System information

Chapter 2. Functional comparisons 19
For these reasons, our general recommendation for a long-term strategy is to
migrate the ATM LAN backbone to an Ethernet backbone. The periphery of an
IBM 8265 backbone is frequently a mixture of Ethernet and token-ring
because ATM and advanced LAN emulation were excellent technologies to
provide a high-speed backbone for both of these media access technologies
as well as to provide for integration between them.
All of this amounts to a general recommendation to build a parallel or overlay
Ethernet backbone to secure an orderly migration. In the process of doing so,
we may take advantage of functions such as MPOA for IP and IPX and of the
high performance of the MSS to bridge non-routable protocols. This is
advantageous because we need a high bandwidth connection between the
two backbones during the transition. In Chapter 4, “ATM LAN backbone
interoperability and migration” on page 67 we will discuss a scenario for ATM
LAN migration in more detail.
The most likely candidate to complement and eventually replace the IBM
8265 switch is Cisco Catalyst 6500. However, if there is a specific, continuing
requirement for ATM interfaces and cell switching, Catalyst 8540 provides an
excellent combination of both ATM and Gigabit Ethernet technologies.
2.2.1 Criteria for comparison
Major functions to consider for interoperability are:
• Interfaces
• Interface signalling
• Call routing, PNNI
• Traffic management
• LAN emulation services
• Layer-3 services
2.2.1.1 Interfaces
The common interfaces for the LAN environment such as OC-3 and OC-12
are readily supported by most manufacturers of ATM LAN switches for UTP
wiring or multi-mode or single mode fiber, or interface converters are
generally available.
ATM-25 is still in use by some customers, but because it did not gain wide
market acceptance, this technology is being phased out by most vendors.
IBM has withdrawn most of its ATM-25 products from marketing. To
investigate a migration strategy, IBM Global Services contacts for your
country are found at
http://www.ibm.com/planetwide.