Summary Bullets:
- 5G transport needs to provide enough capacity, but it also needs to cater to vertical 5G use cases with high-precision and low-latency connections, provided on intelligent infrastructure.
- Another key issue that operators will need to tackle is 5G transport diversity and complexity; as 5G radio site types diversify, operators will need to build more diverse transport networks to cover all types of sites in their network.
In the first wave of 5G deployments, operators and other players in the telecommunications ecosystem have focused primarily on innovation in radio access, allowing for key improvements next-gen radio brings to existing services like mobile broadband. But as operators start to focus on truly game-changing 5G functionality that will enable IIoT and other advanced use cases, the importance of rebuilding and rethinking transport networks for 5G becomes very clear.
Unlike in 3G and 4G, evolved 5G transport not only has to provide plentiful capacity – the usual number quoted is around ten times higher than for LTE – but also needs to provide very high-quality connections to ensure smooth performance of advanced 5G services. Additionally, 5G transport network management mechanisms have to ensure a high degree of flexibility and automation to achieve end-to-end slicing capability, traffic isolation, and granular QoS management.
5G Challenges for Transport Networks
The connection quality requirements are all related to system-wide budgets in synchronization precision, jitter, and latency defined in 5G standards – and, again, represent a quantum leap in network performance compared to previous generations of mobile backhaul.
Additionally, the transport in 5G networks must have precise, deterministic characteristics when it comes to bandwidth, latency, and jitter. These requirements are system-wide, spanning multiple transport sub-systems. This translates into the need to adhere to very high standards of connection quality in every part of the transport network and, consequently, the need to measure and manage service bandwidth and quality parameters throughout the network precisely and dynamically.
For many vendors, these new requirements have spurred the introduction of a new breed of time-sensitive, predominantly IP, transport platforms featuring sophisticated timing and synchronization mechanisms.
Another key feature of 5G radio access is the new levels of diversity in site types and deployment strategies available to operators, driven in part by network disaggregation and virtualization, as well as the introduction of new radio bands. Radio access virtualization and decentralization split the legacy radio base station into separate elements of active or passive antennas, radio heads, and processing and enable operators to combine these elements and deploy them flexibly – either close to each other or sometimes kilometers away.
This effectively splits the former concept of mobile backhaul connecting the radio site to the operator edge into a significantly more complex 5G Xhaul (encompassing fronthaul, midhaul, and backhaul). Each of these transport segments requires specialized equipment with varying deployment characteristics. As a rule of thumb, elements closer to the radio need to be more power efficient and temperature hardened; closer to the operator’s metro network, high routing capacity becomes the most prominent.
Introducing new radio bands suitable for covering indoor and outdoor areas with short-range, high-capacity connectivity – especially the millimeter wave (24 GHz and above) – brings to the fore the challenge of deploying high-performance networking devices in very small packaging and in large numbers in various environments. In other words, as radio access gets closer to the end user, transport networks need to follow.
The traditional way of solving this issue was using microwave backhaul. While microwave will continue to be relevant going forward, its capacity scalability is limited. Instead, many operators and vendors propose massively scaling fiber-based fronthaul networks. Again, there are several different ways of doing this, ranging from active WDM devices serving fronthaul to utilizing fixed broadband optical plant for this purpose.
In Transport, There’s No 5G Without SDN
5G transport also necessitates changes in the way the networks are operated. Traditionally, mobile transport networks have been treated as slowly changing, overprovisioned ‘dumb pipes’ carrying all traffic without discerning what the traffic is or what kind of connection parameters it requires. The concepts of network slicing, differentiated QoS, and traffic isolation demand fully steerable, software-defined and automated network management and operations. With 5G, SDN becomes a necessity and not an afterthought, as usually was the case in the past.
To satisfy operator need for ‘hard’ (fully isolated) network slices, operators and vendors have devised slicing packet network/metro transport network (SPN/MTN) architecture, providing TDM deterministic end-to-end transport channels. The technology has since been accepted as a recommendation by ITU-T.
The introduction of 5G thus represents a quantum leap, bringing with it fundamental changes not only for radio access itself but for transport networks as well. With 5G destined to carry much more traffic, and a completely new breed of services in the future, the demands of 5G will continue to drive the direction and pace of IP and optical transport technology innovation in years to come.