Fragmentation in LFI is based on the optimal fragment size. LNS implementation calculates the two optimal fragment sizes, based on two different criteria:
Optimal fragment size based on the payload efficiency of the fragment considering the fragmentation and transportation header overhead associated with the fragment encapsulation based fragment size.
Optimal fragment size based on the maximum transmission delay of the fragment set by configuration delay based fragment size.
At the end, only one optimal fragment size is selected. The actual fragment’s length is the optimal fragment size.
The parameters required to calculate the optimal fragment sizes are known to the LNS either through configuration or signaling. These, in-advance known parameters are:
Last mile maximum transmission delay (max-fragment-delay obtained by CLI)
Last mile ATM Encapsulation (in the example the last mile is ATM but in general it can be Ethernet for MLPPPoE)
MLPPP encapsulation length (depending on the fragment sequence number format)
The last mile on-the-wire rate for the MLPPPoX bundle
Examine closer each of the two optimal fragment sizes.