5G introduces new applications and use cases that require new technologies to build flexibility into the transport network to lower costs and improve service delivery. One such technology is transport network slicing, which will enable end-to-end service slicing to become reality. Another is packetized fronthaul transport, which efficiently carries 5G eCPRI traffic together with legacy CPRI.

In November 2021, Heavy Reading conducted the third iteration of the Operator Strategies for 5G Transport Market Leadership Survey with project partners Ericsson, Fujitsu, Infinera and Nokia. The 2021 survey attracted 81 qualified network operator responses from around the world who shared their views on transport deployment issues and timelines, fronthaul networks and RAN centralization, routing and synchronization and 5G edge connectivity.

This blog is the second in a four-part series highlighting the key findings from the 2021 study. It focuses on transport network slicing and packetized fronthaul trends.

Transport slicing

Network slicing is an important capability of the 5G system, and transport slicing will be required for end-to-end slicing to become reality. Transport slicing comes in two broad categories — soft slicing and hard slicing — and each has its own set of options. Hard slicing provides circuit-level isolation that eliminates traffic impact from other streams. With packet-level isolation, soft slicing allows for statistical multiplexing efficiencies, but traffic impact from other streams must be managed via traffic engineering and QoS.

But which method of slicing do service providers prefer? Survey data shows that both hard and soft transport slicing techniques will be used by a majority of communications service providers (CSPs) — with the combination of hard and soft slicing selected by 55% of respondents. However, information gleaned from one-on-one discussions with CSPs indicates a preference for soft slicing, when possible. If customer application requirements can be met by either soft or hard slicing, CSPs will choose soft slicing.

The survey data supports this strengthening assessment. While 35% of respondents expect to implement soft slicing alone, just 5% of those surveyed expect to rely solely on hard slicing — a significant 7x difference in appeal. Some applications will require circuit-level isolation (e.g., perhaps in government or financial services, where specific performance or security requirements must be met), but most will not.

Figure 1: What will your organization use for transport network slicing? n=40
Source: Heavy Reading

Segment routing is an emerging Internet Engineering Task Force (IETF) routing technology that helps simplify network traffic engineering and control while maintaining existing MPLS hardware and services. One important use case is protocol simplification by eliminating the need for Label Distribution Protocol (LDP) in core MPLS networks. A second major use case is the replacement of complex RSVP-traffic engineering (TE) in MPLS networks with more scalable segment routing-based traffic engineering. A third use case — which relates directly to 5G — is transport network slicing using segment routing-TE and software-defined networking (SDN) control to create soft slices.

Heavy Reading asked the survey group to identify expected timelines for segment routing in each of these major use cases.

Of the three, protocol simplification is the most advanced, with 25% of CSPs already implementing segment routing and an additional 38% expecting to use segment routing by the end of 2022 — totaling 63% of the survey group by the end of this year. Traffic engineering follows, with 19% having implemented segment routing by the end of 2021 and an additional 41% expecting to use segment routing by the end of 2022 — totaling 60% of CSP respondents by the end of this year.

Compared to these two applications, segment routing for transport slicing lags. Just 12% of respondents reported segment routing use by the end of 2021, though 32% expect to implement segment routing for slicing in 2022 — totaling 44% of CSP respondents by the end of this year.

The survey results are consistent with the overall maturity of the segment routing use cases as CSPs progress from protocol simplification to traffic engineering and, ultimately, transport slicing. Based on the survey results, 2022 and 2023 should see more segment routing deployments for transport slicing.

Figure 2: When does your organization plan to introduce segment routing to support the following applications/functions? n=81
Source: Heavy Reading

Packet fronthaul

5G transport efficiency is improving significantly through the CPRI Consortium's eCPRI specification. However, CSPs will continue to have massive amounts of legacy CPRI streams since 5G and previous mobile generations (particularly 4G) will coexist in networks for many years. Handling legacy CPRI traffic as 5G emerges is a crucial issue for nearly every CSP globally.

To better understand CPRI plans, Heavy Reading asked CSPs to identify which technologies they plan to use to transport legacy CPRI moving forward.

Service providers have multiple means at their disposal to handle legacy CPRI, and the data shows that they intend to make use of all of them. Selected by 64% of the survey group, legacy overlay using dark fiber or WDM is the top choice for legacy CPRI transport, followed by transport via CPRI to eCPRI conversion (selected by 52%). Trailing individually are structure-agnostic radio over Ethernet (RoE; selected by 43%) and structure-aware RoE (selected by 29%). Combined, however, RoE comes out as the top option, selected by 72% of CSPs surveyed.

Fiber-rich networks will make use of dedicated direct fiber transport. Meanwhile, networks with fiber scarcity will use technologies and techniques to boost transport efficiency, including WDM and/or packetized transport, with time-sensitive networking.

Figure 3: Which technologies will your organization use to transport legacy CPRI radio traffic? n=69
Source: Heavy Reading

Looking for more information?

5G Transport: A 2021 Heavy Reading Survey
5G Transport Evolution: Making Advanced Services a Reality

— Sterling Perrin, Senior Principal Analyst – Optical Networks & Transport, Heavy Reading

This blog is sponsored by Nokia.