Call admission control in VoIP systems

1. A method of controlling call admission within a system including a plurality of media gateways interconnected by a packet switched backbone, the method comprising the steps of:

monitoring a level of congestion suffered by incoming packets for a first media gateway, wherein said incoming packets are transmitted from a group of said plurality of media gateways over said backbone, wherein said first media gateway acts as a terminating media gateway for said group of media gateways, and wherein said group of media gateways is organized as a subnet and is identifiable by applying a specific subnet mask to an address in incoming packets from the group of media gateways;

receiving a request for said first media gateway to terminate a new bearer connection extending over said backbone from a second media gateway within said group of media gateways to said first media gateway;

making a decision on the admissibility of the request based upon a previously monitored level of congestion suffered by incoming packets transmitted from said group of media gateways to said first media gateway; and

rejecting or accepting said request based on said decision.

2. The method according to claim 1 , wherein the step of monitoring comprises the step of:

examining said incoming packets to determine whether or not said incoming packets contain a congestion notification flag.

3. The method according to claim 1 , wherein the step of monitoring comprises the step of:

monitoring a rate at which said incoming packets are dropped.

4. The method according to claim 3 , wherein said monitoring further comprises the step of:

examining said incoming packets to determine whether or not said incoming packets contain a congestion notification flag.

5. The method according to claim 1 , wherein the step of monitoring comprises the step of:

associating incoming packets or packet sequences with an originating gateway based upon source addresses or parts of source addresses.

6. The method according to claim 1 , wherein said packet switched backbone is an Internet Protocol (IP) backbone.

7. The method according to claim 1 , wherein said step of making said decision is made at said first media gateway.

8. The method according to claim 1 , wherein said step of making the decision is made at a media gateway controller controlling said first media gateway, and wherein said monitored congestion level is signalled to the media gateway controller by the first media gateway.

9. A media gateway configured to control call admission within a system including a plurality of media gateways interconnected by a packet switched backbone, the media gateway comprising:

an input/output port coupled to a processor, the media gateway being configured to:

monitor a level of congestion suffered by incoming packets transmitted to the media gateway from a group of media gateways over said backbone, wherein said media gateway acts as a terminating media gateway for said group of media gateways, and wherein said group of media gateways is identifiable by applying a specific subnet mask to an address in incoming packets from the group of media gateways;

receive a request for the media gateway to terminate a new bearer connection extending over said backbone from a media gateway within said group of media gateways;

make a decision on the admissibility of the request based upon a previously monitored level of congestion suffered by incoming packets transmitted from said group of media gateways; and

reject or accept said request based on said decision.

10. A media gateway controller arranged to control call admission within a system including a plurality of media gateways interconnected by a packet switched backbone, the media gateway controller comprising:

an input/output port coupled to a processor,

an interface towards a first media gateway, the interface being coupled to the processor,

wherein the media gateway controller is configured to:

receive monitored congestion levels from said first media gateway, the monitored congestion levels being indicative of congestion suffered by incoming packets transmitted to said first media gateway from a group of said plurality of media gateways over said backbone, wherein said first media gateway is configured to act as a terminating media gateway for said group of media gateways and wherein said group of gateways is organized as a subnet and is identifiable by applying a specific subnet mask to an address in incoming packets transmitted to the from the group of media gateways;

receive a call request requiring that said first media gateway terminate a new bearer connection extending over said backbone from a second media gateway within said group of media gateways to said media gateway;

make a decision on the admissibility of the request based upon the congestion suffered by incoming packets for said first media gateway transmitted from said group of media gateways to said first media gateway; and

reject or accept said request based on said decision.

11. A non-transitory, computer-readable medium encoded with a computer program product for controlling call admission within a communication system including a plurality of media gateways interconnected by a packet switched backbone, the computer program product performs the following steps when run on a computer:

monitoring a level of congestion suffered by incoming packets for a first media gateway, wherein said incoming packets are transmitted from a group of said plurality of media gateways over said backbone, wherein said first media gateway is configured to act as a terminating media gateway for said group of media gateways, and wherein said group of media gateways is identifiable by applying a specific subnet mask to an address in incoming packets from the group of media gateways; and

receiving a request for said first media gateway to terminate a new bearer connection extending over said backbone from a second media gateway within said group of media gateways to said first media gateway;

making a decision on the admissibility of the request based upon a previously monitored level of congestion suffered by incoming packets transmitted from said group of media gateways to said first media gateway; and

rejecting or accepting said request based on said decision.

12. The method of claim 1 , further comprising:

in response to detecting the level of congestion suffered by incoming packets exceeds a predetermined threshold, starting a congestion timer;

in response to receiving a subsequent indication of congestion, restarting said congestion timer; and

in response to receiving a subsequent request for said first media gateway to terminate said new bearer connection, rejecting the subsequent request before expiry of said congestion timer.

13. The method according to claim 3 , wherein said monitoring comprises the step of monitoring the rate at which the incoming packets are dropped by the backbone.

14. The method according to claim 1 , wherein said group is located at a site that is remote from the first media gateway.

15. The method according to claim 1 , wherein the address is a source Internet Protocol, IP, address.

16. The method according to claim 1 , comprising starting a congestion timer in response to detecting congestion.

17. The method according to claim 1 , comprising making a decision to reject the request while the congestion timer is running.

18. The method according to claim 1 , comprising:

receiving a request to set up a bearer to a media gateway in the group; and

making a decision to reject the request to set up the bearer to the media gateway in the group while the congestion timer is running.

19. The method according to claim 1 , comprising restarting the congestion timer in response to detecting further congestion in relation to incoming packets received from the group of media gateways.