System information

Chapter 4. ATM LAN backbone interoperability and migration 71
we face the challenge that all the servers reside on Ethernet segments or
VLANs, and all the workstations are on a token-ring.
As the migration of the workstations may well extend over one or two years,
our migration solution must provide ample bandwidth and capacity for
bridging or routing between physical as well as emulated Ethernet and
token-ring LANs.
The developers at Cisco Systems had already anticipated this requirement.
They chose to make the first - and so far only - ATM LAN adapter for Catalyst
6500 an OC-12 adapter with a speed of 622 Mbps.
The Catalyst OC-12 adapter has an on-board LAN emulation client as well as
an MPOA client. This suits our purposes very well. In addition, it provides for
a LAN Emulation Server (LES) and a Broadcast and Unknown Server (BUS).
The capacity of the Catalyst OC-12 adapter for handling LANE traffic is
nominally 400 kpps, which is consistent with the interface speed.
Catalyst 6500 does not support translational bridging nor token-ring ELAN, so
we must rely on an ATM router/bridge to route/translate between Ethernet
and token-ring. Fortunately, this function is readily available.
For the IP traffic, we can distribute the load of translation to the MSS clients in
the IBM 8270 and short-cut route with the MPOA protocol to the MPOA client
in the Catalyst 6500.
In smaller networks, customers have sometimes saved the cost of the IBM
8270 MSS client UFC and purchased only the ATM Uplink UFC. In this case,
the MSS or a Cisco router may be used to do the routing.
Note that this may require additional router capacity. But it is probably more
advantageous to buy an extra router than to replace the ATM Uplink UFCs
with MSS client UFCs. You may use an existing MSS or a Cisco router with an
OC-3 adapter as a “router-on-a-stick” installing a single physical interface in
the router and provisioning it with multiple "virtual interfaces."
A Cisco router with a fully configured IOS Version 12 has all the functions of
the MSS with a few exceptions such as intelligent broadcast reduction (IBM
proprietary function). Although a Cisco router can have full
LECS/LES/BUS/MPS capability, customers are probably inclined to leave
these functions to the MSS at this time. However, if there is a heavy load of
translational bridging, a Cisco 7200 as an one-armed router (OAR) is an
excellent choice.