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Rate vs. Reach of VDSL2 and VDSL2 Bonded

Rate vs. Reach of VDSL2 and VDSL2 Bonded

Today, more than 1 billion households are still connected to a copper line.1 As the reality of supporting HDTV and video in just about every room has become the norm and no longer a luxury, higher bandwidth for Triple Play Services (voice, data, and video) continues to see a growing demand. Leading telco service providers around the globe have struggled to keep up in the past until the introduction of pair bonding, a blessing from the DSL powers above. Through the early deployments of this now globally-adopted technology, 1 operator in the UK was able to deliver roughly 97% of the combined uplink and downlink throughputs of 2 optimized ADSL single circuits, while another in the US reported an average speed improvement of 30% by offering bonded VDSL.

While the evidence and reasoning behind pair-bonding has been around for several years, we’ve discovered through our field work that the implementation has only taken a substantial form of deployment in the US market very recently. In fact, one Tier 1 telco shared with us that although only about 30% of their network is currently comprised of bonded circuits, this number is expected to double in the next few years based on the demand they are seeing from their customers. This reoccurring trend from the market has led us to chime in to the outside plant (OSP) technician’s mantra: Copper is not dead, but alive and well indeed. Well enough, in fact, to support speeds up to 100 Mbps through bonded circuits.

The deployment of pair-bonding continues to be key initiative to support legacy copper networks from a cost-efficiency perspective as it enables faster time-to-market and is less costly as compared to running fiber all the way to the end customer. According to the FCC, running fiber over the Last Mile to the home costs the provider at least $2,500 per subscriber, while taking the approach of providing a hybrid of fiber and copper over the existing plant costs about $500 per subscriber.

Greater Bandwidth via Pair Bonding
In short, pair bonding offers the ability to utilize and combine the speeds of 2 pairs (ADSL2+ or VDSL2) and deliver up to 200 Mbps in some instances, continuing to be a godsend for those end users whose access lines fall outside the maximum reach limit for service deployment on a single wire pair. This also saves many of the Tier 1 telco service providers a great deal of investment and the ability to quickly deliver better bandwidth performance to their large scale of customers, especially those in rural areas.

Figure 1 shows the rate vs. reach of a non-bonded VDSL2 line as compared to a VDSL2 bonded circuit. Pair-bonded VDSL2 can offer 100 Mbps over almost 2,000 feet, 80 Mbps to over 3,000 feet and 50 Mbps up to about a 6,000-foot range. Even over longer loops, bonding is able to maintain greater bandwidth over non-bonded VDSL2.

Figure 1. Rate vs. Reach of VDSL2 and VDSL2 Bonded.

Best Practices for Testing Bonded Circuits
Though bonding has been proven time and time again to yield impressive results, it is equally important for today’s field technicians to have a solid understanding of effective test practices as well as knowing what indicators to look for while testing bonded DSL circuits. Using similar methods of connecting on a single copper pair wire and collecting performance metrics, technicians now use their test set to verify and validate the services running over two pairs simultaneously.

Below are a few key points to consider while performing testing on bonded circuits:
• Services cannot be accurately assessed when conducting single-pair testing in a bonded environment. It is not effective to test each pair independently of the other, as this can result in false positive readings because any noise affecting the other cannot be detected.
• Pairs that are adjacent to each other are typically prime candidates for bonding. Due to their close proximity, crosstalk can be a culprit for limiting bandwidth and can only be detected when testing on bonded circuits.
• A proper understanding of the rate vs. reach tradeoffs is essential to extending the reach of basic DSL services to customers outside the single wire pair service area as well as delivering higher capacity to end users than on a single DSL access link within the single pair service area.

The Truth Is in the Data
With a greater deployment of bonded pairs in today’s copper networks, field technicians depend on their equipment to quickly and accurately understand the speeds that can be carried over these bonded circuits. They also rely on their test set to quickly identify, diagnose, and troubleshoot any problems that prevent them from delivering optimal DSL performance to their customers.

When syncing and authenticating on a DSLAM, the test set will use the group rate to evaluate each pair’s bandwidth capacity. (See Figure 2.) Even if the pairs are unrelated, many test sets on the market will average the group rates and provide false throughput speeds. In theory, the test set may display up and down rates higher or lower than their actual capability. Furthermore, a true bonded test set will not sync up let alone pull false data readings if the pairs under test aren’t connected to the same group.

Figure 2. Technician testing with the Sidekick Plus xDSL Bonded Modem.

Complications also exist when testing on the physical layer. Technicians need to have a full understanding of all DSLAM profile settings when testing on bonded circuits.

Accelerating speeds on existing copper infrastructures through the deployment of bonding continues to be proven as a faster and more cost-effective method to deliver more bandwidth to subscribers. Therefore, it is equally important for today’s field technicians to be armed with test equipment that has the capabilities to effectively reap the numerous benefits that bonding has to offer. Inaccurate readings cripple technicians, causing frustration in the field and what seem to be endless repeat visits to angry customers.

Working with several operators across the globe has allowed Greenlee Communications to further understand and successfully address growing demand to deploy these copper-saving technologies. The ideal test set supports the deployment of pair bonding and vectoring in an all-inclusive unit, allowing technicians to test more quickly and efficiently.

Despite the push for fiber-to-the-home based networks as the final end-goal, bonding continues to be an appealing technology for operators due to the lower level of investment in their current plant, and to quickly ensure that a high quality of experience is delivered to the customer. With DSL still accounting for about 70% of all broadband connections today2, getting the most potential out of the current infrastructures that exist in nearly every US neighborhood certainly remains to be a top priority in the market.

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