FIELD OF INVENTION
The present invention relates to data communications in mobile networks. More specifically, it relates to the hand over of a data connection from one cell to another without tearing down the data connection.
BACKGROUND OF THE INVENTION
The Internet Protocol (“IP”) is an addressing protocol designed to route traffic within a network or between networks. The Internet Protocol is used on many computer networks including the Internet, intranets and other networks. Internet Protocol addresses are typically assigned to “immobile” nodes on a network and the IP address of each node is used to route datagrams to the node through a server connected to the node. An immobile node may be moved to a different server on the computer network, but is typically associated with a static physical location (e.g., 3Com Corporation in Santa Clara, Calif.).
In contrast, mobile nodes may connect to various physical locations on a computer network. A mobile node has its own network address and a semi-permanent relationship with a home agent or server to which the mobile node may occasionally be connected to send and receive datagrams. However, the mobile node can also connect to a foreign agent through which it sends and receives datagrams. An example of one protocol that facilitates communication with mobile nodes over the Internet is the Mobile Internet Protocol (Mobile IP), which allows “mobile” nodes to transparently move between different Internet Protocol sub-networks (“subnets”). Mobile IP is described in Request for Comment (RFC) 2002 IP Mobility Support, C. Perkins, October 1996, herein incorporated by reference, available from the Internet Engineering Task Force (IETF) at www.ietf.org.
Other protocols are also used to support mobile node communications. Often, protocols typically utilized in non-mobile applications, such as the Internet Protocol (IP) and the Point to Point protocol (PPP), are layered on top of a lower level mobile protocol, such as the Radio Frequency Link Protocol (RLP) defined by the International Telephone Union (ITU). However, the use of these non-mobile applications can create inefficiencies as mobile nodes move from one service area to another and connections are broken and reformed accordingly.
Internet Protocol addresses are typically assigned to mobile nodes based on their home Internet Protocol subnet. The home subnet is connected to an external network (e.g., the Internet or an intranet) with a “home agent” that serves as the subnet's gateway router. As is known in the art, the gateway connects computer networks using different networking protocols or operating at different transmission capacities. As is known in the art, a router translates differences between network protocols and routes data packets to an appropriate network node or network device. When a mobile node “roams,” (i.e., dynamically changes its physical location), it periodically transmits “agent solicitation” messages to other gateway routers. A mobile node also listens for “agent advertisement” messages from other gateway routers. When a mobile node receives an agent advertisement message indicating that it is now on a foreign subnet, it registers with the foreign gateway router or “foreign agent” and its home agent. The registration with the home agent indicates that the mobile node is away from “home” (i.e., away from its home subnet). The registration with the foreign agent allows the mobile node to receive data on the foreign subnet.
FIG. 1 shows an architecture 10 that illustrates an example of the connection of a mobile node 20 to public IP network 70. Public IP network 70 includes two foreign agents 30 and 40 that act as tunnel initiators responsive to the establishment of a link with mobile node 20. The network also includes a tunnel endpoint server 50 that is the home agent for mobile node 20 in this example.
When mobile node 20 receives an agent advertisement broadcast from tunnel initiator 30, the mobile node establishes a first link 22 with tunnel initiator 30. Link 22 is a radio frequency communication link between mobile node 20 and tunnel initiator 30. An example of a protocol for link 22 is the Radio Frequency Link Protocol (RLP). Tunnel initiator 30 is a foreign agent for mobile node 20 and, as part of establishing link 22, receives information regarding a home agent from mobile node 20. Note that the information received by tunnel initiator 30 from mobile node 20 also includes the Mobile Identification Number (MIN) for mobile node 20. Using the mobile node's home agent information, tunnel initiator 30 establishes L2TP tunnel 56 to tunnel endpoint server 50, which is the home agent for mobile node 20.
One example of a tunnel initiator or endpoint device is a network access server, such as that described in the patent to Dale M. Walsh et al., U.S. Pat. No. 5,525,595, which is fully incorporated by reference herein and describes an integrated network access server suitable for use in the present invention. Such a device has been commercialized widely by 3Com Corporation (previously U.S. Robotics Corp.) under the trade designation Total Control™ Enterprise Network Hub. Network access servers similar in functionality, architecture and design are available from other companies, including Lucent Technologies and Cisco Systems. The invention is suitable for implementation in network access servers from the above companies, and in other similar devices.
In protocols that support client mobility, mobile node 20 typically senses that it has lost contact with tunnel initiator 30 when it times out waiting for an advertisement message from tunnel initiator 30. Mobile node 20 will then look for an advertisement message from a new foreign agent, such as tunnel initiator 40. When mobile node 20 receives an advertisement message from a foreign agent, tunnel initiator 40 in this case, it sends a registration message that initiates set-up of link 24 and set-up of tunnel connection 66. For further details relating to one example of how mobile nodes move from one foreign agent to another, see RFC 2002 regarding Mobile IP.
Registration of the mobile node 20 typically involves authentication, authorization and accounting (AAA). AAA server 80 interacts with foreign agents and other AAA servers, such as one connected to the mobile node's home network, to authorize, authenticate and perform accounting for the mobile client. To perform AAA services, the registration request from mobile node 20 to the tunnel initiator acting as the foreign agent will include a Network Access Identifier (NAI), such as a Mobile Identification Number (MIN) or Electronic Serial Number (ESN), in an authentication extension of the registration request message. The tunnel initiator will forward the NAI to AAA server 80 that will perform the authentication and authorization, such as a Challenge and Accept Protocol (CHAP) or a cryptographic authentication. Mobility management may also be integrated with the AAA services in AAA server 80, wherein AAA server 80 helps manage registration of the mobile node and handoff of connections between foreign agents.
The AAA server 80 can also be configured to perform tunnel endpoint identification for mobile nodes. In this case, the tunnel initiator queries the AAA server 80 with the MIN supplied by the mobile node 20 to obtain an address for a tunnel endpoint for the connection. The AAA server 80 maintains a database containing entries that match MIN values with tunnel endpoint addresses. The AAA server 80 searches the database for an entry corresponding to the MIN value in the query from the tunnel initiator. The AAA server then returns the tunnel endpoint address from the corresponding entry in a reply message to the tunnel initiator.
The Radio Link Protocol, Code Division Multiple Access (CDMA) protocol, and other mobility protocols allow a mobile node to dynamically change its network connectivity in a manner that is transparent to protocol layers above the Internet Protocol layer. For example, without re-establishing Transmission Control Protocol or User Datagram Protocol sessions. As is known in the art, the Internet Protocol suite includes from lowest-to-highest, a link, network, transport and application layer. The Internet Protocol typically resides in the network layer in the Internet Protocol suite. Transmission Control Protocol and User Datagram Protocol typically reside in the transport layer of the Internet Protocol suite.
When a mobile node connects to a gateway on the Internet, a Point-to-Point Protocol (PPP) session is typically established between the mobile node and the gateway device. As is known in the art, PPP is used to encapsulate network layer datagrams over a serial communications link. For more information on PPP see Internet Engineering Task Force (“IETF”) Request for Comments (“RFC”), RFC-1661, RFC-1662 and RFC-1663 incorporated herein by reference. The gateway, or tunnel initiator, typically initiates establishment of a tunnel connection to a tunnel endpoint server. For example, when a mobile node is connected to a foreign agent, a connection oriented point-to-point communication link, such as a Layer 2 Tunneling Protocol (L2TP) tunnel, is typically established between the foreign agent and the home agent to permit the transfer of data to and from the mobile node. See Layer Two Tunnelling Protocol (L2TP), Request for Comment (RFC) 2661, A. Valencia, et al., June 1999, herein incorporated by reference for all purposes.
FIG. 2 is a message flow diagram illustrating an example of a message exchange 100 that takes place with regard to a call session over an L2TP tunnel. When tunnel initiator 30 receives the registration request 102 from mobile node 20, it begins a tunnel control connection set-up exchange 110. Tunnel initiator 30 initiates tunnel set-up by sending a Start-Control-Connection-Request (SCCRQ) to tunnel endpoint 50. The SCCRQ message 112 will contain the tunnel ID value assigned by tunnel initiator 30 to the tunnel 56 being set-up.
Note that the IP address for tunnel endpoint 50 can be obtained in various ways. For instance, the MIN for mobile node 20 can be used to access a database containing the home agent address for the MIN value. Alternatively, the IP address for the home agent may be contained within the call request message 102 from the mobile node 20.
In response to the SCCRQ message 112, tunnel endpoint 50 sends a Start-Control-Connection-Reply (SCCRP) message 114. Tunnel initiator then sends a Start-Control-Connection-Connected (SCCN) message 116. At this point, the control connection for tunnel connection 56 is established. If no messages for mobile node 20 are waiting in the queue at tunnel endpoint 50, then a Zero-Length-Body (ZLB) acknowledge message 118 is sent to tunnel initiator 30.
Next, a call session is established for the call originated by mobile node 20. The tunnel initiator assigns a session ID value to each call session in order to discriminate between streams on tunnel 56. Each call session corresponds to a single PPP stream between the tunnel initiator and the tunnel endpoint. An incoming call establishment message sequence begins with tunnel initiator 30 sending an Incoming-Call-Request (ICRQ) message 122 to tunnel endpoint 50 that includes a call session ID assigned by tunnel initiator 30. Tunnel endpoint 50 responds with an Incoming-Call-Reply (ICRP) message 124 to tunnel initiator 30, which, in turn, sends an Incoming-Call-Connected (ICCN) message 126 to tunnel endpoint 50. If no messages for mobile node 20 are waiting in the queue at tunnel endpoint 50, then a Zero-Length-Body (ZLB) acknowledge message 128 is sent to tunnel initiator 30.
A tunnel between tunnel initiator 30, the current foreign agent for mobile node 20, and tunnel endpoint 50, the home agent for mobile node 20, is now in place with a call session for mobile node 20. Each data and control packet will contain the tunnel ID and call session ID assigned by the tunnel initiator 30 to differentiate these packets from those of other tunnels and calls that may exist between the tunnel initiator 30 and tunnel endpoint 50.
FIG. 3 is a protocol stack diagram illustrating an example of the protocol relationships in a conventional tunnel structure. As is known in the art, the Open System Interconnection (“OSI”) model is used to describe computer networks. The OSI model consists of seven layers including from lowest-to-highest, a physical, data-link, network, transport, session, application and presentation layer. The physical layer transmits bits over a communication link. The data link layer transmits error free frames of data. The network layer transmits and routes data packets. FIG. 3 illustrates an example of protocol stacks in each of the remote client 20, tunnel initiators 30 and 40, and tunnel endpoint 50 of FIG. 1. Links 22 and 24 for remote client 20 to tunnel initiators 30 and 40, respectively, involve a wireless link protocol, such as RLP. Thus, an RLP to RLP session is represented at layer 1 of the protocol stacks in FIG. 2 between remote client 20 and tunnel initiator 30/40. Because the physical link provided by RLP in this example is a serial link, a serial data link protocol session, such as the point-to-point protocol (PPP), exists between remote client 20 and tunnel initiator 30/40. PPP is described in further detail in RFC 1661 herein incorporated by reference for all purposes.
When a tunnel is established from tunnel initiator 30/40 to tunnel endpoint 50, there are layer 1 (L1) and layer 2 (L2) sessions between the tunnel servers as well as a L2TP session that represents the tunnel itself. Once the tunnel connection is established, a session between network layer peers, such as internet protocol (IP) peers, in the remote client 20 and tunnel endpoint 50 typically exists as well as a session between transport layer peers. Transport layer protocols such as Transmission Control Protocol (“TCP”) and User Datagram Protocol (“UDP”) are often used over IP in computer networks. The Transmission Control Protocol provides a connection-oriented, end-to-end reliable protocol designed to fit into a layered hierarchy of protocols that support multi-network applications. The User Datagram Protocol provides a transaction oriented datagram protocol, where delivery and duplicate packet protection are not guaranteed.
Returning to FIG. 1, as mobile node 20 roams, it may leave the broadcast area, or service area, for tunnel initiator 30 thereby breaking link 22. Tunnel initiator 30 typically detects the loss of link 22 by timing out waiting for a transmission from mobile node 20. When tunnel initiator 30 detects loss of the connection 22 to mobile node 20, it will tear-down the call session and to tunnel endpoint 50 and, if no other call sessions are active over the tunnel 56, will tear-down the tunnel itself.
Returning to FIG. 2, a call session tear-down sequence 130 begins with tunnel initiator 30 sending a Call-Disconnect-Notify (CDN) message 132 to tunnel endpoint 50. The CDN message includes the call session ID for the call corresponding to mobile node 20. The CDN message may also include an Attribute Value Pair (AVP) consisting of a Q.931 Cause Code that indicates the reason for the disconnection. Q.931 is a message oriented signaling protocol defined by the International Telecommunication Union (ITU), as set forth in ITU-T Recommendation 1.451. Tunnel endpoint 50 responds with ZLB-ACK message 134 and removes the call status data relating to the call session ID from its call status table.
When tunnel 56 is torn-down, a tunnel tear-down sequence 140 begins with tunnel initiator 30 sending a Stop-Control-Connection-Notify (StopCCN) message 142 to tunnel endpoint 50. The StopCCN message includes the tunnel ID value for the tunnel. Tunnel endpoint 50 responds with ZLB-ACK message 144 and removes the tunnel status data relating to the tunnel ID value from it tunnel status table.
Returning to FIG. 1, mobile node 20 will detect an agent advertisement from a new agent in the broadcast area where mobile node 20 currently resides. Mobile node 20 will establish a new communication link 24 with the new agent, which in this example is tunnel initiator 40. Tunnel initiator 40 will then establish a new tunnel 66 and call session to tunnel endpoint 50 in the manner described above with regard to tunnel initiator 30.
When the remote client 20 moves out of the service area for tunnel initiator 30 and into the service area for tunnel initiator 40, the PPP session from the remote client to tunnel initiator 30 is lost when communication over link 22 is lost. When link 24 is established, a new PPP session between PPP peers in the stacks of remote client 20 and tunnel initiator 40 must be reestablished. However, when a new PPP session is started for the new link, state information regarding the connection is lost, which is relatively unimportant in voice connections but can result in significant disruption of data connections.
Thus, the need remains for an efficient method for handing off a tunnel connection between a remote client and a server.
SUMMARY OF THE INVENTION
In accordance with preferred embodiments of the present invention, some of the problems associated with handing off a tunnel connection are overcome.
An embodiment of a method for handing off a communication stream in a communications system, according to the present invention, involves receiving a first connection request from a client, where the first connection request includes a client identifier value for the client and, responsive to the first connection request, establishing a first connection from a first connection initiator to a connection endpoint. The method also calls for sensing loss of communication between the client and the first connection initiator and, responsive thereto, transmitting a disconnect message to the connection endpoint, where the disconnect message includes a predetermined handoff code. Responsive to receiving the disconnect message having the handoff code, the method sets forth storing a first set of call information for the first connection from the connection endpoint along with the client identifier value and broadcasting a user moved message from the first connection initiator, where the user moved message includes the client identifier value and a second set of call information for the first connection from the first connection initiator. The method also includes receiving the user moved message in a second connection initiator and, responsive thereto, storing the second set of call information included with the user moved message along with the client identifier value. The method then sets forth receiving a second connection request from the client at the second connection initiator, where the second connection request includes the client identifier value, retrieving the second set of call information using the identifier value for the client, and sending a handoff request message to the connection endpoint, where the handoff request message includes the client identifier value from the second connection request. Responsive to the handoff request message, the method calls for retrieving the first set of call information from using the identifier value for the client and establishing a second connection from the second connection initiator, where the second initiator uses the second set of call information, to the connection endpoint, where the connection endpoint uses the first set of call information.
An embodiment of a network communication system, according to the present invention, includes a first connection initiator device coupled to a network. The first connection initiator has a first network address and is configured to communicate with a mobile client broadcasting within a first service area of the first connection initiator. The first connection initiator is further configured to receive a first connection request from the mobile client that includes a client identifier value for the mobile client and, responsive to the first connection request, obtain a second network address corresponding to the client identifier value, and establish a first connection between the first and second network addresses. The first connection initiator is also configured to detect that the mobile client has left the first service area and, responsive thereto, transmit a disconnect message having a predetermined handoff code to the second network address and transmit a user moved message to a predetermined network broadcast address, where the user moved message includes a first set of call state information from the first connection initiator that pertains to the first connection. The network system also includes a connection endpoint device that is coupled to the network, has the second network address, and is configured to establish the first connection between the first and second network addresses. The connection endpoint is further configured to receive the disconnect message having the predetermined handoff code and, responsive thereto, store a second set of call state information from the connection endpoint that pertains to the first connection along with the client identifier value. The connection endpoint is still further configured to receive a handoff request message from a third network address, where the handoff request message contains the client identifier value, and, responsive thereto, retrieve the second set of call state information and establish a second connection between the second and third network addresses using the second set of call state information. And finally, the network system includes a second connection initiator device coupled to the network, having the third network address. The second connection initiator device is configured to receive the user moved message transmitted to the predetermined network broadcast address and store the first set of call state information along with the client identifier value. The second connection initiator is also configured to communicate with the mobile client broadcasting within a second service area of the second connection initiator and receive a second connection request from the mobile client that includes the client identifier value. Responsive to the second connection request, the second connection initiator is further configured to retrieve the first set of call state information, send the tunnel handoff request message to the second network address, and establish the second connection between the second and third network addresses using the first set of call state information.
The foregoing and other features and advantages of a preferred embodiment of the present invention will be more readily apparent from the following detailed description, which proceeds with references to the accompanying drawings.