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Synchronous Ethernet

Synchronous Ethernet
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Synchronous Ethernet Introduction Ethernet is the ubiquitous communication platform for computer networking in the home and enterprise. The simplicity, performance and cost effectiveness has made Ethernet technology a viable choice for transport networks as well. There are challenges in adapting Ethernet technology to carrier class, highly reliable managed networks. The inherently asynchronous nature of Ethernet has the primary challenge of carrying time sensitive traffic such as real time voice or video data. Rakon’s TCXOs, Mercury/+TM ASIC based OCXOs and conventional discrete OCXOs are ideal for use in Synchronous Ethernet applications. They support ITU-T G.8262 standards for Synchronous Ethernet. From Asynchronous to Synchronous Traditionally, Ethernet nodes were running asynchronously to each other, with a defined ±100 ppm accuracy to the nominal frequency. Consequently, most of the traffic carried over Ethernet was asynchronous and “bursty” in nature. Synchronisation in its strictest sense was not required because of the nature of the traffic passing through. The transceiver buffers were used to take care of the unexpected variations in the data flow. Moreover, the protocol layer implemented flow control using “Pause Frames” which halted the transmission for a specific period of time. As Ethernet started to carry real time voice and video, the traffic patterns changed. Such services demanded Constant Bit Rate or Variable Bit Rate but contiguous traffic, which demanded all nodes in a network from source to destination to have the same average frequency. The timing and synchronisation techniques that were applied to the traditional circuit switched networks became relevant to the Ethernet networks as well. The equipment based on Ethernet networks that support synchronous timing are described as Synchronous Ethernet (SyncE) networks. Synchronised Clocks in Physical Layers The G.8261 describes synchronisation chains including Synchronous Ethernet. A Primary Reference Clock (PRC) traceable reference is introduced into the chain and the clock drives the physical layer, transferring synchronisation in the network. At the receiving node, the physical layer extracts the clock and filters and conditions the clock according to the requirements of the G.8262 Synchronous Ethernet Equipment Clock (EEC) specifications. G.8264 defines Ethernet Synchronisation Messaging Channels (ESMC) to support the physical layer clock transfer. New Zealand (HQ) Auckland | India Bangalore | Singapore Singapore City | China Shenzhen & Shanghai | Taiwan Taipei City | South Korea Seoul | United States Silicon Valley, Chicago & Atlanta | United Kingdom Harlow (London) | France Argenteuil (Paris), Mougins | Germany Frankfurt

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Synchronous Ethernet Synchronous Ethernet Requirements G.8262 defines Option 1 and Option 2 for clocks, optimised for 2.048M interfaces and 1.544M interfaces, respectively. The loop filter bandwidth defined for Option 1 clocks is 1Hz to 10Hz. The loop filter bandwidth required for Option 2 clocks is 0.1Hz and therefor the short term stability of the TCXO used is important to achieve wander generation compliance with temperature variation effects. The jitter compliance is tested on the system interface outputs and is a function of the PLL and the oscillator used in the system. Thus low...

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Synchronous Ethernet 2Pages

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Synchronous Ethernet
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