May 1, 2008

Broadband Access Networks: PON Life

Roy Rubenstein - Total Telecom Magazine

As operators’ network capacity starts to run out they are turning to faster Gigabit PON standards, but regulation could put things on hold.

Optical broadband access is entering a decisive two-year period. By 2010, regulation regarding fibre unbundling, a particular concern in Europe, will be resolved; and next-generation 10 Gigabit passive optical network (PON) standards will be completed.

In fact, deployments of 10 Gigabit PON may have begun before then. Moreover, cable operators, which until now have shunned PON as a telco technology, will have resolved how best to upgrade their network infrastructure using fibre.
 

According to Ovum RHK, 1.6 million FTTx subscribers were added globally in the last quarter of 2007, up 11% from the previous quarter. Asia Pacific accounts for 84% of all global FTTx installations, North America 14%, while Europe has a meagre 2%. One factor accounting for Europe’s low standing is the current regulatory uncertainty, but this is expected to become clearer in July when the EC details its recommendations (see box p.40).

As for technologies, Asia Pacific has settled on the IEEE Ethernet PON (EPON) standard, while North American and European operators favour Gigabit PON. GPON is an International Telecommunication Union (ITU) standard and backed by the Full Service Access Network (FSAN) Group comprising 19 operators and 40 vendors.

EPON is the more mature standard. Only recently has GPON reached the point where it is ready for deployment.
Verizon started GPON deployments with its fibre-based triple-play service FiOS. By the end of 2007 it had 1.5 million FTTx subscribers, all connected using Broadband PON (BPON), the predecessor to GPON, and had passed 9 million homes, half the FiOS rollout target. With GPON, Verizon can now offer 2.5 gigabits per second downstream—four times that of BPON—and 1.25 Gbps upstream.

Europe’s largest incumbents—BT, France Telecom, Deutsche Telekom, Telecom Italia and Telefonica—have all backed GPON either for fibre-to-the-node or fibre-to-the-home deployments.

Saverio Orlando, head of network technical planning at Telecom Italia, says the company’s NGN2 project “will cover more than 2 million homes by the end of 2010, starting in Milan”. Telecom Italia will use GPON for its fibre-to-the-building and FTTH deployments, while for its fibre-to-the-cabinet, Ethernet point-to-point will be used.

“GPON provides TI with a cost-effective solution when compared to Ethernet point-to-point,” says Marco Burzio, Telecom Italia’s head of network technical planning for NGN2. “In addition, accurate capacity evaluations show full support to the evolution of ultra-broadband services thanks to the dynamic bandwidth allocation and quality-of-service support [of GPON].”

France Telecom, which is half way through its commercial pre-launch phase, announced it had 7,268 FTTx customers and had passed 146,000 connectable homes by the end of 2007.

Telenor is the latest European operator to adopt GPON. Last September it said it will deploy FTTx in some urban areas, and its fibre infrastructure deployments have now begun. GPON will be used in greenfield locations while FTTN/VDSL2 will deliver broadband access elsewhere.

“There is a lot of competition for fibre,” says Øyvind Arntzen, manager, optical networks technology, at Telenor, explaining the operator’s decision to deploy FTTx. “There are already 100,000 FTTx subscribers, some 5% to 10% of the total broadband access [in Norway].”

Telenor chose GPON over EPON because of its higher data rate and lower framing overhead. “It [GPON] has a better [payload] efficiency,” says Arntzen. “We did an evaluation of EPON and it is limited to 1 Gbps.” Telenor says it requires GPON’s higher bandwidth capacity for IPTV services.

But the IEEE is responding with a 10 Gigabit EPON standard, to be completed in September. Indeed, expected demand for 10 Gigabit EPON is already spurring chip companies to support the technology. For example, PMC-Sierra offers a development kit supporting the draft standard, while Teknovus says it will have sample chips late this year.

“By the end of 2008 vendors will have integrated the reference designs into their systems and 2009 will see extensive trials [with operators],” says Stephen Haas, director of product marketing at PMC-Sierra’s FTTH division. “2010 will then be the year of deployment.”

And Teresa Mastrangelo, principal analyst at market research firm broadbandtrends.com, says: “The IEEE has been much more aggressive in its move to 10G, whereas there is virtually no activity on 10G GPON.”

FSAN has been working on 10 Gigabit GPON for over 18 months, yet standardisation work has still to start. The lack of urgency is due to operators deeming that GPON’s current data rate is sufficient. Telenor, for example, expects GPON to meet its capacity requirements for the next five–10 years.

“One of the reasons the IEEE is more aggressive on 10G is that there is a perception that 1G EPON is running out of steam,” says Marcus Weldon, the CTO of Alcatel-Lucent’s fixed access division.

It is possible that there will be some harmonisation between the two PON standards at 10 Gigabit speeds. “Incumbents are not happy that there are two different standards,” says Jörg-Peter Elbers, principal engineer at ADVA Optical Networking. “There is some pressure from the incumbents for the ITU-T to adopt as much of the [IEEE] technology as possible [already developed for 10 Gigabit EPON.]”

The 10 Gigabit EPON standard supports two modes: 10 Gbps downstream and 1 Gbps upstream; and 10 Gigabit symmetrical. It uses an extra downstream wavelength at 1577nm to support the higher data rate. Defining an extra wavelength for the downstream means that a single PON optical line terminal (OLT) in the central office can serve a mix of 1 Gigabit and 10 Gigabit optical network terminals (ONTs) found at the PON’s home or building end points.

10 Gigabit GPON also has specified a new wavelength above 1570nm. Indeed, existing GPON ONTs have optical filters that ensure they can run undisturbed alongside next-generation PON deployments whatever they may be.

There are also two modes for 10 Gigabit GPON: a 10 Gbps downstream and 1.25 Gbps upstream; and an accumulated 10G downstream capacity comprising four existing 2.5-Gbps GPONs, each at a distinct wavelength. “Each GPON can be shared with eight rather than 32 users,” says Weldon. However, such an arrangement will require operators to change existing PONs’ outside plant optical splitters, a costly undertaking.

Japan, with its millions of EPON subscribers, is the obvious first market for 10 Gigabit EPON. “NTT is very serious and anxious for 10G EPON,” says Lynn Hutcheson, vice president, communication components, at Ovum RHK.

Telecom Italia says it is greatly interested in next-generation PON: 10G GPON and wavelength division multiplexing PON (WDM-PON), which provides an individual wavelength to a home or building.

One driver for 10G PON is high definition TV. “You can provide several hundred channels [including HDTV] taking up about 6 Gbps [of the PON’s downstream],” says Karl Kloppe, who heads a team tackling innovation projects within Nokia Siemens Networks’ broadband access business unit.

Another 10 Gigabit EPON driver, says Haas, is to enable operators to combine businesses, multi-dwelling units and single families all on the one PON.

But vendors and operators are already looking to extend 10 Gigabit PON.

Nokia Siemens Networks has demonstrated a long reach 10G PON as part of an EU project, and has shipped the prototype to several operators (Total Telecom, April 2007, p.32). Based on GPON, it extends the number of users to 512, with 10 Gbps downstream and 2.5 Gbps upstream, and a reach of 100km using an optical amplifier. Existing PONs typically span 20km. The extended reach promises operators the need for fewer central offices and hence cost savings.

If the optical access roadmap of telcos is becoming clearer, PON’s role as part of cable operators’ network upgrade plans is still unresolved. Cable operators—or so-called MSOs—in the US are upgrading to DOCSIS 3.0—the standard for data over hybrid fibre/coax cable—which will intensify in the second half of this year.

“This is a near term, defensive move,” says Mark Showalter, directing analyst, broadband networks, at Infonetics Research. “The challenge MSOs have is that their hybrid fibre/coax network, which has served them very well, will only take them so far.”

In March, the Society of Cable Telecommunications Engineers announced the launch of work to develop RF over Glass (RFoG) standards that will enable cable services and technologies such as DOCSIS to be delivered over fibre.

“RFoG allows much smaller network segmentation,” says Mark Cannata, director of product management at Tellabs. Instead of a node sharing bandwidth for data services between 500 homes, the same bandwidth can be shared between far fewer homes: 32 homes if RFoG over GPON/EPON were used. “RFoG provides MSOs with a more robust evolution such that they can begin to deploy PON,” he says.

DOCSIS 3.0 delivers up to 160 Mbps to a node. However, according to Victor Blake, a networking consultant working with MSOs, it is limited in the upstream direction to 40 Mbps.

But US cable operators are reluctant to admit to deploying PON because they have already committed to the expense of upgrading DOCSIS. “Everyone [all the MSOs] is doing PON; no one is talking about it,” says Blake.

Interest in PON is more evident among cable service providers outside the US. “We are speaking to a large cable provider in France [about GPON],” says Ron Levin, associate vice president, product marketing, at ECI Telecom’s network solution division. And ntl:Telewest Business confirmed that it is testing PON for business and consumer applications.

Blake has proposed a DOCSIS over EPON scheme. “It’s a DOCSIS OSS running on an off-the-shelf EPON,” he says. He says because DOCSIS over PON is not a standard, vendors have their own interpretations for the technology.
“The MSOs recognise they need to get fibred up,” says Showalter. “The question remains: which technology will win?”

Regulating fibre
Regulation remains a particular concern for European operators that are under pressure to provide altnets with access to their networks. “The European Commission takes an agnostic approach to access technologies and currently does not recognise a difference between fibre and copper,” says broadbandtrends.com’s Teresa Mastrangelo.

Unbundling is more complicated for PON because the fibre connection from the central office is shared between up to 128 users. “They [the Commission] are not comfortable as far as [PON’s] ability to be unbundled,” says Mastrangelo. And until the EC issues its initial recommendations in July, operators remain unsure as to whether they will incur additional costs to the already costly rollout of PON.

“Three of the five [large European incumbent] operators have pulled back largely due to the regulatory environment,” says Floyd Wagner, director of global product marketing at Motorola Access Networks.

“There is a concern and the incumbents are waiting for clarification,” adds ECI’s Levin. “Obviously if you are investing heavily in a fibre infrastructure, you want a return on investment.” But Ovum RHK’s Hutcheson believes the EC understands the importance of FTTx and will frame a policy that encourages deployments. “If the [EC] policy is right, all the operators in Europe are poised and ready to go,” he says.


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