CALIENT Technologies

Move the light, not the fiber

Optical Circuit Switches Become Part of New C-RAN Network Architecture to Boost Mobile Network Bandwidth

Mobile network operators are considering significantly new network architectures to expand network capacity to accommodate the 61% compounded average growth in mobile data that many analysts expect in the coming five years.

One part of this network architecture evolution is increasing the cell site density in a metro area in order to increase the spectral capacity. In essence, this means many smaller cell sites each with their own spectrum capacity replacing or augmenting a macrocell site.C-RAN

I think of it like the old days of Ethernet. Before the advent of switching, most company networks consisted of a 10 Mbps shared broadcast domain. To get more bandwidth, a bridge was added that would create two domains of 10Mbps each. In a similar way by increasing the number of cells in a region, operators are adding pockets of mobile bandwidth that add up to more than that offered by a macrocell.

One way to do this is called Cloud-RAN (for radio access network; C-RAN). C-RAN was originally proposed by China Mobile (download whitepaper PDF here) and has gained significant momentum throughout Asia. Based on that success, mobile operators in the U.S. and around the world are now considering the architecture.

Fiber Front Haul Using S320 OCS

The C-RAN architecture is one that relies on fiber optic “front haul” and that’s where the CALIENT S320 Optical Circuit Switch offers a significant advantage.

C-RAN is designed to simplify the design of dense wireless networks by connecting multiple remote radio units (that is, the antenna and RF signal processing part of a basestation) to a centralized pool of remote baseband processing units (BBU’s) using a fiber-optic network.

To pool the BBUs, there must be a high bandwidth, low latency, low-cost switch network with flexible, extensive topology. This is a critical element of the network design, as summarized in the C-RAN whitepaper:

To achieve high reliability in case of unit failure, in order to recover from error, and to allow flexible resource allocation of BBU, there must be a high bandwidth, low latency, low cost switch network with flexible, extensible topology that interconnects the BBUs in the pool.

The role of the S320 in this network is to create a fronthaul fiber distribution network that allocates BBU capacity from the virtualized pool of baseband processing out to the remote radio units. The switch is protocol agnostic and so can support a wide range of distribution options including dark fiber, passive CWDM or OTN.

Two of the challenges of building a fronthaul network are that latency must be very low, less than 200 milliseconds round trip on the end-end network, and the application can tolerate no more than 10 nanoseconds of jitter.

The S320 provides less than 50 nanoseconds of latency with passive connectivity that has no impact on jitter.

The management of the S320 can leverage CALIENT’s management software or be controlled by other 3rd party orchestration platforms. Either way, operators can redirect BBU capacity based on demand or on time of day – perhaps to provide extra bandwidth during commute times, for example.

With 320 user ports, the S320 has capacity for the largest networks and its fiber-optic ports are protocol agnostic, so that they can support any standard connections speed.

Mobile operators must find a solution to accommodate rapid smartphone and tablet data growth. C-RAN is a promising option, but requires a very high-performance front haul network to be successful. With the S320’s throughput and low latency/jitter, it should be a leading alternative that carriers should consider.

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