One-way delay measurement in a packet-switched communication network

1 . A method for transmitting a bidirectional packet flow carrying live traffic exchanged between a first node and a second node of a packet-switched communication network, said method comprising:

a) at respective predefined time intervals, by said first node, transmitting to said second node a first marked packet of said bidirectional packet flow, and by said second node, transmitting to said first node a second marked packet of said bidirectional packet flow; and

b) during the predefined time intervals, by said first node, transmitting to said second node unmarked packets of said bidirectional packet flow until said second marked packet is received by said first node from said second node and, in response to receiving the second marked packet, transmitting to said second node a third marked packet of said bidirectional packet flow, wherein

a) and b) are repeated cyclically until end of measurement session, and

the first, second, and third marked packets are different for each cyclic repetition of a) and b).

2 . The method according to claim 1 , further comprising:

b′) by said second node, transmitting to said first node unmarked packets of said bidirectional packet flow until said first marked packet is received by said second node from said first node and, in response to receiving the first marked packet, transmitting to said first node a fourth marked packet of said bidirectional packet flow.

3 . The method according to claim 2 , further comprising:

c) by said first node, transmitting to said second node unmarked packets of said bidirectional packet flow until said fourth marked packet is received by said first node from said second node and, in response to receiving the fourth marked packet, transmitting to said second node a fifth marked packet of said bidirectional packet flow.

4 . The method according to claim 2 , wherein a), b), and b′) are repeated cyclically.

5 . The method according to claim 1 , wherein said respective predefined time intervals are substantially a same predefined time interval.

6 . The method according to claim 5 , wherein said first node and said second node comprise reciprocally synchronized local clocks, and wherein a) is started when said local clocks indicate a time n×T0, n being an integer index and T0 being a predefined period.

7 . The method according to claim 6 , wherein said predefined period T0 is higher than a maximum round-trip time plus a maximum one-way delay between said first node and said second node.

8 . The method according to claim 7 , wherein said predefined period T0 is set higher than 3 times a calculated round-trip time between said first node and said second node.

9 . The method according to claim 1 , wherein said first marked packet and said third marked packet comprise different marking values.

10 . A method for performing a one-way delay measurement on a bidirectional packet flow carrying live traffic exchanged between a first node and a second node of a packet-switched communication network, said method comprising the method according to claim 1 , and:

d) by a measurement point placed on a path of said bidirectional packet flow, detecting said first marked packet and said third marked packet, and providing said one-way delay measurement based on a detection time of said first marked packet and/or a detection time of said third marked packet.

11 . The method according to claim 10 , wherein d) comprises providing a one-way delay measurement from said second node to said first node as a time lapsing between detection of said first marked packet and detection of said third marked packet.

12 . The method according to claim 10 , wherein said measurement point is synchronized with said first node, and wherein d) comprises providing a one-way delay measurement from said first node to said measurement point as a time lapsing between transmission of said first marked packet and detection of said first marked packet.

13 . The method according to claim 10 , wherein d) further comprises providing a round-trip time measurement between said first node and said second node as a time lapsing between detection of said first marked packet and detection of another marked packet.

14 . The method according to claim 10 , wherein d) further comprises providing a one-way delay measurement from said first node to said second node as a time lapsing between detection of said second marked packet and detection of another marked packet.

15 . The method according to claim 1 , wherein

said first node and said second node comprise reciprocally synchronized local clocks,

a) is started when said local clocks indicate a time n×T0, n being an integer index and T0 being a predefined period,

said predefined period T0 is higher than a maximum round-trip time plus a maximum one-way delay between said first node and said second node, and

said predefined period T0 is set higher than 3 times a calculated round-trip time between said first node and said second node.

16 . The method according to claim 1 , further comprising

c) by said first node, transmitting to said second node unmarked packets of said bidirectional packet flow until a fourth marked packet is received by said first node from said second node and, in response to receiving the fourth marked packet, transmitting to said second node a fifth marked packet of said bidirectional packet flow, wherein

a), b), and c) are repeated cyclically.

17 . A node for a packet-switched communication network, said node being configured to exchange a bidirectional packet flow carrying live traffic with a further node of said packet-switched communication network, said node comprising:

processing circuitry configured to

a) at a predefined time interval, transmit to said further node a first marked packet of said bidirectional packet flow, and

b) during the predefined time interval, transmit to said further node unmarked packets of said bidirectional packet flow until a second marked packet of said bidirectional packet flow is received by said node from said further node and, in response to receiving the second marked packet, transmit to said further node a third marked packet of said bidirectional packet flow, wherein

the processing circuity is configured to repeat a) and b) cyclically until end of measurement session, and

the first, second, and third marked packets are different for each cyclic repetition of a) and b).

18 . A packet-switched communication network comprising:

a first node; and

a second node, the first node and the second node exchanging a bidirectional packet flow carrying live traffic, wherein:

a) said first node is configured to, at a first predefined time during a time period, transmit to said second node a first marked packet of said bidirectional packet flow, and said second node is configured to, at a second predefined time during the time period, transmit to said first node a second marked packet of said bidirectional packet flow; and

b) said first node is further configured to, during the time period, transmit to said second node unmarked packets of said bidirectional packet flow until said second marked packet is received by said first node from said second node and, in response to receiving the second marked packet, transmit to said second node a third marked packet of said bidirectional packet flow, wherein

a) and b) are repeated cyclically until end of measurement session, and

the first, second, and third marked packets are different for each cyclic repetition of a) and b).

19 . The packet-switched communication network according to claim 18 , further comprising a measurement point placed on a path of said bidirectional packet flow, said measurement point being configured to detect said first marked packet and said third marked packet, and provide a one-way delay measurement based on a detection time of said first marked packet and/or a detection time of said third marked packet.