Knowledge base
The technical guides from our editorial library, kept together here: sizing a PBX by SIP trunks, choosing between trunks and analog lines, designing an IVR call flow, codecs, NAT and remote extensions, fax over IP, wireless endpoints, paging zones and PoE planning. These are the same articles that appear on the blog — the knowledge base is not a second body of writing, it is the engineering half of the same library. The site-type guides (hotels and healthcare) stay on the blog.
Where to start
Three guides in the order a project actually moves — decide the size, then the lines, then the cabling. Each one is a full article on the blog.
- 01
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.
9 min read - 02
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.
8 min read - 03
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.
8 min read
By theme
The same 12 engineering guides grouped by what you are trying to decide.
Choosing the system and sizing it
Extension, trunk and call counts, and the difference between an IP PBX, an EPABX and a PABX.
- IP PBX, EPABX and PABX: the three terms explainedThree 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.IP PBX sizing · 8 min read
- FXS, FXO and VoIP gateways: which one you needTwo 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.Trunks and lines · 9 min read
- SIP trunks vs analog lines: what changes on siteCabling, 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.Trunks and lines · 8 min read
- Sizing an IP PBX: trunks, extensions, callsThe 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.IP PBX sizing · 9 min read
Call handling, voice and fax
Dial plans, IVR and auto attendant design, codecs, and keeping fax working over IP.
- Fax over IP: T.38 against G.711 pass-throughWhy 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.Fax · 8 min read
- Codecs explained: G.711, G.729, G.722 and G.722.2What 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.Voice engineering · 8 min read
- Auto attendant and multi-level IVR: the call flowPrompts, 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.Call flows · 9 min read
Network and endpoints
Remote extensions through NAT, and choosing between DECT, Wi-Fi handsets and desk phones.
- NAT, STUN and remote SIP extensionsWhat 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.Networking · 8 min read
- DECT, Wi-Fi or desk phones: choosing an endpointCoverage, capacity and battery figures for the three endpoint families, plus the cases where a fixed desk phone beats anything portable.Wireless and endpoints · 9 min read
Wiring, power and paging
PoE budgets, running phones over existing cable, and IP public address zoning.
- PoE planning for a floor of SIP phonesWhich models state PoE and which do not, where the published consumption figures sit, how to size the switch, and why port speed matters too.Cabling and power · 8 min read
- IP public address: zones and priorityHow 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.Public address · 10 min read
- IP phones over two-core cable: the retrofitA converter or a switch puts network and power onto the pair already in the wall. The published distances that rule options in and out.Cabling and power · 9 min read
Blog
Blog
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: Last updated: