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

This chapter explored analog signaling technologies, such as loop-start, ground-start, and various E&M signaling approaches. Additionally, this chapter described digital signaling approaches, including CAS (channel associated signaling) and CCS (common channel signaling).

Conversion between analog and digital waveforms involves the process of sampling the original voice wave and converting that sample into a binary value. The Nyquist Theorem specifies the number of samples per second to take from an analog waveform. Specifically, the Nyquist Theorem states that samples should be taken at a rate that equals twice the highest frequency being sampled. For example, if the highest frequency being sampled is 4000 Hz (as it is in the VoIP world), 8000 samples (that is, 2 * 4000) should be taken per second.

Finally, this chapter considered the challenges associated with sending fax and modem transmissions over a network using compression technology (for example, the G.729 CODEC). Approaches for sending fax tones over the IP WAN included Cisco fax relay, T.38 fax relay, T.37 fax store and forward, and fax pass-through. Solutions for modem transmission included modem pass-through and modem relay.