INTERNET-DRAFT S.E. Kille, A.W. Young
October 1995
Expires: April, 1996
A string encoding of Presentation Address
<draft-kille-presentationaddr-00.txt>
Status of this Memo
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Abstract
There are a number of environments where a simple string encoding of
Presentation Address is desirable. This specification defines such a
representation.
This is an update to RFC1278 in particular to support NSAP addresses
for ITOT over IPv6.
INTERNET--DRAFT String encoded P-Address October 1995
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 case of the presentation address containing
network addresses and no selectors.
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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]
<hexoctet> ::= <hexdigit> <hexdigit>
<decimaloctet> ::= <digit> | <digit> <digit>
| <digit> <digit> <digit>
<digitstring> ::= <digit> <digitstring> 10
| <digit>
<otherstring> ::= <other> <otherstring>
| <other>
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<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 only
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| "RFC-1006" "+" <prefix> "+" <ipv4>
[ "+" <port> [ "+" <tset> ]]
| "X.25(80)" "+" <prefix> "+" <dte> 60
[ "+" <cudf-or-pid> "+" <hexstring> ]
| "ECMA-117-Binary" "+" <hexstring> "+" <hexstring>
"+" <hexstring>
| "ECMA-117-Decimal" "+" <digitstring> "+"
<digitstring> "+" <digitstring>
| "ITOT" "+" <ip> [ "+" <port-or-oid> ]
<idi> ::= <digitstring>
<afi> ::= "X121" | "DCC" | "TELEX" | "PSTN" | "ISDN"
| "ICD" | "LOCAL" 70
<prefix> ::= <digit> <digit>
<ipv4> ::= <domainname> -- domain name (e.g., twg.com)
| <dottedquad> -- IPv4 dotted decimal form (e.g., 10.0.0.6)
<ip> ::= <ipv4>
| <ipv6> -- IPv6 conventional string representation
-- (e.g. FEDC:BA98:7654:3210:FEDC:BA98:7654:3210)
<port> ::= <digitstring> 80
<tset> ::= <digitstring>
<port-or-oid> ::= <port>
| <oid>
<oid> ::= <digitstring> "." <digitstringsequence>
<digitstringsequence> ::= <digitstring> "." <digitstringsequence>
| <digitstring>
<dte> ::= <digitstring>
<cudf-or-pid> ::= "CUDF" | "PID"
________________________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"
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TELEX+00728722+RFC-1006+03+10.0.0.6
ICD+0090+ITOT+FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
Note that the RFC 1006 and ITOT encodings 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 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 ITOT format
The encoding of the ITOT format is different in several ways:
1. not all of the information which can be represented in the string
encoding can be encoded in an NSAP address;
2. the value of the encoded NSAP address includes a trailing octet
which has the value '10000000'B, as specified in [ITOT].
3. Only IDI types which permit a DSP with a binary abstract syntax
and length at least 17 octets can be used. At present these are
the DCC and ICD formats.
The additional information in the string encoding which cannot be
represented in the NSAP address is the port or oid. The port is the
TCP port number. The oid is an OBJECT IDENTIFIER which identifies a
particular protocol stack and optional TCP port number. If this
information is present then it must be encoded in protocol information
which accompanies the NSAP address (for example as a
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INTERNET--DRAFT String encoded P-Address October 1995
protocol-information attribute in an X.500 Directory entry or as the
ProtocolInformation element of the AccessPoint type; see
[X.518/IS9594-4]) See [ITOT] for information on the encoding and
interpretation of this protocol information.
6 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''.
7 Standard Macros
No Macros should ever be relied on. However, the following are
suggested as standard.
________________________________________________
|_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+ |
|_Internet-ITOT_____|ICD+0090+ITOT+_____________ |
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8 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
RFC 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.
[ITOT] Y. Pouffary & A. Young ISO Transport Service on top of TCP
[X.518/IS9594-4] Information Technology - Open Systems
Interconnection - The Directory: Procedures for Distributed
Operation ITU-T recommendation X.518(1993) / ISO/IEC 9594-4
: 1993(E)
9 Security Considerations
Security considerations are not discussed in this memo.
10 Authors' Address
Steve Kille, Alan Young EMail: S.Kille@isode.com,
ISODE Consortium A.Young@isode.com
The Dome, The Square Phone: +44 181 332 9091
RICHMOND TW9 1DT Fax: +44 181 332 9019
U.K.
Kille, Young Expires: April, 1996 Page 7