Jitter buffer control method and communication apparatus

A communication apparatus that receives, via a packet network, a packet transmitted by a transmission side, the apparatus comprising:

• a jitter buffer in which after the packet received is written, the packet being is read;
• and
• a control unit that obtains an inter-packet jitter based on difference information between time stamp information at the time of reception of the packet and another time stamp information attached to the packet at the time of transmission of the packet by the transmission side, with regard to at least one of a plurality of the received packets, and that performs control to change a reference frequency in accordance with the inter-packet jitter to transmit the packet from the jitter buffer based on a changed transmission frequency, wherein the control unit comprises:
• a clock correction unit;
• and
• a clock generation circuit that changes a clock frequency, wherein the clock correction unit obtains the inter-packet jitter, based on a difference of:
• difference information, with regard to one packet received, between time stamp information at the time of reception of the one packet and time stamp information attached to the one packet at the time of transmission of the one packet by the transmitting side;
• and
• difference information, with regard to a packet received before the one packet, between time stamp information at the time of reception of the packet and time stamp information attached to the packet at the time of transmission of the packet by the transmitting side,
• the clock correction unit takes as the transmission frequency, a frequency obtained by multiplying, by the reference frequency, a value obtained by dividing the transmission interval of the packets by a value obtained by adding the inter-packet jitter to the transmission interval of packets read from the jitter buffer,
• the clock generation circuit receives transmission frequency information from the clock correction unit, generates a clock of the frequency, and
• the packet is transmitted from the jitter buffer using frequency from the clock generation circuit.

A communication apparatus that receives, via a packet network, a packet transmitted by a transmission side, the apparatus comprising:

• a jitter buffer in which after the packet received is written, the packet being is read:
• and
• a control unit that obtains an inter-packet jitter based on difference information between time stamp information at the time of reception of the packet and another time stamp information attached to the packet at the time of transmission of the packet by the transmission side, with regard to at least one of a plurality of the received packets, and that performs control to change a reference frequency in accordance with the inter-packet jitter to transmit the packet from the jitter buffer based on a changed transmission frequency, wherein the number of packets accumulated in the jitter buffer are monitored for a prescribed time,
• in case the minimum number of accumulated packets between a write pointer indicating a position of writing to the jitter buffer and a read pointer indicating a position of reading from the jitter buffer is greater than or equal to one, it is decided that the position of the write pointer is not a position of the shortest delay, and a correction of the write pointer is performed in a direction that reduces the accumulation of packets so that delay time is a minimum, and
• in case the minimum number of accumulated packets is less than one, it is decided that the position of the write pointer is appropriate, and correction of the write pointer is not performed, and wherein
• when it is decided that correction processing of the write pointer is necessary, the minimum number of accumulated packets and the maximum number of accumulated packets in a prescribed time are measured, a measurement of jitter range is performed, and a correction is performed on the write pointer, so that delay in the jitter buffer is a minimum.

A communication apparatus that receives, via a packet network, a packet transmitted by a transmission side, the apparatus comprising:

• a jitter buffer in which after the packet received is written, the packet being is read;
• and
• a control unit that obtains an inter-packet jitter based on difference information between time stamp information at the time of reception of the packet and another time stamp information attached to the packet at the time of transmission of the packet by the transmission side, with regard to at least one of a plurality of the received packets, and that performs control to change a reference frequency in accordance with the inter-packet jitter to transmit the packet from the jitter buffer based on a chanqed transmission frequency, further comprising:
• a scheduler unit that schedules transmission of a packet from the jitter buffer;
• and
• a packet branching unit that gives a packet received from the packet network to the jitter buffer and gives time stamp information and sequence number of the packet to the scheduler unit, wherein
• in the jitter buffer, packets are accumulated in input order from the packet branching unit, and held for a time period specified by a read pointer and a write pointer, and
• the scheduler unit records time stamp information and a sequence number in sequence, and notifies a storage position within the jitter buffer of the subsequently transmitted packet to the jitter buffer.

A method of controlling a jitter buffer in which a packet received via a packet network from a transmission side is written and read, the method comprising:

• detecting a change of jitter of a received packet:
• controlling the jitter buffer so that, with regard to increase of the jitter, delay in the jitter buffer decreases;
• receiving, via the packet network, a packet transmitted by the transmission side and writing the received packet temporarily into a jitter buffer;
• obtaining a inter-packet litter, with regard to each of a plurality of received packets, based on difference information of time stamp information at the time of reception of the packet, and time stamp information attached to the packet at the time of transmission of the packet by the transmitting side;
• performing control to change a reference frequency according to the inter-packet jitter;
• and
• performing transmission of the packets from the jitter buffer, based on changed transmission frequency, wherein a frequency obtained by multiplying, by the reference frequency, a value obtained by dividing a transmission interval of packets read from the jitter buffer, by a value obtained by adding the inter-packet jitter to the transmission interval of the packets, is taken as the transmission frequency.

A method of controlling a jitter buffer in which a packet received via a packet network from a transmission side is written and read, the method comprising:

• detecting a change of jitter of a received packet;
• controlling the jitter buffer so that, with regard to increase of the jitter, delay in the jitter buffer decreases;
• receiving, via the packet network, a packet transmitted by the transmission side and writing the received packet temporarily into a jitter buffer;
• obtaining a inter-packet jitter, with regard to each of a plurality of received packets, based on difference information of time stamp information at the time of reception of the packet, and time stamp information attached to the packet at the time of transmission of the packet by the transmitting side;
• performing control to change a reference frequency according to the inter-packet jitter;
• and
• performing transmission of the packets from the litter buffer, based on changed transmission frequency, the method further comprising:
• providing time stamp information and sequence number of the packets to a scheduler that schedules transmission of a packet from a jitter buffer;
• the jitter buffer accumulating packets are accumulated in input order, and holding for a time period defined by a read pointer and a write pointer;
• and
• the scheduler recording a received time stamp and a sequence number in sequence, and notifying a storage position in the jitter buffer of the subsequently transmitted packet to the jitter buffer.

A non-transitory computer readable recording medium storing a program that causes a computer comprising a communication apparatus that receives, via a packet network, a packet transmitted from a transmitting side, to execute the processing comprising:

• obtaining an inter-packet litter based on difference information between time stamp information at the time of reception of the packet and another time stamp information attached to the packet at the time of transmission of the packet by the transmission side, with regard to each of a plurality of received packets;
• and
• performing control to change a reference frequency in accordance with the inter-packet jitter to transmit the packet from a litter buffer based on a changed transmission frequency, storing the program causing the computer to execute the processing of:
• taking, as the transmission frequency, a frequency obtained by multiplying, by the reference frequency, a value obtained by dividing a transmission interval of packets read from the jitter buffer by a value obtained by adding the inter-packet jitter to the transmission interval of the packets.