ATM addresses
An ATM address, as defined by the ATM Forum, is 20 octets long and has the following fields:
- The Address Prefix, 13 octets, is interpreted hierarchically (left-to-right) and allows a variable number of hierarchy levels to be defined
- The ID is 6 octets long and makes it possible to use IEEE 802 addresses
- The Selector is a one-octet field used for subaddressing
There are three formats of 20-octet private ATM addresses:
- NSAP Encoded E.164 format
- DCC Format (Data Country Codes specified in ISO 3166)
- ICD Format (International Code Designators identify particular international organizations)
PNNI routing is closely coupled with ATM addresses and they have to be assigned correctly (compare with CIDR)