Sipflex

3CX CONFIGURATION

Configure Sipflex on 3CX.

Create a registration-based trunk using the 3CX Generic SIP Trunk template, your Sipflex pilot number and sip.sipflex.co.uk.

Compatible, not currently listed

Provider status

Sipflex is technically compatible with 3CX but is not currently listed as an officially supported provider under the Sipflex name. Select the Generic SIP Trunk template.

1. Prepare the trunk in Sipflex

  1. Sign in to the Sipflex portal.
  2. Open Voice → Profiles.
  3. Select Registered SIP Trunk as the connection type.
  4. Choose the number that will act as your pilot number.
  5. Save the profile and keep the pilot number and separate trunk password available.

The pilot number authenticates 3CX. Every other number on that profile is delivered as a DDI through the same trunk, and newly added numbers follow that route automatically.

2. Create a Generic SIP Trunk in 3CX

  1. Sign in to 3CX as an administrator and open the SIP trunk area. Navigation labels differ slightly between 3CX versions.
  2. Choose Add SIP Trunk.
  3. For country or provider, search for and select Generic.
  4. Select Generic SIP Trunk.
  5. Enter your Sipflex pilot number as the Main Trunk Number.

3. Enter the General settings

3CX fieldSipflex value
Name for trunkSipflex
Main trunk numberYour Sipflex pilot number
Registrar / server / gatewaysip.sipflex.co.uk
Outbound proxysip.sipflex.co.uk
Auto discoveryEnabled where available
Number of simultaneous callsThe total channel capacity configured in Sipflex
Type of authenticationRegister / account-based
Authentication IDYour Sipflex pilot number
Authentication passwordThe separate trunk password shown in Sipflex
3-way authentication passwordDisabled
Use the trunk password.

The authentication password is the separate voice-trunk password, not your Sipflex portal password.

4. Configure Call Options

Open the trunk's Options tab and use these settings as a baseline. Labels can vary between 3CX releases.

3CX optionRecommended setting
Allow inbound callsEnabled
Allow outbound callsEnabled
Disallow video callsEnabled unless you deliberately require video
PBX delivers audioEnabled
Supports Re-InviteDisabled
Support ReplacesDisabled
Put Public IP in SIP VIA HeaderDisabled
Alternative ProxyDisabled
SRTPDisabled for a basic trunk; enable only with a tested secure-media configuration
Re-register timeout180 seconds
IP used in Contact / SDPUse Default Settings
Transport protocolAny for the basic setup, or TLS when deliberately configured
IP modeAny

5. Set codec priority

In the trunk Options, set the audio codec priority to:

  1. G.722
  2. G.711 A-law
  3. G.729 when installed and licensed

Use RFC2833/RFC4733 DTMF and a media packet time of 20 ms.

6. Route the pilot, add DDIs and set caller ID

  1. Create the inbound route for the pilot number and send it to the extension, queue, IVR or application you choose.
  2. Open the trunk's DDIs tab and add every additional Sipflex number that should route through 3CX.
  3. Create the corresponding 3CX inbound routes. Enter numbers in the same full format delivered by Sipflex.
  4. Open the Caller ID tab and select an authorised Sipflex number as the default outbound caller ID.

Optional forwarded-call caller ID

If you need 3CX to pass the original caller ID on forwarded or diverted calls, open Outbound Parameters and set P-Asserted-Identity: User Part to “OriginatorCallerID” Original Caller number.

7. Add the Sipflex network address to the 3CX allow-list

3CX can automatically block a SIP provider address after repeated security events. Add the current Sipflex signalling address explicitly:

FieldValue
Network address52.56.188.70
Subnet / prefix/32
ActionAllow
DescriptionSipflex SIP trunk
ExpiryA suitably long-lived date, reviewed as part of your security maintenance
  1. Open the 3CX security area and locate the IP blacklist / allow-list controls.
  2. Choose Add a range of IP addresses.
  3. Enter 52.56.188.70 with prefix /32.
  4. Set the action to Allow, add a clear description and save.
Use this address exactly.

The current Sipflex allow-list entry is 52.56.188.70/32.

8. Optional: use TLS transport

  1. Open the Sipflex trunk in 3CX and select the Options tab.
  2. Change Transport Protocol to TLS.
  3. Use sip.sipflex.co.uk with TCP port 5061. Leave discovery enabled where supported.
  4. If your 3CX release asks for a provider PEM certificate, obtain the current Sipflex certificate from Sipflex support; do not reuse an old provider-branded file.
  5. Save the trunk and allow several seconds for it to register again.

Secure media is separate from TLS signalling. Enable SRTP only when both the Sipflex profile and the complete 3CX call path have been configured and tested for it.

9. Save and verify

  1. Save the trunk, wait approximately ten seconds and refresh the trunk list.
  2. Confirm 3CX shows the trunk as Online.
  3. Place an outbound call and verify the presented caller ID.
  4. Call the pilot number and each additional DDI from another network.
  5. Confirm two-way audio and test DTMF through an IVR.
  6. If the trunk is offline, confirm the pilot number, trunk password, registrar and allow-list before changing local routing.

Support scope

Sipflex can confirm the account, registration and provider-side routing. Your 3CX extensions, inbound rules, outbound rules, firewall and application routing remain your responsibility.

Contact Sipflex