Technology White Paper

FTTxJFMabanglo, ECE

Optical Fibers Pave

the Way to Faster Broadband Access

The broadband market is already global in scale, and it is expected that it will explode in the near future. Fiber access networks will provide the technological foundation for this development. As a leading supplier of broadband access networks, Alcatel has been driving forward the standardization and development of passive optical access technologies. These networks, which support the next generation of Ethernet/IP based communication, can provide video, voice and high speed data services to users at a competitive cost. While available solutions are already being deployed, new generation technologies will provide access to more subscribers at higher speeds and over longer fiber lengths.

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OPTICAL FIBERS PAVE THE WAY TO FASTER BROADBAND ACCESS Emerging services and increasing competition are forcing carriers to deploy optical fibers in the access network, ulti- mately serving each subscriber over a dedicated fiber link.

T here is an increasing demand for high bandwidth connec-tions in markets around the world. However, upgrading the bandwidth of traditional technologies, like Digital Sub- scriber Line (DSL), coaxial cable and wireless connections, is becoming ever more challenging as these technologies get

closer to their practical capacity lim- its. Competition between network

meters (Very high speed Digital Subscriber Line; VDSL). Finally, fibers may have a role in backhauling for mobile and fixed wire- less networks.

To optimize fiber use, point-to-multipoint networks are gen- erally used with a few fibers running from the central office to

operators is compelling them to differ- entiate their offers by providing more

Figure 1: Basic fiber access architectures

and better services to their customers, which in turn requires the latest future-proof technologies.

The delivery of triple-play services

(data, voice and video) at competitive prices is essential in this market envi-

PON

passive star

OLTONTs

Optical Ethernet

active star

Remote

Optical Ethernet

point-to-point

ronment. Current fiber access deploy- ments in Japan and the USA offer sub- scribers broadband access at prices in the range of

Central Office

Central Office

Node

Central Office

two to three times DSL service prices, depending on the bitrate and market. Another factor is politics, which is play- ing an important role in steering broad- band deployment. Favorable regula- tions, like the decision of the US Fed- eral Communications Commission

(FCC) not to require unbundling of fiber lines in the access network, sound national broadband policies and the launching of national programs or funding of broadband deployments, are helping in this respect.

Marketing is also an important factor; novel communication technologies are increasingly viewed as a means of increasing the attractiveness and accel- erating the economic development of municipalities, regions and even countries.

Increasing the bandwidth to users means bringing fibers closer to the subscribers. In addition to the ultimate solution of Fiber to the Home (FTTH) sometimes also called Fiber to the Premises (FTTP) or Fiber to the User (FTTU) there is considerable potential for early cost-effective broad- band access deployments using hybrid solutions that combine fiber for the feeder section (Fiber to the Node, FTTN; an active node in the neighborhood) and copper for the final tens of

nodes in the neighborhood from where multiple drop fibers pro- vide the connections to users or to VDSL nodes. In a Passive Optical Network (PON), as shown in Figure 1, signals from the Optical Line Termination (OLT) at the central office are opti- cally broadcast via the feeder fibers into the drop fibers to the Optical Network Termination (ONT). Upstream, Time Division Multiple Access (TDMA) based protocols ensure collision-free transmission from the ONT to the OLT. Alternatively, the active star configuration employs Ethernet switches at the remote nodes to distribute and aggregate the traffic to and from users. Here, the layer 2 protocol is based on Ethernet. As a third option, in point-to-point networks single fiber links connect each subscriber directly to the

central office.

Fiber to the x Today Existing FTTx solutions One existing solution is the

Broadband PON (BPON), an Asynchronous transfer mode PON (APON) enhanced by an optical overlay channel for video services. This widely deployed and mature technology is currently supported by the Alcatel 7340 FTTU.

OPTICAL FIBERS PAVE THE WAY TO FASTER BROADBAND ACCESS

Table 1: PON comparison

Data rate (Mbit/s)

Line coding

Minimum split (on TC layer) Maximum split (on TC layer) Maximum logical reach supported by TC layer

Layer 2 protocols

Standards documents

TDM support

Typical downstream capacity

(for IP data throughput)

Typical upstream capacity

(for IP data throughput)

OAM

Downstream security

ITU-T BPON

down: 1244, 622, 155

up: 622, 155

NRZ (+ scrambling)

32

64

20 km

ATM

ITU-T G.983 series

TDM over ATM

520 Mbit/s (for 622 Mbit/s line rate)

500 Mbit/s (for 622 Mbit/s line rate)

PLOAM + OMCI

Churning or AES

ITU-T GPON

down: 2488, 1244

up: 2488, 1244, 622, 155

NRZ (+ scrambling)

64

128

60 km (with 20 km differential between ONTs) Ethernet, TDM over GEM (GPON Encapsulation Mode), ATM

ITU-T G.984 series

native TDM, TDM over ATM, TDM over Packet

1170 Mbit/s (for 1.244 Gbit/s line rate)

1160 Mbit/s (for 1.244 Gbit/s line rate)

PLOAM + OMCI

AES (counter mode)

IEEE EPON down: 1250 up: 1250

8b/10b

16

not specified

10 km, 20 km

Ethernet

IEEE 802.3ah

TDM over Packet

910 Mbit/s

760-860 Mbit/s

Ethernet OAM

(+ optional SNMP)

not defined

AES: Advanced Encr yption Standard OAM: Operations, Administration and Maintenance

OMCI: ONT Management and Control Interface

PLOAM: Physical Layer OAM

SNMP: Simple Network Management Protocol

TC: Transmission Convergence

It carries analog and interactive digital TV together with voice and data services. Today BPONs are typically deployed with 622 Mbit/s in the downstream direction and 155 Mbit/s upstream, giving each user a downstream capacity of 20 to

30 Mbit/s. The International Telecommunication Union Telecommunications (ITU-T) BPON standard, with its higher- layer functionality, including security, management, flexible configuration and Quality of Service (QoS), ensures straight-

it offers no bitrate flexibility on the physical layer and the band- width efficiency is low because of inefficient line coding and large overhead. However, simple requirements regarding the physical components and service features favored the early availability of commercial EPON components.

Gigabit PON (GPON) was standardized by ITU-T in June

2004. The GPON standard includes a variety of line rates up to 2.488 Gbit/s,

forward interoperability. As a result of its maturity and wide deployment, BPON costs have dramatically decreased, mak- ing it an attractive choice for service

providers contemplating deploying a

symmetric and asymmetric. Together with much reduced coding loss and shorter guard times (i.e. time slots between adjacent optical packets from

Guard time

In Time Division

Multiple Access

(TDMA) networks,

Media Converter (MC) Optical point-to- point transmission technology for access networks.

fiber access solution.

Another is Ethernet point-to-point fiber, including the Japanese media converter and IEEE 802.3ah (Ethernet in the First Mile; EFM) optical point- to-point technology. Media converter technology, which was standardized in

2002 by the Telecommunications Tech- nology Committee (TTC) as TS-1000,

different ONTs), the net bandwidth of the GPON is much higher than in EPON. Besides transporting native Ethernet data, the GPON also effi- ciently transports multimode services

(TDM, voice and ATM). Today, GPON deployment is hampered by the late availability of the basic component technology. However, it is set to catch

like PONs

(upstream direction), optical packets from different subscri- bers are sent to the central node in such way that they arrive sequentially

has been widely deployed in Japan. In contrast, EFM only recently released optical point-to-point physical layer speci- fications for access networks (symmetrical 100 Mbit/s and

1 Gbit/s).

Next generation FTTx solutions

Ethernet PON (EPON), which was ratified in September

2004 as part of IEEE 802.3ah, supports symmetric Gigabit Eth- ernet and is compatible with existing Ethernet networks. (In Japan, the term EPON refers to a proprietary 100 Mbit/s PON, whereas the IEEE EPON is called GE-PON.) One of the main concerns with EPON is that the standard does not specify all the features needed to transport carrier-grade services, so pro- prietary solutions are needed to make it compatible. Moreover,

up with the early EPON deployments.

Table 1 summarizes the main char- acteristics of these PONs.

Worldwide market

North America

Two