Black Box Mixed-Media Fiber Hubs
Installation and User Guide (4/99)
2.5.1
LH8050A-SST (includes an SPM with mm fiber-ST port in the bonus port)
12
LH8050A-SS
The significant feature of the LH8050A-SST is that the built-in switched fiber bonus port
operates in full-duplex mode, sending packets on one fiber
filament while simultaneously and independently receiving
packets on the other. There is no “collision domain” with
full- duplex, and while this violates the specs of traditional
Ethernet, it is accepted in modern network designs.
Therefore, the SPM in the LH8050A-SST extends the
distance limits of Fast Ethernet. In particular, with multi-
mode fiber, it permits Fast Ethernet cable distances of up to
2km, much more than the 412m half-duplex distance limit
otherwise obtainable.
These SPMs can also be configured to operate as a
half-duplex switch port. As shown in the figure, the jumper located on the SPM board by
default is factory set to full-duplex mode (position 2-3). By setting the jumper in position 1-2, it
will operate as shared (half duplex). To operate properly in either half- or full-duplex mode, the
device on the other end of the fiber segment must also be a corresponding mode device. Since
full-duplex Fast Ethernet (802.3x) is a recent standard, it is recommended that the device on the
other end of the segment be another full-
duplex fiber SPM or equal
T
As is typical for bridges and
switches, the internal packet buffer space of
the SPM in the LH8050A-SST temporarily
stores unfiltered packets. It is desirable to
have a large packet buffer for temporary
storage, particularly when operating at
different speeds (such as 10 and 100) or with
different traffic types (shared and full-
duplex). The SPM’s packet buffer is 1Mbps
to maintain high network performance. The MAC address memory is 8KB, suitable for medium
to large networks.
R
X
L
IN
K
FULL
DUPLEX
LH8050A-SST
HALF FULL
DUPLEX MODE
1
HALF FULL
In summary, the LH8050A-SST is an LH8050A hub with a multi-mode fiber optic
switching port module(SPM) built-in. The SPM has 100Mbps ST-type connectors. There are
R
X
L
IN
K
FULL
DUPLEX
1
HALF DUPLEX
HALF FULL
1
FULL DUPLEX
(Default)
FULL/HALF JUMPER
