Communications terminal, communications method, and program and integrated circuit for controlling a reproduction delay time in distributing a stream

1. A communications terminal included among communications terminals each of which receives stream data distributed from a root terminal and reproduces the stream data, the communications terminals having one parent terminal and child terminals, such that the communication terminals form an Application Layer Multicast (ALM) tree to sequentially transmit retransmission data of the stream data from the parent terminal to the child terminals, and the communications terminal comprising:

a reproduction delay time determining unit configured to select a longest round-trip delay time from among round-trip delay times for sections between the root terminal and the communications terminals, and determine a reproduction delay time based on the longest round-trip delay time selected, each of the round-trip delay times being a time required for transmission and reception of data through one of the sections, each section being between two neighboring terminals among the communications terminals on the ALM tree; and

a reproduction control unit configured to reproduce the stream data received from the root terminal delayed by the reproduction delay time determined by the reproduction delay time determining unit.

2. The communications terminal according to claim 1 ,

wherein the reproduction delay time determining unit is configured to determine, as the reproduction delay time, an integral multiple of the longest round-trip delay time.

3. The communications terminal according to claim 1 ,

wherein when a round-trip delay time between the communications terminal and the parent terminal is defined as rtt(self), the reproduction delay time of the communications terminal is defined as x(self), the reproduction delay time of the parent terminal is defined as x(parent), and a positive integer is defined as α self ,

the reproduction delay time determining unit determines

(i) the reproduction delay time x(self) by means of Expression 1 if rtt(self)≧x(parent) is satisfied and

(ii) the reproduction delay time by means of Expression 2 if rtt(self)<x(parent) is satisfied:

X (self)=α self ×rtt (self); and  (Expression 1)

X (self)=(α self −1)× rtt (self)+ x (parent)  (Expression 2).

4. The communications terminal according to claim 1 , further comprising

a retransmission requesting unit configured to, in the case where part of the stream data received from the root terminal is lost, request the parent terminal to transmit retransmission data corresponding to the loss,

wherein the retransmission request unit is configured to repeatedly request the parent terminal to transmit the retransmission data at an interval which is (i) equal to or longer than the round-trip delay time between the communications terminal and the parent terminal and (ii) equal to or shorter than the longest round-trip delay time.

5. The communications terminal according to claim 1 , further comprising:

a round-trip delay time measuring unit configured to measure the round-trip delay time between the communications terminal and the parent terminal; and

a round-trip delay time managing unit configured to (i) receive, from the parent terminal, a round-trip delay time notification including one or more of the round-trip delay times between the root terminal and the parent terminal on the ALM tree and (ii) transmit, to the child terminal, the received round-trip delay time notification together with the round-trip delay time measured by the round-trip delay time measuring unit.

6. The communications terminal according to claim 5 ,

wherein the round-trip delay time managing unit is configured to receive the round-trip delay time notification at predetermined time intervals,

the round-trip delay time measuring unit is configured to measure the round-trip delay time between the communications terminal and the parent terminal at each reception of the round-trip delay time notification, and

at each reception of the round-trip delay time notification, the reproduction delay time determining unit is configured to determine the reproduction delay time based on the one or more round-trip delay times included in the round-trip delay time notification and the round-trip delay time measured by the round-trip delay time measuring unit.

7. A communications terminal included among communications terminals each of which receives stream data distributed from a root terminal and reproduces the stream data,

the communications terminals having one parent terminal and child terminals, such that the communication terminals form an ALM tree to sequentially transmit retransmission data of the stream data from the parent terminal to the child terminals, and the communications terminal comprising:

a reproduction delay time determining unit configured to select a longest round-trip delay time of a section, among sections between the root terminal and the communications terminals, having a greatest loss rate of the stream data, and determine a reproduction delay time based on the longest round-trip delay time selected, each of round-trip delay times being a time required for transmission and reception of data through one of the sections, each section being between two neighboring terminals of the communications terminals on the ALM tree; and

a reproduction control unit configured to reproduce the stream data delayed by the reproduction delay time determined by the reproduction delay time determining unit.

8. The communications terminal according to claim 7 , further comprising:

a loss rate measuring unit configured to measure the loss rate between the communications terminal and the parent terminal; and

a loss rate managing unit configured to (i) receive, from the parent terminal, a loss rate notification including one or more loss rates between the root terminal and the parent terminal on the ALM tree and (ii) transmit, to the child terminal, the loss rate notification together with the loss late measured by the loss rate measuring unit.

9. The communications terminal according to claim 8 ,

wherein the loss rate managing unit is configured to receive the loss rate notification at predetermined time intervals,

the loss rate measuring unit is configured to measure the loss rate between the communications terminal and the parent terminal at each reception of the loss rate notification, and

at each reception of the loss rate notification, the reproduction delay time determining unit is configured to determine the reproduction delay time based on the one or more loss rates included in the loss rate notification and the loss rate measured by the loss rate measuring unit.

10. A communications method executed by a communications terminal included among communications terminals each of which receives stream data distributed from a root terminal and reproduces the stream data,

the communications terminals having one parent terminal and child terminals, such that the communication terminals form an ALM tree to sequentially transmit retransmission data of the stream data from the parent terminal to the child terminals, and the communications method comprising:

selecting a longest round-trip delay time from among round-trip delay times for sections between the root terminal and the communications terminals, and determine a reproduction delay time based on the longest round-trip delay time selected, each of the round-trip delay times being a time required for transmission and reception of data through one of the sections, each section being between two neighboring terminals among the communications terminals on the ALM tree; and

reproducing the stream data received from the root terminal delayed by the reproduction delay time determined in the selecting the longest round-trip delay time.

11. A program stored on a non-transitory computer-readable recording medium and executed by a communications terminal included among communications terminals each of which receives stream data distributed from a root terminal and reproduces the stream data,

the communications terminals having one parent terminal and child terminals, such that the communication terminals form an ALM tree to sequentially transmit retransmission data of the stream data from the parent terminal to the child terminals, and the program causing the communications terminal to execute steps comprising:

selecting a longest round-trip delay time from among round-trip delay times for sections between the root terminal and the communications terminals, and determine a reproduction delay time based on the longest round-trip delay time selected, each of the round-trip delay times being a time required for transmission and reception of data through one of the sections, each section being between two neighboring terminals among the communications terminals on the ALM tree; and

reproducing the stream data received from the root terminal delayed by the reproduction delay time determined in the determining.

12. An integrated circuit in a communications terminal included among communications terminals each of which receives stream data distributed from a root terminal and reproduces the stream data,

the communications terminals having one parent terminal and child terminals, such that the communication terminals form an ALM tree to sequentially transmit retransmission data of the stream data from the parent terminal to the child terminals, and the integrated circuit comprising:

a reproduction delay time determining unit configured to select a longest round-trip delay time from among round-trip delay times for sections between the root terminal and the communications terminals, and determine a reproduction delay time based on the longest round-trip delay time selected, each of the round-trip delay times being a time required for transmission and reception of data through one of the sections, each section being between two neighboring terminals among the communications terminals on the ALM tree; and

a reproduction control unit configured to reproduce the stream data received from the root terminal delayed by the reproduction delay time determined by the reproduction delay time determining unit.