OSI/TS Configuration and Management Manual

Background Information About Addressing
OSI/TS Configuration and Management Manual—424831-001
2-11
Converting NSAP Addresses
Continuing with the example used in the previous two tables, an AFI value of 39
indicates that the IDP authority is ISO DCC and the DSP syntax is binary. Table 2-3
shows that the maximum DSP length for binary ISO DCC is 14 binary octets.
Note that there is no correspondence between the different syntax types. For example,
an NSAP address in decimal digits is not interchangeable with, nor convertible to, an
NSAP address in binary octets: they are two different NSAP addresses, even if they are
governed by the same network addressing authority. However, all NSAP addresses
share in common the fact that when they are encoded for transmission, they must be less
than or equal to 20 binary octets or 40 decimal ISO 646 digits (as specified by ISO
8348, Addendum 2).
Converting NSAP Addresses
Theoretically, an NSAP address constructed according to the rules provided by the
network addressing authority must be converted before it can be included in an NPDU
(network protocol data unit) for transmission over a physical link, as follows:
1. Convert it into computer-readable format—from the basic NSAP address (the
concept) to a format recognized by the Network Layer protocols (discussed in a
following subsection)
2. Encode it and include it in NPDUs (done by the Network Layer protocols)
An encoded NSAP address is unique in the Network Layer protocols all nonprotocol
contexts (national language, system, or any other locally devised semantics) have been
removed. Because it is unique, this encoded address should be used in all written and
verbal communication. The HRPF (hexadecimal reference publication format) has been
defined for this purpose, and is discussed in a following subsection.
Table 2-3. DSP Values
If the IDI Format
(Authority) Is ... Maximum DSP Length Is ...
Binary
Octets
Decimal*
Digits
Characters
(ISO 646)
National
Characters
X.21 (CCITT X.121) 9 24
ISO DCC (ISO 3166) 14 35
F.69 (CCITT F.69) 12 30
E.163 (CCITT E.163) 10 26
E.164 (CCITT E.164) 9 23
ISO ICD (ISO 6523) 13 34
Local 1538197
* If the AFI specifies decimal syntax for the DSP, the network addressing
authority may choose a null length for the DSP. In this case, the NSAP address
consists of the IDI value plus the AFI value.