SIP trunking in the San Francisco Bay Area
Keep the PBX you already own and replace only the lines that feed it, over a circuit we build into your building. Send us the PBX model and we will tell you whether we can trunk it.
A SIP trunk brings outside calls into your phone system as data, in place of a PRI or analog lines, so the extensions, voicemail, dial plan and handsets stay as they are. Cloud PBX is the bigger change, replacing the system itself; our Bay Area business VoIP options set the two side by side.
What a SIP trunk needs from your building
What your PBX speaks
A SIP trunk ends at the phone system you already own, so the first question is whether that system takes SIP itself or needs a gateway in front of it that hands calls to its PRI or analog ports. A gateway is a routine answer for an older system. The make, model and software version settle it.
How many calls run at once
Only calls to and from outside numbers use the trunk; calls between extensions stay inside the PBX. Count the most outside calls your building has up at the same moment. The lines you have today cap that number: a full T1 PRI has 23 voice channels, and an analog line carries one call. The call records your PBX keeps can show how close your busiest hour comes to that cap.
Which numbers have to move
List every number that has to survive the change: the main line, each direct-dial number, the fax, and any number printed on letterhead, a permit, a license or a bank record. In most cases a number can be kept by porting it. A number left off the list tends to surface after the cutover, when calls to it stop.
What is still analog beside the system
A fire alarm dialer, an elevator cab phone, a gate intercom or a fax machine may run on its own copper line beside the PBX, not through it. Find those lines early. We convert them separately, through our POTS line replacement for Bay Area buildings.
One full T1 PRI, every channel busy
23 calls × 87.2 kbps = 2,005.6 kbps
About 2 Mbps up and 2 Mbps down.
Sizing the trunk for an office on one PRI
Say your office in a downtown San Francisco or San Jose tower runs its PBX on one full T1 PRI. Multiply the most calls it can have up at once, 23, by the bandwidth one call uses on the codec the PBX is set to. For G.711, a 64 kbps codec, Cisco puts that at 87.2 kbps in each direction on Ethernet once packet headers are added, at its default 20 ms packet size; G.729, an 8 kbps codec, comes to 31.2 kbps on the same basis.
Every circuit we sell is symmetrical, from 200 Mbps to 10 Gbps, so upload matches download. Those 23 G.711 calls would take about 1% of each direction on our smallest Bay Area business internet circuit.
Codec and PRI figures from Cisco’s Modify Bandwidth Consumption Calculation for Voice Calls (updated December 11, 2023), Unified CCX 11.6 Solution Design Guide (Bandwidth, Latency, and QoS) and Configuring ISDN PRI.
A SIP trunk is only as good as the circuit under it
Steady matters more than fast
A call is a steady stream of small packets running both ways at once, and it breaks up when they arrive late or not at all. A circuit can pass a speed test in the morning and still break up calls at four in the afternoon, because what voice needs is consistency through your busiest hour.
One owner for the path
You can run a trunk over any internet circuit with room for it. Running it over ours changes who answers when calls break up: with the trunk from one company and the circuit from another, each can show its own side healthy. On a circuit we run, the path from your building onto our network has one owner, and you call us.
A second path, if calls cannot stop
If your building cannot lose outside calls at all, it needs a second way in that shares no fiber with the first, and failover that moves traffic across when the first one fails. We build that second way in, as part of our internet redundancy and failover service.
Outages and life-safety lines
Calls to and from outside numbers stop. Extension-to-extension dialing, overhead paging and anything else the PBX handles on its own keep working, because the PBX is still in your building. Ask whoever supplies the trunk to set, in advance, where inbound calls go while it is down, such as to mobiles or another office.
That is your inspector’s call, as the authority having jurisdiction, because fire alarm and elevator lines carry code requirements that ordinary calls do not. What each kind of line has to do is set out in our guides on fire alarm panel phone lines and on elevator phone line requirements.
Send the PBX model and the address
Send both, and you get back whether your system takes a trunk directly or through a gateway, and how our network would reach your building and your floor. Our estimates are free and carry no obligation.