JP2008113157A - Method of compressing data and data transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of compressing data capable of obtaining an optimum compression rate in ROHC compression by continuously changing a value of an RTP header time stamp in an RTP/UDP/IP packet subjected to ROHC compression, and to provide a data transmitter. <P>SOLUTION: There are provided: a client PC 13 acquiring data to be compressed; an ROHC compression section 20 for calculating an addition value added to a time stamp value included in the header information of data corresponding to acquired data; and an RTP time stamp processing section 31 that calculates a value obtained by subtracting the addition value from the time stamp value in acquired current data, determines whether the time stamp value in the current data is corrected based on a calculated value, and corrects a value where the addition value is added to the time stamp value of the last acquisition data as the time stamp value in the current data when the calculated value is the same as the time stamp value of the last acquisition data. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a data compression method and a data transmission device, and more particularly, to a data compression method and a data transmission device based on the Internet Protocol (IP).

Conventionally, various communication techniques for transmitting data from the transmitter side to the receiver side have been devised. Recently, however, the IP-based method is preferred for reasons such as packet orientation and the degree of freedom of the transmission destination. Yes.
Also, when the purpose of transmission is media packet transmission such as voice and moving images, the user datagram protocol (UDP) is used with the IP packet as the lower layer, and the real-time transport protocol is used as the communication method of the higher layer. (Real time Transport Protocol: RTP) is preferably used.

Media packet transmission using RTP / UDP / IP has become the de facto standard, and although there are many cases where this method is often selected to ensure many operational commonities, the overhead is relatively low. It gets bigger.
As a method for reducing the overhead of RTP / UDP / IP and transmitting media packets on a transmission path having a narrower band, for example, “header compression method and apparatus and program” (see Patent Document 1), etc. Several packet header compression methods have been devised, among them robust header compression (ROHC).

  ROHC pays attention to the consistency of RTP / UDP / IP headers between consecutive packets, and information that can be inferred without repeatedly transmitting information that can be inferred by information that has already been transmitted, information that can be inferred, and information that is obtained by calculation The packet header information to be transmitted is compressed by transmitting information for inferring and information that cannot be inferred and changes each time. Here, one of the information that can be inferred is a time stamp in the UDP header in the profile 1 (RTP profile) of ROHC (RFC3095).

  Recently, a wireless device for making a part of an IP route wireless has become a common technology, and one of them is PHS (Personal Handyphone System). In this PHS, a client PC (Client Personal Computer) looks like a modem, and an OS (Operating System) such as Windows (a registered trademark of WINDOWS (registered trademark) or Microsoft) operating on the client PC is connected to the Internet. Intermediary.

  In general, a general-purpose OS such as Windows can execute a VoIP (Voice over Internet Protocol) application. The VoIP application can perform a VoIP call with a SIP (Session Initiation Protocol) telephone on the Internet using, for example, G729A (8 Kbps) as a codec and RTP / UDP / IP.

In general, in a VoIP call using RTP, the RTP time stamp represents the time when the oldest data included in the packet occurs. The frequency of the clock is defined for each payload type (Payload Type: PT), and is a sampling frequency in the case of a voice codec. For example, when an audio codec of 8 kHz sampling is transmitted with a packet length of 20 msec, one packet includes 160 samples of audio data, and the time stamp increases by 160 for each packet.
JP 2002-204260 A

However, in conventional VoIP communication using RTP, the RTP time stamp addition amount is generally added with an equal difference as described above, but there is an application in which the time stamp fluctuates in rare cases. To do.
When an application in which the time stamp fluctuates is used in the above-described packet header compression method, the RTP time stamp value cannot be obtained by calculation. Therefore, the compression device transmits a compressed packet with the RTP time stamp information added thereto. . Taking ROHC (RFC3095) as an example, the information given to the RTP time stamp is a message such as IR or UOR-TS, which is a packet that is on average 5 to 6 bytes larger in size than a normal compressed packet. .

When G729A (8 Kbps) codec is used and 2 codec payloads are loaded on 1 IP packet, RTP packets are distributed every 20 msec. This corresponds to an increase of .4 Kbps and an overhead increase of about 1/4.
In the transmission path of IP packets using radio, there may be a case where the bandwidth can be secured only about 9.6 Kbps. However, the above increase in overhead cannot be ignored, and it is desired to delete this overhead.
An object of the present invention is to provide a data compression method capable of obtaining an optimal compression rate in ROHC compression by continuously changing the value of the RTP header time stamp of an RTP / UDP / IP packet intended for ROHC compression, and A data transmission apparatus is provided.

  In order to achieve the above object, a data compression method according to the present invention includes a data acquisition method for compressing data to be transmitted from a transmission device to a reception device, wherein the transmission device acquires data to be compressed, and A time stamp addition value calculating step for calculating an addition value to be added to the time stamp value included in the header information of the data according to the data acquired in the data acquisition step; and the current data acquired in the data acquisition step Calculating a value obtained by subtracting the added value from the time stamp value in the step, and, based on the calculated value, determining whether or not to correct the time stamp value in the current data; and As a result of the determination, the value calculated in the time stamp value correction determination step is the data acquisition step. Is the same as the time stamp value of the data acquired last time, the value obtained by adding the added value to the time stamp value of the data previously acquired in the data acquisition step is the time stamp value in the current data. And a time stamp value correcting step for correcting as follows.

According to the present invention, in the time stamp addition value calculation step, an addition value to be added to the time stamp value included in the header information of the data is calculated according to the transmission amount of the data acquired in the data acquisition step. preferable.
Further, in the time stamp addition value calculating step, the present invention provides that when the transmission amount of data acquired in the data acquisition step exceeds a reference transmission amount based on an allowable transmission amount in the current communication band, It is preferable to calculate an addition value to be added to the time stamp value included in the header information.
According to the present invention, in the time stamp addition value calculating step, the data transmission amount after compressing the data acquired in the data acquisition step exceeds a reference transmission amount based on an allowable transmission amount in the current communication band. In this case, it is preferable to calculate an addition value to be added to the time stamp value included in the header information of the data.

  The data transmission device according to the present invention includes a data acquisition unit that acquires data to be compressed in the data transmission device that compresses and transmits data to be transmitted to the reception device, and the data acquired by the data acquisition unit. Accordingly, an addition value calculation means for calculating an addition value to be added to the time stamp value included in the header information of the data, and a value obtained by subtracting the addition value from the time stamp value in the current data acquired by the data acquisition means. A determination unit that determines whether or not to correct a time stamp value in the current data based on the calculated value; and a value calculated by the determination unit as a result of the determination is the data acquisition unit If the time stamp value is the same as the time stamp value of the data acquired last time, the time stamp of the data last acquired by the data acquisition means Wherein a value obtained by adding the addition value, is characterized by having a timestamp value correction means for correcting a time stamp value in the current data.

  According to the present invention, by continuously changing the value of the RTP header time stamp of the RTP / UDP / IP packet intended for ROHC compression, an optimal compression ratio can be obtained in ROHC compression.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory diagram showing a schematic configuration of a wireless communication system using a wireless terminal device according to an embodiment of the present invention. As shown in FIG. 1, a wireless communication system 11 using a wireless terminal device (data transmitting device) 10 includes a wireless base station 12 connected to the wireless terminal device 10 by radio and a client PC 13 connected to the wireless terminal device 10. Voice telephone 14 connected to client PC 13, SIP server 15 connected to radio base station 12 via the Internet, opposing SIP telephone 16, and PDSN (Packet Data Serving Node) 17 connected to radio base station 12. have.

The voice communication device 14 is a telephone for VoIP calls that is commercially available nowadays, and includes a speaker for reception, a microphone for transmission, a keypad for various operations, a USB interface for connection with the client PC 13, and the like. I have.
The client PC 13 functions as a PPPoE client (Point-to-Point Protocol over Ethernet Client) and is connected to the wireless terminal device 10 via Ethernet (registered trademark) (Ethernet (registered trademark)).

  The wireless terminal device 10 has a PPPoE server function and accepts a connection request from PPPoE. That is, the wireless terminal device 10 is connected to the wireless base station 12 through a wireless link, and transmits the PPP packet from the client PC 13 to the PDSN 17. The PDSN 17 functions as a PPP server and a DHCP (Dynamic Host Configuration Protocol) server, accepts a PPP connection request from the client PC 13, and passes a global IP address to the client PC 13. The client PC 13 connects to the Internet using a global IP address.

  A VoIP application corresponding to SIP is installed in the client PC 13 and communicates with the SIP server 15 and the opposite SIP telephone 16 via the SIP. When there is a call connection request from the client PC 13, the speaker of the voice communication device 14 connected to the client PC 13 by USB I / F (Universal Serial Bus interface) after being connected to the opposite SIP telephone 16 by guidance of the SIP server 15. The voice call with the opposite SIP telephone 16 is realized using the microphone. As the voice codec, G729A (8 Kbps) is used.

  FIG. 2 is an explanatory diagram showing an example of a protocol stack transition process during a VoIP call using the wireless communication system of FIG. As shown in FIG. 2, when performing a VoIP call using the wireless communication system 11, the client PC 13 converts voice data obtained from the microphone into digital data using the G729 codec, and packs it into RTP / UDP / IP packets. To do. The PPPoE client of the client PC 13 encapsulates the RTP / UDP / IP packet into a PPPoE / IP packet and transmits it to the wireless terminal device 10 using Ethernet as a link channel.

  After encapsulating the PPPoE packet, the wireless terminal device 10 performs ROHC compression on each RTP / UDP / IP header and transmits the header to the wireless base station 12 using a wireless protocol. The radio base station 12 constructs an A10 / GRE (General Routing Encapsulation) packet from the data received from the radio terminal device 10. At this time, the ROHC packet that is ROHC compressed is expanded into an RTP / UDP / IP packet. The A10 / GRE packet is transmitted to the PDSN 17 using Ethernet as a link channel.

FIG. 3 is a block diagram showing an internal structure of the wireless terminal device of FIG. As illustrated in FIG. 3, the wireless terminal device 10 includes a wireless communication unit 18, a transmission buffer 19, a ROHC compression unit 20, a transmission channel context holding unit 21, a reception packet buffer 22, a PPP determination unit 23, a ROHC expansion unit 24, a reception A channel context holding unit 25, a PPP packet construction unit 26, a packet filter 27, a PPP packet extraction processing unit 28, a PPPoE packet construction unit 29, a PC I / F unit 30, and an RTP time stamp processing unit 31 are provided.
The RTP time stamp processing unit 31 includes an RTP time stamp correction unit 32, an RTP time stamp monitoring unit 33, and a changeover switch 34.

  The PC I / F unit 30 has a function of receiving an Ethernet packet received from the Ethernet. Since the Ethernet packet received from the PC I / F unit 30 is a PPPoE packet, it is encapsulated by the PPP packet extraction processing unit 28 into a PPP packet. The client PC 13 uses the protocol type of the PPPoE packet as an IP packet. The packet filter 27 determines whether or not the packet needs ROHC compression by referring to the header information of the PPP packet. In general, it is possible to determine whether or not the packet is for compression by referring to the protocol field of the IP header, the payload type of the RTP packet, and the like.

  When the packet filter 27 determines that the PPP packet is the ROHC compression target packet, the packet filter 27 rewrites the protocol type of the PPP packet to the ROHC protocol, and the ROHC compression unit 20 performs compression. If the packet filter 27 determines that the PPP packet is not a ROHC compression target packet, the packet protocol 27 does not rewrite the PPP protocol type as IP, and does not allow the ROHC compression unit 20 to pass through (uncompressed). In any case, the PPP packet is stored in the transmission buffer 19 and sequentially transmitted to the radio base station 12.

  Next, the RTP time stamp processing unit 31 will be described. Regarding PPP packet processing, the packet filter 27 refers to the contents of the PPP packet to determine whether or not the packet requires ROHC compression. If ROHC compression is necessary, the protocol type of PPP is rewritten to the ROHC protocol. Up to this point, it is the same as the case where the RTP time stamp processing unit 31 is not provided. However, the number unit managed for each context ID by the RTP time stamp processing unit 31, that is, the VoIP with the same IP, UDP port, etc. For each session, the RTP time stamp monitoring unit 33 monitors the time stamp of the RTP header. If the time stamp is not appropriate, the RTP time stamp correcting unit 32 corrects the time stamp.

By performing such control, the time stamp of the RTP header can be corrected to a value appropriate for ROHC compression according to the setting.
Here, specific processing for correcting the time stamp of the RTP header by the RTP time stamp processing unit 31 will be described.
First, the time stamp addition value of the RTP packet is calculated.

  FIG. 4 is an explanatory diagram showing the classification of each information element of the RTP packet in a table. FIG. 5 is an explanatory diagram showing the classification (extract) of the RTP packet PT in a table. As shown in FIGS. 4 and 5, the RTP packet has a field (PT) describing a codec type, and a sampling frequency (KHz) for 1 second can be extracted from this value. In general, in most audio codecs, the sampling frequency is 8 KHz (8000 Hz). Further, from the RTP payload size, the RTP packet transmission interval and the total number of RTP packets transmitted per second can be calculated. With the above two parameters, the added value of the RTP time stamp can be calculated as follows.

G. In the case of a VoIP application that sends 729 (8 KHz) RTP packets at 20 ms intervals,
(1) Calculate the number of RTP packets transmitted per second.
G. Since the throughput of 729 is 8 Kbps (1000 bytes per second), the number of RTP packets transmitted per second can be calculated by dividing the payload size of the RTP packet from this value.
(2) Obtain the RTP time stamp addition value.
G. By dividing the number of RTP packets to be transmitted per second obtained in (1) from the sampling frequency of 729, the target RTP timestamp addition value can be obtained.

Next, the RTP time stamp is checked and corrected in the ROHC compression unit.
FIG. 6 is a flowchart showing a flow of transmission processing by the wireless terminal device according to the present invention. Here, TS is an abbreviation for time stamp. As shown in FIG. 6, when the ROHC compression unit 20 starts processing, it calculates the added value of the TS of the RTP packet (step S101). After the calculation, the RTP TS to be compressed is acquired (step S102). Thereafter, it is determined whether or not the remainder obtained by dividing TS by the added value is 0 (TS% added value = 0?) (Step S103). If the result of determination is 0 (yes), TS is converted to TS of the RTP packet. (Step S104).

On the other hand, if the result of determination in step S103 is not 0 (no), TS is obtained by subtracting the TS% addition value from TS (step S105), and whether TS is TS-SV (TS = TS-). SV?) Is determined (step S106). If the TS is TS-SV (yes) as a result of the determination, the TS is obtained by adding the added value to the TS (step S107). If the TS is not TS-SV (no), the TS remains as it is in the RTP packet. TS (step S104).
Thereafter, the TS is TS-SV, that is, the latest RTP TS transmitted to the ROHC compression unit 20 (step S108), and the process returns to step S102. Thereafter, a loop process that repeats the process from step S102 to step S110 is performed.

  As described above, the data compression method performed by the wireless terminal device 10 is a data compression method for compressing data to be transmitted from the transmission device to the reception device. The data acquisition step in which the transmission device acquires data to be compressed; In accordance with the data acquired in the acquisition step, a time stamp addition value calculation step for calculating an addition value to be added to the time stamp value included in the header information of the data, and a time stamp value in the current data acquired in the data acquisition step A value obtained by subtracting the added value from the time stamp, and based on the calculated value, a time stamp value correction determining step for determining whether to correct the time stamp value in the current data; The value calculated in the correction judgment step is the data type previously acquired in the data acquisition step. If it is the same as the stamp value, a time stamp value correcting step for correcting the value obtained by adding the added value to the time stamp value of the data previously acquired in the data acquiring step as the time stamp value in the current data, and Including.

  That is, when data compression processing by the wireless terminal device 10 is performed, first, the RTP time stamp in the ROHC compression unit 20 is inspected. The RTP time stamp monitoring unit 33 divides the time stamp value of the received RTP packet by the time stamp addition value obtained by the above-described method, and checks whether there is a remainder. Next, as a result of the RTP time stamp check, the RTP time stamp correction unit 32 performs time stamp correction processing on the corresponding RTP packet. In other words, when the obtained value is the same as the previously received RTP by subtracting the remainder obtained by the remainder from the time stamp addition value from the time stamp value of the received RTP packet, the time stamp is added to the obtained value. Add a value.

  As described above, the wireless terminal device 10 that is a data transmission device includes a data acquisition unit (client PC 13) that acquires data for compression in the data transmission device that compresses and transmits data to be transmitted to the reception device, and data In accordance with the data acquired by the acquisition unit, an addition value calculation unit (ROHC compression unit 20) that calculates an addition value to be added to the time stamp value included in the header information of the data, and the current data acquired by the data acquisition unit A determination unit (RTP time stamp processing unit 31) for calculating a value obtained by subtracting the addition value from the time stamp value and determining whether or not to correct the time stamp value in the current data based on the calculated value; As a result of the determination, the value calculated by the determination means is the same as the time stamp value of the data previously acquired by the data acquisition means. In this case, a time stamp value correcting unit (RTP time stamp processing unit 31) that corrects, as a time stamp value in the current data, a value obtained by adding the added value to the time stamp value of the data previously acquired by the data acquiring unit; Have

Therefore, in the wireless terminal device 10 that wirelessly transmits the transmission path of the IP packet, the value of the RTP header time stamp of the RTP / UDP / IP packet intended for ROHC compression is continuously changed. Compression rate can be obtained.
Although the present invention has been described with reference to the above-described embodiment, it is not limited to this embodiment. Therefore, what is implemented as a change aspect without deviating from the meaning of the present invention is also included.

It is explanatory drawing which shows schematic structure of the radio | wireless communications system using the radio | wireless terminal apparatus which concerns on one embodiment of this invention. It is explanatory drawing which showed the example of the protocol stack transition process at the time of the VoIP call using the radio | wireless communications system of FIG. 1 with the table | surface. It is a block diagram which shows the internal structure of the radio | wireless terminal apparatus of FIG. It is explanatory drawing which shows the classification | category of each information element of a RTP packet with a table | surface. It is explanatory drawing which shows the classification | category (extract) of RTP packet PT with a table | surface. It is a flowchart which shows the flow of the transmission process by the radio | wireless terminal apparatus which concerns on this invention.

Explanation of symbols

10 wireless terminal device 11 wireless communication system 12 wireless base station 13 client PC
14 Voice Communication Device 15 SIP Server 16 Opposite SIP Phone 17 PDSN
DESCRIPTION OF SYMBOLS 18 Wireless communication part 19 Transmission buffer 20 ROHC compression part 21 Transmission channel context holding part 22 Reception packet buffer 23 PPP determination part 24 ROHC expansion part 25 Reception channel context holding part 26 PPP packet construction part 27 Packet filter 28 PPP packet extraction process part 29 PPPoE packet construction unit 30 PC I / F unit 31 RTP time stamp processing unit 32 RTP time stamp correction unit 33 RTP time stamp monitoring unit 34 changeover switch

Claims (5)

In a data compression method for compressing data to be transmitted from a transmission device to a reception device,
A data acquisition step in which the transmission device acquires data to be compressed; and
In accordance with the data acquired in the data acquisition step, a time stamp addition value calculation step for calculating an addition value to be added to the time stamp value included in the header information of the data;
A value obtained by subtracting the added value from the time stamp value in the current data acquired in the data acquisition step is calculated, and it is determined whether to correct the time stamp value in the current data based on the calculated value. A time stamp value correction determination step,
As a result of the determination, if the value calculated in the time stamp value correction determination step is the same as the time stamp value of the data acquired last time in the data acquisition step, the data acquired last time in the data acquisition step A time stamp value correcting step of correcting a value obtained by adding the added value to the time stamp value of the current data as a time stamp value in the current data;
A data compression method comprising: In the time stamp addition value calculating step,
The data compression method according to claim 1, wherein an addition value to be added to a time stamp value included in header information of the data is calculated according to a transmission amount of the data acquired in the data acquisition step. In the time stamp addition value calculating step,
When the transmission amount of data acquired in the data acquisition step exceeds the reference transmission amount based on the allowable transmission amount in the current communication band, an addition value to be added to the time stamp value included in the header information of the data is calculated The data compression method according to claim 1, wherein: In the time stamp addition value calculating step,
When the data transmission amount after compressing the data acquired in the data acquisition step exceeds the reference transmission amount based on the allowable transmission amount in the current communication band, to the time stamp value included in the header information of the data The data compression method according to claim 1, wherein an addition value to be added is calculated. In a data transmission device that compresses and transmits data to be transmitted to a reception device,
Data acquisition means for acquiring data for compression;
In accordance with the data acquired by the data acquisition means, an addition value calculation means for calculating an addition value to be added to the time stamp value included in the header information of the data;
A value obtained by subtracting the added value from the time stamp value in the current data acquired by the data acquisition unit is calculated, and it is determined whether to correct the time stamp value in the current data based on the calculated value. A judgment means to
As a result of the determination, if the value calculated by the determination unit is the same as the time stamp value of the data acquired last time by the data acquisition unit, the time stamp value of the data acquired last time by the data acquisition unit And a time stamp value correcting means for correcting a value obtained by adding the added value to a time stamp value in the current data.

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