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ISO/TC-97/SC-6 [Page 19]
RFC 941 April 1985
Network Layer Addressing
8.2.1.2 Format and Allocation of the IDI
A specific combination of IDI format and DSP abstract syntax is
associated with each allocated AFI value, as summarized in Table 8-2:
Table 8-2: AFI Values
___________________
| DSP Syntax |
|___________________|
| | |
__________| Decimal | Binary |
|IDI format| | |
|__________|_________|_________|
| X.121 36 37 |
|______________________________|
| ISO DCC 38 39 |
|______________________________|
| F.69 40 41 |
|______________________________|
| E.163 42 43 |
|______________________________|
| E.164 44 45 |_____________________
|______________________________|Character | National |
|ISO 6523-ICD 46 47 |(ISO 646) |Character |
|______________________________|__________|__________|
| Local 48 49 50 51 |
|____________________________________________________|
The IDI formats are defined as follows:
a) X.121
The IDI consists of a sequence of up to 14 digits allocated
according to CCITT Recommendation X.121. The X.121 number
identifies an authority responsible for allocating and assigning
values of the DSP.
IDP length: Up to 16 digits.
b) ISO DCC
The IDI consists of a three-digit Data Country Code (DCC). ISO DCC
values are allocated by ISO and assigned to ISO member countries or
appropriately sponsored non-member countries or authorities. The
values of the ISO DCC are a subset of the DCC values allocated by
ISO/TC-97/SC-6 [Page 20]
RFC 941 April 1985
Network Layer Addressing
CCITT in Recommendation X.121 to countries or geographical areas.
The DSP is allocated and assigned by the organization that
represents the country identified by the DCC.
IDP length: 5 digits.
c) F.69
The IDI consists of a telex number of up to 8 digits, allocated
according to CCITT Recommendation F.69, commencing with a 2- or
3-digit destination code. The telex number identifies an authority
responsible for allocating and assigning values of the DSP.
IDP length: Up to 10 digits.
d) E.163
The IDI consists of a public switched telephone network (PSTN)
number of up to 12 digits allocated according to CCITT
Recommendation E.163, commencing with the PSTN country code. The
PSTN number identifies an authority responsible for allocating and
assigning values of the DSP.
IDP length: Up to 14 digits.
e) E.164
The IDI consists of an ISDN number of up to 15 digits allocated
according to CCITT Recommendation E.164, commencing with the ISDN
country code. The ISDN number identifies an authority responsible
for allocating and assigning values of the DSP.
IDP length: Up to 17 digits
f) ISO 6523-ICD
The IDI consists of a 4-digit International Code Designator (ICD)
allocated according to ISO 6523. The ICD identifies an
organizational authority responsible for allocating and assigning
values of the DSP. The "structure of the code" required by ISO 6523,
clause 6.3(d), shall be registered as "According to ISO 8348
Addendum 2".
IDP length: 6 digits.
g) LOCAL
The IDI is null.
IDP length: 2 digits.
ISO/TC-97/SC-6 [Page 21]
RFC 941 April 1985
Network Layer Addressing
Note 1:
In cases (a), (c), (d), and (e) above, when the IDP is followed by a
decimal-syntax DSP, no discernible boundary is identified in this
Addendum between the IDP digits and the DSP digits.
Note 2:
A figure illustrating the division of the global network addressing
domain according to these formats is contained in Annex B.
Note 3:
The use of a particular IDI format as the basis for allocating an
NSAP address does not constrain routing to that NSAP to go through
any particular subnetwork. For example, the use of the E.163 IDI
format as the basis for allocating an NSAP address does not mean
that access to the NSAP necessarily involves use of the telephony
subnetwork (see clause 7.3).
Note 4:
Formats a, c, d, and e are based on specific CCITT numbering plans,
and as such may be affected by any changes to those plans. It
should be understood that in identifying and describing these
formats, this Addendum observes the current status of CCITT work on
numbering plans, and does not establish any preference or position
whatsoever concerning the way in which CCITT may choose to modify
the plans, or their relationships with one another, in the future.
Changes to this may be necessary to take any such further work by
CCITT into account. For example, the CCITT numbering plans in some
cases may provide escape mechanisms (such as a zero, 8, or 9 prefix)
from one numbering plan to another. This results in the possibility
of a choice that must be made concerning which of formats a, c, d,
and e should be used for the allocation of NSAP addresses, and may
also lead to suggestions that it is not necessary to include all of
the formats a, c, d, and e in this Addendum. Such choices, however,
are made within the context and responsibility of CCITT, and no
preference for one choice or another is made or implied by this
Addendum.
8.2.2 Abstract Syntax and Allocation of the DSP
Values of the DSP are allocated by the authority identified by the IDI
in the syntax identified by the AFI (see clauses 8.1.1.2 and 8.2.1.2).
The allocating authority specifies the format and semantics of the
DSP. If the authority identified by the IDI authorizes one or more
authorities to allocate semantic parts of the DSP, then all those
authorities must allocate using the same abstract syntax used by the
parent authority.
ISO/TC-97/SC-6 [Page 22]
RFC 941 April 1985
Network Layer Addressing
An authority may choose to allocate NSAP addresses with the DSP in a
decimal or binary abstract syntax for all IDI formats, and may choose
to allocate NSAP addresses with the DSP in a character (ISO 646) or
National Character abstract syntax when the IDI format is "Local" (see
Table 8-2). Clause 9 describes the latter case in detail.
8.2.3 Abstract Syntax of the DSP
The DSP may be allocated by the responsible authority in one of four
syntaxes, depending on the value of the AFI:
a) Binary: The DSP consists of zero or more binary octets, up to
the maximum specified in Table 8-3.
b) Decimal: The DSP consists of zero or more decimal digits, up
to the maximum specified in Table 8-3.
c) Character: The DSP consists of zero or more of those graphic,
characters with no national variant, plus the space
character, from ISO 646, up to the maximum specified
in Table 8-3.
d) National Character: The DSP consists of zero or more characters
from a character set determined by the allocating
authority, up to the maximum specified in Table 8-3.
Table 8-3 gives the maximum length of the DSP in its abstract syntax
for each of the IDI formats defined in clause 8.2.1.2. The
corresponding total NSAP address lengths are given in clause 8.4.
8.3 Network Address Concrete Syntax
As describe in Clause 8.1, the semantics of the NSAP address consists
of three fields in the following order:
a) the AFI, with an abstract syntax of two decimal digits;
b) the IDI, with an abstract syntax of a variable number of decimal
digits; and
ISO/TC-97/SC-6 [Page 23]
RFC 941 April 1985
Network Layer Addressing
Table 8-3: Maximum DSP Length
___________________
| DSP Syntax |
|___________________|
| | |
__________| Decimal | Binary |
|IDI format| | |
|__________|_________|_________|
| X.121 24 9 |
|______________________________|
| ISO DCC 35 14 |
|______________________________|
| F.69 30 12 |
|______________________________|
| E.163 26 10 |
|______________________________|
| E.164 23 9 |_____________________
|______________________________|Character | National |
|ISO 6523-ICD 34 13 |(ISO 646) |Character |
|______________________________|__________|__________|
| Local 38 15 19 7 |
|____________________________________________________|
c) the DSP, with an abstract syntax of a variable number of one and
only one of the following types: binary octets, decimal digits,
characters, or national characters.
This Addendum does not specify the way in which the semantics of an
NSAP address are encoded in Network Layer protocols by a concrete
syntax in NPAI (see Note following this clause). These encodings are
specified in Network Layer protocol standards.
Note: Encoding implies more than a concrete syntax, such as the order
of bit transmission, representation as tones or other signals, etc.
Nevertheless, this Addendum identifies two alternative concrete
syntaxes (see clauses 8.3.1 and 8.3.2) of the Network Address.
Reference to these may be made by Network Layer protocol specification
standards. It is possible that the concrete syntax used to encode the
Network Address as NPAI in a Network Layer protocol may be chosen to be
identical to one of these concrete syntaxes. It is not required that
this be the case, however (see clause 9).
The entire NSAP address taken as a whole may be represented explicitly
as a string of either decimal digits (decimal concrete syntax) or
binary octets (binary concrete syntax) as defined below. Network Layer
ISO/TC-97/SC-6 [Page 24]
RFC 941 April 1985
Network Layer Addressing
protocol specifications making reference to this Addendum shall specify
the way in which either the decimal concrete syntax or the binary
concrete syntax of the NSAP address (or both) is encoded as NPAI (see
clause 6.1.3).
8.3.1 Binary Concrete Syntax
The binary concrete syntax is generated by:
a) using two semi-octets to represent the two digits of the AFI,
yielding a value for each semi-octet in the rage 0000-1001;
b) padding the IDI with leading zero digits if necessary to obtain
the maximum IDI length (specified for each IDI format in clause
8.2.1.2), then using a semi-octet to represent the value of each
decimal digit (including leading padding digits, if preset),
yielding a value in the range 0000-1001; and, if the DSP syntax
is not decimal digits, using the semi-octet value 1111 as a pad
after the final semi-octet (if necessary) to obtain an integral
number of octets;
c) representing a decimal syntax DSP using the technique described in
(b);
d) representing a binary syntax DSP directly as binary octets;
e) when the IDI format is "Local", representing an ISO 646 character
syntax DSP by converting each character to a number in the range
32-127 using the ISO 646 encoding, with zero parity and the
parity bit in the most significant position, reducing the value
by 32, giving a number in the range 0-95, encoding this result as
a pair of decimal digits; and applying the technique described in
(b); and
f) when the IDI format is "Local", representing a National Character
syntax DSP by converting each national character to either one or
two octets according to the rules specified by the authority
responsible for allocating NSAP addresses including national
character DSP syntaxes.
8.3.2 Decimal Concrete Syntax
The decimal concrete syntax is generated by:
a) representing the two digits of the AFI directly as two decimal
digits;
b) padding the IDI with leading zero digits if necessary to obtain
the maximum IDI length (specified for each IDI format in Clause
8.2.1.2), representing the result directly as decimal digits;
ISO/TC-97/SC-6 [Page 25]
RFC 941 April 1985
Network Layer Addressing
c) representing a decimal syntax DSP directly as decimal digits;
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