Abstract:
A call admission control technique allowing flexible and reliable call admissions at an ATM switch in the case of an ATM network including both QoS-specified and QoS-unspecified virtual connections is disclosed. In the case where a QoS (Quality of Service) specified connection request occurs, an estimated bandwidth is calculated which is to be assigned to an existing QoS-unspecified traffic on the link associated with the QoS-specified connection request. A call control processor of the ATM switch determines whether the QoS-specified connection request is accepted, depending on whether a requested bandwidth is smaller than an available bandwidth that is obtained by subtracting an assigned bandwidth and the estimated bandwidth from a full bandwidth of the link.

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. Patent Application Ser. No. 09/615,719 filed Jul. 13, 2000 which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to call admission control techniques in an ATM (asynchronous transfer mode) switch, and more particularly to call admission control method and system for use in the ATM switch handling QoS (quality of service)-specified and QoS-unspecified virtual connections. 
     2. Description of the Related Art 
     In a local-area network (LAN) environment including ATM LANs and legacy LANs, a bandwidth management technique of ATM connections is needed to operate an application requiring a high quality, such as the case of video service. 
     As an example, a CAC ATM-connection bandwidth management system has been disclosed in Japanese Patent Application Unexamined Publication No. 10-271116. This conventional system is provided with a per-connection bandwidth monitor, allowing CAC (Call Admission Control) information to be calculated and displayed on screen. Further, the conventional system is provided with a simulator for predicting an available connection bandwidth. 
     Call Admission Control (CAC) is a function of determining whether a connection request is admitted or denied. More specifically, CAC determines whether the connection request can be accepted at SVC (switched virtual connection) call origination time. The connection request can be accepted only if the QoS for all existing virtual connections would still be satisfied if the request was accepted. 
     However, the conventional CAC has disadvantages in the case where a network using UBR (unspecified bit rate) traffic as normal traffic such as LAN emulation is connected to another network handling QoS-specified virtual connections such as CBR (constant bit rate) or VBR (variable bit rate) virtual connections. 
     More specifically, as shown in  FIG. 4B , it is assumed that the full bandwidth of a line is B, of which a certain portion A QOS  is already assigned to CBR/VBR traffic virtual connections and further a portion is assigned to a UBR traffic virtual connection. In this case, if the requested bandwidth R of a CBR traffic virtual connection is smaller than the available bandwidth A F =(B−A QOS ), then the connection request is accepted regardless of the UBR traffic virtual connection, which may cause the UBR-traffic virtual connection to be suddenly disconnected. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a call admission control method and system allowing flexible and reliable call admissions at an ATM switch in the case of an ATM network including both QoS-specified and QoS-unspecified virtual connections. 
     According to the present invention, a call admission control method includes the steps of: a) receiving a QoS (Quality of Service) specified connection request: b) calculating an assigned bandwidth on a link associated with the QoS-specified connection request; c) calculating an estimated bandwidth to be assigned to an existing QoS-unspecified traffic on the link associated with the QoS-specified connection request; and d) determining whether the QoS-specified connection request is accepted, based on a combination of the assigned bandwidth and the estimated bandwidth. 
     In the step (c), the estimated bandwidth on the link may be obtained based on an average QoS-unspecified traffic of each QoS-unspecified virtual connection existing on the link associated with the QoS-specified connection request. The average QoS-unspecified traffic may be calculated by adding up existing QoS-unspecified traffics obtained at predetermined sampling time intervals. 
     The step (c) may include the steps of: adding up existing QoS-unspecified traffics obtained at predetermined sampling time intervals to produce a first average QoS-unspecified traffic; sequentially storing a first average QoS-unspecified traffic each time a corresponding QoS-unspecified connection is established at the ATM switch; and calculating the estimated bandwidth by averaging a predetermined number of first average QoS-unspecified traffics stored. 
     The step (d) may include the steps of: adding the assigned bandwidth and the estimated bandwidth to produce an currently assigned bandwidth in the link; calculating an available bandwidth of the link by subtracting the currently assigned bandwidth from a full bandwidth of the link; and determining whether the QoS-specified connection request is accepted, depending on a comparison of the available bandwidth and a requested bandwidth of the QoS-specified connection request. 
     According to anther aspect of the present invention, a call admission control system in an ATM switch having a plurality of links connected thereto, includes: a traffic monitor for monitoring a QoS-unspecified traffic for each QoS-unspecified connection existing on each link; a memory for storing a cell traffic management table containing an average QoS-unspecified traffic for each QoS-unspecified connection existing on each link; and a call admission manager for calculating an estimated bandwidth by adding up average QoS-unspecified traffics for all existing QoS-unspecified connections on a link associated with a QoS-specified connection request, wherein the estimated bandwidth is a bandwidth to be assigned to the existing QoS-unspecified connections on the link, and determining whether the QoS-specified connection request is accepted, based on a combination of the estimated bandwidth and an assigned bandwidth that is already assigned in the link. 
     According to further another aspect of the present invention, a call admission control system in an ATM switch having a plurality of links connected thereto, includes: a traffic monitor for monitoring a QoS-unspecified traffic for each QoS-unspecified connection existing on each link; a calculator for adding up existing QoS-unspecified traffics obtained at predetermined sampling time intervals to produce a first average QoS-unspecified traffic, and calculating the estimated bandwidth by averaging a predetermined number of first average QoS-unspecified traffics stored; a memory for storing a cell traffic management database sequentially containing a first average QoS-unspecified traffic each time a QoS-unspecified connection is established at the ATM switch; and a call admission manager for calculating an estimated bandwidth by adding up first average QoS-unspecified traffics for all existing QoS-unspecified connections on a link associated with a QoS-specified connection request, wherein the estimated bandwidth is a bandwidth to be assigned to the existing QoS-unspecified connections on the link, and determining whether the QoS-specified connection request is accepted, based on a combination of the estimated bandwidth and an assigned bandwidth that is already assigned in the link. 
     Since CAC is performed taking into account the bandwidth that is already assigned to the existing QoS-unspecified virtual connection, the UBR-traffic communication is prevented from being suddenly disconnected even in the case of occurrence of a request for a QoS-specified virtual connection requiring a bandwidth greater than the current available bandwidth of a corresponding link. 
     Since a necessary bandwidth is dynamically assigned to the existing UBR-traffic virtual connection, an available bandwidth at that time can be efficiently assigned to a QoS-specified virtual connection request. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a basic configuration of an ATM switch employing a CAC method according to an embodiment of the present invention; 
         FIG. 2A  is a diagram showing the field structure of a cell traffic management table as shown in  FIG. 1 ; 
         FIG. 2B  is a diagram showing the field structure of a call admission management table employed in the embodiment; 
         FIG. 3  is a diagram showing an operation of the ATM switch as shown in  FIG. 1 ; 
         FIG. 4A  is a schematic diagram showing a CAC operation according to the embodiment of the present invention; 
         FIG. 4B  is a schematic diagram showing a conventional CAC operation; and 
         FIG. 5  is a diagram showing a cell traffic management database for use in an ATM switch employing a CAC method according to another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIG. 1 , it is assumed for simplicity that an ATM switch has two input ports, two output ports and a control section. The ATM switch according to an embodiment of the present invention is basically structured by input line modules  1  and  2  each connected to the input lines, an ATM cell switch  3 , output line modules  4  and  5  each connected to the output lines, CPU/SW interface  6 , a data processor (CPU)  10 , and a memory  20  storing a cell traffic management table  21 . 
     Each of the input line modules  3  and  2  extracts cells from transmission frames on a corresponding incoming line and counts the number of received cells for each virtual connection. Each of the input line modules  1  and  2  is provided with a counter for counting received cells. At request of the data processor  10 , the receiving cell count is output to the data processor  10  through the CPU/SW interface  6  as described later. 
     The ATM cell switch  3  performs the routing of cells arriving at each input line to the required output line by mapping the VPI/VCI in the header of the incoming cell into the corresponding output VPI/VCI using virtual connection management information that is previously installed in the ATM cell switch  3 . In this way, a cell arriving at each input line module is transferred to the required output line module through the ATM cell switch  3 . 
     Each of the output line modules  4  and  5  is provided with a buffering section for transmission queue management and a counter for counting the number of cells transmitted to a corresponding outgoing line for each virtual connection. At request of the data processor  10 , the transmitting cell count is output to the data processor  10  through the CPU/SW interface  6  as described later. 
     The CPU/SW interface  6  is designed to exchange the signaling protocol for SVC call control and cell traffic data between the ATM cell switch  3  and the data processor  10 . 
     The data processor  10  is a program-controlled processor used for control of the ATM switch. The data processor  10  implements the following functions by software processing: SVC call controller  11 , call admission decision manager  12 , and cell traffic computation section  13 . 
     The SVC call controller  11  processes the signaling protocol for setup and release of a SVC call and extracts parameters of bandwidth and traffic type for each call setup request. The extracted parameters are transferred as information necessary for call setup processing to the call admission decision manager  12 . Further, the SVC call controller  11  outputs the results of setup and release of a SVC call to the ATM cell switch  3  through the CPU/SW interface  6 . In the ATM cell switch  3 , the virtual connection management information is updated depending on the received setup and release results. 
     The call admission decision manager  12  determines whether a connection request is accepted, depending on the parameters of the connection request and the UBR traffic data received from the cell traffic computation section  13 . The details will be described later. 
     The cell traffic computation section  13  adds up the receiving and transmitting cell counts inputted from the input line modules  1  and  2  and the output line modules  4  and  5  and manages the cell traffic management table  21 . The details will be described later. 
     Table Structure 
     Referring to  FIG. 2A , the cell traffic management table  21  can contain N records and has the following fields: Index D 31 , Line Number D 32 , VPI value D 33 , VCI value D 34 , Average reception traffic (ART) D 35 , Average transmission traffic (ATT) D 36 , and Type of traffic D 37 . The Line Number D 32  indicates an identification number of one of the input line modules and the output line modules. The VPI value D 33  and VCI value D 34  indicate VPI and VCI in the header of a cell. A combination of the Line number D 32 , the VPI value D 33 , and the VCI value D 34  identifies a single virtual connection indicated by the Index D 31 . 
     The Average reception traffic (ART) D 35  indicates the average amount of traffic arriving at the input line module identified by the Line number D 32 . Similarly, the Average transmission traffic (ATT) D 36  indicates the average amount of traffic transmitting from the output line module identified by the Line number D 32 . 
     An average traffic may be calculated from the number of cells per second. For example, the cell traffic computation section  13  samples the count value of the counter provided in each of the input and output line modules once per second and then calculates the differential average of 10 sampled counts. 
     The traffic type D 37  indicates the type of the connection identified by the Index S 31 . Here, the traffic type D 37  indicates whether the connection is of UBR traffic. Therefore, the cell traffic computation section  13  can calculate an average reception/transmission traffic of all UBR-traffic virtual connections currently established in a certain input/output line module by adding up N records contained in the cell traffic management table  21 . 
     Referring to  FIG. 2B , a call admission management table is also used for conventional CAC operation. The call admission management table can contain N records and has the following fields; Index D 41 , Line Number D 42 , VPI value D 43 , VCI value D 44 , Assigned bandwidth D 45 , and Type of traffic D 37 . The fields D 41 -D 44  and D 46  are the same as those of the cell traffic management table  21  as described before. The Assigned bandwidth D 45  indicates the bandwidth currently used or occupied by CBR/VBR/UBR-traffic virtual connections. Therefore, by referring to the call admission management table and the cell traffic management table  21 , as described hereafter, the call admission decision manager  12  can determine whether a connection request is accepted. It is possible to add the Assigned-bandwidth field D 45  to the cell traffic management table  21 . 
     Operation 
     Referring to  FIG. 3 , when receiving a QoS-specified connection request for a CBR/VBR-traffic virtual connection, the SVC call controller  11  extracts requested bandwidth and traffic type parameters from the request. The extracted parameters with the respective identification numbers of the input and output line modules involved are output to the call admission decision manager  12  (step (a)). 
     The call admission decision manager  12  inquires the cell traffic computation section  13  about the bandwidth currently assigned to UBR-traffic virtual connections on the involved input and output line modules (step (b)). 
     As described before, the cell traffic computation section  13  receives the receiving and transmitting cell counts from cell counters  51  and  52  in the input line module and the output line module involved in a corresponding virtual connection (steps (c) and (d)). Then, the cell traffic computation section  13  uses the receiving and transmitting cell counts to create a record including Average reception/transmission traffic in the cell traffic management table  53 . Therefore, in response to the inquiry from the call admission decision manager  12 , the cell traffic computation section  13  adds up N records to calculate an average reception/transmission traffic of all UBR-traffic virtual connections currently established in the input and output line modules. The average reception/transmission traffic of the existing UBR-traffic virtual connections is sent back as an estimated UBR traffic to the call admission decision manager  12  (step (f)). 
     The call admission decision operation will be described with reference to  FIG. 4A . 
     Referring to  FIG. 4A , the call admission decision manager  12  calculates the bandwidth A QOS  already assigned to the CBR/VBR-traffic virtual connections by referring to the Assigned bandwidth field D 45  of the call admission management table (see  FIG. 2B ). Further, the call admission decision manager  12  receives the estimated UBR traffic from the cell traffic computation section  13  and calculates an average bandwidth A UBR  as an estimated bandwidth to be assigned to the existing UBR-traffic virtual connections. In other words, as shown in  FIG. 4A , of the full bandwidth of a line is B, the portion A QOS  is already assigned to CBR/VBR traffic virtual connections and the average bandwidth A UBR  is assumed to be already assigned to UBR traffic virtual connections. 
     In this case, if the requested bandwidth R of the CBR traffic virtual connection is smaller than the available bandwidth A F =(B−A QOS −A UBR ), then the connection request is accepted because the existing UBR traffic virtual connections are substantially protected. If the requested bandwidth R of the CBR traffic virtual connection is greater than the available bandwidth A F =(B−A QOS −A UBR ), then the connection request is denied as shown in  FIG. 4A . If the connection request were accepted in this condition, then the existing UBR-traffic virtual connection would be suddenly disconnected or impaired. According to the present embodiment, such a sudden disconnection or impairment of the existing UBR-traffic virtual connection can be avoided. Such a call admission decision result is sent back to the SVC call controller  11  (step (g)). 
     ANOTHER EMBODIMENT 
     Another embodiment of the present invention is obtained by replacing the cell traffic management table  21  as shown in  FIG. 1  with a cell traffic management database and changing the cell traffic computation program of the cell traffic computation section  13 . 
     As shown in  FIG. 5 , the cell traffic management database stores a history of cell traffic management table, that is, not only a cell traffic management table at time instant t n  but also past cell traffic management tables at time instants t n−1 , t n−2 , . . . . At each of time instants t n , t n−1 , t n−2 , . . . , as described before, the cell traffic computation section  13  calculates a first average reception/transmission traffic of all UBR-traffic virtual connections currently established in the input and output line modules. 
     According to this embodiment, in response to the inquiry from the call admission decision manager  12 , the cell traffic computation section  13  calculates an estimated average reception/transmission traffic of all UBR-traffic virtual connections currently established in the input and output line modules by adding up first average reception/transmission traffics obtained over a time period from the current time instant t n  to the predetermined past time instants t n−1 , t n−2 , . . . . Therefore, even in the case of burst-like UBR traffic, a more equitable call admission control can be achieved. 
     Alternatively, it is possible to sequentially store UBR traffic obtained each time the switching of the ATM switch for UBR traffic is performed. Such UBR traffic data can be used to achieve the similar advantage. 
     Since the present embodiment can be implemented by only changing the call admission control software of the call admission decision manager  12 , the flexible and reliable CAC can be achieved even in the case of LAN emulation environment without changing in hardware. Therefore, a flexible control and an effective utilization of bandwidth in an ATM network become possible.