CONTENT DELIVERY SYSTEM

• US 20150131649A1
• Filed: 04/27/2012
• Published: 05/14/2015
• Est. Priority Date: 05/09/2011
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Gibbons, John, Lee, Robert Ming, Wilson, Graeme Peter, Fraser, Finlay James, Vadgama, Sanjay Rugnath
• Granted Patent: US 9,847,846 B2
• Time in Patent Office: Days
• US Class Current: 370/352
• CPC Class Codes: H04J 3/0632 Synchronisation of packets and cells, e.g. transmission of voice via a packet network, circuit emulation service [CES] queuing arrangements in packet switching elements H04L49/90; synchronising systems for the synchronous transmission of a pulse code modulated video signal with one or more other pulse code modulated signals H04N7/56
• CPC Class Codes: H04J 3/0658 Clock or time synchronisation among packet nodes
• CPC Class Codes: H04L 47/30 in combination with information about buffer occupancy at either end or at transit nodes
• CPC Class Codes: H04M 7/006 Networks other than PSTN/ISDN providing telephone service, e.g. Voice over Internet Protocol (VoIP) , including next generation networks with a packet-switched transport layer H04L65/00 takes precedence; aspects not specific to the type of network H04M3/00; special services in those networks H04M3/42

Abstract

The audio outputs 29 of each of a plurality of telecommunications terminals in a packet switched system are synchronised by having each terminal transmit a stream of packets whose rate, and therefore duration is determined according to a clock generator 25, and is thus indicative of the rate at which the terminal is generating its audio output. The signals from each terminal are transmitted to a common server. For each terminal, the server uses a master dock to compare the duration of the packet stream with an expected duration, and calculates an offset value which is returned to the respective terminal. Each terminal stores the offset value it receives (20) and uses it to adjust the output of its clock generator 25 so that its operations can be synchronised to the server. This allows all the terminals'"'"' digital-to-analogue conversion processes to be synchronised such that all their analogue outputs are co-ordinated, allowing co-located acoustic outputs to be synchronous. A second embodiment maintains synchronisation by maintaining the volume of the data buffer 23 serving the audio output 29 within predetermined limits.

Claims

1. A method of controlling a telecommunications terminal in a packet switched system, wherein:

the terminal transmits to a server a rate-indication signal indicative of the rate at which it generates an audio output,

the server determines an offset value by comparison of the rate-indication signal received from the terminal with a rate set by the server,

the server transmits the offset value to the terminal; and

the terminal applies the offset value to its audio output so that the rate at which the output is generated becomes synchronised to the rate set by the server.

2. A method according to claim 1, the terminal having an internal clock having a predetermined clocking value, the method comprising the steps of:

generating, at the terminal, a stream of packets of a duration determined according to the clocking value;

transmitting the stream of packets over the packet switched system to a server having a master clock;

at the server, determining the duration of the stream of packets according to the master clock;

calculating an offset value indicative of the difference between the duration of the stream determined by the terminal clock and the duration as determined by the master clock;

transmitting the offset value to the terminal;

adjusting the clocking value of the terminal by applying the offset value received from the server;

operating packet handling functions of the terminal according to the adjusted clocking value.

3. A method according to claim 1, the terminal having an internal clock having a predetermined clocking value, the terminal having a data buffer, the method comprising the steps of:

generating, at the terminal, a signal indicative of the buffer depth,

transmitting the buffer depth signal to the server;

at the server, calculating an offset value indicative of the difference between the actual buffer depth and an optimum buffer depth determined by the server;

transmitting the offset value to the terminal;

adjusting the clocking value of the terminal by the offset value;

operating packet handling functions of the terminal according to the adjusted clocking value.

4. A method according to claim 2, wherein the process is repeated at intervals to maintain the clocking value within a predetermined limit from the master clock value.

5. A method according to claim 4, wherein the intervals at which the process is repeated is selected according to the amount of drift in clocking value determined in previous iterations.

6. A method according to claim 1, wherein the packet handling functions controlled by the internal clock include the generation of an audio signal from a packet stream.

7. A telecommunications terminal for connection to a packet switched system, the terminal comprising

an internal clock having a predetermined clocking value

an audio output controlled by the clocking value

a signal generator for generating a rate-indication signal indicative of the rate at which the terminal generates an audio output,

a transmitter for transmitting the rate-indication signal to a server

a receiver for receiving an offset value from the server;

and

a clock adjustment processor for adjusting the clocking value of the internal clock according to the offset value.

8. A telecommunications terminal according to claim 7, further comprising

a test packet generator for generating a predetermined set of data packets at a rate determined according to the clocking value;

a transmitter for transmitting the predetermined set of data packets over the packet switched system to the server.

9. A telecommunications terminal according to claim 7, having a data buffer, and the signal generator being configured to generate a signal indicative of the buffer depth for transmission to the server.

10. A telecommunications terminal according to claim 7, wherein the signal generator is arranged to generate signals for transmission to the server at intervals such as to maintain the clocking value within a predetermined limit from the master clock value.

11. A telecommunications terminal according to claim 10, wherein the intervals at which the process is repeated is selected according to the rate of change in clocking values determined from previous offset values.

12. A telecommunications terminal according to claim 7, comprising an audio signal generator for generating an audio signal from incoming packet streams, the audio signal generator being controlled by the internal clock.

13. A server for connection to a packet switched telecommunications system for controlling one or more telecommunications terminals connected to the system, the server comprising:

a master clock;

a receiver for receiving a rate-indication signal from each terminal indicative of the rate at which each respective terminal generates an audio output,

a processor for calculating, for each terminal, a respective offset value derived from the rate-indication signal received from the terminal, and

a transmitter for transmitting the offset values to the respective terminals.

14. A server according to claim 13, wherein the receiver is arranged to receive a stream of data packets having a notional duration determined by the terminal, and comprising;

a timing means for determining the duration of the received stream of packets according to the master clock

the processor being configured to calculate the offset by comparing the notional duration of the stream with the actual duration of the stream as determined by the master clock.

15. A server according to claim 13, wherein the receiver is arranged to receive a signal from a terminal indicative of buffer depth in the terminal, the processor being configured to determine an offset value indicative of the difference between the actual buffer depth and an optimum buffer depth.

16. A server according to claim 13, further comprising a program store for storing program data for configuring a terminal to operate wherein the server is configured to identify one or more terminals to be synchronised, and to transmit the program data to the terminals so identified, together with address data specific to the server such that the terminals can transmit signals to the server indicative of their clocking rate.