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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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The address resolution in an ATM network is defined as an extension of the ARP<br />

protocol <strong>and</strong> is described in 2.10.1, “Address resolution (ATMARP <strong>and</strong><br />

InATMARP)” on page 47.<br />

There is no mapping from <strong>IP</strong> broadcast or multicast addresses to ATM broadcast<br />

or multicast addresses available. But there are no restrictions for transmitting or<br />

receiving <strong>IP</strong> datagrams specifying any of the four st<strong>and</strong>ard <strong>IP</strong> broadcast address<br />

forms as described in RFC 1122. Members, upon receiving an <strong>IP</strong> broadcast or <strong>IP</strong><br />

subnet broadcast for their LIS, must process the packet as though addressed to<br />

that station.<br />

2.10.3 ATM LAN emulation<br />

Another approach to provide a migration path to a native ATM network is ATM<br />

LAN emulation. ATM LAN emulation is still under construction by ATM Forum<br />

working groups. For the IETF approach, see 2.10.2, “Classical <strong>IP</strong> over ATM” on<br />

page 50. There is no ATM Forum implementation agreement available covering<br />

virtual LANs over ATM, but there are some basic agreements on the different<br />

proposals made to the ATM Forum. The following descriptions are based on the<br />

<strong>IBM</strong> proposals.<br />

The concept of ATM LAN emulation is to construct a system such that the<br />

workstation application software “thinks” it is a member of a real shared medium<br />

LAN, such as a token ring. This method maximizes the reuse of existing LAN<br />

software <strong>and</strong> significantly reduces the cost of migration to ATM. In PC LAN<br />

environments, for example, the LAN emulation layer can be implemented under<br />

the NDIS/ODI-type interface. With such an implementation, all the higher layer<br />

protocols, such as <strong>IP</strong>, <strong>IP</strong>X, NetBIOS, <strong>and</strong> SNA, can be run over ATM networks<br />

without any change.<br />

56 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong>

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