# Patent

## Title
System and method for handover of an access terminal in a communication network

## Abstract

In one embodiment according to the present disclosure, a system for implementing handover of a mobile IP session in a cellular communication network generally includes a processor and a memory for storing one or more context information rules associated with an access terminal. The processor is operable to receive a registration request message from the target radio network controller and in response to receipt of the registration request message, transmit a context information request message to query context information from an anchor IP gateway. The processor is also operable to receive a context information response message from the anchor IP gateway and apply the context information response message to the mobile IP connection. The context information response message including at least one context information rule that is associated with the access terminal.

## Background
RELATED APPLICATION
This application claims priority under 35 U.S.C. §119(e) of U.S. Provisional application Ser. No. 60/780,176, entitled “VERIZON WIRELESS MULTI-MEDIA PLUS (MMD+) PROGRAM SYSTEM ARCHITECTURE DOCUMENT,” filed Mar. 6, 2006, by Flemming Andreasen et al., which is incorporated herein by reference.


TECHNICAL FIELD OF THE INVENTION
This invention relates in general to communication networks, and more particularly to a system for fast handover of an access terminal in a communication network and a method of implementing the same.
BACKGROUND OF THE INVENTION
Cellular communication networks may have a number of base transceiver stations (BTSs) to provide coverage over generally broad geographical areas. Each of these base transceiver stations may be coupled to a radio network controller (RNC) that manages various aspects of cellular communication network. One particular aspect of the cellular communication network that may be managed by the RNC is a process commonly referred to as handover. The process of handover generally refers to actions taken by radio network controller in order to switch an access terminal's point-of-attachment from one BTS to another as the access terminal moves from one location to another.
In practice, a number of cellular communication networks may function together in order to provide a cellular communication environment. Handover between adjacent cellular communication networks providing data communication services is typically provided by a mobile IP protocol. The mobile IP protocol enables access terminals to roam from the home network while maintaining a relatively permanent IP address.
SUMMARY OF THE INVENTION
In one embodiment according to the present disclosure, a system for implementing handover of a mobile IP session in a cellular communication network generally includes a processor and a memory for storing one or more context information rules associated with an access terminal. The processor is operable to receive a registration request message from the target radio network controller and in response to receipt of the registration request message, transmit a context information request message to query context information from an anchor IP gateway. The processor is also operable to receive a context information response message from the anchor IP gateway and apply the context information response message to the mobile IP connection. The context information response message including at least one context information rule that is associated with the access terminal.
Embodiments of the disclosure may provide numerous technical advantages. Some, none, or all embodiments may benefit from the below described advantages. According to one embodiment, a handover mechanism for a mobile IP protocol may be provided that alleviates the need to access authentication or authorization information from a designated home network of an access terminal each time the access terminal roams to a new network. Security keys locally maintained in the anchor IP gateway may be transmitted directly to the target IP gateway during handover. The latency involved with transmitting and receiving authentication or authorization information from the designated home network of the access terminal may be alleviated, which may reduce the overall time required to authenticate the access terminal on the target network.
Other technical advantages will be apparent to one of skill in the art.



BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a diagram of one embodiment of a cellular communication environment according to one embodiment of the present disclosure; and
FIG. 2 is a call-flow diagram illustrating one embodiment of a handover method that may be implemented on the cellular communication environment of FIG. 1.



DETAILED DESCRIPTION OF THE INVENTION
Mobile IP protocol enables a relatively stable mechanism for roaming from one communication network to another. Handover of an access terminal having an active mobile IP session in a cellular communication network, however is generally cumbersome in practice. When roaming, for example, the access terminal is typically authenticated with the target cellular communication network for security purposes. Known authentication mechanisms require correspondence of authentication information with the designated home network of the access terminal, a process that is generally complicated and time consuming.
FIG. 1 shows one embodiment of a cellular communication environment 10 in which may facilitate fast handover of an access terminal according to the teachings of the present disclosure. Cellular communication environment 10 generally includes an anchor network 12a, a target network 12b, and a home network 14 that may be coupled to the IP network 16 for providing various data-based communication services to an access terminal 18. A correspondent node 20 is also coupled to the IP network 16 and generally refers to any suitable node that may communicate with the access terminal 18 through the IP network 16.
According to one embodiment of operation, a system and method for handover of packet-switched services from anchor network 12a to target network 12b is provided that alleviates the need to access authentication or authorization information from the home network 14 of access terminal 18 each time the access terminal 18 roams to a target network 12b. 
The anchor network 12a and target network 12b have been designated as an anchor node and target node, respectively, for the purposes of the following discussion in which the access terminal 18 roams from the anchor network 12a to the target network 12b. The anchor network 12a, however may also be designated as a target node and the target network 12b may be designated as an anchor node for scenarios where the access terminal 18 roams from target network 12b to the anchor network 12a. 
Access terminal 18 may be any suitable cellular communication network aware device, that may be, for example, a cellular telephone, a personal computer, a pager, a pocket computer, a notebook computer, or a personal digital assistant (PDA). Access terminal 18 may communicate with radio access network 22a using any suitable wireless communication network protocol. Examples of a suitable wireless communication network protocols include code division multiple access (CDMA), integrated digital enhanced network (iDEN), and time division multiple access (TDMA) protocols.
Anchor network 12a generally includes a radio access network 22a, and an IP gateway 24a for providing connectivity to the IP network 16. In one embodiment, anchor network 12a may be an IP multimedia subsystem (IMS) that provides various data communication services, such as, packet-switched voice call services, e-mail messaging services, instant messaging services, and IP network access services. In another embodiment, anchor network 12a is an IP multimedia subsystem based upon the multimedia domain (MMD) architecture developed by the 3rd Generation Partnership Project (3GPP).
The radio access network 22 provides an interface for coupling the access terminal 18 to a packet-switched core network, which in this case, is the IP gateway 24a. Radio access network 14 may be any suitable type of high rate packet data (HRPD) network, such as an Universal Mobile Telecommunications System (UTMS) or a Global System for Mobile Communications (GSM) network telecommunication system.
Radio access network 22a may include a radio network controller (RNC) 28a and one or more base tranceiver stations (BTSS) 30a. Each BTS 30a communicates directly with access terminal 18 using radio frequency (RF) transceivers that transmit and receive RF signals from the access terminal 18. The functions of the RNC 28a may be implemented with a processor executing computer instructions stored in a memory. The RNC 28a controls the operation of each of the BTSs 30a and may route signals from the BTS 30a to the IP gateway 24a. 
The IP gateway 24a may be used to route packets between the radio access network 22a and the IP network 16. The functions of the IP gateway 24a may be implemented with a processor executing computer instructions stored in a memory. IP gateway 24a may perform any suitable operations. For example, IP gateway 24a may convert communications from a protocol used by radio access network 22a to a protocol used by the IP network 16, or vice-versa.
Target network 12b generally includes a radio access network 22b and an IP gateway 24b that function in a manner similar to the radio access network 22a and IP gateway 24a of anchor network 12a. Additionally, radio access network 22b may include a RNC 28b and one or more BTSs 30b that function in a manner similar to RNC 28a and BTS 30a of radio access network 22a in anchor network 12a. 
RNC 28a may be coupled to RNC 28b over a HRPD network as described above. RNC 28a may communicate with RNC 28b in order to control various aspects of the cellular communication network, such as handover of access terminal 18 when roaming from anchor network 12a to target network 12b. 
IP gateway 24a may communicate with IP gateway 24b using any suitable communication link. In one embodiment, IP gateway 24a may communicate with IP gateway 24b through an IP peering link 34.
Home network 14a may be any packet-switch enabled network that is managed by a mobility service provider having an executed service agreement with the user of the access terminal 18. In one embodiment, home network 14 may be an IP multimedia subsystem based upon the multimedia domain (MMD) architecture. Home network 14 generally includes a home security manager 36 that is coupled to a home bearer manager 38. The security manager 24a may function as a server for registration of access terminal 18 to the home network 12a or foreign network 12b. Home security manager 36 may have a memory for storage of context information rules 40 associated with the access terminal 18. In one embodiment, these context information rules 40 may be governed by a service agreement entered into between the mobility service provider and owner of the access terminal 18.
Context information rules 40 may include one or more authentication rules or one or more authorization rules that control various aspects of data based communication services provided to the access terminal 18 by the cellular communication environment 10. Authentication rules may include information that is used to verify that the access terminal 18 is a valid user. As such, the authentication rules may include identification information for use with an authentication protocol, such as, for example, an extended authentication protocol (EAP), or point-to-point protocol (PPP). Authorization rules may include information that may be used to control various aspects of data communication services provided to the access terminal 18, which may include, for example, quality of service (QoS), user security, accounting, user mobility, and packet inspection.
The bearer manager 38 is coupled to security manager 36 and IP gateways in anchor network 12a and target network 12b through the IP network 16. The bearer manager 38 may facilitate authentication and/or authorization of access terminal 18 when access terminal 18 forms a point of attachment to either anchor network 12a or target network 12b. 
The home network 14 as described above is a separate entity from the anchor network 12a or target network 12b. The home network 14, however may be the anchor network 12a or target network 12b for scenarios where the access terminal 18 roams from or to the domain, respectively, of the home network 14.
A component of environment 10 may include any suitable arrangement of elements, for example, an interface, logic, memory, other suitable element, or a combination of any of the preceding. An interface receives input, sends output, processes the input and/or output, performs other suitable operation, or performs a combination of any of the preceding. An interface may comprise hardware and/or software.
Logic performs the operations of the component, for example, executes instructions to generate output from input. Logic may include hardware, software, other logic, or a combination of any of the preceding. Certain logic, such as a processor, may manage the operation of a component. Examples of a processor include one or more computers, one or more microprocessors, one or more applications, other logic, or a combination of any of the preceding.
A memory stores information. A memory may comprise computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), database and/or network storage (for example, a server), other computer-readable medium, or a combination of any of the preceding.
Modifications, additions, or omissions may be made to environment 10 without departing from the scope of the invention. The components of environment 10 may be integrated or separated. Moreover, the operations of environment 10 may be performed by more, fewer, or other components. Additionally, operations of environment 10 may be performed using any suitable logic comprising software, hardware, other logic, or any suitable combination of the preceding. As used in this document, “each” refers to each member of a set or each member of a subset of a set.
FIG. 2 is a call-flow diagram showing one embodiment of a method that may be implemented on the cellular communication environment 10 for providing handover of an access terminal 18 in a relatively fast manner. This particular call-flow diagram describes a roaming scenario in which access terminal 18 moves its point of attachment from the anchor network 12a to the target network 12b. It should be appreciated, however that a similar procedure may be performed for a roaming scenario in which the access terminal 18 moves its point of attachment from the target network 12b to the anchor network 12a. 
At step 100, an IP session is initiated between access terminal 18 and correspondent node 20 through RNC 28a, IP gateway 24a, and the bearer manager 38. In this IP session, various forms of data communication services, such as packet-switched voice call services, e-mail messaging services, instant messaging services, and IP network access services may be conducted in a normal manner.
At step 102, the access terminal 18 crosses a mobility boundary between the anchor network 12a and target network 12b. At step 104, a handover session is configured between the access terminal 18 and RNC 28a. At this point, the RNC 28a determines if the point of attachment of access terminal 18 can be transferred to the RNC 28b. If the point of attachment of the access terminal 18 can be transferred, a route update is established in between the access terminal 18 and RNC 28a for this behavior at step 106.
At step 108, the RNC 28a issues a transfer request message to RNC 28b. This transfer request message may include an IP address of the IP gateway 24a. The RNC 28b identifies resources to accept a point of attachment with the access terminal 18 and subsequently issues a transfer request response message to the RNC 28a at step 110. At step 112, SHO legs are connected from RNC 28a to RNC 28b. At step 114, the session between the access terminal 18 and RNC 28a is updated.
At step 116, the RNC 28b sends an All pre-registration request message to the IP gateway 24b. The All pre-registration request message may include the IP address of the IP gateway 24a that was provided to the RNC 28b in step 108. The All pre-registration request message may also include identification parameters and other HRPD session parameters associated with the access terminal 18. At step 118, the IP gateway 24b acknowledges the All pre-registration request message by issuing a registration response message to the RNC 28b and starts preparation for handling an IP session with the access terminal 18.
At step 120, the IP gateway 24b sends a context information request message to the IP gateway 24a. The context information request message may include requests for HRPD session parameters and other information associated with the access terminal 18 for successful handover from IP gateway 24a to IP gateway 24b. The IP gateway 24a uses HRPD session parameters provided in the context information request message to locate the ongoing HRPD session of the access terminal 18 with the RNC 28a. Once located, the IP gateway 24a obtains context information from the ongoing IP session and sends this information in a context information response message to the IP gateway 24b in step 122. At this point, the IP gateway 24b may install any context information rules for the new IP session, such as QoS facets, local admission control properties that may be based upon the QoS facets, or derived security keys.
At step 124, an IP tunnel is established between the IP gateway 24a and IP gateway 24b. The IP tunnel may be sent over any suitable link. In one embodiment, the context information request message may be sent over an IP peering connection established between the IP gateway 24a and the IP gateway 24b. Once the IP tunnel has been established, the IP gateway 24a may begin bicasting packets to the access terminal 18 through RNC 28a and RNC 28b. 
At step 126, the A10 connection between the RNC 28a and the IP gateway 24a may be released. In one embodiment, the RNC 28a may wait for an idle signal condition on the bicasted IP session before releasing A10 connection between the RNC 28a and the anchor IP gateway 24a. Certain embodiments of the present disclosure in which the A10 connection is maintained until an idle signal condition is detected may reduce the number of dropped packets that may occur during the handover procedure.
At step 128, IP gateway 24a sends a proxy agent advertisement message to the IP gateway 24b. In response, the IP gateway 24b sends this advertisement message to the access terminal at step 130.
At step 132, the access terminal 18 sends a mobile IP registration request binding update message to the IP gateway 24b. As step 134, the IP gateway 24b forwards this mobile IP registration request binding update message to the bearer manager 38 for registering the new care of address with the home network 14.
At step 136, the bearer manager 38 sends a mobile IP registration response binding update message to the access terminal 18. At this point, handover of the mobile IP session from the IP gateway 24a to the IP gateway 24b is complete.
At step 138, the correspondent node may transmit its first IP packets, which are destined for receipt by the access terminal 18, to the IP gateway 24b. At step 140, the IP gateway 24b may buffer the first incoming packets in each direction, enforce any available authorization rules, such as quality of service, retrieve any dynamic context information associated with the IP session including traffic flow templates (TFTs) or robust header compression (ROHC) states. At step 142, the IP gateway 24b may negotiate the dynamic context information generated in step 140 with the IP gateway 24a. 
At step 144, the IP packet received by the IP gateway 24b in step 138 and buffered in step 140 is sent to the access terminal 18. At step 146, the IP session between the access terminal 18 and correspondent node 20 continues. The IP session at step 146 differs from step 100, however in that IP packets are now routed and buffered through the IP gateway 24b rather than the IP gateway 24a. 
Modifications, additions, or omissions may be made to the method without departing from the scope of the invention. The method may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order.
Several embodiments of a system and method for providing handover of an access terminal 18 have been described that may be relatively faster than known handover mechanisms for a mobile IP session. In one respect, the handover method as described may alleviate the need to access authentication information from the home network 14 each time the access terminal 18 roams to a new network. Security keys locally maintained in the anchor IP gateway 24a may be transmitted to the target IP gateway 24b during handover. These security keys may be used to authenticate the access terminal 18 on the target IP gateway 24b without accessing master session key information from the home network 14.
The system and method of the present disclosure may also provide a handover mechanism for a mobile IP session that may be triggered by existing handover mechanisms used between adjacent RNCs in a cellular communication environment. Handover of access terminals 18 between RNCs is a well known, established mechanism that is relatively fast and stable. This handover procedure may provide a pre-registration request message to the target IP gateway 24b that triggers handover of the mobile IP session to commence. In this manner, handover of the mobile IP session may occur in a relatively the same time as when handover of the HRPD network occurs.
Although the present invention has been described with several embodiments, myriad changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes, variations, alterations, transformations, and modifications as fall within the scope of the appended claims. The present invention is not intended to be limited, in any way, by any statement in the specification that is not reflected in the claims.

## Claims

1. A system for implementing handover of a mobile Internet Protocol (IP) session in a communication network, comprising:
a memory operable to store at least one context information rule associated with an access terminal; and
a processor operable to:
receive a registration request message from a target radio network controller;
in response to receipt of the registration request message, transmit a context information request message to an anchor IP gateway with a connection to an anchor radio network controller;
receive a context information response message from the anchor IP gateway, the anchor IP gateway waiting for an idle signal condition before releasing the connection to the anchor radio network controller, the context information response message including an authorization rule and the at least one context information rule;
apply the context information rule to the mobile IP by authenticating an access terminal without accessing information from a designated home network;
buffer a first packet from a correspondent node communicating with the access terminal; and
enforce the authorization rule of the context information on the first packet.

2. The system of claim 1, wherein the processor is configured in a target IP gateway.

3. The system of claim 1, wherein the processor is further operable to apply the context information rule by:
authenticating the access terminal using an extended authentication protocol security key included in the context information rule.

4. The system of claim 1, wherein the context information rule comprises an authorization rule that is selected from the group consisting of a quality-of-service level rule, a security level rule, an accounting rule, a mobility rule, a charging rule, and a packet inspection rule.

5. The system of claim 1, wherein the anchor IP gateway is operable to:
wait, following receipt of the context information response message by the processor, for an idle signal condition on the mobile IP session; and
release an A10 connection between the anchor radio network controller and the anchor IP gateway.

6. A method for implementing handover of a mobile Internet Protocol (IP) session in a communication network, comprising:
receiving a registration request message from a target radio network controller;
in response to receipt of the registration request message, transmitting a context information request message to an anchor IP gateway with a connection to an anchor radio network controller, the context information being associated with an access terminal;
receiving a context information response message from an anchor IP gateway, the anchor IP gateway waiting for an idle signal condition before releasing the connection to the anchor radio network controller, the context information response message including an authorization rule and the at least one context information rule;
applying the context information rule to a mobile IP connection by authenticating an access terminal without accessing information from a designated home network;
buffering a first packet from a correspondent node communicating with the access terminal; and
enforcing the authorization rule of the context information on the first packet.

7. The method of claim 6, wherein applying the context information rule further comprises:
authenticating the access terminal using an extended authentication protocol security key included in the context information rule.

8. The method of claim 6, wherein the context information rule comprises an authorization rule that is selected from the group consisting of a quality-of-service level rule, a security level rule, an accounting rule, a mobility rule, a charging rule, and a packet inspection rule.

9. The method of claim 6, further comprising:
waiting, following receipt of the context information response message, for an idle signal condition on the mobile IP session; and
releasing an A10 connection between a anchor radio network controller and the anchor IP gateway.

10. A non-transitory computer-readable storage medium encoded with logic for implementing handover of a mobile Internet Protocol (IP) session in a communication network, the logic operable to:
receive a registration request message from a target radio network controller;
in response to receipt of the registration request message, transmit a context information request message to an anchor IP gateway with a connection to an anchor radio network controller, the context information being associated with an access terminal;
receive a context information response message from the anchor IP gateway, the anchor IP gateway waiting for an idle signal condition before releasing the connection to the anchor radio network controller, the context information response message including an authorization rule and the at least one context information rule;
apply the context information rule to the mobile IP connection by authenticating an access terminal without accessing information from a designated home network;
buffer a first packet from a correspondent node communicating with the access terminal; and
enforce the authorization rule of the context information on the first packet.

11. The non-transitory computer-readable storage medium of claim 10, wherein the computer-readable storage medium is configured in a target IP gateway.

12. The non-transitory computer-readable storage medium of claim 10, wherein the logic is further operable to apply the context information rule by:
authenticating the access terminal using an extended authentication protocol security key included in the context information rule.

13. The non-transitory computer-readable storage medium of claim 10, wherein the context information rule comprises an authorization rule that is selected from the group consisting of a quality-of-service level rule, a security level rule, an accounting rule, a mobility rule, a charging rule, and a packet inspection rule.

14. The non-transitory computer-readable storage medium of claim 10, wherein the logic is further operable to:
wait, following receipt of the context information response message, for an idle signal condition on the mobile IP session; and
release an A10 connection between an anchor radio network controller and the anchor IP gateway.

15. A system for implementing handover of a mobile Internet Protocol (IP) session in a communication network, comprising:
means for receiving a registration request message from a target radio network controller;
in response to receipt of the registration request message, means for transmitting a context information request message to an anchor IP gateway with a connection to an anchor radio network controller, the context information being associated with an access terminal;
means for receiving a context information response message from an anchor IP gateway, the anchor IP gateway waiting for an idle signal condition before releasing the connection to the anchor radio network controller, the context information response message including an authorization rule and the at least one context information rule;
means for applying the context information rule to a mobile IP by authenticating an access terminal without accessing information from a designated home network;
means for buffering a first packet from a correspondent node communicating with the access terminal; and
means for enforcing the authorization rule of the context information on the first packet.