The Printer Working Group's Print Service Interface port, registered in 2003 and little deployed.
IANA assigned 3800 to pwgpsi in May 2003 on behalf of Harry Lewis of the Printer Working Group. PSI, the Print Service Interface, was a PWG effort to define how a client — a printer, mobile device, portal, or service — creates a print job on a print service and resolves the document to be printed; it reached candidate-standard form in 2005. It never displaced IPP, which is what printers actually speak on 631, so this port is a registration you will rarely see occupied.
Expose with care
Print services accept documents and leak device and job metadata; keep any print interface on the internal network regardless of which port it landed on.
$ nmap -Pn -sV -p 3800 TARGETSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.