Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/0005—Control or signalling for completing the hand-off
  • H04W36/0011—Control or signalling for completing the hand-off for data sessions of end-to-end connection
  • H04W36/0033—Control or signalling for completing the hand-off for data sessions of end-to-end connection with transfer of context information
• • 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
  • H04L65/104—Signalling gateways in the network
• • 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
  • H04L65/1083—In-session procedures
• • 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
  • H04L65/1083—In-session procedures
  • H04L65/1095—Inter-network session transfer or sharing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/14—Reselecting a network or an air interface
  • H04W36/144—Reselecting a network or an air interface over a different radio air interface technology
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W80/00—Wireless network protocols or protocol adaptations to wireless operation
  • H04W80/06—Transport layer protocols, e.g. TCP [Transport Control Protocol] over wireless

Definitions

• the invention relates to handoff of a dual mode mobile device between an IP network and a public land mobile network (PLMN), commonly referred to as a cellular network.
• PLMN public land mobile network
• the invention relates to a device and a method for handoff of a VoIP internet telephone call from an IP network to a PLMN and for hand-back of the call to the IP network.
• Internet telephone service such as that provided by Vonage, SIPphone and Skype, is revolutionizing telephone communications and is one of the fastest growing telecommunications applications at the current time.
• the attraction of such services is that voice communication can be had with any internet telephone, fixed line telephone or mobile telephone for little or no cost.
• IP telephone calls to be transferable from the IP medium, whether wired or wireless, to another communications medium, and preferably to be transferable back to the IP medium, whether wired or wireless, without, disconnecting or losing the call.
• Dual mode mobile devices are available that have both wireless IP radio and cellular radio modules so that users can connect to both wireless IP networks and cellular networks using a single device. This allows users to make telephone calls via the normal cellular network when outside the wireless coverage area of an JP network.
• server-based methods to transfer calls between an IP network and a cellular network involve the deployment of changes of software and/or hardware on mobile carriers.
• United States patent 6,327,470 describes a method of transferring a call between fixed and mobile networks for dual mode phones, but this method only works if the mobile carriers and fixed line operators allows call transfer to each other.
• the inventors are not aware of any existing client based method for transferring an existing call made on an IP network to a cellular network, if user moves outside the wireless coverage area of an IP network while on a call, and then for transferring the call back, to the IP network when the wireless device is back within the wireless coverage area of the same or another IP network.
• a device and a method for handoff of a VoIP internet telephone call from an LP network to a cellular network and for hand-back of the call to the IP network in which during or after hand-off of the call an identifier of the hand-off call is obtained and stored and the identifier is used during hand-back of the call to the IP network.
• a mobile device having both internet telephone and cellular telephone operating modes for making either VoIP internet telephone calls or cellular telephone calls.
• the device has a handoff application for handing off a VoIP internet telephone call from the IP network to the cellular network.
• the handoff application detects a handoff condition for handoffof the call and in response thereto initiates a second VoIP call via the IP network to its own cellular subscription on the cellular network.
• the handoff application determines that lhe second call is from the internet subscription of the mobile device and answers the second call.
• the handoff application then initiates transfer of the first VoIP call to the cellular network, and obtains from the VoIP telephone gateway a call leg identifier of the transferred call and stores the call leg identifier in the mobile device. If the handoff application then detects a hand-back condition for handoff of the transferred call from the cellular network back to an IP network it sends a request comprising the call leg identifier to initiate handoff of the transferred call back to the IP network.
• the handoff application subscribes the mobile device to a notification service of the telephone gateway such that the notification service sends the mobile telephone a message containing the call leg identifier of the transferred call.
• the subscription to the notification service can be made during or immediately after setup of the first call.
• the method may also comprise subscribing the mobile device to a notification service of the telephone gateway such that the notification service sends the mobile telephone a message containing the call leg identifier of the transferred call.
• Figure 1 illustrates an exemplary environment in which a wireless handoff scheme according to the invention is practiced.
• Figure 2 illustrates a dual mode wireless telephone handset
• Figure 3 is a flow diagram of steps for handoff of a call from an IP network to a cellular network
• Figure 4 is an example of call flow for handoff of a call from an IP network to a cellular network using Session Initiation Protocol (SIP),
• SIP Session Initiation Protocol
• Figures 5-8 schematically illustrate call connection routing before and after handofTfor different call scenarios.
• Figure 9 is a flow diagram of steps for hand-back of the call from a cellular network to an IP network.
• Figure 10 is an example of call hand-back using SIP.
• Figure 1 1 and 1.2 illustrate call routing before and after handoff in an environment having more than one PSTN gateway.
• Figure 13 illustrates an alternative exemplary environment in which a wired IP phone may handoff a call to a cellular network.
• the invention will now be described as practiced in a dual mode wireless telephone handset for operating in both a wireless IP network and a public land mobile network (PLMN), commonly called a cellular network.
• PLMN public land mobile network
• the telephone has an internet telephone subscription for making voice over IP (VoIP) calls via the IP network and a cellular subscription for making cellular telephone calls via the PLMN.
• VoIP voice over IP
• a dual mode mobile device of the invention could take a different form such as a PDA, palm computer or laptop computer having two wireless modes for connecting to both wireless IP and cellular networks.
• the exemplary embodiment of the invention is described using session initiation protocol (SlP) and real time transport protocol (RTP) for VoIP telephone caJis and uses functionality provided for in that standard. This is also not intended to limit the scope of use or functionality of the invention. Similar functionality is also available in VoIP protocol (H323) and other real time IP standards. It is envisaged that as the popularity of VoIP multi media Communications increase other messaging and data transport protocols may become available in which the invention can be practiced. In the described exemplary embodiment functionality and procedures of SIP and cellular networks are discussed and used. It is understood that these are well-established public standards and full knowledge, functionality and use of the methods provided for within the standards is within the purview of those skill in the art.
• FIG. 1 gives us schematic overview of the exemplary environment in which the invention is practiced.
• a dual mode mobile phone 100 that may connect to either an IP network 105 or a PLMN network 110.
• the PLMN 1 10 is anyone of the commonly use cellular networks worldwide and its type and operation are not important to thy invention except that it has a plurality of base stations 140 that allow wireless connectivity of a subscriber for making telephone calls from a mobile phone as is common place.
• the IP network 105 is a public or private local area network (LAN) or a wide area network (WAN), and may be either private and/or part of a worldwide group of interconnected publicly accessible networks such as the internet.
• LAN local area network
• WAN wide area network
• the LP network 105 has one or more wireless access points 115 for wireless connectivity with radio enabled wireless devices such as the dual mode phone 100. Also connected to die IP network is a VoIP server 125, in the illustrated case a SIP server, for providing an internet telephone service and a PSTN gateway 130 for providing a telephonic interconnection between the IP network 105 and a public switched telephone network (PSTN) 135.
• the SIP server 125 and PSTN gateway 130 might belong to a private group or organization or to an internet telephone service provider from which members of the public may obtain an internet telephone subscription, and may be located remotely from the wireless access points 115 as is commonly the case with internet based applications and services.
• the (PSTN) gateway allows VoIP internet telephone calls to be made between fixed and cellular telephones connected with the PSTN 135 and PLMN 110.
• the dual mode mobile phone 100 schematically illustrated in Figure 2, has an IP radio module 150 containing IP telephone service subscription information for wireless connection with the IP network 105 and a cellular radio module 155 containing cellular network subscription information for wireless connection with the PLMN 1 10.
• the user of the dual mode mobile phone 100 has subscriptions to both an internet telephone service and a cellular telephone service for making telephone calls via either the IP network 105 or the PLMN 110 as desired Using either the IP network 105 or the PLMN 110 the user of the dual mode mobile phone 100 can make telephone calls to users of other internet telephone devices, to fixed line telephones or to other cellular telephone devices.
• the user of the mobile telephone 100 may choose to make his or her telephone calls via the IP network 105 for cost saving reasons.
• PLMNs typically have extensive coverage in most urban, semi-urban and rural areas worldwide, the wireless coverage area of IP networks is less complete and somewhat patchy. Therefore, if the user of lhe dual mode telephone 100 has placed, or received, a telephone call via lhe IP network 105 and is on the move then there may frequently be a need for the dual mode telephone 100 to handoff the call to the cellular network 1 10 before the telephone 100 moves outside of the wireless coverage area of the IP network 105. If the mobile user then moves back within the wireless coverage area of the same or another accessible IP network they may desire, for cost or other reasons, for the call to be handed back to the IP network.
• a handoff application 160 is provided in the dual mode telephone 100 for coordinating handoff of a telephone call established on the IP network 105 to the cellular network 110, and if desired to hand-back the call to the IP network 105.
• the steps in the procedures and example call flow in SlP for handoffof a call from an IP network to a cellular network are shown in Figure 3 and 4 respectively.
• the handoff begins when the dual mode device 100 is on and established VoIP call via the IP network with another party (step 200).
• another party for the purpose of describing the present procedure it is not important whether the call was placed from or to the dual mode device or the other party is another internet telephone device or a fixed line or cellular telephone, however a discussion of this subject if given later with reference to Figures 5-8 and should be noted in relation to obtaining the correct call leg ID for hand-back of a transferred call from the cellular to IP networks.
• a handofT procedure is initiated when the handoff application detects a handoff condition (step 210).
• the handoff condition is not important to the invention and might be when the signal strength of the wireless IP network falls below a threshold value, for example -75dBm and the dual mode telephone 100 is within the coverage area of a usable cellular network (PLMN) with which it has been allowed to register.
• Monitoring of the handoff condition may be by the handoff application 160 or by another application which flags or messages to the handoff application when the handoff condition is met.
• the handofT application 160 Upon detecting the handoff condition the handofT application 160 then initiates a second, simultaneous, VoIP call to the telephone number of dual mode telephone 100 cellular subscription (step 215). The call is received at the cellular subscription number of the dual mode telephone 100.
• the handofT application checks that the call received is the one that was initiated by itself by checking, for example, the caller ' ID, and is not an incoming call from another third party. If the call being received on the cellular subscription originates from the internet telephone subscription of the mobile telephone 100 then the handoff application answers the call in order to establish the cellular connection (step 220). Once the connection with the cellular subscription is established the handoff application transfers the call from the internet subscription to the cellular subscription (step 225). After successful completion of the transfer the original VoIP call is torn down (step 230). The transferred call is connected through the PSTN gateway.
• the handoff application 160 In order to permit successful hand back of the call to the IP network if the telephone 100 again enters an LP network the handoff application 160 must obtain from the PSTN gateway the call leg ID of the new call session between the PSTN gateway and the other party (step 235).
• the call leg ID is stored in memory of the dual mode telephone 100.
• the step of obtaining the call leg ID is shown as the last step, however this is not intended to limit the invention,
• the call leg ID can be obtained at any time after handoff (transfer) of the call to the cellular network but before the call is handed back to the IP network.
• FIG 4 schematically illustrates SlP messaging and call flow involved in the handoff of the call from the wireless IP network to the cellular network in the exemplified embodiment.
• the SIP server is not shown for clarity.
• messaging or call flow on the PSTN/PLMN between the PSTN gateway and the cellular connection on the dual mode telephone 100 The skilled addressee will be able to fully appreciate the required messaging and call flow that occurs in the cellular network to establish the cellular call and as this is not important to the invention it is not shown here.
• the other party is shown for clarity.
• the other party may be either another IP phone operating in an IP network, a fixed line telephone phone connected to a PSTN or a cellular (mobile) telephone operating in a PLMN.
• step 300 there is an existing VoIP call from the dual mode telephone 100 to the other party.
• the call will involve either an RTP session over the IP network 105, or an RTP session over the IP network 105 and two-way voice over the PSTN 135 / PLMN 110.
• the handoff application subscribes the dual mode phone to a dialog event package on the PSTN gateway (step 305).
• the PSTN gateway 130 is not involved in a current call session, because for example the existing call is an IP telephone to IP telephone call or the existing call is through another PSTN gateway as described later, the first NOTIFY message from the PSTN gateway to the dual mode telephone 100 returns a null call leg ID.
• the handoff application then initiates the second VoIP call Io its own cellular subscription using the INVITE method of the SIP protocol in the normal way (step 310). This establishes a second RTP session and two-way voice connection between the internet and cellular subscriptions of the dual mode telephone 100.
• the handoff application then initiates transfer of the call to the cellular connection by sending a REFER request to the other party (step 315).
• the other party replies with a notification that it. is trying to contact the cellular subscription.
• the other party does this by sending an INVITE request with a replace header. If the INVITE is successful the other patty is transferred to the cellular connection (step 320) and second VoIP connection is ended (step 325).
• the other party then notifies dual mode telephone 100 that the transfer was successful and the first VoIP call is also torn down (step 330).
• the event dialog subscription remains valid for a fixed time even after the VoIP calls are torn down and in accordance with the subscription the PSTN gateway 130 notifies the dual mode telephone 100 of the call leg ID for the call between the cellular connection and the other party (step 335).
• the call leg ID is stored in the dual mode telephone 100 for use in retrieving the call to affect hand- back if necessary.
• FIG. 5 to 8 illustrate call flow before and after handoff between the IP and PLMN networks for different calls scenarios.
• Figures 5 and 6 show before and after handotYcal! connections respectively when the other party is another VP telephone 400.
• the call is routed through the TP network 105.
• the PSTN gateway 130 and PSTN 135 to the cellular network 110 with which the dual mode telephone 100 is registered.
• the handoff application musl obtain and store the call leg ID for session 410 between the PSTN gateway 130 and the other party 400 in Figure 6.
• the other party may be another internet telephone device or a fixed line or ceilulat telephone
• the other party may be another internet telephone device or a fixed line or ceilulat telephone
• no actual VoIP call exists within the IP network after the call is handed-off to the cellular network in the case where the other party is a fixed telephone on the PSTN 135 or another cellular telephone.
• a call connection always exists within the PSTN gateway 130 to link the mobile device cellular call to the other party. This call connection is an internal call session of the PSTN gateway 130.
• the handoff application In order to be able to initiate hand-back the call from the cellular network to the IP network the handoff application must have the call leg ID of this call session Figures 7 and 8 show before and after handofFcall connections respectively when the other party is a cellular telephone 405.
• the PSTN gateway 130 and PSTN 135 Before handoff the call is routed through the IP network 105 the PSTN gateway 130 and PSTN 135 to the cellular network 1 10 with which the other phone 405 is registered. After handofFthe call continues to be routed through the PSTN gateway 130 although both phones 100, 405 are registered on the cellular network 1 10.
• the scenario of Figures 7 and 8 also applies when other party is using a fixed line phone on the PSTN 135.
• the handofT application must obtain and store the call leg ID for session 415. in Figure 8, linking the call within the PSTN gateway 130.
• the call leg ID (or dialog ID) for a call session consists of a call-ID value, a local tag and a remote tag.
• the handofY application can obtain the call leg ID for the session, e.g. 410 or 415, between the PSTN gateway 330 and the other party in the transferred call.
• the first way is using Invite-Initiated Dialog Event Package in SlP RFC 4235. This is a client based solution that requires no modification of the PSTN gateway software or firmware.
• the second way is to install a proprietary event package software module in the PSTN gateway that, is S3P RFC 3265 compliant. The following is a discussion of the two methods.
• the handoff application subscribes to a dialog event notification on the PSTN gateway 130 using the SlP SUBSCRIBE method with an event header specifying a dialog package.
• This enables the handoff application to obtain the call leg ID for the session between PSTN gateway 130 and the other party in the transferred call.
• the SUBSCRIBE messages requires an entity to be put in the request URL.
• This entity attribute contains a URL that identifies the user whose dialog information is reported in a NOTIFY body.
• the entity is the cellular number of die dual mode mobile device 100.
• the NOTIFY will return the dialog state (call-leg state) of this entity once its dialog state is created, changed or terminated.
• the following is an example of use of the SUBSCRIBE method in the call flow of Figure 4
• Step 305
• gateway .com S ⁇ P/2.0 To: ⁇ si ⁇ :dualmode_cellular_m ⁇ mber@pstn.gateway.com> From: ⁇ sip:duaUnode__sip_userid@mobile.device.com> > tag ⁇ 193492342 CaIl-CD: 898234234@pstn. gateway. com
• Step 320
• the call is transferred in step 315 and in step 335 the PSTN gateway notifies the dual mode phone of the call leg ID for the new session dialog 3 between the PSTN gateway 130 and the other party.
• ⁇ dialog-info xmlns "urn:ietf:params:xml:ns:dialog-info” version-"0" state-"fuH” entity ⁇ n sip:dualmode_cellular_ numbertSpstn.gateway.com”> ⁇ dialog id ⁇ "as(X)7" call-id- 'x" local-tag ⁇ 'y” remote-tag ⁇ 'z” di recti on :::: “ i ni tiator " > ⁇ state>confl tm ed ⁇ /state> ⁇ /dialog> ⁇ /dialog-info>
• the call leg ID for the new session dialog 3 between the PSTN gateway 130 and the other party in this example is "xyz"
• Step 305
• a hand-back condition is created which is detected by the handoff application (step 240).
• the hand-back condition may be monitored by the handoff application or by another module within the mobile telephone 100.
• the hand-back condition is also not important to the invention and might be when the signals strength of a wireless ⁇ P network with which the IP telephone can register exceeds a threshold value, for example -75dBm.
• a threshold value for example -75dBm.
• the handoff application retrieves the stored call leg ID for the call on the cellular network (step 245).
• the application then initiates a VoIP session via the IP network and by sending the retrieved call leg ID to the other party to initiate handover of the call to the new VoIP session (steps 250,255).
• FIG 10 illustrates messaging and call flows involved in hand-back of the call from the cellular network to the wireless IP network in the exemplified embodiment.
• the handoff application was notified of the call leg ID of the connection at the PSTN gateway.
• the call leg ID is "xyz'. This is stored in the mobile telephone 100
• the handoff application detects the second hand-off condition, i.e. the hand-back condition, it retrieves the stored call leg ID xyz and starts a third VoIP call to initiate a connection with the other party using the SIP INVITE method with a replace header.
• the replace header identities here call leg ID xyz, which is replaced with a session dialog 4 between the VoIP call 3 from the mobile telephone 100 to the other party (step 350).
• the PSTN gateway After reestablishing the call over the IP network between the mobile telephone 100 and the other party the cellular connection is torn down (step 355) and in accordance with the earlier subscriber requests the PSTN gateway issues a notification to the handoff application 160 that the call dialog 3 for the cellular connection was terminated.
• an organization has a first PSTN gateway 420 for routing calls between its IP network 105 and the local PSTN 135.
• the organization also has a second PSTN gateway 425 dedicated to establishing and maintaining a cellular link with dual mode device 100 of the organization when the devices 100 roams from within the organizations IP network to the cellular network.
• an initial call placed or received on the IP network 105 to or from a fixed line or cellular telephone 405 outside the IP network is routed through the first PSTN gateway 420.
• the handofY application 160 establishes a connection with the cellular subscription of its own dual mode telephone 100 using the second PSTN gateway 425.
• the call is linked between the first PSTN gateway 420 and the second PSTN gateway 425.
• the handoff application must obtain and store the call leg ID of the session 430 between the two PSTN gateways Upon retrieval of the call for hand-back to the ⁇ P network the call is reconnected through the first PSTN gateway 420 and the cellular connection through the second PSTN gateway 425 is torn down.
• the IP telephone operates on a wireless IP network.
• the invention is equally applicable to IP telephones operating via a wired network or internet connection.
• Figure 13 illustrates alternative embodiments in which one IP telephone 500 connects directly to a HSB port or other port of a personal computer 505 (PC) and another IP telephone 510 has an Ethernet port for connection directly to an IP network 105.
• the telephones 500, 510 also have cellular network capabilities, and may optionally have other wireless radio capabilities.
• a user on an internet telephone call with one of the telephones on a wired network connection may wish to hand off the call from the [P network to the cellular because they wish to move to another location or because the quality of the network has degraded through increased traffic or the like.
• the user through input means on the telephone, or in the case of telephone 500 via the computer 505, can manually issue an instruction to hand otTthe call to a cellular network.
• the call is handed off in the same way as described above.
• the manual instruction to hand off the call is the handoff condition in the above hand off procedure. If the user returns to the location of the wired network or network quality and speed increases again the user can reconnect the IP telephone to the wired network, if necessary, and issue a further instruction via input means on the telephone or through the computer to which the telephone is connected for the call to be handed back to the IP network.
• the input means for initiating the manual handover condition may be a dedicated button on the IP telephone or may be accessed through a certain menu screen on the telephone.
• the dual mode IP telephone 510 is a hands free speakerphone or conference phone directly connected to the network via an Ethernet connection
• the hands free speakerphone also has a cordless handset 515 resting in a cradle of the telephone base unit.
• the cordless handset has both Digital Enhanced Cordless Telecommunications (DECT) and cellular wireless functions.
• DECT Digital Enhanced Cordless Telecommunications
• a user can make an internet telephone call via the hands free speakerphone, which is connected via the hardwired network, ⁇ f the user wants to move to another location they can pick up the cordless handset. Under normal conditions the cordless handset works in the normal manner of a DECT handset and the call remains connected via the speakerphone base unit. However, if the user has decided to move outside the range of the cordless handset the call can be handed off to a cellular network via push of a "hand oft" button.
• DECT Digital Enhanced Cordless Telecommunications
• the invention may be used to hand off only a part of a data stream being received by an IP telephone to a cellular network connection.
• the dual mode IP telephone has video conferencing functionality in which separate voice and video data streams are transmitted and received over the IP network. If there is degradation of the speed or quality of the IP network either one or both of the voice and image of a video call may become degraded. In any communication voice is more important and the user may choose to hand off the voice part of the video call to the cellular network in order to improve voice quality while keeping the video stream going over the IP network. If the IP network speed or quality increases again the user may choose to hand back the voice part of the call to the IP network.
• the handoff criteria that triggers handoff and or hand back of a call between an [P network and cellular network is not important to the invention.
• the handoff condition could comprise one or more of various factors including, but not limited to, wireless signal strength, current and past transmission and/or reception data error rate, the wireless service provider, quality of service of IP connection, and user manual selection.

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• 2007
  • 2007-10-09 WO PCT/CN2007/070850 patent/WO2009046600A1/en active Application Filing
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