Powerconnect SFP/Fiber connectivity – Options, Requirements and Troubleshooting

Basic requirements for fiber connections on PowerConnect switches:

1. 1. MMF optical cables,
   2. LC connectors, and
   3. SFP transceivers.

1)     Optical Cables :

• •   Single Mode Vs Multi Mode

Single Mode cable has a diameter of 8.3 to 10 microns, through which only one mode will propagate, typically 1310 or 1550nm. SMF gives you a higher transmission rate and up to 50 times more distance than multi-mode, but it also costs more. it has a much smaller core than MM. The small core and single light-wave virtually eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fiber cable type.

 Multi-mode cable has typical core diameters of 50, 62.5, or 100 micrometers. MMF gives you high bandwidth at high speeds over medium distances. Light waves are dispersed into numerous paths, or modes, as they travel through the cable’s core, typically 850 or 1300nm. However, in long cable runs (greater than 3000 feet [914.4 meters]), multiple paths of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission.

 a)      1G solutions :

1G Optical Standard	Wavelength (nm)	Media	Fibre Diameter	Segment Length
SX	850	MMF	62.5	260 m
			50	550 m
LX	1310	MMF	62.5	440 m
			50	550 m
		SMF	9	5 Km
LH	1550	SMF	9	70 Km

b)      10G solutions : SR, LR, LRM etc.

10 G Optical Standard	Wavelength (nm)	Media	Fiber Diameter	Segment Length
SR	850	MMF	62.5 (OM1)	82 m
			50 (OM3)	300 m
LR	1310	SMF	9	25-40 Km
LRM	1310	MMF	62.5 (OM3)	220 m
			50 (OM3)	260 m

      OM3 Cabling Specification

• For many years 62.5/125 m OM1 and conventional 50/125 m MMF (OM2) were widely deployed in data networks. These fibers easily support applications via 1 Gbit/s speeds and, because of their relatively large core size, were ideal for use with LED transmitters. With the deployments of new networks, laser-optimized 50/125 m MMF (OM3) is being used. Cables can be made that support 10 GbE up to 550 meters.

2)    Connectors :

Older PC switches used SC, newer ones LC. In datacom and telecom applications nowadays SFF connectors (e.g. LC) are replacing the traditional connectors (e.g. SC), mainly to pack more connectors on the overcrowded faceplate, due to their smaller size. SC Connectors are frequently found on the previous generation of corporate networking gear, using GBICs.

ID	Name	Coupling Type	Diameter	Typical App
SC	Standard/Subscriber Connector	Snap (Push-Pull)	2.5 mm	Datacom and telcom; extremely common
LC	Lucent Connector	Snap	1.25 mm	High-density connections, SFP transceivers, XFP transceivers

3) Transceivers:

 a)     GBIC :

Used with GE and FC. By offering a standard, hot-swapable electrical interface, one GE port can support a wide range of physical media, from copper to long-wave single-mode optical fiber  at lengths of hundreds of kilometres. GBICs connect to SC type fiber connectors and can use MMF or SM cabling types. Optical GBIC modules are commonly available in the following categories:

• 850 nm (SX) – Shortwave
• 1310 nm (LX) – Longwave

Core diameter, modal bandwidth and distance needed are the only specs required to provide the appropriate GBIC.

Standard	Wavelength	Fiber Type	Core Diameter (um)	Modal Bandwidth (MHz*km)	Max Transmission Distance (m)
1000BASE-SX	850	MMF	62.5	160	722ft (200m)
1000BASE-SX	850	SMF	62.5	200	902ft (275m)
1000BASE-SX	850	SMF	50	400	1620ft (500m)
1000BASE-SX	850	SMF	50	500	1804ft (550m)
1000BASE-LX	1310	MMF	62.5	500	1804ft (550m)
1000BASE-LX	1310	SMF	50	400	1804ft (550m)
1000BASE-LX	1310	SMF	50	5000	1804ft (550m)

b)     SFP Transceivers :

The SFPs connect to LC type fibre connectors and can use MMF or SM cabling types. They offer data rates up to 10 G for Ethernet. SFP transceivers are designed to support SONET, GE, FC, etc. Modules are commonly available in three different wavelengths:

• • •     850 nm (SX) – Shortwave
    •     1310 nm (LX) – Longwave
    •     1550 nm (ZX) – Longwave Extended

 c)      XFP Transceivers: (10G)

 The XFP typically operates at 850nm, 1310nm or 1550nm, and used for 10 G SONET/SDH, FC, GE, 10 GE etc. XFPs connect to LC type fibre connectors and can use MMF or SM cabling types. These are the same components used by the SFP transceiver. XFP modules are commonly available in the following categories:

• • • 850 nm (SR) – Short Range
    • 1310 nm (LR) – Long Range

Standard	Wavelength	Fiber Type	Core Diameter (um)	Modal Bandwidth (MHz*km)	Max Transmission Distance (m)
10GBASE-SR	850	MMF	62.5	160	26m
10GBASE-SR	850	MMF	62.5	200	33m
10GBASE-SR	850	MMF	50	400	66m
10GBASE-SR	850	MMF	50	500	82m
10GBASE-SR	850	MMF	50	2000	300m
10GBASE-SR	850	MMF	50	400	240m
10GBASE-SR	850	MMF	50	500	300m
10GBASE-LR	1310nm	SMF	8.3/9/10	N/A	10km

TROUBLESHOOTING:

• •  Are the cables the correct type for the type of transceiver?  Verify compatible (SR, LR vs. MMF, SM).
  •  Are both transceivers the same type? SR, LR, LRM, etc.
  •  GBIC/SFP/XFP Supported on the device (Check Matrix)? Is it properly seated in network device?
  •  Are cables good, could we try a different cable ?
  • Malfunctioning GBIC/SFP/XFP – disconnect the cable and connect to another optical port with a known good GBIC/SFP/XFP. If link light appears,GBIC/SFP/XFP is bad.
  • Are the cables crossed over so that RX on one transceiver is connected to TX on the other? The local send fibre needs to be connected to a receive port on the remote GBIC/SFP/XFP and vice verca. Swap the cable fibers on one end and verify connectivity.
  • Try a loopback with the switch.  Put 2 transceivers of the same type in the switch, make sure you get the messages on the serial console that the switch sees them, connect one to the other with the same type of fiber cable that you are using in your network.   Do you get link?
  • Are you going through any patch panels or using any cable couplers?  Just to ensure these are good.
  • Port Disabled by UDLD – UDLD has detected a unidirectional link. Fix the cabling issue and re-enable the port. UDLD is a feature of Cisco switches.

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Optical transceiver diagnostics can be performed only when the link is present. If the link is not detected, you will not be able to execute the command. Fiber Optic analysis feature works only on SFPs that support the digital diagnostic standard SFF-4872.

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A loopback test is an aid we often use for debugging physical connection problems. Fiber transceivers have two ports, a transmitter & a receiver. If there is a loopback module handy, it can be used to verify the transceiver is working ok, instead of using another transceiver as its partner. The loopback module directly routes the laser signal from the transmitter port back to the receiver port. This can verify physical issues with the module. Such modules come in SC, LC & MTRJ flavors, and are available in 3 fiber types, 50/125um multimode, 62.5/125um multimode and 9/125um single mode, as well as 3 wavelengths, 850, 1310 and 1550 nm. In case you had such a module handy, it could have been used to test the transceivers. Some modules have a patch cable at the back which can be used for this as well.