Guard Bands – Enablers For Co-existence Of Coherent 100G Signals And Non-coherent 10G NRZ Signals

On , in All Posts, General, Line Side, by Tony Goodchild

The coherent 100G transmission systems from network equipment vendors are showing an amazing robustness and tolerance for high PMD and CD. Some are reporting a PMD tolerance of up to 100ps DGD and above, while the CD tolerance can be in the range of up to 50.000ps/nm. Therefore the ideal network for deploying such coherent […]

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Understanding Polarisation Multiplexing

On , in All Posts, General, Line Side, by Tony Goodchild

Polarisation multiplexing is commonly used in 100Gb/s line side transmission as a method to increase the bit rate over the line without increasing the transmitted symbol rate. Using polarisation controllers it is possible to generate two perpendicular polarised optical signals on the same wavelength for transmission through a single fibre. As two separate signals are […]

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Understanding Phase Modulation For 100G Transmission

On , in All Posts, General, Line Side, by Tony Goodchild

There are a number of challenges to achieving 100Gb/s optical transmission rates using the technologies that have been deployed at 10Gb/s and even 40Gb/s. Using traditional transmission technologies such as NRZ modulation on the line will result in very poor spectral efficiency and a 100G signal using NRZ would not fit into the standard 50GHz […]

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Are Chromatic Dispersion Measurements Required Before Installing Coherent Systems?

On , in All Posts, Line Side, by Tony Goodchild

Bearing in mind that the Chromatic Dispersion (CD) tolerance of coherent systems can be up to 50.000ps/nm it is clear that CD measurements have lost part of their value. (We will be discussing the line side technology and the effect of chromatic and polarisation mode dispersion in an article very soon) However there are several […]

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Alignment Markers And Associated Alarm & Error Conditions

On , in All Posts, Client Side, Errors & Alarms, Ethernet, by Tony Goodchild

The alignment marker is used for the identification of the PCS lanes. They allow the receiving network equipment to identify the lanes as they are received so that that they can be re-ordered. So what is an alignment marker? An alignment marker is a single 66 bit block that is inserted into the stream of […]

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Understanding 100G Ethernet Error & Alarm Conditions – Loss Of Block Lock

On , in All Posts, Client Side, Errors & Alarms, Ethernet, by Tony Goodchild

On the 100G Ethernet interface the Loss Of Block Lock (LOBL) alarm is raised when it is not possible to lock onto the sync. header within the 64b/66b line coded blocks. As the serial stream of blocks are distributed over the 20 PCS lanes during transmission the LOBL alarm should be reported within a specific […]

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Testing The Physical Interface

On , in All Posts, Client Side, Ethernet, General, OTN, by Tony Goodchild

100G testing plans must include specific attention to the physical interface. The CFP interface is no longer a single transmitter and receiver pair that can simply be checked with simple tests such as a basic optical power measurement or receiver sensitivity measurement. Utilising multiple optical lanes simultaneously makes testing the interface more complex and also testing […]

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