This Recommendation | Technical Report provides: a) the description of a means to permit a protocol to be identified; b) a record of the structure and allowable ranges of protocol identifier(s) which can be assigned by ITU-T, ISO/IEC and other authorities; c) a record of the values of protocol identifiers used by OSI Network layer protocols and non-OSI protocols occupying a similar position: in particular, protocols with protocol control information commencing in octet 1 of the protocol data unit (header-oriented protocols), and protocols with protocol control information commencing in the final octet of the protocol data unit (trailer-oriented protocols), are covered; and d) a record of the values that are in use as protocol control information in non-Network layer protocols where they impact on Network layer protocol identification. The application of this Recommendation | Technical Report is: a) in the identification of internationally standardized Network layer protocols operating directly above the Data Link service; b) in the identification of protocols used in conjunction with internationally standardized Network layer protocols that operate directly above the Data Link service; and c) to distinguish between Internationally standardized Network layer protocols, and other internationally standardized protocols used in conjunction with internationally standardized Network layer protocols. This Recommendation | Technical Report is for use by ITU-T Study Groups, ISO/IEC Technical Committees and other authorities in applying the principles contained in clause 4, and in selecting an unused value or values from the range of values permitted in clauses 5 or 6, as appropriate. When a new value is selected, that value and its usage should be brought to the attention of ITU-T Study Group 7 or ISO/IEC JTC 1 SC6 so that this Recommendation | Technical Report can be amended.