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| GPON FTTH技术与市场 |
| 2008年5月22日 10:55
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North American carriers such as Verizon, SBC (now AT&T) and others, are looking to GPON to advance their FTTH rollout efforts. As reported in industry press accounts, senior executives at Regional Bell Operating Companies (RBOCs) have already verbalized their companies’ commitment to 2.5/1.25 Gbps GPON deployments beginning as soon as 2006. This GPON rollout will make GPON the preferred PON technology in North America within the next two years.
3 FTTH Broadband Access Deployment Is Accelerating
Either way, GE-PON and GPON technologies seem to be the clear winners for future
deployments of FTTH broadband access networks as carriers world wide are pursuing the transition to gigabit networking capacity offered by FTTH. With the market for high-speed broadband access continuing to accelerate, the future for gigabit PON is bright. Strategy Analytics, Inc., a telecom market analyst firm predicts that a combination of falling prices and multiservice packages that combine IP TV, telephony and high-speed Internet service will increase the penetration of broadband access during the next five years. It predicts nearly 78 million U.S. consumers will have broadband access by 2010 with half being served by cable operators and 43 percent by telecommunication service providers. This portion will be split between DSL and FTTH access technologies.
Already, in Japan the transition from DSL to FTTH has begun. For the first time, in the first quarter of 2005, the number of new FTTH subscribers was greater than the number of new DSL subscribers according to the Japanese Ministry of Internal Affairs and Communications. This significant milestone has been a wake-up call to the worldwide industry that FTTH is now capable of deployment at prices that appeal to consumers. This in turn is spurring more interest in FTTH and inspiring new services that can profitably offered to consumers.
At present, the appeal of “Triple Play” services combining video, VoIP, and high-speed Internet access is enough to drive carriers to pursue the deployment of FTTH in the broadband access network. According to Michael Howard, CEO of market watcher Infonetics Research, GPON’s 2.5 Gbps service deployments will accelerate in 2006 because of the technology’s ability to support the killer application of high-definition IPTV as well as simultaneously delivering data and voice services to consumers. According to Infonetics, North America accounted for 20 percent of worldwide PON revenue with that number expected to rise to 43 percent by 2008.
4 How PON Technology Works
There are two important facets of high-speed PON networks – support of gigabit and above line rates and the choice of protocols for data payloads through the access network equipment.
Older access technologies including DSL, cable and BPON FTTH, have used a low-cost CPU centric approach to controlling the data flow through access network equipment. An embedded 8- or 16-bit processor in the access interface device controlled the device and managed the data flow. This provides a low-cost means of providing access data path and control functions in the access system. However, this processor-centric approach fails at speeds of a gigabit/second and above. An embedded processor, no matter how fast just can not keep up with the speed of the data stream.Therefore, new architectural approaches must be deployed.
PMC-Sierra employs its GigaPASS™ architecture to connect a set of function-specific hardware processing engines in a wire-speed architecture. This approach enables an entire packet stream to be processed and transported with no delays through the gigabit PON interface.
The GigaPASS approach encompasses three technology platforms, the PON network interface and processing, IP and Ethernet packet processing and an SoC architecture that supports a 32-bit RISC processor with Linux and VxWorks operating systems, middleware, and application specific firmware. This architecture is capable of supporting both GE-PON and GPON data rates ranging from 1 to 2.5 Gbps at wire speed and provides a flexible, programmable and upgradeable device architecture well suited for future-proofing the access network.
Figure 2 The GigaPASS™ Architecture Provides Wire Speed Access at Gbps Speeds
A critical aspect of the GigaPASS architecture is that the data path is separate from the control path processor system. The media interface, queuing, packet processing, classification, encryption/decryption and other data payload processing is done in the wire-speed channel passing data payloads through to the Ethernet media interface on the customer side and the PON network on the central office side.
PON networking is a full duplex, point to multipoint networking technology that uses inexpensive optical splitters to divide a single fiber coming from the backbone of the enterprise or metro network into separate strands feeding individual subscribers in the access network. PONs are “passive” because other than at the central office (CO) and the subscriber customer premise equipment (CPE), there are no active electronics within the access network. This approach greatly simplifies network operation, maintenance and cost.
Figure 3 PON Network Splits Single Fiber Link Into Individual Links to Subscribers
The key PON interface points are in the central office equipment, called the OLT for optical line terminal, and the CPE, called ONU for optical network unit (for GE-PON) and ONT for optical network terminal (for GPON). Regardless of nomenclature, the important difference between OLT and ONT devices is their purpose. OLT devices support management functions and manage up to 128 downstream links. In practice, it is common for only 8 to 32 ports to be linked to a single OLT in the central office. On the other hand the ONT (or ONU) devices are in the CPE and have to support only their own link to the central office. Consequently, the ONT/ONU devices are much less expensive while the OLTs tend to be more capable and therefore more expensive.
Figure 4 The FTTH Access Network – OLTs In The Central Office, ONUs in CPEs
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