In many ways, the telecommunications networks that provide data communication services to residential, business and governmental users parallel the organization of logistics services that distribute physical goods across neighborhoods, cities and countries. Whether it’s data services or physical goods, our world relies on distribution that is cost-effective, efficient and optimized for what is being delivered, and where it is being delivered to.

For example, freight that needs to be transported long distances between cities is best moved with trains and semi-trailers or articulated lorries, while delivery vans and box trucks handle deliveries within a city. Scooters, mopeds or bikes are also well suited for delivering small packages over even shorter distances.

The reasons for this demarcation are obvious. Sending hundreds of delivery vans across a country would be incredibly inefficient in terms of energy use, cost and the number of drivers needed compared to a single train pulling dozens or hundreds of freight cars. And while a lorry may sometimes be needed at a residence, for example, to move the contents of a house or deliver large goods such as a fridge or grand piano, sending articulated lorries to deliver every package or online purchase would be tremendously inefficient in both cost and energy use.

The networks that deliver our communications services are the same. We need different solutions depending on the scale and distances over which data needs to be transported. For optical networks, these solutions can be segmented into three categories:

1. Subsea and long-haul networks, which transport data across oceans and continents

2. Regional networks, which carry traffic across metropolitan areas and their surrounding regions

3. Metro networks, which connect to platforms and customers at the network’s edge.

Today’s core optical networks offer enormous scalability and routinely leverage high-performance 1.2 Tb/s coherent optics and C+L WDM line systems to accommodate traffic growth of 30–40 percent per year. At the same time, traffic and service speeds at the network edge are continuing to scale. For example, IP routers now support 400 Gigabit Ethernet (GE) and 800GE ports, while passive optical network (PON) systems support 10G and 25G, with even greater speeds anticipated soon.

Growing scalability demands at the metro edge

So, what do optical network operators need to scale capacity and service delivery to the metro edge? Before we can answer this question, we need to recognize that metro edge networks support a wide variety of applications, as shown in Figure 1.

Figure 1: Metro edge networks extend connectivity from the core to a wide range of applications and use cases

It’s clear that scaling efforts at the metro edge need to address and accommodate many different use cases, including:

• Business services for enterprise and institutional users: This often involves a range of high-speed services so that end users can connect to offices across a city, country or the globe, as well as to the internet, private and public peering points, and edge cloud services. Business services include connections at fixed bit rates such as 10 Gb/s, 16 Gb/s, 100 Gb/s or greater, and may include fractional and adjustable bit rate services defined by the service provider, with either hard or soft isolation. These services also span a range of protocols, including Fibre Channel, optical transport network (OTN) or Ethernet, the last of which includes a wide range of Carrier Ethernet services defined by the Metro Ethernet Forum (MEF).

• Broadband and mobile backhaul: In many cases, services to residential or enterprise end users are provided by a “last mile” broadband technology such as fiber-to-the-home (FTTH) over PON technology, broadband services over fiber–coax networks, or xDSL over legacy copper access lines, or through wireless connectivity using 5G or fixed wireless access (FWA) technology. In all these cases, the broadband access platform aggregates traffic to and from multiple end users and backhauls this traffic from the metro edge back to the core over some form of aggregation link or metro backhaul network.

• Metro data center interconnection: Sometimes, optical networking to the metro edge involves webscale companies, carriers or enterprises that connect data centers to each other, or to internet exchange (IX) or peering points across short distances within a metropolitan area. These simple point-to-point connections can often be spanned by coherent optics equipped directly in router ports. This approach provides scalable, energy-efficient connectivity between sites by using wavelength division multiplexing (WDM) technology to scale capacity across multiple channels over a single fiber pair.

Building the right optical network for the metro edge

Now let’s look at what optical network operators need to ensure that they have the optimal solution for serving the specific demands of these metro edge applications.

First, network operators need to scale the capacity of optical transport links to meet growing service demands at the metro edge. But unlike long-haul core networks, where the cost or scarcity of fiber and the distances involved require optimization for the highest possible performance in terms of scale and reach, the metro edge needs optimizations that focus on enabling low power consumption and pluggable, small form-factor transceivers.

 Operators with metro networks can leverage pluggable digital coherent optics (DCOs) in QSFP or CFP form factors to scale transport link capacity up to 400 Gb/s or 800 Gb/s per wavelength, and provide the scale needed to aggregate more business services and support metro DCI applications. They can also “scale down” by using pluggable DCOs operating at 100 Gb/s per wavelength to improve the performance of low-capacity edge nodes or backhaul links and allow direct 100G uplinks without the need for separate transponders. By using pluggable DCOs, network operators can right-size metro connection speeds and upgrade data rates by simply changing to different optics, without needing to deploy and spare multiple data rate-specific line cards.

A second key requirement for optical network operators is to choose platforms and solutions optimized specifically for metro edge applications. This includes platforms that are small, compact, scalable and energy-efficient, and not over-designed for core networks, which require significantly more scale and capacity.  These platforms need to support both AC or DC power feeds so they can be used in both telco and customer premises applications, along with an extended operating temperature range so they can be deployed in uncooled outdoor cabinets. 

Edge-optimized line cards and features are also essential. This includes compact multi-service aggregation cards that can support packet and TDM aggregation of a wide range of protocols and port speeds into high-speed uplinks using 100 Gb/s and 400 Gb/s pluggable DCOs. Photonic management of wavelengths must also extend to the metro edge, with compact ROADMs supporting four- or nine-degree connections, for example. These ROADMs are optimal for adding or dropping just a few wavelengths at a node, for use as a two-degree node on an aggregation ring, or for use as a four-degree node to interconnect rings as traffic is aggregated upstream from the edge to the core. 

An optimized solution for the metro edge should, as much as possible, be part of a network operator’s end-to-end optical network. The operator should be able to deploy the solution across its network to ensure maximum operational efficiency and enable end-to-end services. This includes supporting important differentiated features such as synchronization distribution from primary clocks all the way to the edge.

In addition, a metro edge solution should support common line cards across platforms used in the core, metro and edge to minimize sparing costs and training requirements. Having common operating and management systems across the network is also very important. It will allow the service provider to minimize training, enable common operational processes and support optical network automation capabilities from end to end.

Nokia optical network solutions for the metro edge

To learn more about how Nokia is bringing scale and efficiency to the metro edge please visit our metro-edge solutions web page and learn more about our metro-optimized platforms, compact and integrated cards for managing packet, OTN/TDM and wavelength services, and portfolio of 100Gb/s, 400Gb/s and 800Gb/s  pluggable coherent optics.