ATM Addressing

The ATM Forum has adopted the subnetwork model of addressing, in which the ATM layer is responsible for mapping network layer addresses to ATM addresses. Several ATM address formats have been developed - one for public networks and three for private networks. Typically, public ATM networks will use E.164 (Consult Tanenbaum - Computer Networks) numbers, which are also used by Narrowband Integrated Services Digital Network (NISDN) networks. Figure 6 shows the format of private network ATM addresses. The three formats are Data Country Code (DCC), International Code Designator (ICD), and Network Service Access Point (NSAP) encapsulated E.164 addresses.

  

Figure 6: ATM Address Formats

The fields of ATM Addresses are as follows :

AFI	1 byte of authority and format identifier. The AFI field identifies the type of address. The defined values are 45, 47, and 39 for E.164, ICD, and DCC addresses, respectively.
DCC	2 bytes of data country code.
DFI	1 byte of domain specific part (DSP) format identifier.
AA	3 bytes of administrative authority.
RD	2 bytes of routing domain.
Area	2 bytes of area identifier.
ESI	6 bytes of end system identifier, which is an IEEE 802 Media Access Control (MAC) address.
Sel	1 byte of NSAP selector.
ICD	2 bytes of international code designator.
E.164	8 bytes of Integrated Services Digital Network (ISDN) telephone number.

The ATM address formats are modeled on ISO NSAP addresses, but they identify SubNetwork Point of Attachment (SNPA) addresses. Incorporating the MAC address into the ATM address makes it easy to map ATM addresses into existing LANs.