ATM Local Area Internetworking

The main differences between traditional LANs and ATM are:

• LANs are connectionless, ATM is connection-oriented.

• The size of a LAN packet can vary (up to 1500 bytes in Ethernet -- and even higher in other LAN standards). In ATM all cells are 53 bytes.

• LANs support the use of broadcast and group MAC addresses explicitly, providing such services over a switched-based ATM network with point-to-point links in not trivial.

• LANs work mainly in best-effort mode. ATM adopted a similar mode -- the ABR service, but a major issue is how to provide effective congestion control.

There are two common approaches to ATM local area internetworking with existing LAN services and protocols:

1. LAN Emulation (LANE) being developed by the ATM Forum

2. Classical IP over ATM being developed by the Internet Engineering Task Force (IETF)

Figure 13 - Two Approaches to ATM Internetworking

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