This revised version of ITU-T Recommendation G.168 covers the design and testing of digital network echo cancellers for use in circuits where the delay exceeds the limits specified by ITU-T Recommendation G.114 [1] and G.131 [3]. This revision improves the testing methodology and better defines the performance requirements. Many of the tests have been updated and improved. Annex D has been added on realistic echo-path models that are used in the testing of echo cancellers, and Appendix II has been added on the measurement methods for characteristics of echo paths.