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Caller Line Identification

Management Customer [Customer Name] Routing

CLI (Caller Line Identification), aka ANI (Automatic Number Identification), is the From header in SIP. It represents the sender's number in a telephone call. It's the technical term for the mechanism we know as Caller ID.

In VoIP systems, CLI is more than just a way to display the number of incoming calls. It's used as a defense against unidentified call attempts.

CLI provides information to sort incoming calls. It's an important component of billing.

In ConnexCS, CLI lets you restrict and manipulate CLIs and Pre-Asserted Identity on customer calls so that any caller without a valid match gets rejected instantly.

How's CLI derived?

CLI refers to the CLI/ANI field in the From part of the SIP INVITE message. This contains specific information about the caller.

The information contains the name and number of the person starting the call. Also known as "Caller ID" in standard phone systems, CLI is also referred to as "A-Leg" or "A-Number."

It's where the call originates. The call is then terminated at the Dialed Number, the "B-Leg" or "B-Number."

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Default Behaviour

By default, a customer account will pass all calls, even with no configured CLI records. To change this behavior, navigate to Management Customer [Customer Name] Edit Verification and enable Approved CLI's Only.

Approve CLI override

Once you enter the first CLI rule, the behaviour changes to block all, regardless of the "Approved CLI's Only" setting.

CLI verification tool

Besides changing the default behaviour to block, adding a CLI rule gives customers the ability to verify their own CLIs from their Control Panel through a callback system.

A customer can login to their portal and enter a phone number that should belong to them. The ConnexCS system will place a call and give a code that must be entered into the portal. If the codes match, the CLI is then added.

Creating a Record

Click under CLI.

Field details:

  • CLI: To allow the required CLIs, enter the required number or a regular expression (to match and replace).

  • Rewrite CLI: A CLI can be rewritten. For example, you can add 123456789 in the CLI box and then rewrite by adding 987654321 in the rewrite CLI box. (For more advanced CLI manipulation, see Advanced CLI Match & Manipulation below.

  • Pre-Asserted-ID (PAID): To allow the required PAID, enter the required number or a regular expression to match or replace.

  • Rewrite P-Asserted-ID: This is a SIP Header almost same as the FROM header but classified as a private, or network-level identifier. Telephone companies use it to identify call originators. As it's stripped at the call server, the client end-points only see the FROM field. This is helpful when callers obscure their CLI / FROM information, as the network level still requires origination details. The P-Asserted-ID manipulation uses the same syntax as the Replace CLI.

P-Asserted-ID Use Case

If you wanted to allow all calls but assign a specific number (such as the Main Billable number for the business), you would set CLI as ".*" and then enter the desired P-Asserted ID. All calls will then have this number as the P-Asserted-ID.

  • Forced: Enabling this will allow a call if there are no other matching CLIs in the system. This will also replace the CLI that's presented with the CLI entered here. For example, Create a permitted list of CLIs, then select Forced on the CLI to use if none of the others in the permitted list match. (Best practice is to have one unique Forced CLI.)

  • Direction Applied: Select either Termination for calls a customer makes out or Origination (also refers to DIDs) for inbound calls made to our customers. For example, Create a permitted list that exclusively allows calls to or from the same country.

  • Use DID: Pull in DIDs from the customer's account to use either as a Filter or as a Replacement.

  • Dialed Number Match: To route to a specific CLI, you dialied match number. For example, if Dialied matched number is starting with 1, the CLI routes to 11111. The CLI can be a Regular Expression also.

  • Notes: Notes give you information about the CLI.

  • STIR / SHAKEN Certificate: If you apply any STIR / SHAKEN Certificate to a customer's account for calls verification, for example, whether the calls are spam.

  • STIR / SHAKEN Attestation: This is the level of a certification you can select from 3 levels A, B, or C.

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Click Save to complete the CLI configuration.

Allow Customers to add their own Caller Line Identification

Navigate to Management Customer [Customer Name] Edit Verification and select the "Approved CLIs Only" checkbox.

The customer can then go to the Customer Portal CLI section and add numbers there.

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Advanced CLI Match and Manipulation

Filter Examples

The customer can choose which numbers to permit for origination of the calls by configuring a number as a CLI in ConnexCS.

Any number configured as a CLI is a part of the permitted list (unless you use extra settings to block it).

Filter Caller Line Identification by Number

Block all calls that don't have the CLI "123456789":

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
123456789 No Disabled None

Allow various CLIs to pass (by entering 2 or more records):

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
123456789 No Disabled None
987654321 No Disabled None

Filter Caller Line Identification by Pattern

Allow a range of numbers for a customer (this example allows all calls that start with 123456 to pass regardless of the last digits):

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
^123456 No Disabled None

You could also use a more complicated expression to match various ranges.

In this example, the number must start with 123456, followed by 1, 3, or 5, then followed by 1 or 2 numbers.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
^123456[135][0-9]{1,2}$ No Disabled None

This can work in combination with number lists as well.

Filter Caller Line Identification by Direct Inward Dial

If your customers do origination as well as termination, they already have a list of DIDs. Select Filter from "Use DID" to automatically read from the list of DIDs.

Note that you can still add more CLIs along with the DID list.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
No Filter None

Filter Pre-Asserted-Identity by Number or Pattern

The same is true for Pre-Asserted-Identity (PAID) as it's with CLI; you can filter by PAID, as in this example.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
123456789 No Disabled None
^123456[135][0-9]{1,2}$ No Disabled None

Combined Caller Line Identification and Pre-Asserted-Identity Filter

Filters are AND together, meaning that for a call to pass in this example, the CLI would need to be 1122334455 AND the Pre-Asserted-ID would need to be 123456789.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
1122334455 123456789 No Disabled None

Filter Caller Line Identification from a Large List

Our Userspace database allows you to manage large lists of numbers. Once you upload the numbers under Developer Database.

You can use the following options to filter by the uploaded list. Note that the filter is a partial match.

Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
No Disabled [My Database]

Filter Caller Line Identification by Number Type

Filtering by Number Type will block calls that originate from a "type" that you specify; this can be something such as FIXED, MOBILE, etc.

Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Block Type
No Disabled FIXED

Replace Examples

We can also entirely replace the transmitted CLI.

Note that if a replacement occurs, it means that the match was successful and its allowed to pass through.

Direct Replacement

Replacing a 111111111111 with 222222222222.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
111111111111 222222222222 No Disabled None

Pattern Replacement

Replace all calls that begins with a 1 with 222222222222

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
^1 222222222222 No Disabled None

Force Caller Line Identification

When choosing Force CLI, if there is no match present, the CLI marked Force can replace the CLI transmitted on a call.

In the example below, the CLI 111111111111 is sent regardless of what CLI the customer sends.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
111111111111 Yes Disabled None

In the following example, if the customer sends a call with 222222222222, the call gets allowed to pass through, but if the customer were to send 333333333333, the call gets replaced by 111111111111.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
111111111111 Yes Disabled None
222222222222 No Disabled None

Pick Caller Line Identification at Random

You can add various CLIs that forcefully select a random CLI.

In this example, approximately 50% of the calls are sent with 111111111111 and 50% with 222222222222 (provided the customer doesn't send either of those two, otherwise the results would be same).

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
111111111111 Yes Disabled None
222222222222 Yes Disabled None

Large Numbers of Random CLIs

To filter or replace calls with a larger number of CLIs or to perform more complex rules.

Use Scriptforge to create a custom application that reads from a database to achieve far more comprehensive solutions.

Pick Caller Line Identification from Direct Inward Dial

This example shows how to pick a DID already associated with the customer at random for use as the CLI.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
Yes Random None

Pick Caller Line Identification from Direct Inward Dial with Longest Match

You may wish to perform CLI Localization.

For example, if you have various DIDs (in this case, 123456, 123567, and 123789) and are placing a call to 1234987654, the system will find the longest match (in this case, 123456) to use as the CLI.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
Yes Prefix Match None

Pick a Caller Line Identification from a Large List

Our Userspace database allows you to manage large lists of numbers. Once you upload the numbers, you can use the following options to choose a number at random.

Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
Yes Disabled [My Database]

Manipulate Caller Line Identification

Sometimes it can be useful to keep all or part of the transmitted CLI and manipulate it when it gets sent out.

Are you Normalizing?

Normalizing is the process of using a common number format. For ConnexCS, this is the international format.

You shouldn't be using CLI Manipulation to correct the format of a number.

Parameter Rewrite (see Number Manipulation for details) will help achieve this.

Regex Pattern Examples

If a customer sends a call where the CLI starts with a 9 we can strip it out and replace it with a 44.

For example, 9123456789 will become 4423456789.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
^9(.*)$ 44$1 No Disabled None

This may be a little complicated, so we can break this down:

  • ^ is a start anchor, which means that we start the match at the extreme left.
  • 9 is the literal digit 9.
  • ( and ) represent a match group, everything matched within it's placed in the variable $1.
  • $ is an end anchor and it means that we finish the match at the extreme right.

In the Rewrite CLI section, 44 is the literal 44 digits, and $1 will contain what it has matched in the previous stage.

Use Pre-Asserted-Identity as Caller Line Identification

You can use all or part of a sent Pre-Asserted-Identity as the CLI. The following example shows how to capture them all.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
.* ^(?<paid>.*)$ $<paid> No Disabled None

Besides the matched group as above, we've the expression (?<paid>.*). Here, paid represents a variable which stores this information, and it's then available in the CLI rewrite scope as $<paid>.

Variable Scope

Numbered groups (For example, $1, $2) will only be read from the CLI and will be available in the CLI rewrite or in the Pre-Asserted-Identity Rewrite. You can read and use Named groups anywhere.

Manipulate Pre-Asserted-Identity

Manipulate the P-Asserted ID similarly to how we manipulated the CLI. In this case, we must use named groups and still have to match the CLI to allow the call to pass. As before, 9123456789 in the Pre-Asserted-Identity will become 4423456789.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
.* ^9(?<paid>.*)$ 44$<paid> No Disabled None

Use Caller Line Identification

If we want to use the CLI in the Pre-Asserted-Identity it's a little easier as we can just use the numbered group.

CLI Pre-Asserted-ID Rewrite CLI Rewrite P-Asserted-ID Forced Use DID Userspace DB
^(.*)$ $1 No Disabled None

How to Invert a Regular Expression

This will BLOCK all USA Freephone numbers

^ ((?!^1(800|833|844|855|866|877|888)).)*$

Additional Examples

The CLI system uses Regular Expressions to match and replace numbers. Here are some examples:

Number CLI Replace CLI Description
123456789 ^1234 Allows only numbers starting with 1234 to pass
123456789 789$ Allows only numbers ending with 789 to pass
12345678912 ^[0-9]{11,12}$ Allows only numbers with 11 or 12 digits to pass
+123456789 ^+([0-9]+)$ \1 Remove the leading +
01782123456 ^0([1-9]+)$ 44\1 Remove the leading 0 and replace it with 44

To learn more about writing regular expressions, visit RegExr. It includes tutorials and exercises available for all levels of expertise.

Allow list numbers per provider

Use CLI Restrict to allow CLIs to pass through a specific provider. To allow a configured CLI:

  1. Click Management Rate Card.
  2. Select the Provider Rate Card (under the Name column).
  3. Select Properties Advanced.
  4. Enter the CLIs / ANIs you want to allow in the CLI Restrict box.
  5. Click Save.

General Condition 6 (GC6) Compliance

ConnexCS is GC6 compliant for end users, which:

requires Communications Providers (CPs) to provide CLI facilities and ensure that the CLI Data provided with a call includes a valid, dialable telephone number that uniquely identifies the caller." For details on this General Condition, including guidelines for "valid" and "dialable" numbers, see OFCOM's Guidance on CLI Facilities.

To set the "P-Asserted-ID" per customer, see Configure CLI above.

CLI and PAID Responsibilities

  1. If the customers don't offer any CLI, you can add a CLI list but it should be validated.
  2. The customers are allowed to partly modify the format of CLIs. It should be changed to make it more compliant.
  3. If a customer isn't complaining, you can allocate a PAID from YOUR OWN list of CLI's, which can help you trace the calls.
  4. You shouldn't delete any information but you can fix the syntax or format.
  5. You shouldn't present any invalid / false information.