Fast EtherHub 3500 System User’s Guide
1-10 Product Overview
As a device functioning on the media access control (MAC)
layer, the extender modules are protocol independent, and
therefore compatible with IEEE802.3, IEEE802.3u, TCP/IP,
NetWare, DECnet and XNS protocols. They can provide a
connection between conventional 10BASE-T and high-speed
100BASE-TX networks; or can serve as a 2-port bridge in a
100BASE-TX or 100BASE-FX environment. Moreover, where
traditional 100BASE-TX networks restrict the maximum
distance between end-nodes to 205 meters, these modules break
down this barrier. By breaking your network into smaller and
more manageable segments, each linked to the larger network
with a SmartExtender Module, the maximum distance for
communications between end-nodes is unlimited (depending on
the specific timing requirements of your network applications).
Switching Methods
Traditional bridges and routers use a switching method called
store-and-forward in which the entire frame must be received
before performing a table look-up for the destination node and
forwarding the packet to the corresponding port. As a result,
each packet experiences a hefty delay. It may be necessary to
use store-and-forward when a lot data errors are occurring over
the network, or when connecting to very slow devices.
Compared to this “conservative” mode of operation, fragment-
free cut-through switching significantly reduces packet
transmission delay by picking the destination address out of the
header as soon as the first full 64 bytes has been received. This
technique directs the frame to the appropriate segment long
before the full packet has been received. It also cleans up the
data stream by preventing runts from being passed along,
thereby improving data reliability.
Although fragment-free cut-though switching is recommended
as the fastest method for most applications, store and forward is
also supported by the SmartExtender Modules to guarantee