| Internet-Draft | mocha-pab | July 2026 |
| Jennings & Nandakumar | Expires 7 January 2027 | [Page] |
This document defines how a set of devices owned by a common user synchronize a Personal Address Book (PAB) over MOQT. The address book maps identities to human-readable names and contact information, enabling users to maintain a trusted contact list that is consistent across all their devices.¶
This note is to be removed before publishing as an RFC.¶
Status information for this document may be found at https://datatracker.ietf.org/doc/draft-jennings-moq-mocha-pab/.¶
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MOCHA users need to maintain a personal directory of contacts — mapping user identities (e.g., alice@provider.example) to display names and other metadata they trust. This address book must synchronize across all devices belonging to the same user without requiring a centralized contacts server.¶
This document specifies:¶
See BCP 14 [RFC2119] [RFC8174].¶
This document uses terminology defined in [MOCHA-ARCH], including Provider, Organization, UserID, and Device. HDevID is defined in [MOCHA-IDENTITY].¶
The following additional terms are used:¶
The MOQT tracks carrying address book contact cards use the following namespace tuple:¶
("mocha_v1", <Provider>, <OrgID>, "pab", <UserID>)
¶
Where:¶
Each device publishes its address book updates on its own track:¶
Track Name: ("msg", <HDevID>)
¶
Where HDevID identifies the publishing device. Each device
maintains its own track to avoid write conflicts between
devices.¶
There is one group per calendar month. This provides a natural time-based partitioning that allows devices to efficiently fetch recent changes without downloading the entire history.¶
Groups are numbered sequentially, with the group ID derived from the month:¶
Group ID = (year - 2024) * 12 + (month - 1) Example: June 2026 = (2026 - 2024) * 12 + (6 - 1) = 29¶
Each object within a group represents a single contact card operation (add, update, or delete). Objects are sequentially numbered within each group.¶
Namespace: ("mocha_v1", "example.com", "acme", "pab", "alice")
Track: ("msg", "device-a3f2")
Group: 29 (June 2026)
Object: 0, 1, 2, ... (sequential operations)
¶
Each object payload is a JSON [RFC8259] document containing a contact card operation. The card data follows the jCard format defined in [RFC7095].¶
{
"op": "add" | "update" | "delete",
"id": "<contact identity>",
"timestamp": <unix timestamp>,
"card": <jCard object (for add/update)>
}
¶
{
"op": "add",
"id": "bob@example.com",
"timestamp": 1751000000,
"card": ["vcard", [
["version", {}, "text", "4.0"],
["fn", {}, "text", "Bob Smith"],
["email", {}, "text", "bob@example.com"]
]]
}
¶
{
"op": "delete",
"id": "bob@example.com",
"timestamp": 1751100000
}
¶
Each device publishes contact card operations to its own track. When a user adds, modifies, or deletes a contact on any device, that device publishes a new object to the current month's group on its track.¶
Each device subscribes to the tracks of all other devices belonging to the same user. This is achieved by subscribing to the PAB namespace:¶
SUBSCRIBE_NAMESPACE ("mocha_v1", <Provider>, <OrgID>,
"pab", <UserID>)
¶
The relay delivers objects from all device tracks within this namespace, allowing each device to learn of changes made on other devices.¶
When multiple devices publish conflicting operations (e.g., both update the same contact), the operation with the latest timestamp wins. If timestamps are equal, the operation from the lexicographically greater HDevID takes precedence.¶
A newly added device subscribes starting from the earliest available group to reconstruct the full address book state. The device applies all operations in group and object order, with later operations overriding earlier ones for the same contact identity.¶
Access to a user's PAB namespace is restricted to that user's own devices. The Token Service issues C4M tokens (or Privacy Pass tokens) scoped to the user's PAB namespace:¶
publish: ["mocha_v1/<provider>/<org>/pab/<user_id>/msg/<own-device>"] subscribe: ["mocha_v1/<provider>/<org>/pab/<user_id>/*"]¶
Each device can only publish to its own track but can subscribe to all tracks within the user's PAB namespace.¶
This document makes no requests of IANA.¶