Testing Echo Cancellers

GL's Manual Test Suite for testing compliance of ECs with G.168 provides the ultimate flexibility for almost any type of network environment and configuration including :

• Conventional Telephone Networks
• Networks With Satellite Connectivity
• Wireless Networks such as Cellular and PCS

The system uses two of GL's T1 or E1 Cards (Dual HD Cards, USB cards, and Universal cards). One Card emulates the Far End circuit, provides the stimulus to the Echo Canceller, and captures its response. The second Card emulates the Near End circuit, i.e. models the echo path, and injects noise and voice signals. This PC based system also controls the Echo Canceller modes (NLP on/off, freeze, disable, etc.) and provides a captured PCM stream for analysis.

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Main Features

• Far End emulation is performed with GL's GUI-based File Playback and File Record Software (part # XX020)
• Near End emulation of hybrids by using GL's GUI based Delay/Attenuate Software (part # XX062)
• Echo canceller control using standard terminal emulation software, e.g. Hyperterminal
• Millisecond-level visibility and Analysis using GL's GLCView software
• Additional analysis capability using Syntrillium's Adobe Audition Software or Goldwave Software
• All T1 E1 framing formats, signaling modes, and receiver interface strategies supported
• Complete set of G.168 echo path models for emulation of Near End echo paths
• G.168 CSS Single- and Double-Talk files recorded at various power levels
• Detailed procedures for conducting G.168 compliance tests and analyzing results
• VF Input and Output available at telephone handset for subjective evaluation of echo canceller performance
• GL's family of T1 E1 cards and its T1 E1 Analyzer GUI Software and Windows Client Server Software are general-purpose products supporting a wide range of T1 E1 testing requirements

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Delay/Attenuate Software Supports Hybrid Simulation

This application allows you to apply delay, attenuation, and/or filtering to a received signal on any number of timeslots. You may also mix in additional signals from a number of sources, including

• Speech and/or Noise signals from files
• Speech signals inserted via VF input
• Gaussian noise signals generated internally

Transmitted signaling bits may be Onhook/Offhook, user-specified, or passed through from received to transmitted timeslots. Below the Delay/Attenuate Timeslots screen.

For more information, visit GUI Based Echo Canceller Testing

The Delay/Attenuate Timeslots application may receive and transmit on either one or two boards. While there are a number of different operating configurations, the most common and useful are:

• Looping back a processed signal- Applying delay, attenuation, and filtering to a received signal and retransmitting the processed signal on the same board on which it was received. Speech and/or noise may also be mixed in.

Note that the layout of the Delay/Attenuate Timeslots Dialog closely matched this diagram

• Applying pure delay to a signal- A received signal is delayed before being retransmitted
• Inserting a Simulated Echo Loop- A two-board system is inserted into a T1 or E1 trunk and is used to simulate an echo path having known characteristics

The layout of the Delay/Attenuate Timeslots application has been designed to closely resemble the above block diagrams.

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Total Visibility and Analysis with GLCView

GLCView is a GL Software tool developed especially for G.168 testing. Among this product's features:

• Displays files captured during G.168 testing
• Linear and Power displays shown
• Zoom in on power window down to millisecond-level time scale
• User-settable power calculation window from 1 ms to 35 ms
• Multiple files viewable in single window
• Print out graphs

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Supported G.165 and G.168 Tests

Tests		G.165	G.168
Test 1: Steady state residual and returned echo level test (G.168 version 04/2000 only)	NLP On NLP Off	Yes Yes	Yes Yes
Test 2: Convergence test	Test 2A: NLP On Test 2A Part b (G.168 version 01/2007): Re-convergence with NLP On Test 2B: NLP Off Test 2B Part b (G.168 version 01/2007): Re-convergence with NLP Off Test 2C with NLP On: Convergence test in presence of background noise Test 2C with NLP off: Convergence test in presence of background noise Test 2C-c (G.168 version 01/2007) for noise level -55 dBmO: Convergence test with NLP Off and background noise	No No Yes No No No No	Yes Yes Yes Yes Yes Yes Yes
Test 3: Double talk test	Test 3A: low cancelled-end level Test 3B: high cancelled-end level Test 3B Part b (G.168 version 01/2007): stability test with low cancelled-end levels Test 3C: simulated conversation	Yes Yes No No	Yes Yes Yes Yes
Test 4: Leak rate test		Yes	Yes
Test 5: Infinite return loss convergence test		Yes	Yes
Test 6: Non-Divergence on narrow-band signal test		Optional	Yes
Test 7: Stability test		Optional	Yes
Test 8: Overload test		Yes	No
Test 8: Non-convergence of EC on SS5/SS6/SS7 tones in-band signaling and continuity check tones		No	Yes
Test 9: Comfort noise test		Yes	Yes
Test 10: Facsimile test	Test 10A (with NLP On and NLP Off): Canceller operation on the calling station side Test 10B (with NLP On and NLP Off): Canceller operation on the called station side	No No	Yes Yes
Test 12: Residual acoustic echo test		No	Yes
Test 13: Performance with ITU-T low-bit rate coders in echo path		No	Yes
Test 14: Low speed modem test		No	Yes
Test 15: DC Off sets	Test 15A: Test 15B:	No No	Yes Yes
Test 16: DTMF tests	Test 16A: DTMF transparency in the presence of a dial tone Test 16B: DTMF transparency in the presence of speech	No No	Yes Yes

Note: The G.165 and G.168 Tests differ in the time to perform the tests. For example, Test 1 steady state residual test requires 180 seconds in G.168, but it does not specify the exact time in G.165. With small modifications of the test procedures (mainly the times), we can use the G.168 test procedures to perform the G.165 tests. As per the customer's requirement the manual test procedures can be modified. Contact GL for further details

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Resource:

Please Note1: The XX in the Item No. refers to the hardware platform, listed at the bottom of the Buyer's Guide, which the software will be running on. Therefore, XX can either be ETA or EEA (Octal/Quad Boards), PTA or PEA (tProbe Units), XUT or XUE (Dual PCIe Express) depending upon the hardware.

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