Cisco Voice over IP (CVoice) (Authorized Self-Study Guide) (2nd Edition)

This chapter discussed the configuration of various analog and digital voice ports. For example, analog voice ports, such as FXS and FXO ports, need an appropriate signaling type (that is, loop-start or ground-start) to communicate with attached equipment. E&M port configurations also need to match the configurations of the equipment connecting to the E&M ports (for example, a PBX E&M interface). This chapter also reviewed various analog port timing parameters.

Digital port configuration included parameters such as line coding and framing. Additionally, this chapter introduced how DS-0 groups logically combine multiple channels in a digital circuit (for example, a T1), thus reducing the number of required configuration steps. Several show, debug, and test commands assist in the monitoring and troubleshooting of voice ports.

Echo often causes significant quality issues in VoIP networks. Typically, echo results from an impedance mismatch in a two-wire to four-wire hybrid circuit. Fortunately, Cisco voice-enabled routers combat echo via echo suppression and echo cancellation technologies. This chapter explored the commands used to influence the effect of echo on voice calls.