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Network Working Group                            S.E. Hardcastle-KilleRequests for Comments 1278                   University College London                                                         November 1991A string encoding of Presentation AddressStatus of this Memo    This memo provides information for the Internet community.  It    does not specify an Internet standard.  Distribution of this memo    is unlimited.Abstract    There are a number of environments where a simple string encoding    of Presentation Address is desirable.  This specification defines    such a representation.

RFC 1278            String encoded P-Address             November 19911  IntroductionOSI Application Entities use presentation addresses to address otherApplication Entities.  The model for this is defined in [ISO87b].Presentation addresses are stored in the OSI Directory using an ASN.1representation defined by the OSI Directory [CCI88].  Logically, apresentation address consists of: o  A presentation selector o  A session selector o  A transport selector o  A set of network addressesThe selectors are all octet strings, but often have IA5 characterrepresentations.  The format of network addresses is defined in[ISO87a].There is a need to represent presentation addresses as strings in anumber of different contexts.  This Internet Draft defines a formatfor use on the Internet.  It is for display to human users, and itsuse is recommended whenever this needs to be done.  Typically, thiswill be for system managers rather than for end users.  It is notintended for internal storage.This Internet Draft was originally published as UCL Research NoteRN/89/14 [Kil89].  It was agreed as a unified syntax for the THORN andISODE projects.  It is used throughout ISODE.Christian Huitema of Inria and Marshall Rose of PSI Inc.  gave muchuseful input to this document.2  RequirementsThe main requirements are: o  Must be able to specify any legal value. o  Should be clean in the common case of the presentation address    containing network addresses and no selectors.Hardcastle-Kille                                                Page 1

RFC 1278            String encoded P-Address             November 1991 o  Must deal with selectors in the following encodings:    --  IA5    --  Decimal digits encoded as IA5 (this is the most common syntax        in Europe, as it is required by X.400(84) and should receive a        straightforward encoding)    --  Numeric encoded as a 16 bit unsigned integer (US GOSIP). This        is mapped onto two octets, with the first octet being the high        order byte of the integer.    --  General Hexadecimal o  Should give special encodings for the ad hoc encoding proposed in    ``An interim approach to use of Network Addresses'' [HK91].    --  X.25(80) Networks    --  TCP/IP Networks o  Should be extensible for additional forms. o  Should provide a reasonably compact representation .3  FormatThe_BNF_is_given_in_figure_1.__________________________________________<digit> ::= [0-9]<other> ::= [0-9a-zA-Z+-.]<domainchar> ::= [0-9a-zA-Z-.]<hexdigit> ::= [0-9a-fA-F]<hexoctet> ::= <hexdigit> <hexdigit><decimaloctet> ::= <digit> | <digit> <digit>                        | <digit> <digit> <digit><digitstring> ::= <digit> <digitstring>                             10                        | <digit><otherstring> ::= <other> <otherstring>                        | <other>Hardcastle-Kille                                                Page 2

RFC 1278            String encoded P-Address             November 1991<domainstring> ::= <domainchar> <otherstring>                        | <domainchar><hexstring> ::= <hexoctet> <hexstring> | <hexoctet><dotstring> ::= <decimaloctet> "." <dotstring>                | <decimaloctet> "." <decimaloctet>                                                                    20<dothexstring> ::= <dotstring> | <hexstring><presentation-address> ::=                [[[ <psel> "/" ] <ssel> "/" ] <tsel> "/" ]                <network-address-list><network-address-list> ::= <network-address> "_" <network-address-list>30                           | <network-address><psel> ::= <selector><ssel> ::= <selector><tsel> ::= <selector><selector>  ::= '"' <otherstring> '"'        -- IA5                                             -- For chars not in this                                             -- string use hex                | "#" <digitstring>          -- US GOSIP            40                | "'" <hexstring> "'H"       -- Hex                | ""                         -- Empty but present<network-address> ::=   "NS" "+" <dothexstring>                                 -- Concrete Binary Representation                                 -- This is the compact encoding        | <afi> "+" <idi> [ "+" <dsp> ]                                -- A user oriented form        | <idp> "+" <hexstring>                                -- ISO 8348 Compatability           50<idp> ::= <digitstring> -<dsp>  ::=        | "d" <digitstring>          -- Abstract Decimal        | "x" <dothexstring>            -- Abstract Binary        | "l" <otherstring>             -- IA5:  local form onlyHardcastle-Kille                                                Page 3

RFC 1278            String encoded P-Address             November 1991        | "RFC-1006" "+" <prefix> "+" <ip>           [ "+" <port> [ "+" <tset> ]]        | "X.25(80)" "+" <prefix> "+" <dte>                         60           [ "+" <cudf-or-pid> "+" <hexstring> ]        | "ECMA-117-Binary" "+" <hexstring> "+" <hexstring>           "+" <hexstring>        | "ECMA-117-Decimal" "+" <digitstring> "+"           <digitstring> "+" <digitstring><idi> ::= <digitstring><afi> ::= "X121" | "DCC" | "TELEX" | "PSTN" | "ISDN"                | "ICD" | "LOCAL"                                                                    70<prefix> ::= <digit> <digit><ip> ::= <domainstring>                        -- dotted decimal form (e.g., 10.0.0.6)                        -- or domain (e.g., twg.com)<port> ::= <digitstring><tset> ::= <digitstring><dte> ::= <digitstring><cudf-or-pid> ::= "CUDF" | "PID"                                    80________________________Figure_1:__String_BNF__________________________Four examples:"256"/NS+a433bb93c1_NS+aa3106#63/#41/#12/X121+234219200300'3a'H/TELEX+00728722+X.25(80)+02+00002340555+CUDF+"892796"TELEX+00728722+RFC-1006+03+10.0.0.6Note that theRFC 1006 encoding permits use of either a DNS DomainName or an IP address.  The former is primarily for ease of entry.  Ifthis DNS Domain Name maps onto multiple IP addresses, then multiplenetwork addresses should be generated.  The DNS Domain Name form isHardcastle-Kille                                                Page 4

RFC 1278            String encoded P-Address             November 1991for convenient input.  When mapping from an encoded address to stringform, the IP address form should always be used.4  EncodingSelectors are represented in a manner which can be easily encoded.  Inthe NS notation, the concrete binary form of network address is given.Otherwise, this string notation provides a mechanism for representingthe Abstract Syntax of a Network Address.  This must be encodedaccording to Addendum 2 of ISO 8348 [ISO87a].5  MacrosThere are often common addresses, for which a cleaner representationis desired.  This is achieved by use of Macros.  If a<network-address> can be parsed as:<otherstring> "=" *( any )Then the leading string is taken as a Macro, which is substituted.This may be applied recursively.  When presenting Network Address tohumans, the longest available substitution should be used.  Forexample:                       ________________________                       |_Macro_|Value__________ |                       | UK.AC |DCC+826+d110000 |                       |_Leeds_|UK.AC=120______ |Then ``Leeds=22'' would be expanded to ``DCC+826+d11000012022''.6  Standard MacrosNo Macros should ever be relied on.  However, the following aresuggested as standard.Hardcastle-Kille                                                Page 5

RFC 1278            String encoded P-Address             November 1991           ________________________________________________           |_Macro_____________|Value______________________ |           | Int-X25(80)       |TELEX+00728722+X25(80)+01+  |           | Janet-X25(80)     |TELEX+00728722+X25(80)+02+  |           | Internet-RFC-1006 |TELEX+00728722+RFC-1006+03+ |           |_IXI_______________|TELEX+00728722+RFC-1006+06+_|7  ReferencesReferences[CCI88]  The Directory --- overview of concepts, models and services,         December 1988. CCITT X.500 Series Recommendations.[HK91]   S.E. Hardcastle-Kille. Encoding network addresses to support         operation over non-osi lower layers. Request for CommentsRFC 1277, Department of Computer Science, University College         London, November 1991.[ISO87a] Information processing systems - data communications -         network services definition:  Addendum 2 - network layer         addressing, March 1987. ISO TC 97/SC 6.[ISO87b] ISO DIS 7498-3 on naming and addressing, May 1987.         ISO/IEC/JTC-1/SC 21.[Kil89]  S.E. Kille. A string encoding of presentation address.         Research Note RN/89/14, Department of Computer Science,         University College London, February 1989.8  Security ConsiderationsSecurity considerations are not discussed in this memo.9  Author's Address    Steve Hardcastle-Kille    Department of Computer Science    University College London    Gower Street    WC1E 6BTHardcastle-Kille                                                Page 6

RFC 1278            String encoded P-Address             November 1991    England    Phone:  +44-71-380-7294    EMail:  S.Kille@CS.UCL.AC.UKHardcastle-Kille                                                Page 7