RFC 982 UNKNOWN ADDRESSING · INFRASTRUCTURE · ISO
NSAP DSP guidelines: Guidelines for the specification of the structure of the Domain Specific Part (DSP) of the ISO standard NSAP address
A recipe for structuring the local part of ISO network addresses.
RFC EDITOR
Braun, H.W., "Guidelines for the specification of the structure of the Domain Specific Part (DSP) of the ISO standard NSAP address", RFC 982, DOI 10.17487/RFC0982, April 1986, <https://www.rfc-editor.org/info/rfc982>.
BIBTEX
@misc{rfc982,
series = {Request for Comments},
number = 982,
howpublished = {RFC 982},
publisher = {RFC Editor},
doi = {10.17487/RFC0982},
url = {https://www.rfc-editor.org/info/rfc982},
author = {H.W. Braun},
title = {{Guidelines for the specification of the structure of the Domain Specific Part (DSP) of the ISO standard NSAP address}},
pagetotal = 11,
year = 1986,
month = apr,
} RFC text
Contents
Network Working Group ANSI
Request for Comments: 982 April 1986
Guidelines for the Specification of the Structure of the
Domain Specific Part (DSP) of the ISO Standard NSAP Address
ANSI Working Document X3S3.3/85-258
Status of This Memo
The following is a RFC edition of the ANSI "Guidelines for the
Specification of the Structure of the Domain Specific Part (DSP) of
the ISO Standard NSAP Address". It should be understood that this
ANSI working document is in a draft state and subject to change.
These Guidelines are an important prerequirement to allow IP
addressing within the ISO connectionless protocol (CLNS), which
itself is necessary to allow the coexistance of the IP and the CLNS
in the Arpanet attached gateways.
A RFC to specify a suitable IP addressing method for ISOgrams is
currently worked on in Internet Task Forces and should be expected as
an RFC shortly.
This RFC is for informational purposes only and it's distribution
is unlimited. It does not specify a standard for the Arpa-Internet.
Hans-Werner Braun (HWB@GW.UMICH.EDU)
University of Michigan
ANSI Guidelines
TITLE: GUIDELINES FOR THE SPECIFICATION OF THE STRUCTURE OF THE
DOMAIN SPECIFIC PART (DSP) OF THE ISO STANDARD NSAP ADDRESS
STATUS: X3S3.3 WORKING DRAFT
Introduction
There is a substantial amount of interest in providing guidance to
private address administration authorities on preferred formats and
semantics for the Domain Specific Part (DSP) of an NSAP address. In
particular it is felt that use of a limited number of preferred DSP
formats would allow organizations to easily use intermediate and end
systems from a variety of suppliers. This technical report specifies
the way in which the DSP may be constructed so as to facilitate
efficient address assignment.
1. Scope and Field of Application
This Technical Report specifies a recommended syntax and
interpretation for the Domain Specific Part of an NSAP address. NSAP
Address Administration Authorities are urged to use this format when
the equipment comprising an addressing domain is of a heterogeneous
nature.
2. References
ISO 6523 Data Interchange - Structure for the
identification of Organizations
ISO 7498 Information Processing Systems - Open Systems
Interconnection - Basic Reference Model
ISO 8348 Information Processing Systems - Data
Communications - Network Service Definition
ISO DIS 8348/DAD2 Information Processing Systems - Data
Communications - Addendum to the Network
Service Definition Covering Network Layer
Addressing
ISO DIS 8802 Information Processing Systems - Data
Communications - Local Area Networks
ECMA TR/20 Layer 4 to 1 Addressing
ANSI Guidelines
3. Definitions
(This section to be suppled)
4. Abbreviations
(This section to be supplied)
5. Addressing Principles
This section provides a summary of the major points contained in DIS
8348/DAD2, as they are relevant to this technical report.
Network addresses are defined to be hierarchical. An authority may
either assign a complete address, or else may identify a subdomain of
its own addressing domain within which addresses may be further
assigned by an identified authority for the subdomain. This is done
in such a way that all addresses are unique.
When an authority identifies a subdomain, this creates in effect a
prefix which applies to all addresses assigned within the subdomain.
Certain methods of assigning authority are recognized within the body
of DIS 8348/DAD 2. These take account of existing addressing
standards such as X.121. The abstract structure of an address is
shown in Figure 1.
ANSI Guidelines
+---------------------------+---------------------------+
I I I
I I D P I D S P I
I I I
+---------------------------+---------------------------+
: :
: :
V V
+-----+---------------------+
I I I
I AFI I I D I I
I I I
+-----+---------------------+
Figure 1: NSAP Address Structure
The components of this structure are as follows.
IDP: Initial Domain Part
This is the part of the address whose entire content is
standardized. It consists of two parts, the AFI and the IDI.
AFI: Authority and Format Identifier
This specifies the format of the IDI, the authority responsible
for allocating IDI values, and the syntax of the DSP.
IDI: Initial Domain Identifier
This identifies the subdomain from which DSP values are allocated,
and the authority responsible for allocating the values.
DSP: Domain Specific Part
The contents and semantics of the DSP are not specified in DIS
8348/DAD2. Its abstract syntax is however defined by the AFI. In
most cases, this means that the DSP abstract syntax can be either
binary or decimal.
IDI formats specified in DIS 8348/DAD2 identify a number of
authorities for IDI allocation. These are:
1. X.121 (Public data network numbering)
2. F.69 (Telex numbering)
ANSI Guidelines
3. E.163 (Telephone numbering)
4. E.164 (ISDN numbering)
5. ISO DCC (Geographical address assignment under ISO authority.
A subset of the DCC values used in X.121 have been used to
designate the national addressing authorities)
6. ISO 6523-ICD (Non-geographic address assignment under ISO
authority, using the International Code Designators according
to ISO 6523)
7. Local (the IDI is null and the entire address is contained in
the DSP).
6. Analysis
(This section to be supplied)
7. Recommendations
7.1 X.121 DSP format guidelines
Description of Binary syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. If DSP is present, a DSP of 2 or less octets is an NSAP
selector. A DSP between 3 and 9 octets is interpreted in the
manner described below.
The length of the subnetwork identification is fixed at two
octets (16 bits). The assignment of subnetwork
identifications is under the control of the administering
authority for the private domain, except that the value with
both octets hex "FF" is reserved to indicate that the
subnetwork is not explicitly identified.
The length of the subnetwork address may be up to six octets,
and is determined by the DSP length minus three octets. For
subnetworks using DIS 8802 MAC addressing, this field consists
of the octets of the MAC address in the same order as they are
defined in DIS 8802.
The NSAP selector occupies a single octet.
ANSI Guidelines
Description of Decimal syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. If DSP is present, a DSP of 8 or less decimal digits is
an NSAP selector. A DSP between 8 and 23 decimal digits is
interpreted in the manner described below.
The length of the subnetwork identification is fixed at five
decimal digits. The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that a value of "99999" is reserved to
indicate that the subnetwork is not explicitly identified.
The length of the subnetwork address may be up to fifteen
decimal digits, and is determined by the DSP length minus eight
decimal digits.
The NSAP selector occupies three decimal digits.
7.2 ISO DCC DSP format guidelines
Description of Binary syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. The length of the DSP is between 6 and 12 octets.
The first three octets identify an organization which has been
designated as an addressing authority. This authority is
responsible for assigning values to the remainder of the DSP.
The length of the subnetwork identification is fixed at two
octets (16 bits). The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that the value with both octets hex "FF"
is reserved to indicate that the subnetwork is not explicitly
identified.
The length of the subnetwork address may be up to six octets,
and is determined by the DSP length minus three octets. For
subnetworks using DIS 8802 MAC addressing, this field consists
of the octets of the MAC address in the same order as they are
defined in DIS 8802.
The NSAP selector occupies a single octet.
ANSI Guidelines
Description of Decimal syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. The length of the DSP is between 14 and 29 decimal
digits.
The first six digits identify an organization which as been
designated as an addressing authority. This authority is
responsible for assigning values to the remainder of the DSP.
The length of the subnetwork identification is fixed at five
decimal digits. The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that a value of "99999" is reserved to
indicate that the subnetwork is not explicitly identified.
The length of the subnetwork address may be up to fifteen
decimal digits, and is determined by the DSP length minus eight
decimal digits.
The NSAP selector occupies three decimal digits.
7.3 F.69 DSP format guidelines
Description of Binary syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. If DSP is present, a DSP of 2 or less octets is an NSAP
selector. A DSP between 3 and 9 octets is interpreted in the
manner described below. Interpretation of a DSP greater than 9
octets in length is not specified in this report.
The length of the subnetwork identification is fixed at two
octets (16 bits). The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that the value with both octets hex "FF"
is reserved to indicate that the subnetwork is not explicitly
identified.
The length of the subnetwork address may be up to six octets,
and is determined by the DSP length minus three octets. For
subnetworks using DIS 8802 MAC addressing, this field consists
of the octets of the MAC address in the same order as they are
defined in DIS 8802.
ANSI Guidelines
The NSAP selector occupies a single octet.
Description of Decimal syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. If DSP is present, a DSP of 8 or less decimal digits is
an NSAP selector. A DSP between 8 and 23 decimal digits is
interpreted in the manner described below. Interpretation of a
DSP greater than 23 decimal digits in length is not specified
in this report.
The length of the subnetwork identification is fixed at five
decimal digits. The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that a value of "99999" is reserved to
indicate that the subnetwork is not explicitly identified.
The length of the subnetwork address may be up to fifteen
decimal digits, and is determined by the DSP length minute
eight decimal digits.
The NSAP selector occupies three decimal digits.
7.4 E.163 DSP format guidelines
Description of Binary syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. If DSP is present, a DSP of 2 or less octets is an NSAP
selector. A DSP between 3 and 9 octets is interpreted in the
manner described below. Interpretation of a DSP greater than 9
octets in length is not specified in this report.
The length of the subnetwork identification is fixed at two
octets (16 bits). The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that the value with both octets hex "FF"
is reserved to indicate that the subnetwork is not explicitly
identified.
The length of the subnetwork address may be up to six octets,
and is determined by the DSP length minus three octets. For
subnetworks using DIS 8802 MAC addressing, this field consists
of the octets of the MAC address in the same order as they are
defined in DIS 8802.
ANSI Guidelines
The NSAP selector occupies a single octet.
Description of Decimal syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. If DSP is present, a DSP of 8 or less decimal digits is
an NSAP selector. A DSP between 8 and 23 decimal digits is
interpreted in the manner described below. Interpretation of a
DSP greater than 23 decimal digits in length is not specified
in this report.
The length of the subnetwork identification is fixed at five
decimal digits. The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that a value of "99999" is reserved to
indicate that the subnetwork is not explicitly identified.
The length of the subnetwork address may be up to fifteen
decimal digits, and is determined by the DSP length minus eight
decimal digits.
The NSAP selector occupies three decimal digits.
7.5 E.164 DSP format guidelines
Description of Binary syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. If DSP is present, a DSP of 2 or less octets is an NSAP
selector. A DSP between 3 and 9 octets is interpreted in the
manner described below. Interpretation of a DSP greater than 9
octets in length is not specified in this report.
The length of the subnetwork identification is fixed at two
octets (16 bits). The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that the value with both octets hex "FF"
is reserved to indicate that the subnetwork is not explicitly
identified.
The length of the subnetwork address may be up to six octets,
and is determined by the DSP length minus three octets. For
subnetworks using DIS 8802 MAC addressing, this field consists
of the octets of the MAC address in the same order as they are
defined in DIS 8802.
ANSI Guidelines
The NSAP selector occupies a single octet.
Description of Decimal syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. If DSP is present, a DSP of 8 or less decimal digits is
an NSAP selector. A DSP between 8 and 23 decimal digits is
interpreted in the manner described below. Interpretation of a
DSP greater than 23 decimal digits in length is not specified
in this report.
The length of the subnetwork identification is fixed at five
decimal digits. The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that a value of "99999" is reserved to
indicate that the subnetwork is not explicitly identified.
The length of the subnetwork address may be up to fifteen
decimal digits, and is determined by the DSP length minus eight
decimal digits.
The NSAP selector occupies three decimal digits.
7.6 ISO 6523-ICD DSP format guidelines
Description of Binary syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. The length of the DSP is between 5 and 11 octets.
The first two octets identify an organization which has been
designated as an addressing authority. This authority is
responsible for assigning values to the remainder of the DSP.
The length of the subnetwork identification is fixed at two
octets (16 bits). The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that the value with both octets hex "FF"
is reserved to indicate that the subnetwork is not explicitly
identified.
The length of the subnetwork address may be up to six octets,
and is determined by the DSP length minus three octets. For
ANSI Guidelines
subnetworks using DIS 8802 MAC addressing, this field consists
of the octets of the MAC address in the same order as they are
defined in DIS 8802.
The NSAP selector occupies a single octet.
Description of Decimal syntax
The length of the DSP can be determined since the total address
length is known, and the IDP has fixed length for any given AFI
value. The length of the DSP is between 12 and 27 decimal
digits.
The first four digits identify an organization which has been
designated as an addressing authority. This authority is
responsible for assigning values to the remainder of the DSP.
The length of the subnetwork identification is fixed at five
decimal digits. The assignment of subnetwork identifications
is under the control of the administering authority for the
private domain, except that a value of "99999" is reserved to
indicate that the subnetwork is not explicitly identified.
The length of the subnetwork address may be up to fifteen
decimal digits, and is determined by the DSP length minus eight
decimal digits.
The NSAP selector occupies three decimal digits.
7.7 Local DSP format guidelines
No recommendations made.
AI ELI5
On this page
PROBLEMAs organizations deployed ISO systems across networks, they needed a standard way to structure the local portion of addresses (the Domain Specific Part) to ensure efficient assignment and interoperability between systems from different vendors.
MECHANISMRFC 982 provides guidelines for how the DSP should be divided into subnetwork identification, subnetwork address, and NSAP selector fields, with different recommended formats for addresses derived from different numbering authorities.
WHY IT MATTERSOrganizations administering NSAP addresses can now follow a consistent structure, making it easier to hand out addresses and for heterogeneous systems to work together.
§1Addresses for ISO Networks
NSAP (Network Service Access Point) addresses identify services on ISO networks. Like postal addresses, they are hierarchical: each address is split into two parts. The Initial Domain Part (IDP) is standardized and identifies which authority is responsible for allocating the rest of the address. The Domain Specific Part (DSP) is what that authority gets to structure as it likes.
When organizations deploy heterogeneous systems—equipment from different vendors—each using its own DSP structure can cause interoperability problems. This memo provides guidelines for how to divide the DSP consistently across different numbering schemes, so a system from one vendor can understand addresses assigned by another.
A postal address starts with a country code (standardized), then you can structure the rest however you want. But if everyone structures it differently, mail gets lost. This memo gives a standard way to organize the "local" part.
§2The Address Layout
An NSAP address is built in layers. First comes the Authority and Format Identifier (AFI), which specifies the format and the authority in charge. Next is the Initial Domain Identifier (IDI), which pinpoints a particular subdomain under that authority. Together, AFI and IDI form the standardized IDP.
The DSP that follows is left to the administering authority. RFC 982 recommends dividing it into three fixed fields in a specific order. This structure allows different numbering authorities (X.121 for public data networks, telephone numbering for ISDN, organizational codes, and others) to use their own encoding while maintaining a predictable layout.
Think of layers: international body → country → authority → organization → subnetwork → machine → service. Each layer is a separate field. The memo explains which fields are standardized and which the local authority controls.
§3The Three DSP Fields
The DSP contains exactly three fields. First, subnetwork identification, a fixed-size field set by the administering authority to identify which subnetwork the address belongs to. A reserved value (hex FF in binary, 99999 in decimal) means the subnetwork is implicit. Second, subnetwork address, which typically holds the MAC address of a machine on that subnetwork, allowing variable length to accommodate different network types. Third, NSAP selector, a fixed-size field at the end identifying which service or process on the host should handle the packet—similar to a port number in IP.
The RFC specifies these field sizes for each common numbering authority. X.121 addresses, for instance, use 2-octet subnetwork IDs in binary format, but 5 decimal digits in decimal format. ISDN (E.164) and other authorities have their own sizes. Every authority gets both binary and decimal options.
DSP is divided like an envelope: address block + building section + apartment number. The address block size depends on which postal authority you're in, but the pattern is always the same. This memo says: if you're X.121, use these sizes; if you're E.164, use those sizes.
§4Guidance for Addressing Authorities
RFC 982 advises private and public address administration authorities to follow these guidelines when deploying networks with equipment from different suppliers. An authority can choose a numbering scheme (X.121 for public networks, ISO DCC for geography, ISO 6523-ICD for organizational codes) and then apply the corresponding DSP structure recommended in the memo.
This is a working draft and informational only, not a formal standard. The value is in providing a reference structure so that heterogeneous systems can be deployed without extensive reconfiguration. Following these guidelines ensures that an authority's address assignment decisions will work predictably across different vendors' equipment.
If you're handing out addresses in your organization, pick a scheme (company ID, geography, whatever), then follow this memo's layout for the address. Everyone building systems for your network will then understand each other.
§5References
[1]ISO 8348, Information Processing Systems - Data Communications - Network Service Definition.
[2]ISO DIS 8348/DAD2, Information Processing Systems - Data Communications - Addendum to the Network Service Definition Covering Network Layer Addressing.
[3]ISO 6523, Data Interchange - Structure for the identification of Organizations.
[4]ISO 7498, Information Processing Systems - Open Systems Interconnection - Basic Reference Model.