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The contention factor limits the extent to which lightpaths using the same wavelength can be added/dropped in a Reconfigurable Optical Add/Drop Multiplexer(ROADM) when it is operated in a colorless and directionless fashion. This paper presents an analysis to estimate the probability of blocked lightpath requests when a node of this type is used and validates the results for three traffic models. Simulations confirm the validity of the analytical results for lightpath blocking both for various values of the add/drop contention factor C and for changing load distribution in the network. We observe a saturation trend in the lightpath blocking performance as the add/drop port count per bank increases and that a high enough value of C reduces lightpath blocking to levels obtainable from an ideal, comntentionless ROADM. When C is small, limitations on the add/drop port count per bank is observed to be the dominant cause of blocking lightpaths while intra-node contention effects have only a limited impact. With increasing C, blocking is caused more because sufficient link capacity is not available and not because free add/drop ports are not available
The contention factor limits the extent to which lightpaths using the same wavelength can be added / dropped in a Reconfigurable Optical Add / Drop Multiplexer (ROADM) when it is operated in a colorless and directionless fashion. This paper presents an analysis to estimate the probability of blocked lightpath requests when a node of this type is used and validates the results for three traffic models. Simulations confirm the validity of the analytical results for lightpath blocking both for various values of the add / drop contention factor C and for changing load distribution in the We observe a steady trend in the lightpath blocking performance as the add / drop port count per bank increases and that a high enough value of C reduces lightpath blocking to levels obtainable from an ideal, comntentionless ROADM. When C is small, limitations on the add / drop port count per bank is observed to be the dominant cause of blocking lightpaths while intra-node contention effects have only a limited impact. With increasing C, blocking is caused more because sufficient link capacity is not available and not because free add / drop ports are not available