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Chapter 7Performance optimisation for the support of TCIS pIn Barton [8], a comparison of the main characteristics of each protocol was providedfrom an American perspective. Here, an overview and status of each standard isprovided. Furthermore, a technical comparison of the major characteristics, strengths,advantages and disadvantages of each standard are also described.A less extensive comparison but with a European perspective is reported in [55]. In thispaper the authors presented an overview of each protocol followed by a briefcomparison of the major technical characteristics of each standard.An initial performance comparison carried out in this research can be found in [84].This comparison is based on the DVB/DAVIC, DOCSIS and the (withdrawn) IEEE802.14 standard. The comparisons presented in this section focus on services, MAClayer, PHY layer technical characteristics, and performance comparisons in terms ofvolumetric data (at the physical layer), efficiency, mean access delays and maximumsystem throughput.7.4.1 Technical comparisons7.4.1.1 MAC layer comparisonsAt the DVB/DAVIC MAC layer, four access modes are provided. The first mode(contention access) is based on a contention access mechanism, which allows users tosend information at any time with the risk of collisions. The second and third modes(fixed-rate and reservation access) are contentionless, in which the INA either providesa predefined amount of slots to a specific NIU, or a given bit rate requested by an NIUuntil the INA stops the connection on NIU's demand. These access modes aredynamically shared between time slots, which allows the NIUs to know whencontention, reservation or fixed-rate transmission is or is not allowed. This is to avoid acollision for the two contention-less based access modes. The fourth mode is calledranging access, in which slots are used to measure and adjust the time delay and thepower level for upstream transmission.Data transmission in the DOCSIS MAC layer is based on a request/grant scheme. Atregular intervals, the CMTS provides timing, ranging, registration, transmission andcontention resolution information for every CM on the network. In the upstream, each7-25