One way to quantify the EF PHB performance requirement is with the following set of equations relating to packets leaving a node through some interface I to an external communications link:

where dj = departure time of the jth EF packet to depart from I; measured at the time the last bit leaves the node fj = target departure time for the jth EF packet to depart from I; the ideal time at or before which the last bit of that packet leaves the node Ea = Error term for the treatment of individual EF packets; it represents the worst case deviation between actual departure time of an EF packet and the ideal departure time of the same packet aj = arrival time at this node of the last bit of the jth EF packet destined to depart from I Lj = length in bits of the jth EF packet destined to depart from I R = EF configured rate at I in bps; this is not the actual data rate on the line but rather the desired data rate for this EF PHB This definition assumes that EF packets should ideally be served at a rate R or faster.
It must take into account these cases: (1) An EF packet arrives when all previous EF packets have already departed; (2) an EF packet arrives at a device that still contains waiting EF packets. With these facts in mind, explain the equations. Hint: For the second case, there are two subcases.

df>0+ Ea j>0 = fo-do = 0 fj = MAX[aj, MIN(dj-1,fi-1)] + (L/R)