As a consequence of a 50% traffic growth year/year, cable operators need to upgrade their coax infrastructure, so it supports gigabit that is required for future IP-based video services. An upgrade to DOCSIS 3.1 enables this, and the main benefit is that cable operators can leverage their existing cable network assets, in order to compete head-to-head with Fiber-To-The-Home operators.


TDC Group, the largest multi-service operator (MSO) in Denmark, with its headquarter in Copenhagen is the first operator in Europe who upgrades their entire coaxial infrastructure to DOCSIS 3.1, the project started in June 2016 and is targeted to be completed by the end of 2017.


In January 2016 Huawei announced that it is partnering with TDC to upgrade their coaxial network so that it can deliver broadband speeds of up to 1 Gbps with the use of DOCSIS 3.1 ready equipment.


The DOCSIS3.1-compliant architecture involves network-wide end points, optical nodes, amplifiers, passive splitters, and corresponding engineering services, to provide ground-breaking speeds and connectivity.


As part of this project, Huawei did partner with DKT A/S to deliver all components for the passive part of the coax infrastructure.


The article describes some of the lessons learned from this project combined with key findings/conclusions to be used by other MSOs as part of their planning for DOCSIS 3.1 upgrades.


Pay utmost attention to noise, and how to eliminate this

DOCSIS 3.1 offers the possibility of providing1Gbit/s upstream and 10Gbit/s downstream. In order to achieve this, the signal-to-noise ratio must be increased and the upstream as well as the downstream frequency ranges must be made wider. These DOCSIS 3.1 fundamentals define the challenges of the distribution network. The network itself – and so all of its components – must be carefully planned and designed. The DOCSIS 3.1 is adaptive and offers the possibility to use different modulations order for each subscriber, depending on the CNR of the specific channel. If the CNR is high the modulation order is kept high, but if the CNR decreases, then the modulation order will be lowered resulting in a lower bit rate. Going from QAM4096 modulation to QAM1024 modulation decreases the bit rate by (12-10)/12 = 17%, so therefore TDC had an extra focus on making all the network RF-tight, firstly by choosing network components with CLASS A or better performance, secondly by documenting the whole infrastructure allowing faster trouble shooting and better quality of the network in the future., finally they had the right competencies on the network planning team with many years of experience in the cable-TV industry.


Avoid “cold-flow” phenomena

Whenever speaking to network operators about the stability in their network, one fault dominates; the loose connector. Traditionally TDC did spend many man-hours per week just to fasten connectors in their network.

Some indications showed that up to 90% of all network failures are caused by this phenomena. The first action any service technician takes when called out is to tighten all cable connectors. And annoyed by experiencing loose connectors over and over again – no wonder – the temptation to tighten the connectors with a higher torque than recommended is huge. However, this even makes things worse. The loose connectors are not due to too weak tightening; rather it is the effect of the material selection. Most taps and splitters in the network are made by a zinc-alloy, e.g. Zamak 3, which – under long-time stress and even at room temperature – creeps and deforms permanently. So when a cable connector is fastened to the F-female connector on e.g. a tap, the zinc-alloy will start to deform. The more stress (i.e. tightening torque) the faster the creep happens. Eventually, the thread on the female connector is pressed out of shape, the connector is loose, and the noise level in the network grows. In addition, the stress from the temperature dependent change in lengths of connected cables adds to the creep. F-connectors made in brass material have a very low likelihood of self-loosening compared to F-connectors made in die-cast zinc alloy, e.g. Zamak 3. The latter material is typically used in low cost products, and many component suppliers offer these to the broad market today. TDC chose to use DKT’s Signia line of distribution passives. The Signia line approaches and solves these problems by reducing the need for ad-hoc service visits to retighten connectors. This is achieved both by crafting the connectors in the same metal – brass – and with the same plating – nickel-tin – as the cable connectors used in CATV networks, by selecting the proper material for the electronic components, and by designing the protective circuitry. This maximizes service flexibility by not having to replace units due to wear and tear.


Terminate DOCSIS service in the first outlet

In order to prevent any In-home network component/equipment to disturb backward into the network, TDC chose to terminate the DOCSIS service at the first outlet with the cable modem directly connected to the network.

The rationale behind this is that most operators may carefully plan, install, and manage the distribution network; however, as soon as the network penetrates the private property of the subscribers, network operators have no control over what happens in the home. The cable network operators have no say over what equipment subscribers use to connect to the network or which type of installations subscribers may choose. There are numerous examples of how this leads to all sorts of unwanted/unintended effects in the distribution network, mainly in the upstream direction.

For this reason, and for the reason of avoiding excessive cost of refurbishing the subscriber’s in-home network, TDC chose to terminate the DOCSIS 3.1 part right at the home-network interface (demarcation point). Using a proper diplex filter, splitting the signals into forward path broadcast (TV and radio) for distribution inside the subscriber’s premises and forward and return path data connected directly to the DOCSIS 3.1 modem, any unwanted signals in the upstream range generated inside the subscriber’s network is effectively blocked from entering the distribution network.

TDC chose to use DKT’s Push-In-Outlet, where customer easily can install the base unit and upgrade it when the return-path frequency changes from 65 Mhz to 204 MHz.

Benefits were:

  • Excludes distribution of DOCSIS 3.1 within the home, resulting in simpler installations
  • Eliminates Return Path noise contribution from the home (ingress and in-home components) resulting in a more robust network
  • Only first outlet in the home has to be upgraded, rest of the infrastructure can be reused resulting in a lower CAPEX
  • Visit the customer only once, next upgrades will be Do-It-Yourself (DIY) approach resulting in a lower OPEX


Equalization, optimizing return path

Early in the project it became that that it is necessary to use equalizers along the distribution line to compensate for the frequency dependent cable losses. Ideally, the equalizer has a frequency characteristic inverse to a coax cable. A simple straight-line characteristic will not match the cable loss, as this will result in signal levels that are at either too high or too low at different frequencies. Instead, the equalizers must be designed to match the square root behavior of the cable, but at the same time keeping the insertion loss low and the return losses high. This whitepaper explains why equalizers must be used in DOCSIS 3.1 deployment.

Installed DOCSIS installations:

  • The forward path was originally designed so that all customers would have nearly the same signal level at the outlet
  • Impact is that it could, with DOCSIS 3.1, cause attenuation at the far end customer in the return path to be 10-15 dB lower, with the result that the modem sends with too low a signal level

DOCSIS 3.1 implications, if equalizers are installed:

  • For optimized SNR all modems must send within a narrow window
  • Equalizers force a higher attenuation of the far end customer signal level (@lower frequencies), causing the cable modem to increase its output level. The result is that the narrow window size is met, SNR is improved and the QAM requirements are met.

TDC chose to use DKT’s new series of robust equalizers suitable for DOCSIS 3.1 operation.



TDC had to take extra precaution during the upgrade of their networks to DOCSIS 3.1. All passive and active components were exchanges or tuned, network planning of the entire installation was made.


Increased bandwidth demand with the usage of higher frequencies and new channel planning

  • Exchange of ALL coaxial passives in order to support 1218MHz with minimum loss
  • Network planning, optimization as well as calculations are necessary for the whole network

Resulting in significant CAPEX investments, this was required in both the active and passive infrastructure


Establishing a more robust network due to long history with:

  • Failing connections due to lose or corroded connectors
  • Failing taps or splitters due to overvoltage, transients or pulses
  • Interference/Screening/LTE due to LTE interference, and Interference from complementary technologies

This will result in a large OPEX savings, as TDC chose the right quality/performance


Increased focus on in-house/home infrastructure

  • Customer experiences with poor in-house/home installation results in massive unnecessary support center calls
  • Unnecessary truck roll and equipment swap

This will result in a lower churn rate, less truck roll and at least but most importantly increased customer satisfaction


“… DKT has shown its vast experience in the HFC industry, its deep understanding of customer requirements and its unique leading technologies. We are confident that with DKT we can deliver a successful project.”

-Huawei Managing Director, Mr. Binbing Xiao

In 2016, DKT A/S became partners with Huawei, in a project to make Denmark the first country in Europe to upgrade to the new standard, namely DOCSIS 3.1

“We are proud to be selected as the first Danish company to be a technology partner for Huawei, and we look forward to working closely with Huawei on this project. This is the result of focused research and development work and strict focus on what we do best,

Christian Emborg

DKT are proud to be first movers on DOCSIS 3.1, and to be the first passive coaxial product manufacturer with true DOCSIS 3.1 experience from large scale implementations. As early as 2013 DKT made the executive decision to ensure all products were compatible with DOCSIS 3.1. The head start when compared to other companies has provided valuable experience, which is evident in the premium standards in all DKT DOCSIS 3.1 ready products. In our innovation and product development, DKT has been focused on network performance, network economy, and end-user satisfaction. We see Huawei choosing us as a partner in upgrading Denmark, as the result of that.