TCP

How it works

FTP, SFTP, and HTTP/1.1 and HTTP/2 ride TCP. Loss stalls the stream and cuts throughput. RFC 6349 measures that achieved rate. A file copy does not see packets. It sees a stream that slows down.

A 5 GB transfer on a 1 percent loss path averages 12 Mbps on one TCP flow. Four parallel parts reach 40 Mbps. The bytes are the same. The loss recovery is not.

How it differs

TCP is not a file protocol. It does not name files. QUIC is the UDP-based alternative under HTTP/3.

A middlebox that resets long TCP flows kills large uploads.

Resume above TCP so the reset is not fatal.

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 tcp, 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 tcp 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.