ProSBC:Robocall Mitigation

 

Introduction

This document provides instructions on how to configure ProSBC to operate with the TransNexus ClearIP server for Robocall Mitigation. ClearIP is a SIP redirect server that provides advanced Least Cost Routing (LCR), fraud control and STIR (Secure Telephony Identity Revisited) / SHAKEN (Secure Handling of Asserted information using toKENs) features.

ProSBC 3.0.90 or a later version is needed to support secure caller ID using STIR/SHAKEN.

Typical Call Scenarios

This section provides the simplified network diagram with typical call flows.

1. Source of ServiceProvider sends a call to ProSBC.
2. ProSBC forwards the call to ClearIP for Robocall Mitigation process
3. ClearIP analyzes the call for robocall mitigation and toll fraud, then sends one of the following responses to ProSBC
   1. SIP 404 Not Found: No fraud is detected, not a robocall.
   2. SIP 503 Service unavailable: No fraud is detected, not a robocall.
   3. SIP 603 Decline: Fraud is detected, block the call.
4. Upon receiving 404 or 504
5. a: - ProSBC returns SIP 503 (or mapping to the TDM cause code) to the Source switch to perform route advance
6. Call Source (TDM or SIP) --------Invite or SETUP or IAM ---------> ProSBC ----Invite--> ClearIP
7. Call Source (TDM or SIP) <---SIP 503 or REL with 41 or 34 -------- ProSBC < ----503---- ClearIP

1. b: - ProSBC route advances on SIP 503 and sends call to next destination, does not return response to the Source switch
2. Call Source (TDM or SIP) ---Invite or SETUP or IAM ---> ProSBC ----Invite--> ClearIP
3. ProSBC < ----503---- ClearIP
4. ProSBC ----Invite---Next Routes

1. Upon receiving 603
2. ProSBC returns SIP 603 (or mapping to the TDM cause code) to the Source switch, then release the call
3. Call Source (TDM or SIP) -----Invite or SETUP or IAM ------> ProSBC ----Invite--> ClearIP
4. Call Source (TDM or SIP) <---SIP 603 or REL with 21 -------- ProSBC < ----603---- ClearIP

ProSBC Configuration

This section provides ProSBC configuration for the solution.

Configure Routing Script

ProSBC is configured to use routing script to handle SIP 3xx Redirect response.

1. Enable routing script

Gateway->Use script

2. Load routing scripts

Gateway->Routes->Routing Script->Import Script File
   File->txnx_shaken.rb
   ScriptType->TxNx
   Load on startup->unchecked
Gateway->Routes->Routing Script->Import Script File
   File->txnx_routing.rb
   ScriptType->Txnx
   Load on startup->checked

Click here to download txnx_shaken.rb and txnx_routing.rb Routing Scripts

Configure NAP (Network Access Point)

ClearIP-A and ClearIP-B are configured as NAP on ProSBC-A and ProSBC-B respectively. A general SIP endpoint, NAP-ANY, is configured on both ProSBC’s.

• On ProSBC-A

NAPs->Create New NAP
    Name->NAP_ClearIP_A
    Proxy address->x.x.x.x (IP of ClearIP-A)
NAPs->Create New NAP
    Name->NAP_ANY
Use Proxy Address->Unchecked

• On ProSBC-B

NAPs->Create New NAP
    Name->NAP_ClearIP_B
    Proxy address->x.x.x.x (IP of ClearIP-B)
NAPs->Create New NAP
    Name->NAP_ANY
    Use Proxy Address->Unchecked

Note: To configure local routing policy with other destination NAPs, ClearIP NAPs should have the highest priority alone all destination NAPs.

Configure NAP Column

NAP column is used to mark ClearIP as redirect server.

Gateway->Routes->NAP Column->Create New NAP Column
    Name: server_type 
    Type Attributes: NORMAL|REDIRECT
    Default: NORMAL

• Both NAP_ClearIP-A and NAP_ClearIP-B are configured with NAP column server_type REDIRECT.
• NAP_ANY are configured with NAP column server_type NORMAL.

Configure Static Route

A static route to NAP_ANY should be configured on both ProSBC’s to allow ProSBC to try the destination in the SIP 3xx response.

Gateway->Routes->Create New Static Route
    Name->ToEndpoints
    NAP->any
    Remapped_NAP->NAP_ANY

Enable SIP Custom Header

Enable SIP Custom Headers must be checked to pass SHAKEN Identity header and several other headers used by the solution.

Profiles->SIP->Enable SIP Custom Headers

Disable Legacy Redirection Mode

Use legacy redirection mode must be unchecked to allow ProSBC to use routing script to handle SIP 3xx response.

SIP->Editing SIP Configuration->Header Parameters->Use legacy redirection mode [uncheck]

Configure Route Retry Action

Route retry action of 3xx, 404 and 603 must be configured to allow ProSBC to perform failover, fraud control and SHAKEN AS/VS request.

Profiles->Edit Reason Cause Mapping
    300 Multiple Choices->Route retry action->Process call routing
    302 Moved temporarily->Route retry action->Process call routing
    404 Not found->Route retry action->Continue call
    603 Decline->Route retry action->Stop call

Notes:

• The default route retry action of 404 is Stop call.
• The default route retry action of 603 is Continue call.