There are a number of factors that could prevent a trunk from registering and nearly all of them are local network related, by which we mean the configuration of the end client’s gateway devices and PBX.

Initially, these areas must first be investigated prior to raising a support ticket with us.


Step 1: Check The Internet Service


This is especially important to check when a dedicated voice-only internet service is being used.


  1. Is the router correctly connected and showing the correct sequence of status LED’s?
  2. Can you connect a laptop directly to the router via a cabled connection and can the outside world be pinged from it? For example, Start > Run > Command, then type ‘ping’ and ensure there are no time outs. If it can be pinged successfully, ping our ST_ main domain / IP address also.
  3. Can the outside world be pinged from inside the client’s LAN via the internet service where voice traffic will route?
  4. Can the outside world be pinged from the PBX where the trunk is registered?
  5. If the internet service is suspected as being at fault, and if the internet service is broadband, has the underlying analogue line been tested (e.g. BT’s ‘quiet line’ tests), have ADSL microfilters been checked / replaced, has the socket been checked? Please contact your line provider and follow their recommended tests.
  6. If the internet service is suspected as being at fault, and if the internet service is as leased line, ask your provider to confirm that their edge device can be seen and is functional.
  7. Has your internet service provider set the router’s ‘Disable SIP-ALG’ setting to true? In nearly all networks, SIP-ALG should be disabled to allow SIP traffic to route correctly.
  8. Are firewall rules blocking the connection? Is the ST+ main domain / IP address set as a route / policy in the client’s firewall? Is port 5060 (or any specific port you set up for the trunk) open for UDP, TCP?


Step 2: Check The PBX Configuration


Having ensured the internet service is functional, check your PBX configuration. The process for this is different dependent upon the PBX being used.


  1. If you have chosen to set up an authentication based trunk are the three main authentication settings (realm, username and password) correctly entered as the trunk details for your PBX? The realm should either be or the realm set up under your ‘Options’ page.
  2. If you have chosen to set up an IP based trunk (that is, ‘Check IP’ trunk is set on the trunk details page) is the IP address being presented to our platform the same as that set up on the ST+ portal trunk settings?


Step 3: Check The ST+ Portal


  1. The ST+ portal allows you to check if a trunk is registered: when logged on, select your client account and go to the ‘Registrations’ page. If the trunk is showing as registered (that is, there is an entry shown on the ‘Registrations’ page corresponding to the trunk in question), do the ‘Port’ and ‘NAT’ settings match those expected / configured in your client’s firewall?
  2. Have you amended any Trunk Settings or changed your 'SIP Domain'?  If so, you are advised to re-set the trunk password.