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Do you really know 1000BASE-LX / LH SFP?

Do you really know 1000BASE-LX / LH SFP?

1000BASE-LX/LH SFP1000BASE-LX LH SFP, one of the commonly used fiber optic transceivers, is now widely used in optical transmission systems. With the development of 40/100G Ethernet, even 400G Ethernet, this kind of transceiver module is nothing new to the module users. However, few people can deliver a clear answer to the question of what “1000BASE-LX / LH” infers. Well, if you know what it means, congratulations! you are the one of the few. You can skip today’s contents or share your experience to us in the comment. Actually, this post is a simple reference source for the beginners in this field or those who are lack of knowledge with fiber optic transceiver but have a strong interest in it.

To begin with, I’d like to make a brief introduction of 1000BASE-LX / LH SFP. This kind of SFP is similar with the other SFPs in basic working principle and size. But it is compatible with the IEEE 802.3z 1000BASE-LX standard, operating on standard single-mode fiber-optic link spans of up to 10 km and up to 550 m on any multimode fibers. In addition, when used over legacy multimode fiber type, the transmitter should be coupled through a mode conditioning patch cable (see Earlier article: Why Mode Conditioning Patch Cable Necessary for 1000Base-LX / LH Application).

As we know, an optical transceiver module is generally either made for single mode (long distance) or multimode (short distance). But 1000BASE-LX / LH SFP can be used for both singlemode and multimode. In fact, the Ethernet standard defines this optical interface specification as 1000BASE-LX10. However, many vendors as a proprietary extension called either 1000BASE-LX / LH or 1000BASE-LH before it was standardized. Thus, we often see 1000BASE-LX / LH rather than 1000BASE-LX10.

In a word, 1000BASE-LX / LH SFP has two identities. It is single mode by design, but when it gets together with its friend “mode conditioning patch cable“, it can also be used for multimode application. This patch cable inserts a single to multi splice on the transmit path, to “fill” the multimode fiber with light. It is more expensive than normal patch cables, but is necessary if using these on multimode fiber. At present, 1000BASE-LX / LH SFP is the only one kind of fiber optic transceivers which can be used for both singlemode and multimode applications. And these applications are depending on what fiber you use.

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Why Mode Conditioning Patch Cable Necessary for 1000Base-LX/LH Application?

Why Mode Conditioning Patch Cable Necessary for 1000Base-LX/LH Application?

For the users who have the experience of using 1000Base-LX/LH SFP, they may be familiar with the mode conditioning patch cable (MCP cable). What’s mode conditioning patch cable? Why it is required for 1000Base-LX/LH applications? This post will give you the answers.

What’s Mode Conditioning Patch Cable?
Mode Conditioning Patch CableMode conditioning patch cable is used to adapt the single mode output of Gigabit Ethernet (1000Base-LX/LH) transceivers to a multimode applications at 1300nm wavelength. This cable is compliant with the IEEE 802.3z standard and has application in LAN (Local Area Network), Telecommunication system and MAN (Metropolitan Area Systems). All mode conditioning patch cables are made with duplex cable, with a single-mode to multi-mode offset fiber connection part in one of the two legs. This specialized cable helps avoid Differential Mode Delay (DMD) effects that (will be introduced below) can occur when long wave transceiver modules operate at both single-mode and multimode wavelengths. The mode conditioning patch cable causes the single-mode transceiver to create a launch similar to a typical multimode launch.

Why Use Mode Conditioning Patch Cables?
1000Base-LX-LHAs mentioned above, the requirement for mode conditioning patch cable is specified only for 1000Base-LX/LH transceivers transmitting in the 1300-nm window and in applications over multi-mode fiber. And you need to know that mode conditioning patch cable should never be used in 1000BASE-SX links in the 850-nm window. Why? Because transceiver modules used in Gigabit Ethernet (1000Base-LX/LH) launch only single-mode (1300 nm) long wave signals. This poses a problem if an existing fiber network utilizes multimode cable. Here, we need to insert a knowledge point and understand what’s DMD (different mode delay) phenomenon. When a single mode signal is launched into a multimode fiber a phenomenon known as DMD can create multiple signals within the multimode fiber. This effect can confuse the receiver and produce errors. Mode conditioning patch cable utilizes an offset between the single-mode fiber and the multi-mode fiber to eliminate DMD and the resulting multiple signals allowing use of 1000Base-LX over existing multi-mode fiber cable systems.

Structure of Mode Conditioning Patch Cable
The following diagram is the structure of MCP cable. The orange legs are the multi-mode fibers while the yellow leg is the single-mode fiber. And there is a offset fiber connection part in the center to connect the legs. In general, mode conditioning patch cables can be designed with SC, ST, LC, MTRJ fiber optic connectors.


Structure of Mode Conditioning Patch Cable

Notes for Using Mode Conditioning Cables
When using mode conditioning cables to patch an existing multimode cable plant to your Gigabit LX equipment, the following things you should know:

  • Mode conditioning cables are normally used in pairs. That means that you will need MCP cables at each end to connect the equipment to the cable plant. So then these cables are usually ordered in even numbers. The usual reason why someone may order one cable is so they may keep it as a spare.
  • If your Gigabit LX switch is equipped with SC or LC connectors, please ensure to connect the yellow leg (Singlemode) of the cable to the transmit side, and the orange leg (multimode) to the receive side of the equipment. It is imperative that this configuration be maintained on both ends. The swap of transmit and receive can only be done at the cable plant side.

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When it’s best to use GBIC and When to use SFP?

When it’s best to use GBIC and When to use SFP?

There are many kinds of fiber optic transceiver modules in the market, such as GBIC, SFP, SFP+ and so on. In addition, these transceivers are available with a variety of transmitter and receiver types, allowing users to select the appropriate transceiver for each link to provide the required optical reach over the available optical fiber type (e.g. multi-mode fiber or single-mode fiber). In addition, there are a variety of interface types of GBICs and SFPs, like 1000Base-SX, 1000Base-LX/LH, 1000Base-EX or 1000Base-T etc. Faced with too much choice, users are often confused when they need to buy the related products.

Recently many users ask when they choosing a card for their switch/router, they should choose either cards that take SFP or cards that take GBIC. It seems to be a headache for them because they are not clearly know the differences of them. Thus, today, we are mainly going to discuss that when it’s best to use GBIC and when to use SFP.

What Is GBIC (gigabit interface converter)
GBIC is a hot-swappable input/output device that plugs into a Gigabit Ethernet port or slot, linking the port with the network. GBIC is a standard for transceivers, commonly used with Gigabit Ethernet and fiber channel. GBIC module is hot pluggable, this feature allows a suitably designed enclosure to be changed from one type of external interface to another simply by plugging in a GBIC having the alternative external interface. Generally, GBIC is with the SC connector. The GBIC standard is non-proprietary and is defined by the Small Form Factor committee in document number 8053i. The first publication of the proposal was in November 1995. A few corrections and additions were made through September 2000.


What Is SFP (small form-factor pluggable)
SFP is a specification for a new generation of optical modular transceivers. The form factor and electrical interface are specified by a multi-source agreement (MSA). SFP is also known as a Mini GBIC as its function is somewhat similar to the GBIC transceiver while SFP is smaller than it. SFP transceivers are designed to support SONET, gigabit Ethernet, Fibre Channel, and other communications standards. Due to its smaller size, SFP is now more and more widely used for both telecommunication and data communications applications.


GBIC & SFP Interface Types
For every type of GBICs and SFP transceivers, it works with different wavelengths at a designated location or distance. For examples, SX SFP uses 850nm for a maximum of 550 meters, LX SFP uses 1310nm for a maximum 10km, ZX SFP could reach 80km or copper SFP uses a RJ45 interface. We can easily distinguish via the information in their names or models, ie. 1000BASE-T, 1000BASE-SX, 1000BASE-LX/LH, 1000BASE-ZX, 1000BASE-CWDM, or 1000BASE-DWDM. In addition, the DOM function for an SFP is discretionary. It supports the users to locate the real-time working status of SFP. The famous brand of GBICs or SFPs are Cisco, HP, Juniper, Extreme Network and so on. There is a little difference in the features of each brand’s GBICs and SFPs and they support their corresponding brand’s switches/routers.

According to the above definitions of GBIC and SFP, you may have a further understanding on both of them. There is only one difference between GBICs and SFPs. SFP is smaller than GBIC. Because the smaller size of SFP (almost half the volume of GBIC), we can configure double number of ports on the same panel which increases the utilization rates of switches/routers. Other basic functions of SFP is almost the same with the GBIC and they are equal in performance. Though there are some users still using the GBIC as their old divice which can not be updated to support SFP, GBIC will gradually be obsoleted and replaced by SFP. So the answer to the question “When it’s best to use GBIC and When to use SFP?” is obvious. SFP is your choice. Of course, except GBIC and SFP, there are SFP+, XFP, QSFP/QSFP+ etc. new generation of transceivers which can meet all kinds of your requirements. These new types of transceivers will be discussed in other aticle and not state here one by one. If you are interested in them, please focus continuously on my blog. Or if you need these products, Fiberstore will be a good place for you.

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

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. Thus, you could feel relieved to use compatible SFP module for cisco 2960 switch or find cisco 3560 SFP modules from 3rd party optics vendor.

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.

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