Fiber connector types include SC and ST for 1Gb Fibre Channel, Gigabit Ethernet, ESCON, and FICON. A smaller form-factor GBIC, about the size of a networking RJ45 (Ethernet) connector, is the Small Form-factor (SFF); a Small Form-factor Pluggable (SFP) connector is used with 2Gb and 4Gb Fibre Channel, although some products utilize SFPs for 1Gb applications. SFF and SFP are somtiimes referred to as LC connectors. Fibre Channel supports copper and fiber optic interfaces (most implementations are now optical). Fibre Channel utilizes various cable types, including 62.5 and 50 um (micron) Multi-Mode Fiber (MMF) and 9 um Single-Mode Fiber (SMF). Trunk cable is used to physically combine multiple cable strands into a single cable bunch that fans out at each end or has a special connector to attch a fan-out cable (e.g., MTP cable). Some common fiber optic connector types are shown as below. Duplex connectors have two connections attached to each other (pair), where as simplex has individual connectors.
This figure includes LC, SC, simplex (single connector), and duplex (a pair of fiber connects). Two other fiber optic connector types are ESCON Duplex and MIX (FDDI), which are used for ESCON and FDDI configurations, respectively. Various cable and jumper configurations are available, including SC to SC, SC to LC, LC to LC, SC to ST, Simplex, Duplex, and LC to MT-RJ, to name a few. There are also mode conditioners, which enable different types of fiber optic cabling to coexit, for example, using existing ESCOM cables for 1Gb FICON. Connectors, cables, and other accessory optic items are available from a variety of different sources.
Caution: Fiber Optic Care and Handing: Fiber optic cable is relatively flexible compared with traditional bulky storage interfaces and even Unshielded Twisted Pair (UTP) copper cabling used with networking. However, fiber optic cabling is sensitive to bending and sharp turns as well as dust and dirt. Keep your fiber optic connectors clean and if you plan on making many changes resulting in unplugging and replugging connectors, invest in a quality cleaning kit. As part of managing your fiber-optic infrastructure avoid sharp bends and twists in your cabling to prevent damage to the core. Cable bend radius guides can be used to help protect cabling.
Fibre Channel and Ethernet borrow and leverage technologies from each other, particularly at the physical layer. 1Gb Ethernet utilizes fiber optic transmission (8B/10B encoding) technology borrowed from Fibre Channel, with Ethernet operating at a faster clock rate. A 1Gb Ethernet has a slight wire speed theoretical bandwidth advantage of 1.25 Gbps compared with 1.0625 Gbps Fibre Channel, which is about 150 Mbps difference. Some Fibre Channel and Ethernet 1Gb GBICs are interchangeable and support dual clock rates; however, this varies by manufacturer and vendor-supported configurations. At 10Gb Fibre Channel borrows from Ethernet using a common encoding and transmission scheme, including virtual lanes and common coding (65/66B).
Similar to fiber optic cabling having different types for short- and long- haul applications, fiber optic transceivers also have different characteristics and capabilities. Here is a table that shows some common fiber optic transceivers and their characteristics, including cable type and connector type along with supported distance. Fiber optic transceivers include Gigabit Interface Converter (GBIC) for 1Gb, SFPs for 100Mb to 4Gb, and eXtended Fiber plug (XFP) and SFP Plus (SFP+) for 10Gb applications. Note that some fiber optic transceivers, including GBIC modules, SFP modules, SFP+ modules and XFP modules are interchangeable between Fibre Channel and Ethernet devices; however, consult the manufacturers’ material for specific guidelines and supported configurations. Media interface adapters (MIA) can be used to convert from copper electrical to optic.
Transceivers are also used on DWDM technology for sending and transmitting light over various distances and for using different wavelengths. For diagnostic, monitoring, and test purposes there are also loop-back transceivers that simply take the transmit signal and loop it back to the receiver. There are also snoop transceivers, which have an extra connection pair for attachment of optical test tools, sniffers, analyzers, and performance probes. Snoop GBICs bleed off a small amount of the light source and send it to the extra monitoring port for use by diagnostic and monitoring tools. This allows fiber optic and interface analyzers to look at and collect traffic information for diagnostic and troubleshooting applications. Performance analyzers and probes can also be attached to these ports to collect detailed session-level statistics at the network interface up to the protocol layer. This would include SCSI, IP, VI, and FICON reads, writes, I/O size, source, destination, reponse time, signal and synchronization loss, and other pertinent data to aid management, storage resource management, and capacity planning. Another technique for trapping into a fiber optic stream without using snoop GBICs and SFPs is to use a “Y” splitter cable, sometimes called a pigtail cable or splitter device, which is essentially a “Y” in s small connector box.
An emerging trend is to have extra ports, called mirrored ports and spanning ports, available similar to Ethernet switches. Another emerging trend is to have the information from the port itself sent in-band to management software. Analyzers are good for collecting very detailed state information with some retention capabilities, while probes and sniffers tend to take a higher-level view, provding analysis capability, long-term retention of data, and reporting/display capabilities. Depending on your specific needs, you may need both, one or the other, or perhaps neither. From an educational standpoint, it certainly helps to have at least some exposure and training, even if it is a demonstration regarding what these tools can do and how they can be used to help you better understand your storage networking environment and troubleshoot things.
There is another specialized type of transceiver, which is a wavelength (lambda), specific GBIC or SFP, sometimes called CWDM GBIC and CWDM SFP. Regular transceivers transmit light at a common wavelength or light level. By using CWDM technonlogy different transceivers can have different wavelengths assigned to them, for example, at 20 um ITU grid spacing. Each wavelength must be aligned with its correspongding wavelength or the transceivers will not communicate. By using Optical Add-Drop Multiplexer (OADM) devices the various wavelengths are combined to creat a multiplex light source and transmitted over a single-mode fiber optic cabling. The light is demultiplexed at the far end back into the individual wavelengths and sent to the wavelength-specific transceiver.
The figure below shows an example of wavelength-specific transceivers based upon CWDM technology with an ITU grid spacing of 20 nm and an OADM. In this example a server on the left has a wavelength-specific transceiver operating at 1470 nm spacing, that is, multiplex with other wavelengths for long-haul transmission using SMF optical cabling. ON the right, we see that the combined light source is demultiplexed by the OADM and the appropriate wavelength is sent via fiber optic cable to the storage on the right. In this example there is a jumper cable (fiber patch cable) between the server and the OADM on the left, an SMF cable between the OADM on the left and right, and a jumper cable between the OADM on the right and the storage device.
Another example, based on the same figure, would be to introduce a switch (Ethernet, Fibre Channel, FICON) that servers and other devices would attach to on both sides. The switches would then connect to an OADM device using the wavelength-specific transceivers to multiplex their signals over a common SMF fiber optic cable. Consequently, multiplexing can be used to combine Fibre Channel, FICON for storage access, and Ethernet for server access and clustering hearbeat over a common fiber optic cable for long-distance applications.
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