Mobile fronthaul works in tandem with a relatively new type of Radio Access Network (RAN) architecture that consists of centralized baseband controllers and RRHs installed at macro cell sites located kilometers away.

With mobile fronthaul, the RU equipment falls under the RRH heading, but is still located at the macro cell site. Similarly, the BBU moves to a centralized location, where it serves multiple RRHs. The optical links that connect the BBU to multiple RRHs is referred to as Mobile Fronthaul.

In 2003, a consortium of wireless equipment vendors standardized the Common Public Radio Interface (CPRI) protocol that runs over these fronthaul links. CPRI can be carried over tens of kilometers, is compatible with low-cost and ubiquitous SFP/SFP+ pluggables, and uses cost-effective modulation schemes, such as Quadrature Amplitude Modulation (QAM).

Mobile Fronthaul is the movement of data and voice from a cell site to a baseband unit.

CPRI works with numerous optical transceivers, including:

  • 1000Base-SX/LX Ethernet (IEEE 802.3-2002, clause 38)
  • 10GBase-LX4 Ethernet (IEEE 802.3-2005, clause 53)
  • Fibre Channel (FC-PI-4, INCITS revision 8)
  • Infiniband (volume 2, release 1.1, November 2002)
  • 10GBase-S/L/E 10G Ethernet (IEEE 802.3-2008, clause 52)

The capacity, reach, and latency requirements of CPRI (at rates of 2.458 Gb/s, 3.072 Gb/s, 4.915 Gb/s, 6.144 Gb/s, 9.830 Gb/s, and beyond) necessitate fiber connectivity between centralized BBUs and the multiple RRHs. A number of optics satisfy these needs, depending on application specifics such as availability of fiber to the cell site and on the tower feeding the RRHs mounted at the top of its mast.

With a mobile fronthaul network in place, providers can take advantage of Optical Transport Network (OTN) technology to move data from the cell sites to the BBUs. This technology has a number of key advantages, including:

  • Reduction in transport costs: Transporting multiple clients on a single wavelength, while preserving their specific requirements, reduces the overall cost of transport and ensures efficient bandwidth utilization.
  • Scalability beyond 40G: OTN is designed and optimized to support massive-capacity services such as 100GbE, 400G, and even Terabit payloads as needed.
  • Determinism: Dedicated specific and configurable bandwidth guarantees network capacity and managed performance for each client without contention between concurrent services or users.
  • Flexibility: Operators can employ the technologies needed to support current transport demands, while also enabling future adoption of new technologies as business needs dictate.
  • Dynamic infrastructure: OTN and the control plane work in tandem, so the network is dynamic and responsive to upper-layer applications in real time.


Ciena’s broad portfolio of CWDM/DWDM-based transport solutions provides a scalable optical foundation that allows mobile network operators to differentiate their mobile fronthaul service offerings.