RU2364051C2 - Call setup in videophone network - Google Patents

Abstract

FIELD: communication facilities.

SUBSTANCE: invention concerns methods of video call setup in mobile videophone network. Claimed methods of call setup reduce delays in call setup due to anticipating repeated packet transfer (NSRP) till expiration of typical waiting time period required for reception of NSRP acknowledgement packet (ACK) from remote terminal. Retransmitted NSRP packets can be sent again in free periods when modem level of transmitting mobile terminal does not receive other data for transfer to remote mobile terminal, thus taking advantage of vacant pass band. Multiplexed data received by modem can be stored in local buffer at modem level for retransmission. Thus, retransmission does not require generation of original call setup messages or multiplexing. Previously generated and multiplexed data are instead store in buffer at modem level for retransmission.

EFFECT: reduced overhead cost of processing at mobile terminal.

37 cl, 6 dwg, 1 tbl

Description

This patent application claims the priority of application US 60/611199, filed September 16, 2004, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to video telephony, and more particularly to techniques for establishing a call in a video telephone network.

Description of the Related Art

The 3G-H.324M standard, prepared by the International Telecommunication Union (ITU), is an example of a protocol for video conferencing in a mobile wireless network. The 3G-H.324M standard specifies how mobile terminals should handle the flow of audio and video data. The ITU H.245 standard specifies a signaling channel for establishing a video call. Using H.245 control messages, mobile terminals exchange information about the characteristics and open channels of video and audio data. One or more codecs perform encoding and decoding of video and audio data for transmission between mobile terminals to support video conferencing. The ITU H.223 layer multiplexes and demultiplexes the signal and data channels.

During call setup according to H.324M, both mobile terminals indicate their characteristics by exchanging Simple Numbered Repeat Protocol (NSRP) packets containing H.245 call control messages. In general, NSPR is a “stop and wait” protocol in which the terminal transmits one packet, waits for acknowledgment from the remote terminal and only after receiving the acknowledgment continues to transmit the next NSRP packet. For example, upon receiving an incoming NSRP packet from the transmitting terminal, the remote terminal will transmit the NSRP Acceptance Packet (ACK) to the transmitting terminal to confirm that it has actually received the NSRP packet.

Upon receiving the ACK NSRP packet, the transmitting terminal may transmit the next NSRP packet and continue to establish the H.324M call. However, if the transmitting terminal does not receive the NSRP ACK packet during the NSRP timeout period, the transmitting terminal retransmits the previous NSRP packet to the remote terminal. The NSRP ACK confirms that H.245 signaling has been received by the remote terminal, ensuring guaranteed delivery. However, the “stop and wait” aspect of NSRP can cause unwanted delays during call setup, in particular when the core wireless network is error prone, which causes a significant number of NSRP packets to be dropped.

SUMMARY OF THE INVENTION

This invention focuses on techniques for establishing a video call in a mobile video telephone network. These techniques may be implemented in a mobile wireless communication terminal to reduce delays during the establishment of a video conferencing call. These call setup techniques can be applied to H.324M video conferencing systems that rely on the H.245 signaling channel to establish the call and the H.223 multiplex-demultiplex layer (MUX-DEMUX level) for packing and transmitting NSRP packets carrying H. 245. In general, the call setup techniques described in the present invention reduce call setup delays by proactively retransmitting NSRP packets before the timeout period normally required for receiving an ACK NSRP packet from a remote terminal has expired.

Retransmission is “proactive” in the sense that it is not known whether the originally transmitted NSRP packet will actually be discarded. Retransmitted NSRP packets can be retransmitted during “unused” periods in which the modem layer in the transmitting mobile terminal did not receive any other data from the H.223 layer for transmission to the remote mobile terminal, thereby taking advantage of the unused bandwidth. When an NSRP packet is dropped due to network errors, a retransmitted NSRP packet takes its place. If the original NSRP packet is not discarded, the retransmitted packet may be discarded.

By proactively retransmitting the NSRP packet, at least a portion of the delay typically required during the NCRP ACK timeout period for retransmitting the NSRP packets can be eliminated. In addition, in some embodiments of the present invention, the multiplexed data received from the H.223 layer can be locally stored in a buffer at the modem level for retransmission, for example, in the form of packets of a digital network with integrated services (ISDN). In this case, the retransmission of NSRP packets does not require either the re-generation of the initial call setup messages at the H.245 level or the multiplexing at the H.223 level. Instead, previously generated and multiplexed data is stored in a buffer at the modem level for retransmission, which reduces the processing overhead in the mobile terminal.

In one embodiment of the present invention, there is provided a method comprising the steps of transmitting a video call setup packet from a first mobile terminal to a second mobile terminal and retransmit this video call setup packet before the reception acknowledgment packet is received from the second mobile terminal.

In another embodiment of the present invention, there is provided a mobile wireless terminal comprising a wireless transmitter, a wireless receiver and a modem that generates a video call setup packet for transmission by a transmitter to a second mobile terminal and provides this video call setup packet for retransmission by a transmitter before a time period has elapsed waiting for the receipt of the acknowledgment packet from the second mobile terminal.

In a further embodiment of the present invention, there is provided a computer-readable storage medium containing instructions for causing a processor to transmit a video call setup packet from a first mobile terminal to a second mobile terminal and retransmit this video call setup packet before the reception acknowledgment packet is received from the second mobile terminal.

Details of various embodiments are set forth in the accompanying drawings and description below. Other features, objects and advantages will become apparent from the description and drawings, as well as from the claims.

List of drawings

Figure 1 is a flowchart illustrating a methodology for establishing a video call in a videotelephone network.

2 is a block diagram showing an illustrative embodiment of a mobile terminal configured for video telephony.

FIG. 3 is a flowchart illustrating a video call establishment technique.

4 is a block diagram illustrating the arrangement of video call setup packets for transmission to a remote mobile terminal.

5 is a flowchart illustrating a technique for retransmitting video call setup packets to reduce setup delays.

6 is a flowchart illustrating in more detail the arrangement and retransmission of video call setup packets.

Description of Preferred Embodiments

Figure 1 is a flowchart illustrating a methodology for establishing a video call in a videotelephone network. As shown in FIG. 1, the mobile terminal 10A starts establishing a video call with the remote mobile terminal 10B by transmitting (12) to the remote mobile terminal a call setup packet through intermediate wireless network equipment (not shown). In some embodiments of the present invention, the call setup packet may be an NSRP packet containing H.245 call setup information, and the NSRP packet may be packaged in one or more ISDN packets at the modem level of mobile terminal 10A.

To reduce call setup delays in accordance with the present invention, the mobile terminal 10A is configured to proactively retransmit (14) a call setup packet without waiting for an NSRP ACK timeout period, provided that an acknowledgment packet (ACK) has not yet been received (16) from a remote terminal 10B. The transmitting mobile terminal 10A may retransmit a call setup packet during one or more unused periods in which the modem layer of the mobile terminal 10A did not receive any other data from the H.324M stack for transmission to the remote mobile terminal 10B.

The transmitting mobile terminal 10A does not wait for the NSRP ACK to expire before retransmitting the call setup packet. Instead, the transmitting mobile terminal 10A proactively retransmits the call setup packet, for example, when unused bandwidth is available at the modem level, based on the likelihood that the originally transmitted call setup packet will be discarded due to errors in the video telephone network.

Typically, NSRP implementations require an ACK NSRP timeout before the NSRP packet is retransmitted. In accordance with the present invention, proactive retransmission of a call setup packet by a mobile terminal 10A eliminates at least a portion of the delay associated with said wait period and thereby reduces call setup delays in a video telephone network. If the initial call setup packet transmitted by the mobile terminal 10A is discarded, that is, lost during transmission, then the retransmitted call setup packet takes its place. Alternatively, if the initial call setup packet is received by the remote mobile terminal 10B, in which case the ACK packet may eventually come from the remote mobile terminal 10B, the retransmitted call setup packet may be discarded by the remote mobile terminal 10B.

In each case, the transmitting mobile terminal 10A retransmits the call setup packet rationally using unused bandwidth at the modem level. In particular, a call setup packet may be transmitted during unused periods during which the modem layer of the transmitting mobile terminal 10A did not receive any new NSRP information, audio or video information from the H.324M stack. During call setup, audio and video channels are not yet created. Therefore, in the normal case, during call setup, there will be no audio or video data available from the H.324M stack. There will also be significant gaps between NSRP packets due to the inherent implementation of the NSRP “stop and wait” principle.

Therefore, there will be unused time intervals during which the modem level of the mobile terminal 10A does not receive any significant information from the H.223 level. In the normal case, the modem 26 would simply add padding flags to fill in the unused portions of the ISDN packets transmitted by the mobile terminal 10A. However, in accordance with the present invention, unused portions may be involved in order to realize the possibility of efficiently retransmitting call setup packets instead of padding flags, bypassing typical NSRP “stop and wait” requirements. Based on unused bandwidth, retransmission of a call setup packet should have a slight or insignificant adverse effect on the performance of the video telephone network.

FIG. 2 is a block diagram showing an illustrative embodiment of a mobile terminal 10A configured for video telephony. As described here, the mobile terminal 10A may be enabled to proactively retransmit call setup packets, such as NSRP packets, when space is available at the modem level. In the illustrative embodiment of FIG. 2, the mobile terminal 10A includes a video codec 18, an audio codec 20, a H.245 control level module 22, an H.223 multiplexer-demultiplexer (MUX-DEMUX) module 24, a modem 26, a transmission interface 27 receive (TX / RX) and NSRP control channel segmentation and rearrangement (CCSRL) module 28. Together, these components form the H.324M protocol stack. In general, many aspects of the proactive retransmission technique described herein may be implemented in modem 26 of mobile terminal 10A.

Video codec 18 encodes video data received from a video input device, such as a camera or video archive source, in accordance with an industry standard video compression standard protocol such as MPEG-4 or H.263 from ITU for transmission to another mobile terminal. In addition, video codec 18 decodes video data received from another mobile terminal for output to a video output device, such as a display. Similarly, audio codec 20 encodes audio data received from an audio input device, such as a microphone or an audio archive source, in accordance with an audio compression protocol such as AAC (Advanced Audio Coding), AMR (Adaptive Multi-Rate Coding) or QCELP (Linear Prediction Coding with Code Excitation in the implementation of Qualcomm). The audio codec 20 also decodes audio data received from the remote terminal 10B for playback by an audio output device, such as an internal or external speaker, connected to the mobile terminal 10A.

The H.245 control layer module 22 generates H.245 messages for transmission to the remote mobile terminal 10B to establish a video call and processes H.245 messages received from the remote mobile terminal. The CCSRL-NSRP module 28 segments the H.245 messages from the H.245 control layer module 22 into NSRP packets for transmission to the remote terminal and rearranges the received NSRP packets into H.245 messages for processing by the H.245 control layer module 22. Therefore, H.245 call control messages can be segmented for NSRP packetization. In general, the video codec 18, the audio codec 20, and the H.245 control level module 22 are within the adaptation level of the mobile terminal 10A, and the corresponding packets are sent to the MUX-DEMUX H.223 level module 24.

The MUX-DEMUX H.223 level module 24 multiplexes the packets received from the video codec 18, the audio codec 20 and the H.245 control level module 22 into the multiplexing protocol data units (MUX PDUs) and transfers the MUX PDUs to the modem 26 for modulation and transmission remote mobile terminal 10B through the interface 27 TX / RX. The TX / RX interface 27 includes a wireless transmitter and a wireless receiver configured for wireless communication in accordance with any of a variety of different communication techniques, such as code division multiple access (CDMA), wideband CDMA (WCDMA), multiple access time division multiplexing (TDMA) or frequency division multiple access (FDMA), for communication via a wireless communication channel.

The modem 26 can segment and encapsulate the MUX PDUs in ISDN packets, which are then transmitted via the TX / RX interface 27 as a sequence of radio control (RLC) PDUs. Each MUX PDU that has passed the 24 MUX / DEMUX H.223 module carries the information of the NSRP packet. When the call setup is complete, each MUX PDU will also include video and audio information. However, during call setup, typically there will be no video and audio information coming from the adaptation layer. Therefore, each MUX PDU during call setup will contain predominantly NSRP packet information. The MUX / DEMUX H.223 module 24 also demultiplexes packets received from the remote mobile terminal 10B for processing by the video codec 18, the audio codec 20, and the H.245 control layer module 22. Although, to illustrate, video call setup techniques will be described herein in the context of 3G-H.324M, H.245, and H.223, these techniques can be adapted to other accepted, emerging and future mobile video telephony standards and protocols.

If the underlying wireless video telephone network containing the mobile terminals 10A, 10B is error-prone, a significant number of NSRP packets will be discarded, resulting in call setup delays due to the “stop and wait” aspect of a typical NSRP implementation. In particular, a typical NSRP implementation typically requires that the transmitting mobile terminal 10A wait for an ACK packet from the remote mobile terminal 10B before transmitting the next NSRP packet. In addition, in a typical NSRP implementation, NSRP packets are retransmitted only after a timeout period has elapsed. However, in the example of FIG. 2, mobile terminal 10A retransmits NSRP packets containing H.245 messages when modem 26 has available bandwidth. Therefore, the mobile terminal 10A retransmits the NSRP packet to the remote mobile terminal 10B without waiting for the NSRP to time out.

In general, when the remote mobile terminal 10B receives one of the call setup packets from the mobile terminal 10A, the remote mobile terminal 10B transmits an NSRP ACK packet to notify the mobile terminal 10A that it has received the call setup packet. Thus, the mobile terminal 10A knows that the call setup packet that it transmitted is received by the remote mobile terminal 10B, and knows that it can continue the video call setup process by transmitting the next call setup packet. However, until an ACK packet has been received, the mobile terminal 10A continues the proactive retransmission process by retransmitting the NSRP packets when there is available unused space at the modem level. If the ACK packet is received, the mobile terminal 10A terminates the retransmission process and transmits NSRP packets containing the following call establishment message from the H.245 layer.

Although the retransmission of NSRP packets from the mobile terminal 10A to the remote terminal 10B has been described, it should be understood that the mobile terminal 10B also transmits NSRP packets to the mobile terminal 10A. In response to the received NSRP packets, the mobile terminal 10A also transmits NSRP ACK packets to the remote mobile terminal 10B. Therefore, a similar NSRP packet retransmission process can be applied to both the mobile terminal 10A and the mobile terminal 10B.

In addition, in some embodiments, it may be desirable in a similar manner to retransmit ACK packets from the corresponding mobile terminal 10A, 10B. However, ACK packetization in response to retransmitted NSRP packets can provide significant reductions in call setup delay. In particular, instead of retransmitting ACK packets for each NSRP packet, the likelihood of successfully transmitting an ACK packet can be increased simply by increasing the number of retransmitted NSRP messages for which ACK packets are to be generated and transmitted. Therefore, in many cases, it may be sufficient to retransmit NSRP packets without having to retransmit ACK packets.

In the examples of FIGS. 1 and 2, mobile terminals 10A and 10B may be wireless telephones or other wireless devices equipped with video displays and suitable encoders / decoders (codecs). The techniques described here can be implemented in a general purpose microprocessor, a digital signal processor (DSP), a specialized integrated circuit (ASIC), a user-programmable gate array (FPGA), or other equivalent logic devices in a mobile terminal. Therefore, various components, such as video codec 18, audio codec 20, H.245 control level module 22, MUX-DEMUX H.223 level module 24 and modem 26, can be implemented as permanent or programmable functionalities, executing in one or more logical devices. Various aspects of the techniques described herein may be implemented in hardware, software, firmware, or any combination thereof. When implemented in software, the techniques can be embodied in the form of instructions on a computer-readable storage medium such as random access memory (RAM), read-only memory (ROM), volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM) flash memory or the like

Further, according to FIG. 2, in a typical implementation, regardless of whether there is data to transmit from the H.223 layer or not, the modem 26 must periodically transmit ISDN packets to maintain channel fullness. If there is no NSRP information, audio or video information for transmission, the modem would normally fill ISDN packets or their unused portions with fill flags. However, in accordance with the present invention, unused portions of ISDN packets are used to proactively retransmit NSRP packets to a remote mobile terminal 10B so that the NSRP packet information replaces padding flags in ISDN packets. In particular, modem 26 is configured to locally store ISDN packets containing H.223 information in a buffer, and then transmit packets stored in the buffer instead of unused ISDN packets, which would normally include only fill flags.

3 is a flowchart illustrating a video call establishment process in accordance with the present invention. The video call establishment process may be implemented in the mobile terminal 10A, 10B, as shown in FIG. 1 and FIG. 2. Upon initiating a video call, the transmitting terminal 10A transmits (32) a call setup message to the remote mobile terminal 10B. Again, the call setup message may include an H.245 control message generated in the H.245 control unit 22. Ultimately, the H.245 control message is segmented into NSRP packets in the CCSRL-NSRP module, into MUX PDUs in the H.223 MUX-DEMUX layer 24 module, and into ISDN packets in the modem 26 for transmission through the TX / RX interface 27. When the NSRP Receive acknowledgment (ACK) is received (34) from the remote mobile terminal 10B, the transmitting mobile terminal 10A does not retransmit the call setup message. Instead, the transmitting mobile terminal 10A stops and waits for the next call setup message to be generated, for example, by the H.245 control layer module 22. NSRP ACK packets are processed at the upper levels of the H.324M protocol stack, for example, in CCSRL-NSRP module 28. Accordingly, the modem 26 stops retransmission in response to a stop command received from the H.324M protocol stack.

However, until the ACK packet is received (34), the transmitting mobile terminal 10A attempts to proactively retransmit the call setup message, which may entail the retransmission of one or more NSRP packets. If bandwidth (36) is available at the modem level, modem 26 retransmits (38) a call setup message. For example, if modem 26 has not received new NSRP packets, audio or video information from the H.223 level, the modem adds the previously transmitted NSRP packets to one or more retransmitted ISDN packets instead of simply placing the corresponding unused fill flags in ISDN packets. In particular, modem 26 can locally buffer and retrieve ISDN packets containing NSRP packet information for retransmission during unused periods. Thus, NSRP packets are retransmitted using the available bandwidth, which otherwise would have been wasted.

As will be described, previously transmitted ISDN packets can be stored in a buffer by modem 26 to support efficient retransmission of NSRP information. In particular, each ISDN packet can be stored in a buffer during transmission and then retrieved from the buffer for retransmission when there is unused bandwidth. Saving the ISDN packets in the buffer eliminates the need to re-generate each call setup message from the H.245 control layer module 22, as well as re-segmentation to create each NSRP packet in the CCSRL-NSRP module 28 and re-generate the MUX PDU at the H.223 level. Instead of re-generating this information and moving it to the modem level, the modem 26 simply stores the ISDN packets in a local buffer and retrieves them for retransmission, thereby reducing the overhead of retransmission.

4 is a block diagram illustrating the layout of video call setup packets in a transmitting mobile terminal 10A for transmission to a remote mobile terminal 10B. As shown in FIG. 4, during call setup, the adaptation layer only generates 40 NSRP packets. In particular, the H.245 control layer module 22 generates call setup messages that are segmented by the CCSRL-NSRP layer module 22 into NSRP packets, which are depicted as an NSRP packet 40. While a call is being established, video conferencing is not yet in progress. Therefore, the video codec 18 and the audio codec 20 do not form any video or audio information. Therefore, the MUX-DEMUX level (for example, H.223) receives from the adaptation level only 40 NSRP packet.

The MUX-DEMUX layer module 24 segments each NSRP packet 40 and distributes the segments into consecutive PDU 41A MUX, 41B units. Then, the modem 26 distributes each MUX PDU 41 according to the sequence of ISDN packets, and in turn, the sequence of RLC PDUs must go to the TX / RX interface 27 for transmission. In the example of FIG. 4, NSRP packets essentially form the entire payload of the first two ISDN packets 42A, 42B and part of the payload of the third ISDN packet 42C. The third ISDN packet 42C includes a first portion 44 containing NSRP packet information, and a second, unused portion 46 containing only padding bits (FILL).

If there is no additional information available from the adaptation layer, additional ISDN packets, such as 42D, 42E ISDN packets, which should be transmitted periodically by modem 26, would normally contain only fill flags (FILL) as a payload. However, in accordance with the present invention, ISDN packets containing fill flags can be replaced with ISDN packets stored in the buffer containing previously transmitted NSRP packet information, which enables efficient retransmission. In addition, FIG. 4 shows that ISDN packets 42 are further segmented into RLC PDUs 48A-48N for transmission via TX / RX interface 27.

5 is a flowchart illustrating in more detail a technique for retransmitting video call setup packets to reduce video call setup delays. In particular, FIG. 5 shows the storage in the buffer and retrieval of ISDN packets at the modem level in the mobile terminal 10A to maintain efficient retransmission of NSRP packets to the remote terminal 10B. The MUX-DEMUX level module 24 moves the MUX PDUs to the modem 26. The modem 26 forms an ISDN packet for transmission every twenty milliseconds (ms). The first two ISDN packets 42A, 42B mainly contain NSRP packet information, while the third ISDN packet contains NSRP packet information 44 and padding flags 46. Flush flags 46 are included in the third ISDN packet 42C because the remaining information of the NSRP packet from the MUX-DEMUX module 24 is not enough to completely fill the payload of the MUX PDU, resulting in unused bandwidth. Unused bandwidth appears during call setup due to the interval between consecutive NSRP packets and the absence of any video or audio information.

It is important that when each 42A-42C packet is transmitted, a copy of the corresponding ISDN packet is stored by the modem 26 in the local buffer 50 at the modem level. For example, ISDN packets 42A, 42B, and 42C are stored in Memory Buffer Cell 0, Memory Buffer Cell 1, and Memory Buffer Cell 2, respectively. Depending on the number of ISDN packets to be stored, more or fewer Buffer Memory Cells may be used. When the modem 26 does not have additional data to transmit, it is still necessary to transmit ISDN packets every 20 ms to maintain channel fullness. For example, modem 26 may need to send an ISDN packet with 160 bytes of data every 20 ms to interface 27. In the normal case, in the absence of NSRP data, video or audio data, the MUX-DEMUX module 24 does not provide any additional data to the modem 26 at the time when the next ISDN packet is planned. In this case, the modem 26 would transmit “unused” packets 42D, 42E or 42F filled with fill flags.

However, in accordance with the present invention, the modem 26 replaces unused packets 42D, 42E, 42F with buffer packets 42A, 42B, 42C stored in the buffer containing previously transmitted NSRP packet information. In particular, the modem 26 retrieves the stored packets 42A, 42B, 42C from the Memory Buffer Cells 0-2 in the buffer 50 and retransmits these ISDN packets instead of the 42D-42F ISDN packets. Local storage of packets 42A, 42B, 42C in buffer 50 eliminates the need to re-generate H.245 messages and NSRP packets at the upper levels of the H.324M protocol stack. Instead, modem 26 fills 160 unused bytes from buffer 50 with a saved ISDN packet containing NSRP packet information, rather than padding flags. The interface 27 then transmits the RLC PDUs containing the information of the NSRP control packet that was previously transmitted.

Thus, the H.245 call control messages carried by the NSRP packets in the stored packets 42A, 42B, 42C are retransmitted to the remote mobile terminal 10B. Accordingly, even if the core network is error prone and the previous transmission of the NSRP control packet has been lost, this NSRP control packet is proactively retransmitted without having to wait for the NSRP ACK packet or time out. Modem 26 may continue to retransmit packets 42A, 42B, 42C stored in the buffer instead of unused packets 42D, 42E, 42F until a stop command is received from the application layer. A stop command may be generated when the transmitting mobile terminal 10A receives the NSRP ACK packet from the remote mobile terminal 10A. Alternatively, a stop command may be generated when the NSRP timeout period has expired and a new NSRP packet is provided at the adaptation level for retransmission. As an additional alternative, modem 26 can be configured to make only a selected number of retransmission attempts.

When the remote mobile terminal 10B receives the call setup packet, either upon initial transmission or subsequent retransmission, it transmits an ACK packet back to the transmitting mobile terminal 10A. Modem 26 receives the ACK packet and moves it up the protocol stack to the application layer. The application layer recognizes this packet as an ACK packet and understands that the remote mobile terminal 10B has received a call setup packet transmitted by the mobile terminal 10A. In response, the application layer moves an out-of-band control message down the protocol stack to modem 26 with a stop command instructing the modem to stop retransmission of the NSRP packet information and clear the buffer 50. Once the call setup packet is received by the remote mobile terminal 10B, then there is no need to retransmit the call setup packet. Then, if necessary, the adaptation layer forms the next NSRP packet into the sequence of NSRP packets needed to establish the call.

6 is a flowchart illustrating in more detail the arrangement and retransmission of video call setup packets. As shown in FIG. 6, upon receiving (52) a MUX PDU containing information from module 24

MUX-DEMUX H.223, modem 26 segments (54) the MUX PDU and forms (56) an ISDN packet containing the MUX PDU segment. The modem 26 then stores (58) the ISDN packet in local buffer 50 and transmits (60) the ISDN packet to the remote mobile terminal 10B via the TX / RX interface 27. If there are (62) more ISDN packets to be transmitted, the modem 26 proceeds (64) to the next in order memory location in the buffer 50 and repeats steps (56) - (62) to form and transmit the next ISDN packet.

When the last ISDN packet for the MUX PDU has been processed (62), the modem 26 proceeds to determine (66) whether the NSRP ACK packet has been received from the remote mobile terminal 10B. If so, the modem 26 flushes the buffer 50 and returns to processing (52) the next MUX PDU, if it exists at all, from the adaptation level. It is noteworthy that the modem 26 cannot directly determine whether the NSRP ACK packet has been received. Rather, NSRP ACK packet processing is typically performed by an H.245 control module 22. Instead, an indication that the NSRP ACK packet has been received may be the result of an out-of-band stop command that has gone down from the adaptation level when re-arranging and inspecting packets received from the remote 10B mobile terminal.

If the ACK packet has not been received (66), modem 26 determines whether there is available bandwidth in the next ISDN packet, i.e. whether the next ISDN packet will be filled with populate flags or will contain new NSRP information from the pending MUX PDU. If the next ISDN packet has unused bandwidth, modem 26 retrieves (72) the ISDN packet stored in the first Memory Buffer Cell 0 and moves this ISDN packet to the physical layer for transmission (74). Thus, the stored ISDN packet and its contents are retransmitted to the remote mobile terminal 10B.

After transmitting (74) the saved ISDN packet, modem 26 proceeds to the next in order buffer memory cell in buffer 50 and again determines whether the NSRP ACK packet was received (66). If so, there is no need for further retransmission attempts. In this case, the modem 26 flushes the buffer 50 and returns to step (52). If the NSRP ACK packet was not received (66), for example, the stop command was not received from the adaptation level, modem 26 passes through steps (68) and (72) - (76). In particular, modem 26 replaces the next ISDN packet with the ISDN packet stored in the buffer from the next buffer cell in order to allow retransmission of the NSRP packet information. This process continues until the stop command is received from the adaptation layer, in which case the modem 26 processes the next MUX PDU and continues the call setup process.

During the call setup process, the mobile terminal 10A and the remote mobile terminal 10B mutually participate in the exchange of NSRP packets and ACK packets. Accordingly, for transmitting NSRP packets, the remote mobile terminal 10B may carry out a retransmission process similar to that of the transmitting mobile terminal 10A. Also, in some embodiments of the present invention, mobile terminals 10A, 10B may perform a similar process for retransmission of NSRP ACK packets. In this case, the mobile terminals 10A, 10B may use an intelligent buffering algorithm. In particular, instead of retransmitting only the last packet sent by modem 26, this modem can use information received from the adaptation layer in order to intelligently retransmit packets. For example, instead of simply retransmitting new data received from the adaptation layer, modem 26 may be configured to retransmit NSRP packets and NSRP ACK packets in turn. Repeating both NSRP ACK packets and NSRP packets can provide an additional reduction in video call setup time.

Furthermore, in some embodiments of the present invention, the mobile terminals 10A, 10B may be configured to detect whether the opposing mobile terminal enables the same NSRP proactive retransmission process. For example, the mobile terminal 10B can detect whether the mobile terminal 10A enables the proactive retransmission process to be performed by detecting whether the mobile terminal 10A immediately retransmits the transmission of the last transmitted NSRP packet. Detection of the use of the retransmission technique by the remote mobile terminal 10B can be performed at the adaptation level, and then signaled to the modem 26 via an out-of-band command. If both mobile terminals use this technique, then it may be redundant to retransmit NSRP ACK packets, as described above.

Instead, in this situation, the mobile terminals can be configured to simply retransmit NSRP packets that carry H.245 call control messages. Since in this case both mobile terminals 10A, 10B will actively repeat NSRP messages, ACK packets will be generated automatically every time an NSRP packet is received. Therefore, each additionally retransmitted ACK packet may have little added value in terms of reducing call setup delays. If the mobile terminal 10A determines that the remote mobile terminal 10B does not use the NSRP proactive retransmission technique, it is desirable for the transmitting mobile terminal 10A to retransmit the NSRP ACK packets in addition to the call setup NSRP packets.

By retransmitting ISDN packets containing NSRP packet information, mobile terminal 10A can significantly reduce call setup delay. As mentioned above, according to some protocols, MUX PDUs must be transmitted every 20 ms. The techniques described here allow you to retransmit an ISDN packet stored in a buffer containing NSRP packet information from the modem level with a frequency of every 20 ms instead of first re-forming it at the upper levels of the protocol stack, and then re-segmenting and re-multiplexing at the MUX- DEMUX.

Table 1 shows an example of how the proactive retransmission process described here can occur at the modem level. Table 1 illustrates the situation in which the modem intelligently retransmits ISDN packets that contain NSRP packet information, instead of simply retransmitting the last transmitted ISDN packet. In particular, the modem 26 monitors and stores ISDN packets containing NSRP packet information, and then sequentially retrieves them from the local buffer 50 for retransmission when unused bandwidth is available, that is, when the transmitted ISDN packet would otherwise be full.

Table 1 Time
(ms) Data received from H.223 level
(bytes) Modem Actions 0 160 Transmits 160 bytes; saves these 160 bytes in buffer memory cell 0 twenty 160 Transmits 160 bytes; saves these 160 bytes in buffer memory cell 1 40 one hundred Adds padding to the other 60 bytes; transfers 160 bytes; saves these 160 bytes in buffer memory cell 2 60 0 Transmits data from the backup buffer, starting from buffer cell 0 of the memory 80 0 Transmits data from memory buffer cell 1 one hundred 0 Transmits data from memory buffer cell 2 120 0 Transmits data from memory buffer cell 0 140 160 Transmits 160 bytes; clears buffers [0 ... n]; saves these 160 bytes in buffer memory cell 0

Table 1 illustrates the data received by the modem 26 from the MUX-DEMUX H.223 layer, and the corresponding action taken by the modem to retransmit the 160-byte ISDN packet every 20 ms. In Table 1, the amount of data received from the MUX-DEMUX H.223 level is expressed in bytes. As illustrated in Table 1, at 0 ms, the modem 26 receives 160 bytes of NSRP packet information in the form of an MUX PDU from the H.223 level. In response, modem 26 packs these 160 bytes of NSRP packet information into an ISDN packet and transmits this ISDN packet. In addition, modem 26 stores this 160-byte packet in buffer memory cell 0.

At a time of 20 ms, modem 26 receives another 160 bytes of NSRP packet information in the form of MUX PDUs from the H.223 level, retransmits a 160-byte ISDN packet containing the NSRP packet information, and stores this packet in buffer memory cell 1. At 40 ms, modem 26 receives only 100 bytes of NSRP packet information in the form of MUX PDUs from the H.223 layer. In this case, the modem 26 packs the ISDN packet along with 100 bytes of NSRP and 60 bytes of fill flags, transmits the resulting ISDN packet, and stores this packet in memory buffer cell 2. At 60 ms, modem 26 does not accept bytes from the H.223 level, which can be explained by the gap between packets at the adaptation level. In the normal case, modem 26 would completely populate the next ISDN packet with padding flags. However, in accordance with the present invention, the modem 26 retrieves the previously transmitted ISDN packet from the memory buffer cell 0 and retransmits the extracted ISDN packet.

In the same way, at times of 80 ms and 100 ms, when additional data from the H.223 level is not received, the modem 26 extracts the following ISDN packets from the memory buffer cells 1 and 2, respectively, and retransmits these extracted ISDN packets. At a time of 120 ms, when additional data from the H.223 level is not received, the modem 26 starts again from the buffer memory cell 0 and retrieves and retransmits the ISDN packet stored in this memory cell. However, at 140 ms, modem 26 receives another 160 bytes of NSRP packet information in the form of a MUX PDU. In this case, the modem 26 may also receive a stop command from the application layer, for example, in response to the NSRP ACK timeout or the ACK command being received, each of which is processed at the H.245 level, and not in the modem 26.

The newly received information of the NSRP packet may be the result of the re-formation at the H.245 level of the previously transmitted information of the NSRP packet after the NSRP ACK timeout. Alternatively, the newly received information of the NSRP packet may be the result of the formation of new NSRP data containing subsequent H.245 messages during the call setup process after receiving the NSRP ACK from the remote mobile terminal 10B. In any case, when new NSRP packet data is received from the H.223 layer, modem 26 transmits this NSRP packet data from the received MUX PDU in the 160-byte ISDN packet and clears the buffer in order to provide space to store the new NSRP packet.

The proactive retransmission process can continue until the establishment of the video call is completed. It is important to note that this process of retransmission of NSRP packets and, optionally, NSRP ACK packets will only be used during the call setup process, as this technique may not work when audio or video is transmitted from the adaptation layer. Modem 26 may receive a command from the upper levels to clear its buffers after the video protocols have been configured and the transmission of useful audio or video information has begun.

The techniques described here can be highly effective in reducing the delay in establishing a video call compared to traditional methods that rely on the standard NSRP process. For example, in a standard NSRP implementation, regardless of the actual NSRP timeout, if some NSRP message is dropped, a gap will occur that contributes to the call setup delay. If the core network is error prone, the chance of delays may become greater due to the increasing number of discarded NSRP packets. One method to eliminate this is to reduce the NSRP timeout to minimize the pause caused by a dropped NSRP packet. However, this solution may lead to performance degradation due to the amount of overhead required at the H.324 level, such as multiplexing, additional coding, and the complexity of the NSRP retransmission processing at the H.324 level.

Another drawback of this approach is the amount of overhead required to retransmit the NSRP packet after the timeout. In particular, when the NSRP timer expires and the H.324 stack starts retransmission of the NSRP packet, said NSRP packet, which must be transmitted back down to the lower modem level for retransmission, must be re-formed and multiplexed again. That is, the NSRP packet, which must be converted to H.223 MUX PDUs, which are then transmitted to the modem layer to wait for the next transmission, passes through the multiplexing layer (H.223).

In general, proactive retransmission techniques described herein include retransmission of NSRP packets by the mobile terminal whenever there is nothing to transmit at the lower modem level. Instead of waiting for the NSRP acknowledgment packet (ACK) from the remote mobile terminal or timeout, the mobile terminal continues to retransmit the NSRP packet when there is space available at the modem level, and it is time to transmit via the modem. This approach mitigates the drawbacks of the NSRP-compliant stop and wait entity by reducing the retransmission time of the most recent packet.

Therefore, the techniques disclosed in this description adjust the operation mode of the mobile terminal. Instead of transmitting fill flags, when there is no call setup data available for transmission from the upper level, the mobile terminal uses this space instead to transmit the previous useful information, that is, the previously transmitted NSRP packet, directly via the modem. Thus, the mobile terminal does not need to wait for the NSRP to time out. In contrast, the mobile terminal retransmits the previously transmitted NSRP packet, potentially repeatedly, until the NSRP ACK packet is received. The transmitted NSRP packet is stored in the buffer at the modem level and can be extracted from this buffer for retransmission, rather than being recreated at the upper level of the H.324M, thereby reducing the complexity of operating with the H.324M stack.

Various embodiments of the present invention are described. These and other embodiments of the present invention are within the scope of the following claims.

Claims (37)

1. A method for establishing a video call in a mobile video telephony network, comprising the steps of:
transmitting a video call establishment packet from the first mobile terminal to the second mobile terminal; and
retransmit this video call setup packet before the expiration of the time-out period for receiving the acknowledgment packet from the second mobile terminal. 2. The method of claim 1, wherein the retransmission includes retrieving a video call setup packet from a buffer associated with the modem layer in the first mobile terminal, and retrieving the extracted video call setup packet. 3. The method of claim 1, further comprising storing the video call setup packet in a buffer associated with the modem layer in the first mobile terminal, the retransmission includes the step of retrieving the video call setup packet from this buffer and transmitting the extracted video call establishment packet. 4. The method of claim 3, wherein storing the video call setup packet includes storing a plurality of video call setup packets transmitted by the first mobile terminal. 5. The method according to claim 4, in which the video call establishment packets include Integrated Services Digital Network (ISDN) packets containing simple numbered retransmission protocol (NSRP) packet information, wherein the NSRP packet information contains standard H call control messages. 245 from the International Telecommunication Union (ITU). 6. The method according to claim 4, in which the retransmission includes steps in which
retrieving a first call setup packet from a buffer;
transmitting a first call setup packet;
extracting a second call setup packet from the buffer; and
transmitting a second call setup packet. 7. The method of claim 1, wherein the retransmission includes retransmitting the video call establishment packet when unused bandwidth is available in the packet to be transmitted by the first mobile terminal. 8. The method of claim 1, wherein the retransmission includes retransmitting the video call establishment packet when the modem of the mobile terminal detects unused bandwidth in the packet generated by this modem. 9. The method according to claim 1, additionally containing a stage in which
repeating the retransmission of the call setup packet; and stopping the repeated retransmission of the call setup packet upon receiving the acknowledgment packet from the second mobile terminal. 10. The method according to claim 1, additionally containing a stage on which
repeat the retransmission of the call setup packet and stop retransmitting the call setup packet when a video call is started or a stop command is received. 11. The method according to claim 1, additionally containing stages, in which
transmitting acknowledgment packets to the second mobile terminal in response to call setup packets received from the second mobile terminal;
determining whether the second mobile terminal retransmits call setup packets;
retransmit at least some of said acknowledgment packets to the second mobile terminal. 12. The method of claim 11, wherein the retransmission of at least some of said acknowledgment packets includes retransmitting the acknowledgment packets if the second mobile terminal does not retransmit the call setup packets. 13. The method according to claim 1, in which the call setup packets contain call setup information of the H.245 standard from the ITU for organizing video conferencing according to the H.324M standard from the ITU. 14. A mobile wireless communication terminal, comprising
wireless transmitter;
wireless receiver; and
a modem that generates a video call setup packet for transmission by the transmitter to the second mobile terminal and provides this video call setup packet for retransmission by the transmitter before the expiration of a waiting period of the reception of the acknowledgment packet from the second mobile terminal. 15. The mobile terminal of claim 14, further comprising a buffer for storing the video call setup packet, the modem retrieving the video call setup packet from the buffer and providing the extracted video call setup packet for retransmission by the transmitter to the second mobile terminal. 16. The mobile terminal of claim 14, further comprising a buffer for storing the video call setup packet, the modem storing the video call setup packet in the buffer, retrieving the video call setup packet from the buffer, and providing the extracted video call setup packet for retransmission by the transmitter to the second mobile terminal. 17. The mobile terminal of claim 16, wherein the modem stores a plurality of video call setup packets in a buffer. 18. The mobile terminal of claim 17, wherein the video call establishment packets include Integrated Services Digital Network (ISDN) packets containing simple numbered retransmission protocol (NSRP) packet information, and the NSRP packet information comprises standard call control messages H.245 from the International Telecommunication Union (ITU). 19. The mobile terminal of claim 17, wherein the modem is configured to retrieve a first video call setup packet from a buffer; provide a first video call setup packet for retransmission by a transmitter; retrieve a second video call setup packet from the buffer; and provide a second video call setup packet for retransmission by the transmitter. 20. The mobile terminal of claim 14, wherein the modem is configured to provide a video call setup packet for retransmission by the transmitter when unused bandwidth is available in the packet to be transmitted by the first mobile terminal. 21. The mobile terminal of claim 14, wherein the modem is configured to repeat the provision of the video call setup packet for retransmission and complete the retransmission of this call setup packet upon receipt of the acknowledgment packet from the second mobile terminal. 22. The mobile terminal of claim 14, wherein the modem is configured to repeat the provision of the video call setup packet for retransmission, the modem completing the retransmission of the call setup packet when the video call is started or a stop command is received. 23. The mobile terminal of claim 14, wherein the modem is configured to provide acknowledgment packets for transmission to the second mobile terminal in response to receiving a call setup packet from the second mobile terminal. 24. The mobile terminal of claim 23, wherein the modem is configured to retransmit at least some of said acknowledgment packets if the second mobile terminal does not retransmit call setup packets. 25. The mobile terminal of claim 14, wherein the call setup packets contain H.245 standard call setup information from the ITU for establishing video conferencing according to the H.324M standard from ITU. 26. A computer-readable storage medium containing instructions for causing a processor to transmit a video call setup packet from a first mobile terminal to a second mobile terminal; retransmit this video call establishment packet before the expiration of the time-out period for receiving the acknowledgment packet from the second mobile terminal. 27. The computer-readable storage medium of claim 26, wherein said instructions instruct the processor to store the video call setup packet in a buffer associated with the modem layer in the first mobile terminal, retrieve the video call setup packet from the buffer, and retransmit the extracted video call setup packet. 28. The computer-readable storage medium of claim 27, wherein said instructions instruct the processor to store in the buffer a plurality of video call setup packets transmitted by the first mobile terminal. 29. The computer-readable storage medium of claim 28, wherein the video call establishment packets include Integrated Services Digital Network (ISDN) packets containing simple numbered retransmission protocol (NSRP) packet information, and the NSRP packet information comprises call control messages H.245 standard from the International Telecommunication Union (ITU). 30. The computer readable storage medium of claim 28, wherein said instructions instruct the processor
retrieve the first call setup packet from the buffer;
transmit the first call setup packet;
retrieve a second call setup packet from the buffer; and
transmit a second call setup packet. 31. The computer readable storage medium of claim 26, wherein said instructions instruct the processor to retransmit the video call setup packet when the modem of the mobile terminal detects unused bandwidth in the packet generated by this modem. 32. The computer-readable storage medium of claim 26, wherein the call setup packets comprise H.245 standard call setup information from the ITU for establishing video conferencing according to the H.324M standard from ITU. 33. A mobile wireless communication terminal, comprising
wireless transmitter;
wireless receiver;
video codec for generating video information;
audio codec for generating audio information;
H.245 standard control module from the International Telecommunication Union (ITU) for generating video call setup packages;
a simple numbered retransmission protocol (NSRP) protocol module for generating one or more NSRP packets based on video call establishment packets;
an ITU-level H.223 module for multiplexing video, audio and NSRP packets to create one or more multiplexing protocol data units (PDUs MUX);
a modem for generating one or more Integrated Services Digital Network (ISDN) packets based on MUX PDUs, providing ISDN packets to a transmitter for transmission to a second mobile terminal, and providing at least some of these ISDN packets for retransmission by a transmitter before a period has elapsed the reception timeout by the wireless receiver of the acknowledgment packet from the second mobile terminal. 34. The mobile terminal according to claim 33, further comprising a buffer, wherein the modem stores at least some of the mentioned ISDN packets in this buffer, retrieves the stored ISDN packets from the buffer, and provides the extracted ISDN packets for retransmission by the transmitter to the second mobile terminal. 35. The mobile terminal of claim 34, wherein the modem is configured to provide an extracted video call setup packet for retransmission by the transmitter when unused bandwidth is available in the packet to be transmitted by the first mobile terminal. 36. The mobile terminal according to claim 33, wherein the modem is configured to repeat the provision of the video call setup packet for retransmission and complete the retransmission of this video call setup packet upon receiving the acknowledgment packet from the second mobile terminal. 37. The mobile terminal according to claim 33, wherein the modem is configured to repeat the provision of the video call setup packet for retransmission, the modem completing the retransmission of this call setup packet when the video is transmitted or the stop command is received.

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