CLI / CID / DID what is it?

Understanding CLI, CID, and DID in Your PBX System

When building your own phone PBX system, it's crucial to understand a few core concepts—specifically CLI (Calling Line Identification), CID (Caller ID), and DID (Direct Inward Dialing). These directly impact how calls are routed, identified, and presented, both inbound and outbound.

We’ll break down what each of these means, why they matter, and how to configure them properly in your setup. Let’s dive in.

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An example

This is best explained with an example. Company A has five 050 numbers (050-1234560 to 050-1234564). 050-1234560 is the main number. When an employee of company A calls a mobile number, the owner of the mobile phone sees 050-1234560 on their screen. This is called the CLI (Caller Line ID) or CID (Caller ID).

The number 050-1234563 is linked to the helpdesk. In order for a phone system to see which number the company is being called on so it can properly route to the helpdesk, the system needs to know which number the customer dialed. This is called the DID (Dialed ID).

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CLI / CID

Caller Line ID (CLI) / Caller ID (CID): The number that the called party (receiving party) sees on their screen.

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CLI and VoIP phone systems

Usually we set a fixed CLI for the VoIP trunk. Some customers, for example those with an Asterisk system, want to be able to determine the CLI themselves. The checkbox "Use CLI information from the trunk" must be enabled for VoIP trunk. More information about CLI and Asterisk can be found here: CID CLI Asterisk

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Outgoing name (CLI) or CLI namefield

In addition to caller ID (CLI), the SIP protocol also offers the ability to add additional text. For example, Linksys phones support this. This adds extra information in the CLI namefield. For VoIP accounts & VoIP trunks this is called "Outgoing name (CLI)".

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CLI format

We ask our customers to provide the CLI in the following format: Country code with +, area code without 0, phone number (+31501234567). If this is not possible because, for example, the phone system cannot handle the +, then "31501234567" is allowed.

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DID

The number that is being called -> Dialed ID

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DID as CLI

Some clients want to see in their display that they are being called on their 0900 or 020 number. In this case, we pass the DID as CLI. This is only for incoming calls that go to a mobile or fixed destination. For Fixed/Mobile you can enter this in the "Caller ID forwarding" field.

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DID and VoIP

A DID is never passed with a VoIP account. With a VoIP trunk it is. VoIP accounts are therefore used in phones, and VoIP trunks in VoIP phone systems.

If you put a VoIP trunk account in a phone instead of a phone system, this can cause problems. Calls may even be completely rejected. An example of this is the Linksys SPA 942 phone. If the DID is passed in the standard way, calls are rejected by this phone.

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