Patent Publication Number: US-2005135239-A1

Title: Autonomic optimization of wireless local area networks via protocol concentration

Description:
BACKGROUND OF THE INVENTION  
      This invention pertains to wireless networking systems and, more particularly, to a wireless network access point which optimizes wireless local area network traffic by concentrating access point traffic toward a single protocol.  
      Within the past two decades, the development of raw computing power coupled with the proliferation of computer devices has grown at exponential rates. This phenomenal growth, along with the advent of the Internet, has led to a new age of accessibility to other people, other systems, and to information.  
      The simultaneous explosion of information and integration of technology into everyday life has brought on new demands for how people manage and maintain computer systems. The demand for information technology professionals is already outpacing supply when it comes to finding support for someone to manage complex, and even simple computer systems. As access to information becomes omnipresent through personal computers, hand-held devices, and wireless devices, the stability of current infrastructure, systems, and data is at an increasingly greater risk to suffer outages. This increasing complexity, in conjunction with a shortage of skilled information technology professionals, points towards an inevitable need to automate many of the functions associated with computing today.  
      Autonomic computing is one proposal to solve this technological challenge. Autonomic computing is a concept to build a system that regulates itself much in the same way that a person&#39;s autonomic nervous system regulates and protects the person&#39;s body.  
      Within the past decade, there has been accelerated growth in portable computing to meet the demands of a mobile workforce. This voluminous mobile workforce has traditionally relied on a cable connection to a backbone network in order to have access to resources such as printers, e-mail servers, databases, storage, and even Internet connections. Within the past few years alone, the industry has seen rapid deployment of wireless local area networks which offer increased convenience over cable connections to backbone networks. In addition to convenience, wireless networks offer the ability to roam while maintaining a network connection.  
      Recently, a standard for wireless local area networks known as the IEEE 802.11 standard has been adopted and has gained acceptance among the industrial, scientific and medical communities. The IEEE 802.11 standard for wireless networks is a standard for systems that operate in the 2,400-2,483.5 MHz industrial, scientific and medical (ISM) band. The ISM band is available worldwide and allows unlicensed operation of spread spectrum systems. The IEEE 802.11 RF transmissions use multiple signaling schemes (modulations) at different data rates to deliver a single data packet between wireless systems.  
      In a wireless local area network, wireless clients obtain access to resources on the backbone network through the use of an access point. The backbone network is typically on a wired network, such as ethernet, but can also be a second wireless network or any combination thereof. When an access point provides connectivity to resources directly on a wired network, the access point will contain, amongst other things, a wired LAN interface, a bridge function, and a wireless LAN interface in order to bridge traffic between the wireless network and the wired network.  
      Most installations use wireless local area networks as an overlay to an existing ethernet (cabled or wired) network which serves as a backbone or provides access to a backbone and its resources. Typically, access points are provided at various locations to create continuous geographical coverage for the wireless network. Since 802.11 is limited to 30 meters in range and Ethernet is physically limited to 100 meters in length, office environments typically deploy several access points on different backbones. The various wireless access points are assigned to different wireless frequency spectra or channels to allow overlap between wireless ranges.  
      802.11b is a popular IEEE wireless networking standard that has emerged and provides the aforementioned advantages. The new standard, 802.11g, is emerging which provides the advantages of 802.11b at a higher throughput which is on the order of ethernet wired local area network speed. As currently defined, 802.11g networks are backward compatible to 802.11b networks.  
      A problem exists, however, in that 802.11b traffic severely impacts 802.11g performance. 802.11b impacts performance of an 802.11g network because 802.11b clients are not able to recognize 802.11g traffic which follows the standard CSMA/CA physical carrier-sense protocol to avoid collisions. To subjugate this limitation, 802.11b clients must utilize a request to send (RTS)/clear to send (CTS) virtual carrier-sense protocol to avoid collisions and to gain access to the channel for transmission. With only a few 802.11b users on an access point that supports both 802.11g and 802.11b traffic, overall throughput degrades such that any performance benefit of 802.11g disappears. A challenge found, however, is in mitigating the impact introduced to one protocol from another protocol on the same access point according to autonomic computing principles.  
     SUMMARY of the INVENTION  
      It has been discovered that the aforementioned challenges are resolved by identifying which of two or more protocols the client conforms to. When it is determined that the client initiating a first association request conforms to a first protocol, the association of that client is deferred. That client will tend to seek access to the backbone network through association with another access point.  
      However, should a second association request be received by the client conforming to the first protocol whose first association request has been deferred, the client is associated in response to the second association request. As a result of deferring the association, the client may find an alternative access point. Thus, impact introduced to one protocol from another protocol on the same access point is minimized. Simultaneously, clients conforming to the first protocol which have no other access points available are eventually associated regardless.  
      In a specific embodiment, the interval between the first association request and the second association request by the client is taken into account. 
    
    
     BRIEF DESCRIPTION of the DRAWINGS  
      Some of the purposes of the invention having been stated, others will appear as the description proceeds, when taken in connection with the accompanying drawings, in which:  
       FIG. 1  depicts a scenario in which the concepts of the present invention are advantageous;  
       FIG. 2  is a block diagram of an access point configured according to an embodiment of present invention;  
       FIG. 3  is a block diagram of a client configured according to an embodiment of the present invention;  
       FIG. 4  is a flow diagram depicting the logic exercised by the client of  FIG. 3  in maintaining and/or establishing association with the access point of  FIG. 2 ;  
       FIG. 5  is an illustration of the type of table that is maintained according to one embodiment of the present invention; and  
       FIG. 6  is a flow diagram showing the logic exercised by the access point of  FIG. 2  according to an embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION of the ILLUSTRATIVE EMBODIMENTS  
      While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the present invention is shown, it is to be understood at the outset of the description which follows that persons of skill in the appropriate arts may modify the invention here described while still achieving the favorable results of this invention. Accordingly, the description which follows is to be understood as being a broad, teaching disclosure directed to persons of skill in the appropriate arts, and not as limiting upon the present invention.  
      Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in a specific embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.  
      Referring now more particularly to the accompanying drawings,  FIG. 1  depicts a scenario in which the concepts of the present invention are advantageous. Installation  100  consists of two access points  106  and  102  each having roughly circular geographical areas of coverage  108  and  104  respectively. Access points provide access to distributed resources and services via wireless medium for associated wireless clients or stations. Preferably, access points  106  and  102  contain IEEE 802.11 medium access control functionality and physical layer interface to the wireless medium. Wireless clients  114  and  118  are used here to represent a variety of wireless clients throughout installation  100 . The wireless clients  114  and  118  are typically and preferably mobile computing units such as laptops and palmtops. As mobile units, clients  114  and  118  typically would not have printing capabilities nor other resources which would require hardware too large to hand carry. Such printing capabilities and other resources are found on backbone networks  110  and  112  which are coupled, according to installation  100 , to two access points  106  and  102  respectively. Access points  106  and  102 , in turn, provide the resources and services of the backbone network on to the wireless network in order to make the resources and services available to the wireless clients  114  and  118 .  
      Backbone networks  110  and  112  provide installation  100  with the distributed resources and services. The resources and services include but are not limited to print servers and printers, e-mail servers, fax servers, database servers, and Internet access. Backbone networks  110  and  112  are preferably ethernet local area networks, optionally however, connections  110  and  112  can be wireless or optical distribution schemes to the same resources and services. In addition, backbone connections  110  and  112  can be bridge connections which in turn provide the resources and services of the backbone network.  
      Wireless clients  114  and  118  and are able to be configured in ad hoc mode and thereby engage in direct peer-to-peer data transfers and sharing of each other&#39;s resources when their respective signal strengths allow for direct connection. Otherwise, clients  114  and  118  are able reach each other through the backbone networks  110  and  112 ; in which case, their communications would be through the access points to which they are associated.  
       FIG. 2  is a block diagram of an access point configured according to an embodiment of present invention. Access point  200  includes wireless LAN interface  222 , a bridge FIFO or flow controller  202 , and a LAN interface  212 . Wireless interface  222  can be any wireless interface using any wireless medium such as RF, infrared, VHF, UHF, and microwave. However, in the preferred embodiment, wireless LAN interface  222  is implemented as an 802.11compliant wireless local area network interface. LAN interface  212  can be a wired land-based network interface, an optical network interface such as a fiber-optic network interface, or even a second wireless network interface. However, in the preferred embodiment, LAN interface  212  is implemented as an interface for an ethernet land-based network. LAN interface  212  typically connects to or bridges to a backbone network which provides resources and services. Wireless LAN interface  222  provides the resources and services found on the backbone network to wireless clients which are associated to wireless LAN interface  222 .  
      The term—association—as used herein refers to that service which is used to establish access point to client mapping and enable client invocation of the resources and services found on the backbone network.  
      Bridge FIFO/flow controller  202  bridges and controls the flow of traffic between wireless clients coupled through wireless LAN interface  222  and the backbone network coupled to LAN interface  212 . Flow controller  202  maintains a FIFO buffer for bidirectional traffic between interfaces  222  and  212 . Flow controller  202  can be implemented entirely in hardware, or partially in hardware and partially in software/firmware. In the preferred embodiment as shown in  FIG. 2  however, flow controller  202  is implemented with a microprocessor  210  having program storage  208  which stores boot code and microcode for execution on a microprocessor  210 . The boot code is typically executed directly from program storage  208  while the microcode is typically transferred to memory  204  for faster execution. Flow controller  202  also includes an interface controller  206  which performs the lower-level functions including handshaking functions required across interface  232  to the wireless LAN interface  222  and across interface  234  to the LAN interface  212 .  
      The construction of wireless LAN interface  222  includes a physical layer RF transceiver  224 , transmit and receive FIFO&#39;s  230  and  228  respectively, and a low-level controller  226  for interfacing to the flow controller via interface  232 . Wireless LAN interface  222  includes an antenna  233  for coupling electromagnetic energy to the atmosphere. Notice that the term—RF—is used herein as to be consistent with the IEEE 802.11 specifications. Throughout the IEEE 802.11 specifications the direct sequence spread spectrum (DSSS) system therein described targets an RF LAN system having a carried frequency in the 2.4 GHz band designated for industrial, science, and medical (ISM) applications as provided in the USA according to FCC 15.247. In other words, the actual modulation frequencies used by the RF transceiver  224  are in the 2.4 GHz microwave ISM band rather than in the frequency band traditionally known as “RF.” 
      The construction of LAN interface  212  includes a physical layer ethernet transceiver  218 , transmit and receive FlFO&#39;s  220  and  216  and a low-level controller  214  for interfacing to the flow controller via interface  234 . Ethernet transceiver  218  is coupled to the backbone network  110  or  112 .  
      Controller&#39;s  226  and  214  can be implemented in hardware, or as a combination of hardware and software/firmware components. In the preferred embodiment however, controllers  226  and  214  are implemented in hardware for faster operation.  
      Wireless LAN interface  222  and LAN interface  212  implement at least the physical and medium access control layers of the ISO LAN networking model. Higher ISO layers are implemented in the flow controller  202 . However, it is possible to implement the higher layers of the ISO model in interfaces  222  and  212 .  
      Further details concerning the construction and use of access point  200  shall be described in relation to the flow charts which follow. Certain details concerning the construction and use of access points are well known in the art and are omitted so as to not obfuscate the present disclosure in unnecessary detail.  
       FIG. 3  is a block diagram of a client configured according to an embodiment of the present invention. The client  300  includes a physical layer RF transceiver  322 , transmit and receive FIFO&#39;s  328  and  326  respectively, and a low-level controller  324  for interfacing to other components of client  300  through PCI bus  310 . Wireless LAN interface  322  includes an antenna  334  for coupling electromagnetic energy to the atmosphere. Controller  300  further includes video controller  318  which provides control signals to video LCD display  320 . PCI bus controller  308  operationally couples a variety of modules within client  300 . A standard processing subsection is coupled to PCI bus controller  308  and consists of a microprocessor  302 , a memory controller  304 , and to memory  306 . Microprocessor  302  receives its boot code from flash program storage  316  through PCI bus controller  308 . A storage module  312  provides the client with DASD storage for storing application software and application data, and for storing and executing operating system code. Client  300  also includes a keyboard and mouse interface  314  which is coupled to PCI bus controller  308 . Keyboard and mouse interface  314  accepts user input from a supplied keyboard and mouse. Establishing association and wireless connection to access point  200  according to the logic shown in  FIG. 4 , for which a detailed description shall be given in the description which follows, can be performed by controller  324  of wireless LAN interface  322  or by the microprocessor  302  and the controller  324 . However in the preferred embodiment the association and wireless connection to access point  200  is implemented entirely in controller  324  according to logic depicted in  FIG. 4 .  
       FIG. 4  is a flow diagram depicting the logic exercised by the client of  FIG. 3  in maintaining and/or establishing association with the access point of  FIG. 2 . Initially  400 , client  300  scans  402  for any available access points with in its geographical range. A decision  404  is then made regarding whether access points are found. If none are found, client  300  continues to scan  402  for available access points. If one or more access points are found, client  300  will associate and connect  408  to the first available access point which is found to be highest on a predetermined preference list. The preference list can be entered by a user or entered automatically by system administrators through the network upon initial setup. A user would tend to enter, toward the top of list, the access points with which they have had the most success. Often, this is an access point closest to where the user normally physically resides and therefore, by virtue of its proximity to the user, provides the highest signal strength and gives the best signal quality. The client  300  then makes a two phase  410  and  412  determination as to the status of the association and link. First, a determination  410  is made as to whether the association remains active. If the association is not active, client  300  then continues to scan  402  for available access points. If the association is still active, client  300  then makes a determination  412  as to whether the link quality is acceptable. Link quality does not remain static for a variety of different reasons and therefore must be checked periodically. For example, if the client  300  is roaming, i.e., physically moving whether by public transit, automobile, or on foot, access point signal strength will diminish as the client moves away from the access point. Alternatively, link quality can degrade due to external electromagnetic interference. When it is determined  412  that the link quality is acceptable, client  300  maintains the association and proceeds to monitor the status  410  and the quality  412  of the connection. If it is determined  412  that the link quality is not acceptable, client  300  ventures out and scans  402  for alternative access points which might be available within its range in attempting to find a link with a higher level of signal quality.  
       FIG. 5  is an illustration of the type of table that is maintained according to one embodiment of the present invention. Table  250  illustrated in  FIG. 5  is maintained by access point  200  as an aid in determining which clients are to be associated. The logic to be described in relation to  FIG. 6  utilizes the data variables stored in table  250  in making client association decisions. Table  250  is maintained in memory  204  of flow controller  202  found in  FIG. 2 .  
      Column  502  and column  504  of table  250  are reserved for maintaining a log of pending clients. As will be discussed in more detail in relation to the description of  FIG. 6 , column  502  of table  250  contains a unique identifier for the client which has issued an association request to access point  200  for access to the backbone. The unique identifier can be the name, the MAC address, or the IP address of the requesting client. Column  504  contains an entry representative of the point in time when the last beacon was received from a particular client. Alternatively, an entry which is representative of the point in time when the first beacon was received can be stored in column  504  of table  250 . As another alternative, column  504  may contain an entry representative of that point in time when a first or a last beacon was received within a particular interval of time; this implementation is effective in discarding timestamps which are not within an interval of interest.  
       FIG. 6  is a flow diagram showing the logic exercised by the access point  200  of  FIG. 2  according to an embodiment of the present invention. Referring now to  FIG. 6  and to  FIGS. 2 and 5 , processor  210  of flow controller  202  maintain stable  250  in memory  204  of access point  200 . Processor  210  maintains columns  502  and  504  for each client requesting access through access point  200 . In the preferred embodiment, processor  210  of flow controller  202  executes the logic illustrated in  FIG. 6 . However, other embodiments are envisioned in which logic of  FIG. 6  is executed entirely in hardware or alternatively in some combination of hardware and software or firmware. Execution begins  600  with the transmission  602  of a beacon identifying the availability of resources and services through access point  200 . The beacon itself identifies the access point. Clients are preprogrammed to identify such beacons as providing availability to resources and services on the backbone. The access point then waits  605  for clients to respond to the beacons. When at least one client has responded to the beacon, a determination  610  is then made as to whether the client is an 802.11g compliant station. If it is determined  610  that the requesting client is not an 802.11g client, measures  612 ,  614 , and  616  are taken in an effort to steer non 802.11g clients to other access points. If it is determined that the requesting client is an 802.11g client, measures  606 ,  608 , and  618  are taken in associating the client in the usual manner. Measures  612 ,  614 , and  616  are performed in the following manner when the determination  610  is that the requesting client is not an 802.11g client. First, it is determined  612  whether the client requesting access has an entry in column  502  of table  250 . If the client does not have an entry, the client is added  614  to column  502  of table  250  as a pending client; in addition, a timestamp is added to column  504  indicating the time the request from the client was received. In this case, the client does not receive a response from the access point and the client is not associated. Instead of associating the client, access point  200  continues to wait  605  for clients to respond to the beacons. By deferring the non 802.11g client in this fashion, the non 802.11g client is incented to seek association with another access point. Should the non 802.11g client associate with another access point, mitigation of the impact introduced to one protocol from another protocol is achieved. If the second access point is following the same algorithm, the timestamp in the first access point will be earlier than timestamp in the second access point leading to the eventual client association to the first access point by virtue of the earlier timestamp in the first access point. However, should the client fail to find an alternative access point through which to connect to the backbone, the procedure which follows allows for the non 802.11g client to eventually associate. When it is determined  612  that the client does have an entry  502  in table  250 , this indicates that the client has recently requested association by responding to a sent  602  beacon but has been denied a response. The return of this non 802.11g client indicates that no other access point has been found by the non 802.11g client. In the preferred embodiment, it is then determined  616  whether the timestamp entry  504  in table  250  indicates that the non 802.11g client has been delayed for at least a predetermined wait period. In other embodiments, no time is required and a second request to associate can be accepted. If  616  the time period has not been exceeded, the non 802.11g client is again not associated and access point  200  continues by waiting  605  for clients to respond to beacons. However, when it is determined  616  that the predetermined time period has been exceeded, the non 802.11g client is associated as per measures  606 ,  608 , and  618 .  
      Thus, an example will be now be given in accordance with the logic of  FIG. 6  as executed by processor  210  of flow controller  202  of access point  200  in grouping 802.11g and non 802.11g traffic with different access points. Referring now to the scenario  100  given in  FIG. 1 , assume that clients  118  and  114  are 802.11b clients (i.e., non 802.11g) and neither are associated to any access point. Also, assume that both backbone&#39;s  110  and  112  are operational and that access point  102  operates according to the logic of  FIG. 6  in attempting to associate 802.11g clients without delay while steering away non 802.11g clients. Further assume that access point  106  operates as a standard access point (or as an access point of  FIG. 6  with the isolation feature disabled). According to the logic of  FIG. 6 , client  114  responds to beacons from both access points  102  and  106 . Since access point  102  defers 802.11b Clients, an entry is made into table  250  for client  114  and the association of client  114  is deferred. Meanwhile, since access point  106  is a standard access point, access point  106  associates client  114  without delay. As a result of the association with access point  106 , access point  102  will never receive a second response to a beacon. Mitigation of interference from disparate protocols has therefore been achieved on access point  102  with respect to client  114 . With respect to client  118 , client  118  will only hear a beacon from access point  102  and will respond accordingly. Access point  102  will defer the association of client  118  as described. Since client  118  has no other access point option, client  118  will continue to respond to beacons transmitted by access point  102 , and eventually, the predetermined time period will be exceeded and client  118  will be associated to access point  102  even though access point  102  is an 802.11b client (is a non 802.11g client).  
      In the drawings and specifications there has been set forth a preferred embodiment of the invention and, although specific terms are used, the description thus given uses terminology in a generic and descriptive sense only and not for purposes of limitation.