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Notes from planning and configuring IP telephony systems — sizing by SIP trunks, line selection, cabling, codecs and the tests before handover.

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GA10 ATA gateway with an FXS port for connecting an analog phone or fax machine

All articles

Fax1
Cabling and power2
Networking1
Deployment2
Public address1
Healthcare4
Voice engineering1
Wireless and endpoints1
IP PBX sizing2
Call flows1
Trunks and lines2
Intercom3
Hotels3

Fax

Fax over IP: T.38 against G.711 pass-through

Why fax fails on a working voice call, which of the two modes fits which line, the speed defaults that matter, and how to number the fax extension.

NEXVIA Engineering5 August 20268 min read

Office workstation with a desk phone in place on the desk

Cabling and power

PoE planning for a floor of SIP phones

Which models state PoE and which do not, where the published consumption figures sit, how to size the switch, and why port speed matters too.

NEXVIA Engineering15 July 20268 min read

Remote worker using a headset and a softphone away from the office

Networking

NAT, STUN and remote SIP extensions

What breaks when a phone or the PBX sits behind NAT, the punch-through and port-mapping routes, and the two headers that fix one-way audio.

NEXVIA Engineering1 July 20268 min read

Dispatch desk with consoles and screens used during commissioning and handover

Deployment

From enquiry to acceptance: how a project runs

The five answers an enquiry needs, the design pack that turns them into a bill of materials, and the commissioning tests that decide acceptance.

NEXVIA Engineering23 June 202610 min read

Public address

IP public address: zones and priority

How a zone works on a SIP public-address system, how priority is decided, which speaker suits which space, and how legacy speaker lines cross over.

NEXVIA Engineering17 June 202610 min read

KT31 wired bathroom emergency pull cord with a 2 m cord

Healthcare

Wired or wireless nurse call: the trade-off

A 2 m pull cord, a 6 to 25 m radio link, an IP65 button with a battery and an IP44 button with none. How to decide per position instead of per building.

NEXVIA Engineering9 June 20269 min read

X6U desk phone with a 4.3-inch main screen and two side screens

Voice engineering

Codecs explained: G.711, G.729, G.722 and G.722.2

What each codec on the PBX media page is for, where wideband helps, why recording supports only two of them, and the voicemail file names that follow.

NEXVIA Engineering3 June 20268 min read

OM80E IP PBX with three interface board slots for analog lines

Deployment

Migrating from an older PBX to IP: a phased cutover

The inventory that decides the migration, the numbering decision, the line strategy that keeps calls flowing, and five cutover phases with rollback.

NEXVIA Engineering26 May 202610 min read

W610D portable IP DECT handset with a 2-inch colour screen and belt clip

Wireless and endpoints

DECT, Wi-Fi or desk phones: choosing an endpoint

Coverage, capacity and battery figures for the three endpoint families, plus the cases where a fixed desk phone beats anything portable.

NEXVIA Engineering20 May 20269 min read

OM series IP PBX wiring topology: uplink, PSTN lines, analog phones and grounding

IP PBX sizing

IP PBX, EPABX and PABX: the three terms explained

Three names for one function, and one is regional. What a modern private exchange publishes, how the old expectations map onto it, and what to brief.

NEXVIA Engineering12 May 20268 min read

Multi-level IVR flow diagram: a first-level menu leading to product ordering and technical support options

Call flows

Auto attendant and multi-level IVR: the call flow

Prompts, levels, time-of-day routing and the queue behind the operator position: how to lay out an IVR and what to test before the number goes live.

NEXVIA Engineering6 May 20269 min read

GA10 ATA gateway with one FXS port and status indicator LEDs

Trunks and lines

FXS, FXO and VoIP gateways: which one you need

Two port names, two opposite directions. How to read a site device by device, when analog ports belong on the PBX and when a small gateway is cheaper.

NEXVIA Engineering28 April 20269 min read

Care workflow with a call raised at the bedside and answered at the nurse station

Healthcare

Nurse call for a ward: positions and escalation

A ward design method that starts from positions rather than devices: bedside and door-side stations, pull cords, corridor lights and the escalation path.

NEXVIA Engineering22 April 202610 min read

Two-wire topology: a converter placing network and power onto an existing two-core cable run

Cabling and power

IP phones over two-core cable: the retrofit

A converter or a switch puts network and power onto the pair already in the wall. The published distances that rule options in and out.

NEXVIA Engineering14 April 20269 min read

OM50G rear panel showing the analog extension and line ports, PC and WAN ports, USB and console connectors

Trunks and lines

SIP trunks vs analog lines: what changes on site

Cabling, failover and debugging all differ between a SIP trunk and an FXO line. A side-by-side comparison, plus the escape route that keeps calls flowing.

NEXVIA Engineering8 April 20268 min read

i67 face recognition door phone with a touchscreen and numeric keypad

Intercom

Door intercom to door release: relays and fail-safe

What actually opens the door, what a built-in relay can and cannot tell you, fail-safe against fail-secure, and the tests to run before handover.

NEXVIA Engineering31 March 20269 min read

H603W cordless hotel phone with three-colour status indicator and charging base

Hotels

Hotel phone systems: wake-up calls and the PMS

What a hotel PBX has to do beyond dialling: service keys on the room phone, wake-up prompts, room status in the PMS and call permission by room class.

NEXVIA Engineering26 March 20269 min read

PN1 2-wire converter, used to carry network and power over existing two-core cable

Intercom

Elevator intercom: travel cable and power

An elevator intercom is a chain, not a device. Which positions the material names, why the travelling cable decides the design, and what to survey.

NEXVIA Engineering17 March 20269 min read

OM series IP PBX wiring topology: uplink to the internet, PSTN lines, analog phones and grounding

IP PBX sizing

Sizing an IP PBX: trunks, extensions, calls

The manual publishes trunks, not extensions. How to turn a headcount and a busy hour into a model number, with the full ladder of five models.

NEXVIA Engineering12 March 20269 min read

Intercom

Adding office intercom to an existing phone system

Door stations and paging speakers are more SIP extensions, not a second system. Four capacity checks, the power question at the door, and a phased way in.

NEXVIA Engineering3 March 20269 min read

KT30 wireless bathroom pull-cord button with a mounting plate

Healthcare

Care home device ratios: call points per bed

Bedside station, pull cord, corridor light, portable handset: four ratios, four denominators, and the two printed plans that show how they diverge.

NEXVIA Engineering18 February 20269 min read

A320i nurse console with a 10.1-inch touch screen and gooseneck microphone

Healthcare

Hospital phone system compliance checklist

What the product documentation states, what it does not record, and the questions your compliance officer must answer against local code.

NEXVIA Engineering4 February 20269 min read

OM200G IP PBX with four interface card slots for analog ports

Hotels

100-room hotel phone system: the checklist

Room phones, second positions, staff desks, the analog ports a hotel always uses and the switches that power them - a 100-room list from published capacities.

NEXVIA Engineering21 January 20269 min read

H6W hotel room phone with a 3.5-inch colour screen and five programmable service keys

Hotels

How many lines does a guest phone need?

Every guest handset in this range that states a line count states two. What that second line is for, when one number is enough, and where a position needs four.

NEXVIA Engineering14 January 20268 min read

What topics does the blog cover?

Fax · Cabling and power · Networking · Deployment · Public address · Healthcare · Voice engineering · Wireless and endpoints · IP PBX sizing · Call flows · Trunks and lines · Intercom · Hotels

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Notes from planning and configuring IP telephony systems — sizing by SIP trunks, line selection, cabling, codecs and the tests before handover.

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Page author: NEXVIA EngineeringPublished: 2026-09-29Last updated: 2026-10-13

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