Abstract:
Disclosed herein are techniques by which a Layer-2 entity determines whether a mobile terminal requesting association or reassociation therewith determines whether the requesting mobile terminal shall continue using its current IP address or whether it requires a new IP address. The Layer-2 entity makes this determination based upon an examination of the contents of the association or reassociation request message received thereby. Contained in the association or reassociation reply message returned by the Layer-2 entity shall either be an instruction, to the mobile terminal, to continue using its current IP address or a new IP address to be used, by the mobile terminal in place of its current IP address.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   REFERENCE TO A MICROFICHE APPENDIX 
   Not applicable. 
   FIELD OF THE INVENTION 
   The invention is directed to wireless local area networks (“WLANs”) and, more particularly, to an address acquisition technique for use by mobile Layer-2 entities operating in WLANs. By encapsulating Internet protocol (“IP”) address assignments in 802.11 WLAN association services, mobile Layer-2 entities generate less network traffic and consume less power. 
   BACKGROUND OF THE INVENTION 
   In recent years, the number of mobile terminals, for example, laptop computers, digital cellular phones and personal digital assistants (“PDAs”) connected to the Internet has increased dramatically. Together with the increasing number of intelligent mobile terminals has come increased interest in the delivery of IP data and services to such devices. There are, however, certain problems when attempting to deliver IP data to mobile terminals. One problem relates to the current techniques used to assign IP addresses to mobile terminals. More specifically, the current IP address assignment procedure cannot determine whether or not a mobile terminal has roamed into a new domain. As a result, the current address assignment procedure requires that a mobile terminal must change its IP address every time it registers to a new access point (“AP”). In that a new IP address must be generated for a mobile terminal even if it has remained in the same IP domain, the aforementioned procedure represents an inefficient use of signaling resources. Furthermore, the need to repeatedly acquire new IP addresses results in increased power consumption by the mobile terminal. In turn, the increased power consumption will lead to shorter battery lifetimes and service access times for the mobile terminal. It is, therefore, the object of this invention to enhance the efficiency of the process by which an IP address is assigned to a mobile terminal. 
   SUMMARY OF THE INVENTION 
   In various embodiments thereof, the present invention is directed to a method for assigning an IP address to a mobile terminal upon entering a basic service area (“BSA”) served by a Layer-2 entity. In accordance with these methods, the Layer-2 entity determines, on behalf of the mobile terminal, whether the mobile terminal should continue using a current IP address or begin using a new IP address. If the Layer-2 entity determines that the mobile terminal should continue using the current IP address, the Layer-2 entity shall issue an instruction, to the mobile terminal, to continue using the current IP address. Conversely, if the Layer-2 entity determines that the mobile terminal should begin using a new IP address, the Layer-2 entity shall acquire the needed IP address from a Layer-3 entity. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  is a block diagram of a WLAN within which a mobile terminal may operate. 
       FIG. 2A  illustrates a frame body for an association request message suitable for use with a method of acquiring an IP address in accordance with the teachings of the present invention. 
       FIG. 2B  illustrates a frame body for an association response message suitable for use with the method of acquiring an IP address in accordance with the teachings of the present invention. 
       FIG. 2C  illustrates a frame body for a reassociation request message suitable for use with the method of acquiring an IP address in accordance with the teachings of the present invention. 
       FIGS. 2D-2E  illustrate a frame body for a reassociation response message in accordance with the teachings of the present invention. 
       FIG. 3  is a flowchart of a method for acquisition of an IP address by a mobile terminal. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1 , a WLAN  10  within which a mobile terminal  12  may operate will now be described in greater detail. As disclosed herein, the WLAN  10  is configured to comply with IEEE Standard 802.11. However, it is specifically contemplated that 802.11 non-compliant WLANs may also be suitable for the uses contemplated herein. The WLAN  10  is comprised of first and second IP domains  14  and  16 . Of course, it is fully contemplated that the WLAN  10  may instead be comprised of any number of IP domains and that the current disclosure of the WLAN  10  as being comprised of the first and second IP domains  14  and  16  is purely by way of example. An IP domain is a Layer-3 domain and may include any number of APs and basic service sets (“BSSs”). For example, the first IP domain  14  includes first, second and third APs  24 ,  26  and  28  and first, second and third BSSs  30 ,  32  and  34  coupled to the first, second and third APs  24 ,  26  and  28 , respectively. A BSS is a Layer-2 domain, the members of which may communicate within a geographical area known as a basic service area (“BSA”). Thus, the members of the first, second and third BSSs  30 ,  32  and  34  may communicate within first, second and third BSAs  31 ,  33  and  35 , respectively. Each IP domain is served by a single access router (“AR”). Again, for example, the first IP domain  14  is served by an AR  18  coupled to each of the first, second and third APs  24 ,  26  and  28 . 
   In contrast with the first IP domain  14 , the second IP domain  16  includes a single BSS  36 , the members of which may communicate within a BSA  37 . Accordingly, the second IP domain  16  is served by a single AP, which, since the second IP domain  16  includes only a single BSS  36  and a single AP, also serves as an AR, and is, therefore, known as a collocated AR/AP  20 . Finally, the AR  18  is coupled to the collocated AR/AP  20  by a distribution system  22 . Variously, the distribution system  22  may be a wireline distribution system, a wireless distribution system or a combination thereof. Of course, the AR  18  and the collocated AR/AP  20  need not be coupled to one another by the distribution system  22 , in which case the first IP domain  14  would define a first WLAN and the second IP domain would define a second WLAN. 
   When a mobile terminal, for example, mobile terminal  12 , enters the coverage area for an IEEE Standard 802.11 compliant WLAN, for example, the WLAN  10 , the mobile terminal is required to register with the AP serving the BSS for which the mobile terminal had entered the coverage area. For example, as illustrated in  FIG. 1 , the mobile terminal  12  has entered the BSA  31  and must, therefore, register with the AP  24  serving the BSS  30 . Similarly, when the mobile terminal  12  enters the coverage area for another BSS within the WLAN  10 , for example, when the mobile terminal  12  enters the BSA  33 , the mobile terminal  12  is required to register with the AP  26  serving the BSS  32 . 
   Association and reassociation are Layer-2 services, defined by IEEE Standard 802.11, used to register a mobile terminal with an AP. The association and reassociation services are managed by the AP using Layer-2 medium access control (“MAC”) addresses. As roaming between APs has traditionally been managed by Layer-2 protocols, when a mobile terminal associates with a new AP, the mobile terminal will not know if it has changed its IP domain. To solve this problem, in the past, the mobile terminal would be assigned a new IP address whenever the mobile terminal changes BSSs. This entailed signaling to the AR, the Layer-3 entity which processes all IP addressing procedures, even if the mobile terminal had not moved outside its original IP domain. In contrast with the foregoing technique, which required signaling to the Layer-3 entity in order for the mobile terminal to acquire a new IP address regardless of whether a change in IP domain had in fact occurred, the present invention is directed to a method for assigning an IP address to a mobile terminal in which a Layer-2 entity determines, on behalf of the mobile terminal, whether the mobile terminal may continue using a current IP address or must begin using a new IP address. By utilizing a Layer-2 entity to make such a determination on behalf of the mobile terminal, it is contemplated that signaling requirements between the various components of the WLAN shall be reduced. 
   While a full discussion of the standard is beyond the scope of the present application, in accordance with IEEE Std. 802.11, messages exchanged between the various components of the WLAN  10  are arranged in a pre-defined MAC frame format which may be best seen in  FIG. 2A . As may now be seen, a message frame  50  is comprised of a MAC header  52 , a frame body  54  and a frame check sequence (“FCS”)  56 . The MAC header  52  includes frame control, duration, address and sequence control information for the message frame  50 . As will be more fully described below, the contents of the frame body  52  varies depending on the particular type of message being carried in the message frame  52 . Finally, the FCS  56  contains an IEEE 32-bit cyclic redundancy code (“CRC”). 
     FIG. 2B  illustrates a frame body  60  for an association request message. An association request message is issued by a mobile terminal upon entering a BSA serviced by a new AP. As shown in  FIG. 2B , the frame body  60  for an association request message includes a capability information field  64 , a listen interval field  66 , a SSID field  68 , a supported rates field  70 , a mobile IP bit field  72  and a current IP address field  74 . The capability information field  64  contains a number of subfields that are used to indicate requested or advertised capabilities. Typically, the subfields included in the capability information field  64  are an extended service set (“ESS”) subfield, an independent basic service set (“IBSS”) subfield, a contention free (“CF”)-pollable subfield, a CF-poll request subfield and a privacy subfield. The listen interval field  66  is used to indicate, to the AP, how often a mobile terminal awakes to listen to Beacon management frames. The service set identity (“SSID”) field  68  indicates the identity of an ESS or an IBSS. The supported rates field  70  specifies the rates in the operational rate set as described in the MLME_Join.request and MLME_Start.request primitives. The mobile IP bit field  72  is a 1-bit field which is enabled if the mobile terminal is a mobile IPv4 client or a mobile IPv6 client. Conversely, the mobile IP bit field  72  is not enabled if the mobile terminal is an IPv4 client or an IPv6 client. Finally, the current IP address field  74  contains a current IP address for the mobile terminal requesting association. To support IPv6, it is contemplated that the current IP address field  74  must be 128-bits. 
     FIG. 2C  illustrates a frame body  76  for an association reply message. An association reply message is issued by an AP in response to receipt of an association request message issued by a mobile terminal. As shown in  FIG. 2C , the frame body  76  for an association message includes a capability information field  78 , a status code field  80 , an association ID field  82 , a supported rates field  84  and an IP address field  86 . The capability information and supported rates fields  78  and  84  were previously described. The status code field  80  indicates the success or failure of a requested operation. The association ID field  82  is a value assigned by an AP during association that represents the 16-bit ID of the mobile terminal requesting association. Finally, the IP address field  86  will either provide a new IP address for the mobile terminal requesting association or advise the mobile terminal requesting association to continue to use the current IP address. 
     FIG. 2D  illustrates a frame body  88  for a reassociation message. A reassociation message is issued by a mobile terminal during the transfer of an established association from one AP to either another AP or the same AP. As shown in  FIG. 2D , the frame body  88  for a reassociation message includes a capability information field  90 , a listen interval field  92 , a current AP address field  94 , a SSID field  98 , a supported rates field  98 , a mobile IP bit field  100  and a current IP address field  102 . The capability information, listen interval, SSID and supported rates fields  90 ,  92 ,  96  and  98  were previously described. The current AP address field  94  contains the MAC address of the AP with which the mobile terminal issuing the reassociation request is currently associated. The mobile IP bit field  100  is a 1-bit field which is enabled if the mobile terminal is a mobile IPv4 client or a mobile IPv6 client. Conversely, the mobile IP bit field  100  is not enabled if the mobile terminal is an IPv4 client or an IPv6 client. Finally, the current IP address field  102  contains a current IP address for the mobile terminal issuing the reassociation request. To support IPv6, the current IP address field  102  must be 128-bits. 
     FIG. 2E  illustrates a frame body  104  for a reassociation reply message. A reassociation reply message is issued by an AP in response to receipt of a reassociation request message issued by a mobile terminal. As shown in  FIG. 2E , the frame body  104  for a reassociation reply message includes a capability information field  106 , a status code field  108 , an association ID field  110 , a supported rates field  112  and an IP address field  114 . The capability information, status code, association ID and supported rates fields  106 ,  108   110  and  112  were previously described. The IP address field  114  will either provide a new IP address for the mobile terminal requesting reassociation or advise the mobile terminal requesting reassociation to continue to use the current IP address. 
   Referring next to  FIG. 3 , the method by which a mobile terminal, for example, the mobile terminal  12 , will either: (1) acquire a new IP address; or (2) receive instructions to continue using a current IP address; from a level- 2  entity, for example, the AP  24 , in accordance with the teachings of the present invention shall now be described in greater detail. In the description which immediately follows, it is presumed that the mobile terminal  12  is operating in an IPv4 environment. Subsequent passages, however, will address the operation of the mobile terminal  12  in other IP environments, for example, MIPv4, IPv6 or MIPv6. 
   The method commences at step  120  with the AP  24  having knowledge of its IP address, the mobile terminal  12  having knowledge of its IP address and the mobile terminal  12  initiating construction of either an association request message similar to that illustrated in  FIGS. 2A and 2B  or a reassociation request message similar to that illustrated in  FIGS. 2A and 2D . By constructing an association request message or a reassociation request message in accordance with the format previously described, the association request message or reassociation request message shall contain the IP address of the mobile terminal  12  in the current IP address field thereof while the mobile IP bit field will not be enabled. 
   The method then proceeds to step  122  where the mobile terminal  12  forwards the constructed association request message or reassociation request message to the AP  24 . Continuing on to step  124 , the AP  24  determines the current IP address of the mobile terminal  12  by checking the current IP address field  74  of the received association request message or the current IP address field  102  of the received reassociation request message. At step  126 , the AP  24  determines whether the mobile terminal  12  has roamed into a new IP domain. To do so, the AP  24  compares the current IP address of the mobile terminal  12  received as part of the association request message or reassociation request message to the IP address for the AP  24 . If the addresses match, the AP  24  determines that the mobile terminal  12  has stayed in its prior IP domain and that a new IP address is not necessary. Accordingly, the method will proceed to step  128  where the AP  24  generates an association response message similar to that illustrated in  FIGS. 2A and 2C  or a reassociation response message similar to that illustrated in  FIGS. 2A and 2E . In generating the association response message or the reassociation response message at step  128 , the AP  24  will insert a NULL into either the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message. Upon receiving the association response message or the reassociation response message, the mobile terminal  12  will examine the contents of the IP address field  86  or the IP address field  114  and, if the mobile terminal  12  detects a NULL inserted into the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message, the mobile terminal  12  will conclude that it has remained in its prior IP domain and that it may, therefore, continue using its current IP address. The mobile terminal  12  having determined, at step  128 , that it may continue to use its current IP address, the method would then end at step  130 . 
   Returning to step  126 , if, however, it is determined by the AP  24  that the current IP address of the mobile terminal  12  received as part of the association request message or reassociation request message does not match the IP address for the AP  24 , the AP  24  concludes that the mobile terminal  12  has changed IP domains and needs a new IP address. The method will then proceed to step  132  where the AP  24  acquires a new IP address for the mobile terminal  12 . To do so, the AP  24  will first check the mobile IP bit field  72  or  100  to determine if the mobile terminal is a mobile IPv4 client. As the mobile IP bit field  72  or  100  is not enabled, the mobile terminal  12  is operating in an IPv4 environment. Accordingly, in order to acquire a new IP address for the mobile terminal  12 , the AP  24  issues a request for a new IP address to the dynamic host configuration protocol (“DHCP”) server (not shown) which resides within the AR  18 , the level- 3  entity responsible for assigning IP addresses in IPv4. In turn, the DHCP server will issue a reply message to the AP  24  which contains a new IP address for the mobile terminal  12 . Upon receipt of the reply message from the DHCP server, the method proceeds to step  134  where AP  24  generates an association response message similar to that illustrated in  FIGS. 2A and 2C  or a reassociation response message similar to that illustrated in  FIGS. 2A and 2E . In generating the association response message or the reassociation response message at step  134 , the AP  24  will insert the IP address received from the DHCP server into either the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message. The AP  24  will then forward the association response message or the reassociation response message to the mobile terminal  12 . Upon examining the received association response message or reassociation response message and determining that an IP address was inserted into the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message, the mobile terminal  12  will determine that it has changed IP domains and must discontinue usage of its current IP address in favor of the IP address received in the association response message or reassociation response message. The mobile terminal  12  having commenced usage of the newly received IP address, the method would then end at step  130 . 
   The foregoing method will now be described again, this time presuming that the mobile terminal is operating in an MIPv4 environment in which IP addresses are assigned by a foreign agent (“FA”), typically a FA collocated with the AR for that IP domain, if the mobile terminal roams into the FA area. As before, the method commences at step  120  with the AP  24  having knowledge of its IP address, the mobile terminal  12  having knowledge of its IP address and the mobile terminal  12  initiating construction of either an association request message similar to that illustrated in  FIGS. 2A and 2B  or a reassociation request message similar to that illustrated in  FIGS. 2A and 2D . By constructing an association request message or a reassociation request message in accordance with the format previously described, the association request message or reassociation request message shall contain the IP address of the mobile terminal  12  in the current IP address field  74  or  102  thereof while the mobile IP bit field  72  or  100  will be enabled. 
   The method then proceeds to step  122  where the mobile terminal  12  forwards the constructed association request message or reassociation request message to the AP  24 . Continuing on to step  124 , the AP  24  determines the current IP address of the mobile terminal  12  by checking the current IP address field  74  of the received association request message or the current IP address field  102  of the received reassociation request message. At step  126 , the AP  24  determines whether the mobile terminal  12  has roamed into a new IP domain. To do so, the AP  24  compares the current IP address of the mobile terminal  12  received as part of the association request message or reassociation request message to the IP address for the AP  24 . If the addresses match, the AP  24  determines that the mobile terminal  12  has stayed in its prior IP domain and that a new IP address is not necessary. Accordingly, the method will proceed to step  128  where the AP  24  generates an association response message similar to that illustrated in  FIGS. 2A and 2C  or a reassociation response message similar to that illustrated in  FIGS. 2A and 2E . In generating the association response message or the reassociation response message at step  128 , the AP  24  will again insert a NULL into either the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message. Upon detecting the NULL inserted into the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message, the mobile terminal  12  will determine that it has remained in its prior IP domain and may continue to use its current, IP address. The mobile terminal  12  having determined, at step  128 , that it may continue to use its current IP address, the method would then end at step  130 . 
   Returning to step  126 , if, however, it is determined by the AP that the current IP address of the mobile terminal  12  received as part of the association request message or reassociation request message does not match the IP address for the AP  24 , the AP  24  determines that the mobile terminal  12  has changed IP domains and needs a new IP address. The method will then proceed to step  132  where the AP  24  acquires a new IP address for the mobile terminal  12 . To do so, the AP  24  will first check the mobile IP bit field  72  or  100  to determine if the mobile terminal is a mobile IPv4 client. As the mobile IP bit field  72  or  100  is enabled, the mobile terminal  12  is operating in an IPv4 environment. Accordingly, in order to acquire a new IP address for the mobile terminal  12 , the AP  24  issues a request for a new IP address to the FA—the Layer-3 entity responsible for assignment IP addresses in MIPv4—collocated with the AR  18 . In turn, the FA will issue a reply message to the AP  24  which contains the new IP address for the mobile terminal  12 . Upon receipt of the reply message from the FA, the method proceeds to step  134  where AP  24  designates the received IP address as a care-of-address (“CoA”) for the mobile terminal  12  and subsequently generates an association response message similar to that illustrated in  FIGS. 2A and 2C  or a reassociation response message similar to that illustrated in  FIGS. 2A and 2E . In generating the association response message or the reassociation response message at step  134 , the AP  24  will insert the CoA address received from the FA into either the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message. The AP  24  will then forward the association response message or the reassociation response message to the mobile terminal  12 . Upon examining the received association response message or reassociation response message and determining that an IP address was inserted into the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message, the mobile terminal  12  will determine that it has changed IP domains and must discontinue usage of its current IP address in favor of the IP address received in the association response message or reassociation response message. The mobile terminal  12  having commenced usage of the newly received IP address, the method would then end at step  130 . 
   The foregoing method will now be described yet again, this time presuming that the mobile terminal is operating in an IPv6 environment in which a mobile terminal would normally assign its own IP address using the domain prefix and its MAC address and then verify it using the duplicate address detection (“DAD”) procedure. Due to the “hidden mobile terminal” problem which exists in WLAN environments, however, mobile terminals have been unable to verify their IP address. As a result, in IPv6 environments, it has been necessary to turn off the mobile terminal&#39;s IP address autoconfiguration. However, the method described herein enables IP address acquisition in IPv6 without the need of the DAD procedure. As before, the method commences at step  120  with the AP  24  having knowledge of its IP address, the mobile terminal  12  having knowledge of its IP address and the mobile terminal  12  initiating construction of either an association request message similar to that illustrated in  FIGS. 2A and 2B  or a reassociation request message similar to that illustrated in  FIGS. 2A and 2D . By constructing an association request message or a reassociation request message in accordance with the format previously described, the association request message or reassociation request message shall contain the IP address of the mobile terminal  12  in the current IP address field  74  or  102  thereof while the mobile IP bit field  72  or  100  will not be enabled. 
   The method then proceeds to step  122  where the mobile terminal  12  forwards the constructed association request message or reassociation request message to the AP  24 . Continuing on to step  124 , the AP  24  determines the current IP address of the mobile terminal  12  by checking the current IP address field  74  of the received association request message or the current IP address field  102  of the received reassociation request message. At step  126 , the AP  24  determines whether the mobile terminal  12  has roamed into a new IP domain. To do so, the AP  24  compares the current IP address of the mobile terminal  12  received as part of the association request message or reassociation request message to the IP address for the AP  24 . If the addresses match, the AP  24  determines that the mobile terminal  12  has stayed in its prior IP domain and that a new IP address is not necessary. Accordingly, the method will proceed to step  128  where the AP  24  generates an association response message similar to that illustrated in  FIGS. 2A and 2C  or a reassociation response message similar to that illustrated in  FIGS. 2A and 2E . In generating the association response message or the reassociation response message at step  128 , the AP  24  will insert a NULL into either the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message. Upon detecting the NULL inserted into the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message, the mobile terminal  12  will determine that it has remained in its prior IP domain and may continue to use its current IP address. The mobile terminal  12  having determined, at step  128 , that it may continue to use its current IP address, the method would then end at step  130 . 
   Returning to step  126 , if, however, it is determined by the AP that the current IP address of the mobile terminal  12  received as part of the association request message or reassociation request message does not match the IP address for the AP  24 , the AP  24  determines that the mobile terminal  12  has changed IP domains and needs a new IP address. The method will then proceed to step  132  where the AP  24  sends the MAC address and the IP address for the mobile terminal to the AR  18 . In turn, the AR  18 , which maintains MAC address caches for neighboring APs (here, the APs  26  and  28 ) which, together with the AP  24 , collectively define the IP domain  14 , checks the MAC address caches for a duplicate of the received MAC address. If the AR  18  sees a duplicate of the MAC address of the mobile terminal  12  in the MAC address caches, the AR  18  refuses the association or reassociation request message of the mobile terminal  12 . If, however, there is no duplicate of the MAC address, then the association or reassociation request message will be accepted and the AR  18 /AP  24  shall assign a new IP address for the mobile terminal  12  in the manner set forth below. 
   If the mobile already has an IPv6 address, only the subnet prefix will be modified since it has changed its domain. If the mobile terminal  12  is receiving an address for the first time, then the IP address will be constructed using the subnet prefix and the mobile&#39;s 48-bit MAC address extended to a 64-bit EUI interface identifier as described in IETF&#39;s standard RFC 2373 and inserted into either the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message. The AP  24  will then forward the association response message or the reassociation response message to the mobile terminal  12 . Upon examining the received association response message or reassociation response message and determining that an IP address was inserted into the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message, the mobile terminal  12  will determine that it has changed IP domains and must discontinue usage of its current IP address in favor of the IP address received in the association response message or reassociation response message. The mobile terminal  12  having commenced usage of the newly received IP address, the method would then end at step  130 . 
   The foregoing method will now be described one last time, this time presuming that the mobile terminal is operating in a MIPv6 environment. Once again, the method commences at step  120  with the AP  24  having knowledge of its IP address, the mobile terminal  12  having knowledge of its IP address and the mobile terminal  12  constructing either an association request of a reassociation request message containing the IP address of the mobile terminal  12  in the current IP address field thereof and an enabled mobile IP bit. The method then proceeds to step  122  where the mobile terminal  12  forwards the constructed association request message or reassociation request message to the AP  24 . Continuing on to step  124 , the AP  24  determines the current IP address of the mobile terminal  12  by checking the current IP address field  74  of the received association request message or the current IP address field  102  of the received reassociation request message. 
   At step  126 , the AP  24  determines whether the mobile terminal  12  has roamed into a new IP domain. To do so, the AP  24  compares the current IP address of the mobile terminal  12  received as part of the association request message or reassociation request message to the IP address for the AP  24 . If the addresses match, the AP  24  determines that the mobile terminal  12  has stayed in its prior IP domain and that a new IP address is not necessary. Accordingly, the method will proceed to step  128  where the AP  24  generates an association response message or a reassociation response message. In generating the association response message or the reassociation response message at step  128 , the AP  24  will insert a NULL into either the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message. Upon detecting the NULL inserted into the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message, the mobile terminal  12  will determine that it has remained in its prior IP domain and may continue to use its current IP address. The mobile terminal  12  having determined, at step  128 , that it may continue to use its current IP address, the method would then end at step  130 . 
   Returning to step  126 , if, however, it is determined by the AP that the current IP address of the mobile terminal  12  received as part of the association request message or reassociation request message does not match the IP address for the AP  24 , the AP  24  determines that the mobile terminal  12  has changed IP domains and needs a new IP address. The method will then proceed to step  132  where the AP  24  sends the MAC address and the IP address for the mobile terminal to the AR  18 . In turn, the AR  18 , which maintains MAC address caches for neighboring APs (here, the APs  26  and  28 ) which, together with the AP  24 , collectively define the IP domain  14 , checks the MAC address caches for a duplicate of the received MAC address. If the AR  18  sees a duplicate of the MAC address of the mobile terminal  12  in the MAC address caches, the AR  18  refuses the association or reassociation request message of the mobile terminal  12 . If, however, there is no duplicate of the MAC address, then the association or reassociation request message will be accepted and the AR  18 /AP  24  shall assign a new IP address for the mobile terminal  12  in the manner set forth below. 
   If the mobile already has an IPv6 address, only the subnet prefix will be modified since it has changed its domain. If the mobile terminal  12  is receiving an address for the first time, then the IP address will be constructed using the subnet prefix and the mobile&#39;s 48-bit MAC address extended to a 64-bit EUI interface identifier as described in IETF&#39;s standard RFC 2373 and inserted into either the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message. The AP  24  will then forward the association response message or the reassociation response message to the mobile terminal  12 . Upon examining the received association response message or reassociation response message and determining that an IP address was inserted into the IP address field  86  of the association response message or the IP address field  114  of the reassociation response message, the mobile terminal  12  will determine that it has changed IP domains and must discontinue usage of its current IP address in favor of the IP address received in the association response message or reassociation response message. The mobile terminal  12  having commenced usage of the newly received IP address, the method would then end at step  130 . 
   Thus, there has been described and illustrated herein, an address acquisition technique in which IP address assignments are encapsulated into association and reassociation messages. By doing so, mobile Layer-2 entities generate less network traffic and consume less power than prior mobile Layer-2 entities. However, those skilled in the art should recognize that numerous modifications and variations may be made in the techniques disclosed herein without departing substantially from the spirit and scope of the invention. Accordingly, the scope of the invention should only be defined by the claims appended hereto.