Abstract:
A novel Medium Access Control (MAC) architecture for IEEE 802.11 wireless local area networks is disclosed. The illustrative embodiment partitions the medium access control into an Upper Medium Access Control for providing medium-access-control services that are independent of a Physical Control, and a Lower Medium Access Control for providing medium-access-control services that are dependent on the Physical Control. By partitioning the Medium Access Control in this manner, a single Upper Medium Access Control can be employed for any existing or future Physical Control while maintaining full compatibility with the huge installed base of existing IEEE 802.11 equipment. It will be clear to those skilled in the art how to make and use alternative embodiments of the present invention for networks that employ protocols other than IEEE 802. 11.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 60/377,679, filed May 3, 2002, entitled “Exposable Intra-MAC Interface For Wireless LANs,” (Attorney Docket: 680-038us), which is also incorporated by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to telecommunications in general, and, more particularly, to a novel medium access control architecture.  
         BACKGROUND OF THE INVENTION  
         [0003]    [0003]FIG. 1 depicts a schematic diagram of a wireless local area network in the prior art, which comprises: station  101 - 1 , station  101 - 2 , and station  101 - 3 . Before stations  101 - 1 ,  101 - 2 , and  101 - 3  can communicate with each other, there must be an agreement between the stations as to the meaning of the signals that they transmit. For example, the stations must agree on who talks when, what constitutes a “0” and a “1,” how is an error detected and corrected, etc. In the terminology of telecommunications, this agreement is called a protocol.  
           [0004]    In a local area network a communications channel is shared among the stations such that if two or more of the stations transmit messages simultaneously via the shared channel, the messages can become corrupted. Consequently, a local area network protocol must include a mechanism for ensuring that only one station at a time can transmit into the shared-communications channel. This mechanism, which is known as a Medium Access Control, might also provide additional services such as encryption, authentication, and quality of service (QoS) provisioning, as well as management of certain non-communication functions such as power conserving operational states.  
         SUMMARY OF THE INVENTION  
         [0005]    In wireless local area networks that conform to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, the Medium Access Control is theoretically decoupled from the mechanism for controlling the physical (i.e., radio) transmission and receipt of message signals (referred to throughout this specification as the “Physical Control”) but in practice the two are inextricably intertwined.  
           [0006]    The present invention enables the partial decoupling of the Medium Access Control from the Physical Control. This is especially advantageous for IEEE 802.11 wireless networks because it enables the standardization, development, and implementation of some of the medium-access-control services to be decoupled from the standardization, development, and implementation of the Physical Control, while maintaining full compatibility with the installed base of existing 802.11 equipment. This decoupling can result in the savings of tens or hundreds of millions of dollars to semiconductor, computer, and networking companies.  
           [0007]    In particular, the illustrative embodiment decouples some of the medium-access-control services from the Physical Control by bifurcating the Medium Access Control into (i) an Upper Medium Access Control that provides those medium-access-control services that are independent of the Physical Control, and (ii) a Lower Medium Access Control that provides those medium-access-control services that are dependent on the Physical Control.  
           [0008]    Although in this specification the illustrative embodiment is disclosed in the context of IEEE 802.11 local area networks, it will be clear to those skilled in the art how to make and use alternative embodiments of the present invention—including wireline networks and wireless networks—that employ protocols other than IEEE 802.11 (e.g., IEEE P802.15.3, etc.).  
           [0009]    The illustrative embodiment comprises: receiving a service data unit at an Upper Medium Access Control; and outputting a protocol data unit to a Lower Medium Access Control; wherein said protocol data unit is based on: (i) said service data unit, and (ii) a first medium-access-control service that is independent of the state of a Physical Control providing service to said Lower Medium Access Control; and wherein said Lower Medium Access Control provides a second medium-access-control service based on: (i) said protocol data unit, and (ii) the state of said Physical Control. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 depicts a schematic diagram of wireless local area network  100  in accordance with the prior art.  
         [0011]    [0011]FIG. 2 depicts a conceptual architectural diagram of wireless station  101 - i , as shown in FIG. 1, in accordance with the prior art.  
         [0012]    [0012]FIG. 3 depicts a conceptual architectural diagram of a wireless station in accordance with the illustrative embodiment of the present invention.  
         [0013]    [0013]FIG. 4 depicts a data-flow diagram of the illustrative embodiment of the present invention.  
         [0014]    [0014]FIG. 5 depicts a block diagram of the salient components of Upper Medium Access Control  310 , as shown in FIG. 3, in accordance with the illustrative embodiment of the present invention.  
         [0015]    [0015]FIG. 6 depicts a device/control mapping for a wireless station in accordance with the illustrative embodiment of the present invention.  
         [0016]    [0016]FIG. 7 depicts a block diagram of the salient components of Lower Medium Access Control  320 , as shown in FIG. 3, in accordance with the illustrative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]    [0017]FIG. 2 depicts a conceptual architectural diagram of wireless station  101 -i in accordance with the prior art. As shown in FIG. 2, wireless station  101 -i comprises Logical Link Control (LLC)  210 , Medium Access Control  220 , and Physical Control  230 , interconnected as shown.  
         [0018]    Logical Link Control (LLC)  210  performs a variety of tasks such as multiplexing of packets from and demultiplexing of packets to a plurality of network layer entities with transfer of said packets occurring over the single data link provided by the underlying MAC+physical layer, and the establishment and maintainence of logical point-to-point connections over the shared data link, and/or the provision of acknowledgements for individual messages, on behalf of those network protcols needing such connection-oriented or acknowledged conectionless services, as is well-known in the art.  
         [0019]    Medium Access Control  220  performs the channel access function, which ensures that only one station at a time can transmit signals onto the shared-communications channel, as well as frame addressing and detection, the generation and checking of frame check sequences, and LLC protocol data unit delimiting. In addition, Medium Access Control may provide additional services including encryption, authentication, and QoS provisioning, as well as related, non-communication functions such as power management, as is well-known in the art.  
         [0020]    Physical Control  230  administers the physical transmission of signals to other stations and the physical receipt of signals from other stations via the network medium (e.g., radio, Ethernet, etc.), as is well-known in the art.  
         [0021]    [0021]FIG. 3 depicts a conceptual architectural diagram of a wireless station in accordance with the illustrative embodiment of the present invention. As shown in FIG. 3, Medium Access Control  220  is partitioned into Upper Medium Access Control  310  and Lower Medium Access Control  320 . Upper Medium Access Control  310  provides a subset of medium-access-control services that are independent of Physical Control  230 , including transmit queueing, encryption, decryption, authentication, association, re-association, scanning, distribution, and traffic categorization (for the purposes of, for example but without limitation, quality-of-service (QoS) provisioning), as is well-known in the art. The Upper Medium Access Control may also perform those functions within MAC data service and MAC management service that are independent of Physical Control  230 , including power management, queue management, duplicate detection and filtering, fragmentation, defragmentation, queue management.  
         [0022]    Lower Medium Access Control  320  provides remaining medium-access-control services (i.e., those that are dependent on Physical Control  230 ), including channel access, receive validation (e.g., frame control sequence, forward error correction, etc.), and those that involve hard real-time functions and/or are physical layer-implementation dependent, such as response control (e.g., clear-to-send [CTS], acknowledgement [ACK], etc.), as are well-known in the art.  
         [0023]    There are four criteria for determining which functions belong to lower medium access control  320 :  
         [0024]    i. Functions that are specific to a given physical layer or given type of physical layer;  
         [0025]    ii. Functions that require knowledge of the internal state of the physical layer or knowledge of implementation-specific operational characteristics of the physical layer;  
         [0026]    iii. Hard real-time functions necessary to generate conformant communication (signaling) sequences as viewed on the (wireless) medium; and  
         [0027]    iv. Particular other functions that “belong” in the Lower Medium Access Control because of general implementation considerations, or because a party with sufficient clout (e.g., Microsoft, etc.) wants them to be there.  
         [0028]    As shown in FIG. 3, Upper Medium Access Control  310  outputs data to Lower Medium Access Control  320  via path  311 , and receives data from Lower Medium Access Control  320  via path  312 . Similarly, Lower Medium Access Control  320  outputs data to Physical Control  230  via path  221 , and receives data from Physical Control  230  via path  222 . In some embodiments these two, logical paths may be multiplexed onto a single electrical or optical interconnection.  
         [0029]    [0029]FIG. 4 depicts data-flow diagram  400  for the illustrative embodiment of the present invention. As shown in FIG. 4, Upper Medium Access Control  310  receives a service data unit (service data unit- 1 ) from Logical Link Control  210 ; performs the appropriate functions with respect to service data unit- 1  in accordance with the requested service (i.e., functions without hard real-time constraints and independent of Physical Control  230 ), as is well-understood in the art; generates a protocol data unit (protocol data unit- 1 ); and outputs protocol data unit- 1 , accompanied in some cases by control information (e.g. desired transmit data rate and/or modulation, packet lifetime or retry limits, transmission priority, etc.) to Lower Medium Access Control  320 . Lower Medium Access Control  320  receives protocol data unit- 1  as a service data unit (service data unit- 2 ); performs the appropriate functions with respect to service data unit- 2  in accordance with the requested service (i.e., functions with hard real-time constraints and/or dependent on Physical Control  230 ); generates protocol data unit protocol data unit- 2 ; and outputs protocol data unit- 2  and associated control information (e.g. channel selection, modulation type, preamble length, etc.) to Physical Control  230 .  
         [0030]    Physical Control  230  transmits an outgoing signal based on protocol data unit 2  and receives an incoming signal (e.g., acknowledgement [ACK], etc.), as is well-known in the art, and outputs data and reception status (e.g. received signal strength, signal quality, modulation utilized by sender, etc.) based on the incoming signal to Lower Medium Access Control  320 . Lower Medium Access Control  320  receives the outputted data from Physical Control  230  as protocol data unit protocol data unit- 3 ; performs the appropriate functions with respect to protocol data unit- 3  and associated reception status in accordance with the indicated service; generates service data unit service data unit- 3 ; and outputs service data unit- 3  to Upper Medium Access Control  310 . Upper Medium Access Control  310  receives service data unit- 3  from Lower Medium Access Control  320  as protocol data unit protocol data unit- 4 ; performs the appropriate functions with respect to protocol data unit- 4  in accordance with the indicated service; generates service data unit service data unit- 4 ; and outputs service data unit- 4  to Logical Link Control  210 .  
         [0031]    [0031]FIG. 5 depicts a block diagram of the salient components of Upper Medium Access Control  310  in accordance with the illustrative embodiment of the present invention. As depicted in FIG. 5, Upper Medium Access Control  310  comprises circuitry  510 , memory  520 , and circuitry  530 , interconnected as shown. It will be clear to those skilled in the art, after reading this specification, that in some alternative embodiments of the present invention, Upper Medium Access Control  310  is implemented either partially or entirely in software on a host computer&#39;s processor.  
         [0032]    Circuitry  510  comprises standard combinational digital logic and/or analog electronic elements, as is well-known in the art. Combinational digital logic of circuitry  510  writes to and reads from memory  520  in well-known fashion, thereby providing state-based services. Circuitry  510 , in accordance with data flow diagram  400 , receives data via input  211 , performs the appropriate functions without hard real-time constraints and independent of Physical Control  230 , and outputs data and control information to Lower Medium Access Control  320  via output  311 .  
         [0033]    Memory  520  is a random-access memory that stores data for circuitry  510  and circuitry  530 ; it will be clear to those skilled in the art how to make and use memory  520 .  
         [0034]    Circuitry  530  comprises standard combinational digital logic, which writes to and reads from memory  520  in well-known fashion, and/or analog electronic elements, as is well-known in the art. In accordance with data flow diagram  400 , circuitry  530  receives data and status from Lower Medium Access Control  320  via input  312 , performs the appropriate functions without hard real-time constraints and independent of Physical Control  230 , and outputs data to Logical Link Control  210  via output  212 .  
         [0035]    [0035]FIG. 6 depicts a device/control mapping for a wireless station  601 - i  in accordance with the illustrative embodiment of the present invention. As shown in FIG. 6, wireless station  601 - i  comprises microprocessor  602  for implementing the functions of Upper Medium Access Control  310  and Logical Link Control  210 . As will be clear to those skilled in the art, some other embodiments of the present invention might employ alternative device/control mappings (e.g., implementing Upper Medium Access Control  310  outside microprocessor  602 , etc.), and it will be clear to those skilled in the art how to make and use such embodiments.  
         [0036]    [0036]FIG. 7 depicts a block diagram of the salient components of Lower Medium Access Control  320  in accordance with the illustrative embodiment of the present invention. As depicted in FIG. 7, Lower Medium Access Control  320  comprises circuitry  710 , memory  720 , and circuitry  730 , interconnected as shown. It will be clear to those skilled in the art, after reading this specification, that in some alternative embodiments of the present invention, Lower Medium Access Control  320  is implemented either partially or entirely in firmware.  
         [0037]    Circuitry  710  comprises standard combinational digital logic and/or analog electronic elements, as is well-known in the art. Combinational digital logic of circuitry  710  writes to and reads from memory  720  in well-known fashion, thereby providing state-based services. Circuitry  710 , in accordance with data flow diagram  400 , receives data via input  411 , performs the appropriate functions dependent on Physical Control  230 , and outputs data to Physical Control  230  via output  221 .  
         [0038]    Memory  720  is a random-access memory that stores data for circuitry  710  and circuitry  730 ; it will be clear to those skilled in the art how to make and use memory  720 .  
         [0039]    Circuitry  730  comprises standard combinational digital logic, which writes to and reads from memory  720  in well-known fashion, and/or analog electronic elements, as is well-known in the art. In accordance with data flow diagram  400 , circuitry  730  receives data from Physical Control  230  via input  222 , performs the appropriate functions dependent on Physical Control  230 , and outputs data to Upper Medium Access Control  310  via output  312 .  
         [0040]    It is to be understood that the above-described embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by those skilled in the art without departing from the scope of the invention. It is therefore intended that such variations be included within the scope of the following claims and their equivalents.