GB2495007A - Handover method comprising transmitting data packets to a mobile device from the server and also buffering selected data packets containing handover messages - Google Patents

Abstract

Disclosed is a method of performing a handover of a mobile device from a first wireless IP network to a second wireless IP network, the mobile device being connected, via a tunnel, to a Server of a Mobile IP system, and to an information server coupled to the first and second wireless networks, wherein the information server is arranged to provide handover messages to the mobile device to assist the mobile device in performing a handover from the first wireless network to the second wireless network, comprising the steps of: determining that a handover is imminent or in progress and transmitting data packets to the mobile device from the server and also buffering the data packets containing handover messages at the server if the handover is in progress. Data packets containing application data may also be buffered while handover is imminent or in progress.

Description

Improvements in handover between heterogeneous radio networks

BACKGROUND

Technical Field

The present invention relates to an apparatus, system and method associated with assisting handover from one wireless network to another. It finds particular, but not exclusive, use in systems utilising Mobile IP (RFC3344), supported by Media Independent Handover (IEEE 802.21) and other similar technologies, such as ANDSF (Access Network Delivery and Selection Function), used to assist in the handover process.

Description of Related Art

Users of mobile devices, such as telephones, notepad computers and tablet computers typically desire to connect to the Internet from a variety of different locations. There has evolved a large network of publicly accessible wi-fi hot spots or access points (APs).

Especially in the case of mobile telephones, a user may travel between one AP and another whilst connected to the Internet. This can happen if a Voice over IP (VoIP) call is being made or music or video is being streamed, for instance. In other situations, handover between different types of network can be encountered. For instance, a data connection may be established using Wi-Fi, but then handover to a cellular data system, such as 3G, may be required.

Handover between different APs, provided by different entities, can pose a problem in that the data connection to the Internet can be dropped during the handover process.

There therefore exists a need to address these and other problems identified in the prior art. Embodiments of the present invention seek to address and at least ameliorate these problems, and other problems not herein identified.

SUMMARY OF THE INVENTION

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

According to a first aspect of the present invention, there is provided a method of performing a handover of a mobile device from a first wireless network to a second wireless network, the mobile device being operably connected, via a tunnel, to a Server of a Mobile IP system, and to an information server coupled to the first and second wireless networks, wherein the information server is arranged to provide handover messages to the mobile device to assist the mobile device in performing a handover from the first wireless network to the second wireless network, comprising the steps of the mobile device transmitting a handover data packet to the information server via the tunnel; and the mobile device transmitting a handover data packet to the information server via another route.

Preferably, the information server may be one or more of a mobility management and location server. A mobility management server deals with handovers and a location server provides location information.

Preferably the information server is an MIH server.

Preferably, the step of the mobile device transmitting a handover data packet to the information server via another route comprises transmitting the handover data packet directly to the information server, using its IF address.

Preferably, the handover the data packet could be any data packet associated with setting up or implementing the handover, including a packet indicating that handover is complete.

Preferably, an imminent handover may be detected by a weak signal on the current radio interface.

Preferably, registration with the Mobile IF server and the information server is performed substantially simultaneously. This can speed up handover.

According to a second aspect of the present invention, there is provided a mobile device operable to communicate via a first wireless network and a second wireless network, the mobile device being arranged to be operably connected, via a tunnel, to a Server of a Mobile IF system, and to an information server coupled to the first and second wireless networks, wherein the information server is arranged to provide handover messages to the mobile device to assist the mobile device in performing a handover from the first wireless network to the second wireless network, wherein the mobile device is arranged to transmit a handover data packet to the information server via the tunnel and also via another route.

According to a third aspect of the present invention, there is provides a tangible computer readable recording medium having recorded thereon instructions which, when executed, cause a computer to perform a method according to the first aspect.

According to a fourth aspect of the present invention, there is provided a method of performing a handover of a mobile device from a first wireless network to a second wireless network, the mobile device being operably connected, via a tunnel, to a server of a Mobile IP system and to an information server coupled to the first and second wireless networks, wherein the information server is arranged to provide handover messages to the mobile device to assist the mobile device in performing a handover from the first wireless network to the second wireless network, comprising the steps of: determining that a handover is imminent or in progress; and buffering data packets transmitted from the mobile device, wherein handover data packets are transmitted in preference to application data packets.

Preferably, wherein handover data packets and application data packets are buffered separately and application data packets are only transmitted if there are no pending handover data packets.

Alternatively, the buffer sizes associated with handover data packets and application data packets can be dynamically varied to adjust the relative priority assigned to handover and application data packets.

According to a fifth aspect of the present invention, there is provided a mobile device operable to communicate via a first wireless network and a second wireless network, the mobile device being arranged to be operably connected, via a tunnel, to a Server of a Mobile IP system, and to an information server coupled to the first and second wireless networks, wherein the information server is arranged to provide handover messages to the mobile device to assist the mobile device in performing a handover from the first wireless network to the second wireless network, wherein the mobile device is arranged to determine that a handover is imminent or in progress and to buffer data packets transmitted from the mobile device such that handover data packets are transmitted in preference to application data packets.

According to a sixth aspect of the present invention, there is provided a tangible computer readable recording medium having recorded thereon instructions which, when executed, cause a computer to perform a method according to the fourth aspect.

According to a seventh aspect of the present invention, there is provided a method of performing a handover of a mobile device from a first wireless network to a second wireless network, the mobile device being operably connected, via a tunnel, to a server of a Mobile IP system and to an information server coupled to the first and second wireless networks, wherein the information server is arranged to provide handover messages to the mobile device to assist the mobile device in performing a handover from the first wireless network to the second wireless network, comprising the steps of: determining that a handover is imminent or in progress; and transmitting handover data packets to the mobile device from the server and also buffering said handover data packets at the server if the handover is imminent or in progress.

Preferably, application data packets are also buffered at the server if the handover is imminent or in progress.

Preferably, handover status is determined at the server by inspecting data packets to determine the presence of handover packets.

According to an eighth aspect of the present invention, there is provided a server of a Mobile IP system, said server being arranged to be operably coupled to a mobile device via a tunnel, and said mobile device being arranged to be further operably connected to an information server coupled to first and second wireless networks, wherein the information server is arranged to provide handover messages to the mobile device to assist the mobile device in performing a handover from the first wireless network to the second wireless network, wherein upon determining that a handover is imminent or in progress, the server is arranged to transmit handover data packets to the mobile device and also to buffer said handover data packets at the server.

According to a ninth aspect of the present invention, there is provided a tangible computer readable recording medium having recorded thereon instructions which, when executed, cause a computer to perform a method according to the seventh aspect.

Preferably, if the mobile device is in an idle mode i.e. no data is being transferred on the data network, then the device is able to operate in a manner known from the prior art.

However, if the mobile device is not in idle mode and data is being transferred, then one or more of the aspects of the present invention can be utilised to improve performance.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1 shows a prior art system utilising MIH;

Figure 2 shows a prior art system utilising both MIH and MIP; Figure 3 shows a system according to an embodiment of an aspect of the present invention; Figure 4 shows a flowchart relating to an embodiment of an aspect of the present invention; and Figure 5 shows a further flowchart relating to an embodiment of an aspect of the present invention.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

To assist in managing handovers, a system known as Media Independent Handover (MIH) has been developed, which manages the handover of a data connection between different wireless data networks, such as Wi-Fi, WiMax, 3G or other cellular data networks.

This system allows a seamless connection to be maintained with the Internet when a data connection changes during handover.

Figure 1 shows a schematic overview of an MIH-enabled system. A mobile device 1 operating at a first location is assigned an IP address of a.b.c.d while connected via Wi-Fi interface A. The mobile device 1 is MIH-capable and so conducts required MIH communications with MIH server 10 over the interface A. Whilst connected via interface A, the user utilises a video-streaming application, such as a web browser accessing YouTube ®. The web browser establishes a session with the video-streaming server 20 over the Internet. The server 20 then continuously sends video data packets to the mobile device 1 over interface A, having the IP address a.b.c.d. Since MIH is enabled, the mobile device 1 may, at some point, be directed to move to a different interface B. This may be due to deteriorating signal conditions. The device 1 is then assigned a new IP address p.q.r.s over the new interface B. It is possible, but not necessary, that the new MIH server 10' is different to the previous one and in a new location. The mobile device performs registration over the new interface B as required in a known way.

However, a problem with MIH is that it does not maintain the Internet Protocol (IP) address of the mobile device. This means that in the situation described above, connection with the video streaming server 20 is lost due to the change in IP address. This is clearly annoying to the user, who must then re-establish the session with the server 20.

A system to address this problem, known as Mobile IF (MIP, defined in RFC3344), has been developed which provides a single IF address to the mobile device via a tunnelling mechanism over heterogeneous radio interfaces. This is achieved by means of a Mobile IP server which uses a data tunnel for communication with the mobile device and allows an invariant IF address to be associated with the mobile device. This situation is shown schematically in Figure 2.

Here, Mobile device 101 is MIP and MIH enabled, and is connected via Wi-Fi interface A to MIP Home Agent (HA) 130 and then on to the Internet and MIH servers 110. By use of the MIP HA, the mobile device 101 is associated with a constant home IF address x.y.z.w, even though its actual IF address may change as the mobile device 101 moves between networks.

Data packets destined for the mobile device are delivered to the constant IF address and re-routed by the HA 130 which is always aware of the actual IP address of the mobile device.

In Figure 2, the mobile device 101 is connected via tunnel 131 to Home Agent server 130. The mobile device is connected to a video streaming server 120 which is configured to stream video to the constant IP address x.y.z.w. The server 120 does not know or need to know the actual IF address of the mobile device as the HA 130 re-directs all data packets to the mobile device 101 as needed.

When the mobile device moves to a new location, it may be handed over to a new interface B. The new interface B could be a cellular data interface provided by a 30 system.

The actual IP address associated with the mobile device changes to p.q.r.s but data packets are routed via new tunnel 132, setup by the HA 130. Since the apparent IP address of the mobile device has not changed, data packets from the video server 120 still reach the mobile device and the user does not notice any deterioration in performance of the device due to the handover. Indeed, the user may not even be notified of the handover.

However, a problem in such a Mobile IP system with MIH is that during handover, the MIP Home Agent (HA) transmits packets on an old interface for a period of time until the Mobile IF tunnel is correctly established. During this period, a high level of packet loss is observed. A further problem is that handover typically occurs due to a decline in signal strength. In prior art systems, the MIP tunnel needs to be stable before MIH messages can pass through it. Handover can therefore take longer than is desirable.

There follows several techniques for addressing problems experienced during handover in these circumstances. It should be noted that the individual solutions may be employed alone or, where appropriate, combined.

It should be noted that in the various aspects of the invention which follow, the basic hardware requirements of the system (i.e. the mobile device and the fixed network elements) are the same as those in the prior art. The method of operation will vary as described. Use of the same hardware, modified in its operation, assists in ensuring backward compatibility with prior art devices. The modification to know hardware can be achieved by means of suitable programming or by the provision of suitable custom hardware, where appropriate.

According to an embodiment of a first aspect of the present invention, use is made of the fact that data packets can be passed between the Internet and an MIP and MIH enabled mobile device either via the MIP data tunnel or some other means. This is possible since the actual device IP address may be known to the MIH server. If it is not known, then MIH discovery procedures can be used in a known way to locate the server Figure 3 shows the basic system configuration, which differs from Figure 2 in that a separate communication route 233 is established between the mobile device 201 and the MIH server 210.

To implement this, MIH message packets can additionally be sent to the MIH servers by a route outside the data tunnel 231, and hence the handover process is not entirely dependent on the MIP data tunnel being completely established to achieve handover. To do this, the mobile device can be arranged to transmit MIH handover messages to the MIH servers via any other route 233 available, which does not use the MIP tunnel 232, as well as also transmitting via the tunnel.

The step of transmitting to the MIH server outside the tunnel includes transmitting directly to the MIH server, or via any other intermediary device, such a further server or router.

Whichever device responds first (i.e. either the MIP HA 230 or MIH server 210) will give an indication of the status of the handover process. Subsequent responses may be ignored as redundant.

In the event that the MIP HA 230 completes the tunnel construction faster than the MIH servers 210 can complete the handover, then the MIH client initiates a new communication sequence with the MIH MM and IS servers through the tunnel 232 just created on the new radio interface. The handover is considered complete only once the MIH client exchanges all the set of messages as required by the MIH protocol and the MIP tunnel is established.

If the MIH server 210 is not able to complete the handover, then the attempted handover is deemed to have failed. This results in a failure procedure being started, which consists of attempting a handover on the next preferred radio link. This also involves re-establishing an MIP tunnel on the old radio interface and possibly further communication with the MIH servers over the old radio link. These steps are very similar to the handover process itself. If these steps fail, then the mobile device will lose connectivity with the servers and any attempt to recover will be similar to normal mobile device power-on procedures.

In the alternative situation that the MIH servers 210 complete their communication before the MIF' tunnel 232 can be created, then the main thread of the application enters a wait state, awaiting MIP registration with the HA server 210 and the tunnel establishment to complete. If MIP registration is not possible over the new radio interface, then the device may abandon the new radio interface and attempt a new handover to the next preferred radio interface or it may continue on the current interface in idle mode with connectivity only to the MIK servers (and not the MIP HA). This ensures continuous connectivity, but not a constant IP address, meaning that some applications will either not function or will function with a reduced feature set.

However, if MIP registration completes successfully, the MIH client may choose to re-register with the MIH server again through the tunnel 232 established with the HA server. This enables all messages to be transferred via a single route and avoids unnecessary duplication.

Applications can then run on the device with full IP transparency.

By making use of this active redundancy in message transfer, a more robust and reliable handover may be achieved, resulting in an enhanced user experience.

Embodiments according to the second aspect of the present invention provide a mobile device arranged to operate as herein described.

Embodiments according to the third aspect of the present invention provide a tangible computer readable medium to perform the method as herein described.

According to an embodiment of a fourth aspect of the present invention, buffering is used to provide additional data security during handover. In this embodiment, data buffering is performed on server side.

In the first embodiment of the fourth aspect, which is a server-side solution, the MIP Home Agent, which, in the prior art, merely passes data packets to the intended mobile device without examining them further, is made to seek out MIH packets in the data traffic, which are destined for a particular user. To do this, the HA looks for a distinctive MIH signature within data packets. It does this by sniffing' MIH packet headers to search for MIH handover related messages (Candidate query/commit message). Detection of such handover related messages triggers the buffering activity, and any subsequent packets are stored as well as transmitted in the normal way.

The initiation of buffering starts a timer and ongoing buffering continues for a defined period of time. The period of time is selected to suit particular cases, in the assumption that handover is imminent. The timer is necessary, since the handover may yet fail, meaning that no new messages appear on the link. The timer duration can be selected in light of the server's ability to buffer, which may depend on overall network load and/or how many other handovers are in progress. In the event that few active handovers are in place, then more buffer space can be allocated. A typical buffer period may be 5 minutes, although this can be more or less, as needed in a particular instance.

If the HA receives a new registration message on a new link from a new Care of' address from the same user, then a timer is started and runs for a predetermined period, and, at the expiry of the timer, the packets ion the buffer are sent to the HA encapsulation engine which sends them to the mobile device. The encapsulation engine packages up individual datagrams for sending to the mobile device's care of' address.

No further changes are required to the encapsulation engine and any other packets received at that HA that needs to be transmitted to the mobile device will be handled as normal.

By buffering data packets for a particular user in this way, if there is a problem encountered during handover, the data packets are not lost and can be re-transmitted to the user as necessary. In the absence of buffering at the HA, then any data packets which are destined for a particular user can be lost during handover if the handover process is problematic for any reason.

In the event that the handover completes successfully, the buffered data packets can be discarded, and ongoing communications with the device can continue as usual.

Embodiments according to the fifth aspect of the present invention provide a mobile device arranged to operate as herein described.

Embodiments according to the sixth aspect of the present invention provide a tangible computer readable medium to perform the method as herein described.

Embodiments of the seventh aspect of the invention apply data buffering at the device or client side.

In the client-side (or device-side) buffering solution, a different approach is adopted.

During handovers in the prior art, the MIP tunnel is first broken on the old radio link and then re-created on the new radio link to the HA server. During this period, packet loss for packets transmitted via the tunnel can be considerably higher than at other times. Also, in the prior art, all data packets sent via the tunnel in the prior art are treated and transmitted with equal priority.

Typically, applications running on the mobile device which require a constant connection to the Internet are relatively robust with respect to packet loss and often incorporate a buffer of their own to accommodate a temporary loss or deterioration in connection. During handover, it is found that MIH packets, which are relatively infrequent compared to the application data packets, are more important in terms of ensuring link stability and reliability. Therefore, embodiments of the second aspect of the present invention give priority to MIH data packets over application data packets.

The application running on the mobile device is better able to cope with missing application data packets than it is with missing MIH data packets, without which the link may be lost completely, thereby possibly killing the application which may rely on a continuous connection. It is therefore in the interest of the application that handover is completed and a new link is quickly established so that application data packets can once more pass promptly.

In order to prioritise the MIH packets, two buffers are created in the mobile device. The first buffer is for MIH data packets and the second is for application data packets. The two buffers are then operated such that only if the MIH data packet buffer is empty does any data get sent from the application data buffer. In this way, priority is given to any MIH data packets over application data packets. This situation is shown in the flowchart in Figure 4.

At Step 300, the existing data link layer forwards a packet to be transmitted via the tunnel. At step 310, a decision is made whether this is an MIH or handover packet. If it is not a handover packet and is therefore an application data packet, it is added at step 340 to the application data packet buffer or bucket for transmission at step 350. However, if at step 310 it is decided that the packet to be transmitted is an MIH or handover packet, then it is added, at step 320 to the MIH packet buffer or bucket for transmission at step 330. Packets from the application data buffer are only transmitted if the MIH packet buffer is empty.

Figure 5 shows how this decision process operates. At step 400, a transmit message is received. At step 410, a check is made on the status of the MIH bucket or buffer. If there are any packets in this buffer to send, then at step 420, the entire contents of the MIH buffer are transmitted. A check is then made at step 430 whether there are any packets to transmit in the application data buffer. If so, then one packet is transmitted at step 440 before a further check of the MIH buffer is made at step 450. If this reveals that there are further MIH packets to transmit, then step 420 is repeated and operation continues as before. If, however, the check at step 450 reveals no MIH packets in the buffer, then step 440 is repeated by transmitting a single application data packet.

At step 410, if there are no MIH packets in the buffer, then operation continues from step 430 as set out above. In this way, priority is always given to MIH packets over application data packets, ensuring that the handover process has priority over any applications running on the mobile device at the time of handover.

In an alternative embodiment, the size of one or both buffers can be dynamically varied to give more or less priority to either type of data packet.

Although described above in relation to buffering data packets on the client-side, it is clear that applying the same technique at the server-side also yields benefits, by ensuring that MIH or handover packets are prioritised over application data packets. This prioritisation may be applied at only the server-side, only the client-side or both, as required. Maximum benefit is obtained by applying it at both.

Embodiments according to the eighth aspect of the present invention provide a server arranged to operate as herein described.

Embodiments according to the ninth aspect of the present invention provide a tangible computer readable medium to perform the method as herein described.

At least some elements discussed herein may be constructed, partially or wholly, using dedicated special-purpose hardware. Terms such as component', module' or unit' used herein may include, but are not limited to, a hardware device, such as a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks.

At least some elements may be may be configured to reside on an addressable storage medium and be configured to execute on one or more processors. That is, the elements may be implemented in the form of a tangible computer-readable storage medium having recorded thereon instructions that are, in use, executed by a computer or other suitable device. The elements may include, by way of example, components such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, databases, data structures, tables, arrays, and variables. The tangible medium may take any suitable form, but examples include solid-state memory devices (ROM, RAM, EPROM, EEPROM, etc.), optical discs (e.g. Compact Discs, IJVDs, and others), magnetic discs, magnetic tapes and magneto-optic storage devices.

The example embodiments have been described with reference to the example components, modules and units discussed herein. Where appropriate, these functional elements may be combined into fewer elements or separated into additional elements. In some cases the elements are distributed over a plurality of separate computing devices that are coupled by a suitable communications network, including any suitable wired networks or It should be noted that the various different embodiments of the invention described herein may be implemented individually or together, depending on the effect required. There is nothing inherently incompatible between then and greater benefit may be gained by creating a system using more than one of the described embodiments.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (1)

1. <claim-text>CLAIMS1. A method of performing a handover of a mobile device from a first wireless network to a second wireless network, the mobile device being operably connected, via a tunnel, to a server of a Mobile IP system and to an information server coupled to the first and second wireless networks, wherein the information server is arranged to provide handover messages to the mobile device to assist the mobile device in performing a handover from the first wireless network to the second wireless network, comprising the steps of: determining that a handover is imminent or in progress; and transmitting handover data packets to the mobile device from the server and also buffering said handover data packets at the server if the handover is imminent or in progress.</claim-text> <claim-text>2. The method as claimed in claim 1 wherein application data packets are also buffered at the server if the handover is imminent or in progress.</claim-text> <claim-text>3. The method as claimed in claim 1 or 2 wherein handover status is determined at the server by inspecting data packets to determine the presence of handover packets.</claim-text> <claim-text>4. A server of a Mobile IP system, said server being arranged to be operably coupled to a mobile device via a tunnel, and said mobile device being arranged to be further operably connected to an information server coupled to first and second wireless networks, wherein the information server is arranged to provide handover messages to the mobile device to assist the mobile device in performing a handover from the first wireless network to the second wireless network, wherein upon determining that a handover is imminent or in progress, the server is arranged to transmit handover data packets to the mobile device and also to buffer said handover data packets at the server.</claim-text> <claim-text>5. A tangible computer readable recording medium having recorded thereon instructions which, when executed, cause a computer to perform a method according to any of claims ito 3.</claim-text>