JP5083059B2 - Packet relay apparatus and packet relay method - Google Patents

Description

  The present invention relates to a packet relay apparatus and a packet relay method that can control the transmission rate of real-time communication according to the congestion status of an IP (Internet Protocol) network.

RTP / IP for transferring real-time media such as audio and video over IP networks
RTCP (Real-time Transport Protocol / RTP Control Protocol) (RFC3550) is used. In order to realize real-time multimedia communication with UDP (User Datagram Protocol), it is necessary to assign a sequence number indicating the order of packets and to manage the transmission time of packets, and RTP does this. . RTCP assists RTP communication and reports (reports) communication line quality information such as packet loss rate, jitter, and delay time measured at the receiving side terminal to the transmitting side terminal. The transmission rate can be controlled with reference to the above.

Patent Document 1 discloses a method for controlling a transmission rate in accordance with a congestion state of a network. According to this, information from the video quality monitoring unit of the receiving side terminal is received by the frame rate control unit of the transmitting side terminal according to the congestion status of the network, and the video rate is improved by changing the transmission rate. Is going.
JP 2005-322995 A

  In Patent Document 1, since all control is performed by the receiving side terminal and the transmitting side terminal, there is a problem that when the network congestion is local, the recovery of the transmission rate is delayed when the network recovers from the congestion. is there.

  Congestion is a situation where network traffic increases and effective communication cannot be performed at all. In general, when sending packets, etc., the network checks whether it has reached the other party. If not, resend processing such as resending again. However, if the load on the network is heavy and the return of the confirmation packet is delayed, the retransmission packet is erroneously sent earlier, resulting in an even higher load on the network. In this way, the load on the network rises all at once, and a state in which effective communication is hardly possible with only retransmission packets and confirmation packets (and other control packets).

  The present invention has been made to solve the above-described problem, and provides a packet relay apparatus and a packet relay method capable of controlling the transmission rate of real-time communication according to the congestion status of an IP network. With the goal.

To achieve the object, a packet relay device (for example, the packet relay device 100) that relays a packet on the network measures an RTP packet and extracts first quality information (for example, the measurement unit 50). A monitoring unit (for example, the monitoring unit 60) that extracts the second quality information from the RTCP packet, a rate control unit (for example, the rate control unit 40) that controls the control rate according to a control command of the monitoring unit, When the monitoring unit detects a congestion state from the first quality information and the second quality information, the rate control unit lowers the control rate of the RTP packet corresponding to the RTCP packet, and the monitoring unit The second quality information in the RTCP packet is replaced with the first quality information .

  According to the present invention, it is possible to control the transmission rate of real-time communication according to the congestion status of the IP network.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory diagram showing an IP network configuration according to an embodiment of the present invention. The terminal TE2 is connected to the IP network (IP network) NW2, the terminal TE1 is connected to the IP network NW1, and the IP network NW1 and the IP network NW2 are connected by the packet relay device 100. Examples of the terminal include an IP phone and a streaming receiving terminal that mainly transfers and plays multimedia files such as voice and moving images.

  FIG. 2 is a block diagram illustrating a functional configuration of the packet relay apparatus. This will be described with reference to FIG. The packet relay apparatus 100 includes a packet receiving unit 10, a packet transmitting unit 20, a packet determining unit 30, a rate control unit 40, a measuring unit 50 that measures packet quality information, a monitoring unit 60 that monitors a congestion state, and a condition setting unit 70. have. The packet receiving unit 10 and the packet transmitting unit 20 have a function of a network interface unit. Specifically, the case of transmitting from the terminal TE2 to the terminal TE1 will be described. The RTP packet transmitted from the terminal TE2 is received by the packet receiving unit 10, and the packet is transmitted via the packet determination unit 30 and the rate control unit 40. It is transmitted from the transmission unit 20 to the terminal TE1. Also, the terminal TE1 that has received the RTP packet transmits the RTCP packet to the terminal TE2. The transmitted RTCP packet is received via the packet receiver 10 and is transmitted from the packet transmitter 20 to the terminal TE2 via the packet determiner 30 and the rate controller 40. The packet receiving unit 10, the packet transmitting unit 20, the packet determining unit 30, the rate control unit 40, the measuring unit 50, the monitoring unit 60, and the condition setting unit 70 are a CPU (Central Processing Unit), a ROM (Read This is realized by only memory (RAM) and random access memory (RAM).

  The packet determination unit 30 determines the packet type (RTP packet or RTCP packet) and the transmission direction of the packet received by the packet reception unit 10. Based on the determination result, in the case of an RTP packet, the RTP packet is transmitted to the measurement unit 50. In the case of an RTCP packet, the RTCP packet is transmitted to the monitoring unit 60.

  The measurement unit 50 extracts quality information (for example, packet loss rate, jitter) from the received RTP packet. The monitoring unit 60 compares the quality information measured by the terminal TE1 included in the received RTCP packet with the quality information measured by the measurement unit 50, and sets the rate control based on the comparison result. The rate control unit 40 performs rate control of received packets with the rate control value set by the monitoring unit 60. The condition setting unit 70 stores packet identification conditions (see FIG. 4) referred to by the packet determination unit 30, the measurement unit 50, and the monitoring unit 60, parameters for determining quality information, and the like.

  FIG. 3 is a flowchart showing processing from reception of a packet to transmission by the packet relay device. This will be described with reference to FIGS. 1 and 2 as appropriate. When the packet receiving unit 10 receives a packet, the packet determining unit 30 determines whether the received packet is an RTP packet or an RTCP packet (step S1). The determination method is based on whether or not the conditions match based on a packet identification condition table 80 (see FIG. 4) such as a preset IP address and port number. Details will be described with reference to FIG.

  FIG. 4 is an explanatory diagram illustrating an example of a packet identification condition table. The packet identification condition table 80 is stored in the condition setting unit 70 in advance. The packet identification condition table 80 has a type, a source IP address, a destination IP address, a protocol type, a source port number, and a destination port number. For example, the source port number and the destination port number are generally 5004 for RTP packets and 5005 for RTCP packets. Specifically, in the case of the record 81, the RTP packet from the terminal TE2 to the terminal TE1 can be determined from the transmission source IP address, the destination IP address, the transmission source port number, and the destination port number. In the case of the record 84, it is determined as an RTCP packet from the terminal TE1 to the terminal TE2. Similarly, the record 83 is determined as an RTP packet from the terminal TE1 to the terminal TE2, and the record 82 is determined as an RTCP packet from the terminal TE2 to the TE1.

  In step S1, in the case of an RTP packet (steps S1 and RTP), the measurement unit 50 measures quality information defined by RFC3550 or RFC3611. The measurement of quality information here includes extracting predetermined quality information Q1 from the RTP packet information. The quality information Q1 obtained here represents quality information from the transmission side terminal to the packet relay apparatus 100.

  Specifically, when the quality information Q1 is a packet loss rate, it is calculated using the sequence number in the header part of the RTP packet. For example, if the sequence number is missing among the packets whose sequence numbers have consecutive integer values for a predetermined period, the ratio of the number of missing sequence numbers to the total number of sequence numbers for the predetermined period Loss rate (%).

Further, when the quality information Q1 is jitter, it is represented by an average deviation of the time difference between the transmission interval and the reception interval of two consecutive RTP packets. The packet transmission time is stored in the RTP time stamp field in the RTP packet. When the RTP time stamps of the two RTP packets are ST1 and ST2, and the reception times are RT1 and RT2, respectively, the time difference DT is:
DT = (RT2-RT1)-(ST2-ST1) (A1)
Jitter J is J = J + (| DT | −J) / 16 (A2)
It is represented by

  Thereafter, the RTP packet is transmitted after being subjected to rate control in accordance with the rate control setting conditions set or changed in step S6 or step S9 described later (step S3).

  In step S1, in the case of an RTCP packet (steps S1 and RTCP), quality information Q2 is extracted from the RTCP packet (step S4). The quality information Q2 obtained here represents the quality from the transmission side terminal to the reception side terminal. As a specific example of the extraction of the quality information Q2, in the case of the packet loss rate, the fraction lost field in the report block of the SR / RR (transmission report / reception report) packet is extracted. In the case of jitter, an interarrival jitter field in the report block is extracted.

  Note that an application that transmits audio or video data in the transmitting terminal creates a transmission report, and the transmission report includes information on the number of accumulated packets and the number of accumulated bytes transmitted. The receiving terminal can calculate the data reception rate based on this. When receiving the video or audio data, the receiving side terminal periodically issues a reception report of the receiving side terminal to the transmitting side terminal. This includes the maximum sequence number received, the number of missing packets, jitter, and time stamp information necessary for calculating the round trip delay.

  The monitoring unit 60 compares the quality information Q1 obtained in step S2 and the quality information obtained in step S4 with Q2 (step S5). When the quality information Q2 is significantly degraded as compared with the quality information Q1, it is considered that local congestion has occurred between the packet relay device 100 and the receiving side terminal. For this reason, a threshold value may be defined in the condition setting unit 70 in advance for the determination that the deterioration is significant. For example, when the packet loss rate of the quality information Q1 is 10%, the packet loss rate of the quality information Q2 is 20%, and the threshold of the packet loss rate is 5%, it is determined that the deterioration amount is large.

Further, as a determination condition, it may be determined that the deterioration amount is large when the following expression is satisfied.
In the case of the packet loss rate, when the packet loss rate of the quality information Q1 is QL1 and the packet loss rate of the quality information Q2 is QL2, it is expressed by the equation (A3).
QL2> (a1 * QL1) (A3)
In the case of jitter, when the jitter of the quality information Q1 is QJ1, and the jitter of the quality information Q2 is QJ2, it is expressed by equation (A4).
QJ2> (a2 * QJ1) (A4)
Note that a1 and a2 are parameters for determining the deterioration amount, and * means integration.

  In step S5, when the amount of deterioration is large (step S5, large amount of deterioration), the monitoring unit 60 sets rate control (step S6). The packet subject to rate control is an RTP packet related to the RTCP packet. For example, if the reception rate at the packet relay apparatus 100 is 1 Mbps and the loss rate measured at the receiving terminal is 50%, the loss is reduced to 0% by setting the set rate to 500 Kbps, which is 50% of 1 Mbps. The rate to be set is set to 600 Kbps with a margin of 10%. A value of 10% margin may be provided as a parameter of the monitoring unit 60.

As a control setting method, if the current set rate value is R, the rate may be set by the following equation.
For packet loss rate,
R * (QL1 / QL2) * b1 (B1)
Similarly, for jitter,
R * (QJ1 / QJ2) * b2 (B2)
B1 and b2 are parameters for rate control.

  Then, a process of rewriting the quality information Q2 of the received RTCP packet with the quality information Q1 is performed (step S7). By rewriting the quality information Q2 of the RTCP packet that the packet relay apparatus 100 transfers to the transmission side terminal, it is possible to prevent the transmission side terminal that has received the RTCP packet from detecting congestion, so that the transmission side terminal lowers the transmission rate. There is no.

  In step S5, when the deterioration amount is small (step S5, small deterioration amount), the monitoring unit 60 determines whether or not rate control is already being performed (step S8). If rate control is not being implemented (step S5, No), the process is terminated. If rate control is being implemented (step S5, Yes), the rate control setting is changed (step S9). The control at this time is the operation control for releasing the rate control after congestion occurs. For example, when congestion occurs and the control rate in the packet relay device 100 is once set to 600 kbps in step S6, and then the packet loss rate of the quality information Q2 from the receiving terminal is almost 0% In stepwise, the control rate of the packet relay apparatus may be changed to 700 kbps, 800 kbps, or 900 kbps, and finally set to return to the control rate without bandwidth control. Then, after step S9, packet rewriting (step S7) is performed, and a series of processing ends.

As a control setting method, if the current set rate value is R, the rate may be set by the following equation.
R * c (B3)
Note that c is a parameter for rate control.

  In step S5, if the amount of deterioration is large, it is considered that a congestion state has occurred between the packet relay apparatus 100 and the receiving side terminal. In step S5, if the amount of deterioration is small, the congestion state Can be considered as a state in which no occurrence has occurred, or a state in which a congestion state has been recovered.

  According to the present embodiment, the quality information has been described using the packet loss rate and jitter, but it may be a round trip delay time calculated from the time stamp information of the RTCP packet. A method for calculating the round-trip delay time will be described with reference to FIG.

FIG. 5 is an explanatory diagram showing a method for calculating the round-trip delay time. The terminal TE2 transmits the RTCP packet P1 at time T101, the packet relay apparatus 100 receives at time T301, and the terminal TE1 receives at time T201. The terminal TE1 transmits the RTCP packet P2 at time T202. The RTCP packet P2 includes a time D201 from when the RTCP packet P1 is received until the RTCP packet P2 is transmitted. The relay apparatus receives the RTCP packet P2 at time T302, and the terminal TE2 receives it at time T102. At this time, the round-trip delay time between the packet relay apparatus 100 and the terminal TE1 is expressed by the following equation.
T302-T301-D201 (C1)

The round-trip delay time is calculated every time the packet relay apparatus 100 measures, and when the average value is QDavg as the quality information Q1, and then the round-trip delay time measured is QD2 as the quality information Q2, When the equation is satisfied, it is determined that the deterioration amount is large.
QD2> (a3 * QDavg) (C2)
Note that a3 is a parameter for determining the deterioration amount.

The rate control setting in the case of the round trip time is calculated by the following equation.
R * (QDavg / QD2) * b3 (C3)
Note that b3 is a parameter for rate control.

  In this embodiment, when the packet determination unit 30 determines a packet in FIG. 2, the average value QDavg is calculated by the measurement unit 50 by calculating the round trip delay time of the equation (C1), and the quality information of the equation (C2) And the rate control setting of the expression (C3) may be executed by the monitoring unit 60.

  FIG. 6 is an explanatory diagram showing features according to the embodiment of the present invention. FIG. 6 shows the transmission state of the RTP packet from the transmission side terminal and the RTCP packet from the reception side terminal. The characteristics of the packet relay device 100 of this embodiment are (1) the control rate in the packet relay device can be changed based on the quality information Q1 and the quality information Q2, and (2) the quality information Q2 is changed to the quality information Q1. Can be rewritten.

  According to the present embodiment, the packet relay apparatus 100 can quickly follow the congestion state by changing the control rate according to the congestion state. In addition, since the quality information of the RTCP packet transferred to the transmission side terminal is rewritten with the quality information obtained from the RTP packet, the transmission side terminal can suppress the detection of congestion, so that the transmission side terminal reduces the transmission rate. There is no. For this reason, when recovering from congestion, the packet relay apparatus 100 can return the rate control to the original rate value while monitoring the quality information of the RTCP packet. Quality can be obtained.

It is explanatory drawing which shows the IP network structure which concerns on embodiment of this invention. It is a block diagram which shows the function structure of a packet relay apparatus. It is a flowchart which shows the process from receiving a packet in a packet relay apparatus to transmission. It is explanatory drawing which shows an example of a packet identification condition table. It is explanatory drawing which shows the calculation method of a round-trip delay time. It is explanatory drawing which shows the characteristic which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Packet reception part 20 Packet transmission part 30 Packet determination part 40 Rate control part 50 Measurement part 60 Monitoring part 70 Condition setting part NW1, NW2 IP network (IP network)
100 packet relay device TE1, TE2 terminal

Claims (4)

In a packet relay device that relays packets on a network,
A measurement unit that measures RTP packets and extracts first quality information; a monitoring unit that extracts second quality information from RTCP packets;
A rate control unit that controls a control rate according to a control command of the monitoring unit,
When the monitoring unit detects a congestion state from the first quality information and the second quality information, the rate control unit lowers the control rate of the RTP packet corresponding to the RTCP packet, and
The monitoring unit replaces the second quality information in the RTCP packet with the first quality information. The first quality information and the second quality information are packet loss rates or jitters,
2. The congestion state is a state in which the second quality information is larger than an integrated value of the first quality information and a parameter for determining a packet degradation amount. Packet relay device. When the monitoring unit determines that the congestion state has been recovered after detecting the congestion state from the second quality information and the first quality information, the rate control unit corresponds to the RTCP packet The packet relay apparatus according to claim 1, wherein the control rate of the RTP packet is returned to the original control rate before the congestion state is detected. In a packet relay method for relaying a packet on a network,
The measurement unit measures the RTP packet, extracts the first quality information,
The monitoring unit extracts the second quality information from the RTCP packet,
When the monitoring unit detects a congestion state from the first quality information and the second quality information, a rate control unit that controls a control rate according to a control command of the monitoring unit corresponds to the RTCP packet While reducing the control rate of the RTP packet,
The monitoring unit replaces the second quality information in the RTCP packet with the first quality information.

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