Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 12/064,902, filed Sep. 17, 2008, which is the National Stage of International Application No. PCT/SE2005/001247, filed Aug. 26, 2005, the disclosures of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to flow control for transmission of data frames from a node to another node, in particular a network including a first node and a second node or a data transmitting node and a data receiving node, and a method of transmitting data frames from a first node to a second node. 
       BACKGROUND 
       [0003]    The universal mobile telecommunications system (UMTS) is a network technology allowing transmission both of voice and high-speed data. It is part of the third-generation (3G) wireless standards, as specified by the Third-generation partnership project (3GPP). Wideband code-division multiple access (WCDMA), also called wideband CDMA, is one method for radio transmission used in UMTS. UMTS is a development of GSM/GPRS supporting packetized voice and data transmissions. 
         [0004]    The method called high speed downlink packet access (HSDPA) is an enhancement of UMTS for increasing the capability of transmitting data, resulting in a reduced cost per transmitted bit and a greater spectral efficiency, in addition to significant improvements in downlink data speeds. HSDPA can give improvements of at least two to three times the current capacity. It is based on the WCDMA standard and uses the same spectrum. HSDPA uses quadrature phase shift keying (QPSK) and 16-quadrature amplitude modulation (16QAM). 
         [0005]    The HSDPA method uses a distributed architecture in order to achieve a low delay link adaptation by performing the most important process steps in the radio base stations (RBSs) and thus close to the air interface, see  FIG. 1 . HSDPA uses well established processing steps, including fast physical layer (L1) retransmission for faulty packets, combining and link adaptation techniques, to obtain improved packet data transmission. 
         [0006]    The HSDPA process steps basically include:
       scheduling in the radio base stations for the downlink packet data operation;   higher-order modulation;   adaptive modulation and coding;   hybrid automatic repeat requests (HARQs) for retransmissions;   physical layer feedback of the momentary channel condition; and   transmission in a high-speed downlink shared channel (HS-DSCH) allowing several users to share an air interface channel.       
 
         [0013]    In the following some important features of HSDPA will be described. 
         [0014]    1. Adaptive Modulation and Coding 
         [0015]    HSDPA uses advanced link adaptation and adaptive modulation and coding. 
         [0016]    2. Fast Scheduling 
         [0017]    In HSDPA data traffic is scheduled in the radio base stations. HSDPA uses information on channel quality, terminal capabilities, quality of service (QoS), and power/code availability to achieve efficient scheduling of data packet transmissions. 
         [0018]    3. Fast L1 Retransmissions 
         [0019]    When a link error occurs, a mobile terminal immediately requests the retransmission of the lost or erroneous data packets. This operation is denoted as a method including hybrid automatic repeat requests (HARQs) for reducing the delays in and increasing the efficiency of retransmissions. HARQ control is performed in the radio base stations, as illustrated in  FIG. 2 . 
         [0020]    4. Channel Quality Feedback 
         [0021]    In the radio base stations, according to the HSDPA method, estimates of the channel quality of each active user are collected and used. This feedback provides current information on a wide range of channel variable physical layer conditions, including power control, acklnack ratio, QoS, and HSDPA-specific user feedback. 
         [0022]    5. High-Speed Downlink Shared Channels (HS-DSCHs) 
         [0023]    HSDPA operation is carried in high-speed downlink shared channels using a frame length of only two milliseconds, compared to frame lengths of 10, 20, 40 or 80 ins used in previously used downlink shared channels (DSCHs). Such downlink shared channels are downlink transport channels, each of which may be shared by several user equipments. A downlink shared channel is used to carry dedicated control or traffic data from the SRNC (Serving Radio Network Controller). A DSCH will be associated with one or several downlink DCHs (Dedicated Channels). The HS-DSCHs provide 16-level quadrature amplitude modulation (16-QAM), link adaptation, and the combining of retransmissions in L1 with HARQs. HSDPA uses high-speed shared control channels (HS-SCCHs) to carry the required modulation and retransmission information. Uplink high-speed dedicated physical control channels (HS-DPCCHs) carry automatic repeat request (ARQ) acknowledgement messages, provide downlink quality feedback and transmit other necessary control information in the uplinks. 
         [0024]    HSDPA requires a flow control algorithm or method that controls the transmission of data frames in an HS-DSCH, as specified by e.g. TS 25.401 from 3GPP, between a radio network controller and a radio base station. The algorithm for flow control is not standardized, but control messages, e.g. the message “Capacity Allocation”, are standardized. In order to manage the flow control, the RBS calculates the allocations to be carried in the “Capacity Allocation” messages sent to the RNC, and the RNC sends data frames in the HS-DSCH to the RBS according to the information in the “Capacity Allocation” messages, one allocation of capacity for each flow of data. When there is more data to send from the RNC, the information element (IE) “User Buffer Size” (UBS) in the HS-DSCH data frames is larger than zero. When the data frame has emptied the RNC buffer for the respective flow of data, UBS is set to zero. 
         [0025]    The flow control algorithm has to manage limitations for both the air-interface and the Iub HS-DSCH bandwidth, Iub being the interface between an RNC and an RBS. 
         [0026]    More particularly, the transfer of a data frame in an HS-DSCH from an RNC to an RBS is made in the following way. After the RNC has been granted capacity by the RBS, as obtained from a capacity allocation control frame or from an initial capacity allocation control frame received from the RBS, as described in 3GPP TS 25.433, and the RNC has data waiting to be sent, the data frame is used to transfer the data in the HS-DSCH. If the RNC has been granted capacity by the RBS using the initial capacity allocation control frame as described in 3GPP TS 25.433, this capacity is valid for only the first data frame transmission in the HS-DSCH. When data is waiting to be transferred, and a capacity allocation control frame has been received, a data frame in the HS-DSCH will be transmitted immediately according to the received allocation, i.e. using the bandwidth corresponding to this allocation. Each data frame sent in an HS-DSCH includes the information element “User Buffer Size” to indicate the amount of data pending for a respective flow for an indicated priority level. 
       SUMMARY 
       [0027]    It is an object of the invention to provide an efficient flow control algorithm. 
         [0028]    It is another object of the invention to provide a flow control algorithm that considers the fact the data flows can be inactive, i.e. that for some time periods there may be no more data in the flows to be transmitted. 
         [0029]    A flow control method, also called flow control algorithm or flow control function, is proposed that has states stored per radio base station. If such states are not stored per radio base station the detection of inactive users is not needed. However, storing such flow control states per radio base station can result in a better transport network utilization. In the method as proposed herein the value of the information element “User Buffer Size” is used for the flow control. Priority queue flows for which data are waiting to be transmitted get a calculated or estimated capacity allocation, i.e. a highest possible bitrate for transmission, considering the number of priority queue flows and conditions in neighboring networks, and priority queue flows for which no data have been waiting to be transmitted for a predetermined time period get a “background” or minimum predefined capacity allocation value. 
         [0030]    An advantage of this method is that only active priority queue flows compete for the available bandwidth, whereas inactive priority queue flows only use very small capacity allocations. Otherwise, if all priority queue flows would be given the calculated or estimated capacity allocation, i.e. bandwidth or bitrate, some part of the total transmission capacity available for the considered type of data transmission would be wasted, said part corresponding to that bandwidth that is reserved for the inactive priority flows. 
         [0031]    The purpose of using such minimum capacity allocations for inactive priority queue flows is to avoid using the sequence of first sending a message with a capacity request sent from the radio network controller, this resulting in that a capacity allocation message is sent from the radio base station to the radio network controller before data can be start to sent from the radio network controller to the radio base station. The inactive priority flows, i.e. flows for which no data is waiting to be transmitted, are detected by considering the value of the information element “User Buffer Size”, storing states per priority queue and using inactivity timers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The invention will now be described by way of non-limiting embodiments with reference to the accompanying drawings, in which: 
           [0033]      FIG. 1  is a schematic of communication between a radio base station and user equipments using high-speed down-link data transmission, 
           [0034]      FIG. 2  is a schematic illustrating differences in data transmission to user equipments using a shared downlink channel according to two different methods, 
           [0035]      FIG. 3  is a diagram illustrating transmission of data from an application server to an application running in a user equipment using HSDPA and a flow control function for control of Iub, 
           [0036]      FIG. 4  is a diagram illustrating different layers in communication between an RNC and an RBS using HSDPA, 
           [0037]      FIG. 5  is a transmission diagram illustrating a principle for flow control using standardized messages, 
           [0038]      FIG. 6  is a schematic illustrating buffers in an RNC, an RBS and a UE, 
           [0039]      FIG. 7  is a diagram illustrating calculation of the state of a priority queue flow, 
           [0040]      FIG. 8  is a state machine of changes of the state of a priority queue flow, and 
           [0041]      FIG. 9  is a schematic of a radio base station illustrating a flow control unit and related memory cells. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    The general flow of information in a system built according to UMTS including both a mobile telephony network and some other network, for information transmitted from the other network to a user equipment (UE) in the mobile telephony network, using high speed downlink packet access (HSDPA), in particular the flow between a radio network controller (RNC) and a radio base station (RBS) in the mobile telephony network, will now be described with reference to  FIGS. 3-6 . These figures include mainly only units and functions that are relevant to or needed for said general flow of information. 
         [0043]    Many packet data applications use the standardized transmission control protocol (TCP), as specified by IETF, for transmitting data. As seen in  FIG. 3 , data, such as an Internet page, can e.g. be sent from an application server  101  through a public data network (PDN), also called a general purpose network or general network  103 , such as the Internet to an application  105  running in a user equipment  107 , i.e. a mobile terminal. The IETF transmission control protocol has a window size of its own, which limits the number of bytes in the different buffers that the data has to pass between the application server  101  and the user equipment. The radio link control (RLC) sublayer has another window size. Automatic repeat request (ARQ) acknowledgement messages are used both according to TCP and in the RLC sublayer for controlling the correctness of transmissions. 
         [0044]    The general purpose network  103  is connected to the mobile telephony system  104  at a gateway or support node  109 , for GPRS this node including a gateway GPRS support node (GGSN) and a serving GPRS support node (SGSN). The gateway GPRS support node is in GPRS a router that serves as a gateway or interface between packet data networks and mobile telephony networks, in particular between a packet data network such as an internet protocol (IP) network ( 103 ) and a serving GPRS support node in the mobile telephony network  104 . 
         [0045]    The interface between a core network and a radio access network (RAN) is generally called Iu and the packet-switched interface between an SGSN and an RNC  111  is called Iu-PS. The interface between the RNC and an RBS  113  is called Iub and the interface between the RBS  113  and the mobile terminal  107  is called Uu. 
         [0046]    Packets received from the gateway or support node  109  are first stored in SDU buffers  115 . IP packets are stored here, which because of RLC protocol reasons, in particular sequence number limitations, cannot be stored in the RLC buffers. 
         [0047]    Then, in the RNC  111  the information to be sent to an RBS is divided based on terminal and radio base station capabilities, subscription type, radio conditions and possibly QoS requirements, in data to be transmitted in dedicated channels and data to be transmitted in a shared channel, the latter type of data being that considered here. 
         [0048]    A flow control (FC) function is used for controlling communication between the RNC  111  and the RBS  113 , in particular the flow of data frames in the HS-DSCH, using the Iub interface and has the purpose of keeping priority queues (PQs)  127  in the RBS short and not to overflow the Iub transport network, i.e. the transport network between the RNC and the RBS, see the network portions  119 ,  121  in  FIG. 3 . 
         [0049]    Iub Architecture for HSDPA 
         [0050]    The flow control function includes portions  123 ,  125  located in the RNC  111  and in the RBS  113 , respectively. In the RBS it is a part of the MAC-hs (Media Access Control for HSDPA) function  126 . It interacts, using Iub protocol messages carried in Iub control frames, with the flow control portion  123  in the RNC that is part of the MAC-d (Media Access Control, dedicated channels) function  124  in the RNC  111 , see also  FIG. 4 . 
         [0051]    The flows that are controlled by the flow control function  123 ,  125  are the flows of MAC-d protocol data units (PDUs), carried in HS-DSCH data frames according to the Iub frame protocol (FP). 
         [0052]    Each MAC-d PDU arriving to the portion  125  of the flow control function in the RBS  113  is stored in one of the priority queues  127 , waiting to be selected by the scheduler function  129  of the RBS for transmission over the Uu interface to the user equipment  107 . 
         [0053]    In the RBS  113  one priority queue  127  is provided for each HS-DSCH MAC-hs connection of the connected user equipments  107  and one controlled flow of MAC-d PDUs is provided over the Iub interface to each priority queue. Each such flow is in the flow control function denoted a priority queue flow (PQF). A priority queue flow is defined as packets arriving for the same user having the same contents of the “Common Channel Priority Indicator” (CmCH-PI) field, as defined in standard documents. In practice, in most cases there is for each user equipment at each instant only one priority queue flow that is the downlink traffic flow for the respective user, though generally there may be a plurality of priority queues for each connected user equipment  107 . 
         [0054]    Each priority queue flow is transported over the Iub interface by one instance of the Iub frame protocol (FP) using a dedicated AAL2 (ATM Adaptation Layer No. 2) connection as transport bearer. 
         [0055]      FIG. 4  illustrates the layer configuration and corresponding units of the Iub and Uu interfaces.
       The radio link control sublayer portion  401  of the RNC  111  has the main purpose of ensuring a loss-free, i.e. reliable, link over the radio interface for TCP based data transfer. It provides reliability using error detection and recovery by retransmissions. The RLC does segmentation and reassembly of higher layer PDUs. Thus, if only a small part of a PDU has been lost, the full PDU must not be retransmitted. This way the end-to-end congestion control algorithm must not react to the changing radio conditions. The RLC  410  communicates with a radio link control sublayer portion  402  included in an RLC/MAC-d portion  133 , see  FIG. 3 , of the user equipment  107 .   The MAC-d function  124  in the RNC  111  communicates with an MAC-d function  403  included in the RLC/MAC-d portion  133  of the user equipment  107 , see  FIG. 3 . Furthermore, the MAC-d function of the RNC  111  is here illustrated as including an HS-DSCH FP (Frame Protocol) handling unit  404 . This frame protocol handling unit in turn includes the flow control portion  123  and communicates with the flow control portion  125  included in an HS-DSCH FP handling unit  405  of the MAC-hs function  126  of the RBS  113 . The MAC-hs function of the RBS includes the flow control portion  125 , the scheduler  129  and the MAC-hs FIARQ function  131 , see  FIG. 3 . The MAC-hs function  126  in the RBS communicates with the MAC-hs function  135  in the user equipment  107 . The MAC-hs function of the user equipment includes an HARQ function  136 , see also  FIG. 4 , communicating with the MAC-hs HARQ function  131  of the RBS  113 .   The AAL2/ATM VC layer having portions  407 ,  409  in the RNC  111  and the RBS  113 , and   The physical layer (L1) portions  411  in the RNC  111 ,  413 ,  415  in the RBS  113  and  417  in the UE  107 .       
 
         [0060]    For the communication between the RBS  111  and the RNC a transport network  419  such an ATM network and/or a PDH/SDH network is used, compare the transport network portions  119 ,  121  of  FIG. 3 . For the communication between the RBS  111  and the UE  107  a wireless network  421  is used. 
         [0061]    Flow Control Messages Between RNC and RBS 
         [0062]    HSDPA data, i.e. MAC-d PDUs, are sent from the RNC  111  to the RBS  113 . Each MAC-d flow of a given priority level is equal to one priority queue flow and is represented by one queue  117  in the RNC and one queue, a priority queue  127 , in the RBS. A number of MAC-d PDUs are sent in each HS-DSCH FP data frame, belonging to the same MAC-d flow. 
         [0063]    Data frames sent over Iub for each priority queue flow is flow controlled using capacity allocation (CA) messages, sent in control frames from the RBS  113  to the RNC  111 , see  FIG. 5 . A capacity allocation message specifies, as given by a combination of parameters, the maximum bitrate. i.e. the maximum number of MAC-d PDUs that are allowed to be transmitted during a predetermined time period for the considered priority queue flow. From such a message a minimum repetition period can also be obtained. 
         [0064]    For a simple case the RBS  113  decides, based on the filling level of the respective buffer, i.e. the length of the respective priority queue, in the RBS, on air interface conditions, i.e. conditions related to the Uu interface, and on transport network congestion in Uu, the bitrate that should be allocated for the given priority queue to be used by the RNC  111  for transmission in the respective HS-DSCH. The RNC shapes data flows according to the last received capacity allocation messages. Message structures can be found in the document 3GPP TS 25.435, in particular  FIG. 21A , “Data Frame”, and  FIG. 36 , “Capacity Allocation”, and the accompanying text. 
         [0065]    The flow control function  123 ,  125  is aware of the average data rate available for a priority queue flow on the air interface between the RNC and the RBS or at least an estimate of said average data rate. It also knows the number of PDUs from that priority queue flow which are waiting in the RBS buffer for this queue  127 . Based on this information the flow control function can decide to change the allocated rate of the considered priority queue flow. The main goal is to keep a target number of PDUs waiting in the RBS  113 , i.e. not too many and not too few PDUs in each of the priority queues. 
         [0066]    There is one RLC queue  117  per priority queue flow in the RNC  111  and one Mac-hs queue, i.e. priority queue  127 , per priority queue flow in the RBS  113 . 
         [0067]    The buffers for the queues  117 ,  127  are designed in such a way that PDUs are most probably lost only in the transport network of Iu or in the air interface of Uu. 
         [0068]    Purpose of Using a Flow Control Function 
         [0069]    Iub traffic flows in HS-DSCHs are flow controlled by the flow control function  125  of the MAC-hs  126  in the RBS  113 . The Iub protocol messages that can be used for flow control are specified in 3GPP TS 25.435 (Iub). The flow control function itself is not standardized. 
         [0070]    The purpose of the flow control function is to keep an “appropriate” amount of MAC-d PDUs buffered in the RBS  113 , i.e. to keep the RBS priority queues  127  short enough for RLC retransmissions but long enough to ensure throughput when scheduled. 
         [0071]    The same logical RLC buffer for the priority queue flows can be seen as distributed over the RNC  111 , RBS  113  and UE  107 . The MAC-d PDUs to be retransmitted have a higher priority in the RNC than PDUs that are to be sent for the first time from the RNC, see  FIG. 6 . Therefore the RLC RBS portion, the priority queues  127 , shall be “short” or not too long, this being one reason to use a flow control function for controlling transmission in the HS-DSCHs from the RNC  111  to the RBS  113 . 
         [0072]    HS-DSCH traffic is carried over a “best effort” type of quality of service (QoS) in the transport network  119 ,  121 ;  415  between an RNC and an RBS. The flow control function shall regulate the HS-DSCH traffic flow in such a way that loss of MAC-d PDUs, due to too long Iub transport delays, such as caused by overload of the transport network, becomes appropriate. There is a trade-off between having a high frame loss combined with a high bandwidth utilization and a low frame loss combined with a lower bandwidth utilization. 
         [0073]    There are mainly two bandwidth capacity bottlenecks for HSDPA traffic in the transport networks between the RNC  111 , the RBS  113  and the UE  107 , both which must be considered in the flow control function:
       Iub interface   Radio interface in Uu       
 
         [0076]    A flow control function including a special method of allocating capacity for users, using “user states”, will now be described with reference to  FIGS. 7 and 8 . These variables “user states”, also called flow control states or priority queue flow states, are stored in the radio base station for each current user. In particular, detection of inactive users is used. This capacity allocation method can result in a better utilization of the transport network for Iub. 
         [0077]    The method uses the current value of the standardized information element “User Buffer Size” (UBS) for each user for accomplishing the flow control. Priority queue flows having (User Buffer Size)&gt;0 gets a calculated capacity allocation and users having (User Buffer Size)=0 during a predetermined time period, gets a “background” or minimum capacity allocation. 
         [0078]    The user states, denoted pqfStates, are thus defined to have either one of the states active or inactive, these states denoted activePqf and inactivePqf. A user that has an inactive priority queue flow, i.e. for which its pqfState=inactivePqf, does not compete for the available HS bandwidth in transmissions between the RNC and the RBS. Such a user gets a predefined capacity allocation with the purpose of being prepared when data is to be sent from the RNC, without the need of using a capacity request control frame. This predefined capacity allocation does not consume any significant portion of bandwidth taken from the calculated cell HS bitrate. 
         [0079]    For a user that has an active priority queue, i.e. for which its pqfState=activePqf, there are more data to be transmitted. This is indicated by the fact that the information element “User Buffer Size” is larger than zero. The information element “User Buffer Size” is included in HS-DSCH data frames as standardized. Such a user having an active priority queue flow gets a calculated capacity allocation bitrate. 
         [0080]    An inactive priority queue flow, i.e. for which its pqfState=inactivePqf, is a priority queue flow with a “context”, i.e. a priority queue flow for which a priority queue  127  exists in the RBS  113 , but for which there are no more data to be currently transmitted from the RNS  111 . An active priority queue flow is set to be inactive, i.e. it gets its state changed to inactivePqf, if the information element “User Buffer Size” for this queue has been equal to zero for a period longer than a predefined time, denoted ubsZeroTime. 
         [0081]    The capacity allocation method uses as input this fixed parameter ubsZeroTime that is hard-coded and the information element or variable “User Buffer Size” for each existing priority queue flow. The method produces as output the variable pqfState for each existing priority queue flow. The information element “User Buffer Size” is, as standardized, sent by the RNC  111  and indicates the amount of data that is available in the RNC, or is traveling towards the RBS  113 , after having received an HS-DSCH data frame or capacity request. 
         [0082]    For each of the priority queue flows or at least for those of the priority queues that have been assigned one, a UBS inactivity timer is incremented every 2 ms TTI. 
         [0083]    For an active priority queue flow: 
         [0000]    1. as long as “User Buffer Size”&gt;0, the variable pqfState for the user of the priority queue flow remains equal to activePqf.
 
2. as soon as “User Buffer Size” becomes equal to zero, a UBS inactivity timer for this flow is reset and started. If “User Buffer Size” has been equal to zero for the predetermined time period ubsZeroTime, the variable pqfState is set to inactivePqf. If “User Buffer Size” becomes larger than zero before the UBS inactivity timer has expired, the variable pqfState remains equal to activePqf.
 
         [0084]    For an inactive priority queue flow: 
         [0000]    1. as long as “User Buffer Size” is equal to zero, the variable pqfState remains equal to inactivePqf.
 
2. if “User Buffer Size” becomes larger than zero, the variable pqfState is set to activePqf.
 
         [0085]    As seen in  FIG. 7 , in the RBS  113 , at each time when a data frame is received from the RNC  111 , the UBS is extracted and the inactivity timers are incremented. The state of the priority queue flow having data in the received data frame is calculated in a state calculation function  701 . A state machine of the state calculation function illustrates, as seen in  FIG. 8 , that each priority queue flow can take either an active state  801  or an inactive state  803 . 
         [0086]    Thus, at reception of an HS-DSCH data frame from the RNC  111 , the new UBS is compared to zero. 
         [0087]    An active priority queue flow can have the variable UBS larger than zero or equal to zero, see the vivid substate  805  and the waiting substate  807 , respectively.
       If the previous UBS for the active priority queue flow was larger than zero, i.e. the priority queue flow taking the vivid substate  805 , and the new UBS is equal to zero, the waiting substate  807  is instead taken in which the UBS inactivity timer is reset and started.   If the active priority queue flow is in the waiting substate  807  and the new UBS is larger than zero, the vivid substate  805  is instead taken.   If the active priority queue flow is in the waiting substate  807 , the new UBS is equal to zero and the UBS inactivity timer is larger than or equal to the parameter ubsZeroTime, the priority queue flow becomes inactive and takes the inactive state  803 .       
 
         [0091]    An inactive priority queue flow is always in the state  803  but when the new UBS is larger than zero, it becomes active and passes to the vivid substate  805  of the active state  801 . 
         [0092]    In the calculation of capacity allocation for active and inactive priority queue flows the air-interface HS estimated bitrate is compared to the available Iub HS traffic bandwidth. The calculated capacity allocated bitrate, denoted caCalcBitrate, for each of the active priority queue flows is the minimum of the air-interface and Iub bitrates available for the considered priority queue flow. The Iub bitrate is calculated by dividing the estimated available Iub capacity for all priority queues among the different priority queues. An example of the calculation method can be found in the simultaneously filed International patent application, “FLOW CONTROL IN UMTS”, for Telefonaktiebolaget L M Ericsson, inventors Peter Lundh, Szilveszter Nadas, that is incorporated by reference herein. 
         [0093]    Inactive priority queue flows get a minimum CA Bitrate, denoted minCaRate, and thus do not use any significant capacity from the common Tub capacity pool. It can be so small that there is no need for reservation. 
         [0094]    The calculation of capacity allocation for active and inactive priority queue flows uses as inputs the parameter minCaRate and the variable pqfState for each currently existing priority queue flow. It produces as output the variable caCalcBitrate. The calculation is given by the following pseudo-code: 
         [0000]    
       
         
               
               
             
               
               
             
               
               
             
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 IF pqfState is activePqf, 
               
               
                   
                 THEN 
               
             
          
           
               
                   
                 calculate caCalcBitrate normally 
               
             
          
           
               
                   
                 ELSE 
               
             
          
           
               
                   
                 caCalcBitrate = minCaRate 
               
               
                   
                   
               
             
          
         
       
     
         [0095]    For performing the flow control function a flow control unit  901  and some memory cells have to be introduced in the RBS  133  as seen in the diagram of  FIG. 9 . The memory cells include, for each priority queue  127  and hence for each priority queue flow a memory cell  903  for storing the value of the variable pqfState and a memory cell  905  for storing the UBS inactivity timer. Also there is a memory cell  907  for the fixed threshold value ubsZeroTime. The flow control unit  901  includes a unit  909  for incrementing the UBS inactivity timers stored in the cells  905 , a comparator  911  for comparing UBS of a received data frame to zero, a unit  913  for changing the value of the variable pqfState stored in one of the cells  903  when required, a unit  915  for resetting and starting one of the UBS inactivity timers stored in the cells  905  when required, a comparator  917  for comparing one of the UBS inactivity timers stored in the cells  905  to the fixed value of ubsZeroTime when required, and a unit  9191  for calculating, based primarily on the number of priority queues for which the variable pqfState has the value activePqf, but also considering the number of priority queues for which the variable pqfState has the value inactivePqf, the capacity allocations for all priority queues. 
         [0096]    Typically, the available Iub HS traffic bandwidth, that is equal to the total transport network capacity available for all PQFs of the RBS, can be about 0.5 Mbps-30 Mbps. This value must be estimated in the RBS. The minimum CA Bitrate” can typically be 8 kbps-32 kbps, this being in all practical cases a very insignificant portion of the available Iub HS traffic bandwidth.

Technology Category: h