Response time measurement for adaptive playout algorithms

1. A system comprising two endpoints ( 1 , 2 ) communicating with each other by means of a packet-switched network,

said endpoints ( 1 , 2 ) being adapted to estimate jitter from packet arrival times and to modify silence period lengths according to the latest estimate by using adaptation algorithms, wherein a response time (ρ) of the system is measured at a given time instant, the response time being defined as the time elapsed between the capture of a given frame of speech at one endpoint and its playout at the other endpoint plus the same quantity in the other direction, wherein:

a first endpoint ( 1 ) is configured to send a response time request packet to a second endpoint ( 2 ) at a time s r ;

said second endpoint ( 2 ) is configured to receive the response time request packet at a time r r ;

said second endpoint ( 2 ) is configured to send a response time indication packet to said first endpoint ( 1 ) at a time s i ;

said first endpoint ( 1 ) is configured to receive the response time indication packet at a time r i ; and

said first endpoint ( 1 ) is configured to compute the response time (ρ) on the basis of the sending and receiving times,

wherein the response time is used as a parameter in the adaptation algorithms,

wherein the response time request packet sent from said first endpoint ( 1 ) includes information identifying one of the rackets which has been sent at a time s′ by said second endpoint ( 2 ) and received at a time r′ by said first endpoint ( 1 ) since its latest adaptation, and wherein the response time indication packet sent by said second endpoint ( 2 ) includes information identifying one of the packets which has been sent at a time s′ by

said first endpoint ( 1 ) and received at a time r by said second endpoint ( 2 ) since its latest adaptation,

and wherein said second endpoint ( 2 ) is configured to compute s′−s, and indicate the result in the response time indication packet.

2. The system according to claim 1 , wherein said endpoints are adapted to verify that for certain adaptation points the playout (ρ) of a packet can be expressed as p=r+B, where r is a packet reception time and B is a buffer delay chosen by using the algorithms, and to synchronize the playout for other packets with the previous packet playout.

3. The system according to claim 1 , wherein said endpoints ( 1 , 2 ) are adapted to use different ones of said adaptation algorithms.

4. A method of using adaptation algorithms for estimating jitter from packet arrival times and for modifying silence period lengths according to the latest estimate, in communications between two endpoints in a packet-switched network system, said method having the steps of:

measuring a response time (ρ) of the system at a given time instant, the response time being defined as the time elapsed between the capture of a given frame of speech at one endpoint and its playout at the other endpoint plus the same quantity in the other direction, the measuring comprising the steps of

sending (S 1 ) a response time request packet from a first endpoint ( 1 ) to a second endpoint ( 2 ) at a time s r ;

receiving (S 2 ) the response time request packet at said second endpoint ( 2 ) at a time r r ;

sending (S4) a response time indication packet from said second endpoint ( 2 ) to said first endpoint ( 1 ) at a time s i ;

receiving (S5) the response time indication packet at said first endpoint ( 1 ) receiving at a time r i ; and

computing (S 6 ) the response time (ρ) on the basis of the sending and receiving times in said first endpoint ( 1 ); and

using the response time as a parameter in the adaptation algorithms,

wherein the response time request packet sent from said first endpoint ( 1 ) includes information identifying one of the packets which has been sent at a time s′ by said second endpoint ( 2 ) and received at a time r′ by said first endpoint ( 1 ) since its latest adaptation, and wherein the response time indication packet sent from said second endpoint ( 2 ) includes information identifying one of the rackets which has been sent at a time s by said first endpoint ( 1 ) and received at a time r by said second endpoint ( 2 ) since its latest adaptation, and

wherein s′−s i is computed in said second endpoint ( 2 ) (S 3 ) and the result is indicated in the response time indication packet.

5. The method according to claim 4 , wherein in said calculating step the response time (ρ) is calculated according to the following expression:

ρ=( r−r r )+( s−s r )−( r′−r i )+( s′−s i )+( T r +T i )+ D E +D P +D′ E +D′ P

wherein

D E and D+ E are encoding delays of the first and second endpoints, respectively,

D′ p and D p are adaptation playout delays of the first and second endpoints, respectively, and

T r =r r −s r and T i =r−s i , and

wherein

the quantities of D E , D′ p , T r +T i , r′−r 1 and s−s r are known or can be computed in said first endpoint ( 1 ) and the quantities of D′ E , D p , r−r r and s′−s i are indicated in the response time indication packet.