Three hitless line protection switching methods for SDH-based ATM (asynchronous transfer mode) networks are proposed, and the best choice is shown to be the cell alignment method. This method enables forced or manual switching to be performed hitlessly while maintaining full compatibility with the standard protection switching algorithm defined in CCITT Recommendation G.783. This method has the further advantage that it does not cause delay variation upon switching, so that user information is not affected by forced switching. It is shown how the parameters used in this method are designed so that adequate performance for hitless switching can be achieved.
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