Sckipio improves G.fast’s speed, reach and density
Sckipio has enhanced the performance of its G.fast chipset, demonstrating 1 gigabit data rates over 300 meter of telephone wire. The G.fast broadband standard has been specified for 100 meters only. The Israeli start-up has also demonstrated 2 gigabit performance by bonding two telephone wires.
Michael Weissman
“Understand that G.fast is still immature,” says Michael Weissman, co-founder and vice president of marketing at Sckipio. “We have improved the performance of G.fast by 40 percent this summer because we haven’t had time to do the optimisation until now.”
The company also announced a 32-port distribution point unit (DPU), the aggregation unit that is fed via fibre and delivers G.fast to residences.
G.fast is part of the toolbox enabling faster and faster speeds, and fills an important role in the wireline broadband market
The 32-port design is double Sckipio’s current largest DPU design. The DPU uses eight Sckipio 4-port DP3000 distribution port chipsets, and moving to 32 lines requires more demanding processing to tackle the greater crosstalk. Vectoring uses signal processing to implement noise cancellation techniques to counter the crosstalk and is already used for VDSL2.
G.fast
“G.fast is part of the toolbox enabling faster and faster speeds, and fills an important role in the wireline broadband market,” says Julie Kunstler, principal analyst, components at market research firm, Ovum.
G.fast achieves gigabit rates over copper by expanding the usable spectrum to 106 MHz. VDSL2, the current most advanced digital subscriber line (DSL) standard, uses 17 MHz of spectrum. But operating at higher frequencies induces signal attenuation, shortening the reach. VDSL2 is deployed over 1,500 meter links typically whereas G.fast distances will likely be 300 meters or less.
Another issue is signal leakage or crosstalk between copper pairs in a cable bundle that can house tens or hundreds of copper twisted pairs. Moreover, the crosstalk becomes greater with frequency. The leakage causes each twisted pair not only to carry the signal sent but also noise, the sum of the leakage components from neighbouring pairs. Vectoring is used to restore a line's data capacity.
G.fast can be seen as the follow-on to VDSL2 but there are notable differences. Besides the wider 106 MHz spectrum, G.fast uses a different duplexing scheme. DSL uses frequency-division duplexing (FDD) where the data transmission is continuous - upstream (from the home) and downstream - but on different frequency bands or tones. In contrast, G.fast uses time-division duplexing (TDD) where all the spectrum is used to either send data or receive data.
Using TDD, the ability to adapt the upstream and downstream data ratio as well as put G.fast in a low-power mode when idle are features that DSL does not share.
“There are many attributes [of DSL] that are brought into this standard but, at a technical level, G.fast is quite fundamentally different,” says Weissman.
One Tier-1 operator has already done the bake-off and will very soon select its vendors
Status
Sckipio says all the largest operators are testing G.fast in their labs or are conducting field trials but few are going public.
Ovum stresses that telcos are pursuing a variety of broadband strategies with G.fast being just one.
Some operators have decided to deploy fibre, while others are deploying a variety of upgrade technologies - fibre-based and copper-based. G.fast can be a good fit for certain residential neighbourhood topologies, says Kunstler.
The economics of passive optical networking (PON) continues to improve. “The costs of building an optical distribution network has declined significantly, and the costs of PON equipment are reasonable,” says Kunstler, adding that skilled fibre technicians now exist in many countries and working with fibre is easier than ever before.
“Many operators see fibre as important for business services so why not just pull the fibre to support volume-residential and high average-revenue-per-user (ARPU) based business services,” she says. But in some regions, G.fast broadband speeds will be sufficient from a competitive perspective.
“One Tier-1 operator has already done the bake-off and will very soon select its vendors,” says Weissman. “Then the hard work of integrating this into their IT systems starts.”
And BT has announced that it had delivered up to 330 megabit-per-second in a trial of G.fast involving 2,000 homes, and has since announced other trials.
“BT has publically announced it can achieve 500 megabits - up and down - over 300 meters running from their cabinets,” says Weissman. “If BT moves its fibre closer to the distribution point, it will likely achieve 800 or 900 megabit rates.” Accordingly, the average customer could benefit from 500 megabit broadband from as early as 2016. And such broadband performance would be adequate for users for 8 to 10 years, he says
Meanwhile, Sckipio and other G.fast chip vendors, as well as equipment makers are working to ensure that their systems interoperate.
Sckipio has also shown G.fast running over coax cable within multi-dwelling units delivering speeds beyond 1 gigabit. “This allows telcos to compete with cable operators and go in places they have not historically gone,” says Weissman.
Standards work
The ITU-T is working to enhance the G.fast standard further using several techniques.
One is to increase the transmission power which promises to substantially improve performance. Another is to use more advanced modulation to carry extra bits per tone across the wire’s spectrum. The third approach is to double the wire's used spectrum from 106 MHz to 212 MHz.
All three approaches complicate transmission, however. Increasing the signal power and spectrum will increase crosstalk and require more vectoring, while more complex modulation will require advanced signal recovery, as will using more spectrum.
“The guys working in committee need to find the apex of these compromises,” says Weissman, adding that Sckipio believes it can generate a 50 to 70 percent improvement in data rate over a single pair using these enhancements. The standard work is likely be completed next spring.
Sckipio says it has over 30 customers for its chips that are designing over 50 G.fast systems, for the home and/ or the distribution point.
So far Sckipio has announced it is working with Calix, Adtran, Chinese original design manufacturer Cambridge Industries Group (CIG) and Zyxel, and says Sckipio products are on show in over 12 booths at the Broadband World Forum show.
G.fast adds to the broadband options of the service providers
Feature: G.fast
Source: Alcatel-Lucent
Competition is commonly what motivates service providers to upgrade their access networks. And operators are being given every incentive to respond. Cable operators are offering faster broadband rates and then there are initiatives such as Google Fiber.
Internet giant Google is planning 1 Gigabit fibre rollouts in up to 34 US cities covering 9 metro areas. The initiative prompted AT&T to issue its own list of 21 cities it is considering to offer a 1 Gigabit fibre-to-the-home (FTTH) service.
But delivering fibre all the way to the home is costly, and then there is the engineering time required to connect the home gateway to the network. Hence the operator interest in the emerging G.fast standard, the latest digital subscriber line (DSL) development that promises Gigabit rates using the telephone wire.
"G.fast eliminates the need to run fibre for the last 250 meters [to the home]," says Dudi Baum, CEO of Sckipio, an Israeli start-up developing G.fast chipsets. "Providing 1 Gigabit over a copper pair is cheaper and faster to deploy, compared to running fibre all the way."
For G.fast, you need the fibre closer to your house to get the Gigabit and that is not available today with most carriers
Until recently, operators faced a choice of whether to deploy FTTH or use fibre-to-the-node (FTTN) and VDSL to boost broadband rates. Now, such boundaries are disappearing, says Stefaan Vanhastel, marketing director for fixed networks, Alcatel-Lucent. Operators are more pragmatic in their deployments and are choosing the most suitable technology for a given deployment based on what is most cost effective and fastest to deploy.
"It is very much no longer black and white," agrees Julie Kunstler, principal analyst, components at market research firm, Ovum. "The same service providers will be supporting multiple access networks."
The advent of G.fast will enhance the operators' choice, boosting data rates while using existing copper to bridge the gap between the fibre and the home. But the technology is still some way off and views differs as to whether deployments will begin in 2015 or 2016.
"For G.fast, you need the fibre closer to your house to get the Gigabit and that is not available today with most carriers," says Arun Hiremath, director, marketing at DSL chip company, Ikanos Communications. It will likely start with some small scale deployments, he says, "but the carriers will wait a little more for things to mature".
G.fast
G.fast enables Gigabit rates over telephone wire by expanding the usable spectrum to 106MHz. This compares to the 17MHz spectrum used by VDSL2, the current most advanced deployed DSL standard. But adopting the wider spectrum exacerbates two local-loop characteristics that dictate DSL performance: signal attenuation and crosstalk.
Operating at higher frequencies induces signal attenuation, shortening the copper reach over which data can be sent. VDSL2 is deployed over 1,500m links typically, G.fast distances will more likely be 200m or less.
Dudi BaumCrosstalk refers to signal leakage between copper pairs in a cable bundle. A cable can be made up of tens or hundreds of copper twisted pairs. The leakages causes each twisted pair not only to carry the signal sent but also noise, the sum of the leakage components from neighbouring DSL pairs.
Crosstalk becomes more prominent the higher the frequency. "One reason why no one has developed G.fast technology until now is the challenge of handling crosstalk at the much higher frequencies," says Baum. Indeed, from G.fast field trials, observed crosstalk is so severe that from certain frequencies upwards, the interference is as strong as the received signal, says Paul Spruyt, DSL strategist for fixed networks at Alcatel-Lucent.
Vectoring
Vectoring is a technique use to tackle crosstalk and restore a line's data capacity. Vectoring uses digital signal processing to implement noise cancellation, and is already used for VDSL2. "Vectoring is considered a key aspect of G.fast, even more than for VDSL2," says Spruyt.
G.fast can be seen as a logical evolution of VDSL2 but there are also differences. Besides the wider 106MHz spectrum, G.fast has a different duplexing scheme. VDSL2 uses frequency-division duplexing (FDD) where the data transmission is continuous - upstream (from the home) and downstream - but on different frequency bands or tones. In contrast, G.fast uses time-division duplexing (TDD) where all the spectrum is used to either send data (upstream) or receive data.
If a cable carries both services to homes/ businesses, G.fast is started from the 17-106MHz band to avoid overlapping with VDSL2, since crosstalk cannot be cancelled between the two because of their differing duplexing schemes.
Paul Spruyt
Both DSL schemes use discrete multi-tone, where each tone carries data bits. But G.fast uses half the number of tones - 2,048 - with each tone 12 times the bandwidth of the tones used for VDSL2.
Operators can also configure the upstream and downstream ratio more easily using TDD. An 80 percent downstream/ 20 percent upstream is common to the home whereas businesses have symmetric data flows.
Only transmitting or only receiving also simplifies the G.fast analogue front-end circuitry since it is less susceptible to signal echo, whereas such an echo is an issue with VDSL2 due to the simultaneous sending and receiving of data.
Operators want G.fast to deliver 150 Megabit-per-second (Mbps) aggregate data rates over 250m, 200Mbps over 200m, 500Mbps over 100m and up to 1 Gigabit-per-second over shorter spans. This compares to VDSL2's 70Mbps (50Mbps downstream, 20Mbps upstream) over 400m. With vectoring, VDSL2 performance is doubled: 100Mbps downstream and 40Mbps for the same span.
Vectoring works by measuring the crosstalk coupling on each line before the DSLAM - the platform at the cabinet, or the fibre distribution point unit for G.fast - generates anti-noise to null each line's crosstalk.
The crosstalk coupling between the pairs is estimated using special modulated ‘sync’ symbols that are sent between data transmissions. A user's DSL modem expects to see the modulated sync symbol, but in reality receives the symbol distorted with crosstalk from modulated sync symbols transmitted on the neighbouring lines.
The modem measures the error – the crosstalk – and sends it to the DSLAM. The DSLAM correlates the received error values on the ‘victim’ line with the pilot sequences transmitted on all the other ‘disturber’ lines. This way, the DSLAM measures the crosstalk coupling for every disturber–victim pair. Anti-noise is then generated using a vectoring chip in the DSLAM, and injected into the victim line on top of the transmitted signal to cancel the crosstalk picked up, a process repeated for each line.
Such an approach is known as pre-coding: in the downstream direction anti-noise signals are generated and injected in the DSLAM before the signal is transmitted on the line. For the upstream, post-coding is used: the DSLAM generates and adds the anti-noise after reception of the signal distorted with crosstalk. In this case, the DSL modem sends modulated sync symbols and the DSLAM measures the error signal and performs the correlations and anti-noise calculations.
G.fast vectoring is more complex than vectoring for VDSL2.
Besides the strength of the crosstalk at higher frequencies, G.fast uses a power-saving mode that deactivates the line when no data is being sent. The vectoring algorithm must stop generating anti-noise each time the line is deactivated, while quickly generate anti-noise when transmission restarts. A VDSL2 modem line can also be deactivated but this is much less commonplace.
"The number of computations you need to do is proportional to the square of the number of lines," says Spruyt. For G.fast, the lines used are far less - 4 to 24 and even 48 in certain cases - because the G.fast mini-DSLAM is much closer to the home. For VDSL2, the number of lines can be 200 or 400.
However, the symbol rate of G.fast is related to the tone spacing and hence is 12 times faster than VDSL2. That requires faster calculation, but since G.fast has half the number of tones of VDSL2, and crosstalk cancellation is performed for each tone, the overall G.fast processing for G.fast is six times greater.
G.fast vectoring may thus be more complex but the overall computation - and power consumption - of the vectoring processor is lower than VDSL2 due to the fewer DSL lines.
We should expect the first generation of G.fast to consume more power than VDSL2 silicon
Chip developments
The G.fast analogue silicon requires much faster analogue-to-digital and digital-to-analogue converters due to the broader spectrum used, while the G.fast line drivers use a lower transmit power due to the shorter reach requirements. "We should expect the first generation of G.fast to consume more power than VDSL2 silicon," says Spruyt.
Stefaan Vanhastel
The main functional blocks for G.fast and VDSL2 include the baseband digital signal processor, vectoring, the analogue front end, and the line driver. The degree to which they are integrated in silicon - whether one chip or four if the home-gateway functions are included - depends on where they are used.
"The chipsets will be designed differently for the different segments where they are used," says Hiremath. For example, the G.fast modem could be implemented as a single chip that includes the baseband, home gateway, and even the line driver due to the short lengths involved, he says.
Moreover, while the G.fast standard does not require backward compatibility with VDSL2, there is nothing stopping chipmakers from supporting both. The same was true with VDSL2 yet the resulting chipsets also supported ADSL2.
Ikanos has yet to unveil its G.fast silicon but it has announced its Neos development platform for customers to test and trial the technology. Hiremath says its G.fast design is based on the Neos architecture and that it expects first samples later this year.
Start-up Sckipio has also to detail its G.fast silicon design but says it will provide more information in the coming months. G.fast has system requirements that are difficult to meet, says Baum: "The challenge is not to show the technology working but to meet the standard's boundary requirements with a small, efficient design that provides 1 Gigabit." By boundary conditions Baum is referring to performance requirements that the modem needs to achieve, such as certain speeds and distances with a given packet loss, for example.
Sckipio already has first samples of its silicon. The company ported the RTL design of its silicon onto a Cadence Palladium system - a box with hundreds of FPGAs that allows the complete hardware design to be built. The company also has DSL models - bundles of twisted copper pairs measured at greater than 200MHz - to test the design's performance. "We use those models to see the expected performance running our protocol over those wires," says Baum.
Alcatel-Lucent has developed its own vectoring know-how for VDSL2 and has now added G.fast. "Having our own vectoring technology means that we have our own vectoring processing," says Alcatel-Lucent's Vanhastel.
Alcatel-Lucent has conducted G.fast trials with A1 Telecom Austria. "The good news is that we have been able to show that with vectoring, you can get really close to single-user capacity; the same capacity you have if there is only a single user active on the line," says Vanhastel. In the trial using over 100m of cable, G.fast achieved 60Mbps due to crosstalk. "Activating G.fast vectoring it rose to 500Mbps - almost a factor of 10," he says.
Much work remains before G.fast is deployed in the network, says Alcatel-Lucent. The International Telecommunication Union's G.9701 G.fast physical layer document is 300 pages long and while consent has been achieved, approving the standard is expected to take the rest of the year. Interoperability, test, functionality and performance specifications are still to be written by the Broadband Forum and then there are regulatory issues to be overcome: G.fast's 106MHz spectrum overlaps with FM radio, for example.
Sckipio is more upbeat about timescales, believing operators will start deployments in 2015 due to competition including the cable operators. The start-up says it has multiple field trials of its G.fast silicon this year.
Meanwhile, extending the spectrum to 212MHz is the next logical step in the development of G.fast. "Bonding is another concept that could be applied," says Spruyt.
There is life in the plain old telephone service yet.
This is an extended version of an article that first appeared in New Electronics, click here.
VDSL2 vectoring explained
Several system vendors including Adtran, Alcatel-Lucent and ZTE have announced vectoring technology that boosts the performance of very-high-bit-rate digital subscriber line (VDSL2) broadband access technology. Vectoring is used to counter crosstalk - signal leakage between the telephony twisted wire pairs that curtails VDSL2's bit rate performance – as is now explained.
Technology briefing
There is a large uncertainty in the resulting VDSL2 bit rate for a given loop length. With vectoring this uncertainty is almost removed
Paul Spruyt, Alcatel-Lucent
Two key characteristics of the local loop limit the performance of digital subscriber line (DSL) technology: signal attenuation and crosstalk.
Attenuation is due to the limited spectrum of the telephone twisted pair, designed for low frequency voice calls not high-speed data transmission. Analogue telephony uses only 4kHz of spectrum, whereas ADSL uses 1.1MHz and ADSL2+ 2.2MHz. The even higher speed VDSL2 has several flavours: 8b is 8.5MHz, 17a is 17.6MHz while 30a spans 30MHz.
The higher frequencies induce greater attenuation and hence the wider the spectrum, the shorter the copper loop length over which data can be sent. This is why higher speed VDSL2 technology requires the central office or, more commonly, the cabinet to be closer to the user, up to 2.5km away - although in most cases VDSL2 is deployed on loops shorter than 1.5km.
The second effect, crosstalk, describes the leakage of the signal in a copper pair into neighbouring pairs. “All my neighbours get a little bit of the signal sent on my pair, and vice versa: the signal I receive is not only the useful signal transmitted on my pair but also noise, the contributed components from all my active VDSL2 neighbours,” says Paul Spruyt, xDSL technology strategist at Alcatel-Lucent.
Typical a cable bundle comprises several tens to several hundred copper pairs. The signal-to-noise ratio on each pair dictates the overall achievable data rate to the user and on short loops it is the crosstalk that is the main noise culprit.
Vectoring boosts VDSL2 data rates to some 100 megabits-per-second (Mbps) downstream and 40Mbps upstream over 400m. This compares to 50Mbps and 20Mbps, respectively, without vectoring. There is a large uncertainty in the resulting VDSL2 bit rate for a given loop length. "With vectoring this uncertainty is almost removed," says Spruyt.
Vectoring
The term vectoring refers to the digital signal processing (DSP) computations involved to cancel the crosstalk. The computation involves multiplying pre-coder matrices with Nx1 data sets – or vectors – representing the transmit signals.
The crosstalk coupling into each VDSL2 line is measured and used to generate an anti-noise signal in the DSLAM to null the crosstalk on each line.
To calculate the crosstalk coupling between the pairs in the cable bundle, use is made of the ‘sync’ symbol that is sent after every 256 data symbols, equating to a sync symbol every 64ms or about 16 a second.
Each sync symbol is modulated with one bit of a pilot sequence. The length of the pilot sequence is dependent on the number of VDSL2 lines in the vectoring group. In a system with 192 VDSL2 lines, 256-bit-long pilot sequences are used (the next highest power of two).
Moreover, each twisted pair is assigned a unique pilot sequence, with the pilots usually chosen such that they are mutually orthogonal. “If you take two orthogonal pilots sequences and multiply them bit-wise, and you take the average, you always find zero,” says Spruyt. "This characteristic speeds up and simplifies the crosstalk estimation.”
A user's DSL modem expects to see the modulated sync symbol, but in reality sees a modulated sync symbol distorted with crosstalk from the modulated sync symbols transmitted on the neighbouring lines. The modem measures the error – the crosstalk – and sends it back to the DSLAM. The DSLAM correlates the received error values on the ‘victim’ line with the pilot sequences transmitted on all other ‘disturber’ lines. By doing this, the DSLAM gets a measure of the crosstalk coupling for every disturber – victim pair.
The final step is the generation of anti-noise within the DSLAM.
This anti-noise is injected into the victim line on top of the transmit signal such that it cancels the crosstalk signal picked up over the telephone pair. This process is repeated for each line.
Source: Alcatel-Lucent
VDSL2 uses discrete multi-tone (DMT) modulation where each DMT symbol consists of 4096 tones, split between the upstream (from the DSL modem to the DSLAM) and the downstream (to the user) transmissions. All tones are processed independently in the frequency domain. The resulting frequency domain signal including the anti-noise is converted back to the time domain using an inverse fast Fourier transform.
The above describes the crosstalk pre-compensation or pre-coding in the downstream direction: anti-noise signals are generated and injected in the DSLAM prior to transmission of the signal on the line.
For the upstream, the inverse occurs: the DSLAM generates and adds the anti-noise after reception of the signal distorted with crosstalk. This technique is known as post-compensation or post-coding. In this case the DSL modem sends the pilot modulated sync symbols and the DSLAM measures the error signal and performs the correlations and anti-noise calculations.
Challenges
One key challenge is the amount of computations to be performed in real-time. For a fully-vectored 200-line VDSL2 system, some 2,600 billion multiply-accumulates per second - 2.6TMAC/s - need to be calculated. A system of 400 lines would require four times as much processing power, about 10TMAC/s.
Alcatel-Lucent’s first-generation vectoring system that was released end 2011 could process 192 lines. At the recent Broadband World Forum show in October, Alcatel-Lucent unveiled its second-generation system that doubles the capacity to 384 lines.
For larger cable bundles, the crosstalk contributions from certain more distant disturbers to a victim line are negligible. Also, for large vectoring systems, pairs typically do not stay together in the same cable but get split over multiple smaller cables that do not interfere with each other. “There is a possibility to reduce complexity by sparse matrix computations rather than a full matrix,” says Spruyt, but for smaller systems full matrix computation is preferred as the disturbers can’t be ignored.
There are other challenges.
There is a large amount of data to be transferred within the DSLAM associated with the vectoring. According to Alcatel-Lucent, a 48-port VDSL2 card can generate up to 20 Gigabit-per-second (Gbps) of vectoring data.
There is also the need for strict synchronization – for vectoring to work the DMT symbols of all lines need to be aligned within about 1 microsecond. As such, the clock needs to be distributed with great care across the DSLAM.
Adding or removing a VDSL2 line also must not affect active lines which requires that crosstalk is estimated and cancelled before any damage is done. The same applies when switching off a VDSL2 modem which may affect the terminating impedance of a twisted pair and modify the crosstalk coupling. Hence the crosstalk needs to be monitored in real-time.
Zero touch
A further challenge that operators face when upgrading to vectoring is that not all the users' VDSL2 modems may support vectoring. This means that crosstalk from such lines can’t be cancelled which significantly reduces the vectoring benefits for the users with vectoring DSL modems on the same cable.
To tackle this, certain legacy VDSL2 modems can be software upgraded to support vectoring. Others, that can't be upgraded to vectoring, can be software upgraded to a ‘vector friendly’ mode. Crosstalk from such a vector friendly line into neighbouring vectored lines can be cancelled, but the ‘friendly’ line itself does not benefit from the vectoring gain.
Upgrading the modem firmware is also a considerable undertaking for the telecom operators especially when it involves tens or hundreds of thousands of modems.
Moreover, not all the CPEs can be upgraded to friendly mode. To this aim, Alcatel Lucent has developed a 'zero-touch' approach that allows cancelling the crosstalk from legacy VDSL2 lines into a vectored lines without CPE upgrade. “This significantly facilitates and speeds up the roll-out of vectoring” says Spruyt
Further reading:
Boosting VDSL2 Bit Rates with Vectoring
DSL: Will phantom channels become real deployments
ICT could reduce global carbon emissions by 15%
Part 1: Standards and best practices
Keith Dickerson is chair of the International Telecommunication Union's (ITU) working party on information and communications technology (ICT) and climate change.
In a Q&A with Gazettabyte, he discusses how ICT can help reduce emissions in other industries, where the power hot spots are in the network and what the ITU is doing.
"If you benchmark base stations across different countries and different operators, there is a 5:1 difference in their energy consumption"
Keith Dickerson
Q. Why is the ITU addressing power consumption reduction and will its involvement lead to standards?
KD: We are producing standards and best practices. The reason we are involved is simple: ICT – all IT and telecoms equipment - is generating 2% of [carbon] emissions worldwide. But traffic is doubling every two years and the energy consumption of data centres is doubling every five years. If we don’t watch out we will be part of the problem. We want to reduce emissions in the ICT sector and in other sectors. We can reduce emissions in other sectors by 5x or 6x what we emit in our own sector.
Just to understand that figure, you believe ICT can cut emissions in other industries by a factor of six?
KD: We could reduce emissions overall by 15% worldwide. Reducing things like travel and storage of goods and by increasing recycling. All these measures in conjunction, enabled by ICT, could reduce overall emissions by 15%. These sectors include travel, the forestry sector and waste management. The energy sector is huge and we can reduce emissions here by up to 30% using smarter grids.
What are the trends regarding ICT?
KD: ICT accounts for 2% at the moment, maybe 2.5% if you include TV, but it is growing very fast. By 2020 it could be 6% of worldwide emissions if we don’t do something. And you can see why: Broadband access rates are doubling every two years, and although the power-per-bit is coming down, overall power [consumed] is rising.
Where are the hot spots in the network?
The areas where energy consumption is going up most greatly are at the ends of the network. They are in the home equipment and in data centres. Within the network it is still going up, but it is under control and there are clear ways of reducing it.
For example all operators are moving to a next-generation network (NGN) – BT is doing this with its 21CN - and this alone leads to a power reduction. It leads to a significant reduction in switching centres, by a factor of ten. And you can collapse different networks into a single IP network, reducing the energy consumption [associated with running multiple networks]. The equipment in the NGN doesn’t need as much cooling or air conditioning. The use of more advanced access technology such as VDSL2 and PON will by itself lead to a reduction in power-per-bit.
The EU has a broadband code of conduct which sets targets in reducing energy consumption in the access network and that leads to technologies such as standby modes. My home hub, if I don’t use it for awhile, switches to a low-power mode.
The ITU is looking at how to apply these low–power modes to VDSL2. There has also been a very recent proposal to reduce the power levels in PONs. There has been a contribution from the Chinese for a deep-sleep mode for XG-PON. The ITU-T Study Group 13 on future networks is also looking at such techniques, shutting down part of the core network when traffic levels are low such as at night.
What about mobile networks?
If you benchmark them across different countries and different operators there is a 5:1 difference in the energy consumption of base stations. They are running the same standard but their energy efficiency is somewhat different; they have been made at different times and by different vendors.
In a base station, some half of the power is lost in the [signal] coupling to the antenna. If you can make amplifiers more efficient and reduce the amount of cooling and air-condition required by the base station, you can reduce energy consumption by 70 or 80%. If all operators and all counties used best practices here, energy consumption in the mobile network could be reduced by 50% to 70%.
If you could get overall power consumption of a base station down to 100W, you could power it from renewable energy. That would make a huge difference; it could work without having to worry about the reliability of the electricity grid which in India and Africa is a tricky problem. And at the moment the price of diesel fuel [to power standby generators] is going through the roof.
I visited Huawei recently and they have examples of 100W base stations powered by renewable energy, making them independent of the electricity network. At the moment a base station consume more like 1000W and overall they consume over half the overall power used by a mobile operator. At 100W, that wouldn’t be the case.
Other power saving activities in mobile include sharing networks among operators such as Orange and T-Mobile in the UK. And BT has signed a contract with four out of the five UK mobile operators to provide their backhaul and core networks in the future.
What is the ITU doing with regard energy saving schemes?
The ITU set up the working party on ICT and climate change less than two years ago. We have work in three different areas.
One is increasing energy efficiencies in ICT which we are doing through the widespread introduction of best practices. We are relying on the EC to set targets. The ITU, because it has 193 countries involved, finds it very difficult to agree targets. So we issue best practices which show how targets can be met. This covers data centres, broadband and core networks.
Another of our areas is agreeing a common methodology for how to measure the impact of ICT on carbon emissions. We have been working on this for 18 months and the first recommendations should be consented this summer. Overall this work will be completed in the next two years. This will enable you to measure the emissions of ICT by country, or sector, or an individual product or service, or within a company. If companies don’t meet their targets in future they will be fined so it is very important companies are measured in the same way.
A third area of our activities are things like recycling. We have produced a standard for a universal charger for mobile phones. You won’t have to buy a new charger each time you buy a new phone. At the moment thousands of tonnes of chargers go to landfill [waste sites] every year. The standard introduced by the ITU last year only covers 25% of handsets. The revised standard will raise that to 80%.
At the last meeting the Chinese also proposed a universal battery – or a range of batteries. This would means you don’t have to throw away your old battery each time you buy a new mobile. It is all about reducing the amount of equipment that goes into landfill.
We are also doing some other activities. Most telecom equipment use a 50V power supply. We are taking that up to 400V. So a standard power supply for a data centre or a switch would be at 400V. This would mean you would lose a lot less power in the wiring as you would be operating at a lower current - power losses vary according to the square of the current.
These ITU activities coupled with operators moving to new architectures and adopting new technologies will all help yet traffic is doubling every two years. What will be the overall effect?
It all depends on the targets that are set. The EU is putting in more and more severe targets. If companies have to pay a fine if they don’t meet them, they will introduce new technologies more quickly. Companies won’t pay the extra investment unless they have to, I’m afraid, especially during this difficult economic period.
Every year the EC revises the code of conduct on broadband and sets stiffer targets. They are driving the introduction of new technology into the industry, and everyone wants to sign up to show that they are using best practices.
What the ITU is doing is providing the best practices and the standards to help them do that. The rate at which they act will depend on how fast those targets are reduced.
Keith Dickerson is a director at Climate Associates.
Part 2 Operators' power efficiency strategies
DSL: Will phantom channels become real deployments?
Alcatel-Lucent is promoting its DSL Phantom Mode technology as a complement to fibre-to-the-x (FTTx) technology. Operators can use the technology to continue to extend services offerings to existing DSL subscribers as they roll out FTTx over the next decade or more.
But one analyst believes the technology could take years to commercialise and questions whether the announcement is not sending a wrong message to the industry by providing an alternative to fibre.
“The investment required to upgrade DSL is quite small”
Stefaan Vanhastel, Alcatel-Lucent
What has been achieved?
The 300Mbps data rate is achieved using two copper wire pairs between the access equipment and a DSL modem although three DSL ports are required at each end. The rate drops to 100Mbps when the reach is extended to 1km. In comparison very high speed Digital Subscriber Line 2’s (VDSL2) data rate over a single line ranges from 20 to 40Mbps over 1km.
None of the three techniques that Alcatel-Lucent uses – bonding, vectoring and the phantom mode that creates an extra virtual channel alongside the two bonded pairs - is new. What the company claims is that it is the first to combine all three for DSL.
In March Ericsson announced it had achieved 500Mbps over 500m but it used six bonded pairs and vectoring only.
Why is the Phantom Mode important?
The significance of the announcement, according to Alcatel-Lucent, is that operators can continue to offer existing DSL customers new bandwidth-intensive services as they roll out FTTx.
“Rolling out FTTx will take a significant amount of time,” says Stefaan Vanhastel, director of product marketing, wireline networks at Alcatel-Lucent. “Operators are looking to reuse their copper infrastructure in the short-to-medium term - the next 5 to 10 years.”
An operator must have a central office or cabinet equipment 1km or less from the user’s residence as well as having two wire pairs per building or residence. “In many countries two pairs are available,” says Vanhastel.
However, one analyst questions the development and promotion of such copper-enhancing technology.
“I think Alcatel is being disingenuous when they say "fiber will take long to implement, this is an intermediary solution’,” says the analyst, who asked not to be named. “They know full well that customers would see this as a way to hold back on deploying fibre.
“Ultimately to me this is schizophrenia at work. Alcatel-Lucent wants to be all things to all service providers and may be sending the wrong message to the market that they need not invest to sustain the bandwidth demand growth, which is suicidal both for service providers and for Alcatel-Lucent in the long run.”
Alcatel-Lucent does believe operators will invest in DSL alongside FTTx.
“The investment required to upgrade DSL is quite small,” says Vanhastel. “Even with two ports it is a bargain; you get the investment back in one or two months.”
Even operators more advanced in their FTTx deployments will want to offer new higher bandwidth services such as high-definition TV to all their customers.
“What are you going to do? Offer your services to just 50% of your customers?” says Vanhastel “They [the remaining customers] will go elsewhere.”
Method used
The Bell Labs research arm of Alcatel-Lucent has used three techniques to enhance DSL’s speed and reach performance.
- Bonding: The combination of copper line pairs to boost the number of channels – in this case two are bonded - and hence the data rate between access equipment and the DSL modem.
- Vectoring: Noise cancellation techniques using digital signal processing to improve the overall signal-to-noise performance. “It involves measuring the noise on all the lines and generating anti-phase – the inverse signal – such that the two cancel out,” says Vanhastel.
- Phantom mode: The phantom mode technology uses two physical wires to create a third virtual one. The technology was first proposed in the 1880s as a way to add an extra virtual telephone line.
Two physical pairs and the third phantom one. Source: Alcatel-Lucent
Using the phantom mode, only two wire pairs are needed to connect the end equipment. The information on the third “virtual” line is shared over the two physical channels. Using analogue electronics, the data on the third channel is processed and recovered. “We add and subtract through the use of a bunch of transformers,” says Vanhastel. Where the circuitry is placed, whether in the DSLAM access equipment or elsewhere, is to be decided.
To create the virtual wire, a modem supporting three-pair bonding is required. In addition the chipset in the DSL modem must have sufficient processing performance to execute vectoring on three channels. That's because adding the phantom mode degrades the performance of all the channels due to crosstalk. The crosstalk is removed between the channels using vectoring.
What next?
The technology needs to be brought to market. “At the earliest it will be 2012,” says Vanhastel.
But the analyst points out that the technology is lab tested: “Between test labs and implementation, count a significant number of years.”
The concept could even be extended using more wire pairs. The relationship is (N-1) phantom channels for N wire pairs i.e. 1 virtual channel with two pairs, 2 with 3 pairs etc.
Alcatel-Lucent says it has already completed two VDSL2 bonding trials in Asia Pacific, while three operators are undertaking VDSL2 vectoring tests in their labs and will move to testing in the field using a single line this year.
“Bonding is here today, vectoring will be 2011 and the phantom mode will be after that,” says Vanhastel.