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2-2 CHAPTER 2: TR-IN-FE CONCEPTS
TR-in-FE Compared to Traditional Methods
Traditional means of combining Token Ring, Ethernet,
and Fast Ethernet include bridging and routing. With
routing, frame forwarding decisions are made in soft-
ware by looking into the network layer of each frame
and modifying the frame to reflect the standard
format of the media for which it is destined.
Similarly, bridging between these media may be
accomplished using Translational Bridging, sometimes
referred to as SRTB or SRTG. This is necessary with
non-routable protocols like SNA and Netbios. This
type of bridging deals with all the differences
between Token Ring and Ethernet frame formats such
as:
■ Address fields
■ Variable length source-route fields
■ Functional address to multicast address mapping
NetBuilder provides both routing and SRTG function-
ality. The decisions are, again, made in software and
the result is conversion of the source frame to a stan-
dard destination frame format. The benefit of the tra-
ditional means listed above is that all frames are
converted from media to media using standard frame
formats, which allows for simple mixing and match-
ing of products from multiple vendors. The downside
is that these bridges and routers are typically slow,
expensive, and more difficult to manage than switch
products.
TR-in-FE technology works, not by providing frame
conversion, but by using the Fast Ethernet as a trans-
port for the Token Ring frames. This means that every
frame does not need to be parsed deeply, nor does
source route to transparent frame mapping need to
happen.
Presently, TR-in-FE is based on developing standards
and requires that FE server connections and Switch
2000 TR Downlink Modules are 3Com products.
Once approved, TR-in-FE will be able to be integrated
with other vendors. FE switching infrastructure may
be from any vendor.
3Com Token Ring-in-Fast Ethernet System
The 3Com Token Ring-in-Fast Ethernet includes:
■ SuperStack II Switch 2000 TR
■ SuperStack II Switch 2000 TR Token Ring-in-Fast
Ethernet Module
■ Fast Ethernet Switch (SuperStack II Switch 3000)
■ 3Com Fast Ethernet network interface cards (NIC)
Token Ring-in-Fast Ethernet Module
This slide-in module provides a 200 Mbps Full-duplex
Fast Ethernet interface, which enables the Switch
2000 TR to become part of a Fast Ethernet switched
infrastructure. This module allows wire-speed trans-
mission of Token Ring-in-Fast Ethernet frames. Fast
Ethernet can be used to connect Token Ring clients to
Fast Ethernet servers or as an aggregation point for
multiple Token Ring switched connections.