IP or analog telephone system

This article was machine-translated from French and is being reviewed. Prices are in Algerian dinars excl. VAT.

An IP telephone standard (IPBX) routes calls onto your IT network, most often using SIP, to IP phones, applications or gateways. An analog standard (private automatic telephone exchange, or PABX) connects analog stations to telephone lines via dedicated cards, without using an IT network. The right choice depends on the number of stations, sites, desired functions, the quality of your LAN and power supply. This guide compares the two architectures and explains when a mixed solution is most reasonable. AsloTech supplies and installs telephone standards and IPBX from Avaya, NEC and Panasonic on quote.

Architectures: fundamental differences

Analog telephone system

An analog PABX is a cabinet installed in a technical room. It has two families of ports:

• extension ports (FXS type): each powers an analog station with a pair of wires and provides line current and ringing;
• line ports (FXO type): they connect to the operator’s analog lines.

The standard lines route calls between stations, to voicemail or to the outside. Calls that go through operator lines do not depend on a server or Internet. They do, however, require mains power: without a UPS they stop when the power is cut.

Key points: simple, autonomous architecture, low maintenance, standard stations easy to replace (the shop references for example the Panasonic KX-TS500MX wired station).

Limitations :

• each workstation has its own pair from the standard (star wiring);
• expansion is done via cards or modules from the manufacturer, within the model limits;
• advanced features (call recording, mobile app, integration with business software) are limited or optional depending on the model;
• connecting multiple sites is not natural.

IP telephone system (IPBX)

An IPBX is a telephone software. It runs on a dedicated appliance, a server or virtual machine in your premises, or with a host. AsloTech supplies and installs Avaya, NEC and Panasonic IPBX. The model, licenses and sizing are determined on quote, based on the number of stations, lines and desired functions, and planned maintenance. Other families exist on the market: Asterisk (free software, often managed with FreePBX interface), 3CX (commercial software) and turnkey appliances such as Yeastar or Grandstream UCM. We mention them as comparison references, not AsloTech offers.

Workstations and the IPBX communicate in SIP (signalling: port 5060 UDP or TCP, 5061 TLS). Voice flows in RTP, on UDP ports chosen by the IPBX. Internal calls stay on the local network. Only external calls leave, via one of these means:

• a SIP trunk, if your operator offers one;
• a FXO gateway, which connects analog lines to the IPBX;
• a GSM gateway, a SIM card box that connects the IPBX to the mobile network (check with your operator that this setup is allowed by your contract);

Strengths:

• adding a workstation means pulling a network cable and creating an account on the IPBX (with a license per product);
• workstations can be PoE office phones, Wi‑Fi or DECT IP phones, or applications on PC and smartphone;
• depending on the IPBX and its licenses: voicemail sent by e‑mail, queues, conference, call recording, shared directory;
• multiple sites can share the same IPBX via a secure link (see Enterprise VPN: connect two sites securely);

Limitations :

• call quality depends on the local network: cabling, switch, voice priority configuration;
• The IPBX, PoE switch and router must be backed up by a UPS to keep the telephony during a power outage;
• a IPBX with its SIP port open to the Internet is constantly scanned by bots: without protection, it can be used to make fraudulent calls at your expense;
• The configuration (SIP, NAT, codecs, VLAN) requires network skills; otherwise, it is entrusted to a provider.

What IP telephony demands from your network

Bandwidth and codecs

The codec defines how voice is digitized. The actual call bandwidth is higher than the codec because each voice packet carries IP, UDP, RTP and Ethernet headers. The table shows bandwidth per call and direction, with one packet every 20 ms (50 packets per second).

For G.711, the calculation is: (160 bytes voice + 40 bytes IP/UDP/RTP headers + 18 bytes Ethernet) × 8 bits × 50 packets per second = 87,200 bits/s. For G.729: (20 + 40 + 18) × 8 × 50 = 31,200 bits/s. Two endpoints or an endpoint and a trunk must share at least one codec; otherwise the IPBX must transcode, consuming CPU power.

Voice priority, VLAN and PoE

• Voice VLAN: placing phones in a dedicated VLAN (802.1Q) prevents voice from sharing the same domain as computers. The guide VLAN: segment your enterprise network details the method.
• QoS: we mark RTP voice with DSCP EF (46) and SIP signaling in a separate class (CS3, for example). This marking is respected only by equipment you control; public Internet does not guarantee it.
• Target quality: we commonly recommend an end‑to‑end delay below 150 ms in one direction (ITU‑T G.114), jitter below 30 ms and less than 1 % packet loss.
• PoE: a PoE switch powers devices via the network cable. 802.3af supplies up to 15.4 W per port (12.95 W available at the device), 802.3at (PoE+) up to 30 W, 802.3bt up to 60 W (type 3) or 90 W (type 4). Cable length is limited to 100 m. The switch also has a total PoE budget in watts: add the maximum power of each device (15.4 W per device if not specified) and compare this total to the budget, not just the number of ports.
• Cabling : a Category 5e or higher copper cable is sufficient for one station. The category options are covered in Cable Cat6 or Cat6A, and the rack layout is in Network Rack: how to organize it.

Installation and operating costs

Neither architecture is inherently cheaper. Cost depends on the number of devices, sites, and desired functions. The table lists expense items without amounts: store prices for analog devices, IP devices, and a PoE switch are detailed in Price of a standard for 10 devices.

To these stations add recurring costs: operator subscriptions, IPBX licenses and updates, maintenance. The price of an Avaya, NEC or Panasonic standard depends on the model, licenses, number of stations and lines: it is given on quote. Always compare two quotes for the same scope (number of stations, lines, functions, electrical backup).

Service continuity in case of internet outage

What stops depends on where the IPBX is located. An IPBX installed in your premises keeps internal calls during an Internet outage. External calls that go through a SIP trunk stop, while those on analog lines continue. An off‑site hosted IPBX stops with Internet access. Possible protections (secondary provider, backup analog line, 4G access, UPS) are detailed in IP Telephony: what to do during a cut‑off. Power outages are a separate risk: see UPS: how to choose the power.

Hybrid: keep analog and add IP

A site can transition to IP in stages, without replacing everything:

• a FXS gateway (or an analog adapter) connects analog phones, an analog DECT base or a fax to the IPBX: one FXS port per device;
• a FXO gateway connects existing analog lines to the IPBX: one FXO port per line, thus one external call per line;
• some hybrid standards accept analog, digital and IP stations. The shop references NEC items (the CPU SL2100 card, the SIP IP license and the 8IPLD IP station), out of stock as of 06/11/2026, and Avaya IP stations (J129, J179 and J189), in stock (prices in Price of a standard for 10 stations). The sizing of such a system is done on quote;
• fax works poorly over IP: keep them on an analog line, or use G.711 codec or T.38 protocol that the gateway must support;

A smooth migration usually follows this order: upgrade the network (PoE switch, voice VLAN, UPS), install the IPBX, connect existing lines via FXO gateway, then replace stations with IP phones as needed. The SIP trunk comes last if the operator offers it. Telephony hardware from the store is in the telephony category.

Frequently asked questions

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