VX Extension Registration Workflow


How VX registers to an extension. This article uses a hosted extension from Vonage as an example and is applicable on all VX platforms.

In this example, we mention Vonage. Because Vonage is not a part of the Telos Alliance, they are free to change their instructions and/or workflow at will without notifying us. It is only an example. If you are seeking guidance with hosted SIP and your VX, it would be best to consult with the provider to make sure you're doing it correctly.

The Telos VX is a simple SIP endpoint that registers to a generic SIP extension. The workflow shown below comes directly from the VX's internal logger. Here, we'll give a short explanation of what happens when VX requests registration.

SIP Address

The VX uses the following information from your SIP configuration to generate SIP addresses for your extensions:

The address under SIP > General Settings in the SIP Server field is used to generate the data to the right of the @, while the data entered for Extension in the Lines section is placed to the left of the @:


The extension can either be a string of letters, a string of numbers, or a combination of letters and numbers. If you have trouble with registration, you'll first want to check with the provider / PBX administrator and find out if the SIP address VX is sending is correct. If it isn't, use this info to reconfigure the extension so that the SIP address is correct.

Registration workflow

1) Send generic REGISTER request

When requesting registration, the VX will send a generic request with no authentication:

SIP: Ctx (nil) send REGISTER: sip:1234567.ac1.vbspbx.com
2) Normal response from SIP Server

Many servers will reject requests to register without authentication, saying that registration is "Unauthorized." This is normal:

SIP: Ctx 0xa000001 recv REGISTER: 401 Unauthorized
3) VX reacts to the response

The VX, after confirming the presence of a SIP server and after learning that the server is not authorizing generic registration requests, it tries again, except with authentication this time:

SIP: Retrying REGISTER with updated authentication

The VX uses the data entered into the Auth User and Auth Password fields for authentication.
4) Final response from SIP Server

At this point, the VX has confirmed that it is talking to a SIP server and this server has solicited registration with authentication. This is done for security reasons. We wouldn't want VX to be sending unsolicited credentials to possibly unknown places on the network.

The Sever should now be replying with a "success" message:

SIP: Ctx 0xab0001 recv REGISTER: 200 OK

The final result of registration attempts is also shown in the Lines section of the Information > Studio page for the VX Studio being set up / tested.

If your authentication credentials are not correctly entered into the VX, the server will reject the second request (with authentication) as "Unauthorized." At this point the VX gives up and shows the failure:

SIP: Ctx 0xa000001 recv REGISTER: 401 Unauthorized
SIP: Passing message to the context 0xa000001

SIP: REGISTER sip:5555555@1234567.ac1.vbspbx.com: 401 Unauthorized
SIP: Can not authenticate request

SIP: REGISTER failed for sip:5555555@1234567.ac1.vbspbx.com (status code: 401)

Other cause codes are possible here, such as 404 (not found), 408 (Network Timeout), etc. Let's go over the most common:

Registration fails at 401 "Unauthorized"

There are a number of reasons why this would happen. The most common reason is misconfiguration of the authentication credentials in the VX. (Auth User and Auth Password)

In the case of Vonage, their user interface will provide a code in the form of a hashed string for authentication. This hashed string needs to be used as the Extension number and the Auth User in the VX's SIP configuration. (Example in SIP Address section above)

In the case where you need to make adjustments to your extension, it may be best to delete the extension reference and start over using the information provided by the carrier instead of editing an existing extension reference.

Registration fails at 408 "Network Timeout"

This simply means the VX could not reach the server on the network. This points to a basic network problem. I.E. firewall issue, unplugged cable, network/interface configuration issues, etc.

Registration fails at 402 "Bad Extension"

This means that the "left hand" half of the SIP address is incorrect, but the "right hand" half is correct. The VX was able to reach the server, but the server rejected registration because the value entered for extension is not valid data to the server.

Other cause codes are possible if registration fails (such as 404 "not found"). The ones above are the most common. For more info on the cause code you're seeing, you'll want to contact your provider / PBX administrator to find out what that cause code means and why it was sent to the VX.

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