Patent Publication Number: US-2007115883-A1

Title: Method for reducing hand-off latency in mobile networks

Description:
The present invention claims benefit of priority from U.S. Provisional Application No. 60/487,019 filed Jul. 14, 2003, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention concerns mobile networks and, in particular, a method for reduced latency network connection hand-offs.  
      In mobile networks, a mobile device such as a portable computer with a wireless local area network (WLAN) connection may connect to a network (e.g. the Internet) through a stationary access point. When the mobile device is moved, however, it may move to a location that is out of the range of its existing access point but within range of a new access point. Therefore, to prevent loss of connection to the network, the mobile device is “handed-off” from the old access point to the new. This hand-off occurs both on level  2  (i.e. the data link layer) and level  3  (i.e. the network layer) of the open system interconnect (OSI) network model. During the hand-off process, the mobile device may not be able to send and receive data packets until both the level  2  and level  3  connections are resolved with the new access point and router. This handoff latency is undesirable and may even prevent certain applications (e.g. voice over IP, streaming media, and real-time applications) from running due to the relatively long latency and consequent interruption of data flow between the mobile device and the network.  
      At level  2 , the mobile device probes the new access point to identify a channel that it may use to communicate with the access point. Typically, wireless channels correspond to predetermined frequency bands that are defined depending on the communications protocol being used (e.g., 802.11). Because a mobile device may try several channels before finding one on which it can communicate with the new access point, the latency due to establishing a level  2  connection alone may be as much as 400-500 ms.  
      Once a level  2  connection is established, the mobile device may then configure itself i.e., at the network level, level  3 ) with parameters appropriate for the new access router. This is typically done by having the mobile device send a router solicitation message in its new environment. When the router receives the router solicitation message, it responds with a router advertisement message. This message is not sent immediately upon receipt of the router solicitation message but is sent with a random delay to prevent flooding that may occur when multiple routers communicate on the same channel. The router solicitation message and router advertisement message are described in Internet Request for Comments (RFC) 2461 entitled “Neighbor Discovery for IP Version 6 (IPv6).” 
      As an alternative to sending a router solicitation message, the mobile device may wait to receive a router advertisement message which is transmitted periodically by the router via one or more access points. The minimum time between sending these periodic router advertisement messages, however, may be a few seconds. Thus, the total latency to establish a connection after a hand-off may be in the range of one to four seconds.  
      Decreasing the minimum time between periodically transmitted router advertisement messages may decrease this latency to a certain extent, but it may also undesirably increase the data traffic in the communication channel. This problem is most evident in “hot spots,” for example, airport terminals or other public venues where hand-off traffic is likely to be relatively significant. In addition, decreasing the time between router advertisement messages or between a router solicitation message and its corresponding router advertisement message leaves the network open to denial of service (DoS) attacks, in which a malicious mobile device floods the router with router solicitation messages.  
     SUMMARY OF THE INVENTION  
      The present invention is embodied in a method for expediting hand-off of mobile devices among access points and access routers. According to this method, a mobile device that moves from one access point to another periodically transmits information on the level  2  connection of its previous access point on the channel used to access its current access point. Devices connected to the current access point receive this message and can use this information to immediately establish a level  2  connection with the prior access point without probing when they move out of the current access points coverage area.  
      the present invention is also embodied in a method for expediting hand-off of mobile devices between access points. According to this method, a mobile device that moves from one access point to another periodically transmits information on the level  2  connection of its new access point on the channel used to access its prior access point. Devices connected to the prior access point receive this message and can use this information to immediately establish a level  2  connection with the new access point without probing when they move out of the coverage area of their access point.  
      According to another aspect of the invention, a first mobile device that is coupled to access router in a particular area maintains network layer connection information for access routers with which it has communicated. When a new mobile device enters the area, the first device detects the new device and transmits the list, enabling the new device to connect to an access router without transmitting a router solicitation message or receiving a router advertisement message.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:  
       FIG. 1  is a block diagram that illustrates an environment in which one embodiment present invention may be used;  
       FIG. 2  is a block diagram that illustrates an environment and scenario in which another embodiment of the present invention may be used;  
       FIG. 3  is a block diagram that illustrates an environment and scenario in which a further embodiment of the present invention may be used;  
       FIGS. 4A, 4B , and  4 C are exemplary priority lists of stored connection information according to an embodiment of the present invention;  
       FIGS. 5A and 5B  are flow-chart diagrams that are useful for describing the establishment of a level  2  connection according to one embodiment of the present invention;  
       FIGS. 6A and 6B  are flow-chart diagrams that are useful for describing the establishment of a level  2  connection according to another embodiment of the present invention; and  
       FIG. 7  is a flow-chart diagram that is useful for describing the establishment of a level  3  connection according to an embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      One embodiment of the present invention is a method by which mobile devices connected to a wireless network comprised of a plurality of wireless access points and routers may communicate and share channel and network connection information without depending on the network so as to reduce latency in the hand-off of one mobile device from a first wireless access point and/or router to another.  
      Referring now to the drawing, in which like reference numbers refer to like elements throughout the various figures that comprise the drawing,  FIG. 1  is a block diagram which illustrates an exemplary problem that may be addressed by one embodiment of the present invention.  FIG. 1  shows access point  100  having an antenna  102  and a portable computer (mobile device)  104  having an antenna  106 . Both the mobile device  104  and the access point  100  include hardware and software elements that implement a wireless local area network connection  107  between the two devices. In an exemplary embodiment of the invention, these may be, for example, circuitry and software that conform to the IEEE 802.11 wireless networking standard.  
      In the exemplary embodiment shown in  FIG. 1 , mobile device  104  has established the wireless connection  107  with the access point  100  and may be accessing a global information network (e.g. the Internet) through this connection. While the connection is established, mobile device  104  is moved as indicated by the arrow  105 . The mobile device in its moved position is indicated as  104 ′ and its antenna as  106 ′. In its new position, the device  104 ′ no longer has a reliable connection to the access point  100 . It is, however, within the coverage area of a second access point,  110 .  
      To continue the Internet session, the mobile device  104 ′ establishes a connection  109  with access point  110  through antenna  106 ′ and antenna  112 . As described above, the connection is established at both the data link level (level  2 ) with the access point and network level (level  3 ) with an access router, using the notation of the OSI model.  
      As described in an article by A. Mishra et al. entitled “An Empirical Analysis of the IEEE 802.11 MAC Layer Handoff Process,” establishment of a level  2  connection is typically performed by having the mobile device send probe messages to the new access point. Each probe message may, for example, be at a different frequency or according to a different channel protocol. When the mobile device receives a response to a probe message, it knows the channel information from the successful probe and, using this information, establishes a data link connection with the new access point. As described above, the time used in repeatedly probing the access point and responding to the probe may introduce an undesirable delay in the establishment of a new connection. This delay, combined with the delay in establishing a level  3  connection may result in a total delay of several seconds. A delay of this magnitude is at least an annoyance during an internet session and may result in undesirable performance of real-time and streaming applications.  
      In one embodiment of the present invention, an alternative to the method described above for establishing a level  2  connection may desirably reduce the delays in mobile device hand-off. Such an embodiment may be described with respect to the block diagram in  FIG. 2 , which illustrates mobile device D 1  connected to the wireless network through router  203  and access point  200  having antenna  202  and coverage range  201  (shown in phantom). Mobile device D 2  was previously connected to the wireless network through access point  200 , but is currently connected through router  213  and access point  210  having antenna  212  and coverage range  211  (shown in phantom). According to one embodiment of the invention, mobile device D 2  stores the level  2  connection information for the channel used in its connection to access point  200  and level  3  configuration information for router  203 . While connected to access point  210  and router  213 , mobile device D 2  may periodically transmit (shown as concentric circles in phantom) the stored level  2  connection information and level  3  configuration information through the channel used to connect to access point  210 . Those skilled in the art will recognize that mobile device D 2  is not restricted to being within coverage range  211  to do this. Accordingly, any mobile devices that are listening on or connected to the channel used to connect to access point  210  may detect and store the level  2  connection information and level  3  configuration information for the channel used to connect to access point  200 .  
      In an alternate embodiment, mobile device D 1  and mobile device D 2  may both be connected to access point  200 , where mobile device D 2  was previously connected to access point  210  and has, therefore, stored the connection information for access point  200 . While connected to access point  200  and router  203 , mobile device D 2  may then periodically transmit (shown as concentric circles in phantom) the connection information and router configuration information for its current connection to access point  200  and router  203  over the channel it previously used in its connection to access point  210 . Accordingly, any mobile devices that are on a connection with access point  210  (including mobile device D 1 ) may detect and store the connection information about access point  200  and configuration information for router  203 .  
      Therefore, if mobile device D 1  moves along path  2 B outside of the coverage range  201  of access point  200  to point B within the coverage range  211  of access point  210 , then mobile device D 1  will be able to immediately initiate a connection with access point  210  and router  213  using the stored level  2  connection information and level  3  configuration information.  
      In a further embodiment, once mobile device D 1  has made the new connection to access point  210  and router  213 , it may store and periodically transmit the connection information for access point  210  and configuration data for the router  213  over the channel used for its previous connection to access point  200 . Alternately, It may store and periodically transmit the connection information for access point  200  and configuration information for router  203  over the channel used for its current connection to access point  210 .  
      A mobile device may detect movement along path  2 B leading out of coverage range  201  of current access point  200  may be performed by monitoring the signal strength of communications with current access point  200 . If signal strength falls below a predetermined threshold value, then mobile device D 1  may attempt to initiate a connection with new access point  210  for a better signal. Movement outside of coverage range  201  may also be characterized by communications failure such as excessive communications timeouts and too many retries, for example. Those skilled in the art will recognize that there are other methods of detecting and characterizing signal failure as well.  
      Alternatively, or in addition, the access point may include global positioning system (GPS) data indicating its position and each mobile device may include a GPS receiver to continually calculate its position. The mobile device may then connect to the access point that is closest to it by analyzing its own position versus the position information received from the various access points. The GPS data may be monitored over time to determine a direction of travel for the mobile device. This direction may be used to identify a next access point if the mobile device includes stored data for more than one access point.  
      Additionally, there may exist regions where coverage range overlap may lead to mobile device D 1  attempting to switch back and forth repeatedly from access point  200  to access point  210 . One embodiment of the invention corrects this with any one of the many known methods of control systems hysteresis, such as the double-valued response used in a typical thermostat, for example.  
       FIG. 3  Is a block diagram that illustrates another exemplary implementation of the present invention. Mobile device D 2  is connected to the wireless network through router  213 , access point  310  having antenna  312  and coverage range  311  (shown in phantom). Mobile device D 1  was previously connected to the wireless network through router  213  and access point  310 , but is currently connected through access point  300  having antenna  302  and coverage range  301  (shown in phantom). Additionally, mobile device D 3  was also previously connected to the wireless network through router  213  access point  310 , but is currently connected through router  223  and access point  330  having antenna  322  and coverage range  321  (shown in phantom).  
      According to one embodiment of the invention, mobile devices D 1  and D 3  store the level  2  connection information for the channel used in their respective connections to access points  300  and  330  and configuration information for their respective routers  203  and  223 . While connected to access point  310 , mobile device D 1  may periodically transmit (as shown by concentric circles in phantom) this stored level  2  connection information and level  3  configuration data through its current channel. Those skilled in the art will recognize that mobile device D 1  is not restricted to being within coverage range  311  to do this. Mobile device D 3  performs in substantially the same way as described above, and, therefore, any mobile devices that are listening on or connected to the channel used to connect to access point  310  detect and store the level  2  connection information and level  3  configuration information for the respective channels used to connect to the access point  300  and router  203  and the access point  330  and router  223 .  
      In an alternate embodiment, mobile devices D 1 , D 2 , and D 3  may all be connected to router  213  and access point  310 , where mobile device D 1  was previously connected to router  203  and access point  300  and has stored the connection information for access point  300  and configuration data for router  203 . In this example, mobile device D 3  was previously connected to router  223  and access point  330  and has stored the connection information and configuration for the access point and router. While connected to access point  310 , mobile devices D 1  and D 3  may then periodically switch from the channel used in its connection to access point  310  to the channels used for their respective previous access points. With each periodic channel switch, mobile device D 2  may transmit (shown as concentric circles in phantom) the connection information and configuration data for their respective current connections to access point  310  and router  213  over the channels used in their previous connections to access points  300  and  320 . Accordingly, any mobile devices that are on a connection with access point  300  and  320  may detect and store the connection information and configuration data for access point  310  and router  213 .  
      Therefore, if mobile device D 2  moves along path  3 A outside of access point  310  coverage range  311  to point A within the coverage area of access point  300 , then it will be able to immediately initiate a connection with access point  300  and router  203  using the stored level  2  connection information and level  3  configuration data for such a connection. Similarly, if mobile device D 2  moves along path  3 B to point B, it may immediately initiate a connection with access point  330  and configure itself for router  223 .  
      In a further embodiment, once mobile device D 2  has made the new connection to one of access points  300  and  330  and one of the routers  203  and  223 , it may store and periodically transmit the level  2  connection information and level  3  configuration data for its new connection to one of access points  300  and  330  over the channel used for its previous connection to access point  310 . Alternately, it may store and periodically transmit the level  2  connection information for access point  310  and level  3  configuration data for router  213  over the channel used for its new connection to one of access points  300  and  330 .  
      In  FIG. 3 , movement of mobile device D 2  along one of paths  3 A and  3 B may result in a loss of or at least a weaker signal between mobile device D 2  and access point  310 . Consequently, mobile device D 2  may initiate a new connection with one of access points  300  and  330  in order to obtain a stronger connection.  
      Mobile device D 2  may detect its movement and consequent loss of signal strength along one of paths  3 A and  3 B leading out of coverage range  311  of current access point  310  by monitoring the strength of its communications signal with current access point  310 . If signal strength falls below a predetermined threshold value, then mobile device D 2  may attempt to initiate a connection with one of access points  300  and  330  for a better signal as described above. Movement outside of coverage range  311  may also be characterized by communications failure such as excessive communications timeouts and too many retries, for example. Those skilled in the art will recognize that there are other methods of detecting and characterizing signal failure as well.  
      Additionally, there may exist regions where coverage range overlap may lead to mobile device D 2  attempting to switch back and forth repeatedly between access point  311  and one of access points  300  and  330 . One embodiment of the invention may address this problem by implementing a detection of mobile device movement protocol including any one of the many known methods of control systems hysteresis, such as the double-valued response used in a typical thermostat, for example.  
      In one embodiment of the invention, mobile device D 2  may determine which one of access points  300  and  330  to attempt to connect to first by maintaining a priority list of stored level  2  connection information and level  3  configuration data, and initiating a connection to the access point with the highest priority. According to separate exemplary embodiments of the invention, FIGS.  4 A-C illustrate priority lists that may be used. In one embodiment, the table keeps a list of priorities from 1 st  to n th  in order of the last received transmission. In  FIG. 4A , for example, the last received (i.e., newest) transmission is about an access point designated as access point  1  (AP  1 ), which is given 1 st  priority in the list; the second to last transmission is about access point  4  (AP  4 ), which is designated as having 2 nd  priority; and the oldest transmission is about access point x (AP x), which is designated as having nth priority, where “n” can be any desirable number of priorities. Although illustrated as having at least 3 priority levels, the priority list may also be only a single level deep.  
      Alternatively or in addition, the priority list may be maintained based on the relative positions of the mobile device and the access points, based on their GPS data. In this exemplary embodiment the mobile device may continually recalculate its position using GPS data received from its GPS receiver (not shown) and, at the same time, recalculate the respective distances to the stored access points. In this embodiment, the closest access point at any given time would have the highest priority.  
      In a further embodiment of the invention, the table keeps a list of priorities from 1 st  to n th  in order of the total number of transmissions received starting from any predetermined moment in time. In  FIG. 4B , for example, connection information for access point  7  has been received 555 times, which is the most of any other access point. Consequently, access point  7  is given 1 st  priority on the list. The second highest number of received transmission have been directed to connection information for access point  9 , which is therefore given 2nd priority, and so on.  
      In yet another embodiment, the table keeps a list of averages or weighted averages from 1st to n th  priority in order of descending average. The average may be the number of transmissions of connection information received for a particular access point over a predetermined length of time, for example; it may also be the average signal strength of such transmissions received over a predetermined length of time; alternatively it may be a weighted product of the total number of such transmissions received and the average signal strength. In  FIG. 4C , for example, connection information for access point  5  has the a priority average of 55, which is the most of any other access point and may indicate that connection information for access point  5  was received 55 times in the last minute, for example. Consequently, access point  5  is given 1st priority on the list. Access point  22  has a priority average of 40, for example, and is therefore given 2 nd  priority, and so on. Those skilled in the art will recognize that there may be many desirable implementations of the average calculation as one of many possible equations, formulae, or algorithms that provide an indication of preference or priority, without departing from the spirit of the invention.  
      As described above, when a loss of signal strength is detected, a mobile device may initiate an attempt to connect to the access point whose connection information is stored at the top of the priority list. If the attempt to connect fails, then the mobile device may attempt to connect to the next device in the priority list, and may continue down the list until a desirable connection is established.  
      In an alternate embodiment, a mobile device that periodically transmits channel information for a connection to an access point and configuration data for a corresponding router may transmit the channel information and configuration data corresponding to the access point designated as having a first priority.  
      In another embodiment of the invention, mobile devices that periodically transmit channel information and configuration data for a connection to an access point and router may vary the power of their transmission, thereby making the transmission more locality specific. The power may be varied based on the known wireless transmitter parameters in order to obtain larger or smaller coverage ranges of the transmission as desired. Described with reference to  FIG. 3 , for example, it can be seen that if mobile device D 2  were moving along path  3 A, then it may be desirable to give 1 st  priority to connection information for access point  300 . By having mobile devices D 1  and D 3  lower the power of their transmissions, then mobile device D 2  moving along path  3 A, which is closer to mobile device D 1 , will receive stronger transmission from device D 1  than device D 3  (or may not receive the transmission from D 3  at all). Accordingly, the priority list will designate connection information for access point  300  as having 1 st  priority. Similarly, mobile device D 2  moving along path  3 B would have a priority list designating connection information for access point  330  as having 1 st  priority. In this way, devices moving through the network are able to be kept substantially aware of their topology, whereby a more desirable priority list is maintained, allowing lower latency hand-offs.  
      It can be seen by those skilled in the art that in a system with a large number of mobile devices, signal collision and interference may introduce undesirable communications quality. Accordingly, collisions and interference may be addressed by the use of a known protocol such as the IEEE 802.11 Medium Access Control (MAC) protocol, which has built in controls to limit or prevent collisions and device interference. Such protocols may the implement Carrier Sense Multiple Access (CSMA) contention protocol or a variation thereof, for example.  
       FIGS. 5A and 5B  are flowcharts illustrating two embodiments of the present invention for establishing a level  2  connection that may greatly reduce hand-off latency. According to this method, each mobile device has limited communication directly with neighboring mobile devices. At step  410 , the mobile device monitors its current channel for new channel information (i.e. data link level connection information) sent by neighboring devices. When new channel information is received, the mobile device stores the information at step  412 . With reference to the block diagram of  FIG. 1 , in this step, mobile device  104  is monitoring the channel  107  that it has established with access point  100  for messages from another mobile device (not shown) that was previously connected to access point  110  but is now connected to access point  100 . This other mobile device sends the data link layer information on a connection to access point  110  in the channel that it is currently using to communicate with access point  100 .  
      At step  414 , the mobile device detects movement. This may occur, for example, when the mobile device  104 ′ experiences a power reduction in its connection with access point  100 . If movement is not detected at step  414 , the device, if it previously moved from another access point, periodically transmits stored channel information for its prior channel over its current channel communications link, at step  415 , and then transfers control to step  410 , described above.  
      When movement is detected, however, control transfers to step  416 , at which the stored information needed to establish a level  2  connection to access point  110  is retrieved. At step  418 , this information is used to establish the data link connection between the mobile device  104 ′ and the access point  110 . After step  418 , control returns to step  410  which now monitors the newly established channel for channel information from neighboring devices.  
      The method described above assumes that there is already a neighboring device that has moved from having a connection with access point  110  to having a connection with access point  100 . If, however, there is no other mobile device when mobile device  104  moves, the steps shown in  FIG. 5B  are executed. At step  420 , mobile device  104 ′ probes access point  110 , as described above to find a new channel. At step  422 , device  104 ′ establishes connection  109  with access point  110 . Device  104 ′ then stores the connection information for the new channel at step  424  and, at step  426 , periodically transmits the new channel information to neighboring devices, using channel  109 . In this way, other mobile devices (not shown) that are currently communicating with access point  110  can learn how to connect to access point  100  before they need to make the connection.  
       FIGS. 6A and 6B  are flowcharts illustrating two alternative embodiments of the present invention for establishing a level  2  connection. This method operates similarly to the method described above with reference to  FIGS. 5A and 5B  except that the mobile device, upon establishing communications with its new access point periodically transmits the connection information for the new access point using the channel from its previous access point. With reference to the block diagram of  FIG. 1 , in this step, mobile device  104  is monitoring the channel  107  that it has established with access point  100  for messages from another mobile device (not shown) that has already connected to access point  110 . This other mobile device sends the data link layer information on a connection to access point  110  in a channel used to communicate with access point  100  if found, this data is stored at step  432 .  
      At step  434 , the mobile device detects movement. This may occur, for example, when the mobile device  104 ′ experiences a power reduction in its connection with access point  100 . If movement is not detected at step  434 , the device, if it previously moved from another access point, periodically transmits stored channel information about its new channel over its prior channel communications link, at step  435 , and then transfers control to step  430 , described above.  
      When movement is detected, however, control transfers to step  436 , at which the stored information needed to establish a level  2  connection to access point  110  is retrieved. At step  438 , this information is used to establish the data link connection between the mobile device  104 ′ and the access point  110 . After step  438 , control returns to step  430  which now monitors the newly established channel for channel information from neighboring devices.  
      The method described above assumes that there is already a neighboring device that has moved from having a connection with access point  100  to having a connection with access point  110 . If, however, there is no other mobile device when mobile device  104  moves, the steps shown in  FIG. 6B  are executed. At step  440 , mobile device  104 ′ probes access point  110 , as described above to find a new channel. At step  442 , device  104 ′ establishes connection  109  with access point  110 . Device  104 ′ then stores the connection information for the new channel at step  444  and, at step  446 , periodically transmits the new channel information to neighboring devices, using channel  107 . In this way, other mobile devices (not shown) that are currently communicating with access point  100  can learn how to connect to access point  110  before they need to make the connection.  
      In an alternate embodiment, device  104 ′ may store and periodically both transmit channel information for access point  100  over channel  109  and channel information for access point  110  over channel  107 . Accordingly, when devices move, they can make the connection quickly using the stored parameters, as described above.  
       FIG. 7  illustrates another aspect of the invention; the establishment of a network layer or level  3  connection. The method shown in  FIG. 7  may be used together with or separate from the methods described previously. At step  510 , mobile device  104 ′ has just moved and has established a level  2  connection with access point  110 , for example, by any of the methods described previously or shown in  FIGS. 5A, 5B ,  6 A or  6 B or by any other conventional method. Next, at step  512 , mobile device  104 ′ determines if it has received router configuration data from another mobile device (not shown). If it has received the configuration data then, at step  514 , mobile device  104 ′ checks the validity of the data, for example, by determining the validity of security credentials received with the data. If the data is valid the process stores the data at step  516  and establishes the level  3  connection at step  518  using the stored data. The mobile device may then immediately begin its application thread using this connection. If at step  512  the mobile device  104 ′ had not received router configuration data from a peer or if at step  514  the received data was found to be invalid then control is transferred to step  520  to send a router solicitation message.  
      After step  518 , even though the level  3  connection has been established, the exemplary algorithm may branch to step  520  to send a router solicitation information. This optional step, and optional steps  522 ,  524 ,  526  and  530  may be done to ensure that any bad configuration data transmitted by a malicious peer is used only for a short time. After sending the router solicitation message, the connection thread of the mobile device  104 ′ waits at step  522  for router advertisement data. When the router advertisement data is received, it is checked, at step  524 , against the data that was stored at step  516  (if any such data was stored). If the router advertisement data matches the stored data at step  524 , control transfers to step  532 , described below.  
      If, however, the data received at step  522  does not match the stored data then the new data is stored at step  526 , replacing any configuration data that was received from the peer at step  512 . After step  526 , the process, at step  530  establishes a new level  3  connection using the received advertisement data.  
      At step  532 , mobile device  104 ′ enters a loop in which it listens for any new devices establishing a level  2  connection with access point  110  and, when such a connection is detected, at step  534 , device  104 ′ sends the stored router advertisement data. In the flow-chart diagram of  FIG. 6 , it is the data transmitted at step  624  by the other mobile device (not shown) that is received by the mobile device  104 ′ at step  612 .  
      Upon detecting the level  2  connection at step  532 , mobile device  104 ′ may wait a random amount of time before sending the router configuration data while monitoring the transmission channel. This random time interval avoids conflicts with transmissions by other mobile devices. If another mobile device (not shown) sends the router configuration data during this interval or if the router sends its router advertisement data, mobile device  104 ′ may abort its transmission. Additionally, access point  110  may designate one of one or more mobile devices on the network as being responsible for detecting level  2  connections at step  532  and transmitting the router configuration data in step  534 . In such an embodiment, therefore, the random delay may be omitted, since there will only be one designated device responsible for transmitting router configuration data.  
      In one embodiment of the invention, level  2  and  3  connections and connection information conform to the IEEE 802.11 standard, whereby when a mobile device successfully initiates a level  2  connection with an access point, the mobile device attempts to authenticate/associate the access point. A request for authentication is sent from the mobile device to the access point, which replies with an association response. The association response sent by the access point is seen by all other mobile devices on the network, constituting the level  2  detection of step  522 .  
      Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.