TCP/IP Tutorial and Technical Overview - IBM Redbooks

services of a classic LAN; thus, the upper layer does not know of the existence of
ATM. This is both an advantage and a disadvantage, because the knowledge of
the underlying network could be used to provide a more effective
implementation.
In the near future, both approaches will be used depending on the particular
requirements. Over time, when the mapping of applications to ATM is fully
defined and implemented, the scheme of a dedicated ATM implementation might
be used.
2.11 Multiprotocol over ATM (MPOA)
The objectives of MPOA are to:
► Provide end-to-end layer 3 internetworking connectivity across an ATM
network. This is for hosts that are attached either:
– Directly to the ATM network
– Indirectly to the ATM network on an existing LAN
► Support the distribution of the internetwork layer (for example, an IP subnet)
across traditional and ATM-attached devices. Removes the port to layer 3
network restriction of routers to enable the building of protocol-based virtual
LANs (VLANs).
► Ensure interoperability among the distributed routing components while
allowing flexibility in implementations.
► Address how internetwork-layer protocols use the services of an ATM
network.
Although the name is multiprotocol over ATM, the actual work being done at the
moment in the MPOA subworking group is entirely focused on IP.
2.11.1 Benefits of MPOA
MPOA represents the transition from LAN emulation to direct exploitation of ATM
by the internetwork-layer protocols. The advantages are:
► Protocols see ATM as more than just another link. Therefore, we are able to
exploit the facilities of ATM.
► Increases efficiency of the traditional LAN frame structure.
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