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About Metro Ethernet
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Written by: Les Harper
Fiber optic broadband services are high speed data transmission networks wherein data is delivered over cables which are made of bundles of tiny plastic or glass fibres. These fibres transmit information as light pulses that form electromagnetic waves. The methodology is more efficient than the traditional copper wire/ phone line mode of transmission. The strength of the networks lies in high speed, larger carrying capacity, greater resistance to electromagnetic noise such as radios, motors or nearby cables and they cost much less to maintain. Moreover, the signals do not need refreshing during transmission.
As stated, fiber optics use light pulses to transmit information over the network instead of electronic pulses. A transmitter connected to one end of the fiber optic line receives the signal and translates it into light pulses that can be sent across the fiber optic cable. A light emitting diode may be used for generating the light impulses and a lens may be used to funnel the light pulses through the cable. 850 nm near infra-red light is used for short distance transmissions and a 1300 nm light pulse is used for longer distances on multi mode fibre. On single mode fibre 1300 nm is used for shorter distances and 1500 nm for longer distances.
The light pulses travel down the fiber optic line in accordance with the principle of total internal reflection. The clearer and purer the fiber lines within the cable the greater will be the speed of transmission of the light pulses. Generally plastic or glass is used for this purpose. Plastic fiber optics are normally used for short distance transmission and pule glass from silica is used for long distance transmission fibre optic cables. Longer wavelength fibre optic cables may be made from fluoro zirconate, fluroaluminate and chalcoginide glasses.
At the other end of the fibre optic cable is an optical receiver. This has a photo detector that converts light into electricity using a photoelectric effect. The photo detector is generally a semiconductor based photo diode because it is eminently suitable for circuit integration in regenerators and wavelength division multiplexers.
Optical electrical converters are coupled with trans-impendance amplifier and a limiting amplifier to produce a digital signal. The signal is further processed using clock recovery form the data and the application of a phase locked loop.
Normally the data efficiency of the Fibre optic broadband connectivity is such that, it allows users unlimited download limits for audio tracks, photos, software updates, patches for games and DVD quality video transmission. However, there is a peak time limit during which downloads can be restricted by the service provider and this happens when the fibre optic connection is shared across buildings in a locality.
Component compatibility demands that component manufacturers adhere to predefined norms for development of fibre optic broadband components. Today, there are prescribed standards for fibre optic cable manufacture, characteristics and performance design. There are specified criteria for fibre transmitters and receivers that need to be used with conforming systems. Some of the prescribed standards are referred to as 10 Gigabit Ethernet, Fibre Channel, Gigabit Ethernet, HIPPI, Synchronous Digital Hierarchy and Synchronous Optical Networking.
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