Reference configuration · Multi-floor office

300-extension office — reference configuration

Four floors and a branch site on one dial plan: 290 desk and console phones plus ten DECT handsets, a paired OM1000-UC core with dual hot standby, and the multi-site numbering that lets a branch keep its own extension ranges without collisions.

Extensions: 300 — 240 standard desks, 30 team desks, 12 executive, 6 meeting rooms, 2 consoles, 10 DECT handsets
Core: two OM1000-UC units in dual hot standby, 1000 SIP trunks between them
Trunks: 30 configured; each supports up to 200 concurrent calls
DECT: two W710H bases carry up to 30 handsets each and 16 simultaneous calls each
DID/DOD binds up to four outside numbers to an extension or a group
A branch site joins the same network with repeatable numbers and a site prefix

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Open-plan office floor with desk phones and broadcast terminals in place

This is a reference design prepared from the product datasheets, not a record of a named customer installation.

Design parameters — what should you know?

Floors: Four, plus a branch site on the same network
Extensions: 300
Core: 2 × OM1000-UC, dual hot standby
SIP trunks: 30 configured of 1000; up to 200 concurrent calls per trunk
DECT: 2 bases, 10 handsets; up to 300 handsets per system
Numbering: DID/DOD — up to four outside numbers per extension or group

Equipment list for this design — what should you know?

Item	Model	Qty	Note
IP PBX core (pair)	OM1000-UC	2	Paired for dual hot standby; the only model in the range with system-level redundancy. Three fixed IP addresses are required: primary, secondary and a virtual IP
Desk phone, standard	X3U	240	Six SIP lines, 2.8-inch colour screen, dual gigabit ports, integrated PoE
Desk phone, team lead	X6U	30	Twenty SIP lines, 4.3-inch main screen with two 2.4-inch side screens, 60 DSS keys, five LED line keys
Desk phone, executive	V67	12	7-inch Android touch screen, 20 SIP lines, up to 116 DSS keys, built-in 5 MP camera
Meeting-room video phone	X7A + CM60	6	Android 9.0 phone with the CM60 USB HD camera for 1080p calls; 112 DSS keys; integrated PoE
Operator console	X210i	2	Twenty SIP lines and 106 DSS keys with a gooseneck microphone; reception and the main switchboard
DECT base station	W710H	2	Up to 30 handsets and 16 simultaneous calls per base; up to 300 handsets and 200 simultaneous calls for the system; PoE
DECT handset	W610D	10	2-inch colour screen, 16 DSS keys plus a side key, drop-safe from 1.8 m; for warehouse and floor staff
Branch-site PBX (optional)	OM50G	1	62 SIP trunks; joins the network as a normal site. Keep its analog lines as a local escape route if the WAN drops
ATA gateway (optional)	GA10	2	One FXS port and two SIP lines each — the route for a fax machine or a legacy analog phone on a SIP-only core
PoE access switch	Customer network hardware	8	48-port units across four floors, sized to the 290 desk phones, the DECT bases and spare ports

Why the OM1000-UC and not the OM200G — what should you know?

Both models hold 300 extensions on paper, so the decision is made by three other things: trunk headroom, redundancy and whether the site still needs analog ports.

Any requirement for analog ports pushes you back to the OM200G, which takes up to 96 of them
A fax on a SIP-only core needs an ATA gateway such as the GA10, or the OM200G
Dual hot standby pairs two OM1000-UC units and requires three fixed IP addresses on the same subnet

The two candidate cores at this size

	OM1000-UC	OM200G
Maximum SIP trunks	1000	496
Concurrent calls per trunk	200	120
Analog ports	None — SIP only	Up to 96 across four card slots
Dual hot standby	Yes — the only model that supports it	No
Ethernet	4 × gigabit: WAN, AUX, EXP1, EXP2	2 × gigabit
DID/DOD	Yes, with a dedicated manual chapter	Not documented in the manual

This is a reference design prepared from the product datasheets, not a record of a named customer installation.

Multi-site numbering for the branch — what should you know?

Multi-site networking joins PBXs over the IP network so extensions can dial short numbers across sites and share outside lines. The choice you make first is the numbering scheme.

Unique numbering across the network: dial any extension directly, no prefix — the fit for stacked capacity or small regional networks
Repeatable numbering with a site prefix: each site keeps its own number plan and management, which is the scheme for larger head-office and branch structures
One site acts as the management site and must have a fixed IP address; the other sites register to it, and can use a domain name when their address is dynamic
Site authentication is either by site IP address or by IP address and port, the latter only where the port is fixed
Each site can share its outside lines with the others, and cross-site dialling uses a prefix format of # + prefix + site number + extension

Floor by floor: ports, power and voice — what should you know?

290 phones and two DECT bases need PoE ports; eight 48-port switches give the 384 ports this plan needs including spares
Voice uses RTP ports 10010–10266 by default on the PBX — two UDP ports per call, so 128 concurrent calls occupy the whole default range
IP extensions register on port 5060 by default; the registration port can be changed on the PBX, and every phone must be changed with it
QoS marking on the PBX defaults to TOS/DSCP 0x0c, so the switches should trust and carry that marking
The PBX supports 802.1X port authentication where the network enforces it
The DECT system carries warehouse and floor staff; up to 30 handsets per base and 300 per system, with 16 simultaneous calls per base

Frequently asked questions

Is one OM1000-UC enough for 300 extensions?

Yes. Capacity in the manual is stated in SIP trunks — 1000 for this model, each supporting up to 200 concurrent calls — and the manual does not state a maximum number of IP extensions for any model. The second unit in this design is for redundancy, not capacity: dual hot standby keeps calls running if one unit fails, and it is the only model in the range with system-level redundancy.

How does the branch site fit in?

It joins through multi-site networking as a normal site, with the head office as the management site on a fixed IP address. Choose unique numbering if you want prefix-free dialling, or repeatable numbering with a site prefix if the branch manages its own ranges. Sites authenticate by IP address, or by IP address and port where the port is fixed.

We still run a fax machine. Does it work here?

Not directly — the OM1000-UC has no FXS or FXO ports. Put an ATA gateway on the network, such as the GA10 with one FXS port and two SIP lines, or choose the OM200G, which takes up to 96 analog ports. Fax itself runs as T.38 or G.711 pass-through; over an analog line, G.711 pass-through is required.

How does call recording work in this design?

Recording is to a remote recording server only on the OM1000-UC, with the server address set on the PBX (default port 1311). Local recording exists on the OM20G and OM50G only. Port signal capture is not supported on this model, and the manual states no failover time for hot standby, so we confirm that against the current firmware on the quotation.

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