What is the difference between hunt and sequential ring groups?

Hunt (all-at-once) rings every member together and answers fastest but briefly ties up several lines. Sequential rings members in order, which is gentler but slower to reach a person. Choose by how fast a door call must be answered.

How should I route a door call after hours?

Use a time-based schedule sending business-hours calls to reception and after-hours to the duty group, with an explicit overflow chain. Document the rule order, because overlapping schedules resolve by the server's configured precedence.

How do I make the caller ID show which door called?

Number buildings and doors on a flat plan - building A in the 1xxx range, B in 2xxx - and reflect that in the entrance number or caller ID. Keep routing rules referencing ranges, not single hard-coded extensions.

Does the SIP server limit how many door calls run at once?

The server handles signalling and connects media, but signalling and media capacity are different limits. Many INVITEs can be accepted while the switch PoE and uplink cap how many streams run cleanly. Size against your realistic peak.

Can one SIP server host several buildings?

Yes, using dialed-number routing so each building has its own entrance number and groups. Keep a reserved numbering range per building and reference those ranges in routing rules so adding a building never collides with today's assignments.

ENGINEERING · ROUTING · 9 min read

SIP Ring Groups and Call Routing for Buildings

Encode who answers a door call into the SIP server: ring groups, time and source routing, readable numbering, and a sane overflow chain.

2026-11-06 · FlySip engineering · All guides

In a building intercom, the question after 'who is calling' is 'who should answer.' A door call at 2 a.m. should not ring the front-desk phone that is off; a delivery call at noon should not page the night attendant. Ring groups and routing encode those intentions into the SIP server.

This covers the practical blocks: defining ring groups, routing by time and source, numbering buildings and floors so calls are readable, handing a call to a human, and what happens when many calls arrive at once. The aim is configuration you can defend, not a menu of features.

Defining Ring Groups That Match the Org

A ring group is a list of extensions alerted together (hunt) or in sequence (sequential) when a shared number is called - the lobby door, security desk, and duty manager all ring when someone presses the entrance. All-at-once answers faster but ties up more phones; sequential is gentler but slower to reach a person.

Keep membership tied to a role, not a person. 'Security desk' is stable; 'Jane's phone' changes. When a role's device changes, you edit one group instead of every door rule that pointed at a departed extension.

All-at-once (hunt): fastest answer, but briefly consumes several lines.
Sequential: rings in order; gentler but the last member waits.
Role-based: group by function so staffing changes are one edit.
Time out: define overflow to a group or to paging on no answer.

Routing by Time, Source, and Dialed Number

Time-based routing sends the same door call to different groups by schedule: business hours to reception, after hours to duty, holidays to a message or on-call paging. Source routing matters with several entrances: the loading dock rings the warehouse group, the main door rings reception. Dialed-number routing lets one server host many buildings, each with its own entrance.

The trap is overlapping rules. If two time schedules match, or a source rule conflicts with a dialed-number rule, the server picks by configured precedence and the result may surprise you. Document the rule order and test the boundary times - the shift-change hour is when a misordered rule bites.

Time: business / after-hours / holiday schedules with explicit boundaries.
Source: route by which door placed the call.
Dialed number: host multiple buildings, each with its own entrance.
Precedence: write down the rule order; overlaps resolve by priority.

Numbering Buildings and Floors for Readable Calls

When a call arrives, the display should say where it came from without a lookup. Tie the caller ID or entrance number to building and floor: building A entrance = 1xxx, building B = 2xxx, last digits identify the door. This is the same flat, documented plan used in migration - consistency prevents 'which door is this' confusion.

Avoid overloading digits with meaning that changes. A code meaning 'building then floor then door' breaks when a building is added and the width grows. Reserve ranges per building and reference those ranges in routing rules rather than hard-coded single extensions.

Handoff to a Human and to Paging

A ring group that no one answers should not just drop the call. Define overflow: roll to a second group, then to a paging zone so the call is at least audible, then to a recorded message. The handoff chain turns a silent no-answer into a still-visible event.

When a human answers, it is a normal SIP call - the operator can talk, release the door if authorized, or transfer to a resident. The server's job ends at connecting the legs; the door-release is the separate DTMF-and-relay path. Keep these concerns separate so each is testable alone.

Concurrent Calls and Capacity Behavior

Buildings generate bursts: a fire drill, a delivery rush, or a shift change can open many door calls at once. The server processes signalling and connects media; its signalling capacity and the network's media capacity are different limits. A server can accept many INVITEs while the switch PoE and uplink cap how many streams run cleanly.

Plan for the realistic peak, not the absolute maximum. Count the doors that could call together during an incident, add the internal calls they generate, and size the voice VLAN and PoE against that. The product page states capacity figures such as extension and concurrent-session numbers; ask for the test conditions before treating them as your limit.

Capacity note: signalling and media capacity are separate limits. The FlySip product page states extension and concurrent-session figures; verify them against your own peak, asking for the test conditions.

Frequently asked questions

What is the difference between hunt and sequential ring groups?: Hunt (all-at-once) rings every member together and answers fastest but briefly ties up several lines. Sequential rings members in order, which is gentler but slower to reach a person. Choose by how fast a door call must be answered.
How should I route a door call after hours?: Use a time-based schedule sending business-hours calls to reception and after-hours to the duty group, with an explicit overflow chain. Document the rule order, because overlapping schedules resolve by the server's configured precedence.
How do I make the caller ID show which door called?: Number buildings and doors on a flat plan - building A in the 1xxx range, B in 2xxx - and reflect that in the entrance number or caller ID. Keep routing rules referencing ranges, not single hard-coded extensions.
What happens when no one answers a ring group?: Define overflow: roll to a second group, then to a paging zone so the call is audible, then to a recorded message. The handoff chain turns a silent no-answer into a still-visible event instead of a dropped call.
Does the SIP server limit how many door calls run at once?: The server handles signalling and connects media, but signalling and media capacity are different limits. Many INVITEs can be accepted while the switch PoE and uplink cap how many streams run cleanly. Size against your realistic peak.
Can one SIP server host several buildings?: Yes, using dialed-number routing so each building has its own entrance number and groups. Keep a reserved numbering range per building and reference those ranges in routing rules so adding a building never collides with today's assignments.

Plan the underlying network with the VLAN and QoS guide, and migrate legacy systems first using the analog-to-SIP migration plan. See the FlySip product overview for server context.