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--- rb:sfp [30/11/2025 22:34] – [Multimode Fibre] andrew
+++ rb:sfp [09/06/2026 09:16] (current) – [Multimode Fibre] andrew
@@ Line 67: / Line 67: @@
 {{:rb:sfp_152240.jpg?200 |}}
-My guess is that the Single mode SFP are very similar to the Multi Mode, although the lasers may be more powerful, possibly bigger or have a heatsink?
+My guess is that the Single mode SFP are very similar to the Multi Mode, although the lasers may be more powerful due to the extended range for Single Mode, possibly bigger or have a heatsink?
+----
 ===== SFP commands - IOS =====
@@ Line 93: / Line 96: @@
 </code>
+Cisco 2960 series switch, this shows two inserted sfp, neither of which is connected to fibre, hence very low optical power on Rx.
+<code>
+x-1#sh interfaces transceiver
+If device is externally calibrated, only calibrated values are printed.
+++ : high alarm, +  : high warning, -  : low warning, -- : low alarm.
+NA or N/A: not applicable, Tx: transmit, Rx: receive.
+mA: milliamperes, dBm: decibels (milliwatts).
+                                 Optical   Optical
+           Temperature  Voltage  Tx Power  Rx Power
+Port       (Celsius)    (Volts)  (dBm)     (dBm)
+---------  -----------  -------  --------  --------
+Gi1/0/25     36.0       3.38      -5.0     -40.0
+Gi1/0/26     32.5       3.33      -5.1     -40.0
+</code>
+| Tx Power (dBm) | Transmit optical power | –9 to –3 dBm | Too low = failing laser or dirty connector |
+| Rx Power (dBm) | Receive optical power  | –20 to –3 dBm | Too low = excessive fiber loss / bad patch |