A large fraction of OC-192/STM-64 links are between equipment in a single central office (CO). The Optical Internetworking Forum (OIF) recently adopted two Very Short Reach (VSR) OC-192 interface Implementation Agreements to help reduce the cost of these intra-office OC-192 links. VSR-1 is 12 fibers at 1.25 Gbit/s each, using multi-mode ribbon fiber and reaching up to 300 meters. VSR-2 is 10 Gbit/s serial using single mode fiber (SMF) and reaching up to 600m.

This pair was adopted because the parallel optics of VSR-1 will likely be substantially cheaper for the shortest reaches, where the ribbon fiber can be treated like any other patch cable. The serial solution of VSR-2 uses installed SMF and can reach across the largest COs while still offering some potential cost savings compared to SONET short reach (SR) interfaces. The input from the VSR BoF at NANOG-20 was instrumental in reaching this decision.

VSR-1 reaches up to 300 meters and uses 12 lasers signaling at 1.25 Gbit/s. It leverages the 850 nanometer lasers and multi-mode fiber technology used in Gigabit Ethernet. The lasers can be combined in Vertical Cavity Surface Emitting Laser (VCSEL) arrays, and the fibers are joined in a 12-fiber ribbon with a MPO/MTP connector. 10 fibers carry the data, one fiber carries CRC error detection data, and the 12th fiber carries parity of the 10 data fibers. This enables hitless correction of errors on any single fiber, including the loss of a fiber. Field termination is supported, and the link electronics automatically compensate for either ribbon orientation so there is no such thing as a twisted ribbon or a connector put on upside down.

VSR-2 reaches up to 600m and uses serial 10 Gbit/s serial signaling. It is based on ITU G.691 and uses a 1310 nanometer laser over single mode fiber (SMF). Compared to existing SONET Short Reach (SR) interfaces, it relaxes some optical parameters. It allows increased dispersion and reduced reach VSR-1 and VSR-2 are complementary. VSR-1 uses lower speed signals and will likely be the lowest cost OC-192 link for the shortest reaches, where the ribbon fiber can be treated like any other patch cable. VSR-2 uses installed SMF and can reach across very large COs.

About the Presenter
Russ Tuck chairs the OIF's Physical and Link Layer Working Group, which is developing VSR Implementation Agreements. He is Systems Architect at Pluris Terabit Network Systems, where he helps lead the development of scalable and reliable core routers. He previously architected scalable database servers at Pyramid Technology, and scalable supercomputers at MasPar. He earned a Ph.D. in Computer Science from Duke University and carried out his dissertation research at UNC Chapel Hill.