By Harj Ghuman, Cox Communications
MSO networks are evolving from traditional Hybrid Fiber Coax (HFC) to remote PHY (RPD) architectures. A typical 500 home node serving area may transition to one with up to 20 RPDs, each requiring a 10G input to provide sufficient bandwidth. An optical access trunk from the head end to the fiber node area will now have to support a high capacity 200G bi-directional link to support 20 RPDs with 10G. Provisions may also have to be made for a PON/10GPON overlay to feed PON networks as well as high capacity 10G/100G for business services from the same fiber trunk.
There are two optical trunk methodologies currently being investigated:
- A bidirectional 10G DWDM optical trunk.
- A high capacity coherent optical link
A 10G DWDM multi-wavelength optical trunk to each original HFC node area is an efficient low cost solution that makes use of mature, readily available technology. High capacity coherent optical links may eventually be able to fulfill the requirement, but are not yet commercially available in a field hardened, cost effective package. It is likely that networks may have to be designed to allow for the coexistence of both 10G Non-Return to Zero (NRZ) and Coherent networks.
To that end, Cox has developed the OCML (Optical Communications Module Link Extender) concept for cost effectively transporting a mix of DWDM 10GbE, GPON and 10GEPON wavelengths over the same fiber to a typical HFC node serving area.