GB2418566A - Cross layer implemented Handover - Google Patents

Cross layer implemented Handover Download PDF

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Publication number
GB2418566A
GB2418566A GB0421216A GB0421216A GB2418566A GB 2418566 A GB2418566 A GB 2418566A GB 0421216 A GB0421216 A GB 0421216A GB 0421216 A GB0421216 A GB 0421216A GB 2418566 A GB2418566 A GB 2418566A
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United Kingdom
Prior art keywords
network
protocol
message
layer
mobile
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GB0421216A
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GB0421216D0 (en
Inventor
Terence Edwin Dodgson
Vaia Sdralia
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Samsung Electronics Co Ltd
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Samsung Electronics Co Ltd
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Publication date
Application filed by Samsung Electronics Co Ltd filed Critical Samsung Electronics Co Ltd
Priority to GB0421216A priority Critical patent/GB2418566A/en
Publication of GB0421216D0 publication Critical patent/GB0421216D0/en
Publication of GB2418566A publication Critical patent/GB2418566A/en
Pending legal-status Critical Current

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    • 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
    • H04L65/1069—Session establishment or de-establishment
    • 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
    • H04L65/1101—Session protocols
    • H04L65/1104—Session initiation protocol [SIP]
    • 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
    • H04W36/0019—Control or signalling for completing the hand-off for data sessions of end-to-end connection adapted for mobile IP [MIP]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W80/00—Wireless network protocols or protocol adaptations to wireless operation
    • H04W80/04—Network layer protocols, e.g. mobile IP [Internet Protocol]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W80/00—Wireless network protocols or protocol adaptations to wireless operation
    • H04W80/08—Upper layer protocols
    • H04W80/10—Upper layer protocols adapted for application session management, e.g. SIP [Session Initiation Protocol]

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Business, Economics & Management (AREA)
  • General Business, Economics & Management (AREA)
  • Multimedia (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

In a system with a transport level protocol layer and an application level protocol layer, a method of handing over a communication link between a mobile communication device and a first network to a second network by sending a message via a transport level device (or from a Mobile Internet Protocol IP client) to an application level device (or to a Session Initiation Protocol (SIP) user) located in the mobile communication device. A second embodiment of the invention includes a foreign agent server adapted for use during the handover wherein the foreign agent comprises a Session Initiation Protocol proxy server. A third embodiment of the invention includes sending a Session Initiation Protocol RE-INVITE message comprising the step of including a foreign agent server's IP address within the contact field of the message, said foreign agent server adapted for use during the handover of a communication link.

Description

CROSS LAYER IMPLEMENTED HANDOVER
The present invention relates to a method of implementing a communications handover using cross layer messaging, and in particular to sending these messages between a transport level device and an application level device.
Known systems will now be discussed with references to Figures 1 and2.
Figure 1 shows the protocol layers in a standard OSI (Open Systems Interconnection) model.
Figure 2 shows a known handover procedure.
When designing communication and network systems, developers usually refer to the open systems interconnection reference model (OSI model). The OSI model defines the functions of a system by grouping different features in layers as defined by the model. The standard OSI model has seven layers.
Figure I shows the protocol layers used in a standard OSI model. The model 101 indicates a physical layer 103, data link layer 105, network layer 107, transport layer 109, session layer 1 1 1, presentation layer 1 13 and application layer 115.
Usually, the OSI model may be grouped together in a way such that the data link layer 105 and physical layer 103 are labelled the media layer.
Also, the transport layer 109 and the network layer 107 may be labelled together as the transport layer. Finally, the application layer 1 15, presentation layer 113 and session layer 111 may be labelled together as the application layer.
The first layer is the physical layer 103, which defines features such as the type of physical connections used, and the range of frequencies available for broadcasting, for example.
Layer number two is the data link layer 105. The data link layer 105 is used to ensure data is transferred between different networks correctly. The data link layer 105 may also be used to provide means to detect and correct errors produced by the physical layer.
The third layer is the network layer 107. This layer provides means to control the flow of data between a source and destination, determines the route to be taken between the source and destination, and carries out functions such as controlling any congestion of data.
The transport layer 109 is the fourth layer in the OSI model. This layer is used to ensure that data is transferred between the source and destination without the layers five to seven, discussed below, from being required to provide any such function. The transport layer 109 ensures that data is transferred completely between the users of the network system. An example of a transport layer protocol is TCP (Transmission Control Protocol).
The TCP layer works in conjunction with the network layer protocol, IP (Internet Protocol), with the aim to provide a seamless connection between the end users of the network.
Layer five is the session layer 111. This layer provides a means for controlling any communications between the source and destination terminals.
For example, it can allow termination of the communications, or allow the communications to be restarted if problems have been detected.
The presentation layer 113 is the sixth layer of the OSI model. This layer ensures that the seventh layer discussed below (application layer) does not have to concern itself with the way data is represented at the end user station. For example, data may be encoded into one particular type of file, for example an ASCII file.
The final layer in the OSI model is the application layer 115. This layer provides an interface between the applications being run on the network.
In this OSI model layout, a higher layer will issue requests to the layer immediately below it, and respond to requests received from the layer immediately above it. This allows for a modular protocol design, thus allowing designers to design systems that may be interconnected with other systems.
Figure 2 shows an example of a network system including a core network 201 and a mobile host 203. The mobile host 203 is a mobile computing device such as a portable or laptop computer, mobile telephone device, personal digital assistant or any other suitable portable communication device. The core network 201 has attached a home agent 205 used to store information related to the mobile host 203. Further, a correspondent host 207 is also attached to the core network 201.
A user of the mobile host 203 may wish to communicate with the correspondent host 207 in order to use an application loaded on the correspondent host 207. Thus, the mobile host 203 makes an application level protocol request, for example using SIP (Session Initiation Protocol), to connect to the correspondent host 207.
One example of this could be a student studying in a library of the university they are attending who wishes to connect to a server located at a different university. The user's university network would include a server holding IP address information for the user; this server is the home agent.
The server located in the different university is the correspondent host 207.
The Internet is the core network 201. The mobile host 203 could be a laptop computing device, for example.
At such a time when the student wishes to leave the university premises and work from home, it is necessary for a roaming system to be set up so that the mobile host 203' (the laptop) may still communicate with the correspondent host 207 (the server located at the different university) whilst away from the core network 201.
In figure 2 there is shown a first foreign network 211. Also shown is a first foreign agent 209 interconnecting the core network 201 and the first foreign network 211. Thus, when the student is set up at home in the first foreign network 211 with a laptop computer, it is possible for the mobile host 203' to communicate with the correspondent host 207 using roaming. This is realised by using network level messages, such as MIP (Mobile Internet Protocol or Mobile IP) to inform the home agent 205 via the core network 201 of the mobile host's whereabouts.
A care of address is obtained from the first foreign agent 209 in order that the home agent 205 can map the home address of the mobile host 203' to S the care of address. The home address is a unique address associated with that particular mobile host 203'. This allows messages from the home agent 205 and the correspondent host 207 to reach the mobile host 203'.
Further, if the mobile host 203' moves from the first foreign network 211 to a second foreign network 215, a handover sequence is required to allow communications between the mobile host 203" and the correspondent host 207 to continue.
In known systems, when the mobile host 203' moves to the second foreign network 215, the communication session between the correspondent host 207 and the mobile host 203" is terminated. For example, the termination is carried out using an application level protocol message, such as the SIP message BYE. In order for the communications between the mobile host 203" and the correspondent host 207 to continue, the communication session has to be re-established. However, before re-establishing communications, it is necessary to register the new care of address issued by the second foreign agent 213 on the second foreign network 215, by sending this new contact information, with the mobile host's home address, to the home agent 205.
Further, the network level solution in this example adheres to the use of the standard OSI mobile, and so is a more "pure" network solution not involving higher layer protocols. However, this can mean that the final protocol stack is not as efficient as it could be.
The handover sequence in the prior known systems requires the application level communication session to be terminated prior to it being re established during handover. This results in a delay due to the necessity to re establish the communication session, and further results in lost data packets.
The present invention aims to overcome or at least alleviate some or all of the above-mentioned problems.
In one aspect, the present invention provides, in a system with a transport level protocol layer and an application level protocol layer, a method of handing over a communication link between a mobile communication device and a first network to a second network by sending a message via a transport level device to an application level device located in the mobile communication device.
In a further aspect, the present invention provides a mobile communication device comprising a first device arranged to receive and send messages at a transport level and a second device arranged to receive and send messages at an application level, wherein the first device communicates with the second device during hand over of a communication link between the mobile communication device and a first network to a second network.
In yet a further aspect, the present invention provides a foreign agent server adapted for use during the handover of a communication link between a mobile communication device and a first network to a second network, wherein the foreign agent comprises a session initiation protocol proxy server.
In yet a further aspect, the present invention provides a method of sending a session initiation protocol INVITE message comprising the step of including a foreign agent server's Internet protocol address within the contact field of said message, said foreign agent server adapted for use during the handover of a communication link between a mobile communication device and a first network to a second network.
In yet a further aspect, the present invention provides, in a mobile Internet system, a method of handing over a communication link between a mobile communication device and a first network to a second network by sending contact information associated with the second network from a Mobile Internet Protocol client to a Session Initiation Protocol user agent, both the client and user agent located within the mobile communication device.
The present invention provides the advantage of reducing handover time due to cross layer messaging when a mobile communication device moves between two networks. This provides a reduction in the number of data packets lost during the handover procedure and so improves the overall data throughput as a result.
A specific embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows the protocol layers used in the standard OSI model; Figure 2 shows a known handover scenario; Figure 3 shows the registration of a care of address according to an embodiment of the present invention; Figure 4 shows a session set up procedure according to an embodiment of the present invention; Figure 5 shows the general concept of a handover according to an embodiment of the present invention; Figure 6 shows the sequence of messages used in the handover procedure according to an embodiment of the present invention.
EMBODIMENT OF THE PRESENT INVENTION
Figure 3 shows a mobile host 303 located in a first foreign network 313. The core network 301 is the Internet and has attached thereto a mobile host 303, a home agent 305, a correspondent host 307 and a first foreign agent 309. A first SIP proxy server 311 is located at the first foreign agent 309.
The first foreign agent 309 connects the core network 301 to the first foreign network 313.
Two addresses are registered for data routing; the home address of the mobile host 303 and the care of address of the first foreign agent 309. This provides a means to connect the home agent 305 to the first foreign network 313 and the first foreign network 313 to the mobile host 303.
The first foreign agent 309 provides a care of address, i.e. an IP address allocated by the first foreign agent 309 to the mobile host 303 when located in the first foreign network 313. The first foreign agent 309 uses this address to locate the mobile host 303. The care of address is used by the home agent 305 to ensure the correspondent host 307 can contact the mobile host 303 to set up a communication session, and also to pass on any network level MIP messages to the mobile host 303 from the home agent 305.
The care of address is obtained either by the mobile host 303 soliciting for the care of address, or through the mobile host 303 receiving a broadcast advertisement sent by the first foreign agent 309.
During registration of the care of address at the home agent 305, the mobile host 303 sends a communication via the first foreign agent 309 to the home agent 305. The home agent 305 will receive this communication, which includes the care of address issued by the first foreign agent 309 and the home address of the mobile host 303. The home address is stored in the home agent 305 to allow the home agent to recognise the mobile host 303 and track its movement.
The home agent 305 then sends a binding update message to the correspondent host 307 in order to map the care of address to the home address of the mobile host 303 in a binding cache. Thereafter, the correspondent host 307 maintains the binding cache in order to associate the home address of the mobile host 303 with the care of address.
Further, the care of address is registered at the first SIP proxy server 311 in order to map the SIP URI (Universal Resource Identifier), which is permanently stored in the mobile host 303. This SIP URI is assigned to the user of the mobile host 303. The SIP URI allows SIP messages to be correctly delivered and routed to the mobile host 303 when in the first foreign network 313. The care of address is registered at the first SIP proxy server 311 by the mobile host 303 sending a REGISTER message to the first SIP proxy server 311.
After registration of the care of address, a communication session is set up between the mobile host 303 and the correspondent host 307 using application level protocol messages, in this embodiment SIP. The session is set up using SIP protocol messages as shown in Figure 4, and in this embodiment is a video conferencing multi-media session.
Figure 4 indicates a mobile host 303, a first foreign agent 309 with a first SIP proxy server 311 located at the first foreign agent 309, a correspondent host 307, and a location server 409.
The mobile host 303 sends an INVITE SIP message from the SIP user agent located in the mobile host 303 to the first SIP proxy server 311, as shown in step 411. The IP address of the first foreign agent 303 is included within the "contact" field of the INVITE message. This allows application level protocol SIP messages to be forwarded to the first foreign agent 303 in order for the messages to then be forwarded to the mobile host 303 located on the first foreign agent's network.
Within the SIP INVITE message there is located the domain name of the correspondent host 307. In order to determine where the correspondent host 307 is located, the domain name information is passed from the first SIP proxy server 311 to a location server 409, as shown in step 413. The location server 409 in this embodiment is a Domain Name Service (DNS).
The location server 409 returns the correct routing information to the first SIP proxy server 311 in order for the INVITE message to then be forwarded to the correspondent host 307. The INVITE message is then forwarded by the first SIP proxy server 311 to the correspondent host 307, as shown in step 415 in Figure 4.
The next steps, 417-421, indicate the set up of a tunnel between the correspondent host 307 and the first foreign agent 309. An OK 200 message is sent by an SIP user agent located at the correspondent host 307 to the first SIP proxy server 311. This indicates that the correspondent host 307 is ready and able to set up a connection with the mobile host 303 using the parameters indicated in the INVITE message.
The first SIP proxy server 311 forwards the OK 200 message to the mobile host's SIP user agent. As an acknowledgement of receipt of the OK message, the SIP user agent in the mobile host 303 forwards directly to the correspondent host 307 an ACK (acknowledgement) message. After receipt of this acknowledgement message by the correspondent host 307 a communication session is set up between the mobile host 303 and the correspondent host 307 with all application level messages being transmitted between the mobile host 303 and the correspondent host 307 via the first foreign agent 309.
In this embodiment, an RTP (Real Time Protocol) session is set up between the mobile host 303 and the correspondent host 307. This provides a means to send video and audio, for a video conference call, between the mobile host 303 and the correspondent host 307.
Figure 5 shows the general concept of a handover according to this embodiment.
Referring to figure 5, a second foreign network 515 is also connected to the core network 301 via a second foreign agent 517 with a second SIP proxy server 519 located at the second foreign agent 517.
When the mobile host 303 moves from the first foreign network 313 to the second foreign network 515, A to B referenced in figure 5, it is required that a seamless handover is executed such that data packets are not lost between the correspondent host 307 and the mobile host 303. In order to carry out the improved handover, the following steps are carried out with reference to Figure 6.
The new care of address issued by the second foreign agent 517 must be registered at the mobile host's home agent 305. This is carried out at steps 611-615 as shown in Figure 6. At step 611 the mobile host 303 optionally requests a care of address from the second foreign agent 517. As an alternative to this, the foreign agent may broadcast a care of address at selected intervals for any mobile host to pick up.
The second foreign agent 517 sends a care of address back to the mobile host 303 at step 613. Also, the second foreign agent 517 sends the care of address to the home agent 305 in order for the home agent 305 to carry out a binding update at step 615. The binding update is the same as in known systems wherein the home agent 305 will inform the correspondent host 307 of the new care of address if the correspondent host 377 is not already aware of it. The steps 611 to 615 are all carried out using MIP protocol messages.
The second foreign agent 517 provides the new care of address in order to identify the mobile host 303 while it is located on the foreign network.
The next step at 617 is to register the mobile host's SIP URI at the second SIP proxy server 519. This is carried out using the SIP protocol message REGISTER in order to allow any SIP messages received by the SIP proxy server 519 to be forwarded to the SIP user agent located at the mobile host 303. The MIP client at the mobile host 303 also stores the care of address received from the second foreign agent 517.
The next steps involve the mobile host 303 re-inviting the correspondent host 307 to resume the multi-media communication session without the need to terminate the communication session arid so re-establish a new session.
At step 619, the mobile host 303 sends a SIP RE-INVITE message to the second SIP proxy server 519. Within the mobile host 303, the MIP client forwards the care of address of the second foreign agent 517 to the SIP user agent, also located within the mobile host 303.
The SIP user agent inserts the care of address into the "contact" field of the RE-INVITE message in order to update the correspondent host 307 with the location of the mobile host 303. The transference of the care of address stored in the MIP client of the mobile host 303 to the SIP user agent also located within the mobile host is through the use of cross layer messaging. That is, a network level device, in this embodiment the MIP client, forwards a message to an application layer level device in order to improve the handover from one network to another. This provides a more efficient protocol design than when using the traditional OSI model.
The RE-INVITE message containing the second foreign agents care of address is forwarded to the second SIP proxy server 519.
At step 621 the second SIP proxy server 519 requests the location of the correspondent host 307 by passing on the domain name within the RE-INVITE message to a location server 409. The location server 409 returns the location details to the second SIP proxy server 519. The RE-INVITE message is then forwarded by the second SIP proxy server 519 to the correct location of the correspondent host 307 at step 623.
The SIP user agent in the correspondent host 307 returns an OK 200 message back to the SIP user agent in the mobile host 303 via the second SIP proxy server 519. The mobile host 303 acknowledges the receipt of the OK message at step 627 by having the SIP user agent send an ACK message directly to the correspondent host's SIP user agent. The communication session between the correspondent host 307 and the mobile host 303 can now continue via the second foreign agent 517 as shown at step 629.
This scheme provides macro mobility support for SIP based real time multimedia services. The scheme reduces hand off latency and packet loss, and thus improves the overall data throughput as a result.
The invention as described hereinbefore uses higher layer protocols in conjunction with mobile IP such that cross layer information may be exchanged through the use of signalling, in particular, the signalling occurs between the application layer (also considered to be the application, session and presentation layers combined) and the network layer. This produces a more efficient method of communication.
It will be understood that the embodiment of the present invention described herein is by way of example only, and that various changes and modifications maybe made without departing from the scope ofthe invention.
Although the embodiment describes the use of MIP and SIP as the network layer protocols and applications layer protocol messages respectively, any other cross layer messaging may be applied without departing the scope of the invention.
Further, although the embodiment describes a mobile host as a laptop computer, the mobile host may be any other portable communication device suitable for disconnecting and reconnecting at different locations. For example, the mobile host may be a mobile telephone device, notebook or notepad computer, personal digital assistant or the like.

Claims (17)

1. In a system with a transport level protocol layer and an application level protocol layer, a method of handing over a communication link between a mobile communication device and a first network to a second network by sending a message via a transport level device to an application level device located in the mobile communication device.
2. The method of claim 1 further comprising the step of transmitting the message from a lower layer to a higher layer of a layered protocol model.
3. The method of claim 2 wherein the layered protocol model is the Open Systems Interconnection model.
4. The method of claim 1 wherein messages are sent at the transport level using Mobile Internet Protocol.
5. The method of claim 1 wherein messages are sent at the application level using Session Initiation Protocol.
6. The method of claim 5 further comprising the step of sending the Session Initiation Protocol message using the RE-INVITE message format.
7. The method of claim 6 further comprising the step of sending the care of address of the second network in the RE-INVITE message within the
contact field.
8. A mobile communication device comprising a first device arranged to receive and send messages at a transport level and a second device arranged to receive and send messages at an application level, wherein the first device communicates with the second device during hand over of a communication link between the mobile communication device and a first network to a second network.
9. The device of claim 8 further arranged to transmit the message from a lower layer to a higher layer of a layered protocol model.
10. The device of claim 9 wherein the layered protocol model is the Open Systems Interconnection model.
11. The device of claim 8 wherein the transport level device is a Mobile Internet Protocol client.
12. The device of claim 8 wherein the application level device is a Session Initiation Protocol user agent.
13. The device of claim 12 wherein the message sent by the Session Initiation Protocol user agent is in the RE-INVITE message format.
14. The device of claim 13 wherein the RE-INVITE message includes the care of address of the second network in the contact field.
15. A foreign agent server adapted for use during the handover of a communication link between a mobile communication device and a first network to a second network, wherein the foreign agent comprises a session initiation protocol proxy server.
16. A method of sending a session initiation protocol RE-INVITE message comprising the step of including a foreign agent server's Internet protocol address within the contact field of said message, said foreign agent server adapted for use during the handover of a communication link between a mobile communication device and a first network to a second network.
17. In a mobile Internet system, a method of handing over a communication link between a mobile communication device and a first network to a second network by sending contact information associated with the second network from a Mobile Internet Protocol client to a Session Initiation Protocol user agent, both the client and user agent located within the mobile communication device.
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