Protocol-control information

In telecommunications, the term protocol-control information (PCI) has the following meanings:{{cite web|title=CCITT X.200 – Information technology – Reference Model of Open Systems Interconnection for CCITT Applications|date=1988|publisher=International Telecommunication Union (ITU)|url=https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-X.200-198811-S!!PDF-E&type=items}}{{cite book|author-last1=Boait|author-first1=P.|author-last2=Neville|author-first2=G.|author-last3=Norris|author-first3=R.|author-last4=Pickman|author-first4=M.|author-last5=Walmsley|author-first5=J.|editor-last1=Tolhurst|editor-first1=M.|chapter=Definition of OSI Terms|chapter-url=https://link.springer.com/content/pdf/bbm%3A978-1-349-10306-5%2F1.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://link.springer.com/content/pdf/bbm%3A978-1-349-10306-5%2F1.pdf |archive-date=2022-10-09 |url-status=live|title=Open Systems Interconnection|date=1988|series=Macmillan Computer Science Series|publisher=Palgrave|location=London|isbn=978-0-333-46803-6|doi=10.1007/978-1-349-10306-5}}{{cite web|title=ITU-T X.260 {{!}} ISO/IEC 14765 – Information technology – Framework for protocol identification and encapsulation|date=1996|publisher=International Telecommunication Union (ITU)|url=https://handle.itu.int/11.1002/1000/3293}}{{cite web|title=Federal Standard 1037C – Telecommunications: Glossary of Telecommunication Terms|publisher=General Services Administration – Information Technology Service|date=1996|url=https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm}}

1. The queries and replies among communications equipment to determine the respective capabilities of each end of the communications link.
2. For layered systems, information exchanged between entities of a given layer, via the service provided by the next lower layer, to coordinate their joint operation.