CCNA Voice Summary – Part 2

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Analog Connectivity

Analog transmission – using some property of the transmission media to convey a signal. As you speak into an analog phone, the voice is converted into electricity. Analog transmission uses the properties of electricity to transmit signals.

 Analog signaling:

Loop start.

The phone has 2 connections – tip and ring. When the phone is off hook, the loop is connected and the signal passes through the circuit. Suitable for home use. When we have higher call volumes, this signaling would lead to glare. Glare – when you pick up the phone and you are bridged to the wrong incoming call.

Ground start

When the receiver is off hook, the phone shoots a ground signal grounds the ring wire temporarily hence receives a dial tone. Usually used for businesses.

 

Signaling types – supervisor signaling, informational and address signaling.

Supervisor signaling: used to send on hook, off hook and ringing. Ringing is sent using AC current instead of DC. DC current usually has to be looped back to the sending end. The AC does not require it to send back a signal.

Informational signaling – conveys information while you are on the phone. It is used to send dial tone, busy, ring back, congestion, reorder, receiver off hook, no such number and confirmation. These are electric signals that are being sent.

Address signaling – signals dialed digits. Types of Analog signaling – Pulse and DTMF Dual Tone Multi frequency.

Pulse –

DTMF – Each digit on the phone is assigned 2 frequencies to distinguish between the two.

Analog Voice Circuits

FXS – Foreign Exchange Station: Uses 2 wires (tip and ring) in an RJ-11 Port. Connects to the analog phones, Fax and FXO port. Provides power for the analog device and -48 V for ringing, voice progress tones and dial tone.

FXO – Foreign Exchange Office: Uses 2 wires (tip and ring) in an RJ-11 Port. Connects to the CO. Provides supervised disconnect and supports caller Id.

E&M (Earth and Magnet / Ear and Mouth): Uses 4 wires (the middle 2 are tip and ring, the outer ones are E&M that use out of band signaling). Connects to Tie line to PBX, Paging and MoH source.

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