Abstract:
There is disclosed a manner of controlling traffic by admission control in a communication network such as one operable according to GSM standards. When a call setup request is received from an MS, the BSC forwards the request to an MSC, which selects a MGw that is accessible to the BSC via an IP backbone. When notified of the MGw selection, the BSC runs an algorithm to assess the transmission quality of the IP backbone toward the MGw. The BSC then determines whether to reject the call setup request depending on whether the quality level is acceptable as determined by the algorithm. If the call setup proceeds, the MGw may run a similar algorithm to assess the quality of the IP backbone toward the BSC. The BSC and MGw may also check their own bandwidth limitations prior to running their respective algorithms.

Description:
CROSS REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY 
       [0001]    This application is related to, and claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/972,396, which was filed on 14 Sep. 2007, and which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention is directed, in general, to the operation of network communication systems and, more specifically, to a manner of implementing admission control in a communication network, such as a GSM (Global System for Mobile Communications) network, that utilizes an IP (Internet protocol) network backbone. 
       BACKGROUND 
       [0003]    A communication system, in general, provides for voice and perhaps data communication between two or more parties. Generally speaking, every communication system must have a way for subscribers to access the system, including the equipment used by the subscribers themselves, and a core network for transporting voice and data traffic from one access location to another. Some type of signaling system must also be in place to facilitate setting up and ending calls, and for the provision of other call-related services. 
         [0004]    In a standard wireline system, such as a PSTN (public switched telephone system) for example, subscribers use telephones are connected with stationary access points (for example, a phone jack) in a business or residence. The access point is connected, perhaps through intermediary devices, with a telephone company switching office. The switching office provides access to a hierarchically-arranged network of variously-sized lines and trunks, interconnected with switching and other equipment, that route each call to its destination. When the caller initiates a call by picking up the telephone and dialing a number, a circuit is established through the network to the called party. The circuit remains dedicated to the call until it is completed, then the network resources used for the session are released for use on other calls. 
         [0005]    In a mobile communication system, such a PLMN (public land mobile network), subscribers may and frequently do move from one geographic location to another. Instead of a telephone plugged into a jack, a subscriber wishing to make a call uses a MS (mobile station) with a relatively low-power radio transceiver to communicate over an air interface a nearby antenna. There are typically a large number of such antennas distributed over the network coverage area. Each of the antennas is connected with a core network for the routing and transmission of calls. A signaling system is also present in a PLMN so that calls may be set up and ended properly. The signaling system is also used to allow a mobile subscriber to switch from communicating with one antenna to another to allow for relocation even while a call is in progress. 
         [0006]    Mobile communication systems are constructed and operating according to a set of standards and protocols. One type system is referred to as GSM (Global System for Mobile communication) and is used extensively throughout the world. Selected components of a typical GSM PLMN  10  are illustrated in  FIG. 1 .  FIG. 1  is presented for the purpose of introducing various network components and will be described only briefly. MSs (mobile stations) access the PLMN  10  through a nearby antenna over an air interface. In the example of  FIG. 1 , there is shown three BSSs (base stations systems referred to as  16 ,  17 , and  18 . BSS  16  includes BSC (base station controller)  41 , which is in communication with BTSs (base transceiver stations)  42  and  43 . The BTSs include the actual antenna for communication and, as an example, MS  12  is depicted as communicating with BTS  42 . Similarly, BSS  17  includes BSC  31 , which communicates with BTS  32  and BTS  33 , and BSS  18  includes BCS  35  and BTS  36 . Here, BTS  36  is shown in communication with MS  14 . 
         [0007]    Communication between MS  12  and MS  14  is arranged when their respective BSS contacts an MSC with which they are in communication. As shown here, BSS  16  is in communication with MSC  20 , and BSS  18  communicates with MSC  30 . Through MSC  20  and MSC  30 , the call between the two MSs can be arranged. During setup, the MSCs may consult the HLR  15 , which tracks the identity and location of MS that belong to PLMN  10 . Each MS registers periodically with a nearby BTS and their location may be reported to HLR  15  at that time. An MS from another PLMN may register as well, with their current location stored in a VLR (not shown) associated with each MSC, and reported to the HLR of their PLMN (also not shown). 
         [0008]    Although only two MS are shown in  FIG. 1 , there are typically a large number. At times, the capacity of the network may be reached. In that event, access to the network must be limited. This may be done through admission control. For example, in the PLMN  10  of  FIG. 1 , voice transport in the interface between a BSC and its respective MSC (referred to sometimes as the “A interface”) uses TDM (time division multiplexing). In TDM each transported frame has a number of time slots, and each time slot may be assigned to a particular call so that many calls may be handled by the same transmission channel. When there are no time slots left to assign, an incoming call request must be rejected. 
         [0009]    It is becoming frequently common, however, for communication networks to utilize a packet-switched network, usually operable according to the IP (Internet protocol), to transport voice and other signals. A packet-switched network does not assign time slots, but rather breaks up transmissions into a number of packets of information, each of which is provided with a destination address and routed through the network. IP networks include a large number of routers and similar devices, but do not establish a fixed path for each transmission. Rather, each packet is routed individually, and the several packets of a given transmission may each take different routes through the network. An identifier associated with each packet enables the destination device to reassemble them to form the original transmission. Individual packets are sometimes lost, due to network congestion or equipment malfunction, and lost packets are sometimes re-sent upon request. In general, the small amount of information lost with each packet, which is sometimes recovered through retransmission, does not always affect the transported voice content significantly. 
         [0010]    If too many packets are lost, however, the quality of the transmission may degrade. If the loss is attributable to network congestion, numerous requests for re-sending packets compounds the problem. As should be apparent, some form of admission control for such a network would be desirable. Since time slots or circuits are not assigned for the IP portion of the network (sometimes referred to as the IP backbone), however, traditional methods of admission control cannot be used. 
         [0011]    This need is exacerbated where the A interface extends across the packet-switched network, since access control in this configuration cannot be imposed in the traditional fashion. The A interface may be extended in this fashion so that only one MGw is required for a call being carried across the network (see  FIG. 2 ). Using only a single MGw, generally speaking, increases the capacity of the network without a large capital expenditure. The IP network may still become congested, however, with an accompanying degradation in quality. There is a need, therefore, for an admission control solution for use in communication networks that utilize an IP backbone. 
       SUMMARY 
       [0012]    To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a method and arrangement for implementing admission control in a communication network that utilizes an IP backbone. 
         [0013]    In one aspect, the present invention is a method of admission control including the steps of receiving, in a BSC (base station controller), a call setup request from a MS (mobile station), notifying an MSC (mobile switching center) of the call setup request, selection, by the MSC, of a MGw (media gateway) for the call, determining, by the BSC, of the transmission quality towards the MGw through a packet-switched network, and determining whether to refuse the call setup request based on the determined transmission quality towards the MGw. The BSC may continually or periodically monitor the quality of transmission toward a number of MGws, perhaps all MGws to which it has access via the packet-switched network, in preparation for making the determination regarding a call setup request. 
         [0014]    In some embodiments, the MGw, once selected, may also determine the transmission quality towards the BSC and make a determination on that basis whether to refuse the call setup request. If the call setup request is refused by the selected MGw, an alternate MGw may be selected. Transmission bandwidth limits may in some applications be imposed on either or both of the BSC and the selected gateway. In that case, the limited node may first determine whether the respective bandwidth limit has been reached, usually before determining whether to reject the call setup request based on transmission quality. Transmission quality is usually a function of packet loss rate in the relevant direction, but may also or instead consider other factors. 
         [0015]    In another aspect, the present invention is a system for controlling traffic in a GSM communication network, the system including a BSC arranged to monitor transmission quality toward at least one MGw over an IP (Internet protocol) network, and further arranged to, upon receiving a call setup request, request selection of a MGw and to determine whether to refuse the call setup request based on transmission quality toward the selected MGw. The system further includes an MSC arranged to select a MGw upon receiving the request from the BSC and a MGw arranged to, upon being selected by the MSC, determine transmission quality toward the BSC, and further arranged to determine whether to refuse the call setup request based on transmission quality toward the BSC. 
         [0016]    In yet another aspect, the present invention is a node, such as a BSC, for use in a communication network, the node being arranged to receive a call setup request, to request a MGw for handling the call, to receive a MGw selection, to determine transmission quality toward the selected MGw over an IP network, and to determine whether to refuse the call setup request based on the transmission quality toward the selected MGw. The determination of transmission quality preferably includes determining a packet loss rate for transmissions toward the selected MGw. The node may also determine whether it has reached a transmission bandwidth limit, if any, preferably prior to requesting selection of an MGw for handling the call. 
         [0017]    The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form. 
         [0018]    Before undertaking the DETAILED DESCRIPTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. In particular, a controller may comprise one or more data processors, and associated input/output devices and memory, that execute one or more application programs and/or an operating system program. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which: 
           [0020]      FIG. 1  is a simplified schematic diagram illustrating selected components of a typical GSM network. 
           [0021]      FIG. 2  is a simplified schematic diagram illustrating selected components of a GSM network in which an embodiment of the present invention may be implemented. 
           [0022]      FIG. 3  is a simplified schematic diagram illustrating selected components of a communication network operable according to an embodiment of the present invention. 
           [0023]      FIG. 4  is a flow diagram illustrating a method of facilitating access control according to the present invention. 
           [0024]      FIG. 5  is a message flow diagram illustrating the messaging used to set up a call subject to admission control according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIGS. 2 through 5 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged communications system. 
         [0026]    The present invention is directed to the efficient use of network resources that, in turn, tends reduces the amount of resources required to support a given level of traffic. More specifically, the present invention facilitates the use of a single MGw (media gateway) for call completion using an A over IP interface. The present invention will now be explained in more detail. 
         [0027]    The present invention is advantageously implemented in a communication network such as a GSM network.  FIG. 2  is a simplified block diagram illustrating selected components of a communication network  200  in which an embodiment of the present invention may be implemented, for example, when MS (mobile station)  212  attempts to place a call to MS  214 . In this configuration, MS  212  contacts BTS (base transceiver station)  235  with a call setup request over an air interface referred to as the Um interface. BTS  235  in turn passes this request to the BSC (base station controller)  230  over the Abis interface. 
         [0028]    When BSC  230  receives the call setup request, it sends a BSSAP (base station system application part) protocol message to MSC (mobile switching center)  210  over what is referred to as the A interface. In this configuration, an analogous arrangement is used between MSC  215 , BSC  240 , BTS  245 , and MS  214 . MCSs  210  and  215  communicate with each to set up the call other using the BICC (bearer independent call control) protocol. Each of them selects a MGw for handling the call, here MGw  220  and MGw  225 , which use between them the NbUP (Nb (interface) user plane) protocol. IPBCP (IP bearer control protocol) is used for bearer establishment. 
         [0029]    In this configuration, however, the use of two MSCs and two MGws for setting up the session between MS  212  and MS  214 , which is not atypical, is presumed. In many instances nowadays, however, a savings in resources may be attained by employing only a single media gateway. This is done by extending the A interface over an packet-switched network, so that communication over the A interface takes place between the BSC attempting to set up a call and a single MSC and MGw. This will be more clearly apparent with reference to  FIG. 3 . 
         [0030]      FIG. 3  is a simplified schematic diagram illustrating selected components of a communication network  300  operable according to an embodiment of the present invention. Communication network includes an IP backbone  301 . Note that numerous nodes of IP backbone  301  are represented in  FIG. 3  but without specific reference or indication of their nature. For the purposes of describing the present invention, it is simply presumed that they are represent the constituent parts of IP backbone  301  that are used to route packet-based communications. 
         [0031]    On one side of the IP backbone  301  is a BSS (base station system)  305 . BSS  305 , in this illustration, includes a BSC  310  and two BSTs  315  and  320 . BSS  305  (specifically BSC  310 ) may communicate via the IP backbone  301  with one or more MSCs. The interface between a BSS and an MSC or MGw is called the A interface, and one that includes an IP backbone is sometimes referred to as an AoverIP interface. In  FIG. 3 , for example, BSC  310  may communicate with MSC  325 . An AoverIP interface established between them may be used for sending messages related to call setup, for example. 
         [0032]    MSC  325  is in communication with two MGws (media gateways), MGw  330  and MGw  335 . Packets from BSC  310  may be sent to either MGw  330  or MGw  335  on the IP layer, also over the AoverIP interface. As this is being done, the BSC  310  monitors the average packet loss towards each of MGw  130  and MGw  135 , and towards any other similar MGw or similar node (not shown). Other measures of the transmission quality between the BSC and a given MGw may be made as well, for example the presence and amount of jitter or packet reordering. These quality indicators may be monitored continually or periodically. In either case a value associated with the transmission quality is saved for future reference when a call setup request is received, as explained in more detail below. 
         [0033]      FIG. 4  is a flow diagram illustrating a method  400  of facilitating access control in a GSM communication network. Note that the method may also be implemented in other similarly-arranged networks as well. At Start, it is presumed that the hardware and software necessary to performing the method is available and operational. The method then begins when a call setup request is received (step  405 ). Upon receiving the request, the BSC determines whether a predetermined bandwidth limit on the transmission of calls over the A interface has been reached (step  410 ). This predetermined bandwidth limit may be static (unchanging or subject only to change by a network operator) or dynamic, that is continually adjusted or adjustable based on predetermined factors. 
         [0034]    If the BSC bandwidth limit has been reached (met or exceeded), then the call setup request is denied (step  415 ). If it has not been reached, then a MGw is selected (step  420 ). In accordance with the present invention, this may be any MGw in communication with the IP backbone, but is of course it is selected based at least in part on the destination specified in the call setup request. In most applications, the BSC communicates with the MSC (not separately shown) and the MSC selects the MGw. When a MGw has been selected, the MSC seizes a termination with the selected MGw (step not shown). 
         [0035]    The selected MGw then determines whether a predetermined bandwidth limit on the transmission of calls over the A interface toward the BSC has been reached (step  425 ). As with the BSC, this predetermined bandwidth limit may be static or dynamic. If the MGw bandwidth limit has been reached (met or exceeded), then the MGw rejects the call setup request (step  415 ). In one embodiment, the call setup request is simply rejected entirely. In another embodiment (not shown) a refusal by one MGw leads to the selection of another by the MSC, if the other is appropriate for routing the call. In yet another embodiment (also not shown), a TDM-based connection to a MGw may be established if the a selected MGw rejects the call setup request. If the MGw bandwidth limit has not been reached, an IP address and port number for the call is transmitted from the MGw to the BSC that received the call setup request via the MSC that selected the MGw (step  430 ). 
         [0036]    In the embodiment of  FIG. 4 , when the BSC receives the MGw&#39;s IP address and port number, it determines whether the quality of transmissions toward the selected MGw fall within an acceptable range (step  435 ). In a preferred embodiment, this quality determination includes determining whether the observed packet loss of packets transmitted by the BSC the A interface falls beyond a certain threshold. Preferably, the BSC monitors packet loss to all MGws that it may access over the IP network. This may be done continually or on a periodic basis. A quality value for each potential A interface may then be stored for reference when a call setup request is received. Note that other parameters aside from packet loss may be included in the determination of this step as well. 
         [0037]    If the BSC determines that the transmission quality does not fall within an acceptable range, then the call setup request is rejected (step  415 ). If the transmission quality toward the MGw is acceptable, then the BSC accepts the call and provides the MGw, via the MSC, with an IP address and port number for the BSC side of the A interface (step  440 ). 
         [0038]    In the embodiment of  FIG. 4 , the MGw then determines whether the quality of transmission toward the BSC fall within an acceptable range (step  445 ). This determination may include determining the packet loss rate or other factors. If the quality of transmission does not fall within an acceptable range, the call is released (step  416 ). Note that the term “released” is used here as the call was (provisionally) accepted by the BSC. For simplicity however, this will be considered equivalent to “rejecting” the call setup request. If, on the other hand, the transmission quality is acceptable, the call is completed (step  450 ). 
         [0039]      FIG. 5  is a message flow diagram  500  illustrating the messaging used to set up a call with admission control according to an embodiment of the present invention. This Figure illustrates, among other things, the trigger points for MBAC (measurement based admission control) and SAC (session admission control) checks, which were generally alluded to in reference to  FIG. 4 . Note that this illustrates the messages used according to this embodiment of the present invention. There may be and frequently are other messages involved in call setup. 
         [0040]    In the embodiment of  FIG. 5 , the message flow diagram represents includes selected communication network nodes, namely, MS  505 , BSC  510 , MSC  515 , and MGw  520 . MS  505  is attempting to set up a call with MS  530 , which, if successful, will be conducted through BSC  525 . 
         [0041]    When an MS, such as MS  505  wishes to set up a call, for example to MS  530 , it establishes contact with the communication network BSC, in this case BSC  510 , via a BST (not shown in  FIG. 5 ). The BSC  510  then transmits a BSSAP SETUP message to MSC  515  over the A interface. In accordance with this embodiment of the present invention, however, prior to sending the BSSAP SETUP message, the BSC runs a SAC (session admission control) algorithm * 550  to determine if it is permitted to allocate additional bandwidth for the call. As explained above, if the BSC transmission bandwidth limit has been reached, the call will be rejected. The BSSAP SETUP message is transmitted only if the additional bandwidth allocation is allowed. For the purposes of illustrating the message flow of  FIG. 5 , however, it will be assumed that the SAC algorithm (and the subsequent checks as well) allow the call to be set up. 
         [0042]    When the BSSAP SETUP message is received by the MSC  515 , it is acknowledged using a CALL PROCEEDING message. The MSC  515  then selects a MGw to handle the call; in this embodiment, MGw  520 . MSC  515  then sends a GCP (gateway control protocol) ADD REQ command to MGw  520  to add a termination for the call. 
         [0043]    In this embodiment, receipt of the ADD REQ command is acknowledged by the MGw  520 , but only if additional bandwidth for the call may be allocated. To determine this, an SAC algorithm * 555  is executed in the MGw  520 . If additional bandwidth for the call is permitted (as is presumed here), then the MGw  520  sends the acknowledgement ADD REPLY, including the IP address and port of the A interface termination. The MSC  515  then forwards the MGw termination and A interface IP address and port number to the BSC  510  in an ASSIGNMENT REQUEST message. 
         [0044]    After receiving the ASSIGNMENT REQUEST message, the BSC  510  executes an MBAC (measurement based admission control) algorithm * 560  using the IP address of selected MGw  520  to determine if the quality of the IP backbone is currently sufficient. As mentioned above, this determination may be made based on a previously-measured packet loss rate toward MGw  520 . If so, an ASSIGNMENT COMPLETE message is sent from the BSC to the MSC  515 . The ASSIGNMENT COMPLETE message includes the IP address and port of the BSC  525  termination. 
         [0045]    The MSC then sends a GCP MOD REQ command including the IP address of port of the MGw. Upon receiving the MOD REQ command, the MGw  520  executes a MBAC algorithm * 565  to check the transmission quality toward BSC  510 . If the quality of the IP backbone is currently sufficient, the call is established (not shown). 
         [0046]    In this manner, the present invention provides for admission control in a communication network that accommodates extension of the A interface across a packet-switched network. This enables efficient operation of the network while utilizing fewer network resources for each call, thereby reducing the need for capital expenditure by the network operator while enhancing the quality of call places through the network. 
         [0047]    Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.