Innovations target deployment challenges
As commercial deployment of very high speed digital subscriber line 2 (VDSL2) vectoring technology ramps up, 3 innovations are helping communication service providers (CSPs) address key challenges:
- Upgrading legacy VDSL2 customer premises equipment (CPE): To achieve the full gain on vectored lines, all legacy VDSL2 CPE must be upgraded to vectoring or vectoring-friendly mode. These upgrades are time consuming, and not all legacy VDSL2 CPE supports such upgrades. With zero-touch vectoring technology, CSPs can benefit from vectoring gains on vectored lines without “touching” the legacy VDSL2 CPE.
- Deploying cost-effective coverage: CSPs need VDSL2 vectoring solutions that are sized for different subscriber densities — from large fiber to the node (FTTN) deployments serving hundreds of subscribers to fiber to the curb (FTTC) deployments serving dozens of subscribers. With scalable vectoring solutions, CSPs have the flexibility to cost effectively support a range of subscriber densities.
- Ensuring efficient operations: CSPs need the tools to efficiently troubleshoot and operate vectored lines. With the Motive Network Analyzer, CSPs have the information needed to quickly and accurately identify the root cause of problems on vectored lines.
Zero-touch vectoring for quick and easy introduction
Migrating legacy CPE is the biggest challenge CSPs face in a vectoring roll-out. Even a single legacy VDSL2 line in a binder can reduce the vectoring gains on other lines. To avoid this situation, all legacy VDSL2 CPE must be upgraded to either vectoring or vectoring-friendly mode. CSPs currently use 2 approaches to upgrade legacy VDSL2 CPE:
- Firmware upgrade to vectoring mode: This is the ideal approach because it converts legacy VDSL2 CPE into vectoring CPE. The legacy VDSL2 lines become vectoring lines and receive the full vectoring gain and do not impact the vectoring gain on the other lines in the binder. Many VDSL2 CPE, especially more recent models, can be made G.Vector (ITU-T G.993.5)-compliant with a firmware upgrade.
- Firmware upgrade to vectoring-friendly mode: CPE that cannot be upgraded to vectoring mode may be upgradeable to vectoring-friendly mode (ITU-T G.993.2 Annex X or Y). In this mode, legacy VDSL2 lines do not receive the vectoring gain, but at least they do not impact the vectoring gains on other lines in the binder. Although vectoring-friendly mode represents only a small extension to the VDSL2 standard, in reality only a limited number of CPE models support this mode.
The current approaches create two challenges for CSPs:
- Not all legacy VDSL2 CPE can be upgraded to vectoring or vectoring-friendly mode. That means any remaining legacy lines will reduce vectoring gains on the other lines.
- Upgrading legacy VDSL2 CPE is logistically difficult. The CSP must upgrade hundreds of thousands of CPE before vectoring can be activated. This requires significant time and effort and can delay vectoring deployments. Any number of issues can arise during upgrades — firmware updates can fail, end users might have switched off their CPE during the upgrade window, or they might have disabled the remote update feature.
Zero-touch vectoring technology solves the legacy VDSL2 CPE challenge for CSPs automatically. Clever signal processing in the DSL access node ensures that cross-talk from legacy VDSL2 lines into vectored lines can be measured, and canceled without requiring any new functionality in the legacy VDSL2 CPE. As a result, firmware upgrades are not required; legacy VDSL2 CPE behave as if they are “vectoring-friendly” without being touched. With zero-touch vectoring technology, CSPs have a quick and easy way to introduce vectoring in their network. They don’t have to worry about the affects of legacy VDSL2 CPE or spend time on network-wide CPE upgrades. Zero-touch vectoring also provides a “safety-net”, by providing a solution when no firmware upgrades are available for a certain VDSL2 CPE model. A two-step approach to zero-touch vectoring is recommended (Figure 2):
- CSPs can switch customers who are willing to pay for higher bit rates to vectoring (either by shipping a new vectoring CPE, or by upgrading the existing VDSL2 CPE to vectoring, if supported), and use zero-touch vectoring for all other legacy VDSL2 lines. Together, these actions enable full downstream vectoring gains on the vectored lines.
- CSPs can then upgrade legacy VDSL2 CPE to vectoring or vectoring-friendly mode at their leisure to unlock full upstream vectoring gains on the vectored lines as well. If the CPE supports neither vectoring nor vectoring-friendly mode, zero-touch vectoring provides a safety net because it can support all legacy VDSL2 CPE.
Scalable vectoring solutions for cost-effective coverage
The second challenge CSPs face is to cost effectively connect their subscribers.
- In high-density areas, CSPs typically use a FTTN deployment model and cabinets to serve between 100 and 400 subscribers.
- In low-density areas, CSPs use smaller cabinets or small sealed nodes to serve anywhere from a few dozen to 100 subscribers.
To cover various subscriber densities in the most cost-effective way, CSPs need vectoring solutions that scale from dozens of lines to hundreds of lines. Recent advances in vectoring solutions bring CSPs new levels of scalability, reach and speed.
Today, leading vectoring solutions support up to 384 lines, which is twice the original line support, to address dense urban areas. They also support system level vectoring across multiple line cards, either in the same system or in different, collocated systems. With the addition of a 48-port sealed enclosure, these vectoring solutions now scale from 48 ports to 384 ports. In addition, CSPs can now combine VDSL2 bonding and vectoring on the same lines. This allows CSPs that have two lines available per household to maximally increase the reach of VDSL2 services, the bit rate delivered to the home, or both.
A network analyzer for efficient troubleshooting
After vectoring is deployed, CSPs need tools to efficiently operate and troubleshoot the network. As a base requirement, CSPs need all of the same single-line troubleshooting capabilities they use on unvectored VDSL2 lines:
- Single-ended Line Testing (SELT)
- Dual-ended Line Testing (DELT)
- Metallic Line Testing (MELT)
The requirement for these capabilities may sound obvious, but ensuring these tests function properly on vectored lines is more complex than on unvectored lines. For example, the test signals used by SELT can interfere with the vectoring on neighboring lines. Vectoring also adds a new dimension to troubleshooting: the binder concept. In a binder, a problem on line 17 might actually be caused by line 23. As a result, performing only single-line troubleshooting on a line might not lead CSPs to the root cause of the problem. A network analyzer that supports crosstalk mapping allows CSPs to detect the correct root cause of problems in a binder. For each line in the binder, the network analyzer shows which other lines are the dominant crosstalkers. It also keeps track of the crosstalking lines over time. This information gives support engineers all of the information needed to efficiently identify the root cause of problems.
Continuous copper innovations
For the past year, CSPs around the world have been proving that vectoring technology delivers on its promise. Based on their positive trial experiences, CSPs are eager to move to the commercial deployment phase. Until recently, mass deployment of vectoring technology came with major challenges. Now, 3 innovations have emerged to help CSPs simplify and accelerate vectoring deployments. So what’s next? With vectoring a reality, there are a number of things that CSPs can do to further boost the speeds on their existing copper infrastructure:
- A potential step after deploying VDSL2 vectoring plus VDSL2 bonding is to use Phantom mode. Phantom mode creates a third virtual pair between two physical pairs, providing speeds up to 2.5 times that of a single vectored line.
- Operators can further shorten loop lengths using mini-DSLAMs (48 to 96 subscribers) or even micro-DSLAMs (48 ports or less). These are typically used in FTTCurb deployments, serving a few tens of households within a short distance (a few hundred meters).
- For very short loops (250m or less), G.fast technology could deliver hundreds of Mbps by using a wider frequency band for transmission. G.fast is currently in standardization and commercial systems are still a few years out. As with VDSL2, one really needs vectoring (G.fast vectoring in this case) to get the full gain.
Additional vectoring innovations are already in development. Check back to TechZine regularly to make sure you are among the first to learn how copper technologies are being pushed to new limits. To contact the authors or request additional information, please send an e-mail to firstname.lastname@example.org.