JP2014072546A - Content distribution device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform highly accurate control of a packet transmission band.SOLUTION: A content distribution device is provided with: an internal clock timer 205 for counting an internal clock; an external clock counter 201 for counting an external clock more accurate than the internal clock; an external clock counter read out unit 202 for reading counter values from the external clock counter 201; and a transmission processing program 203 which sets a cycle with the counter value of the external clock counter 201 as a reference, reads out the counter value of the external clock counter 201 by the external clock counter read out unit 202 every time it periodically starts in the cycle by the internal clock timer 205, calculates the number of transmission packets on the basis of a difference between the read-out counter value and a cycle start time so that a fixed amount of packets is transmitted every cycle, and transmits packets of the number of calculated transmission packets.

Description

  Embodiments described herein relate generally to a content distribution apparatus that distributes content in packets via an IP network.

  When content such as video is distributed via an IP network, if the transmission rate is different between the transmission side (content distribution device) and the reception side (transmitter), a buffer overflow or a buffer underflow occurs on the reception side.

  As a method for preventing this, there is a method of synchronizing the clocks on the transmission side and the reception side. However, in the method dependent on the transmission side clock via the IP network (subordinate synchronization), fluctuation of the transmission side clock becomes a problem.

  In the method of transmitting and receiving using independent clocks on the transmission side and the reception side (independent synchronization), the transmission side performs accurate communication bandwidth control based on a high-accuracy clock, and the reception side performs reception processing with a high-accuracy clock. There is a need to do.

JP 2004-96684 A

  However, since the transmission processing is executed by software processing by a server or a personal computer, the clock by the OS (Operating System) timer does not have sufficient clock accuracy. In addition, fluctuations in software startup time caused stable communication bandwidth control.

  An object of the present embodiment is to provide a content distribution apparatus capable of realizing highly accurate packet transmission bandwidth control.

  The content distribution apparatus according to the present embodiment is a content distribution apparatus that transmits a packet of content, an internal clock timer that counts an internal clock, an external clock counter that counts an external clock with higher accuracy than the internal clock, Reading means for reading a counter value from an external clock counter, and a period is set based on the counter value of the external clock counter, and the reading means causes the external clock to be Calculating means for reading the counter value of the clock counter and calculating the number of transmitted packets based on the difference between the read counter value and the start time of the period so that a fixed amount of packets are transmitted every period; Transmitting means for transmitting packets of the calculated number of transmitted packets; It is intended to comprise.

1 is an overall configuration diagram of a content distribution system according to an embodiment. The functional block diagram which shows the structural example of a content delivery apparatus. The functional block diagram which shows the structural example of a receiver. The flowchart which shows a packet transmission process. The figure which shows a packet transmission image.

  The content distribution apparatus according to this embodiment will be described below with reference to the drawings.

  FIG. 1 is an overall configuration diagram of a content distribution system according to the present embodiment. The content distribution apparatus 2 (transmission side) and the transmitter 3 (reception side) are connected via the IP network 1, and the transmitter 3 can communicate wirelessly with the terminal 4 existing in the cover area. For example, content such as video and live content are stream-distributed to a plurality of transmitters 3 by IP multicast communication from the content distribution device 2, and the plurality of transmitters 3 modulates the content received by IP packets into radio signals and transmits the terminal 4 Send to.

  FIG. 2 is a functional block diagram illustrating a configuration example of the content distribution device 2. The content distribution apparatus 2 includes an external clock counter 201, an external clock counter reading unit 202, a transmission processing program 203, a content memory 204, and an OS (Operating System) timer 205.

  The external clock counter 201 is a counter having a function of generating a high-precision clock by an internal oscillator and counting the clock.

  The external clock counter reading unit 202 has a function of reading the counter value of the external clock of the external clock counter 201.

  The transmission processing program 203 has a function of inputting content from the content memory 204 and transmitting it as an IP packet. The transmission processing program 203 is periodically started by the OS clock timer 205 and transmits IP packets to the IP network 1. The counter value of the external clock is read out via the external clock counter reading unit 202, and the number of IP packet transmissions is calculated by packet transmission processing, which will be described later, thereby realizing highly accurate transmission bandwidth control.

  FIG. 3 is a functional block diagram illustrating a configuration example of the transmitter 3. The transmitter 3 includes an IP reception processing program 301, a reception buffer 302, a reception processing unit 303, and an external clock 304.

  The IP reception processing program 301 has a function of receiving an IP packet sent from the content distribution apparatus 2 via the IP network 1 and storing the received IP packet in the reception buffer 302.

  The reception processing unit 303 has a function of modulating an IP packet stored in the reception buffer 302 into a radio signal according to a high precision clock generated by the external clock 304 and outputting the radio signal.

  Note that a GPS (Global Positioning System) clock may be used as an external clock on the transmission side and the reception side.

  Next, transmission band control performed by the content distribution apparatus 2 configured as shown in FIG. 2 will be described. The transmission band guarantees that Px packets are transmitted at a certain time Tx, and an algorithm is required that has as few transmission bursts as possible (no variation in transmission speed). Therefore, the transmission processing program 203 performs packet transmission processing as shown in FIG. In FIG. 4, Flag is a flag indicating the start state of periodic transmission, Ti is an external counter value indicating the start time, Ts is an external counter value indicating the start time of the cycle, and Pi is an accumulated value transmitted up to that point. The number of packets, P is the number of packets to be transmitted at the time of activation, Tx is the period time, Px is the number of packets to be transmitted in the period time to realize the specified bandwidth, and ta is the time interval activated by the OS clock timer. .

  The transmission processing program 203 is periodically started at the ta interval by the OS clock timer 205 based on the internal clock. The activated transmission processing program 203 first checks the flag (step S1). If the flag is off (in the case of initial activation), the process proceeds to step S2, and a predetermined threshold value is maintained until the activated program state is stabilized. It will be in a waiting state until the above time passes (step S2). When the time equal to or greater than the threshold value has elapsed, the transmission processing program 203 sets Flag to On (step S3), reads the external counter value Ti by the external clock counter reading unit 202 as the period initial setting process (step S4), and sets the value Ti to The cycle start time Ts is set, and the cumulative transmission packet number Pi is set to 0 (step S5).

  On the other hand, if the flag is On in step S1 (when it is not initially activated), the external counter value Ti is read by the external clock counter reading unit 202 (step S6), and the number P of packets to be transmitted this time is calculated as follows (step S6). Step S7).

  That is, the cumulative number of packets to be sent in the elapsed time (Ti−Ts) from the beginning of the cycle is calculated by (Ti−Ts) × Px / Tx. Since the cumulative number of packets sent up to the previous time is Pi, the difference is obtained as the number of packets P to be transmitted this time as shown in the following equation 1.

P = ((Ti−Ts) × Px / Tx) −Pi (Expression 1)
Furthermore, when the number P of transmission packets is larger than a predetermined value, the transmission processing program 203 performs a head cut process (step S8). In some cases, the startup of the program is delayed due to variations in the startup time of the OS, and the interval from the previous startup time becomes large. When the number of transmission packets P is larger than a predetermined value, the number of transmissions of the number of transmission packets P is reduced (cut off) to prevent traffic fluctuations.

  Then, the transmission processing program 203 transmits IP packets having the number of transmission packets P (step S9), and adds the number of packets actually transmitted to the cumulative number of packets Pi (step S10). When the elapsed time (Ti-Ts) from the beginning of the cycle becomes larger than the cycle time Tx (step S11), the next cycle is set as shown in the following equation 2 (step S12).

Ts = Ts + Tx, Pi = Pi−Px (Expression 2)
According to Equation 2, the setting of the start time of the next cycle and the process of carrying forward the fraction of the number of packets for each cycle after the next cycle are performed.

  FIG. 5 shows a packet transmission image by the processing of FIG. In FIG. 5, the vertical axis represents the cumulative number of packets Pi, the horizontal axis represents the elapsed time, and the cycle time Tx is 63 × 51 seconds. Also,. In FIG. 5, the timing at which the program is actually started and the number P of packets to be transmitted at that time are indicated by hatched portions, and the expected cumulative number of transmitted packets Px is indicated by bold lines. That is, the fraction shown by Pi-Px in FIG. 5 is carried over to the next cycle every cycle.

  As described above, in the present embodiment, by using a high-precision external counter in the above equation 1, packet transmission in a stable transmission band can be realized without depending on variations in the OS activation cycle ta. Moreover, in order to suppress the burst property to a small extent, it can be realized by reducing the value of ta (for example, it is usually 5 ms instead of 10 to 100 ms). In addition, the rounding error that occurs when obtaining the number P of transmission packets is carried over by the error in the calculation in the next start-up period (5 ms), so that no calculation error occurs. Further, in the initialization process of one cycle Tx as shown in the above formula 2, the calculation error can be eliminated by carrying over to the next cycle the number of packets actually transmitted.

  Therefore, according to the present embodiment, in content distribution using independent clocks on the transmission side and the reception side, the packet transmission bandwidth is kept constant with high accuracy, no error occurs in transmission and reception, and high speed is achieved with simple hardware and software processing. Accurate packet transmission bandwidth control can be realized. In addition, since transmission processing is performed at short intervals, bandwidth control with few traffic bursts can be realized.

  Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... IP network, 2 ... Content delivery apparatus, 3 ... Transmitter, 4 ... Terminal, 201 ... External clock counter, 202 ... External clock counter reading part, 203 ... Transmission processing program, 204 ... Content memory, 205 ... OS clock timer , 301 ... IP reception processing program, 302 ... reception buffer, 303 ... reception processing unit, 304 ... external clock.

Claims (3)

A content distribution device that packet-transmits content,
An internal clock timer that counts the internal clock;
An external clock counter for counting an external clock with higher accuracy than the internal clock;
Reading means for reading a counter value from the external clock counter;
The cycle is set based on the counter value of the external clock counter, and the counter value of the external clock counter is read by the reading means every time the internal clock timer is periodically started within the cycle. Calculation means for calculating the number of transmitted packets based on the difference between the read counter value and the start time of the cycle so that a certain amount of packets are transmitted;
A content distribution apparatus comprising: a transmission unit configured to transmit packets of the calculated number of transmission packets.   The content distribution apparatus according to claim 1, further comprising means for carrying forward the fraction of the cumulative number of packets transmitted for each period after the next period.   The content distribution apparatus according to claim 1, wherein the calculation unit performs a truncation process on the number of transmission packets when the calculated number of transmission packets exceeds a predetermined threshold.

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