Abstract:
The present invention discloses a process unit ( 10 ) comprising a real data generator ( 12 ), a buffer ( 14 ) buffering the data and a queue length monitor ( 16 ), which regulates the data generator ( 12 ) depending on the queue length. The system is characterized by a dummy load generator ( 18 ), storing dummy data in the same buffer ( 14 ) at a dummy data rate. The queue length monitor ( 16 ) regulates this dummy data rate. The process unit ( 10 ) may also be used in a system ( 1 ), further comprising a transmitter ( 20 ), a link ( 22 ) and a receiver ( 24 ) and possibly also other process units. The advantages with the present invention is that a faster regulation can be achieved, also for slowly reacting process units, which counteract overflow in the buffers ( 14 ). Furthermore, the queue lengths are possible to reduce and the delays of data are reduced.

Description:
TECHNICAL FIELD 
   The present invention generally relates to data communication, and in particular to data communication between devices having limited bandwidth. 
   BACKGROUND 
   In many systems of today, data communication between different devices is one of the basic procedures on which the operation of the system depends. There are a large number of systems using data communication, e.g. telecommunication systems, industrial monitoring and control systems and traffic surveillance systems. There is often a requirement that the transfer time of the data does not exceed a maximum time, or that the transfer time is predictable within certain limits. At the same time, communication at high bandwidth is often expensive and the capacity of the communication links is mostly adapted to handle a normal high-intensity communication situation. However, abnormal traffic situations may cause congestion or loss of information. Thus, there is a general wish to monitor the capacity situation in different communication links in order to control the intensity of the data communication. 
   A method often used to handle temporary link capacity variations is to include buffers, which temporarily store the data until free link capacity is available. However, in order to handle large capacity variations, the size of the buffers has to be large. A disadvantage with this solution is that large buffers are expensive and that the delay in a large buffer may be unacceptably large. Instead, a regulation of the production of data to be communicated is required. By monitoring the capacity need and the free link capacity, such a regulation may be performed. However, such monitoring normally requires an additional data communication in the opposite direction, a feedback of information in the opposite direction compared with the normal communication, which requires additional hardware or results in a lower mean link capacity. 
   In prior art, solutions are presented, where a buffer of a transmission link is monitored. When the number of waiting messages or data packets increases, it may be that the link capacity temporarily is exceeded, and when the number of waiting messages or data packets decreases, free link capacity is used for shortening the queues. When the link capacity is exceeded, a regulation of the process generating the messages or data may be performed in order to reduce the generation rate of messages. However, if more than one process uses the same transmission link, the situation becomes more complicated, and an interconnection between the different processes is often necessary Furthermore, if the regulation of a process is slow, i.e. if the time from that a regulation starts until there is a noticeable change of the output rate, the buffer still has to be large in order to store all messages created in the meantime. 
   A general problem with certain devices according to prior art is that they give rise to large delays and that they require comparatively large buffer areas. 
   In the U.S. Pat. No. 6,091,709 a QoS management system for packet switched networks is disclosed. The basic idea concerns a problem specific to packet transmission networks—to meet guaranteed real-time services. A packet router system comprising a number of queues with different priorities. The mean delay of the packets in each queue, by time-stamping the packets at the entering into the queue. Intermittent monitoring of the mean age of the packets are performed. If the mean delay is under a first threshold, filler flow is directed to the queue, to get the queue to operate just around this threshold. The filler flow may consist of packets from queues with lower priority or if such are not available “dummy packets”. If a second delay threshold is passed, further packets directed to that queue is discarded. The thresholds are defined by using a relation between enqueued traffic and delay. The entire method relies heavily on the reliability of this relation curve, but no indications about how such curve is obtained are presented. The provision of reliable relation curves are far from simple. The procedure is particularly developed for systems being real-time critical and having a number of priority levels. The applicability on unity-priority systems is questionable. Furthermore, since an average forwarding delay is used, the method will have severe problems in handling burst-like traffic. Moreover, a measure of the average delay in a queue does not immediately concern the actual available or requested buffer length. Another problem of the above technique is that the process does not operate properly at longer congestion periods or at very sudden increases in traffic intensity. 
   SUMMARY 
   A general object of the present invention is thus to improve the regulation of the amount of information to be sent on a communication link. A further object is to provide a regulation, which counteracts exceeded transmission capacity and overflow in buffers. Another object is to provide a regulation, which reduces the problems if the transmission capacity of the link is exceeded. Yet another object of the present invention is to decrease the queue lengths in the buffers to reduce the delays of information. 
   The above objects are achieved by units, systems and methods according to the present claims. In general, a process unit, producing real data for communication with other units, comprises a real data generator, a first buffer buffering the data and a queue length monitor, which regulates the data generator depending on the queue length in the buffer. The system is characterized by a dummy load generator, storing dummy data in the buffer at a dummy data rate. The queue length monitor regulates the dummy data rate. The process unit may also be used in a system, further comprising a transmitter, a link and a receiver and possibly also other process units. 
   The advantage with the present invention is that a faster regulation can be achieved, also for slowly reacting process units, which faster regulation counteracts overflow in the buffers. Furthermore, the queue lengths are possible to reduce and the delays of data are reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which: 
       FIG. 1  is a schematic block diagram illustrating an embodiment of a process system comprising one process unit according to the present invention; 
       FIG. 2   a  is a diagram illustrating an exemplifying situation of data generation and transmission rates in a process system according to prior art; 
       FIG. 2   b  is a diagram illustrating an exemplifying situation of data generation and transmission rates in an embodiment of a process system according to the present invention; 
       FIG. 3  is a schematic block diagram illustrating another embodiment of a process system comprising two process units according to the present invention; 
       FIG. 4  is a flow diagram illustrating a transmission process according to the present invention; and 
       FIG. 5  is a schematic block diagram of a mobile telephony system, in which a process system according to the present invention can be used. 
   

   DETAILED DESCRIPTION 
   In  FIG. 1 , an embodiment of a process system  1  is illustrated. A process unit  10  comprises a real data generator  12 . The real data generator  12  performs the main task of the process unit  10  and the output data from that process is intended to be sent to another part of the process system  1 . The process unit is for this purpose served by a transmitter  20 , which sends information (messages) from the process unit further on a communication link  22  to a receiver  24 . The output from the real data generator  12  is real data, which is stored in a buffer  14 , waiting for the transmitter  20  to poll the data for transmission. 
   A monitoring unit  16  monitors the buffer  14 . By measuring the length of the queue, i.e. the amount of data waiting for transmission, information about whether the capacity of the link  22  is reached or not is obtained. If the presently available link  22  capacity for the process unit  10  is too small, the number of waiting messages will increase. If the queue length instead decreases, the rate in which the messages are created is lower than the available link  22  capacity. A longer queue gives longer delay times, so one important task is to reduce the number of messages waiting in the buffer  14 . If the number of messages in the buffer  14  starts to increase, the monitoring unit  16  informs the real data generator  12  about the congestion in the transmission link  22 , and the real data generator  12  regulates the rate in which output data is created. In such a manner, an overload of the buffer may be avoided. 
   However, when the regulation of the real data generator  12  is slow, e.g. when only the number of started jobs may be reduced, and when jobs under processing can not be influenced, the solution of the present invention comes into useful operation. According to the present invention, the process unit also comprises a dummy load generator  18 . Under normal operation, the dummy load generator  18  generates dummy data, and sends the dummy data for storage in the same buffer  14  as for the real data messages at a “dummy data rate”. This rate is the rate of generating dummy data, or even more correctly, the rate at which the dummy data is stored in the buffer  14 . The dummy data typically does not comprise any useful information and is only used for filling-up purposes. The dummy load generator  18  typically has a maximum dummy data rate, and the dummy data rate at a certain moment may therefore vary from zero up to this maximum dummy data rate. When there is available capacity of the link  22 , the dummy messages are just sent as any other messages and do not occupy any capacity from the real messages. The buffer  14  is in this situation substantially empty (except for a very short temporary use just upon writing into the buffer). The receiver  24  identifies the dummy data and ignores or discards it. The dummy data is therefore not brought further in the system. 
   When the total data generation rate, i.e. the real data generation rate plus the dummy data rate, exceeds the available capacity of the link  22 , a queue starts to build up in the buffer  14 . In such a situation, the dummy data competes with the real data about the transmission resources. The dummy data rate is reduced, based on the queue length in the buffer  14 , in order to release transmission capacity. The dummy data rate and the total data generation rate drop quickly, solving the problem of temporary lack of capacity. However, since the dummy data load only corresponds to a small part of the total available transmission capacity, the available transmission capacity is only slightly larger than the real data load. 
   The need for regulating the dummy data load acts as a warning about a possible coming lack of transmission capacity. It is therefore of interest to also start regulating the real data generation rate, in order to meet a coming congestion. The fast regulation of the dummy load thus operates as a buffer in order to give the process unit time enough to regulate down the real data generation rate. Accordingly, the monitoring of the buffer  14  controls both the real data generation rate and the dummy data rate. 
   The maximum dummy data rate is preferably adjusted to the properties of the process unit in which the dummy load generator is incorporated. A real data generator with a large inertia regarding generation rate needs a higher maximum dummy data rate in order to accomplish the necessary pre-notification of a congestion in the transmission system. The regulation response time of the real data generator constitutes the base on which the maximum value of the dummy data rate is determined. A fast responding real data generator needs a low maximum dummy data rate and a slowly responding real data generator needs a high maximum dummy data rate. 
   The simplest way of regulating the load of dummy data is to turn it on and off, i.e. to select between the maximum dummy data rate and zero. However, such a regulation is quite inflexible, leading to unnecessary restrictive real data generation rates. Accordingly, the regulation of the dummy data rate is preferably performed stepwise or continuously (down to the size of the basic transmission unit). 
   In order to visualize the operation of the present invention, an example of a situation of data generation and transmission rates in a process system  10  according to prior art is illustrated in  FIG. 2   a . A broken line  50  in the upper part of the figure illustrates the transmission capacity of a transmission link. The transmission capacity starts at the maximum value, but decreases rapidly between the time t 1  and the time t 6  to 70% of its maximum value. The normal data generation rate of the process unit, illustrated as a solid line  51  in the figure, is in this example 80% of the maximum transmission capacity, and when the full transmission capacity is available, all data can be transmitted without delays. In a system according to prior art, the process unit is unaware of the beginning decrease of available transmission rate  50  at t 1 . At the time t 4 , the data generation rate  51  exceeds the available transmission rate  50  and a queue starts to build up in the buffer, as indicated by the line  52  in the bottom part of  FIG. 2   a . At time t 5 , this build-up is detected and interpreted as a congestion. The process unit is regulated to give a final data generation rate  51  of 60% of the maximum available transmission rate, but due to the inertia in the process unit, the actual decrease in the generation rate  51  does not start until time t 7 . The data generation rate  51  of the process unit drops below the presently available transmission rate  50  at t 8  and reaches the goal of the regulation at t 9 . In the meantime, a queue has built up in the buffer. The queue length  52  increases until the real data generation rate  51  is lower than the transmission rate  50 , i.e. until t 8 . When the available transmission rate  50  becomes higher than the data generation rate  51 , the queue length starts to decrease again, but the queue will not be empty until the time t 10 . The buffer size necessary for avoiding overload of the buffer is considerable during the regulation of the process unit. The delay time for a message, stored temporary in the buffer, is closely related to the present length of the queue and the available transmission rate. An estimated delay time in the queue in the buffer for messages in the described system is indicated by the dotted line  56 . When the queue length increases, the delay of messages also increases. This is particularly serious, since a queue build-up normally is caused by a decrease in transmission rate, which also by itself increases the delay times. 
     FIG. 2   b , illustrates the same situation, but for a process system according to the present invention. Also here, the transmission rate decreases from 100% to 70% between t 1  and t 6 , as indicated by the broken line  50  in the upper part of the figure. A real data generation rate of 80% of the maximum transmission rate is present, as illustrated by the solid line  53 . According to the invention, a dummy data rate is present, illustrated by a solid line  54 . In this example, the starting level of the dummy data rate  54  is 10% of the maximum transmission rate. As before, in the beginning, the transmission rate  50  is sufficient, and there are no delays of the data. The real data is delivered as fast as it should have been also without dummy load. However, at the time t 2 , the total data generation rate exceeds the actual transmission rate, that is, the sum of the real data generation rate  53  and the dummy data rate  54 . A queue is starting to build up in the buffer, as indicated by  55  in the bottom of the figure. At t 3 , this build-up is detected and interpreted as a congestion. The dummy load  54  is quickly stopped and a regulation of the real data generation rate  53  down to 60% is ordered. Due to the inertia in the process unit, the actual decrease in the generation rate  53  does not start until time t 5 . In the meantime a margin is available due to the drop in the dummy data rate  54 , which keeps the queue length down. At t 7 , the regulation of the process unit is finished. In this example, the buffer is emptied from its last waiting data already at the same time t 7 . As seen in the bottom of  FIG. 2   b , the buffer queue length can be kept very short, which reduces the requirements of necessary buffer size as well as the delay time of the data. An estimated delay time in the queue in the buffer for messages in the described system is indicated by the dotted line  57 , which obviously is much less serious than in the system of  FIG. 2   a.    
   At t 7 , the dummy load is again turned on, now at a slightly lower rate, in order to assist at the next occasion where the transmission rate changes. In order to detect a subsequent increase in actual transmission rate, the dummy data rate is intermittently increased temporarily. If a queue starts to build up, it is reduced again. If the increased dummy data rate does not give rise to any buffer queue, the process unit can be regulated to a higher real data generation rate. 
   In  FIG. 3 , a system  1  with two process units  10   a ,  10   b  sharing a common transmission link  22  is illustrated. Each one of the process units  10   a ,  10   b  comprises a real data generator  12   a ,  12   b , which performs the main task of the process unit  10   a ,  10   b . The output data is temporarily stored in a real data buffer  26   a ,  26   b  before it is stored in a main buffer  14   a ,  14   b . The process units  10   a  and  10   b  are connected to one common transmitter  20 , which polls data from both main buffers  14   a ,  14   b  to be transmitted on the common link  22  to a receiver  24 . According to the present invention, each one of the process units  10   a ,  10   b  also comprises a monitoring unit  16   a ,  16   b  and a dummy load generator  18   a ,  18   b . Each process unit  10   a ,  10   b  is arranged in a similar manner as the process unit in FIG.  1 . 
   The two separate process units  10   a ,  10   b  may present different behavior regarding the response time and the real data generation rate of the real data generator  12   a ,  12   b . The dummy load generator  18   a  may therefore be arranged in a different manner, compared with the dummy load generator  18   b.    
   As above, the regulation response time for the real data generators in the different process units  10   a ,  10   b  is preferably used to determine the maximum storing rate of dummy data. When having more than one process unit connected to the same transmission link  22 , the behavior may be different for the different units. 
   A process unit having a high rate of real data generation and thus having a higher utilization of the transmission link  22  than other process units is preferably furnished with a larger maximum dummy data rate in order to be able to regulate in time. Now a first example of how the dummy load may be distributed will be described. Assume that process unit  10   a  have a “long-term” average real data generation rate of 50% of the normally total available transmission capacity of the link  22 , and the corresponding rate for process unit  10   b  is 25%. The “long-term” average is here intended to cover any normal fluctuations in real data generation rates during e.g. several days. If the regulation response times for the process units  10   a  and  10   b  are similar, a predetermined maximum dummy data rate of the dummy data generator  18   a  is preferably twice of that of dummy data generator  18   b , e.g. 5% and 2.5%, respectively. In such a case, there is available. capacity reserved by means of dummy load so that both real data generators may increase their respective load by 10% above the long-term average without any problems. The maximum dummy data rate is in this example set to a predetermined value. 
   In a second example, the maximum dummy data rate is not constant, but is regulated. This regulated maximum dummy data rate could be a function of the present real data generation rate (and as stated above, the regulation response time). For example, the regulated maximum dummy data rate could be proportional to the present real data generation rate. In the system of  FIG. 3 , the real data buffers  26   a ,  26   b  may be used to measure the present real data generation rate. 
   Depending on the method used by the device controlling the poll of the main buffers  14   a ,  14   b  there could be a queue growth in one of the queues, while not in the other. For example, one of the process units could send dummy data at its maximum dummy data rate and have no restriction on the real data generation rate, while the other process unit sends no dummy data and has a growing queue of real data in its buffer  14 . In such a case, it could be preferable to be able to redistribute the dummy load in order not to occupy capacity for any real data. Both process units could instead decrease their dummy load, allowing a larger real load. In such a situation, a regulation communication  28  has to be provided between the dummy load generators, either directly or indirectly. In  FIG. 3 , the regulation communication  28  is schematically drawn as a direct connection, however, as described below the actual connection could be made indirectly through other means of the system, as indicated by the broken line  32 . 
   An alternative for a regulation communication  28  is to use a process unit  30  on the receiver side of the link  22 . The process unit  30  may measure the received amount of data. An alternative is to use the dummy load to transmit data telling how much dummy load that is transmitted at the moment. The a dummy load may in a similar way also contain information about e.g. the generation rate of real data, the degree of regulation of the real data generator, the length of the queue and the growth rate in queue length in buffers  14 . However, since the dummy data may be stopped at any time instance, the information sent by the dummy data should not be vital for the immediate operation. The process unit  30  may however e.g. calculate appropriate regulated maximum dummy data rates and transmit such information back to the process units  10   a  and  10   b  in order to redistribute the regulated maximum dummy data rate and perhaps also regulate the real data generation rate. Such redistribution of dummy load could be performed in such a slow pace that the communication does not occupy the link  22  too much in the direction opposite of the direction of the real data flow. 
   Another alternative for a regulation communication  28  is of course to have direct communication between the dummy data generators, negotiating about the available dummy data load. 
   The redistribution of dummy load can be performed in different manners. An alternative is to decrease the regulated maximum dummy data rates for the process units with the presently highest dummy data rate. Presume a process system with two process units, where both process units have a regulated maximum dummy data rate of 5% each. Suppose that one process unit sends dummy data at a rate of 5% and has no restriction on the real data generation rate, while the other process unit sends no dummy data and has a growing queue of real data in its buffer. By decreasing the regulated maximum dummy data rate of the process unit that sends dummy data, some capacity will be set free to reduce the rate at which the queue of the other process unit is growing. To set even more capacity free, the first process unit could even be explicitly ordered to regulate its real data generation. In this example, information about present dummy data rate and present growth rate in the queue of each process unit has to be communicated, put together and used to calculate new regulated maximum dummy data rates. The new regulated maximum dummy data rates should be communicated back to the process units. 
   Another example of redistribution of dummy load is described below. A process system has a number of process units with different real data generation rates. Let the heaviest loaded process unit send all dummy data. If all the process units are polled with the same priority, then the heaviest loaded process unit will detect a congestion first. In this example, information about present real data generation rate of each process unit has to be communicated and put together to give new regulated maximum dummy data rates. The new regulated maximum dummy data rates should be communicated back to at most two process units. 
   Yet another example of redistribution of dummy load is described below. Let the regulated maximum dummy data rate for each process unit equal a predetermined total maximum dummy data rate multiplied by the present real data generation rate of the process unit divided by the present total real data generation rate for all process units. Then the predetermined total maximum dummy data rate is constant for the link, distributed proportionally to the present real data generation rate of each process unit. In this example, information about present real data generation rate of each process unit has to be communicated and summed up. The sum could then be sent back to each process unit to calculate its regulated maximum dummy data rate. 
     FIG. 4  illustrates a general procedure according to the present invention. The different steps are not intended to be viewed as steps in a restricted order, but should merely represent steps, which are available for the system to take. Some steps could even be performed in parallel. The procedure starts in step  100 . In step  102 , a process generates real data to be sent to another part of the system. According to the invention, dummy data is generated in step  104 . Step  106  presents the storage of the real data into a buffer of the process unit, and step  108  presents the corresponding storage of the dummy data into the same buffer. In step  110 , the data of the buffer, real or dummy, is transmitted on an outgoing link. In step  112 , the buffer is monitored in order to measure the queue length and detect any significant increase in the queue length. The result of the monitoring step is used in step  114  to regulate the rate of the real data generator and in step  116  to regulate the rate of the dummy data generator. The procedure is ended in step  118 . The actual order of the steps is not absolutely fixed, although e.g. the generating steps have to be taken before the storage steps. 
     FIG. 5  illustrates a schematic block diagram of a mobile telephony system  2 , in which a process system according to the present invention can be used. A Mobile Switching Center (MSC)  40  is connected to higher levels (not shown) of a mobile telephony network through a connection  42 . The MSC  40  is in this example connected to five Base Stations (BSs)  44  via control signaling links  22 A- 22 E. The BSs  44  may control a number of cells based around an antenna  46 . The antennas are used to communicate with one or more mobile stations  48  in each cell. Two control signaling links  22 B,  22 C are separate for the respective BS. However, the BSs  44  may also be cascade connected, i.e. one BS may be reached via another BS and control links  22 D,  22 E. Different functions, belonging to different cells in one and the same BS  44  or cascade connected BSs, have to compete about the capacity of the same control signaling link  22 A-E. 
   In some cases a high signaling level may occur. This can be caused by many subscribers wanting to make a call, which means that many originating calls from mobile stations  48  are made. If the control signaling link  22  A-E is exposed to disturbances, the available transmission capacity may be reduced, and at the same time some capacity is occupied by retransmitting disturbed data. Furthermore, other functionality may be introduced in the system using the control signaling link  22  A-E, such as e.g. sending of SMS messages (Short Message Service). The above described functions could all increase the signaling level, which may lead to an improper operation of the mobile telephony network. 
   In the Japanese mobile communication system, PDC standard RCR STD-27, there is a function specified as Radio Network Access Regulation (RNAR). One way to regulate the generation of real load sent from BS to MSC over the control signaling link  22  A-E is to use RNAR. With this function it is possible to restrict one or more mobile station groups from making originating calls. The restriction is made by broadcasting a message from the base station to the mobile stations. In the same way it is possible to restrict one or more mobile station groups from making location registrations. In the standard, general mobile stations are divided into eight mobile station groups. RNAR could be used, e.g. in situations with high signaling levels in order to reduce the delays and the amount of buffered data and to increase the throughput. This leads to a decreased number of rejected calls and less collisions in the radio interface. 
   From the occasion when a message including the restriction is sent to the mobile stations until all the mobile stations in the restricted group are silent, obeying the restriction, it could take up to about 21 seconds. If a mobile station  48  tries to make an originating call, it makes four attempts separated with about  6  seconds. During this time (3×6 seconds) the mobile station  48  is unreachable for the restriction message. It takes around 3 seconds from the initiation of the regulation until an available mobile station discovers that the regulation is active. This means that in the worst case, when an attempt for an originating call just has started, it may take up to 18+3=21 seconds before the mobile station  48  is aware of the restriction. The data belonging to originating calls and location registrations are sent from the mobile station  48  to the base station  44  over a radio interface. The base station  44  then sends data further on to the MSC  40  via the control signaling link  22  A-E. This link also carries data from different functions as well. Several devices within a BS  44  or several BSs  44  could share a common control signaling link  22  A-E. There is also load on the control signaling link  22  A-E from other functions than originating calls and location registrations. There are thus a lot of possible messages to be sent, even after a RNAR restriction has been ordered. 
   In the present system, the only way to monitor the load on the control signaling link  22  A-E is to see whether the amount of buffered data on the sending side of the control signaling link is increasing or not. The control signaling link  22  A-E then has to get overloaded before there is any indication of high load. Therefore it is necessary to wait for detection of overload before regulation of the load could be started, by restricting one or several mobile station  48  groups. Three BSs  44  are in this example connected to the same control signaling link  22 A. To send a message to the MSC  40  over the control signaling link  22  A-E, the BS  44  puts the message in a queue which is polled by the device controlling the control signaling link. The BS  44  is also arranged to measure the queue length of the buffer. According to the present invention, the BSs  44  also comprise a dummy data generator. 
   As an example, each BS  44  is allowed to send dummy data of an amount of 5% of the theoretical control signaling link capacity, i.e. the bit rate from the dummy messages makes up 5% of the maximum bit rate of the link. The capacity on a link could be lower than the theoretical value because of “bad connections” which could lead to retransmissions. If the link is not congested, there will not be any long queues or long delays in those queues. 
   If the queue in one of the BSs  44  is detected to grow, the link utilization is over 100% of the link capacity at that moment. But 15% of the theoretical link capacity, corresponding to 15% or more of the current link capacity, is used for dummy load. The BS  44  could then impose a restriction on additional mobile station  48  groups regarding e.g. originating calls or location registrations to lower the load on the control signaling link  22  A-E. Since it takes long time before the restriction has effect, the BS  44  decreases the dummy load at the same time. The BS  44  regulates the dummy load so that the queue does not increase and is kept short, but preferably is still sending as much dummy load as possible (but always less than 5% each). The regulation is done so that the real load has priority over the dummy load. In this way, the total real link load from each BS could increase 5% of the theoretical link capacity before it is a real congestion with growing queues, which gives the restriction time to take effect. 
   If the BS  44  finds it possible to send 5% dummy load again without increasing the queue length, then this could be an indication to lower the number of restricted mobile station  48  groups. On the MSC  40  side of the link  22  A-E, all dummy messages are thrown away. 
   It will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departure from the scope thereof, which is defined by the appended claims.