JOHN WILLIAMSON 5G & BEYOND
evolving to support 25GbE clients. “With metro WDM networks capable of 400G and even 600G wavelengths, there is no shortage of capacity available – the issue is doing so cost effectively via photonic integration and pluggable optics,” he says. “WDM is also inherently protocol agnostic and can address any new 5G protocols such as eCPRI.” Ethernet (along with WDM) should also play a starring role in 5G. “Ethernet has a clear role to play in 5G as all 5G transport is Ethernet or eCPRI, which uses Ethernet and is essentially a new EtherType,” remarks Baldry. “This Ethernet will typically be carried over WDM optical channels in a packet-optical network.” But current networks may not quite cut the mustard. ProLab’s technologist Anthony Clarkson accepts that using newer technologies over existing fibre could get part of the way towards 5G, but there may be limitations. Passive Optical Networks (PONs) are a case in point. One of ProLab’s large European operator customers doesn’t think, for example, that it’s practical to re-use existing residential PONs as they stand for 5G. “The bandwidth isn’t as good, you need lower split ratios, and you probably want physical traffic separation,” reports
ABSTRACT ART Help may be at hand. Mersh
software to significantly reduce latency to meet the stringent latency requirements of 5G fronthaul interfaces. This enables dense small cells to be accommodated cost-effectively by TDM-PON. A second DBA software can also be applied to OLTs in FTTH services that require high bandwidth efficiency. MAKING UP FIBRE SHORTFALL In some aspirant 5G markets, deep fibre is already becoming a fact of life; in others, conspicuously less so. Either way, experts believe that, notwithstanding any currently unused excess optical capacity in some parts of the network in some geographic markets, 5G will generally require larger, more pervasive fibre footprints than currently exist. “The reality is that in order to be able to support a proper, full 5G roll-out, there’s going to be a lot more fibre deployed,” contends Clarkson. “And that’s going to be green field fibre rather than dark fibre in the main.” In fact, research by Sterlite Tech suggests that moving from 3G to 4G involved a three to three-and-a-half times increase in fibre deployments over a seven-to-eight year period. “In the 5G investment cycle maybe two to three further amounts of fibre may be required compared to what has been deployed so far,” judges Sterlite Tech’s CEO, Telecom Products, Ankit Agarwal. An obvious driver of fibre expansion is the projected proliferation/densification of small cells necessary to support the coverage and capacity advertised for 5G. “More cells cause increased interference with one another and as a result, increased coordination is needed between the cells,” notes Menendez. “This leads to the adoption of Centralised RAN architectures, which rely on optical fronthaul. More cells will require fibre connectivity either on their own, or linked backed to an existing macro site.” “5G represents a huge opportunity for the optical networking community with substantial new network buildouts and some challenging design and performance criteria that will drive innovation and product development,” concludes Baldry, adding that these are tough challenges that the industry is already rising to.
acknowledges that the low latency required by 5G services means key elements of operators’ PON networks will need to evolve to meet new demands. “Previously, this would have meant rebuilding an Optical Line Terminal (OLT) from the preliminary stage of development, for example, a remake of the PON chip which requires a large amount of investment,” he says. “However, by applying network virtualisation technologies such as NFV and SDN to OLTs, this expense can be
where they exist, 5G is likely to fully utilise dedicated fibres or wavelengths
Clarkson. In similar vein, Baldry states that
eliminated and time-to-market for new services can be accelerated.” This sort of outcome is what the BBF’s PON Abstraction Interface for Time Critical Applications (TCAs) project with NTT aims to achieve through the disaggregation of time-critical PON functions, opening up the possibility for operators to support 5G fronthaul interfaces and services for business users. Mersh reports quick progress on the TCA project, and in June two scenarios were demonstrated. The first showed how a future OLT could be optimised with Dynamic Bandwidth Allocation (DBA)
where they exist, 5G is likely to fully utilise dedicated fibres or wavelengths. However, not all access networks have 100% fibre availability or the fibre may already be used in a PON, such as EPON or GPON, so dedicated wavelengths may not be possible. “These PONs could play a role in 5G transport, although very careful attention needs to be paid to some of the network performance aspects such as synchronisation if this is delivered by the network itself to the cell site,” comments Baldry.
In its most ambitious iteration, the 5G X-haul initiative aims at integrating 5G backhaul and fronthaul to create a software manageable transport network that can be run over fibre, copper or radio, or combinations thereof. Infinera attaches considerable importance to X-haul. “X-haul is highly significant as this forms a common network to support the variety of transport services needed to support 5G,” says Baldry. “X-haul is required to support high performance eCPRI transport plus 5G and 4G backhaul circuits, which is distinctly different from today’s networks where CPRI-based fronthaul and Ethernet-based backhaul are different network domains. The network therefore needs to dynamically support a variety of transport requirements whilst maintaining the best possible network economics and efficiencies.” X-haul: getting it together
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| ISSUE 14 | Q3 2018
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