Method, a Computer Program Product, and a Carrier for Indicating One-Way Latency in a Data Network

• US 20070268850A1
• Filed: 01/14/2005
• Published: 11/22/2007
• Est. Priority Date: 09/22/2004
• Status: Active Grant

• Current Assignee: Accedian Networks Inc. (Cisco Systems, Inc.)
• Original Assignee: Accedian Networks Inc. (Cisco Systems, Inc.)
• Inventors: Hansson, Kjell, Hagsand, Olof
• Granted Patent: US 8,218,576 B2
• Time in Patent Office: Days
• US Class Current: 370/315
• CPC Class Codes: G06F 1/12 Synchronisation of different clock signals provided by a plurality of clock generators
• CPC Class Codes: H04J 3/0638 Clock or time synchronisation among nodes; Internode synchronisation synchronization for ring networks H04L12/422; data switching networks with synchronous transmission H04L12/43
• CPC Class Codes: H04J 3/0667 Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays arrangements for monitoring round trip delays in packet switching networks H04L43/0864
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 2212/00 Encapsulation of packets
• CPC Class Codes: H04L 43/067 using time frame reporting
• CPC Class Codes: H04L 43/0852 Delays
• CPC Class Codes: H04L 43/0858 One way delays
• CPC Class Codes: H04L 65/65 Network streaming protocols, e.g. real-time transport protocol [RTP] or real-time control protocol [RTCP]
• CPC Class Codes: H04L 67/1095 Replication or mirroring of data, e.g. scheduling or transport for data synchronisation between network nodes
• CPC Class Codes: H04L 7/10 Arrangements for initial synchronisation

Abstract

Disclosed herein is a method, a computer program product, and a carrier for indicating one-way latency in a data network (N) between a first node (A) and a second node (B), wherein the data network (N) lacks continuous clock synchronization, comprising: a pre-synchronisation step, a measuring step, a post-synchronisation step, an interpolation step, and generating a latency profile. The present invention also relates to a computer program product incorporating the method, a carrier comprising the computer program product, and a method for indicating server functionality based on the first aspect.

Claims

1. Method for indicating one-way latency in a data network (N), without continuous clock synchronization, between a first node (A) and a second node (B), comprising:

a pre-synchronisation step,

a measuring step,

a post-synchronisation step,

an interpolation step, and

generating a latency profile.

2. Method according to claim 1, wherein the pre-synchronisation step comprises:

sending a predetermined message from the first node (A) to the second node (B), -receiving at the first node (A) a predetermined message sent by the second node (B),

calculating an offset according to ((T₂−

T₁)+(T₃−

T₄))/2,

where T₁ is the sending time from the first node (A), T₂ is the receiving time at the second node (B), T₃ is the sending time at the second node (B), and T₄ is the receiving time at the first node (A), and

setting a clock difference to the offset, and

setting an absolute clock to T₄.

3. Method according to claim 2, wherein the pre-synchronisation step comprises

sending the predetermined message N times, -receiving the predetermined message, -generating N round-trip-time items according to T_i,4−

T_i,1−

(T_i,3−

T_i,2), where i is in the interval [1 . . . N],

generating N offset items, -retrieving the minimum round-trip-time item, -setting the clock difference to the offset related to the minimum round-trip-time item, and

setting the absolute clock to T_i,4 for the i having the minimum round-trip-time item.

4. Method according to claim 1, further comprising:

measuring the overhead for making measurements at the sender.

5. Method according to claim 1, further comprising:

measuring the overhead for making measurements at the receiver.

6. Method according to claim 1, wherein the measuring step comprises:

sending a predetedetermined message from the first node (A) to the second node (B),

storing the sending time for the sending,

receiving the predetermined message at the second node (B), and

storing the receiving time for the receiving.

7. Method according to claim 6, wherein the measuring step comprises

sending a predetermined message from the first node (A) to the second node (B) N times chronologically equidistantly,

storing the sending time for each sending,

receiving the predetermined message at the second node (B), and

storing the receiving time for each receiving.

8. Method according to claim 1, wherein the post-synchronisation step comprises

sending a predetermined message from the first node (A) to the second node (B), -receiving at the first node (A) a predetermined message sent by the second node (B),

calculating an offset according to ((T₂−

T₁)+(T₃-T₄))/2,

where T₁ is the sending time from the first node (A), T₂ is the receiving time at the second node (B), T₃ is the sending time at the second node (B), and T₄ is the receiving time at the first node (A), and

setting a clock difference to the offset, and

setting an absolute clock to T₄.

9. Method according to claim 1, wherein the interpolation step comprises

calculating the one-way latency in the data network between a first node (A) and a second node (B) according to:

rate bias=(offset of the post-synchronisation step−

offset of the pre-synchronisation step)/(absolute clock for post-synchronisation step−

absolute clock for the pre-synchronisation), and latency=the time at which the second node (B) received the predetermined message−

(the time at which the first node (A) sent the predetermined message+the offset of the pre-synchronisation step+(the time at which the first node (A) sent the predetermined message−

the absolute clock of the pre-synchronisation step)).

10. Method according to claim 9, wherein the interpolation step comprises—

calculating the one-way latency in the data network (N) between a first node (A) and a second node (B) according to claim 9 for the N messages sent between the first and second nodes (A, B).

11. Method according to claim 1, further comprising:

an overhead term corresponding to the overhead for making measurements at at least one of the first and second nodes (A, B), −

calculating the one-way latency in the data network between a first node (A) and a second node (B) according to;

latency=the time at which the second node (B) received the predetermined message−

(the time at which the first node (A) sent the predetermined message+the offset of the pre-synchronisation step+ratebias(the time at which the first node (A) sent the predetermined message−

the absolute clock of the pre-synchronisation step))−

the overhead term.

12. Method according to claim 11, wherein the interpolation step comprise

calculating the one-way latency in the data network between a first node (A) and a second node (B) according to:

rate bias=(offset of the post-synchronisation step−

offset of the pre-synchronisation step)/(absolute clock for post-synchronisation step−

absolute clock for the pre-synchronisation), and latency=the time at which the second node (B) received the predetermined message−

(the time at which the first node (A) sent the predetermined message+the offset of the pre-synchronisation step+(the time at which the first node (A) sent the predetermined message−

the absolute clock of the pre-synchronisation step)), for the N messages sent between the first and second nodes (A, B).

13. A computer program product loadable into the internal memory of a computer, comprising software code portions for performing the method of claim 1, when run on a computer.

14. A carrier comprising the computer program product according to claim 13.

15. Method for indicating server functionality according to claim 1.