Method and apparatus for measuring voice grade of service in an IP network

• US 6,512,746 B1
• Filed: 09/11/1998
• Issued: 01/28/2003
• Est. Priority Date: 09/11/1998
• Status: Expired due to Term

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Sand, Israel Elchonin
• Primary Examiner(s): Yao, Kwang Bin
• Application Number:
  US09/151,448
• Time in Patent Office: 1,600 Days
• Field of Search: 370/229,230,230.1,231,232,235,236,395.2,395.21,395.52,241,250,252,253,352,353
• US Class Current: 370/252
• CPC Class Codes: H04L 41/147 for predicting network behaviour
• CPC Class Codes: H04L 41/5003 Managing SLA; Interaction between SLA and QoS
• CPC Class Codes: H04L 41/5009 Determining service level performance parameters or violations of service level contracts, e.g. violations of agreed response time or mean time between failures [MTBF]
• CPC Class Codes: H04L 41/5067 Customer-centric QoS measurements
• CPC Class Codes: H04L 41/5087 wherein the managed service relates to voice services management of VoIP services H04M7/0081
• CPC Class Codes: H04L 43/00 Arrangements for monitoring or testing data switching networks
• CPC Class Codes: H04L 43/0829 Packet loss
• CPC Class Codes: H04L 43/0852 Delays
• CPC Class Codes: H04L 43/087 Jitter
• CPC Class Codes: H04L 43/106 using time related information in packets, e.g. by adding timestamps

Abstract

A method for use of IN-service Non-intrusive measuring Device (INMD) for proving Service Level Agreements (SLAs) and pro-active maintenance in IP telephony networks is described. The INMD is currently used only in connection oriented TDM telephony networks and therefore cannot be used directly in the connectionless-featured IP telephony networks. The method for use of INMD to measure voice transmission quality in IP telephony networks include a set of pre-processes for processing IP voice datagrams, and converting the pre-processed datagrams to a format suitable for INMD before the INMD evaluates data in the datagrams for voice GOS. Various tests and co-processes are also used to determine network performance parameters. An IP telephony measurement apparatus for practicing the method is also described. A method for calibrating the device and algorithms is also provided to ensure a high level of confidence in the measurement accuracy.

Claims

1. A method for using In-service Non-intrusive Measuring Devices (INMD) for assessment of transmission quality in Internet Protocol (IP) telephony networks comprising the steps of:

1) collecting a group of IP datagrams associated with a speech sample of an end-to-end IP telephony session from at least one IP interface point by identifying a packet flow associated with the IP telephony session;

2) processing the IP datagrams and converting the datagrams into a format suitable for INMD processing;

3) using an INMD process to assess a plurality of voice grade performance parameters related to the IP telephony session.

2. A method as claimed in claim 1 wherein the step of using the INMD process to assess the voice grade performance includes a step of computing a voice Grad Of Service (GOS) performance using a method specified in ATSI T1 LB 566.

3. A method as claimed in claim 2 further comprising a step of:

4) calculating a percent Good or Better (%GOB) score relevant to the voice GOS performance.

4. A method as claimed in claim 3 further comprising a step of:

5) correlating the voice GOS performance to performance of the IP telephony network.

5. A method as claimed in claim 1 wherein the IP datagrams collected in step 1 comprise H.323 frames encapsulated in Realtime Transport Protocol (RTP), encapsulated in User Datagram Protocol (UDP), encapsulated in the IP datagram.

6. A method as claimed in claim 1 wherein step 1 further comprises a step of smoothing out any delay variation in the speech sample using header information in the IP datagrams.

7. A method as claimed in claim 1 wherein step 1 further comprises a step of computing a group of network performance parameters using header information in the IP datagrams.

8. A method as claimed in claim 1 wherein step 2 further comprises a step of determining a speech compression algorithm used in the IP datagrams by examining data encapsulated in the packets.

9. A method as claimed in claim 1 wherein the step of collecting the IP datagrams of the speech sample is performed respectively at a far end IP interface point and a near end IP interface point.

10. A method as claimed in claim 9 wherein the step of using the INMD to assess the converted IP datagrams collected from the far end IP interface point further comprises a step of computing voice grade performance parameters related to speech level and noise, and the step of using the INMD to access the converted IP datagrams collected from the near end IP interface point further comprises a step of computing voice grade performance parameters relating to echo path delay and loss.

11. A method as claimed in claim 4 wherein step 5 further comprises:

tabulating a plurality of performance data for the measured end-to-end IP telephony connection as identified by a pair of source/destination addresses, the data including analogue voice parameters, the voice GOS and the IP network performance; and

correlating the network performance and the analogue voice parameters using the tabulated data to verify a Service Level Agreement (SLA), and for use in network maintenance.

12. A method as claimed in claim 1 wherein step 1 further comprises a step of storing IP source and destination address information associated with each IP datagram, and further comprises storing a datagram timestamp used for a post correlation analysis.

13. A method as claimed in claim 7 further comprising a step of storing a timestamp for post correlation analysis.

14. A method as claimed in claim 7 wherein the step of computing network performance parameters comprises computing delay, packet loss and delay variation using the header information, which includes a sequence number, timestamp and length information.

15. A method as claimed in claim 1 wherein step 2 further comprises a step of using an error mitigation process to remove an effect of errors and packet loss.

16. A method as claimed in claim 1 wherein step 2 further comprises a step of inserting background noise during a silent period in the end-to-end IP telephony session.

17. A method as claimed in claim 1 wherein step 3 further comprises a step of performing a process to active speech detection.

18. A method as claimed in claim 1 wherein step 3 further comprises a step of performing a co-process for tones.

19. A method as claimed in claim 1 wherein step 3 further comprises a step of performing a process for double talk detection.

20. A method as claimed in claim 1 wherein step 3 further comprises a step of performing a co-process for echo cancellation.

21. A method as claimed in claim 1 wherein step 2 comprises a step of operating a Digital Signal Processor (DSP) to process the IP datagrams.

22. A method as claimed in claim 6 wherein the step of smoothing out any delay variation comprises a step of using header information associated with the RTP protocol header.

23. A method as claimed in claim 7 wherein the step of smoothing out any delay variation comprises a step of using header information associated with the RTP protocol header.

24. An initial calibration process for calibrating an IP telephony measurement apparatus comprising the steps of:

creating an IP datagram calibration file using speech samples having a known GOS;

processing IP datagrams from the IP datagram calibration file using the IP telephony measurement apparatus to convert the IP datagrams into data in a format suitable for INMD processing;

processing the data using INMD functionality of the IP telephony measurement apparatus to determine a GOS value associated with the IP datagrams;

comparing tie GOS value with a GOS associated with the speech samples used to create the IP datagram calibration file, and

adjusting the IP telephony measurement apparatus until the GOS values are equal, within a certain predefined limit.

25. A method as claimed in claim 24 wherein the step of creating the IP datagrams comprises a step of creating the IP datagrams using an IP telephony terminal which is known to be good.

26. A method as claimed in claim 25 further comprising a step of using the IP telephony measurement apparatus in conjunction with a known speech sample having a known GOS and a related IP datagram file to calibrate both a far end and near end gateways when the IP telephony measurement apparatus is determined good.

27. A method as claimed in claim 26 further comprising a step of sending the IP datagram file to the far end gateway and looping the datagram file back using a four-wire analogue interface to return the datagram file to the measurement apparatus.

28. An apparatus for assessment of IP telephony networks transmission quality comprising:

an In-service Non-intrusive Measurement Device (INMD) processing function adapted to assess voice grade performance parameters in a connection oriented Time Division Multiplexer (TDM); and

a processor adapted to convert a group of IP datagrams associated with an end-to-end IP telephony connection to data in a data format suitable for input to the INMD processing function for assessment of the voice grade performance parameters.

29. An apparatus as claimed in claim 28 further comprising a data collector adapted to collect the IP datagrams by identifying a packet flow associated with an IF telephony session.

30. An apparatus as claimed in claim 28 wherein the INMD processing function further comprises a function for computing a voice Grade Of Service (GOS) performance specified in ATSI T1 LB 566.

31. An apparatus as claimed in claim 28 wherein the apparatus is co-located with an IP voice gateway.

32. An apparatus as claimed in claim 28 wherein the apparatus is a stand-alone device in the end-to-end IP telephony connection.

33. An apparatus as claimed in claim 30 further comprising a processor adapted to correlate the voice GOS performance to IP network performance.

34. An apparatus as claimed in claim 30 wherein the converting processor is adapted to use header information in the IP datagrams to smooth out any delay variation in a speech sample and further adapted to compute a group of network performance parameters.

35. An apparatus as claimed in claim 34 wherein the converting processor further comprises a Digital Signal Processor (DSP) to facilitate computations.

36. An apparatus as claimed in claim 28 wherein the connection is linked to a far end IP interface point and a near end IP interface point of the IP telephony session.

37. An apparatus as claimed in claim 36 wherein the INMD processing function is adapted to compute voice grade performance parameters relating to speech level and noise from the converted IP datagrams collected from the far end IP interface point and further adapted to compute voice grade performance parameters relating to echo path delay and loss from the converted IP datagrams collected from the near end IP interface point.

38. An apparatus as claimed in claim 30 wherein the INMD processing function further comprises a function adapted to calculate a percent Good Or Better (%GOB) score relevant to the voice GOS performance.

39. An apparatus as claimed in claim 34 wherein the correlating processor is adapted to tabulate a plurality of performance data for the assessed end-to-end IP telephony connection as identified by a pair of source/destination addresses, the data including analogue voice parameters, the voice GOS and the IP network performance;

and is further adapted to correlate the network performance and the analogue voice parameters using the tabulated data to verify a Service Level Agreement (SLA) and for use in network maintenance.

40. An apparatus as claimed in claim 34 wherein the converting processor is adapted to compute delay, packet loss and delay variation using header information that includes a sequence number, timestamp and packet length information.

41. An apparatus as claimed in claim 28 wherein the converting processor is adapted to conduct an error mitigation process to remove an effect of errors and packet loss.

42. An apparatus as claimed in claim 28 wherein the converting processor is further adapted to conduct a process for an insertion of background noise during a silent period during the end-to-end IP telephony connection.