ProSBC:SHAKEN

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FreeSBC Configuration for SHAKEN Revision History Revision Date of Issue Changes 1.0.0 July 18, 2018 Initial draft

Contents Revision History 1 Contents 1 1 Introduction 2 2 Network Diagram and Call Scenarios 2 3 FreeSBC Configuration 3 3.1 Configure Routing Script 3 3.1.1 Txnx_routing.rb 3 3.1.2 Txnx_shaken.rb 4 3.2 Configure NAP (Network Access Point) 6 3.3 Configure NAP Column 7 3.4 Configure Static Route 7 3.5 Enable SIP Custom Header 7 3.6 Disable Legacy Redirection Mode 7 3.7 Configure Route Retry Action 7

  1 Introduction

Contents

Introduction

This document provides instructions on how to configure FreeSBC to interoperate with the TransNexus OSPrey server. OSPrey 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. FreeSBC 3.0.90 or later version is needed to support secure caller ID using STIR/SHAKEN.

Network Diagram and Call Scenarios

This section provides the simplified network diagram containing two telephone service providers, and the call scenarios. 

FreeSBC OSPrey Diagram.png
  1. Source of ServiceProvider-A sends a call to FreeSBC-A.
  2. FreeSBC-A forwards the call to OSPrey-A, which is a SIP redirect server providing LCR, fraud control, SHAKEN AS (Authentication Service) and other features.
  3. OSPrey-A performs LCR, fraud control and SHAKEN AS logic, then sends one of the following responses to FreeSBC-A
    1. SIP 404 Not Found: No fraud or SHAKEN AS error is detected, and routing information is unavailable.
    2. SIP 603 Decline: Fraud is detected or SHAKEN AS request fails.
    3. SIP 3xx Redirect: Destination information (FreeSBC-B of ServiceProvider-B) and a SIP Identity header including a digitally signed token that includes the calling number (secure caller ID).
  4. FreeSBC-A processes the response
    1. SIP 404 Not Found: FreeSBC-A tries the next destination configured in its local routing policy.
    2. SIP 603 Decline: Proxies the response back to Source to block the call.
    3. SIP 3xx Redirect: Forwards the call to FreeSBC-B with the Identity header.
  5. FreeSBC-B forwards the call to OSPrey-B, which is a SIP redirect server providing fraud control, SHAKEN VS (Verification Service) and other features.
  6. OSPrey-B performs fraud control and SHAKEN VS logic, and then sends one of the following SIP responses to FreeSBC-B.
    1. SIP 404 Not Found: No fraud or SHAKEN VS error is detected, and routing information is unavailable.
    2. SIP 603 Decline: Fraud is detected or SHAKEN VS request fails.
    3. SIP 3xx Redirect: Destination information (Destination of ServiceProvider-B) is attached.
  7. FreeSBC-B processes the response
    1. SIP 404 Not Found: FreeSBC-B tries the next destination configured in its local routing policy.
    2. SIP 603 Decline: Proxies the response back to FreeSBC-A to block the call.
    3. SIP 3xx Redirect: Forwards the call to Destination.

Note: A variant scenario is that Destination of ServiceProvider-B is configured as the next destination in the local routing policy of ServiceProvider-B, OSPrey-B returns SIP 404 Not Found, then FreeSBC-B does failover to Destination.

FreeSBC Configuration

This section provides FreeSBC configuration for the solution.

Configure Routing Script

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

  1. Enable routing script 
Gateway->Use script
  1. 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

Txnx_routing.rb

#
# Script version 1.0
#
# Version history:
#  1.0  First version of this script
#

require 'base_routing'
require 'txnx_shaken'

# This script routes calls in the mostsimple fashion. The behavior is the same as routing without ruby scripts
# with the addition of nap availability.
#
# Routing is in the following order:
#
# * Matching: BaseRouting.route_match
#   * :call_field_name => :called - Match the called number of the call to a route.
#   * :call_field_name => :calling - Match the calling number of the call to a route.
#   * :call_field_name => :nap - Match the nap of the call to a route.
#   * :call_field_name => :called, :route_field_name => :remapped_called - Remap the called
#     number for the outgoing call.
#   * :call_field_name => :calling, :route_field_name => :remapped_calling - Remap the calling
#     number for the outgoing call.
#   * :call_field_name => :nap, :route_field_name => :remapped_nap - Remap the nap for the outgoing call.
#     This means setting the destination nap for the route.
#


class TxnxRouting < BaseRouting
  include TxnxShaken

  before_filter :method => :txnx_shaken

  route_match :call_field_name => :called
  route_match :call_field_name => :calling
  route_match :call_field_name => :nap
  route_remap :call_field_name => :called, :route_field_name => :remapped_called
  route_remap :call_field_name => :calling, :route_field_name => :remapped_calling
  route_remap :call_field_name => :nap, :route_field_name => :remapped_nap
  route_order :route_field_name => :priority
end

@@routing = TxnxRouting.new

def init_routes(routes)
  @@routing.init routes
end

def route(call, nap_list)
  @@routing.route call, nap_list
end

Txnx_shaken.rb

#
# Script version 1.0
#
# Version history:
#  1.0  First version of this script
#
# This before-matching filter is used to test some ideas.
#
#
# In order to use this module, follow the steps below:
# 1- Add the "require 'txnx_shaken'" statement at the top of the main
#    script.
# 2- Add the "include TxnxShaken" statement in the main routing class.
# 3- Add the filter "before_filter :method => :txnx_shaken" in the
#    main routing class.
#

module TxnxShaken
  def init_txnx_shaken(params)
    params
  end

  def txnx_shaken(params)
    call = params[:call]
    contacts = params[:contacts]

    # Added this to support request_uri 3xx routing
    call[:request_uri_forward_enabled] = 'true'

    # Verify if this routing query is for an incoming call
    # To find this, we look at the contact index (it should be zero)
    if (contacts[:index].to_i == 0)
      log_trace :always, "TxnxShaken: INVITE"

      # Add P-Source-Device header
      custom_header = "P-Source-Device:" + call[:sip_remote_addr]
      
      # Extract Identity header
      sip_header = call[:sip_header]
      if !sip_header.nil?
        headers = sip_header.split(/\n+/)
        headers.each do |header|
          if header.match(/^Identity:/)
            # Save Identity header to pass to redirect logic
            params[:user_context] = { "identity_header" => header }
            # Add Identity header to pass to OSPrey
            custom_header += "\n" + header
            break
          end
        end
      end

      # Pass custom headers to OSPrey
      call[:sip_header] = custom_header

      # Replace current routes with a list of redirect routes with priority
      newroutes = []
      nap_lists = params[:naps]
      nap_lists.each do |nap_list, nap_info|
        if nap_info[:server_type] == "REDIRECT"
          newroutes << { :name => nap_info[:name], :remapped_nap => nap_info[:name] , :priority => nap_info[:priority] }
        end
      end
      params[:routes] = newroutes
    else
      log_trace :always, "TxnxShaken: REDIRECT"

      # Get Identity header
      identity_header = nil
      context = params[:user_context]
      if !(context.nil? || context.empty?)
        identity_header = context[:identity_header]
      end
      if identity_header.nil? || identity_header.empty?
        # Extract X-Identity header
        sip_header = call[:sip_header]
        if !sip_header.nil?
          headers = sip_header.split(/\n+/)
          headers.each do |header|
            if header.match(/^X-Identity:/)
             identity_header = header
              break
            end
          end
        end
      end

      # Add Identity header to pass to destination
      if !(identity_header.nil? || identity_header.empty?)
        call[:sip_header] = identity_header
      else
        call[:sip_header] = nil
      end
    end

    params[:call] = call

    params
  end
end

Configure NAP (Network Access Point)

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

  • On FreeSBC-A 
NAPs->Create New NAP
    Name->NAP_OSPrey_A
    Proxy address->x.x.x.x (IP of OSPrey-A)
NAPs->Create New NAP
    Name->NAP_ANY
Use Proxy Address->Unchecked
  • On FreeSBC-B 
NAPs->Create New NAP
    Name->NAP_OSPrey_B
    Proxy address->x.x.x.x (IP of OSPrey-B)
NAPs->Create New NAP
    Name->NAP_ANY
    Use Proxy Address->Unchecked

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

Configure NAP Column

NAP column is used to mark OSPrey as redirect server. 

Gateway->Routes->NAP Column->Create New NAP Column
    Name: server_type 
    Type Attributes: NORMAL|REDIRECT
    Default: NORMAL
  • Both NAP_OSPrey-A and NAP_OSPrey-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 FreeSBC’s to allow FreeSBC 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 FreeSBC to use routing script to handle SIP 3xx response. 

SIP->Editing SIP Configuration->Header Parameters->Use legacy redirection mode

Configure Route Retry Action

Route retry action of 3xx, 404 and 603 must be configured to allow FreeSBC 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.
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