CCNA Voice Summary – Part 1

Introduction to VoIP

Why Use VOIP

Cost Savings: reduced wiring – one single cable for both phone and computer; reduced telecommuter costs since they connect to the HQ via internet; Free long distance between branches and HQ; Single inbox for voicemail, fax and email using unity connection; Saves office space using extension mobility; Open architecture – the use of standard compliant protocols.

Why Use WAN connection over PSTN Connection: Bandwidth compression over WAN; Free long distance; Get rid of the tie lies- get rid of the monthly cost.

How to Move to VOIP

New companies start VoIP systems from scratch. Older companies go in 2 phases: Phase 1 – Keep the old internal network but re-equip the voice gateways that will connect to the WAN and the PSTN; Phase 2 – Get rid of all the PBX systems and use end to end VoIP.

Traditional PBX (Post Branch Exchange)

This was a way of privatizing a company from the Central Office. It emulates the Central Office. It is divided into 2 sides: The Line/ Station side connects to the phones; The Trunk side connects to the Local PSTN, Central office or another PBX through tie-trunks. Everything in a PBX flows through a Time Division Multiplexing- TDM backplane. This causes a blocked architecture in PBXs whereby we cannot have all the phones in a large PBX site talking at the same time since there isn’t enough bandwidth.

Disadvantages of PBX Architecture

• Dedicated separate lines for voice in PBX.
• TDM Backplane caused congestion at peaks hours
• Not enough channels for all phones attached to make a call.