Parallel transfer

How it works

One TCP flow on a lossy path underuses the link. Parallel parts help until they congest the same link. Order is restored at complete. A single-file protocol with one stream will not do this by itself.

A 20 GB upload on one stream holds 40 Mbps. Four parts hold 110 Mbps on the same 200 Mbps path. Eight parts do not improve and the office phones start to clip. They cap at four.

How it differs

Parallel is not duplicate. You send each byte once, in a part. Two full copies are a mistake.

A complete call with a missing part fails the object. Do not mark success per part only.

Wait for every part.

On the ticket

• The practical close is a log line: time, actor, byte count, result.
• Without that line the transfer is a story.
• With it, the next person can see whether this door did what the ticket claimed.
• If the path is shared, say so in the partner profile so a later change does not silently pick a different limit, key, or region.
• On a real ticket, write down the door, the byte count, and the clock.
• For parallel transfer, that means naming the host or bucket, the expected size, and the time the other side must have a complete file.
• A progress bar is not that record.
• A 200 response that arrives before the complete call is not that record.
• If a retry is allowed, say how many and whether it resumes.
• If a person must approve the send, name the person.
• Partners who receive parallel transfer files should match on hash or size before they import.
• A same-length corrupt file passes a size check and fails a hash.
• Keep the published hash off the only channel an attacker can edit, or treat it as a corruption check rather than a substitution check.
• When the path changes, new key, new region, new cap, update the profile the same day so the next run does not use a stale limit.