A string encoding of Presentation Address
RFC 1278

Document Type RFC - Informational (November 1991; No errata)
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Network Working Group                            S.E. Hardcastle-Kille
Requests for Comments 1278                   University College London
                                                         November 1991

              A string encoding of Presentation Address

Status of this Memo
    This memo provides information for the Internet community.  It
    does not specify an Internet standard.  Distribution of this memo
    is unlimited.

    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 1991

1  Introduction

OSI Application Entities use presentation addresses to address other
Application Entities.  The model for this is defined in [ISO87b].
Presentation addresses are stored in the OSI Directory using an ASN.1
representation defined by the OSI Directory [CCI88].  Logically, a
presentation address consists of:

 o  A presentation selector

 o  A session selector

 o  A transport selector

 o  A set of network addresses

The selectors are all octet strings, but often have IA5 character
representations.  The format of network addresses is defined in
There is a need to represent presentation addresses as strings in a
number of different contexts.  This Internet Draft defines a format
for use on the Internet.  It is for display to human users, and its
use is recommended whenever this needs to be done.  Typically, this
will be for system managers rather than for end users.  It is not
intended for internal storage.

This Internet Draft was originally published as UCL Research Note
RN/89/14 [Kil89].  It was agreed as a unified syntax for the THORN and
ISODE projects.  It is used throughout ISODE.
Christian Huitema of Inria and Marshall Rose of PSI Inc.  gave much
useful input to this document.

2  Requirements

The 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  Format


<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>

<dothexstring> ::= <dotstring> | <hexstring>

<presentation-address> ::=
                [[[ <psel> "/" ] <ssel> "/" ] <tsel> "/" ]

<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
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