which there may be a number. The TDM telephones are connected to the PBX via twisted pair wires 22. When a call Is made from phone 10 to phone 12 the PBX enables the connection between the two pairs of twisted wires 22 to ee:e:e ë - 3 allow send and receive messages to be sent between the two phones 10 and 12. This is well known to the person skilled in the art.

Figure 2 shows a typical IP POX. Two Internet Protocol (IP) telephones 24 and 26 are shown connected to an IP network 28. The Internet Protocol (IP) network is connected to a call server 30. The IP phones are distributed throughout the IP network and are connected via an IP infrastructure. There is no centralised switching hardware, but instead a call server which enables addressing from one call to the other in an appropriate manner that is known to the man skilled in the art.

Figure 3 shows a system according to the present invention. An IP network 100 is connected to a plurality of telephones 102, 102a, 102b via an IP media gateway (IPMG) 104, 104a and 104b. More than one telephone may be connected to each IPMG. The IPMG's are located and distributed throughout the IP network. A call server 106 is also connected to the IP network. If required, a redundant call server 106a may also be connected to the IP network to provide redundancy should the first call server fail in any way. Each call server includes a database 108 and 108a, the function of which will be described in more detail later.

Referring now to Figure 4, the IPMG 400 is a module which is distributed in an IP network and contains a controller 310, tone generating circuits 320, a conference circuits 330, TDM switching matrix circuits 340, voice gateway circuits 350 and one or more interface to line cards 360 hereinafter called line interfaces. In addition there is an Ethernet interface circuit 370 which is connected directly to the IP network 380. As will be appreciated the circuits could all be implemented as software and thus in this context circuits is not limited to something physical, but will include anything where their functionality of the circuits may be carried out. In addition it will be appreciated there could be one or more of each of the "circuits " referenced. The gateway controller or microprocessor 310 communicates with a central call processor through the Ethernet interface port. It acts as an interface between the central call server and the TDM devices such as tone generators, conference circuits, TDM switching matrix, voice gateways and line interfaces. The tone generator is a tone source that provides call progress tones such as dial tone, busy tone, ring back tone, digital tones etc. The conference circuit is a conference device that mixes TDM audio media streams from different source signals to provide conference functionality when required. The TDM switching matrix is a time slot interchange chip which switches TDM audio media :. :. a. - 4

streams from source channels to destination channels as required by the process. A voice gateway is a device that converts the TDM audio media stream to IP audio media stream and vice versa. The line interface is a hardware line card which provides an interface with additional phones, either through analogue or digital and traditional trunks.

Referring now to Figures 5 though 8, four different examples are shown of how a call may be connected between two or more telephones 380 in each of the drawings.

When the IPMG registers with the central call server, some IPMG configuration data in the call server are downloaded to the IPMG. These elements of configuration data are used to map the configured resources or devices in the call server to the hardware in the IPMG and vice versa. This mapping is utilised to identify the source and destination hardware during call processing. As has already been described in the four examples above, this process will enable the call to be made from any type of phone to any other type of phone.

In order to set up a speech path between two traditional phones in the same IPMG the central call server sends a speech path setup message to the IPMG switches on a two way speech path between the originating telephone and the terminating telephone.

To clear down the speech path, the central call server sends a speech path clear down message to the IPMG. The IPMG clears down the speech path between the two telephones thereby effecting disconnection between the phones.

Figure 5 relates to the circumstance where there are two TDM phones making a call through the same IPMG. The steps of the call are outlined below: 1. Caller lifts handset of TDM phone 380a. Line interface 360a sends off hook event from TDM phone 380a to Gateway (GW) controller 31 Oa. GW Controller 31 Oa relays message to Central Call Server 106.

2. Central Call Server 106 sends message to GW controller 310a to switch dial tone from Tone Generator 320 via Switching Matrix 340a to TDM phone 380a.

3. Caller dials first digit of destination directory number. GW Controller 310a relays the digit dialled to Call Server 106.

4. Central Call Server 106 sends message to GW Controller 310a to switch off the dial tone to TDM phone 380a.

:. ::e e:e - 5 5. GW Controller 31 Oa cuts off the dial tone to TDM phone 380a and continues to relay digits dialled to the Central Call Server 106.

6. Central Call Server 106 processes all dialled digits, looks up the database 110 for the location of the destination terminal, and sends message to GW Controller 31 Oa to send ring back tone to TDM phone 380a and ring TDM phone 380b.

7. GW Controller 31 Oa switches Switching Matrix 340 to connect ring back tone to TDM phone 380a and rings TDM phone 380b.

8. Called party answers. Line Interface 360b sends off hook event from TDM phone 380b to GW Controller 31 Oa, which relays the message to Central Call Server 106.

9. Central Call Server 106 sends message to GW Controller 31 Oa to remove ring back tone to TDM phone 380a, to remove ringing to TDM phone 380b and to connect the speech path between TDM phones 380a and 380b.

10. GW Controller 31 Oa removes ring back tone to TDM phone 380a, ringing to TDM phone 380b and connects the speech path between TDM phone 380a and 380b through the TDM switching Matrix 340a.

11. At the end of the call, the caller hangs up. Line interface 360a sends the on hook event from TDM phone 380a to GW Controller 31 Oa which relays it to the Central Call Server 106.

12. Central Call Server 106 sends message to GW Controller 310a to remove the connection in Switching Matrix 340 for the speech path between TDM phones 380a and 380b.

13. GW Controller 31 Oa removes the speech path in Switching Matrix 340a for the speech path between TDM phones 380a and 380b.

14. Called party goes on hook. Line interface 360b send on hook event from TDM phone 380b to GW Controller 31 Oa, which relay it to Central Call Server 106.

15. Central Call Server 106 completes the clearing of the call - 6 Referring now to Figure 6, this shows an example of two TDM sets making a connection through two different IPMGs.

In this example where two traditional phones are connected via two different IPMGs the central call server allocates a DSP resource to each traditional telephone in their own IPMG and sends a speech path setup message to each IPMG. Each IPMG switches on a two way speech path between the allocated DSP resource and the traditional telephone. The central call server then sets up the direct audio IP media streams between the two DSP resources to complete the speech path setup. Similarly, to clear down the speech path, the central call server turns off the audio IP media streams between the DSP resources and sends a speech path clear down message to the IPMG. The IPMG clears down the speech paths between the DSP resource and the transitional telephone to complete the disconnection of the telephone conversation.

The following list shows the events which occur in order for the call to be made.

1. Caller lifts handset of TDM phone 380a. Line interface 360a sends off hook event from TDM phone 380a to GW controller 310a. GW Controller 310a relays message to Central Call Server 106.

2. Central Call Server 106 sends message to GW controller 310a to switch dial tone from Tone Generator 320a via Switching Matrix 340a to TDM phone 380a.

5. GW Controller 310a switches off the dial tone to TDM phone 380a and continues to relay digits dialled to the Central Call Server 106.

6. Central Call Server 106 processes all dialled digits, looks up the database 110 for the location of the destination terminal, sends message to GW Controller 310b to ring TDM phone 380b, and sends message to GW Controller 310a to connect ring back tone to TDM phone 380a.

ac eeese - 7 7. GW Controller 31 Ob rings TDM phone 380b. GW Controller 31 Oa connects ring back tone to TDM phone 380a though Switching Matrix 340a.

8. Called party answers. Line Interface 360b sends off hook event from TDM phone 380b to GW Controller 310b, which relays the message to Central Call Server 106.

9. Central Call Server 106 sends message to GW Controller 31 Oa to remove the ring back tone to TDM phone 380a and to set up the speech path between TDM phones 380a and Voice Gateway 350a, message to GW 31 Ob to remove ringing to TDM phone 380b and to set up speech path between TDM phone 380b, messages to Voice Gateways 350a and 350b to set up a direct iP media path 100 between them.

10. GW Controller 310a removes the ring back tone to TDM phone 380a and connects the speech path in Switching Matrix 340a between Voice Gateway 350a and TDM phone 380a. GW Controller 310b removes ringing to TDM phone 380b and connects the speech path In Switching Matrix 340b between Voice Gateway 350b and TDM phone 380b. Voice Gateways 350a and 350b set up the direct IP media path 100 to each other.

11. At the end of the call, the caller hangs up. Line interface 360a sends the on hook event from TDM phone 380a to GW Controller 31 Oa which relays it to the Central Call Server 1 06.

12. Central Call Server 106 sends messages to GW Controller 31 Oa to disconnect the speech path in Switching Matrix 340a between TDM phones 380a and Voice Gateway 350a, to GW Controller 31 Ob to disconnect the speech path in Switching Matrix 340b between TDM phones 380b and Voice Gateway 350b, to Voice Gateways 350a and 350b to release the direct IP media path 100 between them.

13. GW Controller 310a disconnects the speech path in Switching Matrix 340a between TDM phone 380a and Voice Gateway 350a. GW controller 310b disconnects the speech path in Switching Matnx 340b between TDM phone 380b and Voice Gateway 350b. Voice Gateways 350a and 350b release the direct IP media path 100 between them.

:. :e Ad. - 8

14. Called party goes on hook. Line interface 360b send on hook event from TDM phone 380b to GW Controller 31 Ob, which relay it to Central Call Server 106.

15. Central Call Server 106 completes the clearing of the call.

There is TDM switching path between phone 380a and 380b and the voice gateways 350a and 350b and IP switching path between the voice gateways.

Figure 7 shows the example of a TDM set making a telephone call to an IP phone and shows the media path there through.

To set up a speech path between the traditional TDM telephone and an IP telephone or virtual trunk the central call server allocates a DSP resource to the traditional telephone and sends a speech path setup message to the IPMG. The IPMG switches on a two way speech path between the allocated DSP resource and the traditional telephone. The central call server sets up direct audio IP media streams between the DSP resource and the IP set or the virtual trunk. To clear down the speech path, the central call server turns off the audio media streams between the allocated DSP resource and the IP phone or virtual trunk and sends a speech path clear down message to the IPMG. The IPMG switches off the speech path between the allocated DSP resource and the traditional phone and the connection is broken.

The following steps show the events that occur through the IPMG and other elements of the network in order for the call to be made: 1. Caller lifts handset of TDM phone 380a. Line interface 360a sends off hook event from TDM phone 380a to GW controller 310a. GW Controller 310a relays message to Central Call Server 106.

4. Central Call Server 106 sends message to GW Controller 310a to switch off the dial tone to TDM phone 380a. c.

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c:. :.: :: ce. - 9 -

6. Central Call Server 106 processes all dialled digits, looks up the database 110 for the location of the destination terminal, sends message to IP phone 40a to ring the set, and sends message to GW Controller 31 Oa to connect ring back tone to TDM phone 380a.

7. IP phone 40a turns on ring tone. GW Controller 31 Oa connects ring back tone to TDM phone 380a through Switching Matrix 340a.

8. Called party answers. IP phone sends off hook event Central Call Server 106.

9. Central Call Server 106 sends message to GW Controller 310a to remove the ring back tone to TDM phone 380a and to set up the speech path between TDM phones 380a and Voice Gateway 350a, message to IP phone 40a to remove ring tone and set up direct IP media path 100 to Voice Gateway 350a, and message to Voice Gateway 350a to set up a direct IP media path to IP phone 40a.

10. GW Controller 310a removes the ring back tone to TDM phone 380a and connects the speech path in Switching Matrix 340a between Voice Gateway 350a and TDM phone 380a. Voice Gateways 350a sets up the direct IP media path to IP phone 40a. IP phone 40a sets up direct IP media path 100 to Voice Gateway 350a.

12. Central Call Server 106 sends messages to GW Controller 31 Oa to disconnect the speech path in Switching Matrix 340a between TDM phones 380a and Voice Gateway 350a, to Voice Gateways 350a to release the direct IP media path to IP phone 40a, and to IP phone 40a to release direct IP media path 100 to Voice Gateway 350a.

13. GW Controller 310a disconnects the speech path in Switching Matnx 340a between TDM phone 380a and Voice Gateway 350a. Voice Gateways 350a 10 releases the direct IP media path IP phone 40a. IP phone 40a releases the direct IP media path 100 to Voice Gate 350a.

14. Called party goes on hook. IP phone sends on hook event message to Central Call Server 106.

15. Central Call Server 106 completes the clearing of the call.

In Figure 8 the network shows the example of how a conference call can be made between a number of different TDM sets and an IP phone through a single IPMG. In this example, the conference circuit mixes and redistributes the TDM outputs. The necessary steps to make the call are identified below.

5. GW Controller 31 Oa cuts off the dial tone to TDM phone 380a and continues to relay digits dialled to the Central Call Server 106.

6. Central Call Server 106 processes all dialled digits, looks up the database 110 for the destination phone, sends message to GW Controller 310b to ring TDM phone 380b, and sends message to GW Controller 310a to send ring back tone to TDM phone 380a.

7. GW Controller 310a switches Switching Matrix 340 to connect ring back tone to TDM phone 380a and rings TDM phone 380b.

8. Called party on TDM phone 380b answers. Line Interface 360b sends off hook event from TDM phone 380b to GW Controller 31 Oa, which relays the message to Central Call Server 106.

ë ce. e. . i e - 11 9. Central Call Server 106 sends message to GW Controller 31 Oa to remove ring back tone to TDM phone 380a, to remove ringing to TDM phone 380b and to connect the speech path between TDM phones 3380a and 380b.

10. GW Controller 310a removes ring back tone to TDM phone 380a, ringing to TDM phone 380b and connects the speech path between TDM phone 380a and 380b through the TDM switching Matrix 340a.

11. Caller on TDM phone 380a presses the Conference key. Line Interface 360 sends the Conference key pressed event message to GW Controller 310a, which relays the message to Central Call Server 106.

12. Central Call Server sends messages to GW Controller 310a to disconnect speech path between TDM phones 380a and 380b, to put TDM phone 380b on hold and connect dial tone to TDM phone 380a.

13. GW Controller 310a disconnects speech path between TDM phone 380a and 380b, and connects dial tone to TDM phone 380a through Switching Matrix 3400a.

14. Caller on TDM phone 380a dials first digit of directory number of IP phone 400a. GW Controller 31 Oa relays the first digit to Central Call Server 106.

15. Central Call Server 106 to GW Controller to switch off dial tone to TDM phone 380a.

16. GW Controller 31 Oa cuts off the dial tone to TDM phone 380a and continues to relay digits dialled to the Central Call Server 106.

17. Central Call Server 106 processes all dialled digits, looks up the database 110 for the destination phone, sends message to IP phone 400a to give ring tone, and sends message to GW Controller 310a to send ring back tone to TDM phone 380a.

18. GW Controller 310a connects ring back tone to TDM phone 380a through Switching Matrix 340a. IP phone 40a gives ring tone.

19. User on IP phone 40a answers. IP phone 40a sends on hook event message to Central Call Server 106.

:e::e :.e - 12 20. Central Call Server a sends message to GW Controller 31 Oa to disconnect ring back tone to TDM phone 380a, connect the speech path between TDM phone 380a and Voice Gateway 350a, message to Voice Gateway to set direct IP media path 100 to IP phone 40a, and message to IP phone 40a to stop the ring tone and set up direct IP media path to Voice Gateway 350a.

21. GW Controller 310a disconnects the ring back tone to TDM phone 380a and connects the speech path in the Switching Matrix between TDM phone 380a and Voice Gateway 350a. Voice Gateway 350a sets up direct IP media path to IP phone 40a. IP phone 40a sets up direct media path to Voice Gateway 350a. Caller on TDM phone 380a is talking to user on IP phone 40a.

22. Caller on TDM phone 380a presses the Conference key again. Line Interface 360a sends the Conference key pressed event to Central Call Server 106.

23. Central Call Server finds free Conference Circuit 330a and sends messages to GW Controller 310a to set up the Conference Circuit 330a, to disconnect the speech path between the TDM phone 380a and Voice Gateway 350a, to connect the speech path between TDM phone 380a and Conference Circuit 330a, the speech between TDM phone 380b and the Conference Circuit 330a, and the speech path between Voice Gateway 350a and Conference Circuit 330a.

24. GW Controller 310a sets up Conference Circuit 330a, disconnects speech path between TDM phone 380a and Voice Gateway 350a, connects speech path between TDM phone 350a and Conference Circuit 330a, speech path between TDM phone 350a and Conference Circuit 330a.

25. Users on TDM phone 380a, TDM phone 380b, and IP phone 40a hang up.

Line Interfaces 360a and 360b send on hook event messages to GW Controller 310a, which relays the messages to the Central Call Server 106. IP phone 40a releases the direct IP media path 100 to Voice Gateway 350a and sends on hook event message to Central Call Server 106.

26. Central Call Server 106 sends messages to GW Controller 310a to release Conference Circuit 330a, to disconnect the speech paths between TDM phone 380a and Conference Circuit 33a, between TDM phone 380b and Conference Circuit 330a, and between Voice Gateway 350a and Conference Circuit 330a, ë e - 13 and message to Voice Gateway 350a to release direct IP media path 100 to IP phone 40a.

27. GW Controller 31 Oa releases Conference Circuit 330a, disconnects the speech paths in the Switching Matrix 340 between TDM phone 380a and Conference Circuit 330a, between TDM phone 380b and Conference Circuit 330a, and between Voice Gateway 350a and Conference Circuit 330a. Voice Gateway 350a releases direct IP media path 100 to IP phone 40a.

Whilst this invention is most ideally suited to converting a network from traditional TDM based network to an IP type network, the same technology could also be used to convert for different formats within networks. In addition, as there are a number of IP media gateways geographically distributed and controlled by a centralized call server within the IP network, the system is less vulnerable to disasters such as fires, floods, earthquakes and others, since the centralised resources which usually operate in a network can be replicated in one or more additional redundancy servers at different geographic locations. This decentralization is an excellent way of ensuring disaster recovery for tone and conference hardware is achieved. Further, this decentralization is useful in conferencing facilities where it is important for people to be able to get access to the information necessary to join a conference without there being risks of a server being down. By utilising an IP network and a number of call servers which include a redundancy element risks of known systems are mitigated.

Further advantages of the invention include the ability to distribute TDM devices in an IP environment and reuse some or all of TDM the hardware including tones and conference facilities In the distributed IP environment.

Claims

ce:e::e e.:.e - 14

1. A media gateway in a telephone network for connecting a call from a first type terminal to a second type terminal comprising: a detector for identifying a characteristic of the first type terminal; determining means for determining the destination of a call; route planning means for determining the route to connect the first and second type terminals using both first and second type call formats and thereby effecting the connection.