RFC1278 - A string encoding of Presentation Address

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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.

Abstract

There are a number of environments where a simple string encoding

of Presentation Address is desirable. This specification defines

sUCh a representation.

RFC1278 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

[ISO87a].

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.

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RFC1278 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

The_BNF_is_given_in_figure_1.__________________________________________

<digit> ::= [0-9]

<other> ::= [0-9a-zA-Z+-.]

<domainchar> ::= [0-9a-zA-Z-.]

<hexdigit> ::= [0-9a-fA-F]

<digitstring> ::= <digit> <digitstring> 10

<digit>

<other>

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RFC1278 String encoded P-Address November 1991

<presentation-address> ::=

[[[ <psel> "/" ] <ssel> "/" ] <tsel> "/" ]

<network-address-list>

<network-address-list> ::= <network-address> "_" <network-address-list>30

<network-address>

<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

-- ISO 8348 Compatability 50

<idp> ::= <digitstring> -

<dsp> ::=

"d" <digitstring> -- Abstract Decimal

"x" <dothexstring> -- Abstract Binary

"l" <otherstring> -- IA5: local form only

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RFC1278 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> "+"

<afi> ::= "X121" "DCC" "TELEX" "PSTN" "ISDN"

"ICD" "LOCAL"

-- dotted decimal form (e.g., 10.0.0.6)

-- or domain (e.g., twg.com)

<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+10.0.0.6

Note that the RFC1006 encoding permits use of either a DNS Domain

Name or an IP address. The former is primarily for ease of entry. If

this DNS Domain Name maps onto multiple IP addresses, then multiple

network addresses should be generated. The DNS Domain Name form is

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RFC1278 String encoded P-Address November 1991

for convenient input. When mapping from an encoded address to string

form, the IP address form should always be used.

4 Encoding

Selectors are represented in a manner which can be easily encoded. In

the NS notation, the concrete binary form of network address is given.

Otherwise, this string notation provides a mechanism for representing

the Abstract Syntax of a Network Address. This must be encoded

according to Addendum 2 of ISO 8348 [ISO87a].

5 Macros

There are often common addresses, for which a cleaner representation

is 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 to

humans, the longest available substitution should be used. For

example:

________________________

_Macro_Value__________

UK.AC DCC+826+d110000

_Leeds_UK.AC=120______

Then ``Leeds=22'' would be eXPanded to ``DCC+826+d11000012022''.

6 Standard Macros

No Macros should ever be relied on. However, the following are

suggested as standard.

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RFC1278 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 References

References

[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 Comments

RFC1277, 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 Considerations

Security considerations are not discussed in this memo.

9 Author's Address

Steve Hardcastle-Kille

Department of Computer Science

University College London

Gower Street

WC1E 6BT

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RFC1278 String encoded P-Address November 1991

England

Phone: +44-71-380-7294

EMail: S.Kille@CS.UCL.AC.UK

Hardcastle-Kille