Energy consumption of telecommunication access networks

VDSL2-Vectoring HFC FTTH – PtP FTTH – GPON Downstream data rate [Mbit/s] 100 400 1,000 1,000 Upstream data rate [MBit/s] 40 10 1,000 500 Annual downstream volume per subscriber [Tbyte/year] 394 1,577 3,942 3,942 Annual upstream volume per subscriber [Tbyte/year] 158 39 3,942 1,971 Maximum annual traffic volume for all subscriber down + up stream [Zbyte/year] 14 41 200 150 Annual subscribers traffic volume per kWh 4 Tbyte 8 Tbyte 47 Tbyte 56 Tbyte Figure 32: Comparison of the energy consumption normalized to the maximal annual transmission volume. Performance related energy efficiency or energetic performance is a key figure to compare different access technologies. Nevertheless, another important figure is the number of active network elements and locations. DSL technologies are based on the copper twisted pair telephone network. The telephone network, however, was designed to transmit audio communication signals and not high frequency data. One of the main implications is the considerable length limitations of DSL technologies – higher data rates need shorter cable length. An improvement in data rate can only be achieved by reducing the cable length. Therefore, new active network elements, so called Outdoor DSLAMs, have to be built close to the subscribers. This has to be repeated until the new infrastructure has reached the subscriber directly. This increases the number of active network elements significantly and is shown in Figure 33. Another aspect of future DSL technologies, like G.fast, is reverse powering of access network elements. In this case, the last network element, e.g. in the sidewalk, has to be supplied by the subscribers with electricity. Currently, it is still unclear who will bear the cost of reverse powering – the subscribers or the network operators. The HFC is based on the coax television network. This network was designed for the transmission of high- frequency video signals over long distances. An implementation of data transmission was, therefore, initially unproblematic – even over longer distances. The overall transmission capacity could also be increased by adapting the DOCSIS standards. However, it should be noted that HFC is a shared medium, in which all customers within one service group share the available total transmission capacity. At a certain point, the subscriber’s data rate can only be increased by decreasing the service group size, so that fewer subscribers have to share the total transmission capacity. Because an active fibre node feeds every service group, increasing the subscriber’s data rate also increases the number of active elements – see Figure 33. FTTH technologies are based on passive distribution networks between a central office/PoP and the subscriber. That means that no active network elements are needed in the distribution network for signal transmission. Increased data rates are achieved by developing the transmission standards and exchange of the active PoP components and customer premises equipment. With GPON, a reduction in the splitting ratio may be necessary in special cases. This will require additional splitters in the distribution network, but these are also passive and do not require any power supply. However, if the splitting ratio is reduced, further GPON ports are required in the PoP but the number of active network elements is not modified during the capacity increase in FTTH networks Figure 33. 30