DOWNLOAD MY Ph.D Thesis - UNAM

Chapter 4Simulation and analytical modelling pThe number of MCI frames, MCI (needed in Equation 4.17) that would be scheduledbefore the current MCI frame expires is then calculated as D lah over the length of thesubsequent MCI frames (MCI t ). Thus:⎧ Dlah⎪when Dlahmod MCIt= 0MCItMCI= ⎨(4.20)⎪ Dlah+ 1 otherwise⎪⎩MCItFor this analysis (when D IU_proc ≈ 100 ms), the scheduler look-ahead delay results inD lah = 705 µs, hence MCI = 705·10 -6 / 750·10 -6 ≈ 1. Consequently, the secondcomponent of delay of the service time in idle state results in Xt= 1⋅MCI .2 tOn the other hand, if we consider a large processing delay (e.g D IU_proc ≈ 500 ms), thenthe second component of delay of the service time becomes:−6−6Xt2= 1105 ⋅10/ 750 ⋅10≈ 2 ⋅ MCI tIn order to get a complete formula for X idle we now need to calculate the thirdcomponent of delay, X t3 , which is related to the number of MCI frames required totransmit a data packet (Pk mci ) and is given by:X3= Pk ⋅ MCI(4.21)where Pk mci can be calculated by using the following equations:tmcitPkslot⎧ Pk⎪= ⎨⎪ Pk⎪⎩sizesize+ AAL5AAL5PDU+ AAL5AAL5PDUheaderheader+ 1when Pksize+ AAL5headermod AAL5PDU= 0otherwise(4.22)In this equation, Pk slots gives the number of upstream slots required to transmit a datapacket, Pk size is the length of the packet size in bytes to be transmitted, AAL5 header (= 8bytes) corresponds to the protocol overhead caused by the encapsulation of PDUmessages into ATM cells, AAL5 PDU (= 48 bytes) is the payload of an ATM cell.4-25