DOWNLOAD MY Ph.D Thesis - UNAM

Chapter 7Performance optimisation for the support of TCIS pmaximum throughput achieved per cable modem, effects of varying the packet size inisochronous streams and maximum system capacity in terms of active cable modems.For the DOCSIS protocol, the CSF (v.13) based on the OPNET simulation package wasused [77]. The simulation parameters considered for the performance analysis aresummarised in Table 7.5. In both protocols a scheduler at the headend with a simpleFIFO service was used. For the DOCSIS protocol, priority service was not considered,since the DVB/DAVIC standard does not support traffic prioritisation. Therefore, allstreams generated are assumed to have the same access priority.In addition, the default upstream data rate of 3.088 Mbps for the DVB/DAVIC protocolwas selected. The corresponding data rate for the DOCSIS protocol was set at 2.056Mbps. The concatenation and piggyback features of the DOCSIS protocol were notconsidered for this analysis, since such characteristics are not supported by theDVB/DAVIC protocol.Table 7.5 – Simulation parameters.Parameter DOCSIS DVB/DAVICUpstream channel capacity (QPSK) 2.56 Mbps 3.088 MbpsNumber of cable modems Up to 350 Up to 350Minislot/slot size in bytes 16 (minislot) 64 (slot), 21 (minislot)Max. No. of minislots/slots in MAP/MCI Max. 4096 Fixed 36Min. No. of contention slots in MAP/MCI 16 [2-3]Contention resolution algorithm Exponential backoff algorithm Splitting tree algorithmMax. number of IEs in MAP 240 ---------FEC-T bytes 3-SD, 5-LD* 3Codeword length 75-SD, 245-LD* 53 (ATM cells)Last codeword shortened True ---------Guard time size 2 bytes (variable) 1 byte (Fixed)Distance from nearest/farthest modem to the headend 10-16Km, rnd. distributed 10-16Km. rnd. distributedSimulation time 60 seconds 60 seconds*SD = Short data codeword, LD = Large data codewordA) Protocol efficiency and volumetric data comparisonsThis analysis addresses a comparison of the volume of data (transferred upstream by auser data request transmission) and protocol efficiency for the DVB/DAVIC and theDOCSIS standards.7-28