GssPolicies/InumberPolicies

I-Numbers are persistent XRIs that enable a Resource to be identified independent of changes to its location, representation, ownership, or even the I-Names or other semantics associated with it. I-Numbers are the key to establishing and maintaining persistent XDI data sharing relationships. The V1 GSS includes the specifications for three public I-Number Registry Services: Global Personal I-Number Service, Global Organizational I-Number Service, and Global Network I-Number Service. This page contains the GSS policies governing I-Number syntax and normalization, synonyms, resolution, status, and transfer, plus reserved I-Numbers.

2. I-Number Syntax and Normalization

Although the GRS assigns only the first subsegment of an XDI.ORG Community I-Number, efficient resolution of XDI.ORG Community I-Numbers is similar to efficient routing of IP addresses – it requires agreement by all participants in the addressing community to a common set of addressing rules. The policies in this section govern the syntax, normalization, and delegation rules that apply to the entire Community I-Number (i.e., the entire XRI Authority segment of any I-Number rooted on the GRS).

In particular, due to the special persistence requirements of I-Numbers, the XDI.ORG Community I-Number space requires scaling, federation, and delegation characteristics similar to that of IP (Internet Protocol) infrastructure. Therefore the policies governing the syntax of XDI.ORG Community I-Numbers are modeled closely on those of 128-bit IPv6 addressing architecture (see RFC 2373), with the following key differences:

An XDI.ORG Community I-Number is not a fixed 128-bit value but a path of 128-bit values (so each authority has its own 128-bit namespace.)
The 128-bit values of each path segment are expressed as 16-bit dot-delimited subsegments (like IPv6, each 16 bit value is expressed as a hex quad).
Rather than using double colons to compress zero-value 16-bit segments, left-padded zero values are assumed.

See the InameInumberTechFaq for examples.

2.1. Community I-Number Syntax Policy

An XDI.ORG Community I-Number MUST conform to the XRI Specifications for persistent XRIs for XRI Authorities. In addition it MUST conform to the following ABNF:

  comm-inum         = global-inum *comm-inum-subseg
 
  global-inum       = global-per-inum / global-org-inum / global-net-inum
 
  global-per-inum   = "=!" hex-128 
 
  global-org-inum   = "@!" hex-128
 
  global-net-inum   = "!!" %x1001-FFFE
 
  hex-128           = hex-16 *7("." hex16)
 
  hex-16            = 1*4HEXDIG
 
  comm-inum-subseg  = "!" ( hex-128 / comm-inum-xref )
 
  comm-inum-xref    = "(" comm-inum ")"

In this ABNF:

If a hex-128 value consists of less than 8 hex-16 segments, the segments present MUST be interpreted as representing the least significant (rightmost) bits of the 128-bit address space;
If a hex-16 value consists of less than 4 hex digits, the digits present MUST be interpreted as representing the least significant (rightmost) bits of the 16-bit address space.
The hex value in the global-net-inum production excludes the ranges reserved by the Reserved Global I-Number Policy (below).

A Community I-Number MUST also conform with the Community I-Number Normalization Policy.

2.2. Global I-Number Syntax Policy

A Global I-Number MUST conform to the Community I-Number Syntax Policy. In addition:

A Global Personal I-Number MUST conform to the global-per-inum production of the Community I-Number Syntax Policy.
A Global Organizational I-Number MUST conform to the global-org-inum production of the Community I-Number Syntax Policy.
A Global Network I-Number MUST conform to the global-net-inum production of the Community I-Number Syntax Policy.

2.3. Global Personal and Organizational I-Number Assignment Policy

The value for the hex-128 production of a Global Personal I-Number or Global Organizational I-Number MUST be a 64-bit value randomly-generated by the GRS and confirmed to be unique in the target Registry prior to assignment.

2.4. Global Network I-Number Assignment Policy

Global Network I-Numbers MUST be assigned sequentially to XDI.ORG-Accredited Registrars on a first-come, first-served basis with the exception of those assigned before or during the Early Global Services program.

2.5. Community I-Number Normalization Policy

Per the XRI Specifications, all hexadecimal digits in Community I-Numbers MUST be normalized to uppercase.

2.6. Community I-Number Delegation Policy

All XDI.ORG Community I-Numbers assigned at any delegation level MUST conform to the Community I-Number Syntax Policy and the Community I-Number Persistence Policy. Within the XDI.ORG Community, all Registrars MUST require in their Registration Agreements that Registrants observe this obligation at all levels of delegation.

2.7. Implementation Notes

2.7.1. XRI Server/Resolver Optimization

A key benefit of the Community I-Number Syntax Policy is that XRI servers and resolvers in the XDI.ORG Community will be able to optimize Community I-Number storage and caching based on the fixed 128-bit addressing segments.

2.7.2. Delegated Network I-Numbers

The GRS assigns Global Network I-Numbers only to XDI.ORG-Accredited Registrars (see GssPolicies/RegistrarPolicies). Individuals or organizations who wish to serve as a Network Authority addressable within the XDI.ORG Community, but who do not wish to become an XDI.ORG-Accredited I-Broker, may register a Delegated Network I-Number with an XDI.ORG-Accredited Registrar or one if its existing Delegates.

2.7.3. 64-Bit Global Personal and Organizational I-Numbers

Although the Community I-Number Syntax Policy permits 128-bit values in the hex-128 production of a Global Personal I-Number or Global Organizational I-Number, the Global Personal and Organizational I-Number Assignment Policy specifies that a 64-bit value will be randomly generated by the GRS. This is because a 64-bit addressing space (roughly 18 million trillion entries) is sufficiently large enough to meet the GRS requirements for the next several centuries while still enabling randomly generated values that meet the Minimum Information Policy (see GssPolicies/PrivacyPolicy). 64-bit values also require only 16 rather than 32 hex digits for encoding, making Global I-Numbers easier for network administrators and others who will sometimes need to transcode them manually.

3. I-Number Synonyms

These policies specify the rules for Global I-Number synonyms. See the ResolutionTechFaq for examples.

3.1. Global Personal and Organizational I-Number Synonym Policy

A Global Personal or Organizational I-Number MUST have at least one and MAY have more than one Network I-Number as an External Synonym that conforms to the following ABNF:

  net-inum-syn      = net-inum-auth "!(" global-inum ")"
  net-inum-auth     = Network I-Number of Delegating Authority
  global-inum       = Global Personal or Organizational I-Number

3.2. Global I-Number Synonym Priority Policy

If a Global I-Number has more than one External Synonym, the Registrant SHOULD indicate the order in which the External Synonyms shall be returned in a GRS resolution response.

3.3. Implementation Notes

3.3.1. Multiple I-Broker Accounts

Registrants may wish to have more than one Network I-Number as an External Synonym if they maintain multiple accounts at different I-Brokers for redundancy. For this reason I-Brokers should ask Registrants during the Global I-Name registration process if the Registrant wishes to register the Global I-Number and Global I-Number to more than one I-Broker account.

4. I-Number Resolution

The following policy specifies the rules for Global I-Number resolution.

4.1. Global I-Number Resolution Policy

A GRS resolution response for a Global Personal or Organizational I-Number MUST return the same values as specified in the Global I-Name Resolution Policy, with the exception that the Global Personal or Organizational I-Number being resolved does not need to be included as an Internal Synonym.

A GRS resolution response for a Global Network I-Number MUST return the following values:

The XRI Authority URIs (XAUs) registered to this Global Network I-Number together with the default “xri://$res*auth.res/XRIA” Authority Type.
The Local Access URIs (LAUs) registered to this Global Network I-Number together with the default “xri://$res*local.access/X2R” Service Type.

4.2. Implementation Notes

4.2.1. XRI Resolver Optimization

Because the only difference between the GRS resolution response for a Global I-Name and a Global I-Number and is that the former includes the Global I-Number as an Internal Synonym, XRI resolvers can optimize cache performance by using Global I-Name resolution data to satisfy Global I-Number resolution requests.

5. I-Number Status

When the registration of a reassignable identifier such as a domain name or an I-Name expires or is terminated, the identifier simply returns to the pool of available identifiers. However if the registration of a persistent identifier (e.g., an I-Number or URN) expires or is terminated, it must be handled differently because the identifier is required to continuously represent the target Resource to which it is assigned.

This includes the following scenarios:

The target Resource no longer exists, or at least no longer has a network location or representation.
The target Resource still exists but its network location or representation is indeterminate for a period of time.
The target Resource still exists but its Authority no longer exists or their account is no longer active.
The Authority explicitly wishes to terminate the association of the persistent identifier with the target Resource.

The following policies address these potential changes to the status of a Global I-Number.

5.1. Global I-Number Suspension Policy

The Authority for a Global I-Number MUST have the option to suspend its resolution. A suspended Global I-Number MUST return a null resolution value and a GRS status value of "Suspended" as specified in the GSS Operational Specifications (GssOpSpecs). If the registration of a suspended Global I-Number is subsequently terminated, this policy is superceded by the Global I-Number Termination Policy. If the registration of a suspended Global I-Number subsequently expires, this policy is superceded by the Global I-Number Expiration Policy.

5.2. Global I-Number Termination Policy

The Authority for a Global I-Number MUST have the option to terminate its resolution. A terminated Global I-Number MUST return a null resolution value and a GRS status value of "Terminated" as specified in the GSS Operational Specifications (GssOpSpecs). A terminated Global I-Number MAY be reactivated if the Authority requesting reactivation can provide the authentication credentials that were current at the time of termination. If the registration of a terminated Global I-Number subsequently expires, this policy is superceded by the Global I-Number Expiration Policy.

5.3. Global I-Number Expiration Policy

If the registration of a Global I-Number expires and is not renewed, the Global I-Number MUST return its last registered resolution value (including a null value if it was suspended or terminated) and a GRS status value of "Expired" as specified in the GSS Operational Specifications (GssOpSpecs). An expired Global I-Number MAY be reactivated if the Authority requesting reactivation can provide the authentication credentials that were current at the time of expiration.

5.4. Implementation Notes

5.4.1. Delegating Control to a Trustee

The registration of a Global I-Name may be maintained beyond the lifetime of the original Registrant by delegating control to one or more Trustees. See Trustee Service under GssPolicies/DataProtectionPolicies.

5.4.2. Perpetuating Resolution of Expired Global I-Numbers

The XDI.ORG Community, as represented by XDI.ORG, ultimately bears the responsibility for maintaining resolution of a continually expanding set of expired Global I-Numbers. Future versions of the GSS may contain additional policies governing this function. In addition, XDI.ORG should self-insure by building an endowment to cover these costs.

5.4.3. Perpetuating Resolution of Expired Community I-Numbers

XDI.ORG-Accredited Registrars bear the same responsibility for Delegated I-Numbers, i.e., for maintaining resolution of expired Community I-Numbers below the global level. Registrars and other I-Brokers may self-insure or may form trust federations to collectively perform Community I-Number archiving or otherwise share these costs.

6. I-Number Transfer

As a persistent identifier, an I-Number is intended to be assigned once to a target Resource and never reassigned to another Resource. However this does not mean that the binding between an I-Number and one or more specific locations, representations, or I-Names for the target Resource may not change. From this perspective, a Global I-Number may be transferred to another Registrant if it will still continue to identify the same target Resource. It may also be transferred to another Registrar.

The following policies govern the transferability of Global I-Numbers.

6.1. Community I-Number Persistence Policy

Once assigned to represent a Resource, a Global I-Number or a Community I-Number MUST NOT be reassigned to represent a different Resource.

6.2. Global Personal I-Number Transfer Policy

A Global Personal I-Number MUST NOT be transferred between Registrants because it represents an individual as an Authority. However a Registrant MAY transfer the registration of a Global Personal I-Number between Registrars. A Registrant MAY also grant control of a Global Personal I-Number to one or more Trustees (see GssPolicies/DataProtectionPolicies).

6.3. Global Organizational I-Number Transfer Policy

Because it represents a non-personal Authority, a Global Organizational I-Number that is not subject to dispute, non-payment, or other encumbrances MAY be transferred between Registrants as long as it continues to represent the same Authority. A Registrant MAY also transfer registration of a Global Personal I-Number between Registrars. A Registrant MAY also grant control of a Global Organizational I-Number to one or more Trustees (see GssPolicies/DataProtectionPolicies).

6.4. Global Network I-Number Transfer Policy

Because it represents a Network Authority, a Global Network I-Number that is not subject to dispute, non-payment, or other encumbrances MAY be transferred between Registrants as long as it continues to represent the same Network Authority. A Registrant MAY also grant control of a Global Network I-Number to one or more Trustees (see GssPolicies/DataProtectionPolicies).

6.5. Implementation Notes

6.5.1. Persistence and Federated Identifiers

Persistence is an operational requirement that must be enforced by all Authorities who participate in segments of a federated identifier. Within the XDI.ORG Community, XDI.ORG can only directly enforce persistence at the GRS level. The Community I-Number Delegation Policy extends this obligation to all Delegated Authorities, however enforcement lies with each Authority.

Persistence of I-Numbers assigned by Authorities outside the XDI.ORG Community is beyond the scope of the GSS.

6.5.2. Persistence and Trustees

When a Global I-Number needs to be maintained beyond the lifetime of the original Registrant (which will often be the case), the original Registrant must assign one or more Trustees. See GssPolicies/DataProtectionPolicies.

7. Reserved I-Numbers

Since Global Personal I-Numbers and Global Organizational I-Numbers are generated automatically by the GRS, only Global Network I-Numbers have reserved values.

7.1. Reserved Global Network I-Number Policy

For Global Network I-Numbers, the range below and including the hexadecimal value "1000" and the upper-end value "FFFF" are reserved for XDI.ORG and MUST NOT be registered.

In addition, the Global Network I-Number "!!1000" is reserved for internal testing (i.e., for use as the XRI "local-loop-back" address.)

The range of Global Network I-Numbers from "!!0990" to "!!0999" inclusive is reserved for public use in XRI documentation and examples (to avoid conflicts with actual registered XRIs).

7.2. Implementation Notes

7.2.1. Future Expansion

This policy reserves 1/16th of the initial 16-bit Global Network I-Number space (4097 out of the 65536 possible I-Numbers) for special purposes. In addition the Community I-Number Syntax Policy inherently reserves all 128-bit Global Network I-Numbers as a future option. The combination of these two approaches provides maximum flexibility for future optimization of the Global Network I-Number space.