Tag - xdsl

G.fast challenges

The Challenges With Replicating G.fast Speeds in the Real-World

Internet Service Providers (ISPs) competing with cable service providers are watching the development of G.Fast, a new xDSL technology that promises to deliver fiber-like speeds using legacy copper lines.G.Fast is the next generation of xDSL services that will benefit customer premises located near distribution points.The increased usage of cloud-computing, video streaming, and the awaited arrival of the Internet of Things (IoT) revolution (expected to increase Big Data) have further increased the demand for faster broadband speeds. Internet Service Providers are seeking newer methods to improve broadband speeds to rates that exceed 100mbps to remain competitive.  Internet Service Providers (ISPs) have been able to deploy high-speed broadband using legacy copper lines with xDSL technologies such as ADSL and VDSL. But with G.fast, ISPs are hoping to achieve near 1Gbps speeds in shorter loop lengths.Receive a Complementary ConsultationG.fast provides a wider frequency band than VDSL2. VDSL2 supports a frequency profile of up to 30 MHz. G. Fast’s frequency band currently supports 106 MHz profiles but newer generations of G.fast are expected to support 212 MHz frequency bands. These wider frequencies can provide near-gigabit speeds in laboratory settings.

G.fast Performance in the Real World

But the challenge for ISPs is replicating those laboratory results in real-world settings. Trial runs in real-world scenarios have successfully been able to achieve speeds of up to 330 Mbps.UK’s Openreach Telecom company has deployed trial runs in Huntingdon, Cambridgeshire and received favorable customer feedback.

G.fast Setbacks

Huawei notes that one of the main issues with G.fast is minimizing the total cost of ownership. G.fast is still a bleeding edge technology and access service providers are experimenting with ways to maximize the commercial viability for G.fast.G.fast’s higher frequencies overlap with VDSL and VDSL2’s broadband spectrum making it difficult for network architectures to support both xDSL access technologies.Providers are faced with another challenge: G.fast support for short loop lengths entails drop point installations. Huawei notes that these types of deployments are characterized by their low-port counts. G.fast SetbacksBroadband providers are considering expanding port-count, but at the cost of sacrificing bandwidth. A higher port count will increase the amount of lines a DPU binder supports, and hence, increase the complexity of vectoring processes. According to Huawei, “the vectoring complexity of G.fast is 6 to 12 times [more complex than] that of VDSL2 Profile 14a with the same port count”.  Nonetheless, the company remains optimistic concluding that “Over the next few years, vectoring processors that are more scalable are expected to become available.”Huawei also anticipates that G.fast deployment will be particularly difficult in brownfields that boast a large amount of VDSL2 subscribers.  ISPs will need to entice customers to upgrade to G.fast to be able to “re-farm… the spectrum to improve bandwidth after the VDSL2 CPEs are removed from the network”.Getting subscribers to upgrade can prove particularly difficult if they find their existing VDSL2 speeds satisfactory.

Reverse Power Feeding

G.fast will rely on reverse power feeding to draw power from customer premise equipment to power G.fast DSLAMs. G.fast has even shown to require less power than VDSL2 with energy-efficient features. Reverse power-feeding will help reduce costs for distribution point installations.

TDD (Time Division Duplexing)

G.fast will rely on Time-Division Duplexing or TDD to transmit data.  TDD uses pre-assigned time frames to alternate between sending and receiving signals. TDD gives ISPs the ability to customize the allocation of bandwidth between upload and download speeds and create asymmetrical profiles. 

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Our Top Ten Most Frequently Asked Questions About VDSL

We’ve compiled a list of the most commonly asked questions about VDSL & VDSL2. If you’re interested in learning more about ADSL and ADSL2+, visit our ADSLs/2+ FAQ here.

1. What is VDSL/VDSL2?

VDSL, or Very-High-Bit-Rate Digital Subscriber line, allows Internet Service Providers to provide fast connection speeds via legacy copper lines. VDSL and VDSL2 can provide faster broadband performance when compared to ADSL/2+ up to approximately 1.5km distances. After 1.5 km distances, VDSL2 exhibits performance rates comparable to ADSL2+.

2. How fast is VDSL in comparison to VDSL2?

VDSL speeds vary depending on copper loop lengths and other factors in a networking environment. Pair-bonding is another factor that influences VDSL speeds. VDSL can support downstream and upstream rates of 100 Mbps. VDSL2 on the other hand, can reach theoretic downstream and upstream data rates of up to 200 Mbps at its source. VDSL2 also supports a wider frequency range of 30 MHz in comparison to VDSL’s 12 Mhz frequency range. Both VDSL generations quickly deteriorate after certain distances. At 1 km, both VDSL versions begin to exhibit similar speeds. At approximately 1.6 km, VDSL performance becomes comparable to ADSL2+.VDSL vs VDSL2 Comparison Chart

3. What is the farthest distance VDSL2 can reach?

The maximum range for VDSL2 is approximately 1,200 meters. After approximately 1600 meters, VDSL2’s performance quickly deteriorates yielding speeds comparable to ADSL2+.

4. How does VDSL2 achieve higher data rates than VDSL and ADSL2/2+?

Copper loop lines are susceptible to signal attenuation and copper loop lengths which limit fast transmission speeds. To achieve data rates over 100 Mbps, VDSL2 relies on port-bonding and vectoring.

5. What is pair-bonding?

VDSL2 supports the capability of bonding two or more twisted copper pairs to increase banding. But pair-bonding also functions to extend the reach of a copper network. Two DSL Line circuits that connect to a customer’s modem can be bonded. Or as explained by Ospmag, pair-bonding requires 2 VDSL2 lines which “can be combined into a “virtual “gig pipe” that allows operators to double the bitrate for existing subscribers.”Pair-bonding can be compared to adding more lanes to a freeway so that it can support more traffic. This enables Internet Service Providers (ISPs) to offer different data rate packages to subscribers.

6. What is VDSL2 Vectoring?

VDSL2 uses vectoring to remove crosstalk and interference reduces actual performance. VDSL2 measures crosstalk from all lines in a network and applies anti-phase signals to cancel out noise. VDSL2 vectoring works in similar fashion to noise-cancelling headphones. Crosstalk allows VDSL2 speeds to achieve longer distances than VDSL.  Assia Inc.  specifies that “Vectored VDSL is most suitable for deployment from a node, and is the most economical in terms of required capital expenditure.”

7. What is the purpose of the different VDSL2 profiles?

VDSL2 supports 8 distinct “profiles” with varying maximum downstream and upstream throughput as well as different bandwidth frequencies and transceiver power.Different profiles are optimal for different deployment scenarios.For example, profiles 8a-8b and 12a-12b are ideal for Fiber to the Node (FTTN) deployments. Profiles 17a can be used for Fiber to the Cabinet (FTTCAB), and Fiber to the Building (FTTB) can utilize profile 30a.
Different VDSL Profiles

Img Src: http://www.globaltelecomsbusiness.com/pdf/ZTE%20VDSL2--A%20Feasible%20Solution%20for%20Last%20Mile-Nov.pdf

8. Do you recommend using 2 different VDSL2 profiles on distinct modems connected to a DSLAM?

Having a cable bundle consisting of 2 or more VDSL2 profiles will exhibit intermittent sync, port status errors and poor performance. The 30a profile will run on 30 Mhz while the 17a profile will run on 17Mhz. The 30a profile can "bleed" over to the 17a profile.  Many chipset manufactures such as Broadcom have stepped away from VDSL2 30a due to this very reason.Our recommendation is to force all subscriber interfaces to sync at 17a if you have modems that do not support 30a. Users shouldn't have an issue if all ports are synced on the same VDSL2 profile.

9. Are VDSL2/2+ units compatible with previous versions of VDSL2?

VDSL2 units are backwards compatible with VDSL Units. When a VDSL2 unit is connected to a compatible VDSL unit, VDSL2 bandwidth will revert to VDSL’s maximum supported 12Mhz frequency range.

10. Are there faster DSL technologies than VDSL2?

Yes! G.Fast is a standard still in development that has shown the ability to transmit gigabit speeds using legacy copper lines in laboratory settings. Openreach, the dominant telecom provider in the UK, is spearheading the new technology, deploying trial runs to determine if the new technology is commercially viable. However, G.Fast, like VDSL, is only effective in deployments where customer premises reside near cabinets.To learn more about G.Fast, click here.

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