Skip to main content
Send calls from your 3CX phone system to a Bland agent, and let the agent transfer callers back to your 3CX extensions, queues, and ring groups. 3CX connects to Bland as a SIP trunk over TLS, with SRTP media.

​
What works

  • Calls from 3CX to your agent
  • Outbound calls from your agent through 3CX
  • Transfers back to 3CX extensions, with SIP REFER
  • The original caller ID, passed to the agent in SIP headers

​
Prerequisites

  • 3CX version 20, reachable from the internet on a fully qualified domain name (FQDN), for example yourcompany.3cx.com
  • Admin access to the 3CX Management Console
  • A Bland account with SIP trunking enabled. If there is no SIP tab under Phone numbers, contact Bland support

​
Configure 3CX

1

Add a SIP trunk for Bland

In the 3CX Management Console, go to Voice & Chat and add a SIP trunk. Set the server to your Bland region, for example us2.sip.bland.ai, port 5061, transport TLS. The other regions are under Connection endpoints.Use IP-based authentication, with no registration. If 3CX asks for a main trunk number, enter one of the numbers you will route to Bland.
2

Set encryption and codecs

Set call encryption (SRTP) to Mandatory. Bland rejects calls offered with plain RTP.Put G.711 first in the codec list: PCMA (A-law) outside North America, PCMU (μ-law) in North America. Leave direct media off, so audio flows through 3CX.
3

Check the public IP

In 3CX’s network settings, make sure 3CX advertises its real public IP. If automatic detection picks the wrong one, set it by hand. A wrong public IP is the most common cause of one-way or silent calls.
4

Allow Bland on your firewall

Allow TLS on port 5061 and SRTP on UDP 16384 to 32768 from all six of Bland’s IPs for your region.
5

Route calls to Bland

Send the calls the agent should answer to the Bland trunk. For example, forward a DID, an IVR option, or a queue overflow to a number on the Bland trunk, with an outbound rule that picks the Bland trunk for that number.

​
Configure Bland

1

Open the setup wizard

At All agents, go to Dispatch, then Phone numbers, then the SIP tab, and press Create trunk.
2

Provider

Pick 3CX and enter your 3CX FQDN, for example yourcompany.3cx.com. Add a port only if 3CX listens for TLS on a port other than 5061.
3

Firewall

Confirm you allow-listed Bland’s IPs, and continue.
4

Authentication

Pick IP-based and press Create trunk.
5

Numbers

Add the numbers 3CX sends to Bland, in E.164 format, for example +61370000000.
6

Assign an agent

Under Phone numbers, press Configure on the number and pick the agent under Assignment.
You know it worked when a call forwarded from 3CX reaches the agent and shows up on the trunk’s Overview tab.

​
Transfer callers back to 3CX

Use SIP REFER. 3CX resolves the extension, rings it, and Bland leaves the call. In the agent’s Transfer Call node, turn on Allow SIP/DID targets and Hand off via SIP REFER. Enter the target as a SIP URI with the extension number:
Use the extension, queue, or ring group number 3CX knows internally, not a phone number. 3CX’s dial plan doesn’t map an E.164 target back to an extension.
Use REFER rather than a new INVITE with 3CX. 3CX identifies a trunk by the IP a call comes from, and silently drops a new INVITE from an address it doesn’t map to the Bland trunk. A REFER travels inside the call 3CX already accepted. See Transfers for every transfer method.

​
Caller ID

When 3CX forwards a call to Bland, it sends the original caller in the P-Asserted-Identity, Remote-Party-ID, and Diversion headers. Your agent reads them as {{sip_header_x-original-pai}}, {{sip_header_x-original-rpid}}, and {{sip_header_x-original-diversion}}. See SIP headers. A value of anonymous means the caller withheld their number. To keep the original caller in the From header too, set these outbound parameters on the Bland trunk in 3CX:
  • From: User Part: OriginatorCallerID
  • From: Display Name: OriginatorCallerDisplayName
This doesn’t apply to calls forwarded through a ring group, because the ring group places a new call.

​
Common failures

3CX advertises the wrong public IP, or the RTP range is blocked. Set the public IP by hand, and allow UDP 16384 to 32768 to and from Bland’s media IPs.
SRTP isn’t on. Set call encryption to Mandatory on the Bland trunk in 3CX.
Bland doesn’t recognize your 3CX’s IP. Check the trunk in Bland uses IP-based authentication, and contact Bland support if your public IP changed.
Use port 5061 with TLS, and make sure 3CX trusts the Let’s Encrypt ISRG Root X1 CA.
The transfer used a new INVITE from an IP 3CX doesn’t map to the trunk. Turn on Hand off via SIP REFER.
3CX can’t route an E.164 target to an internal extension. Use the extension in the SIP URI, for example sip:1018@yourcompany.3cx.com.
The BYE didn’t reach Bland. Check nothing between 3CX and Bland closes the TLS connection early, and share the call’s SIP trace with Bland support. 3CX’s own packet capture helps compare both sides.

​
Next steps

Transfers

REFER, new INVITE, and warm transfers.

Network and security

Bland’s regions, IPs, and TLS and SRTP.
Docs for agents: llms.txt