Patent Publication Number: US-8116281-B2

Title: Network gateway and method for relocating the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to mobility management, and, more particularly, to dynamically relocating network gateways in Connectivity Service Network anchored mobility management. 
     2. Description of the Related Art 
     IEEE standard 802.16 defines the wireless MAN™ air interface specification for wireless Metropolitan Area Networks (MANs). The standard heralds the entry of broadband wireless access as a major new tool in the effort to link homes and businesses to core telecommunications networks worldwide. The WiMAX Forum further proposed the WiMAX Forum Network Architecture compatible with IEEE 802.16. Since the IEEE 802.16 series is designed for wider coverage and broader bandwidth, it is viewed as one of the leading standards in 4 th  generation communication systems. 
     The network structures of the WiMAX Forum Network Architecture are framed by Access Service Networks (ASNs) and Connectivity Service Networks (CSNs). The Access Service Network (ASN) provides wireless radio access to WiMAX subscribers. It consists of one or more ASN Gateways (ASN GWs) and Base Stations (BSs). ASNs are connected by CSN, which provides Internet Protocol (IP) connectivity services. 
     ASN anchored mobility management and CSN anchored mobility management are both defined in the WiMAX Forum Network Architecture. ASN anchored mobility management refers to procedures associated with the Mobile Station (MS) movement between BSs and ASNs without changing a reference point. CSN anchored mobility management is based on Mobile IP (MIP) for constructing new connections between CSN and a new ASN GW. 
       FIG. 1  shows the roaming and handover under ASN anchored mobility management and CSN anchored mobility management. In connection (1), MS establishes a connection with BS A, a connection between BS A and ASN GW A, and a connection between ASN GW and Home Agent (HA) which is located in home CSN. If the MS moves along route (2), a new connection (3) is established between the MS, BS B, ASN GW B, ASN A, and HA. In this situation, ASN GW A is called the anchored ASN GW, and ASN GW B is called the severing ASN GW. Handover latency could be reduced in this way but the end-to-end delay may be longer, and the load of ASN GW A may become heavy if there are too many MSs anchored with ASN GW A. 
     In some conditions, the system performs ASN GW relocation for requesting MS performing CSN mobility management. Thus, connection (4) is established between MS, BS B, ASN GW B and HA. However, the WiMAX Forum Network Architecture standards do not specify when to carry out the ASN GW relocation. Since the traffic management of gateways is a key factor of network efficiency, introduction of appropriate relocation methods is highly anticipated. 
     SUMMARY OF THE INVENTION 
     Accordingly, a method for relocating network gateways is provided. The method begins with calculating a weighted moving average WMA DR (x) of drop ratios during the x th  detection interval DDI x . The (x+1) th  detection interval DDI x+1  is set according to the weighted moving average. If WMA DR (X) is less than a low drop ratio (L_DR), the DDI x+1  is set as a long detection interval (L_DI). Otherwise, the DDI x+1  is set as a short detection interval (S_DI). When the weighted moving average WMA DR (x) is equal to or exceeds a high drop ratio (H_DR), a user relocation function is performed. 
     A method for relocating network gateways by predicting the loading of the gateway is also provided. First, the weighted moving average WMA DR (x) of drop ratios during the x th  detection interval DDI x  is calculated. The (x+1) th  detection interval DDI x+1  is set according to the weighted moving average. When the weighted moving average WMA DR (x) is equal to or exceeds a high drop ratio, a user relocation function is initiated. A predicted moving average WMÂ DR (x+S_PI) is estimated. If the predicted moving average WMÂ DR (x+S_PI) exceeds the high drop ratio, the user relocation function is performed. If the predicted moving average is less than the high drop ratio but exceeds a medium drop ratio (M_DR), a second predicted moving average WMÂ DR (x+L_PI) is estimated. If WMÂ DR (x+L_PI) exceeds the high drop ratio, the user relocation function is performed. 
     In other aspects of the invention, a network gateway is also provided. The network gateway comprises a processor and a user interface. The processor calculates a moving average of drop ratios within a detection interval and updates the next detection interval according to the moving average. The user interface requests at least one user device to activate a CSN mobility management procedure when the moving average exceeds a high drop ratio. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described according to the appended drawings in which: 
         FIG. 1  shows the WiMAX Forum Network Architecture of the prior art; 
         FIG. 2  shows a flow chart of packet traffic management according to one embodiment of the invention; 
         FIG. 3  shows a flow chart of a method for relocating network gateways according to one embodiment of the invention; 
         FIG. 4  shows a flow chart of the user relocation function according to one embodiment of the invention; 
         FIGS. 5 and 6  show examples of the determination of weighted moving average WMA DR (x) and the detection intervals; 
         FIG. 7  shows another method for relocating network gateways according to one embodiment of the invention; 
         FIG. 8  shows an example of drop ratios under different detection intervals; and 
         FIG. 9  shows a network gateway block diagram according to one embodiment of the invention. 
     
    
    
     PREFERRED EMBODIMENT OF THE PRESENT INVENTION 
     In one aspect of the invention, the method for relocating network gateways can be roughly divided into two phases: a queue prediction phase and a user relocation phase. In the queue prediction phase, a detection interval is dynamically adjusted according to the traffic load of a queue. When the traffic load is low, the detection interval is longer; and when the traffic load is heavy, the detection interval is shorter for monitoring the drop ratio more intensively. If the traffic load exceeds a threshold, the user relocation phase is started. Users who use the anchored mobility service are requested to activate a CSN mobility management procedure to alleviate the load of ASN GW. 
       FIG. 3  shows a flow chart of a method for relocating network gateways  300  according to one embodiment of the invention. In step S 301 , a weighted moving average WMA DR (x) of drop ratios during the x th  detection interval DDI x  is calculated. In some embodiments of the invention, WMA DR (x) can be calculated by equation (1), 
                       W   ⁢           ⁢   M   ⁢           ⁢       A     D   ⁢           ⁢   R       ⁡     (   x   )         =         ∑     i   =     x   -   n       x     ⁢     (       DDI   i     ×     W   i     ×   D   ⁢           ⁢     R   i       )           ∑     i   =     x   -   n       x     ⁢     (       DDI   i     ×     W   i       )           ,           (   1   )               
where n is the window width of moving average, DDI i  is the i th  detection interval, DR i  is the i th  drop ratio, and W i  is the i th  weight. In some embodiments, n is an integer greater than a minimum width MIN-DRs and less than a maximum width MAX-DRs. If n is less than the minimum width MIN-DRs, the weighted moving average WMA DR (x) may collect insufficient drop ratios. If n exceeds the maximum width MAX-DRs, the weighted moving average WMA DR (x) cannot reflect the latest changes of drop ratios. In step S 302 , the (x+1) th  detection interval DDI x+1  is set. If WMA DR (x) is less than a low drop ratio, and the drop ratio of the x th  detection interval is less than the low drop ratio, the DDI x+1  is set as a long detection interval; otherwise, the DDI x+1  is set as a short detection interval. In step S 303  and S 304 , when the weighted moving average WMA DR (x) is equal to or exceeds a high drop ratio, a user relocation function is performed.
 
       FIG. 4  shows a flow chart of the user relocation function. In step S 401 , N i  users are randomly selected. The N i  users are requested to activate the CSN mobility management procedures, wherein i is an integer indicating how many times the step S 401  has been executed. In step S 402 , the drop ratio within a relocation interval DR RI  is checked. If DR RI  exceeds the low drop ratio, N i+1  users are randomly selected in step S 403 . The N i+1  users are requested to activate the CSN mobility management procedures, wherein N i+1  is an integer larger than N i . If DR RI  is less than the low drop ratio, in step S 404 , the (x+1) th  detection interval DDI x+1  is set, and returns to method  300 . In some embodiments, N 1  is 1, and N i+1  equals N i  times two. 
     In some embodiments of the invention, the drop ratios can be measured by packet traffic management.  FIG. 2  shows a flow chart of packet traffic management  200 . In step S 201 , the arrived packets are marked when the packets in an ASN GW queue exceed a threshold value, and a mark rate is recorded. The packets stored in the ASN GW queue are packets waiting for transfer to other gateways. In steps S 202  and S 203 , when the ASN GW queue is full, the drop rate of the arrived packets is also recorded. The drop ratio is then determined by the ratio of the number of marked and dropped packets to the number of the received packets in one time interval. The drop ratio can be regarded as an index of traffic load of ASN GW. In some embodiments of the invention, the packets are marked according to a Random Early Detection (RED) algorithm or other similar algorithm. 
     For further illustration, an example combining  FIG. 5  shows how the detection interval DDI is determined, and when to initiate the user relocation function. In this example, the low drop ratio is set at 10%, the high drop ratio is set at 30%, the long detection interval L_DI is set at 20 seconds, the short detection interval S_DI is set at 10 seconds, MAX-DRs is set at 10, and relocation interval is set at 5 seconds. In  FIG. 5 , the numbers shown in frames are the drop ratios of corresponding interval. At t 3 , WMA DR (t 3 ) is 30%, exceeding the high drop ratio. Thus after t 3 , the user relocation function is initiated. At relocation interval t 3 -t 4 , a user who is using the anchored mobility service is randomly selected. The selected user is requested to activate a CSN mobility management procedure. In relocation interval t 3 -t 4 , the DR RI , 20%, is higher than the low drop ratio 10%. Thus in the next relocation interval t 4 -t 5 , 2 users are selected and requested to perform the CSN mobility management procedures. In relocation interval t 5 -t 6 , the DR RI , is 8%, less than the low drop ratio. Hence after t 6 , the detection interval is set as the long detection interval. 
       FIG. 6  shows an example of the determination of weighted moving average WMA DR (x). In this example, the low drop ratio is set at 10%, high drop ratio is set at 30%, long detection interval is set at 20 seconds, short detection interval is set at 10 seconds, n is 10, and W i  is i times 0.1. In interval t 9 -t 10 , WMA DR (t 10 ) is calculated as equation (2): 
                     W   ⁢           ⁢   M   ⁢           ⁢     A     D   ⁢           ⁢   R         =                 10   ×   1.0   ×   60   ⁢   %     +     10   ×   0.9   ×   60   ⁢   %     +   …   +                 20   ×   0.4   ×   10   ⁢   %     +   …               10   ×   1.0     +     10   ×   0.9     +   …   +     20   ×   0.4     +   …       ≅     30   ⁢   %               (   2   )               
Since WMA DR (t 10 ) exceeds H_DR, after t 10  the user relocation function is performed.
 
       FIG. 7  shows another gateway relocation method  700 . By predicting the traffic of ASN GW in advance, the user relocation function can be performed before ASN GW overloads. In step S 701 , the weighted moving average WMA DR (x) of the drop ratio during the x th  detection interval DDI x  is calculated. In some embodiments, drop ratios can be obtained by method  200 , and a weighted moving average WMA DR (x) can be obtained by applying equation (1). In step S 702 , the (x+1) th  detection interval DDI x+1  is set. If WMA DR (X) is less than a low drop ratio, and the drop ratio of the x th  detection interval is less than the low drop ratio, the DDI x+1  is set as a long detection interval; otherwise, the DDI x+1  is set as a short detection interval. In step S 703  and S 704 , when the weighted moving average WMA DR (x) is equal to or exceeds a high drop ratio, a user relocation function is performed. Drop ratios are collected in step S 705  to ensure that the moving average is based on sufficient information. Steps S 706 -S 711  are related to ASN GW traffic prediction. In step S 706 , a predicted moving average WMÂ DR (x+S_PI) is estimated. If the predicted moving average WMÂ DR (x+S_PI) exceeds the high drop ratio, the user relocation function is performed, as shown in step S 707 -S 708 . If the WMÂ DR (x+S_PI) is less than the high drop ratio but exceeds a medium drop ratio (M_DR), a second predicted moving average WMÂ DR (x+L_PI) is estimated in step S 710 . If the second predicted moving average WMÂ DR (x+L_PI) exceeds the high drop ratio, the user relocation function is performed. In some preferred embodiments, the predicted moving average WMÂ DR (x+S_PI) is estimated by equation (3): 
     
       
         
           
             
               
                 
                   
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     The estimation of the second predicted moving average of future WMÂ DR (x+L_PI) is similar with the predicted moving average WMÂ DR  (x+S_PI); thus the description is skipped herein. 
     For further comprehension, an example of method  700  is described. In the example, the low drop ratio is set at 10%, the medium drop ratio is set at 25%, the high drop ratio is set at 30%, the long detection interval L_DI is set at 20 seconds, the short detection interval S_DI is set at 10 seconds, MAX-DRs is set at 10, and relocation interval is set at 5 seconds.  FIG. 8  shows drop ratios under different detection intervals. After t 5 , the weighted moving average WMA DR (x) exceeds the low drop ratio, hence the moving average of future WMÂ DR (x+S_PI) is estimated. 
       FIG. 9  shows a network gateway diagram according to one embodiment of the invention. The network gateway  90  comprises a processor  902  and a user interface  904 . The processor  902  calculates weighted moving average WMA DR (x), and updates the (x+1) th  detection interval DDI x+1 . User interface  904  requests at least one user device to perform the user relocation function when the weighted moving average WMA DR (x) exceeds the high drop ratio. In some embodiments of the invention, the network gateway  90  further comprises a traffic management module  908 . When the packets stored in the ASN GW queue exceed a threshold value, the traffic management module  908  marks arrived packets according to an RED algorithm. When the ASN GW queue is full, the drop ratio of packets is also recorded. In other embodiments of the invention, the network gateway  90  further comprises an estimator  906  for estimating predicted moving average WMA DR (x+S_PI) and the second predicted moving average WMÂ DR (x+L_PI). 
     According to some embodiments of the invention, the traffic of anchored ASN GW is analyzed. If the loading of an anchored ASN GW is heavy, relocations are performed. In other embodiments, the future traffic of anchored ASN GW is predicted. The anchored ASN GW can perform mobility management before its loading is too heavy. Under these circumstances, the connection quality is not delayed due to ASN GW overloading. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.