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Chapter 7Performance optimisation for the support of TCIS pSimilarly, the DOCSIS stepped curve is caused by the encapsulation of PDU messagesinto codewords (of ≈ 220 bytes), which are then transmitted as a continuous series ofminislots. Figure 7.20 shows the PDU structures for this protocol. For instance, for thesame user data of 1450 bytes, the DOCSIS protocol requests (1450-payload + 20-TCP +20-IP + 3-LLC + 18-MAC + 6-DOCSIS MAC) / 245 byte-codeword = 6 largecodewords + 1 short codeword ≈ 1590 bytes (or ≈100 minislots), for an upstreamefficiency of 91%. Here, every codeword includes 10 bytes of FEC information tocorrect up to 5 bytes over the MAC PDU. Without FEC the volumetric data at the PHYlayer becomes of 1520 bytes (≈95 minislots) for an increased efficiency up to 95%.MAC-Hdr.14-byte1493-byte IP PDUMAC-FCS4-byteMAC Frame (MAC-PDU)PreambleDOCSIS MAC6-bytes220-byte Packet DataFEC220-byte Packet Data1511-byte IMAC PDUFEC197-byte Packet DataFECDOCSIS MAC FrameGuradTimeCodewordsDOCSISMAC&PHY10-bytes 230-byte FEC Codeword (1)230-byte Codeword (2)207-byte FEC Codeword (7) 1-byteFigure 7.20 – DOCSIS upstream PDU structures.B) Maxim throughput achieved per cable modemIn order to obtain the maximum throughput per cable modem that each protocol canachieve, a single node (cable modem) network was considered with typical Ethernetpacket sizes ranging from 64 to 1518 bytes. A traffic generator within the node was setto produce the maximum number of packets that it could receive from the CPEinterface, (as introduced in Section 5.4.7.1), which was a 10 Mbps constant stream withvariable number of packet per second depending on the packet size.All references to packet size in this analysis (and also in the following analyses) willrefer to the size of the packet as it enters the system from the CPE interface. This wouldbe the packet size that the cable modem submits for delivery over the cable network,which does not include CATV MAC and PHY overheads. However, the CPE MAC andpossible layer 2 and layer 3 overheads are included.7-30
aChapter 7Performance optimisation for the support of TCIS pThe maximum throughput and upstream channel utilisation versus the packet sizegenerated is shown in Figure 7.21. In terms of throughput (Figure 7.21a), the DOCSISprotocol is superior to the DVB/DAVIC protocol. For the maximum Ethernet packetsize (1518 bytes), the maximum sustainable throughput per DOCSIS cable modem was≈ 1.6 Mbps, which corresponds to about 62% of the upstream channel capacity, incomparison to ≈ 1 Mbps (32% of the cc) achieved by each DVB/DAVIC cable modem.In terms of utilisation (Figure 7.21b), the difference was 19% of the link capacity infavour of the DOCSIS protocol.However, for small packet sizes under 256 bytes, results reveal that bothcommunication protocols are highly inefficient. The maximum throughput does notexceed 25% of the link capacity even though the offered load was a constant 10 Mbpsstream. The worst case scenario is released for the 64-byte packet size, where thethroughput was as low as 2% of the cc (≈ 56 kbps) for DVB/DAVIC cable modems, incomparison to 7% of the nominal channel capacity (≈ 181 kbps) provided by theDOCSIS cable modems.A closer analysis of the difference between throughput and utilisation, simulation resultsshowed that an increased protocol overhead is involved in the DVB/DAVIC protocolthat reduce considerably the protocol efficiency, as examined in the previous scenario.Throuhgput (Mbps)2.01.81.61.41.21.00.80.60.40.20.0a) System Throughput b) UtilisationDOCSIS: 2.5Mbps UpDVB: 3Mbps Up64 128 256 512 768 1024 1280 1518Packet Size (bytes)Utilisation (Mbps)2.01.81.61.41.21.00.80.60.40.20.0DOCSIS: 2.5Mbps UpDVB: 3Mbps Up64 128 256 512 768 1024 1280 1518Packet Size (bytes)Figure 7.21– Maximum channel capacity for DVB/DAVIC and DOCSIS for one node.7-31
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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 3The DVB/DAVIC protocol pEu
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Chapter 3The DVB/DAVIC protocol pMA
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Chapter 3The DVB/DAVIC protocol pTh
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Chapter 3The DVB/DAVIC protocol p3.
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Chapter 4Simulation and analytical
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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
Page 233 and 234: Referencesp[50] N. F. Huang, C. A.
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
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Appendix D Verification test p209 2
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Appendix EResults for a 6 Mbps upst
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Appendix FGuide to CD-ROM p IEEE802
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