Registration-based Carriers

Most UK and European providers expect the phone system to register to them rather than recognising its IP address. Voiceflex, Andrews & Arnold, sipgate and many others work this way, and Gamma can be provisioned either way.

Registration is also the only way to connect a site whose public IP address can change, because there is no fixed address for the carrier to recognise.

When to use it

Use registration when the carrier issued you a username and password and expects your system to sign in, rather than asking for your IP address.

Ask the carrier which of these applies. Some providers offer both and provision one or the other when the account is created, so it is worth confirming rather than assuming.

Before you start

Obtain from the carrier:

• the SIP host to register to, and the port and transport
• the authentication username and password
• the registration realm or domain, if it differs from the host
• the address-of-record, if it is not the same as the username
• your inbound numbers and an authorised outbound caller ID

Some carriers issue an account identifier to authenticate with and a separate main number as the address-of-record. Ask which is which.

Add the trunk

1. Open the SessionPBX project and select Call Routing.
2. On SIP trunks, select Add trunk.
3. Name the trunk. Choose your carrier if it is listed, or Generic carrier (registration).
4. On Connection, enter the carrier host, port and transport.
5. On Authentication, choose Username and password and enter the credentials.
6. Turn on Register to this carrier.
7. Leave Registration user blank unless the carrier gave you an address-of-record that differs from the username.
8. Leave Registration expiry at 3600 unless the carrier asked for something else.
9. Enter your numbers on Inbound and your caller ID on Outbound.

Select Create trunk.

How registration behaves

SessionPBX registers as soon as the trunk is saved, and refreshes well before the registration expires.

If the carrier requires a longer registration period than you asked for, it says so when it answers and SessionPBX adopts that period automatically. The value you entered is left as you set it.

If the carrier is unreachable, SessionPBX retries with an increasing delay rather than continuously, and resumes normal refreshes once it succeeds.

Turning the Register to this carrier switch off tells the carrier to drop the registration rather than leaving it to lapse.

Test

1. Confirm with the carrier that your registration is showing as active on their side.
2. Call one of your numbers from an outside phone and confirm the right extensions ring.
3. Enable Outbound PSTN for one member, call a public number, and confirm two-way audio and the presented caller ID.

If the carrier does not show a registration, the usual causes are a realm that does not match, an address-of-record that differs from the username, or a firewall between the site and the carrier.

Limitations

Registration is supported over UDP. TLS registration is not yet available, so a carrier that requires it cannot be used with registration.