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Broadcom Switch Blends 4G/5G Radios

May 1, 2018

Author: Bob Wheeler

Broadcom is sampling a new Ethernet switch chip that uniquely enables Common Public Radio Inter­face (CPRI) ports for 4G-cellular fronthaul. Monterey (BCM56670) is an 800Gbps switch that also supports the 802.1CM draft standard necessary for wireless fronthaul. It allows OEMs to create aggregation nodes that connect remote radio heads (RRHs) to a central baseband unit (BBU). Existing 4G RRHs implement CPRI, which uses a constant bit rate and time-division multiplexing, whereas new 5G RRHs employ Ethernet interfaces. By supporting both interface types, Monterey offers a single-chip solution for an aggregation node.

The new design implements 24 dual-mode ports that handle both CPRI and Ethernet along with 40 Ethernet-only ports. Like Broadcom’s Quartz switch, Monterey implements the IEEE Time-Sensitive Networking (TSN) standards. IEEE 802.1CM specifies a fronthaul profile that builds on underlying mechanisms defined in previous TSN standards. For CPRI, Monterey adds 24 radio-mapper blocks that Quartz and competing Ethernet switch chips omit. The mappers handle CPRI framing and perform radio-over-Ethernet (RoE) encapsulation, which essentially carries the I&Q signals from an RRH using Ethernet packets.

Monterey reaches the market at a time when wireless fronthaul is evolving to handle 5G bandwidths. By supporting installed 4G RRHs, it enables common-BBU pooling either at the tower or in a cloud RAN (C-RAN) as operators deploy 5G radios. The primary alternative is multiplexing at the optical layer using wavelength-division multiplexing (WDM), dedicating one wavelength per RRH. Broadcom’s Ethernet-based implementation aligns better with 5G architecture, however, while supporting the 4G radios that will be needed for years to come.

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