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Chapter 8Final conclusions pand suffers an overhead penalty for Segmentation and Reassembly (SAR) in an attemptto provide a faster transmission for QoS over the ATM protocol, while the DOCSISuses a scheme that favours the delivery of variable length Internet protocol packetsrather than ATM transfer.8.3 Application of results to the IndustryThe results presented in this dissertation can be used in implementation for theEuropean cable modem protocol (DVB/DAVIC) by cable network operators andmanufactures. For example, results for mean access delay, throughput and utilisation(discussed in Chapter 5) can act as a guideline as to how subscribers should be allocatedin the upstream in order to achieve a desired performance and service level balance.In addition, by using the given performance levels for different loading scenarios, anappropriate charging scheme can be selected. Analysis on capital investment may bebased on results presented herein by deriving how the network could be segmented inorder to provide services with specific performance requirements. In general,recommendations for operators and service providers on how to achieve optimumsystem performance are as follows.The effects of the ‘Maximum Contention Access Message Length’ (Section 5.4.3)revealed that an increase in the overall system performance could be up to 3% by settingthe this parameter to 1. This parameter can be modified by the operator using the devicemanager at the headend. The ‘Maximum Reservation Access Message Length’ can alsobe modified by the service operator. A recommendation is to set this parameter to 32slots if the subscriber service is only for Internet traffic. If the service is also for voiceover IP, (with a best effort service) this parameter should be reduced to about 6 slots,but there is a drawback, reducing this parameter increases the risk of collisions ofreservation request and this results in a loss in system performance of about 6% in anattempt to provide short delays for the delivery of VoIP streams (as indicated in Figure5.12), on high periods of congestion.8-15
Chapter 8Final conclusions pThe optimisation of the number of contention slots carried out in Sections 6.2.2.1 and6.2.2.2 for the exponential backoff algorithm and the splitting tree algorithm,respectively, showed that a simple contention slots allocator can increase performanceby up to ≈ 10% (Figure 6.2 and Figure 6.5). This mechanism can be directlyimplemented by manufacturers by slightly modifying the DVB/DAVIC MAC protocol.The only parameter that is needed for the operation of the Simple-CSA is the ‘Min. o.of CSs per signalling frame’ , which was not defined by the DVB/DAVIC standard.This parameter can be added to the set of operational parameters of the INA and thenmodified via the device manager, either by the manufacturer or by the operator. Resultspresented in Section 6.2.2.1 can be used as a guidance of how to set the correct numberof contention slots (for optimum performance).Similarly, the Forced-CSA can also be implemented by the manufacturer by simpleadding the parameter forced contention slots (FSc), which represents the number ofslots added to the signalling frame after a collision occurred. This scheme was the bestcontention slot allocator, because it dynamically adjusts the number of contention slotsneeded to resolve collisions according to the traffic load, and achieves an increase in theoverall system performance by up to 3% more than the figure reported by the Simple-CSA. We recommend setting this parameter to 2 for optimum system performance.The optimisation of the two contention resolution algorithms used by the DVB/DAVICprotocol (approached in Section 6.3) does not require the intervention of themanufacturer. For the exponential backoff algorithm we recommend to the operator touse the backoff windows of Bw[4-6] and Bw[4-8], which performs well for Internet andVoIP traffic. For the splitting tree algorithm the Entry spreading factor should be set to6 for best system performance.From results presented in Section 6.3.3, we recommend that cable network operatorsbuy EuroModems that support the splitting tree algorithm. In this Section 6.3.3 it wasshown that this algorithm always performs better than the exponential backoffalgorithm, regardless of the traffic load and number of active stations. AlthoughEuroModems with this functionality tend to be more expensive than EuroModemssupporting only the exponential backoff algorithm, this extra cost is compensated for by8-16
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I would like to thank all the peopl
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CHAPTER 6: OPTIMISATIO OF CRA ALGOR
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FIGURE 5.17 - SYSTEM THROUGHPUT VS.
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LIST OF TABLESTABLE 2.1 - NEXT GENE
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Chapter 1Introduction pBecause of h
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Chapter 1Introduction pA first step
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Chapter 1Introduction passumption i
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Chapter 1Introduction ppolynomial b
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Chapter 1Introduction pIn general,
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Chapter 1Introduction pminislots to
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Chapter 1Introduction pThe authors
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Chapter 1Introduction prate access
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Chapter 1Introduction p1.4 Overview
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Chapter 2OVERVIEW OF CURRENT CATVNE
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Chapter 2Overview of current CATV n
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Chapter 3THE DVB/DAVIC PROTOCOL3.1
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Chapter 5Upstream channel capacity
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Chapter 6Optimisation of CRA using
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Page 231 and 232: Referencesp[17] I. Cidon, and M. Si
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Page 235 and 236: Referencesp[85] V. Rangel, R. Edwar
Page 237 and 238: Referencesp[112] K. Sriram, “Meth
Page 239 and 240: APPEDIX A: GLOSSARYAALABRADSLATMBCB
Page 241 and 242: Appendix AGlossary pkbpsLANLLCMACMA
Page 243 and 244: Appendix AGlossary pUSBUWVDSLVoDVoI
Page 245 and 246: Appendix BProtocol stack and packet
Page 247 and 248: Appendix BProtocol stack and packet
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Page 253 and 254: Appendix EResults for a 6 Mbps upst
Page 255: Appendix FGuide to CD-ROM p IEEE802
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