From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Sun Apr 18 2004 - 18:46:25 GMT-3
At 3:54 PM -0400 4/18/04, Scott Morris wrote:
>That's acutally valid as well (I went back to look things up)... With the
>implementation of ISIS, CLNS actually accepts different formats of the area
>and system ID messages. The AFI actually indicates the rest of the format
>of the address (foreign to most of us, and WAY beyond the realm of caring
>for many!).
>
>The AFI format, at least all that I am aware of, have a 0 as the first bit
>of the first nibble, which really means that you have 0-7 as a valid first
>hex character instead of 0-F.
>
>ATM is a little different, where it's a 12-20 byte rendition under more
>stringent rules.
>
>HTH,
>
>Scott
>
From my book, _Designing Addressing Architectures for Routing and
Switching_, here's an excerpt from the subset of NSAP formats used
for ATM endpoint identifiers. There are a good many more NSAP
formats, dealing with such things as Telex and X.25 as well. Also,
every (from wetware) NSAP format, has two AFI values, one defining
the rest of the NSAP as binary encoding and the other defining the
rest as binary-coded decimal. You will most commonly see the ICD
binary format, AFI=0x47.
>Understanding the exact procedure of [OSI] self-configuration
>requires knowledge of routing protocols, which is beyond the scope
>of this textbook. Simply assume that the MAC sublayer address of a
>device can be prefixed with information on how to find this address
>in the overall address space. The basic idea is that end hosts can
>listen for announcements from routers, which contain an Initial
>Domain Part (IDP) and a High-Order Domain-Specific Part (HO-DSP).
>The end host knows its own MAC address, and prefixes this with the
>IDP and HO-DSP. A one-byte selector field is appended.
>
ICD International Code Designator Format
>Figure 8.8 shows an example of the International Code Designator
>(ICD) format for NSAPs, as administered for the U.S. government.
>
>In the International Code Designator (ICD) space, which begins with
>the Authority and Format Identifier (AFI) value 0x47, ISO delegated
>IDI codes 0x0005 and 0x0006 to the U.S. government (as NIST), which,
>in turn, delegated civil agency code 0x0005 administration to the
>General Services Administration and military code 0x0006 to the
>Defense Information Systems Agency (DISA). Code 0x0004 is delegated
>to the OSINET interoperability research network.
>
>Following the IDP, the DSP begins with a one-byte Domain-Specific
>Identifier. A three-byte Administrative administrative Authority
>authority field follows; the value of this field is controlled by
>the organization with the ISO-assigned IDI. In this example, GSA
>assigns AA values in the ICD 0x05 space, while DISA administers AA
>values in the ICD 0x06 space. Another way to say this is that any
>public NSAP that begins 0x470005 will be a US government address
>administered by GSA.
>
>The next two bytes are reserved, followed by a two-byte routing
>domain (RD) identifier, and a two-byte area identifier. This string
>of bytes, from the AFI to the area identifier, forms the high-order
>DSP (HO-DSP).
>The next six bytes are the end system identifier, and the last byte
>is the selector.
>
>ATM endpoint addressing uses four variants of the NSAP address:.
> ISO Data Country Code
> ISO International Code Designator
> ITU-T (former CCITT) E.164 private
> ITU-T E.164 public format
>Private networks are required to support the first three types,
>while public networks either must support the fourth, or the first
>three types. The first three are "data-oriented," in that they
>contain a six-byte end station identifier that often, in practice,
>is a MAC address. The ICD format was described above.
>
>Data Country Codes (DCC)
>
>Data country codes (DCCs) are associated with national addressing
>authorities. The IDP has an AFI that is 0x39 and a two-byte IDI with
>a value from the ISO 3166 country code space. The DSP is identical
>to that used with the ICD format.
>E.164 Private
>
>The "full NSAP" version of this format begins eginning with an AFI
>of 0x45, and the IDI is an 8-byte, binary-encoded field. It is
>followed by a DSP composed of a RD and AREA field, followed in turn
>by the six-byte end system ID and a selector field.
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