Protocol-control information
In telecommunications, the term protocol-control information (PCI) has the following meanings:<ref>Template:Cite web</ref><ref>Template:Cite book</ref><ref>Template:Cite web</ref><ref>Template:Cite web</ref>
- The queries and replies among communications equipment to determine the respective capabilities of each end of the communications link.
- 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.