What Is a SIP Server Address, and What Do You Enter in the Phone?

Definition: the server the phone "knows"

An IP phone, a softphone or an adapter does not know on its own which PBX it belongs to. Someone has to tell it: "Your PBX is here." That is the SIP server address. The phone sends its registration message to it, and all of its requests go through it — dial, transfer, hang up.

Different interfaces call it by different names: SIP Server, Registrar, Domain, Proxy, Host or "registration server." Sometimes there is one field, and sometimes two — one for the domain and one for the "Outbound Proxy." In most cloud PBXs it is enough to fill in the same address in the main field.

The simple comparison: the address of a post office branch. To receive letters, you have to register at the right branch. If you wrote a different branch — the letters will not arrive, even if your name and ID are correct.

Server name versus IP address

There are two ways to write the server address:

• A name (domain) — something like sip.example.com. The phone asks the DNS, the phone book of the internet, what the numeric address of that name is, and connects to it.
• An IP address — four numbers, for example 203.0.113.10. The phone connects directly, without asking anyone.

The numeric address looks more "direct," so some people prefer it. In practice, in a cloud PBX, a name is almost always the right choice:

Why this matters especially in the cloud

A cloud PBX runs on servers that can change: moving to new hardware, adding a backup site, shifting load between countries. When the phones know only a name, all these changes are invisible to them. Someone updates the DNS record, and the phones, the next time they renew their registration, reach the new address.

When the phones know an IP address, every such change is an operation: you have to get to every device, in the office, at employees' homes, in the branches. And one phone that was forgotten will keep trying to register to an address that no longer exists.

There is one case where an IP address is useful: when the DNS on the local network does not work well, and you want to check whether the problem is in the name or in the connection itself. This is a temporary test, not a permanent setting.

The port

After the address there is sometimes a number after a colon, for example sip.example.com:5060. This is the port — the "door" on the server that the phone contacts. The common values:

• 5060 — the standard SIP port, over UDP or TCP.
• 5061 — the usual port for encrypted SIP (TLS).
• A different port — some systems use a different port, for example to get around routers that interfere with port 5060.

If the extension details do not include a port, you usually leave the phone's default. If one is listed, copy it exactly. A wrong port looks exactly like a server that does not respond.

Next to the port there is sometimes a "Transport" field: UDP, TCP or TLS. This is the way the messages travel. Here too — use what appears in the extension details.

The extension's username and password

The server address tells the phone where to turn. The username and password tell the server who is turning to it. In phone interfaces there are several fields that look similar, and that is confusing:

The extension's password is not the password for logging in to the control panel, and not the voicemail box password. These are three separate things. Confusing them is a common reason for an extension that does not register.

What to enter in the phone — an organized list

When you set up a phone or a softphone manually, these are the fields to fill in, in order:

1. Server address — the address that appears in the extension details in the control panel. Copy it exactly, with no spaces and no "http."
2. Port and Transport — only if they appear in the extension details.
3. Username — as in the extension details.
4. Authentication ID — the same, unless stated otherwise.
5. Password — copy it, do not type it from memory. Note upper and lower case.
6. Display name — whatever is convenient for you, for example "Office — Rivka."
7. Save — then wait a few seconds and check that the account is marked "registered."

Tip: when you set up several phones, it is worth preparing a table of extension, username and location, and marking each one that was checked with a test call, incoming and outgoing.

Automatic setup — why you usually do not need to type anything

In an organization with dozens of phones, typing an address, username and password by hand on every device is a recipe for mistakes. That is why most manufacturers support automatic setup (Provisioning): the phone turns on, contacts a configuration server, and gets all the details from there — the server address, the extension, the password, the language, the clock and the buttons.

The advantage is not only in the installation. When something needs to change — for example, moving to a new server name — you change it on the configuration server, and the phones update themselves. Manual typing remains mainly for a softphone on a mobile phone or a single device that came from somewhere else.

Common mistakes

• A space at the end of the address or password — when copying from an email, an invisible space sometimes gets in. That is enough to make the registration fail.
• "http://" or "www" before the name — a SIP server address is not a website address. Write only the name itself.
• A look-alike character — 0 instead of O, 1 instead of l. It is better to copy than to type.
• Different Domain and Proxy fields — when one server was entered in one field and another server in the other. Unless instructed otherwise, use the same address in both, or only in the main one.
• A port from memory — "always 5060" is not always right.
• A duplicate account — the same extension was set up twice on the same phone, in two accounts, and they compete with each other.

How to check that the address is correct

When a phone does not register and you suspect the address, you can check in a few simple steps:

1. Compare what is written in the phone, letter by letter, with the address that appears in the extension details in the control panel.
2. Set up the same extension in a softphone on a mobile phone, over mobile data. If it registers there, the address and the password are correct, and the problem is in the office network or in the phone.
3. Check in the phone's log or status what it reports: "Timeout" hints at the address or the port; a repeating "401" or "403" hints at the username or the password. See SIP response codes.
4. If the phone reports that it "cannot find the server," the DNS on the network may not be working. On a computer on the same network, you can check whether websites open.

An example from the field

In the office of the "Ben Shimon Movers" company (a made-up name), an outside technician set up all the phones a few years ago with the server's IP address, "to make it faster." When the company moved to a new system, it turned out that every one of the eighteen phones had to be visited, including two in a warehouse in another city.

In the new setup, all the phones got a server name, not an address. That way, any future change to the servers will not require touching them. And the difference in speed? Not noticeable at all — the DNS lookup is done once and remembered by the device for a while.

UDP, TCP or TLS — what is the difference

The Transport field determines how the management messages travel between the phone and the server. For most users it is a technical detail to copy and forget, but it is worth understanding what it means:

Important: if the phone is set to TLS and the server expects UDP, or the other way around, the registration will fail as if the address were wrong. The setting must match exactly what appears in the extension details.

How many phones, how many accounts

An IP phone can usually hold several SIP accounts at the same time — each with its own server address, username and password. This is useful, for example, when the same device serves both the secretary's extension and the gemach's line.

But it is also a source of confusion: when something does not work, you need to check which account is involved. It is worth giving each account a clear display name, so the user knows which line they are dialing from.