Evolve Personalized Call Screening¶
Evolve ® Personalized Call Screening (PCS) service is a flexible and customizable solution for screening both incoming and outgoing calls. This service preserves the integrity of your network by identifying and attesting to calls made by your Subscribers. This service also provides privacy by eliminating calls that use a computerized auto-dialer to deliver prerecorded messages known as robocalls. To prevent many types of unwanted calls, calls can be screened using several different methods including Subscriber-maintained lists, simple human CAPTCHA tests, or recorded calling party greetings.
PCS implements industry-standard STIR/SHAKEN for call authentication and verification. PCS can act as both the STI-AS and the STI-VS in the core of the network.
Customizable Order of Screening¶
PCS offers the ability to choose the order of screening methods that are applied to terminating calls. Additionally, any calls that would be blocked based on call treatment can be configured per Subscriber to connect to voice mail instead of being disconnected.
Whitelist¶
User-defined list of caller IDs to always allow and connect the call. These lists can be managed by the Service Provider on behalf of all Subscribers using the PCS service (global whitelist) or by the individual Subscriber.
Blacklist¶
User-defined list of caller IDs to always block and terminate the call. These lists can be managed by the Service Provider on behalf of all Subscribers using the PCS service (global blacklist) or by the individual Subscriber.
Audio CAPTCHA¶
An Audio CAPTCHA is meant to provide a simple ‘are you human’ test. With CAPTCHA, the caller is prompted to dial a randomly generated 4-8 digit sequence as authentication.
Recorded Greeting¶
Callers are prompted to record a greeting that is played to the called party prior to connecting the call. When the called party answers the call, they will first hear the recorded greeting and then be presented with menu options to connect the call, block the call, or send the call to voice mail.
Note
When the called party does not answer and the call is forwarded to voice mail, there will be a delay and then the calling party will hear a recording that the called party is not available and the call will be ended.
TNS TM Call Guardian¶
With TNS Call Guardian, calls are given a score based on trusted analytics for the detection of call spoofing. TNS Call Guardian performs a real-time telephone number reputation analysis, and call handling decisions are made based on the given score to provide an accurate and timely detection of robocallers in the market.
STIR/SHAKEN¶
The STIR/SHAKEN call treatment on the terminating side of the call verifies that the call has a valid certificate in the Identity header and is used as a way to prevent caller ID spoofing. Calls will have their caller ID digitally signed as legitimate by originating carriers and validated by other carriers before reaching the called party. This allows the called party to know that the call is in fact from the number that is displayed as the caller ID.
Origination¶
PCS can be provisioned to identify origination sources, which are the phone numbers and IP addresses that identify your Subscribers. The call treatment on the origination side of screening will recognize calls initiated by your Subscribers and apply the appropriate certificate, signature (if applicable), and attestation level to the Identity headers of the call following the SHAKEN protocol.
Separation of Roles¶
PCS is designed for multi-tenancy with three distinct roles. These roles are Platform Owners, Service Providers, and Subscribers. Each of these roles have their own responsibilities and functions.
Platform Owners
The Platform Owner is the entity that deploys the network which runs PCS. The Platform Owner is responsible for defining physical egress routes and other network specifics. Additionally, Platform Owners create and define Service Providers.
Service Providers
A Service Provider is the entity that offers PCS as a service to Subscribers. The Service Provider is responsible for defining the call treatment sequence, allocating Subscribers and numbers to Subscribers, and determining the amount of customization for Subscribers.
Subscribers
Subscribers are the individuals or business entities that subscribe to the PCS service. Subscribers’ calls are screened by rules defined by Service Providers. Subscribers may be able to customize certain aspects of the call screening.
Signaling¶
PCS is deployed in the network and is designed to handle AIN Termination_Attempt and SIP INVITE signals to process call screening treatment prior to the call terminating.
The rest of this chapter details the specific call flow of various call treatments.
Note
Wireshark traces of a call flow can be viewed by clicking the link provided below the diagram.
AIN Queries and Responses¶
AIN Termination_Attempt Authorized
The following diagram shows the message exchange when a Termination_Attempt trigger is received from a number that passes all the screening criteria.
AIN Termination_Attempt Disconnected
The following diagram shows the message exchange when a Termination_Attempt trigger is received from a number that does not pass the screening criteria.
AIN Termination_Attempt with Media Required
There are several screening options, such as Audio CAPTCHA and Recorded Greeting, that require an interactive media exchange. In these cases, the IN Termination_Attempt is forwarded to a designated SIP address, such as a soft switch or signaling gateway, where the call can then be handled as a SIP call with RTP media.
The following diagram shows the message exchange when a Termination_Attempt trigger is received from a number that requires a media response.
SIP Queries and Responses¶
SIP INVITE Authorized
The following diagram shows the message exchange when an INVITE trigger is received from a number that passes all the screening criteria.
SIP INVITE Authorized with Media
The following diagram shows the message exchange when an INVITE trigger is received from a number that passes all the screening criteria after media is required. Screening options such as Audio CAPTCHA and Recorded Greeting use media in the screening process.
SIP INVITE Forbidden
The following diagram shows the message exchange when an INVITE trigger is received from a number that does not pass the screening criteria and does not require media in order to block the call. Blacklisted calls and calls with a low reputation score from the TNS Call Guardian would respond this way.
SIP INVITE BYE with Media
The following diagram shows the message exchange when an INVITE trigger is received from a number that requires media to screen and does not pass the screening criteria. Calls that fail the Audio CAPTCHA screening or were rejected by the called party would respond this way.
SIP INVITE with STIR/SHAKEN
The following diagram shows the message exchange when an INVITE is received from a number that requires their caller ID to be digitally signed as legitimate by originating carriers and is validated before reaching the called party.
Combined AIN/SIP Query and Response¶
The following diagram shows the message exchange when a Termination_Attempt trigger is received from a number that requires a media response. The call is forwarded to a designated SIP address and then screened from there.
CAMEL Queries and Responses¶
The following diagram shows the message exchange when an Initial DP trigger is received from a number that passes all the screening criteria.
The following diagram shows the message exchange when an Initial DP trigger is received from a number that fails the blacklist or reputation screening criteria.
Combined CAMEL/SIP Query and Response¶
The following diagram shows the message exchange when an Initial DP trigger is received from a number that requires a media response. The call is forwarded to a designated SIP address and then screened from there.
