Tech Note #22: Asynchronous Transfer Mode (ATM) Addresses
1998 Bionic Buffalo Corporation; All Rights Reserved.
14 September 1998
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unknown types of numbers may use one of the three standard formats, or may use another
In the three standard address formats, an Authority and Format Identifier (AFI), consisting of
two BCD digits in a single octet, indicates the format of address used. Not all networks support
all of the formats.
Data Country Code (DCC) format (AFI=39)
International Code Designator (ICD) format (AFI=47)
ISDN Telephone Number (E.164) format (AFI=44 for decimal numbers, AFI=45 for
Each of these address formats includes a single octet selector field, which is ignored by ATM
itself, but which may be used by the end systems as needed. Together with the AFI and selector
octets, the total available space for addresses in the setup message is 20 octets (160 bits) for each
Some networks, by private agreement among the parties, also may support other forms of
addressing. However, the available address space in all cases is limited to the same 20 octets
used for the standard formats.
Architecturally, the standard addresses are equivalent to OSI Network Service Access Point
(NSAP) addresses, and have the same formats. The selector field is equivalent to an NSAP
This format conforms to IEEE 802.x recommendations, as commonly used in LANs,
but also found in other environments. The authority for the country specified in the
Data Country Code (DCC) field of the address assigns or delegates assignment of the
addresses. ISO 3166 gives the DCC values.
The third field of the address, after the AFI and DCC, is the Domain Format Identifier
(DFI), which gives the format of the rest of the address. The administrative authority
identifies the national organization, which allocates the subsequent fields of the address.
The routing domain (RD) and area identifier (AREA) are part of a hierarchical address
space organization. The end-system identifier (ESI) gives the address of the specific
end-point. To allow autoconfiguration of addresses, the network can base the ESI on
the MAC address.