scope:

Scope, Purpose, & Application

This document defines a mechanism that provides real-time notification in the backward call direction (towards the calling party), that the associated call was blocked by the indicated voice service provider due to analytics-based call processing. It ensures that voice service providers can continue to use analytics to block calls suspected to be illegal, fraudulent or for other reasons undesirable, while providing real-time notice to callers.

To provide such notification, this standard defines a profile of the SIP 603 response code defined in RFC 3261, SIP: Session Initiation Protocol, herein referred to as "603+". A SIP 603+ response is differentiated from a SIP 603 response in two ways:

1. Its status line¹ uses a unique reason phrase, "Network Blocked", rather than the SIP 603 default Reason Phrase "Decline" specified in RFC 3261 [Ref 1].

2. It contains a SIP Reason header defined in RFC 3326, The Reason Header Field for the Session Initiation Protocol (SIP), encoded per this standard.

Any 603 response received without the syntax defined in the standard included should be treated as currently handled today.

This standard is primarily developed for, and to be adopted by, US voice service providers. It is not precluded from being used internationally. Other countries may adopt theis standard and it may be implemented through bilateral agreements with business partners in the US pursuant to their business agreements.

¹ The first line of a SIP response message is called the "status line".