Asynchronous Transfer Mode

ATM Addresses

ATM addresses are needed to support the use of virtual connections through an ATM network. At the simplest level, ATM addresses are 20 bytes in length and composed of three distinct parts. Figure 14.8 shows the three parts of the 20-byte ATM address.

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Figure 14.8 Simplified View of ATM Addressing

This ATM address breaks down into the following three basic parts:

ATM switch identifier The first 13 bytes identify a particular switch in the ATM network. The use of this portion of the address can vary considerably depending on which address format is in use. Each of the three major ATM addressing schemes in use provides information about ATM switch location differently. The three formats are the data country/region code (DCC) format, international code designator (ICD) format, and the E.164 format proposed by the ITU-T for international telephone numbering use in broadband ISDN networks.

Adapter MAC address The next 6 bytes identify a physical endpoint, such as a specific ATM adapter, using a media access control (MAC) layer address that is physically assigned to the ATM hardware by the manufacturer. The use and assignment of MAC addresses for ATM hardware is identical to MAC addressing for other Institute of Electrical and Electronic Engineers (IEEE) 802.x technologies, such as Ethernet and Token Ring.

Selector (SEL) The last byte is used to select a logical connection endpoint on the physical ATM adapter.

Although all ATM addresses fit this basic three-part structure, there are significant differences in the exact format of the first 13 bytes of any given address, depending on the addressing format that is being used or whether the ATM network is for public or private use.

In summary, the 20-byte ATM address is in the hierarchical format starting with the switch at the highest level, down to the adapter, and then down to the logical endpoint.

All of the three ATM address formats that are currently in widespread use (DCC, ICD, and E.164) include the following characteristics:

Compliance with the Network Service Access Point (NSAP) addressing plan as proposed by the Open Standards Interconnection (OSI) protocol suite of the International Standards Organization (ISO).
Each can be used to establish and interconnect privately-built ATM networks that support switched virtual circuits (SVCs).

Addressing in Detail

The type of ATM address used depends on whether the addresses are for a public or private ATM network. ATM addresses are used to establish virtual circuit connections between ATM endpoints. Figure 14.9 shows the three primary address formats.

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Figure 14.9 Primary ATM Address Formats

The three formats are known as data country/region code (DCC), International Code Designator (ICD), and E.164 addresses. The E.164 address format is designed specifically for public ATM networks. While a detailed explanation of each field is beyond the scope of this chapter, the most important fields from these address formats are listed in Table 14.1.

Table 14.1 Primary ATM Address Format Fields

Address Fields	Function
AFI	The single-byte authority and format identifier (AFI) identifies the type of address.
DCC	The defined values are 45 for E.164, 47 for ICD and 39 for DCC addresses.
AA	This single byte identifies the domain -specific part (DSP) of the address.
Reserve	Reserved for future use
RD	2 bytes of routing domain information
Area	2 bytes of area identifier
ESI	6 bytes of end system identifier, which is an IEEE 802.x media access control (MAC) address.
SEL	1 byte of NSAP selector
ICD	2 bytes of international code designator
E.164	8 bytes (16 digits) of the Integrated Services Digital Network (ISDN) telephone number

Incorporating the MAC address into the ATM address using the End System Identifier field makes it easier to adapt ATM addresses into existing LAN technologies that use IEEE 802.x address types.

Important

For long term success, it is important to plan for E.164 Public Network Integration.

Although Bellcore administers the area code and address assignment of PSTN telephone numbers used throughout North America, assignment and registration of unique E.164 ISDN telephone numbers is still relatively new.

If you are building a private ATM network and intend to eventually link it with public ATM networks, consider obtaining a public E.164 address to use when configuring and implementing ATM on your internal network.

Applying for an E.164 phone number is similar to acquiring a reserved set of phone numbers for a private business to use with traditional telephone service. For example, a large business could apply for and obtain a set of local dialing extensions or thousands group (such as 555-5000), and then assign phone numbers for PBX configuration as direct inbound dial (DID) numbers to individual phones or handsets. To find out who is responsible for registering public E.164 addresses in your area, check with your local ATM network service provider.