Trunks | Hams AI Docs

A trunk is the SIP connection between the call center and a carrier. Without a trunk, no call comes in or goes out. This page describes how to add, change, and delete a trunk. To learn how a trunk reaches Hams, see SIP connection.

Only administrators can see and change trunks.

The Trunks tab. Each trunk shows its host, transport, direction, recording policy, status, and connection.

Fields

Field	What it does	Rules
Name	Names the trunk in lists.	Required. 1 to 128 characters. Each trunk in the account needs a different name.
Domain	Sets the SIP domain of the trunk.	Required. You choose it when you create the trunk. You cannot change it later.
Host	Sets the address of the SIP server of your carrier.	Required. 1 to 255 characters. Use a hostname or an IP address.
Transport	Sets the protocol for SIP signaling.	UDP, TCP, or TLS. The default is UDP. TLS encrypts the signaling.
Direction	Sets which calls the trunk carries.	Inbound, Outbound, or Both. The default is Both.
Port	Sets the SIP signaling port.	A whole number from 1 to 65535. The default is `5060`.
Register	Makes the trunk register with the carrier. If your carrier needs registration before it sends or receives calls, turn it on.	Off by default. If you turn it on, you must fill in Auth username, Auth secret, and Auth realm.
Auth username	Sets the SIP user name that your carrier gave you.	Shows only when Register is on. Up to 128 characters. Set Auth username, Auth secret, and Auth realm together, or set none of them.
Auth secret	Sets the SIP password that your carrier gave you.	Shows only when Register is on. Up to 255 characters. The system never shows a saved secret. When you edit a trunk, leave the field blank to keep the current secret.
Auth realm	Sets the authentication realm of your carrier.	Shows only when Register is on. Up to 255 characters. Many carriers use the SIP host as the realm.
Monitor connection (SIP OPTIONS keepalive)	Sends probes to the trunk and reports its live status.	Off by default. It has no effect on an Inbound trunk.
Trust identity headers	Takes the caller from the SIP header `P-Asserted-Identity`. Also lets call flows read who forwarded the call and why.	Off by default. The field does not show for an Outbound trunk. See Trust identity headers.
Default caller ID	Sets the number that an outbound call shows when the extension has no outbound caller ID.	Optional. The field does not show for an Inbound trunk. Use an optional `+`, then 3 to 15 digits, `*`, or `#`.
Codecs	Limits the audio codecs that the trunk can use.	Choose from `PCMU`, `PCMA`, `G722`, `G729`, `GSM`, `G723`, `iLBC`, `opus`, `speex`, `AMR`, and `AMR-WB`. The list is in priority order. To accept the codecs that your carrier offers, leave the list empty.
Max inbound channels	Limits the calls that arrive on the trunk at the same time.	A whole number from 1 to 10000. Leave it empty for no limit. The trunk rejects calls over the limit.
Max outbound channels	Limits the calls that leave through the trunk at the same time.	A whole number from 1 to 10000. Leave it empty for no limit. The trunk rejects calls over the limit.
Allowed source CIDRs	Lists the IP ranges that can send calls to the trunk.	One CIDR range or IP address for each line. Up to 100 entries. A single IP address becomes a range of one address. IPv4 and IPv6 both work.
Track carrier IP via DNS	Resolves the host name and trusts the IP addresses that it returns for inbound calls. Use it for a carrier whose IP address changes.	Off by default. The field does not show for an Outbound trunk. It is a convenience, not a security control. The Resolved IPs list shows the result.
Call recording	Sets the recording decision for calls on the trunk.	Inherit, On, or Off. The default is Inherit. See Call recording.
Active	Turns the trunk on or off.	On by default.

Add a trunk

Before you start, make sure that the account has at least one SIP domain. See SIP domains.

Open the Trunks tab

Click Settings in the Cloud Call Center sidebar. Click the Trunks tab.

Open the form

Click Create Trunk. The Create trunk drawer opens.

Fill in the carrier values

Enter the Name. Select the Domain. Enter the Host and the Port. Select the Transport and the Direction.

Add the credentials

If your carrier needs registration, turn on Register. Enter the Auth username, the Auth secret, and the Auth realm.

Save the trunk

Click Create. The drawer closes and the trunk shows in the list.

To change a trunk, click its row. Change the fields. Click Save. You cannot change the Domain of an existing trunk.

Trust identity headers

A carrier or PBX can tell the call center who calls and who forwarded the call. It does this in SIP headers. The call center believes these headers only when you turn on Trust identity headers on the trunk.

Turn on Trust identity headers only for a carrier or PBX that you trust. The setting decides the caller number that call flows and call history show. A false sender can show a false number.

When Trust identity headers is on, these changes apply to inbound calls on the trunk:

The caller number comes from the header P-Asserted-Identity. If the header is missing or not valid, the caller number comes from the header From.
The header Diversion or History-Info gives the number that forwarded the call and the reason. A call flow reads them as call.redirected_from and call.redirect_reason. See Redirected calls.

When the setting is off, the system ignores these headers. The values call.redirected_from and call.redirect_reason are empty.

The field does not show for an Outbound trunk, because the trunk gets no inbound calls.

The Trust identity headers switch in the trunk drawer.

Registered trunks

If Register is on, the call center registers with your carrier. The carrier can then send calls to the contact that the call center registered. These calls enter the call flow of the DID. The system takes the DID from the header To, or from the header P-Called-Party-ID.

Default caller ID

The Default caller ID is the number that an outbound call shows when the extension has no Outbound Caller ID. If the trunk has none either, the call shows the extension number. The caller_out rewrite rules of the outbound route still apply to this number. For the rules, see Outbound routes.

Status and connection

The Status column shows Active or Inactive. The Connection column shows the live state of the trunk. The page checks the state every 20 seconds. A change can take up to 90 seconds to show.

Connection	Meaning
Online	The carrier answers the probes. The badge also shows the response time.
Unreachable	The carrier does not answer the probes.
Not monitored	Monitor connection (SIP OPTIONS keepalive) is off. The trunk still works.
N/A	The trunk is Inbound. It has no outbound side to probe.
Unknown	The system cannot read the state of the trunk.

If Register is on, the drawer of the trunk also shows Registered or Not registered.

Call recording

The Call recording setting decides if the system records calls on the trunk. The trunk is the first level of the decision. A DID or an outbound route can change the decision. A queue can change it in the middle of a call.

Setting	What happens
Inherit	The trunk makes no decision. The next level decides. If no level decides, the system does not record the call.
On	The system records the call. A later level can change this, unless you lock the decision.
Off	The system does not record the call. A later level can change this, unless you lock the decision.

Turn on Lock this decision so that no later level can change the decision. Use it where the law makes recording mandatory.

The lock has no effect while the setting is Inherit. People listen to recordings in Call history and recordings.

Change the direction

If you narrow the Direction, the DIDs and outbound routes stay on the trunk. Only the removed side stops.

If you remove Inbound, the DIDs on the trunk do not get calls any more. If you remove Outbound, the outbound routes on the trunk do not send calls any more.

The Change trunk direction? dialog shows how many DIDs and outbound routes this affects. Click Change anyway to save the change.

Delete a trunk

Move all DIDs and outbound routes to another trunk before you delete a trunk. The system does not delete a trunk that a DID or an outbound route uses. You cannot undo a delete.

To delete a trunk, open the actions menu of its row. Click Delete. Click Delete again in the dialog.