Verification Involving PSTN Reachability (vipr)

Last modified: 2014-01-24


Real-time Applications and Infrastructure Area Director(s)

Real-time Applications and Infrastructure Area Advisor

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Description of Working Group:

There are two globally deployed address spaces for communications used by more than a billion people daily - phone numbers and DNS rooted address such as web servers and email addresses. The inter-domain signaling design of SIP is primarily designed for email style addresses yet a large percentage of SIP deployments mostly use phone numbers for identifying users, thus DNS lookups are not sufficient. The goal of this working group is to enable inter-domain communications over the Internet, using protocols such as SIP, while still allowing people to use phone numbers to identify the person with whom they wish to communicate.

The VIPR WG will develop a peer to peer based approach to finding domains that claim to be responsible for a given phone number to mitigate the involvement of centralized entities to avoid some of the issues encountered by past attempts to support SIP inter-domain communications. Validation protocols will be developed to ensure a reasonable likelihood that a given domain actually is responsible for the phone number. In this context, "responsible" means an administrative domain, which is at least one of the domains, to which a PSTN call to this phone number would be routed. Once the domain responsible for the phone number is found, existing protocols, such as SIP, can be used for inter-domain communications.

Some validation protocols may be based on knowledge gathered around a PSTN call; for example, the ability to prove a call was received over the PSTN based on start and stop times. Other validation schemes, such as examining fingerprints or watermarking of PSTN media to show that a domain received a particular PSTN phone call, may also be considered by the working group. This validation will be accomplished using publicly available open interfaces to the PSTN, so the validation can be performed by any domain wishing to participate. The WG will select and standardize at least one validation scheme.

The validation mechanism requires a domain to gather and maintain information related to PSTN calls. This information is used by call agents such as phones, SBCs and IP PBXs to route calls. The WG will also develop mechanisms to detect in a timely manner that a given domain is no longer responsible for a phone number. The WG will define a client-server protocol between these call agents and the entity within a domain that maintains the information.

To help mitigate SPAM issues when using SIP between domains, the WG will define a mechanism to enable one domain to check that incoming SIP messages are coming from a validated phone number. A phone number is considered validated if it is coming from a domain to which the calling domain had previously successfully placed a PSTN call. The working group will define new SIP headers and option tags, as necessary, to enable this.

The essential characteristic of VIPR is establishing authentication by PSTN reachability when it is not possible to use a direct reference to ENUM databases or other direct assertions of PSTN number ownership. Elements such as public ENUM easily coexist with VIPR but no direct interaction with ENUM will be required. The solution set defined by this WG will be incrementally deployable using only existing interfaces to the PSTN. No changes will be required to existing PSTN capabilities, no new database access is needed nor is any new support from PSTN service providers required.

The WG will produce the following deliverables:

  1. A document describing the requirements, problem statement and architectural approach to support SIP inter-domain communications.
  2. A document describing the use of the p2psip protocol (RELOAD) as applied to this problem space.
  3. A document defining a scheme for validating the phone numbers using publicly available open interfaces to the PSTN.
  4. A document defining client-server protocol between call agents and the entity within a domain that gathers and maintains information related to PSTN calls.
  5. A document describing a mechanism to mitigate SPAM issues.

The working group will carefully coordinate with the security area, O&M area, as well as the appropriate RAI WGs such as sipcore and p2psip.

Goals and Milestones

Sep 2011
Submit Requirements, Problem statement, and architecture overview for publication as Informational
Dec 2011
Submit Peer to peer base protocol specification for publication as Proposed Standard
Dec 2011
Submit PSTN based number validation techniques for publication as Proposed Standard
Apr 2012
Submit Specification of authorization tokens to mitigate SPAM for publication as Proposed Standard
Apr 2012
Submit Protocol for call agents to exchange call and routing information for publication as Proposed Standard

No Internet-Drafts

No Request for Comments

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