Seeing the Gentle on the Finish of the Tunnel

The longer term is fiber, and the current is Knowledge Over Cable System Interface Specification (DOCSIS). What’s the proper funding profile to get from right this moment to tomorrow? To help Cable Operators with their funding planning, this weblog shares just a few technique and know-how choices from a CTO’s viewpoint.

Fiber to the Dwelling (FTTH)

There’s an inevitable shift forward from DOCSIS to passive optical networking (PON). The DOCSIS journey went from 1 Mbps to 1 Gbps, with an extension to 10 Gbps. Fiber is beginning at 1 Gbps, at the moment at 10 Gbps, and is headed to 100 Gbps. There are a number of Communication Service Suppliers (CSPs) right this moment who’re providing 5×5 Gbps and even 8×8 Gbps service over 10 Gbps symmetrical (XGS) Passive Optical Community (PON). Cable operators deploy each traditional HFC in addition to fiber to the house (FTTH), so they’re uniquely positioned to learn from the continued broadband funding.

The USA authorities is committing $99B into broadband funding over the subsequent a number of years, with many applications concentrating on PON (3). By my calculations, there may be sufficient funding to wire many of the USA with PON (4). This drastically lowers the economics and accelerates the timeframes of PON. The weblog, Three Causes to Put together for Your Subsequent Broadband Infrastructure Funding, presents extra particulars on how a Cable Operator will be prepared for Federal funding.

Even with this infusion of funding, PON and HFC plant upgrades could also be slowed by provide and labor shortages. A advice might be for operators to put aside a share of the federal government funding for training and coaching to assist develop the mandatory workforce for PON deployment. This selection will probably be mentioned by the Cable Business’s training affiliation, which is internet hosting Cable-Tec Expo, in Philadelphia this week, the primary in-person gathering in over 2 years.

PON has an fascinating funding story. As soon as put in, subsequent migrations to new know-how will be positioned on totally different wavelengths. Meaning the passive fiber plant doesn’t need to be rebuilt as PON strikes from 2.5G, to 10G, to 25/50G, and ultimately to 100G. A passive fiber plant additionally has fewer upkeep prices. There are even some thrilling PON applied sciences that use fiber faucets as an alternative of splitters (5) that may scale back the quantity of fiber and splicing wanted in a plant.

FTTH = FTTC + Drop Cable

Let’s check out PON from an installer’s viewpoint. There will probably be one crew that builds the community down the road. That entails laying conduit, blowing fiber bundles via them, after which fusion splicing the assorted fiber bundles collectively. That’s fiber to the curb (FTTC). Then there’s a subsequent crew that installs the drop fiber to the house and installs the CPE. So, an operator would first construct a FTTC community, after which later add drop cable to create FTTH occurrences.

One public baseline value for FTTC in city is $1000/HHP (so, not together with the drop cable and CPE prices) (6). For a number of dwelling items (MDUs), this could be much less, and for rural, this could be extra. A tough quantity for a drop cable set up and CPE is $450.

This funding in fiber can then get adjusted to account for:

  • how a lot authorities funding is obtained,
  • a number of generational use (10G to 100G), and
  • the decrease operational prices of fiber.

It’s as much as every operator to do that calculation, however an HFC improve must are available lower than the adjusted value of fiber.

We’ve regarded briefly at PON. Let’s now have a look at the present decisions for HFC and DOCSIS and see how they evaluate. Then you may decide how your broadband is holding up.


Within the cellular world, telcos could buy 20 MHz of nationwide spectrum for billions of {dollars}. In HFC, spectrum additionally has a price, and that’s of value of rebuilding and/or retooling of the HFC plant.

HFC plant spectrum is decided by the nodes, amps, passives, and high quality of the coax. Whereas it’s conceivable to improve the nodes and amps, upgrading all of the passives similar to faucets is a much bigger time and monetary dedication.

Does it make sense to pay for brand new spectrum when you may unencumber outdated spectrum?

An alternate means so as to add spectrum to DOCSIS is to repurpose the digital video spectrum from the Transferring Footage Professional Group Transport Stream (MPEG-TS) video to IP video over DOCSIS. The trick is to do that whereas retaining the video income. An entire IP video answer will probably be wanted for PON anyway in order that funding will get made. Making use of that IP video answer to HFC might be a way more cost-effective means of accelerating DOCSIS spectrum than extending the DOCSIS spectrum. When you preserve MPEG-TS video and pay for extra spectrum for DOCSIS, one necessary perspective is that you’re actually investing to maintain video within the spectrum.

Every 6 MHz video channel is equal to nearly 60 Mbps of information spectrum (with 4K OFDM). Meaning 64 channels (384 MHz of spectrum) of video can be price nearly 640 Mbps, which might roughly double the DOCSIS spectrum on an 862 MHz plant.

The DAA Capability Calculator (7) in Determine 1 exhibits the D3.1 spectrum with 64 channels of video current. HFC crops with lower than 1002 MHz of spectrum will probably be restricted to gigabit providers or much less. In reality, the conversion of video spectrum needs to be prioritized within the areas of the HFC plant which have much less spectrum.

DOCSIS 3.1 with Video
DOCSIS 3.1 with Video


The remark right here is that HFC, like cellular, will be measured by how a lot it prices to acquire spectrum, and the way re-purposing spectrum could also be cheaper than shopping for new spectrum.


Whereas DOCSIS 3.1 (D3.1) helps as much as 1218 MHz within the downstream (DS), many HFC crops are nonetheless at 650, 750, 862, or 1002 MHz. Determine 2 exhibits that if all of the video spectrum is transformed to DOCSIS spectrum, these older crops can assist 5 to 9 Gbps within the downstream.

DOCSIS 3.1 without Video
DOCSIS 3.1 with out Video

D3.1 additionally helps 42, 85, and 204 MHz return paths. The 204 MHz return path presents about 1.7 Gbps (2 ATDMA plus 2K OFDMA channels), which can assist 1 Gbps upstream (US) providers. Mixed with the downstream, that will enable D3.1 to supply 5×1 Mbps to eight×1 Mbps (DSxUS) service choices which have the potential to be aggressive with 2.5G and 10G PON.

85 MHz is one other return path choice. It’s going to enable roughly 400 Mbps upstream service as an alternative of 1 Gbps, which can be ok, and matches present Wi-Fi efficiency. It can be accomplished with the present HFC plant and current cable modem termination methods (CMTS). A 204 MHz return path requires the Distributed Entry Structure (DAA) or a brand new proprietary digital return path.  Additionally word {that a} 1218×204 MHz HFC plant has about the identical downstream spectrum as a 1002×42 MHz HFC plant.

The capability of DOCSIS 3.1 has not been totally realized in deployment. Realizing the potential of DOCSIS 3.1 inside current HFC plant may show to be very cost-effective.


DOCSIS 4.0 (D4.0) ESD (extended-spectrum DOCSIS) extends the higher frequency of the HFC plant as excessive as 1794 MHz, with future choices of as much as 3 GHz (8)(9). The upside of ESD is barely extra downstream spectrum and the chance to maneuver the return path to 396 MHz or 492 MHz.

The problem of D4.0 ESD is the associated fee and time of changing all of the passives. For each single node, there might be 20 amplifiers and over 100 passive faucets. If passives are to get replaced, it is sensible to interchange them with 1794 MHz or greater elements.

D4.0 ESD has additionally been traditionally coupled with the Distant MAC/PHY (RMACPHY) venture which basically places a Layer 2 CMTS within the fiber node. This re-invention of the CMTS footprint has sophisticated the deployment of ESD with out including any important options over Distant PHY (RPHY).

ESD with RPHY can be a neater technical answer because the RPHY DOCSIS and Video cores can be appropriate, and the Distant PHY Gadget (RPD) would wish upgrading. RPHY was invented by Cisco in 2005 (10) and revised in 2013 (11). In evaluating RPHY to the cellular 5G structure, the RPD is successfully a “DOCSIS radio.” The RPD is like an open radio entry community (ORAN) radio unit (RU) with the RPHY Cores being akin to the distributed unit (DU)/centralized unit (CU) and 5G Core. RPHY was an inspiration that created the Small Cell Discussion board (SCF) 5G community practical software platform interface (nFAPI) cut up 6 (12). The RPHY future roadmap nonetheless has a lot of potential forward of it on decreasing latency for lengthy converged interconnect community (CIN) paths and convergence with cellular.



DOCSIS 4.0 ESD requires a major improve to the HFC plant that features nodes, amps, passives, and a few coax. ESD operation is a minor extension to the DOCSIS and RPHY protocols. Coupled with RMACPHY, although, it turns into rather more complicated to roll out.


D4.0 full duplex (FDX) retains the identical downstream spectrum whereas extending the upstream spectrum by sharing a portion of the downstream spectrum with the upstream spectrum. The most important upside of FDX is that the plant passives will be retained if there may be already sufficient downstream bandwidth. This lowers the deployment value and deployment occasions.

FDX DOCSIS was first invented at Cisco in 2014, shared with the business in 2015, demonstrated a Node/Amp system at ANGA in 2017, and product launched in 2018 (13).

FDX DOCSIS is exclusive from different earlier FDX applied sciences by no less than 3 ways:

  1. FDX DOCSIS is level to multi-point, whereas earlier FDX applied sciences had been point-to-point. This required the distinctive growth of interference teams (IGs) and transmission teams (TGs) to managed cable modems (CMs) which are geographically adjoining to one another.
  2. FDX DOCSIS operates on an lively plant with a series of echo cancellers (ECs) within the hooked up nodes and amps. Earlier wireline and wi-fi FDX applied sciences had been single hop.
  3. FDX DOCSIS spectrum is 576 MHz, which is rather more spectrum than wi-fi or telephony applied sciences used

The problem for FDX is the potential value and complexity of echo cancellers (ECs) primarily based on digital signaling processing (DSP) that should be added to the nodes, amps, and CMs. FDX can be challenged in an amplified community attributable to a number of ECs and cascaded IGs. Market timing can be a difficulty. When FDX lastly does change into accessible for mass market, it should be in comparison with PON from a long-term funding viewpoint for value and throughput.

Listed below are some fascinating observations on FDX DOCSIS that may be seen in determine 3.

  • FDX DOCSIS doesn’t add any downstream spectrum. As a substitute, it retains the DS spectrum when the upstream spectrum is elevated. Thus, the funding in FDX DOCSIS is basically for a sooner upstream.
  • A 750 MHz plant may benefit extra from FDX DOCSIS than a 1002 MHz plant, as a 750 MHz plant has much less downstream spectrum, and can lose a better share of its spectrum to an upstream improve.
  • A 1002×85 MHz plant with out FDX has 120 MHz (1.2 Gbps) extra most downstream knowledge bandwidth than a plant with FDX enabled, because of the 120 MHz FDX keep-out zone, which permits MPEG-TS video however not DOCSIS.

FDX DOCSIS upgrades the nodes, amps, and CMs with echo cancellers. That is new and sophisticated know-how, but when there may be already sufficient downstream spectrum, FDX DOCSIS does depart the passives in place, which lowers prices and time to market. Navigating your community’s transformation is a complete end-to-end journey. Cisco may help to information the best way.


Cable operators have a number of choices accessible:

  1. Overbuild with PON
  2. Rebuild with DOCSIS 4.0 ESD
  3. Improve with DOCSIS 4.0 FDX
  4. Hold D3.1, add a 85 or 204 MHz improve, and selectively migrate MPEG video to IP video

These are sorted in descending value, absent of different issues. The elephant within the room is that with US authorities supplemental funding, multi-generational 10G to 100G advantages and competitiveness of fiber, and decrease working prices, this record could also be sorted fairly otherwise.

As a consequence of know-how and aggressive pressures, choices 2 via 4 additionally infer deferring fiber funding and deployment to a later cut-off date. The price of fiber is just not eradicated, however it’s postponed, which can make sense for some enterprise circumstances however not in others. Overbuilding the HFC plant with PON was not a sensible consideration in Canada and the US till the latest authorities initiatives. The remainder of the world, together with giant components of Mexico and Europe, have already migrated to a PON first method.

A lot of the DOCSIS choices enable roughly a 5×1 Gbps service providing, with D4.0 permitting as much as 5×3 Gbps providing. Whereas this needs to be enough to compete with an equal or barely greater providing from FTTH, the actual determination needs to be primarily based on the worth of the funding.

Fascinated with studying extra?  Meet with Cisco at SCTE Cable-Tec Expo this week. I’ll be there together with just a few colleagues to debate this matter and extra. Cisco is proud to be sponsoring the SCTE Awards Luncheon. Can’t make it to Philadelphia this week. Try this video which takes a deeper dive into these matters.

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