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(ASN.1, X.208, X.680) AnISO/ITU-T standard for transmitting structured data onnetworks, originally defined in 1984 as part of CCITTX.409 '84. ASN.1 moved to its own standard, X.208, in 1988due to wide applicability. The substantially revised 1995version is covered by the X.680 series.ASN.1 defines the abstract syntax of information but doesnot restrict the way the information is encoded. VariousASN.1 encoding rules provide the transfer syntax (aconcrete representation) of the data values whose abstractsyntax is described in ASN.1. The standard ASN.1 encodingrules include BER (Basic Encoding Rules - X.209), CER(Canonical Encoding Rules), DER (Distinguished EncodingRules) and PER (Packed Encoding Rules).ASN.1 together with specific ASN.1 encoding rules facilitatesthe exchange of structured data especially betweenapplication programs over networks by describing datastructures in a way that is independent of machinearchitecture and implementation language.OSI Application layer protocols such as X.400 MHSelectronic mail, X.500 directory services and SNMP useASN.1 to describe the PDUs they exchange.Documents describing the ASN.1 notations: ITU-T Rec. X.680,ISO 8824-1; ITU-T Rec. X.681, ISO 8824-2; ITU-TRec. X.682, ISO 8824-3; ITU-T Rec. X.683, ISO 8824-4Documents describing the ASN.1 encoding rules: ITU-TRec. X.690, ISO 8825-1; ITU-T Rec. X.691, ISO 8825-2.[M. Sample et al, "Implementing Efficient Encoders andDecoders for Network Data Representations", IEEE Infocom 93Proc, v.3, pp. 1143-1153, Mar 1993. Available from Logica,UK].See also snacc.