Abstract:
A system and method for granting an association request from a mobile terminal, determining, during a predetermined time interval after granting the association request, if the mobile terminal has received traffic from a network and sent traffic to the network and sending a broadcast update packet to the network if it is determined that the mobile terminal has not both received traffic from and sent traffic to the network within the predetermined time interval.

Description:
BACKGROUND 
       [0001]    Wireless networks, of both large and small scales, are increasingly prevalent in the modern world. Such networks are developed for, and used by, both businesses and individuals. 
         [0002]    One of the challenges present in designing and managing large-scale wireless networks with multiple base stations involves coordination of communications to and from mobile devices that move from one base station to another. A common example of such a device is a mobile telephone that is moving through its coverage area, with its connection being passed from one signal tower to another. 
         [0003]    As a result of this type of movement, data that is being sent to a mobile device may be routed to the wrong base station, resulting in the need to use further bandwidth to forward such network traffic to the current base station. In some cases, data can even be lost entirely. 
       SUMMARY OF THE INVENTION 
       [0004]    A method for granting an association request from a mobile terminal, determining, during a predetermined time interval after granting the association request, if the mobile terminal has received traffic from a network and sent traffic to the network and sending a broadcast update packet to the network if it is determined that the mobile terminal has not both received traffic from and sent traffic to the network within the predetermined time interval. 
         [0005]    A system having a network switch and a plurality of base stations, wherein, when a mobile terminal roams from a first of the plurality of base stations to a second of the plurality of base stations, the second of the plurality of base stations sends a broadcast update packet to the network bridge if no two-way traffic occurs to the mobile terminal within a predetermined time interval after the mobile terminal roams to the second of the plurality of base stations. 
         [0006]    A method for determining, by a base station, whether traffic has been sent to and received from an associated mobile terminal during a predetermined time interval and sending, by the base station, a broadcast update packet to a network if the base station has determined that traffic has only been sent to the mobile terminal during the predetermined time interval. 
         [0007]    A device having a memory storing a set of instructions and a processor executing the set of instructions, the set of instructions operable to grant an association request from a mobile terminal, determine, during a predetermined time interval after granting the association request, if the mobile terminal has received traffic from a network and sent traffic to the network and send a broadcast update packet to the network if it is determined that the mobile terminal has not both received traffic from and sent traffic to the network within the predetermined time interval. 
         [0008]    A device having a memory storing a set of instructions and a processor executing the set of instructions, the set of instructions operable to determine whether traffic has been sent to and received from an associated mobile terminal during a predetermined time interval and send a broadcast update packet to a network if it is determined that traffic has only been sent to the mobile terminal during the predetermined time interval. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  shows an exemplary system according to the present invention. 
           [0010]      FIG. 2  shows an exemplary method for updating network forwarding tables according to the present invention. 
           [0011]      FIG. 3  shows another exemplary method for updating network forwarding tables according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The exemplary embodiments of the present invention describe a system and methods for updating network forwarding tables. The exemplary embodiments ensure that network forwarding tables remain updated while minimizing the use of bandwidth for redundant updating. The exemplary system and methods will be discussed in detail below. 
         [0013]    It is noted that the terms “base station” is used throughout this description to refer to a device that enables a mobile terminal to wirelessly access a data network. Furthermore, the terms “mobile terminal” and “mobile device” are used interchangeably to refer to any hardware device that may wirelessly access such a network (e.g., a mobile phone, a mobile computer, a personal digital assistant (“PDA”), etc.). 
         [0014]    Many current and future wireless access networks are moving the wired portion of their networks toward Ethernet-based technologies. Such networks typically consist of a plurality of base stations (“BS”). Present networking standards use complicated tunneling techniques to support mobility when a terminal moves among various BS. Using Ethernet-based networks, however, such complexity can be removed without loss of performance. 
         [0015]    This improvement is accomplished by the use of one of Ethernet&#39;s native characteristics, learned bridge forwarding, to direct user traffic to the correct BS by the implicit learning of ports where traffic source addresses appear. This is typically accomplished by a BS transmitting a broadcast update packet with a mobile terminal&#39;s source address into the wired Ethernet network, at the point when the mobile terminal is handed off to the BS, in order to update the learned bridge forwarding tables in one or more of the Ethernet switches comprising the access network. 
         [0016]    If the mobile terminal is active, normal user traffic is often enough to update the necessary forwarding tables in the Ethernet bridges after handoff. However, this does not occur in all forwarding situations; therefore, using broadcast update packets (e.g., gratuitous Address Resolution Protocol (“ARP”) packets for networks operating under IPv4 or Neighbor Discovery (“ND”) mechanism packets for networks using IPv6) at the time of handoff is a reliable and commonly-used way to rapidly update bridge forwarding tables in an Ethernet-based network. 
         [0017]    The use of broadcast update packets in this manner involves two drawbacks. First, the use of broadcast update packets causes an increase in the amount of traffic on the network. Second, numerous entries are made in the forwarding tables in Ethernet bridges that do not actually handle the traffic for a particular mobile terminal. Either of these may be the limiting factor on the size of an Ethernet-based mobile network. The exemplary embodiments of the present invention alleviate this issue by intelligently deciding whether such a broadcast packet is needed. 
         [0018]      FIG. 1  shows an exemplary system  100  according to the present invention. The exemplary system  100  may act in accordance with the exemplary method  200  shown in  FIG. 2 . The system  100  includes at least one network switch  110  that is a component of a broader data network  120 . The data network  120  may contain a plurality of network switches  110 , with the precise number network switches  110  depending on the scale of the data network  120 ; however, for clarity, only one network switch  110  is shown in  FIG. 1 . The network switch  110  may be connected to the data network  120  via a wired Ethernet connection. 
         [0019]    The network switch  110  may also be connected to a plurality of base stations  130 ,  132  via wired Ethernet connections. The base stations  130 ,  132  provide wireless connectivity for mobile devices. As for the network switch  110 , the precise number of base stations  130 ,  132  present within the system  100  may vary depending on the size of the data network  120 ; for purposes of clarity, only two base stations  130 ,  132  are shown in  FIG. 1 . 
         [0020]    One or more mobile terminals  140  may wirelessly interface with the data network  120  via the base stations  130 ,  132 . As previously discussed, the mobile terminal  140  may be, for example, a mobile telephone, a mobile computer, a PDA, etc. Those of ordinary skill in the art will understand that the number of mobile terminals  140  communicating with the data network  120  may vary depending on factors including the specific implementation of the data network  120 , the time of day, the day of the week, etc. If the data network  120  is a cellular telephone network, for example, there may be thousands of mobile terminals  140  in communication with the data network  120  through various base stations  130 ,  132  at any given point in time. 
         [0021]    In the first step  210  of exemplary method  200 , a mobile terminal  140  forms a communications link with a first base station  130 . Step  210  may be, for example, the initiation of a telephone call by the user of mobile terminal  140  in an implementation wherein mobile terminal  140  is a mobile phone. In step  220 , the mobile terminal  140  roams to an area covered by a second base station  132  of the system  100 . Such roaming will typically correspond to a physical relocation of the user of the mobile terminal  140 , such as by walking or driving. In step  230 , the mobile terminal  140  reassociates with the second base station  132 ; this is also referred to as the mobile terminal  140  being “handed over” to the second base station  132 . 
         [0022]    In step  240 , the second base station  132  initiates a countdown timer. The timer is typically set within a range of several seconds to tens of seconds, and is fine-tuned using measurements made during normal operations as a tradeoff between broadcast updates and encapsulated forwarding or dropped packets due to outdated forwarding tables. Once the timer expires, in step  250  the base station  132  determines whether, while the timer was pending, the mobile terminal  140  exchanged any two-way traffic with the data network  120  through the base station  132 . If, in step  250 , the base station  132  determines that no two-way traffic has been exchanged, then the method proceeds to step  260 , wherein the base station  132  sends a broadcast update packet, as described above, to the wired data network  120 . After step  260 , the method proceeds to step  270  (described below). If, however, it is determined in step  250  that two-way traffic has been exchanged between the mobile terminal  140  and the data network  120  via the base station  132 , the method proceeds directly to step  270  without performing step  260 . 
         [0023]    Ethernet learned bridging forwarding relies fundamentally on two-way traffic, since it updates forwarding tables based on the source address of received packets and the port at which it observes the receipt of such packets. Thus, any normal two-way traffic to and from the mobile terminal  140  after handoff is sufficient to update all necessary bridge tables for any existing connections; ARP/ND process, a normal part of IP operation, handles any new connections. Accordingly, any amount of normal two-way traffic to and from the mobile terminal  140  is sufficient for the method to proceed from step  250  to step  270 , as described above, without sending the broadcast update packet in step  260 . 
         [0024]    In step  270 , the forwarding tables in the data network  120  (i.e. in the network switch  110 ) are updated to reflect that the mobile terminal  140  is now communicating with the data network  120  via the second base station  132  rather than the first base station  130 . This enables the proper routing of network traffic to the mobile terminal  140 , and is part of the normal operation of switched Ethernet. 
         [0025]    The first base station  130 , which the mobile terminal  140  has roamed away from, forwards any buffered packets or in-transit packets that it receives to the second base station  132 . This forwarding may be, for example, by MACinMAC, IP tunneling, VLAN, MPLS, etc. These are not considered “native” communications and do not affect the above-described method. 
         [0026]    Most packet traffic is two-way in nature, so in most handoff instances the sending of a broadcast packet in step  260  will be unnecessary. However, if the base station  132  observes only one-way traffic to the mobile terminal  140  (e.g., a data download by mobile terminal  140 ), tunneled traffic from the previous base station  130 , or no traffic at all, there is a risk that inconsistent forwarding tables will be present in some Ethernet bridges. This risk is corrected by sending out a broadcast update packet, as in step  260 . 
         [0027]    In another exemplary embodiment, the system  100  follows the steps of exemplary method  300 , shown in  FIG. 3 . In step  310 , the mobile terminal  140  associates with one of the base stations  130 ,  132  in a manner described above. For clarity of language, this exemplary method will assume that the mobile terminal is associated with the base station  130 . Association in step  310  may be, for example, in one of the manners described above, such as by initiating communications with the base station  130  or by being handed off to the base station  130  from another base station (e.g., base station  132 ) while roaming during ongoing communications. In step  320 , one-way traffic from the data network  120  to the mobile terminal  140  begins. One-way traffic may be, for example, downloading of data to mobile terminal  140 . 
         [0028]    In step  330 , the base station  130  initiates a countdown timer, similar to that described above with reference to step  240  of exemplary method  200 . This timer is typically set to half the length of the forwarding table aging timers in the network. The default (and, therefore, most common) value of the aging timer is 300 seconds; as a result, the most common length of the timer initiated in step  330  is 150 seconds. Once the timer expires, in step  340  the base station  130  determines whether, while the timer was pending, the mobile terminal  140  solely continued receiving one-way traffic from the data network  120  through the base station  130 . If, in step  340 , the base station  130  determines that traffic during the timed period has been solely one-way to the mobile terminal  140 , then the method proceeds to step  350 , wherein the base station  130  sends a broadcast update packet, as described above, to the wired data network  120 . After step  350 , the method proceeds to step  360 . If, however, it is determined in step  340  that upstream traffic from the mobile terminal  140  to the data network  120  via the base station  130  has also occurred during the timed period, the method proceeds directly to step  360  without performing step  350 . 
         [0029]    In step  360 , the forwarding tables in the data network  120  (i.e. in network switch  110 ) are updated to reflect that the mobile terminal  140  continues to be associated with the base station  130 . This enables the proper routing of network traffic to the mobile terminal  140 . Unlike the above exemplary method  200 , which facilitates proper routing of network traffic to a mobile terminal  140  that has roamed from one of the base stations  130 ,  132  to another, the exemplary method  300  serves to maintain proper routing of network traffic to a mobile terminal  140  that has remained associated with the same base station  130  despite the fact that a network switch  110  may purge the forwarding entry for the mobile terminal  140  after a period of time has elapsed due to a lack of packets received from the mobile terminal  140 . 
         [0030]    The exemplary embodiments of the present invention prevent forwarding table inconsistencies in Ethernet-based mobile access networks. Moreover, they do so without the overhead of sending broadcast update packets at every handoff event, and without unnecessary increase in the sizes of forwarding tables in switches that are not handling the traffic for a particular mobile terminal. 
         [0031]    As a result, such Ethernet-based networks can be deployed on larger scales. Separate IP subnets are required less frequently, and IP layer mobility can be handled with MIP or other tunneling methods. 
         [0032]    It will be apparent to those skilled in the art that various modifications may be made in the present invention, without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.