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Spectrum Slot Allocation for Individual Connection Request

The spectrum slot allocation of an individual connection request can be performed using one of the following allocation policies [97].

First Fit

In the first fit spectrum allocation policy [98,99], the spectrum slots are indexed and a list of indexes of available and used slots is maintained. This policy always attempts to choose the lowest indexed slot from the list of available slots and allocates it to the lightpath to serve the connection request. When the call is completed, the slot is returned to the list of available slots. By selecting spectrum in this manner, existing connections will be packed into a smaller number of spectrum slots, leaving a larger number of spectrum slots available for future use. Implementing this policy, does not require global information of the network. The first fit spectrum allocation policy is considered to be one of the best spectrum allocation policies due to its lower blocking probability and computation complexity.

Random Fit

In the random fit policy [6,98], a list of free or available spectrum slots is maintained. When a connection request arrives in the network, this policy randomly selects a slot from the list of available slots and allocates it to the lightpath used to serve the connection request. After assigning a slot to a lightpath, the list of available slots is updated by deleting the used slot from the free list. When a call is completed, its slot is added to the list of free or available slots. By selecting spectrum in a random manner, it can reduce the possibility of multiple connections choosing the same spectrum which is possible if spectrum allocation is performed in a distributed manner.

Last Fit

This policy [6,100] always attempts to choose the highest indexed slot from the list of available slots and allocates it to the lightpath to serve the connection request. When the call is completed, the slot is returned back to the list of available slots.

 
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