LAN environments. In MPOA installations, routers are referred to as MPOA servers. When one station wants to transmit to another station, it queries its local MPOA server for the remote station's ATM address. The local server then queries its neighbor devices for information about the remote station's location. When a server finally responds, the orig- inating station uses the information to establish a connection with the remote station, while the other servers cache the information for fur- ther use. MPOA promises a great deal, but it is complex to implement and requires other ATM "components," such as the Private NNI capability, to work properly. Furthermore, it's being challenged by at least one alter- native technology, known as IP switching. IP switching is far less overhead intensive than MPOA. Furthermore, it takes advantage of a known (but often ignored) reality in the LAN interconnection world: Most routers today use IP as their core protocol and the great majority of LANs are still Ethernet. This means that a great deal of simplification can be done by crafting networks to operate around these two technological bases. And in fact, this is precisely what IP switching does. By using existing, low-overhead protocols, the IP- switching software creates new ATM connections dynamically and quickly, updating switch tables on the fly. In IP-switching environments, IP resides on top of ATM within a device (see Figure 7-13) providing the best of both protocols. If two communicating devices wish to exchange information and they have done so before, an ATM mapping already exists and no layer three involvement (IP) is required-the ATM switch portion of the service simply creates the connection at high speed. If an Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Transport Technologies Transport Technologies Figure 7-13 IP switching address looku