Upgrading a Legacy PBX System to Voice over

Upgrading a Legacy PBX System to Voice over Internet Protocol (Vo. IP) By: Candice Dick

What is a PBX System? • Acronym for Private Branch Exchange. • It is a private telephone network used for managing calls internally ( within the company) and externally for an organization( routing to a Public Switched Telephone Network - PSTN). • PSTN is the circuit-switched network operated by the Telecommunication Carrier where voice calls are transmitted. • There are 4 types of endpoints/phones on a PBX – Analog, Digital, Voice over IP (Vo. IP) and Session Initiation Protocol (SIP).

The 4 Types of PBX Systems • On-Premise Traditional PBX – located at the business, uses analog/digital systems. • Hosted Traditional PBX – located off-site, uses analog/digital systems. • On-Premise IP PBX – located at the business, uses IP communications. • Hosted IP PBX – located off-site, uses IP communications.

Legacy/Traditional PBX System (Internal) OFFICE Legacy PBX BOX RJ 11 Ext 2052 RJ 11 Ext 2050 RJ 11 Ext 2051 Routes Call Accordingly RJ 11 Ext 2058 Ø Phone with extension, calls another phone with extension within the organization.

Legacy/Traditional PBX System (Internal to External) OFFICE RJ 11 Ext 2052 Legacy PBX BOX External Phone Public Switched Telephone Network (PSTN) 4 Analog Phone Lines PSTN lines Ø Phone with extension, calls phone outside of the organization. RJ 11 Ext 2050 RJ 11 Ext 2051 Sends call from Ext through an Available Line RJ 11 Ext 2058

Legacy/Traditional PBX System (External to Internal) OFFICE Dials Pilot Number e. g. 663 -GATE RJ 11 Legacy PBX BOX External Phone Public Switched Telephone Network (PSTN) 4 Analog Phone Lines PSTN lines Ø Phone outside of the organization, calls phone within the organization. Ext 2052 RJ 11 Ext 2050 RJ 11 Ext 2051 Sends call through Available Line RJ 11 Ext 2058

Migration Process (Legacy PBX to Vo. IP) • Add an IP-PBX (connect to Legacy PBX , LAN and PSTN) and IP-phones to the existing network. • Link Channel Bank to IP-PBX as internal capacity may be reached to connect more Analog phones. • Eliminate Legacy PBX and let IP-PBX takes full control.

High Level Diagram of a Vo. IP System

SIP Call Flow for a Successful Call Ø A sends INVITE request to B. Ø B acknowledges request and responds to A. Ø A is satisfied and awaits for B to jump into the media. Ø B then alerts A that the call is RINGING. Ø B answers and the OK message goes to A. Ø A lets B know that it is ready to send Media. Ø Both User Agents are in conversation (RTK packets flows). Ø A requests to hang up by sending BYE request. Ø B acknowledges BYE request and session is terminated.

Session Initiation Protocol (SIP) • SIP is a protocol in Vo. IP communications used to make video and voice calls. • Vo. IP is the transmission of Voice and Multimedia over an IP network. • A SIP call is made by sending messages over the internet between endpoints known as SIP addresses. • SIP Troubleshooting Tools: Wireshark (packet analyser), SNGREP (displays SIP call messages flow).