A New Approach to Upgrading Optical Networking at the Edge


September 15, 2020


In a world of 5G wireless networks and 400G Ethernet connections, it is easy to forget that other technologies can deliver significant benefits for users.

Various technologies can drive enhanced services for carriers and their customers, thanks to some recent innovations. While the optical transport network (OTN) has been in the backbone of many carrier networks, offering the benefits of OTN directly to customers that require bandwidths below 1 Gbps has required complex and expensive network systems with up to five layers of multiplexing.

Huawei’s new Liquid OTN solution seeks to massively reduce the complexity of low rate OTN connections and provide an all-optical upgrade path for users of low rate, time-division multiplexing (TDM) services such as E1 (2 Mbps) and E3 (34 Mbps).

Much of the world’s TDM and Synchronous Optical Networking/Synchronous Digital Hierarchy (SONET/SDH) equipment is reaching the end of its life. Yet, many organizations use these types of services and value the bandwidth guarantees and network resiliency they provide.

Various forms of circuit emulation have been developed for carrying TDM and SONET/SDH services over packet switched networks. However, the quality of service (QoS) is then dependent on the underlying Ethernet, MPLS or IP network. Standard OTN allows carriers to manage end-to-end QoS, and will efficiently transport SONET/SDH or Ethernet client signals of 1 Gbps and above. Lower rate TDM and SONET/SDH client signals must be multiplexed into a higher rate connection before they can be transported over a standard OTN network.

OTN: History 101

OTN was developed in the late 1990s as a digital wrapper around client signals before they are transported over a wavelength-division multiplexing (WDM) network. The first OTN implementations were designed to support SONET/SDH clients and line rates of 2.5 Gbps (ODU1) and 10 Gbps (ODU2). Virtual concatenation (VCAT) has been used to split up SONET/SDH bandwidth for lower bandwidth clients (e.g., VCAT12 = 2 Mbps).

The OTN hierarchy has subsequently been extended to support higher line rates, including 40 Gbps (ODU3), 100 Gbps (ODU4) and N x 100 Gbps (OTUCn). ODU0 and ODUFlex were also introduced to allow the efficient mapping of gigabit Ethernet and higher rate clients onto OTN. In an OTN/TDM network that has very low rate clients (2 Mbps) and very high bandwidth backbone (400 Gbps), there could be five levels of multiplexing (VC12/VC4/ODU1/ODU4/OTUCn). This introduces significant complexity, cost and latency.

Enhancing Customer Experience with Small-Granularity OTN

Much of the development effort for 5G has been about delivering low-latency services and guaranteed bandwidth for specific applications to enhance customer experience. These themes were extremely prominent during the Huawei Products and Solutions launch in London at the end of February.

Read more: Geared Up for 5G: The Latest Tech, Innovations & Use Cases

The event was heavily focused on 5G but also covered several other product developments, including Huawei’s Liquid OTN. This solution has been designed to overcome the limitations of OTN when supporting low-rate services and deliver the guaranteed bandwidth and resiliency expected by existing TDM service customers.

Huawei’s Liquid OTN introduces optical service unit containers to support flexible bandwidth definition down to 2 Mbps, which is the same granularity level as legacy SDH services. The solution supports hitless and continuous bandwidth adjustment from 2 Mbps to over 100 Gbps (N x 2 Mbps) to ensure maximum network resource utilization and supports differentiated latency levels. Huawei claims that the Liquid OTN solution reduces per-site latency by 70% through flattening the network transport layers. The result is an all-optical connectivity solution that can deliver on bandwidth and latency guarantees for a wide range of service applications and may benefit a variety of industry verticals.

OTN remains a key part of the global network infrastructure. Huawei’s Liquid OTN approach should enable operators to maximize the value of their OTN networks by directly supporting fixed rate optical services from 2 Mbps to over 100 Gbps and simplifying the multiplexing hierarchy. Best effort services are adequate for many applications. But for those applications and organizations that need guaranteed bandwidth, low latency and resilient optical connections, this new small granularity OTN technology offers some significant benefits.

About the Author

Simon Stanley, Analyst At Large, Heavy Reading

Simon is Founder and Principal Consultant at Earlswood Marketing Ltd., an independent market analyst and consulting company based in the UK. His recent work has included investment due diligence, market analysis for investors and business/product strategy for semiconductor companies.

Simon has written extensively for Heavy Reading and Light Reading. His reports and Webinars cover a variety of communications-related subjects, including SDN/NFV, LTE, 40G/100G/400G components, ATCA, MicroTCA, multicore processors, switch fabric chipsets, network processors and packet-optical silicon. He has also run several Light Reading events covering next-generation networking components and ATCA.

Disclaimer: Any views and/or opinions expressed in this post by individual authors or contributors are their personal views and/or opinions and do not necessarily reflect the views and/or opinions of Huawei Technologies.

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