5G services -- Investment in a new generation network is ultimately about the value it delivers to customers. More than any prior generation, 5G is services-led in the sense that application performance requirements are driving standardization, design and implementation of the new network. Interestingly, 5G can leverage advances already made by today's state-of-the-art software-defined networking (SDN) to deliver services. Micro-segmentation, for example, maps directly to the 5G network slice concept.

The new RAN architecture -- The specification of the central unit (CU) and distributed unit (DU) in 5G in effect formalizes the Cloud RAN architecture. In addition to the classic RF over optical fronthaul and IP backhaul, 5G looks set to specify two new functional splits: a higher-layer split at the PDCP/Layer 3 that will run over packet transport and a lower-layer split (at Layer 1.5) that can run over eCPRI over optical. Fronthaul, and the related "crosshaul," between radio sites and controllers is, therefore, at the heart of the 5G transport discussion.

Mapping 5G to edge data centers -- In a Cloud RAN architecture the radio controller is deployed at a hub location -- typically a redesigned central office or basestation hotel type facility. At the same time, to meet low-latency targets, operators are looking to distribute network functionality, content and application logic to the edge. The scene is set, then, to combine these trends into a new distributed service provider network architecture. 5G adds another dimension to edge data center networking designs already underway.

Transport technologies -- To make all this possible requires connectivity, the event will, of course, focus on transport. Predominantly we expect optical -- dark fiber, active and passive WDM, NG-PON, Carrier Ethernet, and so on -- to be used, but also cable DOCSIS and wireless over high capacity microwave and perhaps free space optics, can play role. In time, even self-back-hauled radio designs may be viable. (See Building the 5G Transport Network.)