Figure 1. Examples of mid/high-split and extended spectrum DOCSIS. They offer significant improvements to upstream and downstream bandwidth and performance.
"Split" is a reference to the separation or spectrum allocation between Return (Upstream) and Forward (Downstream) signals in DOCSIS coaxial cable plants (HFC, R-PHY, DAA). Mid, High, and Ultra High split bandwidth upgrades are considered cost effective solutions to stay competitive in brownfield markets, while FTTx/PON fiber deployment seems to be the preferred choice for greenfield.
- In the original spectral allocation splits, the Return (US) signals were limited to around 42 MHz (USA) or 65 MHz (Europe).
- Mid-Split allocates a bit more spectral bandwidth to the Return signals, to around 85 MHz, allowing faster and more reliable upstream data rates.
- High-Split moves the Return spectrum allocation even higher, to around 204 MHz, giving much more bandwidth to the upstream (US) for even faster speed. This is often combined with 1.2 GHz Extended Spectrum DOCSIS 3.1 (ESD) for the Downstream (DS), to offer much higher (more competitive) upstream and downstream data rates.
- This DOCSIS 3.1 ESD spectrum allocation allows up to two upstream OFDMA blocks (96 MHz each) and up to two downstream OFDM blocks (192 MHz each), for up to >1 Gbps US and >3 Gbps DS.
- The DOCSIS 3.1+ ESD definition allows two upstream OFDMA blocks (96 MHz each) and up to four downstream OFDM blocks (192 MHz each), for up to >1 Gbps US and >6 Gbps DS.
- Ultra-High Split moves the spectral allocation split even higher, to around 396 MHz or 684 MHz, giving a significant amount of bandwidth to the upstream for significantly faster upload speed. The idea is to combine it with 1.8 GHz Extended Spectrum DOCSIS 4.0 (ESD) for the downstream, to offer much higher (more competitive) upstream and downstream data rates and certain symmetrical high-speed services.
- This DOCSIS 4.0 ESD spectrum allocation allows up to eight upstream OFDMA blocks (96 MHz each) and up to seven downstream OFDM blocks (192 MHz each), for up to >6 Gbps US and 10 Gbps DS. It also allows multi-gigabit symmetrical services.
- ESD refers to extending the usable coax spectrum to 1.2 GHz in the short term and up to 1.8 GHz (and maybe 3 GHz) in the long term, to allow existing HFC plants to evolve along FTTx optical distribution networks (ODN) and stay competitive during the transition to fiber optics.
Of course, the implementation of new bandwidth allocations requires updating, qualifying, validating and troubleshooting all new passive and active elements in the coax plants being updated, to make sure they comply with the new bandwidth requirements. For modern hybrid R-PHY/DAA/PON networks, this can be verified by (frequency) sweeping the coax segments with a new generation of portable meters (test sets) supporting the new extended frequency ranges. Portability is key because the fiber feeders are now digital and the remaining coaxial segments are at the edge of the HFC network. Centralized sweep generators are no longer viable for this application.
The latest (2024) DOCSIS 4.0 Cable Modems can now achieve downstream speeds of 9 Gbit/s and upstream speeds greater than 2 Gbit/s, using ultra-high split (684 MHz). This 2024 interop testing was performed against various DOCSIS 4.0 Remote Phy Devices and DOCSIS 3.1 CMTSs. (Source: CableLabs D4.0 Interop).
Why DOCSIS 4.0 and ESD Matter to Cable Operators?
-
They maximize HFC bandwidth capacity, enabling the broadband/cable industry to reach its long-defined 10G initiative.
-
Practically, D4.0 ESD enables multi-gigabit symmetrical service, supporting downstream and upstream speeds up to 6 Gbps, to better compete in the current speed wars with FTTx/PON providers.
-
In reality, there is nothing complex about D4.0 ESD. It can be a natural and cost-effective upgrade cycle from D3.1.
-
Uses same MAC Features, same channel definitions.
-
Troubleshooting and plant readiness developed for D3.1 applies to D4.0 ESD.
-
-
Compelling upgrade cost:
-
For brownfields, D4.0 network upgrades remain cost effective at around $100 to $200 per home passed versus much higher cost PON overbuilds.
-
For greenfield deployments, FTTx/PON seems to be the obvious choice.
-
Future Spectrum Allocations? At the 2024 SCTE TechExpo trade show, we saw credible development announcements from Broadcom, Charter and Comcast for supporting future 3 GHz HFC networks, which could be considered DOCSIS ‘5.0’. The goal is to support 25 Gbit/s downstream speeds. (Press release: 25G DOCSIS)
For more details, refer to the Extended Spectrum DOCSIS (ESD) & High Split Article and visit the DOCSIS 3.1/4.0 resources page.
Related Test Solutions
- SWP-BOX - Portable Sweep Generator (supports extended spectrum)
- CX380C - Advanced Plant Maintenance Meter (handheld sweep receiver)
- CX310 - DOCSIS 3.1 Installation Tool