Abstract:
In Internet Protocol (IP) telephony systems, H.323 gateways delay communications transmissions and compromise quality by requiring multiple codec translations between originating and destination endpoints.  
     A method and several novel components to reduce communications delays and improve video and audio quality in IP telephony systems are described. The method and components apply a single coder-decoder (codec) for the entire communication path between originating or calling endpoints and destination or called endpoints when calls are connected through H.323 gateways.  
     The method and components enable H.323 gateways to offer codec capabilities to endpoints even though the H.323 gateways themselves do not have required codec algorithms. This “profession” of codec capabilities that gateways themselves do not possess allows such gateways to dynamically support any codec virtually, as long as the endpoints themselves have the required codec algorithms.

Description:
BACKGROUND OF INVENTION  
       DESCRIPTION OF THE RELATED ART  
         [0001]    With the growth in demand for H.323 packet-based multimedia communications systems for telecommunications platforms, there has evolved many products and technologies to meet the growing need for IP Telephony. Many such technologies conform to the standards defined by International Telecommunications Union (ITU) document ITU-T Recommendation H.323 Packet-Based Multimedia Communications Systems.  
           [0002]    The basic definition of a H.323 gateway as given by ITU is, “An H.323 gateway (GW) is an endpoint on the network which provides for real-time, two-way communications between H.323 terminals on the packet-based network and other ITU terminals on a switched circuit network, or to another H.323 Endpoint.” 
           [0003]    Today, coder-decoder (codec) capabilities for communications from one H.323 endpoint (EP) to another endpoint using a H.323 gateway are negotiated separately and independently by the H.323 gateway between these terminal endpoints. The H.323 gateway will match and decide capabilities with its connecting endpoints based on the set of native codecs in a priority list built into the gateway. If a H.323 gateway lacks the codec capabilities to match a connecting H.323 endpoint (EP), then the calling EP will not be able to call its destination through this gateway even though both endpoints may share a common codec capability.  
           [0004]    This represents a major weakness in the current art of H.323 products and therefore necessitates one critical requirement: H.323 gateway products must support a well-established codec such as G.723.1, or have a large a multiplicity of codecs.  
           [0005]    Although the presence of a wide range of codecs on a H.323 gateway does have its advantages, there are price-and-performance tradeoffs. Many of the better codec algorithms are patented and costs are involved in licensing their technology for use. Each codec also requires guaranteed amounts of short but intensive computer processing cycles to code and decode at high speeds. This means that increased investments in hardware for H.323 gateways are required to support multiple codecs. This adversely affects the prices of H.323 gateways.  
           [0006]    Another issue is the delay resulting from codec translations. In performing codec translations, H.323 gateways operate by decoding all incoming codec formats to a common format, commonly either linear PCM or G.711. Then the outgoing process will encode from the common format to the destination codec.  
           [0007]    In a call between two endpoints using a H.323 gateway where the two endpoints are using low bandwidth connections (for example dial-up modems connected to internet service providers), up to two codec translations are often needed by the gateway. There is firstly a translation from incoming format to a common format like G.711 or PCM linear using a hardware or software transcoder unit, followed by a translation from G.711 or PCM linear to the codec of the destination.  
           [0008]    The findings noted by U.S. Pat. No. 6,256,612 in the prior art clearly substantiates that multiple codec translations have adverse effects on speech quality resulting from delays. With the current state of the Internet where quality of service is not assured, such delays in multimedia delivery of greater than 150 milliseconds is often not tolerable by users.  
           [0009]    With reference to the prior art, it is noted that H.323 endpoints are able to establish communications without the use of gateways. Furthermore U.S. Pat. No. 6,373,839 describes a method by which endpoints maintain “common codec attribute lists” so that the highest priority common codec is always determined. Such a method will not have pervasive acceptance unless the use of special variants of H.323 endpoint devices with “common codec attribute lists” become the de-facto standard.  
           [0010]    Therefore, due to these and other drawbacks in codec translations in H.323 systems, a significant improvement is needed in H.323 telephony.  
         SUMMARY OF THE INVENTION  
         [0011]    This invention relates to a method of reducing communications delay, thereby improving video and audio quality in Internet Protocol Telephony (IP Telephony) systems that conform to the H.323, H.225 and H.245 family of International Telecommunications Union (ITU) standards for packet-based multimedia communication systems.  
           [0012]    A method to reduce communications delay by reducing the number of codec translations in current methods is required. Such an invention will enable a single codec to be implemented for an entire communications path without need for special H.323 endpoint devices, as described in U.S. Pat. No. 6,373,839. Such an invention will not require out-of-band signaling such as that described in U.S. Pat. No. 6,256,612, and will be able to achieve its objectives by working algorithmically within the in-band signaling protocol requirements stated in ITU H.225 and H.245. The invention described herein provides such a novel method with novel components to achieve these objectives  
           [0013]    In one aspect, the present invention is a method of reducing communications delays in H.323 communication systems by enabling a single coder-decoder (codec) for the entire communication path between calling endpoint and called endpoint when the call is connected through a H.323 gateway.  
           [0014]    The endpoints making calls using this invention have their call signaling and control protocol synchronized in-band, such that the codec list of the calling endpoint is sent to the called endpoint, and the single codec selected is common to the two endpoints but which may not be available on the gateway. This significantly reduces latency resulting from codec translations. Because it is in-band, this method will work between any standards-compliant H.323 client endpoints.  
           [0015]    When the communications path of calling endpoint and called endpoint are interconnected by more than a single gateway, the present invention provides a method for the interconnecting gateways to synchronize the call signaling and control protocol along the entire path such that calling endpoint and called endpoint arrive at using the highest priority codec common between them on the entire communications path.  
           [0016]    This is an advantageous step as it means service providers can improve the quality and lower the cost of Internet multimedia communications simply by asking subscribers to make calls through these enhanced gateways of the present invention.  
           [0017]    The present invention is easy to implement as service providers need not persuade subscribers to use new H.323 client devices with special non-standard enhancements.  
           [0018]    In another aspect, the method described here enables an enhanced H.323 gateway to connect two endpoints together such that the gateway is able to profess support of a codec it does not actually possess. Instead the gateway manages the call signaling and control protocol of the two endpoints such that a codec format common to the two endpoints is accepted. The enhanced gateway establishes a novel component of this invention, a Virtual Codec Unit (VCU), between the logical channels of the two endpoints that pass multimedia data packets with the correct frame rate, frame size and other necessary codec attributes to control the requirements of the codec used by the two terminal endpoints.  
           [0019]    In yet another aspect, the enhanced gateways also possess another novel component, a codec attributes update interface, through an out-of-band signaling method, thereby allowing H.323 clients to use proprietary and private codec implementations between themselves without changes to the gateways. This makes it suitable for organizations needing additional security, such as the military. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a prior art message flow diagram illustrating the H.323 protocol exchanges between two endpoints and a gateway using the conventional H.323 Q.931 and H.245 call control and signaling recommendations;  
         [0021]    [0021]FIG. 2 is a message flow diagram illustrating the H.323 protocol exchanges to establish a call between endpoints via a gateway with all nodes using the H.323 Fast Connect call signaling and control protocol (Fast Connect) in accordance with the invention;  
         [0022]    [0022]FIG. 3 is a message flow diagram illustrating the H.323 protocol exchanges between two endpoints and gateway when the present invention is used by the gateway, and the calling endpoint and the gateway agrees on using Fast Connect, while the gateway and called endpoint is not using Fast Connect;  
         [0023]    [0023]FIG. 4 is a message flow diagram illustrating the H.323 protocol exchanges endpoints and gateway when all nodes are not using Fast Connect;  
         [0024]    [0024]FIG. 5 is a simplified block diagram illustrating a Virtual End-to-End Codec (VEEC) method of selecting a codec in accordance with the invention;  
         [0025]    [0025]FIG. 6 is a diagram illustrating how the VEEC method of FIG. 5 is used to select a single coder-decoder for a communications path interconnected by multiple H.323 routing nodes; and  
         [0026]    [0026]FIG. 7 is a block diagram illustrating an exemplary H.323 gateway apparatus and its functional components in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    [0027]FIG. 1 is a message flow diagram illustrating the prior art of protocol exchanges between two H.323 endpoints and a gateway using the conventional International Telecommunications Union recommendations H.323 (ITU-H.323).  
         [0028]    The calling endpoint EP- 1   100  supports codec capabilities G.723.1 and G.711. The conventional gateway GW  90  supports codec capabilities G.729 and G.711. The other endpoint EP-2  102  supports codec capabilities G.723.1, G.729 and G.711. These local codec lists are in order of highest to lowest priority as recommended in ITU-H.323. There is no direct path from endpoint EP-1 to the called endpoint EP-2, so the connection is made through gateway GW  90 .  
         [0029]    Endpoint EP-1 transmits a Q.931 setup request  103  to gateway GW where the destination of EP-2 is specified in the setup request in accordance with ITU-H.323. In the prior art, ITU-H.323 categorises the H.323 call signaling and control protocol into Phase A and Phase B.  
         [0030]    Phase A begins at  103  and  104  where Q.931 setup requests are initiated, and the GW monitors and maintains call proceedings and alerts from EP-2  106  to EP-1  105 . Phase A ends when the Q.931 Connect request  110  from EP-2 is received by GW and a corresponding Q.931 Connect  109  is established from GW to EP-1.  
         [0031]    Phase B starts at endpoint EP-1 requesting H.245 codec capabilities exchange  112  with GW and GW requesting H.245 codec capabilities exchange  111  with endpoint EP-2.  
         [0032]    The gateway GW services the incoming call and the outgoing call independently. At  115  GW and EP-1 conclude the H.245 capabilities exchange using G.711 as this is the only common codec between them. Between EP-2 and GW at  113 , G.729 is chosen as the highest priority codec common to both.  
         [0033]    However EP-2 and GW share two common codecs G.729 and G.711. If EP-2 and GW did not have G.729 and G.711 listed in the identical order as illustrated, they will have ended with using two different codec for transmission and reception. For example if EP-2 had prioritised G.711 before G.729, and both use the priorities of their local list to decide the codec of choice, EP-2 will chose G.711 to transmit to GW and GW will chose G.729 to transmit to EP-2, resulting in two codecs being used.  
         [0034]    Another undesirable result is that although EP-1 and EP-2 share the codec G.723.1 they are unable to use it because GW does not have similar capability. Thus gateways of the current technology can disadvantage the use of codecs between endpoints in the ITU-H.323 recommendations.  
         [0035]    The present invention is advantageous as it provides a method for codec selection that is an improvement over the prior art as described in the following aspects.  
         [0036]    Firstly, it is able to extend the use of a codec capability across gateways even if the gateways do not possess the codec capability (i.e. the codec algorithm). In the prior art, a gateway must have the common codec capability of two connecting endpoints in order for these two endpoints to use the common codec. The present invention defines and uses a Virtual Codec Unit (VCU) to overcome this undesirable effect.  
         [0037]    Secondly, the use of two different codecs between endpoints for receive and transmit channels is eliminated. The present invention defines a Virtual End-to-End Codec (VEEC) method that bias the gateway into selecting a common codec for both receive and transmit channels.  
         [0038]    The Virtual End-to-End Codec (VEEC) method applied in the embodiment on ITU-T Recommendation H.323 was derived from research into techniques of in-band synchronization of the call signaling and control protocols Q.931 and H.245 between two endpoints and a H.323 gateway.  
         [0039]    Three scenarios utilizing VEEC in the present invention is described below to illustrate its use.  
         [0040]    [0040]FIG. 2 is a message flow diagram illustrating the VEEC method according to the teachings of the present invention when the H.323 Fast Connect call signaling and control protocol (Fast Connect) is used on both the originating session  214  between endpoint EP-1  100  and gateway GW  101  (a product of this invention), and at the destination session  215  between endpoint EP-2  102  and GW.  
         [0041]    As the codec list arrives early with the Q.931 setup request  202  in the Fast Connect, the gateway GW spawns a new process GW-EP-A  200  to service EP-1. In the teachings of this present invention, the gateway GW extracts the codec list of EP-1 from the Q.931 setup message and makes preparations to extend the codec list  203  from EP-1 to EP-2, optionally including GW&#39;s local codec list, by creating a remote codec list. The gateway GW spawns a new process GW-EP-B  201 , which sends this remote codec list in the Fast Connect Q.931 request  217  to destination endpoint EP-2. As a result of the present invention, endpoint EP-2 receives the remote codec list  204 .  
         [0042]    The destination endpoint EP-2 sends Q.931 proceeding and alert messages until the Q.931 Connect  206 . When the gateway process GW-EP-B receives the Connect Q.931 message  206  from EP-2, it also receives indication that EP-1 will use the extended codec G.723.1.  
         [0043]    According to this invention, the gateway GW now completes its Q.931 session  207  with EP-1. Process GW-EP-A sends the G.723.1 codec selected by EP-2 in the Q.931 Connect  208  to EP-1. The resulting H.245 exchange  209  between EP-1 and GW-EP-A will confirm G.723.1 as the single virtual codec to use in the transmitting and receive logical channels  212 . A similar H.245 exchange  211  takes place between GW-EP-B and EP-2.  
         [0044]    In the teachings of the present invention, the destination endpoint (EP)  102  is delivered an extended list of codec capabilities  204  consisting of the codec list of the originating endpoint (EP)  100  and optionally the codecs of gateways in the call path, the actual combination being beyond the scope of this invention. Therefore the destination endpoint will always be making its codec choice from a more comprehensive list of available codec than without this invention.  
         [0045]    Once the destination EP decides on a codec  206 , the chosen codec is the only codec passed back to the originating endpoint  208 . As the originating endpoint receives one codec capability to chose from in the H.245 exchange  209 , a single end-to-end codec is guaranteed to be used along the entire communications path.  
         [0046]    By extending the native codec from endpoint to endpoint, the Virtual End-to-End Codec (VEEC) method of the present invention reduces communications delay by eliminating the need for multiple codec translations to be done at the gateway.  
         [0047]    selecting a single common codec across the entire communications path, an accurate utilization of effective bandwidth is possible. For if both endpoints are using low bandwidth codecs, then any high bandwidth codec utilized by gateways in between the communications path will effectively have to reduce throughput to the lowest codec denominator at the endpoints.  
         [0048]    It will be apparent to someone skilled in the art that the GW, a product of this invention, claims or professes support of the G.723.1 codec even though it does not possess the codec algorithm. To facilitate this virtual codec in the present invention, the basic attributes of the virtual codec, such as its frame size, frame rate, maximum and minimum frame delay must be made available to a Virtual Codec Unit (VCU)  120 , a component of the present invention, in order to manage and enhance the effective delivery of the media packets between EP-1 and EP-2.  
         [0049]    [0049]FIG. 3 describes the message flow illustrating a case where the H323 incoming call signalling and control protocol  330  between originating endpoint EP-1  100  and gateway GW  101 , a product of this invention, is in the Fast Connect mode and the connecting H.323 call signalling and control protocol  340  between GW  101  and destination endpoint EP-2  102  is in non-Fast Connect mode.  
         [0050]    The originating endpoint EP-1 initiates the Q.931 setup request  300  using the H.323 Fast Connect call signaling and control protocol. On receiving the request, the gateway starts endpoint process GW-EP-A  200  that receives the codec lists of EP-1 and call destination information referring to EP-2. The gateway  101  GW starts a new process GW-EP-B  201  that initiates a standard Q.931 call setup request message  302  to destination endpoint EP-2.  
         [0051]    In this illustration, EP-2 and gateway process GW-EP-B have decided to use non-Fast Connect call signalling and control protocol. As a result, the Q.931 Setup request  302  does not contain any codec list. This results in a longer call control and signalling sequence where gateway GW has to complete the Q.931 Connection phase (or Phase A) before H.245 capabilities exchange begins.  
         [0052]    Process GW-EP-B then waits on proceeding and alert messages  303  from endpoint EP-2 until the Q.931 Connect  304  confirmation arrives from EP-2.  
         [0053]    According to the teachings of this invention, the gateway GW prepares to extend a remote codec list  313  to EP-2, consisting of EP-1 codec list and optionally the GW codec list, the actual combination being beyond this invention. The remote codec list is sent in the start of H.245 Capability Set Request  315  to destination endpoint EP-2.  
         [0054]    The remote codec list is ordered by the GW, placing the codec list of EP-1 in front of its own codec list. A GW could also be configured to ignore its own codec list and instead, send only the codec of the originating endpoint  100  in the H.245 Capability Set Message. Other alternative strategies to achieve the same results, while not described here, are within the scope and spirit of the present invention.  
         [0055]    The teachings of the present invention will result in endpoint EP-2 receiving the capability G.723.1  314  in the remote codec list. The G.723.1 codec is common to EP-1  100  and EP-2  102  but not found in GW  101 . The codec G.723.1 is therefore extended through GW  101 , a product of this invention, from endpoint EP-1  100  to endpoint EP-2  102 . Endpoint EP-2 confirms the use of the extended codec G.723.1 in the H.245 exchange  305  response to GW-EP-B.  
         [0056]    According to the present invention, the gateway GW now completes the Q.931 session  306  with EP-1. GW-EP-A passes G.723.1 as the only codec in the Q.931 Connect  307  request to endpoint EP-1. The subsequest H.245 Capability Acknowledgement messages  308  and  309  confirm that a single codec G.723.1 is used by endpoints and gateways on entire communications path.  
         [0057]    A person skilled in the art will recognise that with the present invention, it is not possible for endpoints EP-1 or EP-2 to select different codecs for the transmit and receive channels since the GW, a product of this invention, always identifies a single codec in the H.245 negotiation. The GW is also certain that the selected end-to-end codec must be supported by both endpoints since it was instrumental in extending the codec capabilites of both endpoints during the H.323 setup, in accordance with the present invention.  
         [0058]    The gateway GW, however, needs to activate the Virtual Codec Unit  312 , a component of the present invention, so that media packet data of G.723.1 (or whichever codec that is selected) is relayed in conformance to the attributes of the frame characteristics of the codec.  
         [0059]    [0059]FIG. 4 is a message flow diagram describing how a gateway GW  101 , a product of the present invention, would synchronize the call signaling and control protocol exchanges between originating endpoint EP-1  100  and destination endpoint EP-2  102  under the following assumptions:  
         [0060]    Endpoint EP-1 is using the basic H.323 call control and signaling protocol without Fast Connect.  
         [0061]    Gateway GW is configured to receive both Fast Connect and non-Fast Connect modes of call control and signaling.  
         [0062]    Gateway GW is configured to opt for a Fast Connect mode of call control and signaling.  
         [0063]    The originating endpoint  100  EP-1 initiates a Q.931 setup request  400  to the gateway GW. This setup request starts an endpoint process GW-EP-A  200 . Process GW-EP-A obtains the caller destination of endpoint EP-2 to call  413  from the Q.931 setup message.  
         [0064]    According to the teachings of the present invention, gateway GW  101  requires the codec list from the originating endpoint EP-1 before it can initiate a Q.931 setup to the destination endpoint EP-2.  
         [0065]    However under International Telecommunications Union H.323 recommendations (ITU-H.323), originating endpoints not using Fast Connect call signaling and control protocol will wait for a Q.931 connect message to solicit for their endpoint codes list.  
         [0066]    Therefore to solicit the codec list, process GW-EP-A sends an early Q.931 Connect message  401  back to EP-1. This step is a novel variation of Q.931 call signaling and control protocol claimed under the teachings of the present invention since GW has not really connected with destination endpoint  102  EP-2 at this stage of the process.  
         [0067]    a result, endpoint EP-1 starts H.245 terminal capabilities exchange request  402  and sends its priority ordered codec list {G.723.1, G.711} to GW-EP-A. The gateway GW makes preparations to extend the codec list  403  received from EP-1 to EP-2, optionally including the gateway GW local codec list into a remote codec list. The gateway GW starts new process GW-EP-B  201 , which initiates a Q.931 Fast Connect Setup request  404  with the remote codec list to destination endpoint EP-2  102 .  
         [0068]    a result of the teachings of the present invention, the destination endpoint EP-2 has received a list of codecs  414  extending the codec list of the originating endpoint EP-1 to EP-2 via the gateway GW  101 , a product of the present invention.  
         [0069]    In this scenario, endpoint EP-2 is able to select codec G.723.1 within its repertoire of capabilities. EP-2 responds with a Q.931 connect message  405  back to GW-EP-B, indicating G.723.1 as the chosen codec. The gateway GW starts to complete its H.245 capabilities exchange  406  with originating endpoint EP-1. Process GW-EP-A then sends the H.245 terminal capability acknowledgement  407  with G.723.1 as the choice to EP-1. The following H.245 acknowledgement messages  408  to  410  confirm the use of codec G.723.1 as the end-to-end codec taught by the present invention.  
         [0070]    By managing the call connection between endpoint  100  EP-1 and endpoint  102  EP-2 as described above, the gateway GW  101 , a product of this invention, succeeds in enabling a single coder-decoder to be used, even whilst the gateway itself does not need to possess the selected G.723.1 codec capability. The gateway GW starts and maintains a Virtual Codec Unit (VCU)  120  to manage data packets in G.723.1 (or whichever selected codec) content and this novel capability enhances the transmission of data, and hence, the quality of audio between the opened logical channels.  
         [0071]    A person skilled in the art will appreciate that in the present invention, this Virtual End-to-End Codec selection is biased towards the destination endpoint. Through synchronization of the Q.931 and H.245 call signaling and control protocol as taught by the present invention, the destination endpoint  414  receives a biased codec list consisting of the possible capabilities of the endpoints and gateways on the communications path. Therefore, the destination endpoint will always be making its codec choice from a more comprehensive list of available codecs than without this invention. This has a desirable effect as it ensures that the destination endpoint can always select the best codec.  
         [0072]    It will also be appreciated by a person skilled in the art that in the present invention, the gateways can biased the codec selection list given to the destination endpoint in more ways than has been described.  
         [0073]    For example, the G.711 codec requires relatively high bandwidth at 64 Kbps for audio. A gateway in the present invention could thus improve the quality of transmission by using a gatekeeper and the International Telecommunications Union (ITU) H.225 RAS signaling functions to ascertain if a destination endpoint is connected to the Internet at bandwidths lower than 64 Kbps. At this speed, G.711 may not produce audio of a desired quality. The gateway  403  in this invention may then alter its strategy and drop G.711 or have G.729 ordered ahead of G.711 in the remote codec list sent to destination endpoint. Similar methods and strategies may be used without departing from the spirit or scope of the present invention.  
         [0074]    [0074]FIG. 5 is a block diagram  130  illustrating the Virtual End-to-End Codec method of the present invention. At the stage before a call is initiated  500 , the originating endpoint  501  includes a prioritized list of codecs D, A, B, C. The destination endpoint  503  lists codecs B, C, D, E in order of priority. A gateway device of this invention GW  502  is used to interconnect the two endpoints, listing codecs E, F, G as its preferred list. After the Q.931 Setup in fast connect mode  504 , the gateway now derives a merged list of possible codecs (D, A, B, C, E, F, G) forming the remote codec list  505 .  
         [0075]    If the destination endpoint conforms to conventional ITU H.323 systems, it will select the first codec on its local priority list that also matches the remote codec list. As shown in this particular illustration, codec B is selected in  508 .  
         [0076]    Since the built-in codec list of the gateway GW is also included in the remote codec list, there is probability that a codec not supported by the originating endpoint but supported by the gateway GW is chosen. As this is undesirable, the GW codec list will then be ignored in step  505  and only the originating endpoint&#39;s codecs are passed in the remote list. The result is that at end of the call control protocol  509 , the gateway will have to use a Virtual Codec Unit  510 , a component of the present invention, to relay the media packets between the endpoints.  
         [0077]    [0077]FIG. 6 illustrates the teachings of the present invention in a typical telephony over Internet application. The routing of data packets through multiple gateway routers called “hopping points” facilitates all Internet traffic. Assuming for example, that the endpoint computers EP-1 and EP-2 share an Internet traffic path interconnected by three gateway routers  600  as depicted in FIG. 6. These gateway routers GW-A  602 , GW-B  603  and GW-C  604  all support H.323 protocol but in addition have the ability to implement an end-to-end coder-decoder in accordance with the methods taught in the invention. EP-1  601  and EP-2  602  are two H.323 endpoints that wish to initiate communications via H.323 protocol. EP-1 uses a gatekeeper  606  to determine whether it should connect to GW-A for establishing the Q.931 Setup  607 .  
         [0078]    Using the current invention, GW-A, GW-B, GW-C can act as transparent extenders  608  for the Q.931 requests and H.245 capability exchanges for EP-1 and EP-2 to setup a H.323 communications path between the endpoints, using a single end-to-end coder-decoder that is known and acceptable between the two endpoints.  
         [0079]    The present invention is advantageous as the Virtual Codec Unit (VCU) and Virtual End-to-End Codec (VEEC) method can be embedded in hardware as special add-on adaptors or attachments to existing gateway routers, transforming them to gateway routers that support the teachings of the present invention and H.323 protocol.  
         [0080]    The invention can also be manifested as software and added to software-based routers and computers to enhance such equipment, enabling them to support the VEEC method in synchronizing the H.323 call signaling and control protocol. The requirement of coder-decoder functionality in software or hardware is made redundant with this invention for H.323 gateways. This then provides an attractive proposition for service providers to offer Internet telephony services to customers with lower capital investment requirements.  
         [0081]    While the present invention as described has used voice transmission for illustration, it will be apparent to one skilled on the art that other multimedia data may be similarly transmitted between H.323 endpoints using the present invention.  
         [0082]    Again, while the present invention is illustrated as transmission of multimedia between two endpoints, communications between more than two endpoints along plural logical channels is also possible and is within the scope and spirit of the present invention.  
         [0083]    [0083]FIG. 7 is a general block diagram of a H.323 gateway  700  according to an embodiment of the present invention. The gateway is connected to a packet network  701 , which physically allows the gateway to be accessible by other H.323 devices and for the gateway to access other H.323 devices.  
         [0084]    [0084]FIG. 7 also shows the components included within the scope of the ITU-H.323: H.225.0 layer  702 , System Control Unit  703 , Audio Codec  704 , Video Codec  705 , Data Interface  706  and Receive Path Delay  707 . The video input/output (I/O) Interface  708  and audio I/O Interface  709  may be part of a gateway if the gateway is to support direct connect with external equipment such as phone sets, video monitors, cameras, public switched telephone network (PSTN) switches, etc.  
         [0085]    In order to fulfill the Virtual End-to-End Codec (VEEC) method of the present invention, the gateway  700  will have to include the Single Codec Negotiation Module  130  (SCNM), another component of the present invention, and the Virtual Codec Unit  120  (VCU). The SCNM is a logic module used to control the H.323 call signaling protocol between connecting H.323 endpoints so that the methods of extending codec capabilities from endpoint to endpoint, codec list extension and single end-to-end codec determination, as taught in the present invention, may be implemented. The VCU completes the VEEC method of professing support for extended codec even though it does not possess the codec algorithm.  
         [0086]    facilitate use of this extended codec in the present invention, the basic attributes of the codec, such as its frame size, frame rate, maximum and minimum frame delay are made available to the VCU from some permanent memory Data Store Device  140  as shown in FIG. 7. The actual ITU-H.323 Audio and Video Codec in the gateway would also require these codec attributes for their algorithms, so such an attribute data store can be a shared resource.  
         [0087]    In addition, the gateway of the present invention could have a Codec Update Interface (CUI)  150  unit, another component of the present invention, as shown. The CUI defines the concept for dynamic updates of special codec for this invention as follows.  
         [0088]    If two endpoints wish to communicate with each other through a gateway of this invention, and the endpoints want to use a special codec whose attributes are not defined in the gateway, one of the endpoints would first use the Codec Update Interface (CUI) to update the gateway with the attributes of the special codec. Then the two endpoints can begin their H.323 call control and signaling protocol through the gateway. The gateway Virtual End-to-End Codec (VEEC) method will implement the special codec between the endpoints, as taught by this invention.  
         [0089]    Thus, the CUI facilitates the dynamic addition, deletion, modification and updating of extra codec attributes to improve and extend the capabilities of the VEEC method on the gateway. The CUI would be an out-of-band signaling protocol that will not interfere with the H.323 protocol supported on the same gateway.