Journal of High Speed Networks

Multicast transmission is utilized in Time Division Multiple Access (TDMA) Passive Optical Networks (PONs) to efficiently and selectively send downstream data to subsets of users. For example, multicast can be exploited in open access PONs to offer various services provided by different providers to the end-users. In this scenario, the minimization of the energy consumption, which is one of the greatest contributors to PON CAPEX, would benefit not only service providers but also end-users.

This paper proposes an energy efficient multicasting solution based on energy efficient optical network units (ONUs). Energy savings are achieved by setting to sleep mode the ONUs that need not receive downstream data, i.e. are not subscribed to a multicast group. Sleep mode is combined with an optimal multicast group scheduling to minimize the transitions from sleep to active mode, which consume power for achieving synchronization.

Results show that energy efficient multicast transmission reduces the energy consumption with respect to the current broadcast-based transmission. The improvement is more significant when only one user is connected to an ONU (i.e., FTTH) than when several users are connected to the same ONU (i.e., FTTB). This is due to the fact that the higher is the number of subscribers connected to an ONU the higher is the likelihood that an ONU must be active most of the time.

The paper provides estimates how deployment of fast fixed broadband may affect consumption of energy by subscriber's electronic devices. New subscribers are expected to buy additional equipment: PCs, laptops, TV sets, game consoles, etc. and more intensively use all devices connected to the net. The effects are independent of access technology, as long as certain key services are supported.

Resulting increase of electricity consumption by households will likely require costly investment in new power plants. In case of fossil fuel power generation, negative environmental consequences will be noticeable. However, progress in reducing device power consumption and replacement of desktop PCs with laptops and other portable devices shall considerably mitigate these effects.

Operating costs and scalability of nowadays telecommunication networks are largely impacted by energy consumption of network equipments. In packet switching devices it is especially due to packet processing, queuing, and input/output interface functionalities. Different approaches to reduce energy consumption in packet switches are emerging, some exploit under-laid optical bypass of transit traffic to reduce their capacity and interfaces, others simplify their operations or turn off some of their functionalities when unnecessary. The IEEE standardization body developed a standard on Energy Efficient Ethernet (IEEE P802.3az) that defined a mechanism allowing to de-activate the Physical layer elements during periods of low link utilization. It is based on a protocol that coordinates transitions to and from a lower power consumption mode without changing the link status and dropping frames. Time needed by such transitions is, however, comparable with packet transmission time; that makes energy efficiency of the method far from being proportional to interfaces unused capacity. Solutions proposed in the literature to improve EEE performance are mainly based on the buffer and burst approach, which, making the transmission non continuous, creates more opportunities for long sleeping period. Such solutions, however, if applied across the network, strongly impact packet delay requirements. In this paper, a traffic management mechanism that controls sleeping period to reduce EEE transitions overhead while meeting delay constraints of data flows is proposed. Starting from the consideration that in Ethernet network provisioning is static, i.e. service level agreement parameters of each flow are configured on switches output ports of its path via management plane at the set-up phase, the proposed method off-line determines, for each output port, if the activation of a dummy flow, associated to the quiet period, can provide power consumption reduction without impacting data flows delay requirements. On ports where the dummy flow is activated the sleeping period is triggered by the scheduler mechanism each time a dummy packet is served. A comparative analysis between the standard EEE, with and without the support of buffer and burst functionality, and the proposed method has been carried out in order to quantify the improvements in terms of energy efficiency and to assess its effectiveness in terms of Quality of Service (QoS).