3com 2000 TR Manual De Usuario

C

HAPTER

 2: TR-

IN

-FE C

ONCEPTS

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. 

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)

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.