Abstract:
A bandwidth adjustment server (BWAS) ( 109 ) is provided which monitors system bandwidth usage, sends requests to terminals ( 102 A,  102 B and/or  106 ), to identify their coding capabilities, and directs each of the terminals to adjust their coding algorithms based on system bandwidth usage. If system bandwidth usage is high, the BWAS ( 109 ) requires the terminals to employ a less bandwidth intensive coding algorithm; similarly, when system bandwidth usage is low, the BWAS ( 109 ) will allow the terminals to employ higher bandwidth use coding algorithms.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to telecommunications systems, and in particular, to an improved telephony-over-LAN (local area network) system. 
     Modern telephony-over-LAN (ToL) systems allow each endpoint (e.g., client, gateway) to choose a default hierarchy of coding algorithms. For example, an endpoint might be configured to first try using adaptive pulse code modulation (ADPCM), next G.723, then GSM, etc., until a common codec supported by both the calling and called endpoints is found. 
     However, the endpoints or clients typically have static configurations of preferred codecs. As a consequence, network bandwidth is assigned on a simple availability basis, without regard to other users who might wish to place phone calls in the future. As a consequence, a few users who communicating using coding algorithms that result in high bandwidth consumption could use the entire network bandwidth, without even realizing bandwidth was in short supply, thereby preventing others from placing calls. As such, system bandwidth may be inefficiently utilized and even result in denial of service to some users. 
     While certain data modems, such as described in U.S. Pat. No. 5,546,395, allow for dynamic bandwidth adjustment between two communicating endpoints, by way of selecting the compression rates for voice transmission and the modulation rate, such systems do not allow for broad network-based supervision of bandwidth allocation. 
     SUMMARY OF THE INVENTION 
     These and other drawbacks in the prior art are overcome in large part by a coding algorithm policy adjustment system according to the present invention. A bandwidth adjustment server or bandwidth allocation server (BWAS) is provided which monitors system bandwidth usage, sends requests to user terminals to identify their coding capabilities, and directs each of the user terminals to adjust their coding algorithms based on system bandwidth usage. If system bandwidth usage is high, the BWAS requires the user terminals to employ a less bandwidth-intense coding algorithm; similarly, when system bandwidth usage is low, the BWAS will allow the user terminals to employ higher bandwidth-use coding algorithms. 
     The BWAS is configured with a first threshold identified as the threshold for reducing the coder/decoder (codec) speeds of the idle endpoints. The BWAS monitors system traffic, or communicates with other system monitors to determine system bandwidth usage. The BWAS sends a message to the user terminals, requiring them to identify their coding capabilities and the specific hierarchy used by them. Once this information is returned to the BWAS, the BWAS sends another message requiring the user terminals to lower their bandwidth usage by selecting a lower speed codec. When network traffic drops below a second pre-configured threshold, the BWAS sends another message allowing the user terminals to restore their original codec choices. 
    
    
     A better understanding of the invention is obtained when the following detailed description is considered in conjunction with the following drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram illustrating a telecommunications system according to an embodiment of the invention; 
     FIG. 2 is a diagram of an exemplary H.323 interface according to an embodiment of the invention; 
     FIG. 3 is a diagram illustrating an exemplary bandwidth allocation server (BWAS) according to an embodiment of the invention; 
     FIG. 4 is a flowchart illustrating operation of an embodiment of the invention; 
     FIG. 5 is a flowchart illustrating operation of another embodiment of the invention; and 
     FIG. 6 is a flowchart illustrating communication employing an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a diagram illustrating a telecommunications system  100  according to an embodiment of the present invention. In particular, the telecommunications system  100  includes a local area network (LAN) or packet network  101 . Coupled to the LAN  101  may be a variety of H.323 terminals  102 A,  102 B, a multipoint control unit (MCU)  104 , an H.323 gateway  106 , an H.323 gatekeeper  108 , a LAN server  112  and a plurality of other devices such as personal computers (not shown). The H.323 terminals  102 A,  102 B are in compliance with the H.323 standard. Thus, the H.323 terminals  102 A,  102 B support H.245 for negotiation of channel usage, Q.931 for call signaling and call setup, registration admission status (RAS), and RTP/RTCP for sequencing audio and video packets. The H.323 terminals  102 A,  102 B may further implement audio and video codecs, T.120 data conferencing protocols and MCU capabilities. Further details concerning the Recommendation H.323 may be obtained from the International Telecommunications Union (ITU); the Recommendation is hereby incorporated by reference in its entirety as if fully set forth herein. In addition, the gatekeeper  108  has coupled thereto a bandwidth allocation server (BWAS)  109  according to a specific embodiment of the invention. As will be discussed in greater detail below, the BWAS  109  monitors system bandwidth usage and directs each H.323 terminal to adopt a particular codec or coding algorithm according to bandwidth availability. It is noted that in other specific embodiments the BWAS functionality may also be incorporated into the gatekeeper  109 , placed on any terminal or server, or embodied as a separate unit separately coupled to the network  101 , as long as the BWAS can communicate with the endpoints. Thus, the figures are merely exemplary. 
     A logical diagram of an H.323 interface to LAN  101  is shown in FIG. 2, according to an embodiment of the present invention. The interface includes a known network terminal/device  10  utilizing the ITU-T H.323 protocol, and a packet network interface  13  that is coupled to network terminal  10 . Network interface  13  couples the H.323 device to LAN  101 . H.323 terminals/devices and equipment carry real-time voice, video and/or data. It should be noted that H.323 is an umbrella recommendation that sets standards for multimedia communications, including telephony-over-LAN communications. The network can include packet-switched Transmission Control Protocol/Internet Protocol (TCP/IP) and Internet Packet Exchange (IPX) over Ethernet, Fast Ethernet and Token Ring networks. 
     The network terminal  10  is coupled to a video input/output (I/O) interface  28 , an audio I/O interface  12 , an user application interface  19 , and a system control user interface (SCUI)  20 . Network terminal  10  also includes an H.225 layer  24 , a video coder/decoder (codec)  15 , an audio codec  14 , H.245 protocol functionality  18 , Q.931 protocol functionality  16 , and RAS protocol functionality  17 . 
     As seen in FIG. 2, the video I/O interface  28  which may be part of the standard H.323 device connects to the video codec  15  such as an H.261 codec for encoding and decoding video signals. Coupled between video I/O interface  28  and H.225 layer  24 , video codec  15  translates encoded video signals to H.225 protocol signals. Although the H.261 codec can be the video codec used for an H.323 terminal, other video codecs, such as H.263 codecs and others, may also be used for encoding and decoding video. The H.245 protocol is used to exchange terminal capability information such as the video coding algorithm. Generally, the called terminal specifies its capabilities to the calling terminal. 
     Audio I/O interface  12 , which may be part of a standard H.323 terminal, connects to the audio codec  14 , such as a G.711 codec, for encoding and decoding audio signals. Coupled to audio I/O interface  12 , audio codec  14  is coupled to H.225 layer  24  and translates audio signals to H.225 protocol signals. Although the G.711 codec is the mandatory audio codec for an H.323 terminal, other audio codecs, such as G.728, G.729, G.723.1, G.722, MPEG1 audio, etc. may also be used for encoding and decoding speech, in accordance with the present invention. G.723.1 typically is a preferred codec because of its reasonably low bit rate, which enables preservation of link bandwidth, particularly in slower speed network connections. As is known, when communicating, H.323 terminals use a common coding algorithm or codec supported by all entities to the conversation/conference. This information is exchanged during an H.245 capability exchange phase. 
     The control layer  11  interfaced with SCUI  20  provides signaling and flow control for proper operation of the H.323 terminal. In particular, all non-audio and non-video control signaling is handled via SCUI  20 . Coupled to SCUI  20  in the control layer  11  are H.245 layer  18 , Q.931 layer  16  and RAS layer  17 , which couple to H.225 layer  24 . Thus, SCUI  20  interfaces to the H.245 standard which is the media control protocol that allows capability exchange, channel negotiation, switching of media modes and other miscellaneous commands and indications for multimedia communications. SCUI  20  also interfaces to the Q.931 protocol which defines the setup, teardown, and control of H.323 communication sessions. SCUI  20  further interfaces to the Registration, Admission, Status (RAS) protocol that defines how H.323 entities can access H.323 gatekeepers to perform among other things address translation, thereby allowing H.323 endpoints to locate other H.323 endpoints via an H.323 gatekeeper. The H.225 standard layer  24 , which is derived from the Q.931 standard, is the protocol for establishing connection between two or more H.323 terminals and also formats the transmitted video, audio, data and control streams into messages for output to the network interface  13  (e.g., transport over IP network  101 ). The H.225 layer  24  also retrieves the received video, audio, data and control streams from messages that have been input from network interface  50 . In addition, in accordance with the present invention, the H.323 terminal&#39;s control layer  11  may also include a coding resource unit  111  which is used to communicate coding resources to the bandwidth allocation server (BWAS), as will be described further below. User application interface  19 , which may be a T.120 protocol interface as well as other types of protocol interfaces, also is coupled between H.225 layer  24  and a user device  21 , which may be for example data equipment. Thus, an H.323 network may be configured to include several different devices. For example, the network may include a terminal for enabling users connected to a LAN to speak, a terminal (i.e., gateway) for enabling a caller resident on the LAN to call a second user through the public switched network, and/or a terminal for enabling the adapter to communicate through a wireless trunk, using a wireless telephone. The device may also implement supplementary services according to the H.450 protocol specification. 
     The H.323 gateway  106  (FIG. 1) generally provides a translation function between H.323 conferencing endpoints and other terminal types and performs call setup and clearing on both the LAN side and switched circuit network (e.g., public switched telephone network or PSTN) side. The H.323 gatekeeper  108  performs address translation from LAN aliases for terminals and gateways to IP or IPX addresses (as defined in the RAS specification) as well as bandwidth management (also specified within the RAS specification). The H.323 gatekeeper  108  may further be used for call routing. Further, according to a specific embodiment of the present invention, the gatekeeper  108  may include BWAS  109  which is used to specify coding algorithms (e.g., audio, video and/or both) which may be used by particular H.323 terminals, based on available system bandwidth. The BWAS  109  communicates the required coding algorithm to the H.323 terminals using RAS messaging. The H.323 terminals then use standard H.245 signaling to negotiate coding capabilities among themselves. It is noted that, while described primarily with regard to audio coding, the present invention is equally applicable to video coding as well. 
     More particularly, an exemplary BWAS  109  is illustrated in FIG.  3 . The BWAS  109  includes a network interface  304  (which may simply be part of the standard gatekeeper interface in some embodiments) which allows for communication to and from the network terminals. In particular, RAS messaging may be employed by BWAS  109  to control bandwidth usage by defining the codecs that may be used by the idle H.323 terminals. 
     A bandwidth monitor  306  and a control processor  302  are coupled to the network interface  304 . The bandwidth monitor  306  monitors bandwidth usage, for example, by counting the number of active calls being processed by the gatekeeper or by other known methods, e.g., monitoring bit rates. The control processor  302  is coupled to a memory  308  which is used to store bandwidth threshold information, for example in the form of look-up tables. The memory  308  may also be used to store information concerning the. coding capabilities of each of the H.323 terminals. In the discussion below, “H.323 terminals” may be any H.323 endpoint such as an H.323 client or an H.323 connection in gateway  106 . The control processor  302  supervises coding request transmissions, reception of the coding information, and determination of whether a coding adjustment is necessary. In specific embodiments, the BWAS  109  continuously monitors traffic on the local segment to determine whether traffic has crossed any thresholds, and BWAS  109  may communicate with other monitoring agents located on other segments to determine their bandwidth usage. Therefore, BWAS  109  can measure and track the network traffic to make the determinations of the relevant thresholds being crossed, as discussed below. 
     As an example, a flowchart illustrating operation of one embodiment of the invention is shown in FIG.  4 . In a step  402 , the bandwidth allocation server (BWAS)  109  receives configuration information concerning the bandwidth threshold X, which is the threshold that must be met before reducing codec speeds. The threshold X, typically measured in Megabits per second (Mbps), is stored in the memory  308 . In a step  404 , the BWAS  109  similarly receives configuration information concerning the threshold Y, which is the threshold that must be met before restoring coding algorithm choices. The threshold Y is also stored in the memory  308 . Of course, the order of receiving thresholds X and Y may be reversed. 
     Next, in a step  406 , the BWAS  109  sends a request message to the H.323 terminals, requesting that they return an indication of their available coding algorithms and hierarchies. According to one embodiment, the request is in the form of an RAS message. The request message is received at the H.323 terminals in their coding resource units  111  (see FIG.  2 ). The terminals&#39; coding resource units  111  access this information, in a manner similar to that in which the terminals access coding information prior to beginning communication with another endpoint. The information is then transferred to the BWAS  109 , either in the form of an RAS message or by using H.245 signaling. 
     In a step  408 , the coding algorithms/hierarchy information is received by the BWAS  109  via the network interface  304  and stored by the processor  302  in the memory  308 . Next, in a step  410 , the BWAS  109 , in particular the bandwidth monitor  306 , proceeds to monitor system bandwidth usage. A signal representative of system bandwidth usage is provided to the processor  302 , which accesses the memory  308  for the threshold value X. The processor compares the system bandwidth usage against the threshold value X, and determines, in a step  412 , whether system bandwidth usage has exceeded the threshold X. If not, the bandwidth monitor  306  continues to monitor bandwidth usage (return to step  410 ). However, if bandwidth usage is determined to exceed the threshold X, then in a step  414 , the BWAS  109  sends a command to the H.323 terminals ordering them to adjust their coding hierarchies so that a lower speed codec is employed (the adjustment can be either stepping down to the next fastest allowed coding algorithm or alternatively stepping down directly to a selected algorithm, e.g., the slowest coding algorithm). Again, this may take the form of an RAS message or H.245 signaling. Each H.323 terminal&#39;s coding resource unit  111  then adjusts the hierarchy so that the higher-speed, more bandwidth-intense coding algorithms are not employed. 
     The determination of how far to lower the bandwidth in step  414  may be based on a variety of factors, including load, traffic expectations, and the like. It being understood that any of a variety of methods may be employed, an exemplary method is described as follows. The BWAS  109  calculates the remaining network bandwidth divided by the number of idle users to obtain a demand, D, which is the demand allocable to each of the users if it placed a call. The demand, D, is then modified by two preconfigured factors which are stored in the memory  308 . The first factor is the percentage of voice load allowed (VLA), representative of, for example, the percentage of bandwidth remaining after data usage is determined. Thus, if data calls are allowed 60% of network bandwidth, then VLA=40%. The second factor is the percentage of calls expected to be activated (EA). For example, if there are 100 terminals, and only half are expected to be active at any time, then EA=50%. A modified demand (MD) is then calculated according to the following formula: MD=(D*VLA)/EA. For example, if the threshold X were to be exceeded such that 1 Mbps network bandwidth is remaining, and 50 idle users were present, then D would be 1 Mbps/50 users=20 kilobits per second (kbps)/user. The modified demand (MD) would then be (20 kbps/user*40%)/50%=16 kbps/user. 
     Based on the modified demand (MD), the BWAS  109  determines that the first coding algorithm in each H.323 terminal&#39;s hierarchy that is lower than MD should be selected. In the example above, the first coding algorithm that is 16 kbps or lower should be selected. If the terminal does not have such a coding algorithm, the next lowest is to be employed (alternatively, the lowest coding algorithm is to be employed). Each H.323 terminal is provided with a message from BWAS  109  directing it to reset its coding algorithm to the appropriate coding algorithm. 
     Returning to FIG. 4, the BWAS  109  continues in step  416  to monitor system bandwidth usage. Again, the bandwidth monitor  306  provides a signal to the processor  302  indicative of system bandwidth usage. In response, the processor  302  accesses the memory  308  for the threshold Y. As discussed above, the threshold Y is the bandwidth usage threshold below which the default hierarchy of coding algorithms may be employed. The processor  302  then compares the bandwidth usage provided from the bandwidth monitor  306  with the threshold Y, in a step  418 . If usage has not fallen below the threshold Y, then the bandwidth monitor continues to monitor bandwidth usage (return to step  416 ). If, however, the bandwidth usage has fallen below the threshold Y, then in a step  420 , the BWAS  109  sends a message to each of the H.323 terminals directing them to restore their predetermined choice of coding algorithms or, alternatively, a BWAS specified coding algorithm (for example, the re-adjustment can be stepping up to the next fastest coding algorithm or alternatively stepping up directly to a selected algorithm, e.g., the fastest coding algorithm). Each terminal&#39;s coding resource unit  111  then re-adjusts the coding algorithm hierarchy accordingly. 
     An alternative embodiment of a method for adjusting bandwidth according to the present invention is described with reference to FIG.  5 . In particular, FIG. 5 is a flowchart illustrating a method in which coding algorithm information is not required by the BWAS  109 . Instead, the BWAS  109  simply monitors bandwidth usage and orders each H.323 terminal to adjust to slower coding algorithms according to a fixed, predetermined schedule along the algorithm hierarchy. 
     In a step  502 , the bandwidth allocation server (BWAS)  109  receives configuration information concerning the bandwidth threshold X, which is the threshold that must be met before reducing codec speeds. The threshold X, typically measured in Mbps, is stored in the memory  308 . In a step  504 , the BWAS  109  similarly receives configuration information concerning the threshold Y, which is the threshold that must be met before restoring coding algorithm choices. The threshold Y is also stored in the memory  308 . Of course, the order of receiving thresholds X and Y is not important. 
     Next, in a step  506 , the BWAS  109 , more particularly the bandwidth monitor  306 , monitors the system bandwidth usage. Again, a signal representative of system bandwidth usage is provided to the control processor  302 , which accesses the memory  308  for the threshold value X. The processor compares the system bandwidth usage against the threshold value X, and determines in a step  508  whether system bandwidth usage has exceeded the threshold X. If not, the bandwidth monitor  306  continues to monitor bandwidth usage (return to step  506 ). However, if bandwidth usage is determined to exceed the threshold X, then in a step  510  the BWAS  109  sends a command to the H.323 terminals ordering them to adjust their coding hierarchies (the adjustment being either stepping down to the next fastest coding algorithm or alternatively stepping down directly to a selected algorithm, e.g., their slowest coding algorithms). Each H.323 terminal&#39;s coding resource unit  111  then adjusts the hierarchy so that the higher-speed, more bandwidth-intense coding algorithms are not employed. 
     According to this embodiment, the selection in step  510  of the slower coding algorithm is done on a predetermined basis. For example, the BWAS  109  may send an RAS command or H.245 signaling to the H.323 terminals to step down to the next fastest coding algorithm. Alternatively, the BWAS  109  may command the H.323 terminals to step down directly to their slowest coding algorithms. The coding resource unit  111  of each of the H.323 terminals receives the message and adjusts its terminal&#39;s coding hierarchy. 
     Once the H.323 terminals have re-set their default choices for coding algorithms, the bandwidth monitor  306  continues to monitor bandwidth usage, in a step  512 . The bandwidth monitor  306  provides a signal indicative of bandwidth usage to the processor  302 . The processor  302 , in turn, accesses the memory  308  for the threshold value Y. The processor then performs a compare operation, comparing the threshold value Y with the bandwidth signal received from the bandwidth monitor  306 , in a step  514 . If the bandwidth usage level is above or equal to Y, then the system continues to monitor usage (return to step  512 ). If, however, bandwidth usage levels drop below the threshold value Y, then the processor  302  issues a command onto the network allowing the H.323 terminals to re-adjust their coding algorithm hierarchies. Again, this may take the form of an RAS message or H.245 signaling, with the re-adjustment being either stepping up to the next fastest coding algorithm or alternatively stepping up directly to a selected algorithm, e.g., the fastest coding algorithm. Each H.323 terminal&#39;s coding resource unit  111  then adjusts accordingly the coding hierarchy so that the higher-speed, more bandwidth-intense coding algorithms are allowed to be employed. 
     In the various specific embodiments of the present invention discussed above, the bandwidth can thus be continuously monitored for changes in network traffic such that dynamic adjustment of the coding algorithms is accomplished. 
     In the above embodiments, once the H.323 terminals receive their new coding hierarchies, calls are processed in the standard fashion. Thus, for example, turning now to FIG. 6, a flowchart illustrating call set-up employing a coding hierarchy adjustment system according to the invention is shown. In particular, in a step  602 , a calling H.323 terminal issues an Admission Request (ARQ) message to the gatekeeper  108 . In a step  604 , the gatekeeper  108  accepts by issuing an Admission Confirm (ACF) message (it is noted that the gatekeeper  108  could reject by responding with an Admission Reject (ARJ) message, but for purposes of illustration, it is assumed that an ACF message is sent). In a step  606 , the calling H.323 terminal sends a Q.931 Setup message to the called H.323 terminal. In a step  608 , the called H.323 terminal sends an ARQ message to the gatekeeper  108  which responds with an ACF message in a step  610  (again, a reject message may also be provided, rather than an accept message). Once this acceptance has issued, an H.245 sequence follows, in a step  612 , in which the calling and called H.323 terminals communicate with one another concerning the common coding algorithm which is to be employed. As discussed above, the H.323 terminals must find a common algorithm. The H.323 terminals step through their hierarchies until one is found. According to the present invention, this determination may be based on use of the bandwidth-adjusted new coding hierarchy. It is noted that the H.245 sequence may also include bandwidth requests and allocations according to the H.323 Recommendation. Such standard bandwidth messaging is unaffected by the present invention, except to the extent that the individual H.323 terminals base their bandwidth requests upon bandwidth requirement determinations that have resulted after their readjustments in response to the BWAS  109 . 
     Finally, when the call is terminated, in a step  614 , both H.323 terminals send a Disengage Request (DRQ) message to the gatekeeper  108 . In turn, the gatekeeper  108  responds with a Disengage Confirm (DCF) message.