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METHOD AND APPARATUS FOR
EXTENDING A MOBILE UNIT DATA PATH
BETWEEN ACCESS POINTS
CROSS-REFERENCE TO RELATED 5
APPLICATIONS
This application claims priority to U.S. Provisional Patent Application No. 60/619,346, filed Oct. 15, 2004, entitled Method and Apparatus To Improve The IEEE 802.xx Mobil- 10 ity Performance By Tunneling IEEE §802.xx Traffic From an Existing Access Point to a "New" Access Point, the content of which is hereby incorporated herein by reference.
BACKGROUND 15
1. Field
This application relates to wireless communications and, more particularly, to a method and apparatus for extending a mobile unit data path between access points in a wireless 20 network.
2. Description of the Related Art
Wireless networks generally include one or more access points located in an area to provide wireless services to mobile units with the area. Generally, a particular access point 25 will be selected to provide wireless service to a given mobile unit. The selection may be based on quality of signal, load at the access point, and a number of other factors. Once selected, the mobile unit will communicate through the access point to receive wireless communication services on the wireless net- 30 work. Although there are many different wireless protocols, the focus of this application will be on a protocol defined in the IEEE 802.11 standard.
As a mobile unit moves within a wireless network, it may move away from the access point that is providing it with 35 service and need to find a new access point with which it may connect. The process of changing associations from one access point to another access point is commonly referred to as a handover. A mobile unit may need to perform a handover in other situations as well, for example where the access 40 points are mobile, where an access point experiences failure, or in other situations where network conditions make it more desirable for a mobile unit to interface with a different access point.
When security is implemented on a wireless network, such 45 as when 802.1 li is implemented, the handover process may be relatively computationally intensive and require the mobile unit and access point to exchange many messages. Examples of the types of messages that may be exchanged include authentication request and response messages, reas- 50 sociation request and response messages, security handshake messages such as the four-way 802.1 li handshake or messages associated with the full authentication process specified in 802.1X. Additionally, the mobile unit and access point may exchange quality of service information such as the informa- 55 tion specified in 802.1 le (TSPEC), and optionally other messages. The processing associated with generating and responding to these messages may take a fair amount of time, which delays the handover between access points.
In addition to the messaging between the mobile unit and 60 the access point, additional exchanges also may be required in connection with the handover. For example, the access point may be required to exchange messages with a back-end Authentication Server (AS), policy server (PS) in 802.11 e, or other types of servers. The distance between the access point 65 and these servers, the speed of the back-end network, the number of exchanges that must take place, and the congestion
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at the servers, all may contribute to delaying handovers between access points. Where the mobile unit is actively receiving or transmitting data, such as in connection with Voice over Internet Protocol (VoIP) and audio or video streaming, a relatively long handover-induced delay may be unacceptable. Particularly in situations where a given mobile unit may need to handover between access points relatively frequently, the delays associated with performing handovers may become unacceptable.
One way to attempt to accelerate the handover process is to cause some information associated with the mobile unit to be stored at neighboring access points other than the access point that is currently handling communications for that mobile unit. If a handover to a neighboring access point is then required, the theory is that the access point will have already completed part of the handover process to thereby enable the handover to occur more quickly. While this may work in particular situations, it requires every mobile unit to be known on multiple access points. This requires access points that are not responsible for a given mobile unit to expend processor resources to begin the handover process, and to use up valuable memory space to store information about a mobile unit that may never become active on that access point.
SUMMARY OF THE DISCLOSURE
A method and apparatus for enabling the transfer of a mobile unit data path between access points in a wireless network
Fast transitions between access points in a wireless network may be accomplished by causing a tunnel to be established between an old access point and a new access point, and causing the data path between a mobile unit and the old access point to be extended through the data tunnel and the new access point. By allowing the data path to be extended through the new access point while leveraging the parameters of the association relationship established with the old access point, including for example security and quality of service, the data path to the mobile unit may remain open and communication with the mobile unit is not disrupted while transitioning between access points.
On the old access point, the data may be looped through the interfaces set up when the data path was initially established, so that the context associated with the data path does not need to be switched to enable the data to be tunneled across the network. Additionally, on the new access point, since the new access point is not responsible for security on the data path, the new access point may simply forward the data to the mobile unit without requiring the mobile unit to undergo authentication signaling. Thus, the transition between access points may be performed quickly to extend the data path through the new access point. Optionally, once the data path has been extended, the mobile unit and new access point may then engage in authentication and other messaging to formally affect a handover of the data path to the new access point.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
Aspects of the present invention are pointed out with particularity in the claims. The following drawings disclose one ormore embodiments forpurposes of illustration only andare not intended to limit the scope of the invention. In the follow3
ing drawings, like references indicate similar elements. For purposes of clarity, not every element may be labeled in every figure. In the figures:
FIGS. 1-3 are functional block diagrams of a communication network including a MU configured to roam between 5 access points according to an embodiment of the invention;
FIG. 4 is a flow diagram of a process of enabling the transfer of a mobile unit data path between access points in a wireless network according to an embodiment of the invention; 10
FIG. 5 shows one possible exchange of messages that may be used to transition access points according to an embodiment of the invention; and
FIG. 6 is a functional block diagram of an access point according to an embodiment of the invention. 15
DETAILED DESCRIPTION
The following detailed description sets forth numerous 2Q specific details to provide a thorough understanding of the invention. However, those skilled in the art will appreciate that the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, protocols, algorithms, and circuits have not ^ been described in detail so as not to obscure the invention.
FIG. 1 illustrates an example of a network 10 in which wireless access points 12 (12a, 12b) are configured to provide wireless service to mobile units 14. The access points may be connected to high bandwidth resources such as by intercon- 30 necting to a switch 16. The access points may also be directly interconnected if desired.
When a mobile unit 14 moves away from the access point that is providing it with wireless services (access point 12a), or when the access point moves away from the mobile unit, 35 the mobile unit may form a new association with a different access point (126) to continue receiving wireless services on the communication network. Since the process of reestablishing a connection between the mobile unit and a new access point 12b is relatively lengthy, according to an embodiment of 40 the invention as shown in FIG. 2, a fast transition may occur in which data 20 is tunneled over tunnel 18 from the first access point 12a to the second access point 12b, and relayed by the second access point 12b to the mobile unit 14 over tunnel 19 without having the mobile unit 14 go through the 45 whole authentication process with the second access point 12b. Thus, the established, secure data path between the mobile unit 14 and the old access point 12a is extended via tunnels 18 and 19 through the new access point 12b.
By causing the data path to be immediately extended 50 through the new access point 12b, the mobile unit may continue to use the secure data path established with the old access point while the transition from the first access point to the second access point occurs. Alternatively, it may be that the data is continued to be tunneled from the first access point 55 12a to the second access point 12b and a full handover between access points does not occur. Thus, in this alternative scenario, mobility between access points is accomplished without requiring handovers to occur or while allowing the handovers to occur less frequently. Where a handover is to 60 occur, as shown in FIG. 3, the mobile unit will go through the conventional authentication and authorization processes with the new access point 12b, and then a formal transfer of responsibility from the first access point to the second access point 12b will occur. When this happens, the tunnels 18 and 65 19 will be terminated and communication will occur directly between the new access point 12b and the mobile unit 14. At
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this point mobile unit 14 has reestablished a connection with the network 10 via new access point 12b.
Tunnels may extend between multiple access points as the mobile unit moves around the network and attaches to new access points. For example, if the mobile unit were to move to a third access point, a third tunnel may be established from the old access point 12a to the third access point (not shown). Thus, as the mobile unit moves on the network, new tunnels may be created between access points so that the data path may continue to follow the mobile unit on the network. Alternatively, the third access point may be configured to create a tunnel back to the second access point 12b, which has a tunnel to the first access point 12a.
FIG. 4 is a flow diagram of a process of enabling the transfer of a mobile unit data path between access points in a wireless network according to an embodiment of the invention. While particular messages may be described in connection with FIG. 4, the invention is not limited to this particular sequence of messages as other sequences may be used as well. Also, the messages in the following description have been given particular names for ease of reference. The names of the messages may change without departing from the scope of the invention.
As shown in FIG. 4, when a mobile unit switches from a first access point to a second access point, it may send a transition notification message to the old access point (100). This message is optional, since the mobile unit may not be able to communicate with the old access point. However, where possible, transmission of the message to the old access point may accelerate establishment of a tunnel from the old access point to the new access point. Additionally, this message may form a signal to the old access point that the old access point should stop sending data to the mobile unit and begin buffering that data.
Upon receipt of a transition notification message, the old access point 12a will suspend traffic forwarding and buffer the traffic for the mobile unit (110). By doing so, the old access point will save any traffic that is intended to be transmitted to the mobile unit until the tunnel is established so that the access point will not lose any data during the transition between access points.
The mobile unit will next send a transition tunnel request to the new access point 12b (120) to notify the new access point of its intention to extend an existing association with the old access point through the new access point and to inform the new access point of the identity of the old access point 12a. The new access point, upon receipt of this message, will establish a tunnel with the old access point 12a (130) and allow data to be transmitted via the tunnel from the old access point to the new access point and, via the new access point, to the mobile unit via a second tunnel. Specifically, as shown in FIG. 4, the new access point 12b receives MAC Protocol Data Units (MPDUs) from the old access point and encapsulates the mobile unit's MPDUs into a new 802.11 Management Frame (MF) for tunneled delivery to the mobile unit via tunnel 19. Similarly, data from the mobile unit may be transmitted over the second tunnel 19 from the mobile unit to the new access point and from there over the first tunnel 18 to the old access point. Although the MPDUs may be encapsulated into management frames on the second tunnel 19 from the new access point 12b to the mobile unit 14, the invention is not limited in this regard as the MPDUs may also be encapsulated into data frames for transmission over the tunnel 19, or alternately sent as regular, unencapsulated, data frames.
Until a reassociation occurs to transfer responsibility from the old access point 12a to the new access point 12b, MPDUs are tunneled from the old access point to the new access point
(140). Traffic may be tunneled indefinitely or reassociation may occur relatively quickly, depending on the particular circumstances. For example, access points may be mounted on the same rack of a telecommunications switching system with connections to local or remote antennas. In this instance, 5 it may not make sense to move the context of the session from a process associated with the first access point to a process associated with the second access point since the two access points exist within the same switching system unit, data closet, central office, orotherproviderfacilities. Additionally, 10 the access points may actually be virtual access points implemented as processes in the same network element which is in turn connected to the actual remote simple RF devices or antennas. In this instance, it may not make sense to cause a handover to occur and cause effort, time, and resources to be 15 expended to reauthenticate the mobile unit with the new virtual access point. Thus, tunneling of traffic between the access points may persist indefinitely.
Where transition from the first to the second access point is to be completed, once a new data path is set up between the 20 new access point 12b and the mobile unit, the tunnel 19 between the access point 12b and the mobile unit 14 and the tunnel 18 between the access points 12a, 12b will be terminated (150), and communication will commence over the new data path. 25
FIG. 5 illustrates an example exchange of messages that may occur to implement an embodiment of the invention. The invention is not limited to this particular exchange of messages, however, as many different types of messages may be used to set up a tunnel 18 between the old and new access 30 points, to set up a tunnel 19 between the new access point 12b and the mobile unit, and to cause data traffic to be delivered over the tunnels 18, 19. Similarly, additional messages may be used to carry additional pieces of information depending on the embodiment selected to implement the invention. The 35 invention will be described in the context of 802.11. The invention is not limited in this regard as embodiments of the invention may also be used in connection with other wireless protocols as well, such as 802.15 (commonly referred to as Bluetooth) and 802.16 or 802.16e (commonly referred to as 40 WiMax).
As shown in FIG. 5, initially data (500) from a source such as server 17 is passed over the communication network to the old access point 12a and received at the access point on an interface such as an 802.3 MAC. A distribution system (DS), 45 also referred to as a gate, in the old access point 12a is open to pass the data (502) received on the old access point 802.3 port to the old access point 802.11 MAC. The data (504) is transmitted from the old access point's 802.11 MAC to the mobile unit. In the reverse direction (not shown), the data from the 50 mobile unit follows the same path—from the mobile unit to the 802.11 MAC of the access point 12a, and out the 802.3 MAC of the old access point 12a onto the network 10.
When a mobile unit is to transition to a new access point 12b, it may optionally send a notification request (506) to the 55 old access point 12a. The notification request (506) may include the ID of the new access point 12b, to allow the old access point to learn the identity of the new access point. The notification request may optionally allow the old access point to suspend forwarding of data to the mobile unit and begin 60 buffering data for transmission to the mobile unit once the tunnel has been established.
The old access point 12a will generate a notification response (508) to indicate to the mobile unit that the notification request has been received. The notification request 65 (506) and response (508) are optional messages that may be used to notify the old access point that a transition will be
occurring to a new access point. These messages may be omitted if desired or if it is not possible for the mobile unit to transmit these messages due to signal conditions on the network. The notification request may be helpful to the old access point since it can be used by the old access point as an instruction to begin buffering MPDUs rather than transmitting them over the wireless network to the mobile unit.
The mobile unit will also initiate communications with the new access point 12b. In the embodiment shown in FIG. 5, the mobile unit is configured to start this process by sending a tunnel request (510) to the new access point 12b. The tunnel request (510) may be formatted according to the 802.11 protocol and will be received at the new access point's 802.11 MAC. The tunnel request (510) may be formatted to provide the new access point with the identity of the old access point and may contain other identifying information to enable the new access point to set up a tunnel with the old access point. For example, the tunnel request (510) may include mobile unit identifying information to enable the mobile unit to be identified to the old access point so that the old access point may determine whether communication should be provided over the tunnel with the new access point. The identifying information, in this instance, enables the old access point to ensure that the mobile unit is the same mobile unit that was previously communicating with the old access point so that the old access point is able to extend the secure channel to the same mobile unit across the new tunnel via the new access point. Additionally, encryption information may be included in the tunnel request to enable the participants to verify the mobile unit as the same mobile unit that was previously communicating with the old access point.
The new access point will interface with the old access point by sending an extend request message (512) to the old access point. The extend request message will identify the new access point and the mobile unit, and can contain any other information required to establish the tunnel between the two access points. Optionally, the tunnel between the access points may be secured, e.g. via a key exchange between the access points, although the invention is not limited in this manner. The tunnel may be extended directly between the access points or may pass through one or more intermediate network elements 16 on the communication network 10.
The old access point, upon receipt of the extend request message (512) will generate a extend response message (514) to indicate to the new access point whether the tunnel will be established. The extend response message (514) may contain whatever parameters are required to establish the tunnel between the access points. Optionally, the extend response message (514) may contain any MPDUs that have been buffered for the mobile unit by the old access point, although the invention is not limited in this regard as the buffered MPDUs may be transmitted separately at a later time once the tunnel is established.
Once the tunnel has been established, the new access point will generate and transmit a tunnel response message (516) to the mobile unit to let the mobile unit know that the tunnel has been successfully established, and that the mobile unit may communicate via the new access point 12b. Optionally, where MPDUs have been transmitted to the new access point 12b by the old access point 12a, the tunnel response message (516) may include MPDUs that have been received by the new access point for the mobile unit. After a successful request, the new access point will encapsulate tunneled data traffic from the old access point into 802.11 management frames, thereby creating a second tunnel 19 between the access point and mobile unit, and transmit the encapsulated frames to the mobile unit. As mentioned above, the MPDUs may also be
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