Tag Archives: 1000BASE-SX

How to Match Fiber Patch Cable for Your Multimode SFP?

When you prepare to connect some SFPs with fiber patch cords, you may find SFPs are multimode modules while your fiber cables are single-mode. Try to connect those optics to fiber cable, but no green light and the link fails. So multimode SFPs can’t work over single-mode fiber cables. To avoid the wasting of time and money, you should better know well about single-mode and multimode SFPs and fiber patch cords.

Single-mode and Multimode SFP

SFP, small form factor pluggable transceiver, can support the data rate up to 1Gbps. SFPs can be divided into single-mode and multimode modules.

For single-mode SFPs, there are “LX” for 1310 nm and “EX” “EZX” for 1550 nm. Single-mode SFPs are designed to transmit signals over long distances. For example, Cisco GLC-LH-SM-15 compatible 1000BASE-LX/LH SFP 1310nm 15km DOM transceiver, main product information is shown as follows:

  • Wavelength: 1310 nm
  • Interface: LC duplex
  • Max Cable Distance: 15 km
  • Max Data Rate: 1000Mbps
  • Cable Type: SMF

Comparatively, multimode SFPs are identified with “SX”. This kind of optics is specially for short distance data transmission. For instance, Cisco GLC-SX-MM compatible 1000BASE-SX SFP 850nm 550m transceiver, this is a typical multimode SFP.

  • Wavelength: 850 nm
  • Interface: LC duplex
  • Max Cable Distance: 550m over OM2 MMF
  • Max Data Rate: 1000Mbps
  • Cable Type: MMF

SFP-LX and SFP-SX

Single-mode Fiber Cable and Multimode Fiber Cable

Fiber patch cables are used to connect transceivers on your switch/device. You have to buy the right fiber cable type for your optics. Fiber cable has two different categories: single-mode and multimode.

Generally, single-mode fiber cable can support further distance because of lower attenuation, but the price is higher. While multimode fiber cable has a larger core, usually multimode fiber cable is constructed in 50/125 and 62.5/125. It allows multiple modes of light to propagate. When the light passes through the core, the light reflections increases and more data can be transmitted at given time. As the high dispersion during signal transmission, the link distance gets reduced. So multimode fiber cable is for short distance application. Multimode fiber cable is a little more complex than single-mode fiber cable since it includes four different types of OM1, OM2, OM3, OM4. OM1 and OM2 fiber patch cable can support the data rate up to 10Gbps. OM3 and OM4 are laser optimized so that they can be used in high density data center to support the data rate of 40Gbps and 100Gbps. The following table shows how long each kind of fiber cable can reach running at different data rate.

Fiber Mode Cable Type 1GbE 10GbE 40GbE 100GbE
Single-mode OS2 100km 40km 40km 40km
Multimode OM1 275m(SX) 33m(SR) / /
OM2 550m(SX) 82m(SR) / /
OM3 550m(SX) 300m(SR) 100m 100m
OM4 1000m(SX) 400m(SR) 150m 150m

Note: “SR” implies multimode 10Gpbs SFP+.

For more information about single-mode and multimode fiber cable, you can refer to my previous articles:
What Is Single Mode Fiber?
What Are OM1, OM2, OM3 and OM4?

Solutions for Multimode SFP

If you have Cisco Catalyst 3650 WS-C3650-48PS switches with 4x1G uplink ports, to build a 300m-network link, you are gonna purchase fiber patch cable and SFP modules. What kind of optical equipment should you choose?

As to the SFP module, you need Cisco GLC-SX-MM 1000BASE-SX SFP. Or you can spend less money on third-party SFPs with 100% compatibility. Next step, you need to find suitable fiber patch cable to match this type of SFP. Since 1000BASE-SX SFP is multimode, of course you need multimode fiber cable. Considering the distance of 300 meters, OM1 can only reach 275 meters. So OM2 is the best choice for it’s the cheapest and can reach 550 meters.

1000BASE-SX SFP connection

Conclusion

It’s obvious that multimode SFPs can’t work over single-mode fiber cables. When buying SFPs, watch the standards on the label carefully and find if it’s “SX” or “LX”, “EX”. If it shows “SX”, then find multimode fiber patch cable. It’s not very difficult to choose right cable for your SFP modules.

What’s Your Opinion Of Using 3rd Party SFP Modules On Cisco Catalyst Switch?

In general, the cost of an original brand SFP module is more expensive than a 3rd party one. Take Cisco 1000BASE-SX SFP (GLC-SX-MMD) for example, the list price of Cisco is about $ 500.00, but you can easily find a 3rd party SFP modules that can take a discount at up to 90% off. As the cost of SFP transceiver keep adding up over time, many labs or companies are seeking for SFP alternatives to help cut down the costs on these expensive modules. However, a frequent customer problem with Cisco’s new line of Catalyst switches is that they do not support 3rd party (non-Cisco) SFPs – or at least they do not seem to. If you’ve just replaced your network switches and tried using any 3rd party SFPs to connect your network backbone, you’ll quickly stumble across an error similar to the following:

Error message

%PHY-4-UNSUPPORTED_TRANSCEIVER: Unsupported transceiver found in Gi1/0/0
%GBIC_SECURITY_CRYPT-4-VN_DATA_CRC_ERROR: GBIC in port 65538 has bad crc

When you see this error, it means that your Cisco Catalyst switch has just disabled the GBIC port. Why? When a SFP is inserted into a switch’s GBIC port, the switch immediately reads a number of values from the SFP and if it doesn’t like what it sees, it throws the above error message and disables the port. Simple to understand, your Cisco Catalyst switches are configured by default not to work with the 3rd party (non-Cisco) SFPs.

As we know, all SFP modules contain a number of recorded values in their EEPROM that include:

  • Vendor Name
  • Vendor ID
  • Serial Number
  • Security Code
  • CRC

How To Solve This Issue & Successfully Use 3rd Party SFPs On Your Cisco Switch

When the errors displayed, many users will be very nervous and even begin to regret using the 3rd party SFPs. Is there no hope for a solution when facing such situation? Just be relax, the following content will give you some tips on it.

There are two undocumented commands which can be used to force the Cisco Catalyst switch to enable the GBIC port and use the 3rd party SFP.

3750G-Stack(config)# service unsupported-transceiver

Warning: When Cisco determines that a fault or defect can be traced to the use of third-party transceivers installed by a customer or reseller, then, at Cisco’s discretion, Cisco may withhold support under warranty or a Cisco support program. In the course of providing support for a Cisco networking product Cisco may require that the end user install Cisco transceivers if Cisco determines that removing third-party parts will assist Cisco in diagnosing the cause of a support issue.

3750G-Stack(config)# no errdisable detect cause gbic-invalid

When entering the “service unsupported-transceiver” command, the switch (eg. 3750G) will automatically throw a warning message as a last hope to prevent the usage of a 3rd party SFP. The “no errdisable detect cause gbic-invalid” command will help ensure the GBIC port is not disabled when inserting an invalid GIBC. In addition, since the service unsupported-transceiver is undocumented, if you try searching for the command with the usual method “service ?”, you won’t find it.

According to the test, Cisco 2960G, 3560G, 3750G, 4507R and 4507R-E Catalyst switches all accept both “service unsupported-transceiver” & “no errdisable detect cause gbic-invalid commands” commands without a problem. In fact, if the Catalyst switch is running IOS 12.2(25)SE and above, the undocumented commands are available.

Opinion on 3rd Party SFP Modules

People have different opinions on “Whether I should use 3rd party SFPs”. It seems a difficult question for them as the attractive price but unknown performance of the 3rd SFPs. In fact, take Catalyst 3750 Series Switches for example, starting from 12.2(25)SE release, the user has the option via CLI to turn on the support for 3rd party SFPs. However, you should remember that the Cisco TAC will not support such 3rd party SFPs. In the event of any link error involving such 3rd party SFPs the customer will have to replace 3rd party SFPs with Cisco SFPs before any troubleshooting can be done by TAC.

Thus, it is very necessary to use quality assurance SFP modules. Actually, there are some high quality SFP modules OEM vendors, such as Fiberstore. You would not worry about the compatibility of the usage. Because there is a perfect system from the production to shipment. All the products are tested before they shipped and ensure the 100% compatible and high quality. In addition, you can save more as the price is also very competitive.

GLC-SX-MMD

Some common types of SFPs supported on Cisco Catalyst 3750 Series Switches

  • 1000BASE-LX/LH SFP (GLC-LH-SM=)
  • 1000BASE-SX SFP (GLC-SX-MM=)
  • 1000BASE-ZX SFP (GLC-ZX-SM=)
  • 1000BASE-T SFP (GLC-T=)
  • 1000BASE-BX SFP 1490nm (GLC-BX-D=) (12.2(25)SEB and later)
  • 1000BASE-BX SFP 1310nm (GLC-BX-U=) (12.2(25)SEB and later)