Handoff decision making for heterogeneous network environments

1 . A method comprising:

receiving session initiation protocol (SIP) messages via a wireless local area network (WLAN), the SIP messages comprising data identifying at least one current network characteristic; and

determining whether a handoff trigger for a mobile device is detected using the at least one current network characteristic.

2 . The method of claim 1 wherein determining whether the handoff trigger is detected comprises:

comparing the at least one current network characteristic with a threshold.

3 . The method of claim 2 wherein the threshold is defined by a carrier.

4 . The method of claim 1 wherein determining whether the handoff trigger is detected comprises:

determining whether a wireless local area network (WLAN) providing service to the mobile device is overloaded.

5 . The method of claim 1 wherein determining whether the handoff trigger is detected comprises:

determining whether a cell with desired parameters is available in a cellular wide area network (WAN).

6 . The method of claim 1 wherein the at least one current network characteristic comprises at least one of a signal strength indicator and an error rate.

7 . The method of claim 1 firther comprising:

selecting a target cell to serve the mobile device.

8 . The method of claim 7 wherein the target cell is selected based on a mobile device location and characteristics of nearby cells.

9 . The method of claim 7 further comprising:

evaluating the target cell based on policy criteria; and

executing a handover from the WLAN to a cellular wide area network (WAN) if the target cell meets the policy criteria.

10 . The method of claim 9 wherein the handover policy criteria comprises at least one of a security criterion, a carrier preference and a timing criterion.

11 . The method of claim 1 wherein the at least one current network characteristic is included in an attachment of a SIP message.

12 . The method of claim 11 wherein a type of the attachment is specified in one of a plurality of header fields of the SIP message.

13 . The method of claim 1 further comprising:

receiving a registration message from the mobile device in a roaming mode, the registration message comprising contact information for the mobile device; and

storing the contact information in a SIP register.

14 . The method of claim 13 further comprising:

determining, based on the contact information, that a location of the mobile device has changed; and

updating the location of the mobile device in a home location register (HLR).

15 . The method of claim 13 wherein the registration message comprises a SIP registration message.

16 . An apparatus comprising:

a message receiver to receive session initiation protocol (SIP) messages via a wireless local area network (WLAN), the SIP messages comprising data identifying at least one current network characteristic; and

a handover trigger detector to determine whether a handoff trigger for a mobile device is detected using the at least one current network characteristic.

17 . The apparatus of claim 16 wherein the handover trigger determines whether the handoff trigger is detected by comparing the at least one current network characteristic with a threshold.

18 . The apparatus of claim 17 wherein the threshold is defined by a carrier.

19 . The apparatus of claim 16 wherein the handover trigger determines whether the handoff trigger is detected by determining whether a wireless local area network (WLAN) providing service to the mobile device is overloaded.

20 . The apparatus of claim 16 wherein the handover trigger determines whether the handoff trigger is detected by determining whether a cell with desired parameters is available in a cellular wide area network (WAN).

21 . The apparatus of claim 16 wherein the at least one current network characteristic comprises at least one of a signal strength indicator and an error rate.

22 . The apparatus of claim 16 further comprising a target cell selector to select a target cell to serve the mobile device.

23 . The apparatus of claim 16 wherein the at least one current network characteristic is included in an attachment of a SIP message.

24 . The apparatus of claim 23 wherein a type of the attachment is specified in one of a plurality of header fields of the SIP message.

25 . A system comprising:

means for receiving session initiation protocol (SIP) messages via a wireless local area network (WLAN), the SIP messages comprising data identifying at least one current network characteristic; and

means for determining whether a handoff trigger for a mobile device is detected using the at least one current network characteristic.

26 . A computer readable medium comprising executable instructions which when executed on a processing system cause said processing system to perform a method comprising:

receiving session initiation protocol (SIP) messages via a wireless local area network (WLAN), the SIP messages comprising data identifying at least one current network characteristic; and

determining whether a handoff trigger for a mobile device is detected using the at least one current network characteristic.