Abstract:
A method and system is used in a communication network for charging a flat- rate for a customer&#39;s Nominal Bit Rate (NBR p ) of the network as well as providing a variable actual Nominal Bit Rate (NBR r ) suitable for momentarily desired high nominal bit rates requested by the customer. In one embodiment, the network provides a maximum pool size (S max ) which is predefined between a network operator and the customer. In another embodiment, instead of having the maximum pool size, the network provides the variable NBR r  by filling the NBR pool progressively as a function of NBR p , a customer&#39;s desired Nominal Bit Rate (NBR d ), and a constant z, for a period of time. A momentarily much higher NBR r  can be provided based on the capacity of the filled NBR pool.

Description:
RELATED PATENT APPLICATION 
     The present invention relates to U.S. patent application entitled “USE ALLOWED PRIORITY LEVEL FOR ROUTING DECISION IN SIMA NETWORKS”, Ser. No. 09/146,862 filed Sep. 3, 1998; U.S. patent application entitled “USE OF PRIORITIES DEFINED BY A CUSTOMER IN A SIMA NETWORK”, Ser. No. 09/159,005 filed Sep. 23, 1998; U.S. patent application entitled “NOMINAL BIT RATE NETWORK SERVICE”, Ser. No. 08/821,273, filed Mar. 20, 1997; U.S. patent application entitled “CELL SCHEDULING SYSTEM AND METHOD FOR NETWORK NODES”, Ser. No. 08/822,266, filed Mar. 20, 1997, now U.S. Pat. No. 6,081,505; and U.S. patent application entitled “ACCOUNTING SYSTEM AND METHOD FOR A NOMINAL BIT RATE NETWORK SERVICE”, Ser. No. 08/822,270, filed Mar. 20, 1997, now U.S. Pat. No. 6,047,326; the subject matter of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to communication systems, and more particularly, to a method and system for managing information communicated over a Simple Integrated Media Access (SIMA) network with a Nominal Bit Rate (NBR) pool. 
     2. Description of Related Art 
     Simple Integrated Media Access (SIMA) is a new way of introducing new properties for packet-based data networks, such as TCP/IP or ATM networks. The basic idea of SIMA relies on the use of eight packet-discarding priority levels, as described in details in the above-mentioned patent applications, entitled “NOMINAL BIT RATE NETWORK SERVICE”, NC 7664, Ser. No. 08/821,273, filed Mar.20, 1997; U.S. patent application entitled “CELL SCHEDULING SYSTEM AND METHOD FOR NETWORK NODES”, NC 7665, Ser. No. 08/822,266, filed Mar. 20, 1997; and U.S. patent application entitled “ACCOUNTING SYSTEM AND METHOD FOR A NOMINAL BIT RATE NETWORK SERVICE”, NC 7701, Ser. No. 08/822,270, filed Mar. 20, 1997; the subject matter of which are hereby incorporated by reference. Every data packet is equipped with a priority level (PL) that can be an integer between 0 and 7. In the latest SIMA literature, the term “priority level” is often replaced by “drop preference” which has the same meaning as “priority level”. 
     In a SIMA network, priority is used for selecting packets that are discarded during congestion of a network node. The priority is determined from the ratio of a momentary actual bit rate of the source (a customer) to the Nominal Bit Rate (NBR) assigned to the source (the customer). This determination is performed in a network access node that is the first network element to receive a packet from a customer equipment. 
     A conventional way of managing customer charging on Internet is based on flat- rate, that is, each customer pays a monthly fee and gets certain Internet service. Since the management of a more complicated charging scheme for every individual customer means excessive management and cost, the flat-rate charging scheme is currently a prevalent way. 
     SIMA network with this type of simple flat-rate charging scheme is presently available for the customer. The monthly fee, for example $X, is translated to a certain NBR. The available network capacity is then divided among competing connections proportional to the NBR of each connection or customer. With typical data applications and low bit rate real-time applications, this SIMA network system may work properly. However, if a SIMA customer has, for instance, a permanent or flat-rate NBR of 50 kbit/s, and he/she desires to send a video stream with a speed of 500 kbit/s (i.e. higher NBR), the outcome could be totally unsatisfactory in using the simple flat-rate charging scheme. The priority of the packets (or called frames or cells) of information will be so low that the packet loss ratio will be very high. Consequently, the video quality will be very low for any practical purpose. This problem can be solved by combining the flat rate scheme and a time-dependent charging scheme presented in the above-mentioned U.S. patent applications. Although this solution is technically quite simple, it requires many changes in customer&#39;s management and charging. For example, the customer has to keep track of what period of time that he/she has requested for what NBR, other than the permanent NBR, and how much it is for such NBR, etc. 
     Accordingly, there is a need in the communication industry for a network management architecture and method that can combine the simplicity of flat-rate charging and the flexibility of time-dependent scheme into a SIMA network system. 
     SUMMARY OF THE INVENTION 
     The present invention relates to communication systems, and more particularly, to a method and system for managing information communicated over a SIMA network with a Nominal Bit Rate (NBR) pool. 
     To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a NBR pool that is used with SIMA network so that a customer of a network service provider is allowed to change his/her NBR without any actual time-dependent charging. The NBR pool method and apparatus of the present invention has both the simplicity of flat-rate charging and the flexibility of time-dependent scheme. The advantage of this system is that a “pure” flat-rate charging is possible even though the customer is allowed to change the NBR. 
     In one embodiment of the present invention, a NBR pool is established such that each SIMA customer has a permanent NBR based on the monthly fee (flat or fixed fee) or some other fee schedules, such as semi-monthly, weekly, or annual fees, etc. In addition, the customer is allowed to momentarily use a higher NBR, but only during a limited time period and for a limited amount. 
     Further in one embodiment of the present invention, the NBR pool unit controls an actual NBR used for determining the SIMA priorities based on a NBR desired by the customer, a permanent NBR, and the maximum pool size. 
     The present invention also relates to a method of charging a flat-rate for a customer&#39;s use of a communication network and providing variable actual nominal bit rate (NBR r ) to suit for momentarily desired nominal bit rates requested by the customer. 
     In one embodiment, a method of generating an actual Nominal Bit Rate (NBRr r ) to determine a priority in a SIMA network for a customer which desires a NBR d  to transmit a packet of information via the network, comprises: providing a flat-rate Nominal Bit Rate (NBR p ) for the customer, the NBR p  being predefined between the customer and the network; providing a NBR pool having a maximum pool size (S max ), the S max  being predefined between the customer and the network, the NBR pool being filled by a customer&#39;s NBR p  and depleted by a customer&#39;s NBR d ; and generating the NBR r  based on the NBR p , the S max , and the NBR d . 
     Still in one embodiment of the present invention, the generating NBR r  includes determining a size of the NBR pool, wherein when the NBR pool is empty, the NBR r  is the NBR p ; when the size of the NBR pool is not smaller than the maximum pool size S max , the NBR r  is the NBR d ; when the size of the NBR pool is smaller than the maximum pool size S max  but not empty, the NBR r  is a sum of the NBR p  and a NBR pool rate; the NBR pool rate being determined by the size of the NBR pool being divided by a time interval (Δt), the time interval being a time period for the network to change the actual Nominal Bit Rate. 
     Further in one embodiment of the present invention, the time interval is approximately one minute. 
     Yet in one embodiment of the present invention, the maximum pool size is approximately one giga bits. 
     The present invention also relates to a system of charging a flat-rate for a customer&#39;s use of a communication network and providing variable actual nominal bit rate (NBR r ) suitable for momentarily desired nominal bit rates requested by the customer. 
     In one embodiment, a system of generating an actual Nominal Bit Rate (NBR r ) 20 to determine a priority in a SIMA network for a customer which desires a NBR d  to transmit a packet of information via the network, comprises: a customer management unit, the customer management unit providing a flat-rate Nominal Bit Rate (NBR p ) for the customer, the NBR p  being predefined between the customer and the network, and providing a NBR pool having a maximum pool size (S max ), the S max  being predefined between the customer and the network, the NBR pool being filled by a customer&#39;s NBR p  and depleted by a customer&#39;s NBR d ; and a NBR pool unit for generating the NBR r  based on the NBR p , the S max  and the NBR d . 
     Still in one embodiment, the NBR pool unit determines a size of the NBR pool, wherein when the NBR pool is empty, the NBR pool unit generates the NBR r  to be the NBR p ; when the size of the NBR pool is not smaller than the maximum pool size S max , the NBR pool unit generates the NBR r  to be the NBR d ; when the size of the NBR pool is smaller than the maximum pool size S max  but not empty, the NBR pool unit generates the NBR r  to be a sum of the NBR p  and a NBR pool rate; the NBR pool rate being determined by the size of the NBR pool being divided by a time interval (Δt), the time interval being a time period for the network to change the actual Nominal Bit Rate. 
     In an alternative embodiment, instead of having a maximum pool size, the NBR pool is filled and/or emptied not proportional to NBR p , NBR d , but progressively as a function of NBR p , NBR d . In one embodiment, the NBR pool is filled either by not using the NBR p  or by using a NBR r  lower than the NBR p . The reserved NBR pool, upon a certain time period, can be used to serve a corresponding much higher NBR r  under a certain period of time. The longer the NBR pool is filled or not used, the higher the NBR r  can be used, and the longer the use of a higher NBR r  can last. Accordingly, the desired NBR d  is the NBR r , and the time of using this NBR r  is determined based on the fact that the NBR pool does not become negative. 
     Further in the alternative embodiment, a constant z is predefined by the network operator to determine how the NBR pool is progressively filled and/or emptied as a function of NBR. The constant z can be 0, 1, 1.5, 2, etc. When the constant z is zero, the NBR pool is filled and/or emptied proportional to NBR p , NBR r  used by the customer as discussed in the first embodiment. In another embodiment, the constant z is one. Furthermore, the constant z can be implemented in the pay rate charged to the customer. 
     Further in one embodiment, a size of the NBR pool is determined. The NBR pool is filled by using a first NBR r  lower than the NBR p  for a first period of time and is emptied by using a second NBR r  higher than the NBR p  for a second period of time. The second NBR r  and the corresponding second period of time are determined by the first NBR r  and the corresponding first period of time and the constant z. 
     One advantage of the alternative embodiment is that it allows the customer to be able to use temporarily much higher NBR than what they normally use. In particular, it allows the customer to pay a low rate for a normal use of a low NBR but temporarily using a much higher NBR. 
     These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings in which like reference numbers represent corresponding parts throughout: 
     FIG. 1 illustrates SIMA network nodes used in communication from one customer to the other in a SIMA network in which a NBR pool unit of the present invention can be adapted. 
     FIG. 2 is a block diagram of one embodiment of a NBR pool adapted for a SIMA network according to the present invention. 
     FIG. 3 is a block diagram of an alternative embodiment of a NBR pool adapted for a SIMA network according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description of the exemplary embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration the specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized as structural changes may be made without departing from the scope of the present invention. 
     The present invention discloses a NBR pool that is used with SIMA network so that a customer of a network service provider is allowed to change his/her NBR without any actual time-dependent charging. The NBR pool method and apparatus of the present invention has both the simplicity of flat-rate charging and the flexibility of time-dependent scheme. 
     Accordingly, the present invention provides a new approach to manage the SIMA network charging scheme using customer&#39; NBR. In particular, a NBR pool unit controls the actual NBR used for determining the SIMA priorities based on the NBR desired by the customer, the customer&#39;s flat rate (or called “permanent”) NBR, and a maximum pool size. 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 NBR 
                 Nominal Bit Rate (bits/s) 
               
               
                 NBR p   
                 Permanent NBR bought by a customer (based on the 
               
               
                   
                 flat-rate paid) (bits/s) 
               
               
                 NBR d   
                 Desired NBR by the customer (during the use of 
               
               
                   
                 the network) (bits/s) 
               
               
                 NBR r   
                 Actual NBR used during the period (bits/s) 
               
               
                 S max   
                 Maximum size of a NBR pool (bits) 
               
               
                 CE (Figure 1) 
                 Customer Equipment 
               
               
                 A (Figure 1) 
                 SIMA network access node 
               
               
                 C (Figure 1) 
                 SIMA network core node 
               
               
                 ATM 
                 Asynchronous Transfer Mode 
               
               
                 SIMA 
                 Simple Integrated Media Access 
               
               
                 PL: 
                 Priority Level 
               
               
                 Δt 
                 A time interval between the network changing the 
               
               
                   
                 actual Nominal Bit Rate (NBR r ) (second) 
               
               
                 Period 
                 A period of time during which the NBR used by the 
               
               
                   
                 customer (NBR r ) (second) 
               
               
                 S(0) 
                 Pool filling level at the beginning of a period (bits) 
               
               
                 S(t) 
                 Pool filling level at the end of period (bits) 
               
               
                 t 
                 Duration of the period (seconds) 
               
               
                 z 
                 Constant (e.g. 0, 1, 2, . . . etc.) 
               
               
                   
               
             
          
         
       
     
     In FIG. 1, a NBR pool unit or system  100  in accordance with the present invention is adapted to a SIMA (Simple Integrated Media Access) network  102 . It is appreciated that the NBR pool unit  100  can also be adapted to or equipped with other networks, such as a conventional Internet Media Access network, etc. 
     Generally, when a customer or customer equipment (CE 1 ) sends data packets or cells of information to another customer or customer equipment (CE 2 ), customer CE 1  accesses the network at node A 1  (network access node). There are several routes, for examples, A 1 C 1 C 2 , A 1 C 1 C 4 , A 1 C 3 C 4 , to reach another network access node A 2  accessible to customer or customer equipment CE 2 . C 1 , C 2 , C 3 , C 4  are network core nodes. Accordingly, packets (frames or cells) of information are transmitted from one customer to the other customer via the network access nodes and network core nodes. 
     FIG. 2 illustrates a block diagram of a NBR pool unit  200  for the SIMA network  102  according to the present invention. Packets of information  202  are transmitted from a customer equipment  204  to a SIMA access node  206 . An actual NBR, NBR,, for determining priority level of the packets  202  at the SIMA access node  206 , is provided by the NBR pool unit  200 . The NBR pool unit  200  is coupled to the customer management unit  208  which provides the pool unit  200  with a permanent or flat-rate NBR, NBR p , and the maximum size of the pool S max . The permanent NBR and the maximum pool size can be selected by the customer based on the fee paid to the network service provider. The NBR pool unit  200  is also coupled to the customer equipment  204  which provides the NBR pool unit  200  with the momentary NBR desired by the customer, NBR d . Based on the values of NBR p , S max , and NBR d , the NBR pool unit  200  determines the actual NBR value, NBR r . 
     The NBR pool unit  200  has a changeable pool size (bit) which does not exceed the maximum size of pool: S max  (bit). When the NBR pool service is started, the pool size is full, that is: 
     
       
           S ( t= 0)= S   max   
       
     
     The network may change the actual bit rate NBR r , at intervals of Δt. In determining the actual bit rate NBR r , the NBR pool unit  200  operates a following method for the next interval: 
     
       
         
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 S(t+Δt) = S(t) − Δt · NBR d  + Δt · NBR p   
               
               
                   
                 If S(t+Δt) &gt;= S max   
               
             
          
           
               
                   
                 then 
               
             
          
           
               
                   
                 NBR r  = NBR d   
               
               
                   
                 S(t+Δt) = S max   
               
             
          
           
               
                   
                 else if S(t+Δt) &gt;= 0 
               
             
          
           
               
                   
                 then 
               
             
          
           
               
                   
                 NBR r  = NBR d   
               
             
          
           
               
                   
                 else 
               
             
          
           
               
                   
                 NBR r  = NBR p  + S(t)/Δt 
               
               
                   
                 S(t+Δt) = 0 
               
               
                   
                   
               
             
          
         
       
     
     Accordingly, the NBR pool is filled by rate NBR p  and depleted by rate NBR d  as long as there is something in the pool to be used for a desired NBR. For example, if the pool is empty, the permanent NBR p  is used for the desired NBR r . If the pool has not yet reserved enough for he desired NBR d  for the entire period Δt, the pool unit provides an actual NBR as being a NBR such that the pool is empty exactly at the end of the period Δt. In other words, the actual NBR can be the NBR p  with additional bit rate determined by the formerly available pool size S(t) and the interval  66  t. Thereafter, the pool is empty. 
     The time constant  66  t may be short enough for practical uses—the main issue is that most customers are satisfied. On the other hand, the time constant Δt is long enough in order to avoid very short and strong peaks of high priority traffic sent to the network, which could deteriorate the predictability SIMA network services. In one embodiment, the time constant Δt is approximately 1 minute. It is appreciated that other suitable values, such as 1.5 minutes, 10 seconds, etc., can be used without departure from the principles of the present invention. 
     As mentioned above, the maximum pool size, S max , of the pool also has an effect on the charging scheme, for example, the monthly fee, as a very large pool for all customers makes the network dimensioning more difficult which costs more. A relatively smaller sized pool can be used for a standard service. In one embodiment, the maximum pool size, S max , is approximately 1 giga bits. It is appreciated that other suitable values can be used, such as 500 mega bits, 10 giga bits, etc., can be used without departure from the principles of the present invention. In practice, the actual determination of the parameters, Δt and S max , can be predetermined or predefined by the network operator. 
     In NBR pool operation according to the present invention, the customer management unit 208 provides a customer&#39;s permanent or flat-rate NBC p , a maximum pool size. Based on the NBR p , S max , and the customer&#39;s momentarily desired NBR d , the NBR pool unit  200  generates an actual NBR for determining the priority level of the packets of information to be transmitted from the customer equipment  204  to SIMA access node  206 . 
     Accordingly, the present invention allows the customer&#39;s NBR to be changed without any actual time-dependent charging. One of the advantages of a network system equipped with the NBR pool unit  200  is that a pure flat-rate charging is possible even though the customer is allowed to change the NBR. 
     In FIG. 3, an alternative embodiment of a NBR pool  300  adapted for a SIMA network is shown. Packets of information  302  are transmitted from a customer equipment  304  to a SIMA access node  306 . An actual NBR, NBR,, for determining priority level of the packets  302  at the SIMA access node  306 , is provided by the NBR pool unit  300 . The NBR pool unit  300  is coupled to the customer management unit 308 which provides the pool unit  300  with a permanent or flat-rate NBR, NBR p , and the network constant z. The NBR p  can be selected by the customer based on the fee paid to the network service provider. The constant z can be provided by the network service provider, e.g. z is 0, 1, 1.5, 2, or other suitable constant within the principles of the invention. The constant z can also be selected by a customer based on a fee paid to the network service provider. The NBR pool unit  300  is also coupled to the customer equipment  304  which provides the NBR pool unit  300  with the momentarily much higher NBR desired by the customer. Based on the values of NBR p , z, and NBR r , the NBR pool unit  300  provides the desired much higher NBR, NBR r . 
     In the alternative embodiment, the NBR pool can be filled either by not using the NBR p  or by using a NBR r  lower than the NBR p . The reserved NBR pool after a certain time period can be used to serve a corresponding much higher NBR r  for a certain period of time. The longer the NBR pool is filled or not used, the higher the NBR r  can be used, and the longer the use of a higher NBR r  can last. Accordingly, the NBR r  serves the desired NBR for a period of time, and the time of serving this desired NBR is determined based on the fact that the NBR pool does not become negative. 
     Formulae for the network to determine a pool filling level at the end of the period is as follows:          S        (   t   )       =       S        (   0   )       +     t   ·     (       NBR   p     -         (       NBR   r       NBR   p       )     z          NBR   r         )                                
     In addition, one criteria on which the network operates is that the network does not allow the filling level of the pool to become negative. Therefore:          NBR   r                   can                 be                 at                 most        :                       NBR   p     ·       (         S        (   0   )         t   ·     NBR   p         +   1     )       1   /     (     1   +   z     )                                  
     As shown in the formula, if z=0, the first embodiment of the present invention as discussed above is obtained, i.e.          S        (   t   )       =       S        (   0   )       +     t   ·     (       NBR   p     -         (       NBR   r       NBR   p       )     z          NBR   r         )                                
     If z approaches infinity, a conventional system without a NBR pool is obtained. The constant z can be any suitable number, such as 0, 1, 1.5, 2, etc. In one preferred embodiment, the constant z is set to be 1. It is appreciated that the network operator can set and/or reset the constant z without departure from the principles of the present invention. It is also appreciated that the constant z can be predefined by the network operator or predefined between the network operator and the customer. 
     If it is supposed that NBR p  is, for instance, 100 kbit/s, the customer can use the pool as presented in the following Table 1. In each case the NBR pool is empty at the beginning. Then, the customer is filling the NBR pool by setting NBR=0 for a period t(1). During the next period from t(1) to t(2), the customer is draining the NBR pool in a way that it will be empty just at the end of the period. 
     As shown in the Table, the NBR that can be used during the second period depends strongly on the constant z. 
     
       
         
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 NBR(1) 
                 t(1) 
                 S(1) 
                 t2-t1 
                   
                 NBR(2) 
                 kbit/s 
                   
               
               
                 Case 
                 S(0) 
                 kbit/s 
                 hour 
                 Mbit 
                 min 
                 z = 0 
                 z = 1 
                 z = 2 
                 (S2) 
               
               
                   
               
             
             
               
                 1 
                 0 
                 0 
                 1/60 
                    6 
                  1 
                   200 
                  141 
                 126 
                 0 
               
               
                 2 
                 0 
                 0 
                  1 
                   360 
                  1 
                   6100 
                  781 
                 394 
                 0 
               
               
                 3 
                 0 
                 0 
                  1 
                   360 
                  10 
                   700 
                  265 
                 191 
                 0 
               
               
                 4 
                 0 
                 0 
                  1 
                   360 
                 120 
                   150 
                  124 
                 114 
                 0 
               
               
                 5 
                 0 
                 0 
                 24 
                  8640 
                  1 
                  144100 
                  3796 
                 1129  
                 0 
               
               
                 6 
                 0 
                 0 
                 24 
                  8640 
                  10 
                  14500 
                  1204 
                 525 
                 0 
               
               
                 7 
                 0 
                 0 
                 24 
                  8640 
                 120 
                   1300 
                  360 
                 235 
                 0 
               
               
                 8 
                 0 
                 0 
                 14*24 
                 120960 
                  1 
                 2016100 
                 14198 
                 2721  
                 0 
               
               
                 9 
                 0 
                 0 
                 14*24 
                 120960 
                  10 
                  201700 
                  4491 
                 1263  
                 0 
               
               
                 10  
                 0 
                 0 
                 14*24 
                 120960 
                 120 
                  16900 
                  1300 
                 553 
                 0 
               
               
                   
               
             
          
         
       
     
     For instance, in case 6 using the above formula, the customer fills a NBR pool by keeping NBR zero for 24 hours such that at the end of the 24 hours, the occupancy level of the NBR pool is 8.64 Gbit: 
     The NBR pool is filled in the first 24 hrs, and the pool level S is: 
     
       
           S (24hrs)=0+24*3600( s )*(100−(0/100 0 *0)=8640*10(Kbit/ s )or 8640(Mbit/ s ) or 8.64(Gbit/ s ). 
       
     
     The NBR pool can then be drained depending on what the customer&#39;s desire is. If the customer needs 10 minutes in the second period and the constant z is 0, then the NBR r  at most in the second period can be:                NBR   r     =         NBR   p     ·       (         S        (   0   )         t   ·     NBR   p         +   1     )       1   /     (     1   +   z     )           =                100   *     (     8640   *     10   3            (     kbit   /   s     )     /                                            (     10   *   60   *   100     )     +   1     )       1               =                14500                     (     kbit   /   s     )     .                                    
     Similarly, if the constant z is 1, the NBR r  at most can be 1204 (kbit/s) for 10 minutes; if the constant z is 2, the NBR r  at most can be 525 (kbit/s) for 10 minutes. 
     Therefore, if z is 0, the customer can have as high NBR as 14.5 Mbit/s for a period of 10 minutes before the pool is empty, whereas with z=1, the corresponding NBR that the customer can have is only about 1.2 Mbit/s. From the operator&#39;s viewpoint, the first period NBR value could bring about serious difficulties as regards the network dimensioning while the latter one could be quite harmless. Note that in case when z=1, the average NBR over the periods t1 and t2 is only 8.3 kbit/s ((0*24*3600+1204*10*60)/(24*3600+10*60)=8.3 kbit/s), whereas in case when z=0, the average NBR is 100 kbit/s ((0*24*3600+14500*10*60)/(24*3600+10*60)=100 kbit/s). 
     Further, if the NBR r  of 300 kbit/s is desired by the customer for a video phone call of 10 minutes. Then, in case of z=0, the customer needs to keep NBR zero only for 20 minutes to make the call possible. The corresponding periods for cases z=1 and z=2 are 80 min. and 260 min., respectively. 
     Finally, if the paid permanent NBR p  is 100 kbit/s and the customer is using permanently only 50 kbit/s, the customer can have a NBR r  of 500 kbit/s every day for 45 minutes (assume the constant z is 1. The calculation is as follows: 
     
       
           S( 24hrs)=0+24*3600( s )*(100−(50/100) 1 *50)=75*24*3600(Kbit/ s ) 
       
     
     
       
         
           
             
               NBR 
               r 
             
             = 
             
               
                 NBR 
                 p 
               
               · 
               
                 
                   ( 
                   
                     
                       
                         S 
                          
                         
                           ( 
                           0 
                           ) 
                         
                       
                       
                         t 
                         · 
                         
                           NBR 
                           p 
                         
                       
                     
                     + 
                     1 
                   
                   ) 
                 
                 
                   1 
                   / 
                   
                     ( 
                     
                       1 
                       + 
                       z 
                     
                     ) 
                   
                 
               
             
           
         
         
           
             500 
             = 
             
               100 
               * 
               
                 
                   ( 
                   
                     ( 
                     
                       
                         75 
                         * 
                         24 
                         * 
                         3600 
                          
                         
                           
                             ( 
                             
                               kbit 
                               / 
                               s 
                             
                             ) 
                           
                           / 
                           
                             ( 
                             
                               t 
                               * 
                               100 
                             
                             ) 
                           
                         
                       
                       + 
                       1 
                     
                     ) 
                   
                   ) 
                 
                 
                   1 
                   / 
                   2 
                 
               
             
           
         
         
           
             t 
             = 
             
               
                 2700 
                  
                 
                     
                 
                  
                 
                   ( 
                   s 
                   ) 
                 
               
               = 
               
                 45 
                  
                 
                     
                 
                  
                 
                   min 
                   . 
                 
               
             
           
         
                 
         
             
         
      
     
     Further, similar to the first embodiment, the NBR r  remains constant over a period that could be of the order of 1 minute. 
     Accordingly, in this alternative embodiment, the emptying rate of the NBR pool is not directly the difference between NBR p  and NBR r  as in the first preferred embodiment, but it depends on the NBR p  to NBR r  ratio. In this way, it is not necessary to limit a pool size (S max ), although the customer is given an option to decide whether s/he would want to limit a pool size, i.e., either using a scheme having a maximum pool size or using a scheme without having a maximum pool size. Alternatively, the two schemes can be combined in a suitable manner which gives the customer an option to choose one of the schemes without departure from the scope of the present invention. 
     The main advantage of the alternative embodiment as described above is that it takes automatically into account the fact that the contingent high bit rate peaks make the network dimensioning very difficult. In this scheme, the customer can momentarily have quite high NBR r  but at the expense of having a much lower average NBR r . On the other hand, the main advantage of the first embodiment as described above is that it provides the customer a higher average NBR r  at the expense of not having as high NBR r  as the customer desires. 
     The foregoing description of the exemplary embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not with this detailed description, but rather by the claims appended hereto.