On Sat, Oct 10, 2009 at 10:16:43AM +0200, Patrick wrote: > Thank to Frank and Steve for your answers > My understanding is that you need to place on operator premise an > equipment that checks first the availability of the user on VoIP. If > not registered, it's routing the call through the cellular network. > Is it correct ? > But during the handover (wifi to GSM), how does it works ? Is it the > operator that initiates a call on the GSM network. If so, I guess the > mobile device need to have some logic to seamlessly switch between the > 2 channels, isn't it ? > If it's the mobile device that initiates the call to the GSM network, > it will also require some logic to do that. > So my question is, is the handover something standard in every mobile > device supporting GSM and VoIP or do you require an extra piece of > software to do the trick ? > Is this principal applies to every "transport technology", I mean VoIP > through WIfi or VoIP over 3G ?
GSM calls are handled by an MSC (which is an SS7 switch) that talks to BSCs (basestation controllers) which talk to BTS (basestations), of course MSCs also talk to other MSCs. The GSM operator will have a UMA gateway in the network. A UMA phone will 'listen' for both GSM and WiFi and if it detects that the WiFi is 'known' it connects to that and it will connect through to the UMA gateway and the GSM network will switch the call to WiFi, if the user wanders off the WiFi area it will switch back to normal GSM operation. So the phone has to be UMA aware and the operator has to support it. On a normal GSM phone it is possible to write software that will switch calls between VoIP and GSM but you then generally have to control the endpoint of the call, so the GSM call usually goes through a VoIP access system and the software will switch the call to VoIP if it can, but the end-point is always the VoIP system that then calls the real number dialed. i.e. when the user dials a number it doesn't really go to that number directly, goes through the VoIP company who then can switch the transport in-between them and the handset. Steve -- NetTek Ltd UK mob +44 7775 755503 UK +44 20 7993 2612 / US +1 310 857 7715 / Fax +44 20 7483 2455 Skype/GoogleTalk/AIM/Gizmo/.Mac/Twitter/FriendFeed stevekennedyuk Euro Tech News Blog http://eurotechnews.blogspot.com MSN st...@gbnet.net _______________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- AstriCon 2009 - October 13 - 15 Phoenix, Arizona Register Now: http://www.astricon.net asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
