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Black Box Modular Switches Installation and User Guide (8/99)
35
reduce the buffer space used. When the available free-buffer queue increases
, the Switch will send
a “RESUME" packet to indicate the transmitter to start sending the packets. Of course, the
transmitting device must also support the 802.3x flow control standard in order to communicate
properly during normal operation.
Note: When in Half-Duplex mode, the Modular-switch implements a back-
pressure algorithm on 10/100 Mb ports for flow control. That is, the switch prevents
frames from entering the device by forcing a collision indication on the half-duplex
ports that are receiving. This temporary “collision” delay allows the available buffer
space to improve, as the switch catches up with the traffic flow.
4.7 Power Budget Calculations for LE14XXA-Series 4PM’s with Fiber Media
Receiver Sensitivity and Transmitter Power are the paramet
ers necessary to compute
the power budget. To calculate the power budget of different fiber media installations using
LE14XXA models, the following equations should be used:
OPB (Optical Power Budget) = P
T
(min) - P
R
(min)
where P
T
= Transmitter Output Power, and P
R
= Receiver Sensitivity
Worst case OPB = OPB - 1dB(for LED aging) - 1dB(for insertion loss)
Worst case distance = {Worst case OPB, in dB} / [Cable Loss, in dB/Km]
where the “Cable Loss” for 62.5/125 and 50/125µm (M.m) is 2.8 dB/km,
and the “Cable Loss” for 100/140 (Multi-mode) is 3.3 dB/km,
and the “Cable Loss” for 9/125 (Single-mode) is 0.5 dB/km
The following data has been collected from component manufacturer’s (HP’s and Siemens’) web
sites and catalogs to provide guidance to network designers and installers.
Fiber
Port
Module
Speed,
Std.
Mode
Std.
km
fdx
(hdx)
Wave
-
lengt
h
nm
Cable
Size
µm
X’mitr
Outpu
t
P
T ,
dB
R’cvr
Sens.
P
R
,
dB
Wors
t
OPB,
dB
Worst*
distanc
e Km,
fdx
typica
l
OPB,
dB
typical*
distanc
e
Km, fdx
LE1424C
10 Mb
FL
Multi-
mode
2
(2)
850
62.5/12
5
100/14
0
50/125
-15.0
-9.5
-19.5
-31
-31
-31
14
19.5
9.5
5
5.9
3.4
17
23.5
13.5
6
7
4.8
LE1428C
100Mb
FX
Multi-
mode
2
(0.4)
1300
62.5/12
5
50/125
-20
-23.5
-31
-31
9.0
5.5
2.5
2.0
14
12
5
4
LE1421C
100Mb
FX
Single-
mode
18+
(0.4)
1300
9/125 -15 -31 14 28
17.5 35
LE1422C
100Mb
FX
Multi-
mode
2
(0.4)
1300
62.5/12
5
50/125
-20
-23.5
-31
-31
9.0
5.5
3.0
2.0
15.8
12.2
5.5
4.0