Data center bandwidth continues to increase. 10 gigabit per second (Gb/s) links, once-considered blazing fast, are already starting to make way for 100 Gb/s and more. To pave the road to even higher speeds, a variety of IEEE and fiber channel standards, as well as industry specifications, are being defined to enable a cost-effective migration path to 200 Gb/s, 400 Gb/s and beyond, supporting multimode and singlemode fiber.
To better understand the available options, it is useful to become familiar with the alphabet soup that makes up the suffixes used to distinguish transceiver types. Let’s start with the IEEE suffixes used for 10G: 10GBASE-SR, 10GBASE-LR and 10GBASE-ER. SR is always used for multimode and stands for Short Reach (i.e. 400 meters on OM4). LR and ER are used for singlemode, with LR being Long Reach (10 kilometers), and ER being Extended Reach (40 km). Pretty simple so far, right?
Well, suffixes get a bit more complex to account for the techniques used to achieve faster speeds, including the use of multiple fibers and/or multiple wavelengths, with a numeric designator added to indicate the number of wavelengths or fibers used. For 100G on singlemode, for example, the LR4 suffix refers to the use of four wavelengths on each fiber, but for 100G on multimode the SR4 suffix refers to the use of four fiber pairs. Additional suffixes for multimode include a 100G SR10 variant (ten pairs) and a 400G SR16 variant (sixteen pairs).
Outside of the IEEE, multi-source agreements (MSAs) have their own suffixes. The SWDM Alliance uses the SWDM4 suffix for Short Wave Division Multiplexing over duplex multimode, and its numeric designator refers to four wavelengths over each fiber. MSAs for singlemode have introduced PSM4 for Parallel Single Mode using four fibers and CWDM4 for Coarse Wave Division Multiplexing using four wavelengths.
Currently, several new suffixes are being adopted in IEEE for new 100G, 200G and 400G standards. An SR2 suffix was introduced for 100G using 2 multimode pairs. A DR (Datacenter Reach) suffix was introduced for 500 m singlemode, and DR4 has been adopted to designate four fiber pairs. Another new suffix, FR (said to stand for Fiber Reach), was introduced for 2 km singlemode solutions, with FR4 indicating four wavelengths and FR8 indicating eight wavelengths. Not so simple any more, right?
A potential project being discussed by IEEE experts may help clear up the confusion in numeric designations. Given that multiple fibers and multiple wavelengths may be used simultaneously, it will probably become necessary to remove the ambiguity sooner or later. Discussions under way in IEEE for higher speeds over a reduced number of multimode pairs include a proposal to combine the number of fiber pairs and the number of wavelengths under a new suffix scheme.
The proposed scheme includes the numeric designator for the number of fiber pairs followed by the designator for the number of wavelengths, separated by a dot. Using this scheme, the suffix for 200G multimode using one pair of fibers and four wavelengths would be SR1.4 (one pair dot four wavelengths), while other options for 200G and 400G may include SR2.4 (two pairs dot four wavelengths) or SR4.2 (four pairs dot two wavelengths).
With an increasing amount of fiber on the menu for data center diets, understanding this alphabet soup is a good starting point when making decisions regarding infrastructure choices.