Abstract:
The present invention is directed to voice communication devices in which an audio stream is divided into a sequence of individual packets, each of which is routed via pathways that can vary depending on the availability of network resources. All embodiments of the invention rely on an acoustic prioritization agent that assigns a priority value to the packets. The priority value is based on factors such as whether the packet contains voice activity and the degree of acoustic similarity between this packet and adjacent packets in the sequence. A confidence level, associated with the priority value, may also be assigned. In one embodiment, network congestion is reduced by deliberately failing to transmit packets that are judged to be acoustically similar to adjacent packets; the expectation is that, under these circumstances, traditional packet loss concealment algorithms in the receiving device will construct an acceptably accurate replica of the missing packet. In another embodiment, the receiving device can reduce the number of packets stored in its jitter buffer, and therefore the latency of the speech signal, by selectively deleting one or more packets within sustained silences or non-varying speech events. In both embodiments, the ability of the system to drop appropriate packets may be enhanced by taking into account the confidence levels associated with the priority assessments.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 10/262,621 filed on Sep. 30, 2002 and entitled “PACKET PRIORITIZATION AND ASSOCIATED BANDWIDTH AND BUFFER MANAGEMENT TECHNIQUES FOR AUDIO OVER IP”, the entire disclosure of which is herein incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to audio communications over distributed processing networks and specifically to voice communications over data networks. 
     BACKGROUND OF THE INVENTION 
     Convergence of the telephone network and the Internet is driving the move to packet-based transmission for telecommunication networks. As will be appreciated, a “packet” is a group of consecutive bytes (e.g. a datagram in TCP/IP) sent from one computer to another over a network. In Internet Protocol or IP telephony or Voice Over IP (VoIP), a telephone call is sent via a series of data packets on a fully digital communication channel. This is effected by digitizing the voice stream, encoding the digitized stream with a codec, and dividing the digitized stream into a series of packets (typically in 20 millisecond increments). Each packet includes a header, trailer, and data payload of one to several frames of encoded speech. Integration of voice and data onto a single network offers significantly improved bandwidth efficiency for both private and public network operators. 
     In voice communications, high end-to-end voice quality in packet transmission depends principally on the speech codec used, the end-to-end delay across the network and variation in the delay (jitter), and packet loss across the channel. To prevent excessive voice quality degradation from transcoding, it is necessary to control whether and where transcodings occur and what combinations of codecs are used. End-to-end delays on the order of milliseconds can have a dramatic impact on voice quality. When end-to-end delay exceeds about 150 to 200 milliseconds one way, voice quality is noticeably impaired. Voice packets can take an endless number of routes to a given destination and can arrive at different times, with some arriving too late for use by the receiver. Some packets can be discarded by computational components such as routers in the network due to network congestion. When an audio packet is lost, one or more frames are lost too, with a concomitant loss in voice quality. 
     Conventional VoIP architectures have developed techniques to resolve network congestion and relieve the above issues. In one technique, voice activity detection (VAD) or silence suppression is employed to detect the absence of audio (or detect the presence of audio) and conserve bandwidth by preventing the transmission of “silent” packets over the network. Most conversations include about 50% silence. When only silence is detected for a specified amount of time, VAD informs the Packet Voice Protocol and prevents the encoder output from being transported across the network. VAD is, however, unreliable and the sensitivity of many VAD algorithms imperfect. To exacerbate these problems, VAD has only a binary output (namely silence or no silence) and in borderline cases must decide whether to drop or send the packet. When the “silence” threshold is set too low, VAD is rendered meaningless and when too high audio information can be erroneously classified as “silence” and lost to the listener. The loss of audio information can cause the audio to be choppy or clipped. In another technique, a receive buffer is maintained at the receiving node to provide additional time for late and out-of-order packets to arrive. Typically, the buffer has a capacity of around 150 milliseconds. Most but not all packets will arrive before the time slot for the packet to be played is reached. The receive buffer can be filled to capacity at which point packets may be dropped. In extreme cases, substantial, consecutive parts of the audio stream are lost due to the limited capacity of the receive buffer leading to severe reductions in voice quality. Although packet loss concealment algorithms at the receiver can reconstruct missing packets, packet reconstruction is based on the contents of one or more temporally adjacent packets which can be acoustically dissimilar to the missing packet(s), particularly when several consecutive packets are lost, and therefore the reconstructed packet(s) can have very little relation to the contents of the missing packet(s). 
     SUMMARY OF THE INVENTION 
     These and other needs are addressed by the various embodiments and configurations of the present invention. The present invention is directed generally to a computational architecture for efficient management of transmission bandwidth and/or receive buffer latency. 
     In one embodiment of the present invention, a transmitter for a voice stream is provided that comprises: 
     (a) a packet protocol interface operable to convert one or more selected segments (e.g., frames) of the voice stream into a packet and 
     (b) an acoustic prioritization agent operable to control processing of the selected segment and/or packet based on one or more of (i) a level of confidence that the contents of the selected segment are not the product of voice activity (e.g., are silence), (ii) a type of voice activity (e.g., plosive) associated with or contained in the contents of the selected segment, and (iii) a degree of acoustic similarity between the selected segment and another segment of the voice stream. 
     The level of confidence permits the voice activity detector to provide a ternary output as opposed to the conventional binary output. The prioritization agent can use the level of confidence in the ternary output, possibly coupled with one or measures of the traffic patterns on the network, to determine dynamically whether or not to send the “silent” packet and, if so, use a lower transmission priority or class for the packet. 
     The type of voice activity permits the prioritization agent to identify extremely important parts of the voice stream and assign a higher transmission priorities and/or class to the packet(s) containing these parts of the voice stream. The use of a higher transmission priority and/or class can significantly reduce the likelihood that the packet(s) will arrive late, out of order, or not at all. 
     The comparison of temporally adjacent packets to yield a degree of acoustic similarity permits the prioritization agent to control bandwidth effectively. The agent can use the degree of similarity, possibly coupled with one or measures of the traffic patterns on the network, to determine dynamically whether or not to send a “similar” packet and, if so, use a lower transmission priority or class for the packet. Packet loss concealment algorithms at the receiver can be used to reconstruct the omitted packet(s) to form a voiced signal that closely matches the original signal waveform. Compared to conventional transmission devices, fewer packets can be sent over the network to realize an acceptable signal waveform. 
     In another embodiment of the present invention, a receiver for a voice stream is provided that comprises: 
     (a) a receive buffer containing a plurality of packets associated with voice communications; and 
     (b) a buffer manager operable to remove some of the packets from the receive buffer while leaving other packets in the receive buffer based on a level of importance associated with the packets. 
     In one configuration, the level of importance of the each of the packets is indicated by a corresponding value marker. The level of importance or value marker can be based on any suitable criteria, including a level of confidence that contents of the packet contain voice activity, a degree of similarity of temporally adjacent packets, the significance of the audio in the packet to receiver understanding or fidelity, and combinations thereof. 
     In another configuration, the buffer manager performs time compression around the removed packet(s) to prevent reconstruction of the packets by the packet loss concealment algorithm. This can be performed by, for example, resetting a packet counter indicating an ordering of the packets, such as by assigning the packet counter of the removed packet to a packet remaining in the receive buffer. 
     In another configuration, the buffer manager only removes packet(s) from the buffer when the buffer delay or capacity equals or exceeds a predetermined level. When the buffer is not in an overcapacity situation, it is undesirable to degrade the quality of voice communications, even if only slightly. 
     The various embodiments of the present invention can provide a number of advantages. First, the present invention can decrease substantially network congestion by dropping unnecessary packets, thereby providing lower end-to-end delays across the network, lower degrees of variation in the delay (jitter), and lower levels of packet loss across the channel. Second, the various embodiments of the present invention can handle effectively the bursty traffic and best-effort delivery problems commonly encountered in conventional networks while maintaining consistently and reliably high levels of voice quality reliably. Third, voice quality can be improved relative to conventional voice activity detectors by not discarding “silent” packets in borderline cases. 
     These and other advantages will be apparent from the disclosure of the invention(s) contained herein. 
     The above-described embodiments and configurations are neither complete nor exhaustive. As will be appreciated, other embodiments of the invention are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a simple network for a VoIP session between two endpoints according to a first embodiment of the present invention; 
         FIG. 2  is a block diagram of the functional components of a transmitting voice communication device according to the first embodiment; 
         FIG. 3  is a block diagram of the functional components of a receiving voice communication device according to the first embodiment; 
         FIG. 4  is a flow chart of a voice activity detector according to a second embodiment of the present invention; 
         FIG. 5  is a flow chart of a codec according to a third embodiment of the present invention; 
         FIG. 6  is a flow chart of a packet prioritizing algorithm according to a second embodiment of the present invention; 
         FIG. 7  is a block diagram illustrating time compression according to a fourth embodiment of the present invention; and 
         FIG. 8  is a flow chart of a buffer management algorithm according to the fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a simplistic VoIP network architecture according to a first embodiment of the present invention. First and second voice communication devices  100  and  104  transmit and receive VoIP packets. The packets can be transmitted over one of two paths. The first and shortest path is via networks  108  and  112  and router  116 . The second and longer path is via networks  108 ,  112 , and  120  and routers  124  and  128 . Depending upon the path followed, the packets can arrive at either of the communication devices at different times. As will be appreciated, network architectures suitable for the present invention can include any number of networks and routers and other intermediate nodes, such as transcoding gateways, servers, switches, base transceiver stations, base station controllers, modems, router, and multiplexers and employ any suitable packet-switching protocols, whether using connection oriented or connectionless services, including without limitation Internet Protocol or IP, Ethernet, and Asynchronous Transfer Mode or ATM. 
     As will be further appreciated, the first and second voice communication devices  100  and  104  can be any communication devices configured to transmit and/or receive packets over a data network, such as the Internet. For example, the voice communication devices  100  and  104  can be a personal computer, a laptop computer, a wired analog or digital telephone, a wireless analog or digital telephone, intercom, and radio or video broadcast studio equipment. 
       FIG. 2  depicts an embodiment of a transmitting voice communication device. The device  200  includes, from left to right, a first user interface  204  for outputting signals inputted by the first user (not shown) and an outgoing voice stream  206  received from the first user, an analog-to-digital converter  208 , a Pulse Code Modulation or PMC interface  212 , an echo canceller  216 , a Voice Activity Detector or VAD  10 , a voice codec  14 , a packet protocol interface  18  and an acoustic prioritizing agent  232 . 
     The first user interface  204  is conventional and be configured in many different forms depending upon the particular implementation. For example, the user interface  204  can be configured as an analog telephone or as a PC. The analog-to-digital converter  208  converts, by known techniques, the analog outgoing voice stream  206  received from the first user interface  204  into an outgoing digital voice stream  210 . 
     The PCM interface  212 , inter alia, forwards the outgoing digital voice stream  210  to appropriate downstream processing modules for processing. 
     The echo canceller  216  performs echo cancellation on the digital stream  214 , which is commonly a sampled, full-duplex voice port signal. Echo cancellation is preferably G.165 compliant. 
     The VAD  10  monitors packet structures in the incoming digital voice stream  216  received from the echo canceller  216  for voice activity. When no voice activity is detected for a configurable period of time, the VAD  10  informs the acoustic prioritizing agent  232  of the corresponding packet structure(s) in which no voice activity was detected and provides a level of confidence that the corresponding packet structure(s) contains no meaningful voice activity. This output is typically provided on a packet structure-by-packet structure basis. These operations of the VAD are discussed below with reference to  FIG. 4 . 
     VAD  10  can also measure the idle noise characteristics of the first user interface  204  and report this information to the packet protocol interface  18  in order to relay this information to the other voice communication device for comfort noise generation (discussed below) when no voice activity is detected. 
     The voice codec  14  encodes the voice data in the packet structures for transmission over the data network and compares the acoustic information (each frame of which includes spectral information such as sound or audio amplitude as a function of frequency) in temporally adjacent packet structures and assigns to each packet an indicator of the difference between the acoustic information in adjacent packet structures. These operations are discussed below with reference to  FIG. 5 . As shown in box  236 , the voice codec typically include, in memory, numerous voice codecs capable of different compression ratios. Although only codecs G.711, G,723.1, G.726, G.728, and G.78 are shown, it is to be understood that any voice codec whether known currently or developed in the future could be in memory. Voice codecs encode and/or compress the voice data in the packet structures. For example, a compression of 8:1 is achievable with the G.78 voice codec (thus the normal 64 Kbps PCM signal is transmitted in only 8 Kbps). The encoding functions of codecs are further described in Michaelis,  Speech Digitization and Compression,  in the  International Encyclopedia of Ergonomics and Human Factors , edited by Warkowski, 2001; ITU-T Recommendation G.78  General Aspects of Digital Transmission Systems, Coding of Speech at  8  kbit/s using Conjugate - Structure Algebraic - Code - Excited Linear - Prediction , March 1996; and Mahfuz,  Packet Loss Concealment for Voice Transmission Over IP Networks , September 2001, each of which is incorporated herein by this reference. 
     The prioritization agent  232  efficiently manages the transmission bandwidth and the receive buffer latency. The prioritization agent (a) determines for each packet structure, based on the corresponding difference in acoustic information between the selected packet structure and a temporally adjacent packet structure (received from the codec), a relative importance of the acoustic information contained in the selected packet structure to maintaining an acceptable level of voice quality and/or (b) determines for each packet structure containing acoustic information classified by the VAD  10  as being “silent” a relative importance based on the level of confidence (output by the VAD for that packet structure) that the acoustic information corresponds to no voice activity. The acoustic prioritization agent, based on the differing levels of importance, causes the communication device to process differently the packets corresponding to the packet structures. The packet processing is discussed in detail below with reference to  FIG. 6 . 
     The packet protocol interface  18  assembles into packets and sequences the outgoing encoded voice stream and configures the packet headers for the various protocols and/or layers required for transmission to the second voice communication device  300  ( FIG. 3 ). Typically, voice packetization protocols use a sequence number field in the transmit packet stream to maintain temporal integrity of voice during playout. Under this approach, the transmitter inserts a packet counter, such as the contents of a free-running, modulo-16 packet counter, into each transmitted packet, allowing the receiver to detect lost packets and properly reproduce silence intervals during playout at the receiving communication device. In one configuration, the importance assigned by the acoustic prioritizing agent can be used to configure the fields in the header to provide higher or lower transmission priorities. This option is discussed in detail below in connection with  FIG. 6 . 
     The packetization parameters, namely the packet size and the beginning and ending points of the packet are communicated by the packet protocol interface  18  to the VAD  10  and codec  14  via the acoustic prioritization agent  232 . The packet structure represents the portion of the voice stream that will be included within a corresponding packet&#39;s payload. In other words, a one-to-one correspondence exists between each packet structure and each packet. As will be appreciated, it is important that packetization parameter synchronization be maintained between these components to maintain the integrity of the output of the acoustic prioritization agent. 
       FIG. 3  depicts an embodiment of a receiving (or second) voice communication device  300 . The device  300  includes, from right to left, the packet protocol interface  18  to remove the header information from the packet payload, the voice codec  14  for decoding and/or decompressing the received packet payloads to form an incoming digital voice stream  302 , an adaptive playout unit  304  to process the received packet payloads, the echo canceller  216  for performing echo cancellation on the incoming digital voice stream  306 , the PCM interface  212  for performing continuous phase resampling of the incoming digital voice stream  316  to avoid sample slips and forwarding the echo cancelled incoming voice stream  316  to a digital-to-analog converter  308  that converts the echo cancelled incoming voice stream  320  into an analog voice stream  324 , and second user interface  312  for outputting to the second user the analog voice stream  324 . 
     The adaptive playout unit  304  includes a packet loss concealment agent  328 , a receive buffer  336 , and a receive buffer manager  332 . The adaptive playout unit  304  can further include a continuous-phase resampler (not shown) that removes timing frequency offset without causing packet slips or loss of data for voice or voiceband modem signals and a timing jitter measurement module (not shown) that allows adaptive control of FIFO delay. The packet loss concealment agent  328  reconstructs missing packets based on the contents of temporally adjacent received packets. As will be appreciated, the packet loss concealment agent can perform packet reconstruction in a multiplicity of ways, such as replaying the last packet in place of the lost packet and generating synthetic speech using a circular history buffer to cover the missing packet. Preferred packet loss concealment algorithms preserve the spectral characteristics of the speaker&#39;s voice and maintain a smooth transition between the estimated signal and the surrounding original. In one configuration, packet loss concealment is performed by the codec. 
     The receive buffer  336  alleviates the effects of late packet arrival by buffering received voice packets. In most applications the receive buffer  336  is a First-In-First-Out or FIFO buffer that stores voice codewords before playout and removes timing jitter from the incoming packet sequence. As will be appreciated, the buffer  336  can dynamically increase and decrease in size as required to deal with late packets when the network is uncongested while avoiding unnecessary delays when network traffic is congested. 
     The buffer manager  332  efficiently manages the increase in latency (or end-to-end delay) introduced by the receive buffer  336  by dropping (low importance) enqueued packets as set forth in detail below in connection with  FIGS. 7 and 8 . 
     In addition to packet payload decryption and/or decompression, the voice codec  18  can also include a comfort noise generator (not shown) that, during periods of transmit silence when no packets are sent, generates a local noise signal that is presented to the listener. The generated noise attempts to match the true background noise. Without comfort noise, the listener can conclude that the line has gone dead. 
     Analog-to-digital and digital-to-analog converters  208  and  308 , the pulse code modulation interface  212 , the echo canceller  216   a  and  b , packet loss concealment agent  328 , and receive buffer  336  are conventional. 
     Although  FIGS. 2 and 3  depict voice communication devices in simplex configurations, it is to be understood that each of the voice communication devices  200  and  300  can act both as a transmitter and receiver in a duplexed configuration. The operation of the VAD  10  will now be described with reference to  FIGS. 2 and 4 . 
     In the first step  400 , the VAD  10  gets packet structure j  from the echo canceled digital voice stream  218 . Packet structure counter i is initially set to one. In step  404 , the VAD  10  analyzes the acoustic information in packet structure j  to identify by known techniques whether or not the acoustic information qualifies as “silence” or “no silence” and determine a level of confidence that the acoustic information does not contain meaningful or valuable acoustic information. The level of confidence can be determined by known statistical techniques, such as energy level measurement, least mean square adaptive filter (Widrow and Hoff 1959), and other Stochastic Gradient Algorithms. In one configuration, the acoustic threshold(s) used to categorize frames or packets as “silence” versus “nonsilence” vary dynamically, depending upon the traffic congestion of the network. The congestion of the network can be quantified by known techniques, such as by jitter determined by the timing measurement module (not shown) in the adaptive playout unit of the sending or receiving communication device, which would be forwarded to the VAD  10 . Other selected parameters include latency or end-to-end delay, number of lost or dropped packets, number of packets received out-of-order, processing delay, propagation delay, and receive buffer delay/length. When the selected parameter(s) reach or fall below selected levels, the threshold can be reset to predetermined levels. 
     In step  408 , the VAD  10  next determines whether or not packet structure j  is categorized as “silent” or “nonsilent”. When packet structure j  is categorized as being “silent”, the VAD  10 , in step  412 , notifies the acoustic prioritization agent  232  of the packet structure j  beginning and/or endpoint(s), packet length, the “silent” categorization of packet structure j , and the level of confidence associated with the “silent” categorization of packet structure. When packet structure j  is categorized as “nonsilent” or after step  412 , the VAD  10  in step  416  sets counter j equal to j+1 and in step  420  determines whether there is a next packet structure j . If so, VAD  10  returns to and repeats step  400 . If not, VAD  10  terminates operation until a new series of packet structures is received. 
     The operation of the codec  14  will now be described with reference to  FIGS. 2 and 5 . In steps  500 ,  504  and  512 , respectively, the codec  14  gets packet structure j , packet structure j−1 , and packet structure j+1 . Packet structure counter j is, of course, initially set to one. 
     In steps  508  and  516 , respectively, the codec  14  compares packet structure j  with packet structure j−1 , and packet structure j  with packet structure j+1 . As will be appreciated, the comparison can be done by any suitable technique, either currently or in the future known by those skilled in the art. For example, the amplitude and/or frequency waveforms (spectral information) formed by the collective frames in each packet can be mathematically compared and the difference(s) quantified by one or more selected measures or simply by a binary output such as “similar” or “dissimilar”. Acoustic comparison techniques are discussed in Michaelis, et a.,  A Human Factors Engineer&#39;s Introduction to Speech Synthesizers , in  Directions in Human - Computer Interaction , edited by Badre, et al., 1982, which is incorporated herein by this reference. If a binary output is employed, the threshold selected for the distinction between “similar” and “dissimilar” can vary dynamically based on one or more selected measures or parameters of network congestion. Suitable measures or parameters include those set forth previously. When the measures increase or decrease to selected levels the threshold is varied in a predetermined fashion. 
     In step  520 , the codec  14  outputs the packet structure similarities/nonsimilarities determined in steps  508  and  516  to the acoustic prioritization agent  232 . Although not required, the codec  14  can further provide a level of confidence regarding the binary output. The level of confidence can be determined by any suitable statistical techniques, including those set forth previously. Next in step  524 , the codec encodes packet structure. As will be appreciated, the comparison steps  508  and  516  and encoding step  524  can be conducted in any order, including in parallel. The counter is incremented in step  528 , and in step  532 , the codec determines whether or not there is a next packet structure. 
     The operation of the acoustic prioritization agent  232  will now be discussed with reference to with  FIGS. 2 and 6 . 
     In step  600 , the acoustic prioritizing agent  232  gets packet j  (which corresponds to packet structure j ). In step  604 , the agent  232  determines whether VAD  10  categorized packet structure j  as “silence”. When the corresponding packet structure j  has been categorized as “silence”, the agent  232 , in step  608 , processes packet j  based on the level of confidence reported by the VAD  10  for packet structure j . 
     The processing of “silent” packets can take differing forms. In one configuration, a packet having a corresponding level of confidence less than a selected silence threshold Y is dropped. In other words, the agent requests the packet protocol interface  18  to prevent packet j  from being transported across the network. A “silence” packet having a corresponding level of confidence more than the selected threshold is sent. The priority of the packet can be set at a lower level than the priorities of “nonsilence” packets. “Priority” can take many forms depending on the particular protocols and network topology in use. For example, priority can refer to a service class or type (for protocols such as Differentiated Services and Internet Integrated Services), and priority level (for protocols such as Ethernet). For example, “silent” packets can be sent via the assured forwarding class while “nonsilence” packets are sent via the expedited forwarding (code point) class. This can be done, for example, by suitably marking, in the Type of Service or Traffic Class fields, as appropriate. In yet another configuration, a value marker indicative of the importance of the packet to voice quality is placed in the header and/or payload of the packet. The value marker can be used by intermediate nodes, such as routers, and/or by the buffer manager  332  ( FIG. 3 ) to discard packets in appropriate applications. For example, when traffic congestion is found to exist using any of the parameters set forth above, value markers having values less than a predetermined level can be dropped during transit or after reception. This configuration is discussed in detail with reference to  FIGS. 7 and 8 . Multiple “silence” packet thresholds can be employed for differing types of packet processing, depending on the application. As will be appreciated, the various thresholds can vary dynamically depending on the degree of network congestion as set forth previously. 
     When the corresponding packet structure j  has been categorized as “nonsilence”, the agent  232 , in step  618 , determines whether the degree of similarity between the corresponding packet structure j  and packet structure j−1  (as determined by the codec  14 ) is greater than or equal to a selected similarity threshold X. If so, the agent  232  proceeds to step  628  (discussed below). If not, the agent  232  proceeds to step  624 . In step  624 , the agent determines whether the degree of similarity between the corresponding packet structure j  and packet structure j+1  (as determined by the codec  14 ) is greater than or equal to the selected similarity threshold X. If so, the agent  232  proceeds to step  628 . 
     In step  628 , the agent  232  processes packet j  based on the magnitude of the degree of similarity and/or on the treatment of the temporally adjacent packet j−1 . As in the case of “silent” packets, the processing of similar packets can take differing forms. In one configuration, a packet having a degree of similarity more than the selected similarity threshold X is dropped. In other words, the agent requests the packet protocol interface  18  to prevent packet j  from being transported across the network. The packet loss concealment agent  328  ( FIG. 3 ) in the second communication device  300  will reconstruct the dropped packet. In that event, the magnitude of X is determined by the packet reconstruction efficiency and accuracy of the packet loss concealment algorithm. If the preceding packet j−1  were dropped, packet j  may be forwarded, as the dropping of too many consecutive packets can have a detrimental impact on the efficiency and accuracy of the packet loss concealment agent  328 . In another configuration, multiple transmission priorities are used depending on the degree of similarity. For example, a packet having a degree of similarity more than the selected threshold is sent with a lower priority. The priority of the packet is set at a lower level than the priorities of dissimilar packets. As noted above, “priority” can take many forms depending on the particular protocols and network topology in use. In yet another configuration, the value marker indicative of the importance of the packet to voice quality is placed in the header and/or payload of the packet. The value marker can be used as set forth previously and below to cause the dropping of packets having value markers below one or more selected marker value thresholds. Multiple priority levels can be employed for multiple similarity thresholds, depending on the application. As will be appreciated, the various similarity and marker value thresholds can vary dynamically depending on the degree of network congestion as set forth previously. 
     After steps  608  and  628  and in the event in step  624  that the similarity between the corresponding packet structure j  and packet structure j+1  (as determined by the codec  14 ) is less than the selected similarity threshold X, the agent  232  proceeds to step  612 . In step  612 , the counter j is incremented by one. In step  616 , the agent  232  determines whether there is a next packet j . When there is a next packet j , the agent  232  proceeds to and repeats step  600 . When there is no next packet j , the agent  232  proceeds to step  632  and terminates operation until more packet structures are received for packetization. 
     The operation of the buffer manager  332  will now be described with reference to FIGS.  3  and  7 - 8 . In step  800 , the buffer manager  332  determines whether the buffer delay (or length) is greater than or equal to a buffer threshold Y. If not, the buffer manager  332  repeats step  800 . If so, the buffer manager  332  in step  804  gets packet k  from the receive buffer  336 . Initially, of course the counter k is set to 1 to denote the packet in the first position in the receive buffer (or at the head of the buffer). Alternatively, the manager  332  can retrieve the last packet in the receive buffer (or at the tail of the buffer). 
     In step  808 , the manager  332  determines if the packet is expendable; that is, whether the value of the value marker is less than (or greater depending on the configuration) a selected value threshold. When the value of the value marker is less than the selected value threshold, the packet k  in step  812  is discarded or removed from the buffer and in step  816  the surrounding enqueued packets are time compressed around the slot previously occupied by packet k . 
     Time compression is demonstrated with reference to  FIG. 7 . The buffer  336  is shown as having various packets  700   a - e , each packet payload representing a corresponding time interval of the voice stream. If the manager determines that packet  700   b  (which corresponds to the time interval t 2  to t 3 ) is expendable, the manager  332  first removes the packet  700   b  from the queue  336   a  and then moves packets  700   c - e  ahead in the queue. To perform time compression, the packet counters for packets  700   c - e  are decremented such that packet  700   c  now occupies the time slot t 2  to t 3 , packet  700   d  time slot t 2  to t 3 , and packet  700   d  time slot t 3  to t 4 . In this manner, the packet loss concealment agent  328  will be unaware that packet  700   b  has been discarded and will not attempt to reconstruct the packet. In contrast, if a packet is omitted from an ordering of packets, the packet loss concealment agent  328  will recognize the omission by the break in the packet counter sequence. The agent  328  will then attempt to reconstruct the packet. 
     Returning again to  FIG. 8 , the manager  332  in step  820  increments the counter k and repeats step  800  for the next packet. 
     A number of variations and modifications of the invention can be used. It would be possible to provide for some features of the invention without providing others. 
     For example in one alternative embodiment, the prioritizing agent&#39;s priority assignment based on the type of “silence” detected can be performed by the VAD  200 . 
     In another alternative embodiment though  FIG. 2  is suitable for use with a VoIP architecture using Embedded Communication Objects interworking with a telephone system and packet network, it is to be understood that the configuration of the VAD  10 , codec  14 , prioritizing agent  232  and/or buffer manager  332  of the present invention can vary significantly depending upon the application and the protocols employed. For example, the prioritizing agent  232  can be included in an alternate location in the embodiment of  FIG. 2 , and the buffer manager in an alternate location in the embodiment of  FIG. 3 . The prioritizing agent and/or buffer manager can interface with different components than those shown in  FIG. 2  for other types of user interfaces, such as a PC, wireless telephone, and laptop. The prioritizing agent and/or buffer manager can be included in an intermediate node between communication devices, such as in a switch, transcoding device, translating device, router, gateway, etc. 
     In another embodiment, the packet comparison operation of the codec is performed by another component. For example, the VAD and/or acoustic prioritization agent performs these functions. 
     In another embodiment, the level of confidence determination of the VAD is performed by another component. For example, the codec and/or acoustic prioritization agent performs these functions. 
     In yet a further embodiment, the codec and/or VAD, during packet structure processing attempt to identify acoustic events of great importance, such as plosives. When such acoustic events are identified (e.g., when the difference identified by the codec exceeds a predetermined threshold), the acoustic prioritizing agent  232  can cause the packets corresponding to the packet structures to have extremely high priorities and/or be marked with value markers indicating that the packet is not to be dropped under any circumstances. The loss of a packet containing such important acoustic events often cannot be reconstructed accurately by the packet loss concealment agent  328 . 
     In yet a further embodiment, the analyses performed by the codec, VAD, and acoustic prioritizing agent are performed on a frame level rather than a packet level. “Silent” frames and/or acoustically similar frames are omitted from the packet payloads. The procedural mechanisms for these embodiments are similar to that for packets in  FIGS. 4 and 5 . In fact, the replacement of “frame” for “packet structure” and “packet” in  FIGS. 4 and 5  provides a configuration of this embodiment. 
     In yet another embodiment, the algorithms of  FIGS. 6 and 8  are state driven. In other words, the algorithms are not triggered until network congestion exceeds a predetermined amount. The trigger for the state to be entered can be based on any of the performance parameters set forth above increasing above or decreasing below predetermined thresholds. 
     In yet a further embodiment, the dropping of packets based on the value of the value marker is performed by an intermediate node, such as a router. This embodiment is particularly useful in a network employing any of the Multi Protocol Labeling Switching, ATM, and Integrated Services Controlled Load and Differentiate Services. 
     In yet a further embodiment, the positions of the codec and adaptive playout unit in  FIG. 3  are reversed. Thus, the receive buffer  336  contains encoded packets rather than decoded packets. 
     In yet a further embodiment, the acoustic prioritization agent  232  processes packet structures before and/or after encryption. 
     In yet a further embodiment, a value marker is not employed and the buffer manager itself performs the packet/frame comparison to identify acoustically similar packets that can be expended in the event that buffer length/delay reaches undesired levels. 
     In other embodiments, the VAD  10 , codec  14 , acoustic prioritization agent  232 , and/or buffer manager  332  are implemented as software and/or hardware, such as a logic circuit, e.g., an Application Specific Integrated Circuit or ASIC. 
     The present invention, in various embodiments, includes components, methods, processes, systems and/or apparatus substantially as depicted and described herein, including various embodiments, subcombinations, and subsets thereof. Those of skill in the art will understand how to make and use the present invention after understanding the present disclosure. The present invention, in various embodiments, includes providing devices and processes in the absence of items not depicted and/or described herein or in various embodiments hereof, including in the absence of such items as may have been used in previous devices or processes, e.g., for improving performance, achieving ease and\or reducing cost of implementation. 
     The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to the form or forms disclosed herein. Although the description of the invention has included description of one or more embodiments and certain variations and modifications, other variations and modifications are within the scope of the invention, e.g., as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.