I try to know what is debug use for ? Is it relate to voice or
application ? Thanks all.
Cookie debugging is on
Chapter 1, "Using Debug Commands," explains how you enter debug commands, use the debug ? and debug all commands, and generate and redirect debug command output. Read this chapter first before proceeding to Chapter 3, "Debug Commands."
Chapter 2, "Conditionally Triggered Debugging," describes how you can enable a router to generate debugging messages for packets entering or leaving the router on a specified interface; by default, debugging is enabled on all interfaces.
Chapter 3, "Debug Commands," presents reference information on commands you use to debug your internetwork. The chapter includes command function descriptions, sample output displays, and explanations of these displays.
Appendix A, "X.25 Cause and Diagnostic Codes," lists the codes that can appear in output from the debug x25 all, debug x25 events, and debug x25 vc commands.
Appendix B, "ISDN Switch Types, Codes, and Values," lists the supported ISDN switch types. It also contains the ISDN cause codes, cause values, bearer capability values, and progress values that can appear in output from the debug isdn q921, debug isdn q931, and debug isdn event commands.