Network Profiles and the Course Adapter

A name is not a specification

The historical Visa-named APIs implement a synthetic teaching profile. VS, DE63 tags, DE62 mappings, and bitmap encoding are course conventions.

An actual route needs its applicable network/processor specification.

Track separate states

Authorization approved → clearing pending → settlement processing.

A local timeout means no answer by the deadline. It does not prove the remote transaction failed. A sent reversal is not a completed reversal.

Predict cursor movement

VS115123456789012345202I25040002

Envelope ends at 2; tag 1 header at 5; value at 20. Tag 2 header ends at 23; value at 25. Tag 5 header ends at 28; value at 32.

Length counts value bytes only.

Which bytes are malformed?

VSZ03AB: declared three bytes, only two remain → error.

VSZ02ABQ: this permissive course parser ignores the final fragment. That behavior is explicitly limited, not a production padding rule.

Encoding is independent of membership

Binary 0x72 becomes ASCII 72 (bytes 0x37 0x32). Fields represented by the original byte: 2, 3, 4, 7.

A primary bitmap occupies 8 binary bytes or 16 hex characters.

Missing context cannot be reconstructed

2026-01-01 00:30 +04:00 is 2025-12-31 20:30 UTC.

A time-only field cannot establish the date rollover. Terminal PIN capability cannot establish PIN verification. A VS prefix cannot establish message authenticity.

Reconstruction task

Write the target profile before writing an adapter: framing, data encoding, length encoding, field constraints, correlation, error behavior, and lifecycle rules.

Primary sources and exact exercise boundaries are linked in the lesson.