EID Data Formatting¶

This guide provides a deep dive into how Endpoint Identifiers (EIDs) are formatted and represented within the bespokebpv7 library.

Overview¶

An EID (Endpoint Identifier) is used in BPv7 to identify the source, destination, and report-to endpoints of a bundle. In the wire format, EIDs are stored as CBOR arrays. To make them human-readable, the library provides utilities to convert between URI strings and these internal CBOR representations.

EID String Formats¶

The library supports two primary EID schemes: the IPN (Interplanetary Networking) scheme and the DTN scheme.

IPN Scheme¶

The IPN scheme is commonly used in DTN implementations for space applications (like ION). It typically follows the format: ipn:allocator.node.service

• Allocator: A 32-bit integer identifying the authority that assigned the node number. The Default Allocator is 0.
• Node: A 32-bit integer identifying the specific node. The symbol ! is used to represent the local node (2^32 - 1).
• Service: A 32-bit integer identifying the specific service on that node.

Example: "ipn:2.1" (where 2 is the node and 1 is the service, using the Default Allocator).

DTN Scheme¶

The DTN scheme is a more general URI-based scheme. It typically follows the format: dtn://example/path or simply dtn:name.

Example: "dtn://example/path"

Internal CBOR Representation¶

Internally, bespokebpv7 represents EIDs as CBOR arrays consisting of a scheme code and a scheme-specific part (SSP).

General Format: [scheme_code, scheme_specific_part]

IPN Internal Structure¶

For the IPN scheme, the scheme-specific part is itself a list: [allocator, node, service].

• "ipn:2.1" \(\rightarrow\) [2, [0, 2, 1]] (Default allocator 0 is explicitly stored in the full list).
• Note: Some legacy implementations may pack the allocator and node into a single 64-bit "Fully Qualified Node Name" (FQNN), but the recommended BPv7 format uses the 3-element list.

Utility Functions¶

The following functions in src/bespokebpv7/utils.py handle the conversion between string and internal formats.

parse_eid_string(eid_str)¶

Converts a human-readable EID string into the internal CBOR list format.

• Input: A string (e.g., "ipn:2.1") or an existing list.
• Output: A list [scheme_code, ssp].
• Behavior:
• If the string contains :, it splits the scheme from the rest.
• If the scheme is ipn, it parses the allocator, node, and service.
• Otherwise, it defaults to the dtn scheme.

format_eid(eid)¶

Converts an internal CBOR list back into a human-readable URI string.

• Input: A list [scheme_code, ssp].
• Output: A string (e.g., "ipn:2.1").
• Behavior:
• For SchemeCode.IPN, it reconstructs the ipn:allocator.node.service string. If the allocator is 0, it is omitted from the resulting string for brevity.
• For SchemeCode.DTN, it returns dtn:ssp.

Standard Reference¶

For detailed specifications on EID formats and the Bundle Protocol version 7, refer to RFC 9171.