This FAQ shows the configuration requirements for a SIP Trunk Plus SIP trunk.  Before starting you will need to have the details emailed to you when you set up our SIP Trunk Plus SIP trunk.

Please note that the configuration steps required are different depending upon version of 3CX being used.

3CX Version 14...


The most straightforward way to create a SIP Trunk Plus trunk is to select the standard '500ltd' 3CX trunk template, then edit the trunk and changed the domain name to (or to your C NAME DNS record).  Then follow the steps outlined in 1(r) onwards below.

3CX Version 12 / 'First Principles' Instructions...


Step 1: Configure ‘VoIP Provider’


a) Log into the 3CX Management Console.

b) In the 3CX main navigation tree, select ‘VoIP Providers’.

c) In the new window, select ‘Add Provider’.

d) Enter the provider name as, for example, ‘500 SIP Trunk +’, set ‘Country’ as ‘Generic’ and ‘Provider’ as ‘Generic VoIP Provider’, then press the ‘Next’ button.


e) On the new screen enter the ‘SIP server hostname or IP’ and 'Outbound proxy hostname or IP' as '' (or set  ‘SIP server hostname or IP’ to ‘’, leaving the latter as '', if using our old architecture - or, if you are using your own realm as detailed in your reseller level 'Options' page, use that for ‘SIP server hostname or IP’ instead). All other settings can be left as default, then press the ‘Next’ button.

f) Set the ‘External Number’ as the main / headline trunk number, in the example below this is 01727515517. Repeat for the ‘Authentication ID’.
g) Enter the ‘Authentication Password’ for the trunk.

h) Set the ‘Maximum simultaneous calls’ as the number of channels / call limit you allocated to the trunk in the ST+ portal, then press the ‘Next’ button.


i) Choose the appropriate routing destination for the main trunk CLI, then press the ‘Next’ button.


j) Configure the first rule for the trunk (or press ‘Skip’).

k) Select the ‘Trunk’ ‘500 SIP Trunk +’ now displayed under the ‘VoIP Providers’ sub-menu.

l) On the newly opened window select the ‘Advanced’ tab.

m) Change the field ‘Require registration for’ to ‘In and Outgoing Calls’.

n) Importantly, bearing in mind the CODECs that SIP Trunk Plus supports, ensure that the 'Available Codecs' and 'Assigned Codecs' are as detailed below, in particularly ensuring that G729 is not an 'Assigned Codec'.  In doing this you will ensure that all calls route correctly to all destinations.  We recommend best practise by setting a short registration timeout trunk setting to make best use of our auto-failover facility so we recommend that you set the ‘registration expiry timeout’ setting (shown as 'Time between registration attempts' below) to be equal to 5 minutes (300 seconds) on both on the trunk and for good measure on all end devices also via your phone system’s device profiles / device settings.  Ensure also that 'Require registration for' is set to 'In and outgoing calls' and set other settings as appropriate for your network.


o) Select the ‘Outbound Parameters’ tab.

p) In the ‘SIP Field’ column, find and select ‘From: User Part’ ‘AuthID Authentication’.

q) Press the ‘Delete’ button then press ‘Apply’.

If CLI presentation / number spoofing is required, please refer to the settings detailed in I Can’t Get Spoofing / Number (CLI) Presentation to Work. 

r) Select the ‘DID’ tab.

s) In the edit box above the ‘Add’ button, type in the required numbers and select ‘Add’ / the ‘<’ ‘>’ arrow buttons to ‘Add’ / ’Remove’ them as required.

t) Press ‘Apply’.


u) Select the ‘Source ID’ tab.

v) Tick / check the ‘Source identification by DID’.

w) Select the ‘Add DID’ button and choose the DID’s you added from step ‘q)’ above.

x) Press ‘Apply’ then ‘OK’.


Step 2: Confirm Registration


a) In the 3CX main navigation tree, select ‘Ports/Trunks Status’.

b) Observer the status for your SIP Trunk Plus trunk, in the example this was ‘500 SIP Trunk +’: it should be green ‘Registered (idle)’ when the trunk is not in use, or yellow ‘Connected’ if the trunk is in use. If it shows red ‘Not Registered’, repeat ‘Step 1’, paying particularly attention to steps f) and g).

Step 3: Check Registration Parameters


a) Log into the SIP Trunk Plus portal.

b) Select the appropriate client account then select the ‘Sip registrations’ tab. You should see that the trunk is registered. Check that the ‘Port’ and ‘NAT’ settings match those of your PBX and of any firewall / gateway devices.


Step 4: Test


Via a connect device that matches the inbound / outbound rules you have set up for the SIP Trunk Plus trunk:


a) Make an inbound call to the main / headline trunk number. Ensure two-way voice and ensure the call last more than 60 seconds.

b) If applicable, make an inbound call to a DDI that is assigned to the trunk but which is not the main / headline trunk number. Ensure two-way voice and ensure the call last more than 60 seconds.

c) Make an outbound call. Ensure two-way voice and ensure the call last more than 60 seconds.