MÍ OPINIÓN PERSONAL SOBRE EL PROYECTO

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One of the first decisions to be made when looking at a fiber network is determining if it is better to use active or passive fiber electronics. This is a key decision because it impacts the way the fiber network is constructed.

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The Active Optical Network (AON) dedicates a fiber from each user back to the electronics. This means each customer has a dedicated path to the electronics and does not share bandwidth directly with another customer in the neighborhood. An AON network has many more field lasers than a passive network since there is a 1 to 1 ratio between field lasers and customers.

In an AON network, everything is encoded as data between the electronics and the customer. This means all services must be digitized and delivered as an IP data stream to the user. The AON uses only 2 wavelengths on each fiber - one for transmittal of data to the users and one for transmittal of data from the users.

Since everything on an AON is data, the only possible video product is IPTV. IPTV delivers one channel at a time to each TV in the house as customers request it. This is a different model than normal broadcast TV and minimizes the number of channels that are being broadcast on the network. With traditional cable TV the system sends all of the channels all of the time to everybody. With IPTV, a customer must have a settop box for each TV that wants to receive its own channels.

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The current vendors making Active Optical Network equipment includes Enablence, Occam / Calix and PacketFront. Since PON equipment has won a much greater market share than AON equipment this part of the industry has been in a decline for a few years.

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The other choice is to build a Passive Optical Network (PON) which uses passive hardware to "split" the signals so that a single high-powered laser can be shared by up to 64 customers (more typically by 32 customers). This technology requires less fiber than an AON since many customers in a row or in an area share the same single fiber over which the information carried on the fiber is ‘split’ into 32 individual fiber drop paths for delivery to homes or businesses. In construction, one feeder fiber “feeds” a passive splitter that takes the information that is transmitted onto the feeder fiber and distributes across 32 or 64 individual fiber drops similar to

the way water in a single pipe can be sent to 32 individual locations by placing a 1-to-multiple pipe junction on a single feeder water pipe.

PON technology uses bandwidth on the fiber differently than the AON. The PON electronics divides up the optical wavelengths on the fiber to allow 1 wavelength to transmit data and voice to the users, another wavelength to receive data and voice from the users and a third optional wavelength to transmit RF video (like normal broadcast CATV video) to the users over one fiber strand. In this manner, the PON network can transport both analog signals and digital signals into the home.

A PON network has the ability to transmit video at the RF level and have it split into multiple fibers drops. This means that a PON does not need to require a settop box to deliver analog cable TV. A PON also uses existing wiring more easily since the video signal is delivered in the same way as the existing Cable TV video is delivered by the cable company. This gives easier access to existing telephone and cable wiring.

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The current vendors for PON equipment include Alcatel-Lucent, Adtran, Huawei, Calix and Enablence.

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Today passive optical networks use the GPON (Gigabit Passive Optical Network) technology. This technology uses Ethernet signaling for the customer delivery path. In a GPON system there is still the capability for two separate data streams – one for cable TV and a second for voice and data. The currently available GPON technology can deliver 2.4 Gbps of downstream data and 1.2 Gbps of upstream.

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A new GPON standard called 10-GPON will enable 10 Gbps downstream and 2.5 Gbps upstream to be shared among 32 customers. This technology is being designed to coexist with existing GPON technology which holds great potential for future upgrades in network capacity.

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There is now also a variation of GPON called WDM PON which uses a different color or laser light to each of the customers. This brings some of the best of an active network in to the PON network since this makes it possible to deliver a different amounts, and even dedicated amounts of bandwidth to each customer.

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FTTH technology is expected to continue to grow in available bandwidth as volume sales of the technology decrease laser costs. The limiting factor is the development of these cheaper lasers. Already in the lab are systems that will deliver a terabyte of download speed and such technology upgrades will be introduced as laser prices drop.

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Active Optical Network Advantages

• Does not require as much complex pre-planning and engineering. With AON there is a separate fiber to each customer, making it easier to engineer as you go.

• A single point of failure will affect fewer customers

• Can support multiple service providers. This allows for an open access system with

multiple CATV or data providers. A wholesale provider is given access to customers one fiber at a time.

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Disadvantages

• Uses More Fiber. Since there is a home run fiber to each customer, there is much

more fiber in the network. This also means fiber bundles are much larger in the field since they contain multiple fibers. This means a lot more splicing during construction or during repairs.

• Cannot support RF video broadcast TV (only IPTV). An AON system requires every

customer to get a settop box (a settop box for every separate TV, in fact), thus increasing capital costs.

• Shares data and CATV bandwidth in the same data stream. Today an AON system can

cost effectively deliver 1 Gigabit of data to each home. This is not a shared pipe with neighbors and each customer can get a dedicated 1 gigabit pipe. However, this one data stream must support CATV, data and voice together. Thus, if a customer is watching multiple HDTV sets, the amount of bandwidth left for data will be something less than a gigabit.

• Requires additional home wiring. Since the AON provides only one bandwidth (the

data stream), the video service (IPTV) always requires a high bandwidth data wire, such as category 5 or 6 wire to each TV location.

• Active field devices require backup power throughout the network. This means many

more locations in the network that need battery or generator backup to engineer for power failures.

• The CATV head-end is more expensive. An AON system must use IPTV and

therefore sends every signal out in digital format in an IP packet, meaning there are no analog channels.

• It’s harder to serve T1s. Some telephone customers will still want to purchase

traditional T1s to support existing telephone systems. T1s are harder (but not

impossible) to serve on AON compared to PON. However, T1s are a dying product in most markets.

• More space is required for electronics because there are more fiber terminations onto

the electronics. If the electronics are located in the field, the cabinets housing the electronics and fiber terminations can be very large. This means most cabinets need to be on private land and not on public rights-of-way.

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Passive Optical Network Advantages

• Uses less fiber than an AON since multiple customers in a neighborhood use the same fiber back to the electronics.

• Can support both RF Broadcast TV and digital IPTV.

• Can deliver analog TV without a settop box.

• Has a separate bandwidth stream for CATV and data services.

• Much more efficient use of bandwidth at the customer premise. A GPON network

delivers 2.4 Gbps of data to a small cluster of houses and an individual customer will normally have access to much of this bandwidth for data transmission, thus giving the customer a faster bandwidth experience at his home. By contrast, a typical Cable TV system shares 150 Mbps between 500 homes and an AON shares bandwidth farther into the core network.

• For the most part you can use existing home wiring. The PON network is delivered to

the side of the house and can use existing telephone and cable wiring as long as they are conveniently located and in good working order.

• No field electronic devices. The key word about a PON network is that it is Passive.

This means that no power is needed except in those locations, generally at major hubs, where the provider places electronics.

• Can easily provide traditional T-1s for larger business customers using business

ONTs.

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Disadvantages

• Customer must be within 12 miles of substation when using 1 X 32 splitter. This

means with very large installations that multiple hubs are required. For the normal town this is not a limitation.

• Cannot easily support open access systems. Because multiple customers share the

same electronics and same fiber, it is more of a challenge to allow multiple service providers to share the system. It can be done. An AON is much better suited for an open access network.

• More customers potentially are affected by a fiber failure in the field.

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We chose a GPON PON network for the Austin design for the following reasons:

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• More Bandwidth. This delivers more bandwidth to each customer, bringing a better

customer experience.

• Easier and less expensive construction. There are literally 32 times fewer fibers going

to each neighborhood network with PON, vastly reducing the complexity of construction and future repairs.

• The design we chose puts a fiber hut near to each existing electrical substation. All

customers in the city and rural areas are within range of one of these huts.

• A PON network can use most existing home wiring. The PON network is delivered to

the side of the house and can use existing telephone and cable wiring as long as they are conveniently located. There is also now an option to put the PON terminating device (ONT) inside the home.

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