Packetized Fronthaul: The First Step Towards 5G Transport

By Ryan Perera

With the recent introduction of ultra-low cost 4G feature phones in India, we are likely to see an accelerated phasing out of 2G and 3G networks in the country. Indian operators will need to start preparing their transport networks to expand 4G and eventually, 5G. While 5G promises to deliver enhanced mobile broadband, with speeds reaching approximately ~10Gbps, other key drivers include massive numbers of connected things communicating between other devices and the network (otherwise known as the Internet of Things) and ultra-reliable machine communications known as mission critical delay sensitive traffic. These will place enormous pressure on the way underlying transport networks are designed.

As 5G radio standardization gains traction, operators now have a sufficient frame work to set the groundwork for 5G transport networks. It will be a fibre based network with a centralized RAN (C-RAN) architecture. C-RAN, first introduced with the arrival of 4G networks, has huge potential for much needed resource virtualization and scale. This is achieved by decoupling base band units (BBU) from cell sites and centralizing them, followed by low cost and low power remote radio units (RRU) being installed on cell sites. The transport segment between BBU and RRU, more commonly known as fronthaul, is a critical part of transport planning.

A starting point for operators involves deploying Common Public Radio Interface (CPRI) based fronthaul with LTE-A/LTE-A Pro in select dense metros before building out 5G. However, current CPRI can be costly due to the deployment of technology such as dedicated fibre. To scale 5G, Indian operators require a more scalable and cost effective fronthaul solution.

The good news is that the standard bodies are about to release a new specification known as eCPRI. By using functional partition inside the physical layer, eCPRI enables a ten-fold reduction in bandwidth requirements, scale as per use plane traffic and most importantly use of main stream, lower cost technologies such as Ethernet.

‘Packetized Fronthaul’ could be used for LTE/LTE-A/LTE-A Pro CPRI-based fronthaul as well as 5G eCPRI. Many of the packetized fronthaul technologies will be relevant to 5G as well including Next Generation Fronthaul Interface (NGFI) and the Time-Sensitive Networking (TSN) standards being developed by the IEEE’s 802.1 working group. These will start to appear in 5G Access Transport Networks to handle deterministic traffic flows such as urLLC (Ultra Reliability Low Latency Communication) applications.

Indian operators can also leverage the high speed fixed 5G access to complement the last-mile access market while circumventing the typical challenges associated with wireline access such as right of way or coverage issues. Again, the underlying backhaul transport network will need to have the right level of scale and cost structure.

Slicing to Size

In 5G networks, network slicing is being planned in the radio network and the packet core. To realise the full benefit of network slicing, the underlying transport network also needs to work in tandem. Network slicing in transport can be hard slicing (e.g. OTN, Wavelength, FlexE) and soft slicing (e.g. segment routing, EVPN, E3 VPN). Each transport network slice is defined by a network slice template, which can be centrally orchestrated.

In summary, with the expansions of 4G networks and eventual evolution into 5G, Indian operators need to lay the ground work for future transport networks. In particular, the front-haul and back-haul transport architectures will be the most critical. With the advancements in new eCPRI standards, packetized fronthaul architecture using Ethernet could offer Indian operators much needed scale and the cost efficiency.

(The author is Vice President & Country Head, Ciena Communications, India)

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