Building the 5G Transport Network
The coming 5G era is not just about handsets, sensors and other mobile devices. The wireline network has a critical role to play in 5G by providing the backhaul and new fronthaul infrastructure that will enable all the interesting high bandwidth and ultra-low latency applications for those millions of end devices. In fact, the industry has recognized that this wireline infrastructure must be put in place before 5G applications can be rolled out in volume -- making the next two years an urgent time for 5G wireline access networks.
With this sense of urgency in mind, Light Reading has launched its inaugural 5G Transport & Networking Strategies event to take place in New York City on November 10. Co-Chaired by 5G Principal Analyst Gabriel Brown and me, the event focuses on the 5G RAN and the connectivity between RAN sites, data centers and cloud services providers.
While the half-day event will explore 5G radio issues as well as transport issues, my own focus is on the optical transport network. The separation of the remote radio head (RRH) from the baseband unit (BBU) pools, dictated by 5G is opening an unchartered territory in the 5G fronthaul network -- the high-bandwidth connection between the cell tower-based RRH and the network-based BBU pool.
The industry consensus is that the physical medium for the 5G fronthaul network will be fiber. However, beyond this consensus point, there are many options being put forward and much debate -- including choice of transport protocols and even basic physical layer decisions for fiber. The leading physical layer contenders are:
- Dark Fiber: Unlit fiber leased by the mobile operator, which then lights it up with its own optical equipment.
- Passive WDM: colored pluggable SFPs (CWDM or DWDM) that don't require amplifiers between the BBU to the RRH.
- NG-PON2: ITU's GPON standard successor, allowing four wavelengths at 10 Gbit/s per wavelength out to ONUs (symmetrical). Allows multiple waves per tower/ONU as needed.
- Active WDM: WDM transponders at each end of the 5G RRH and the BBU.
Each option has different puts and takes across the spectrums of performance, costs and manageability.
Above the physical layer, protocol decisions must be made. Operators have declared traditional CPRI inefficient for 5G, but a new enhanced CPRI spec (called eCPRI) promises to remove at least some of old CPRI’s inefficiencies in carrying data. Whether eCPRI’s improvements are enough, however, remains an open question. Beyond eCPRI, there is a lot of interest in adapting Ethernet transport for fronthaul networks -- though work must be done to make Ethernet time-sensitive for 5G applications. OTN is also mentioned, and we are even starting to hear about completely new options for 5G fronthaul.
As the above paragraphs illustrate, there are a lot of questions and a great deal to be decided just on the transport network alone, in advance of 5G adoption. The time to discuss and debate these issues is now, and that's what we intend to do at 5G Transport & Networking Strategies on November 10. We hope you will be able to join us and contribute to this essential dialogue.