Читать книгу Smart Grid Telecommunications - Ramon Ferrús - Страница 44

The impact of telecommunication services on Smart Grid operations is a key aspect of the enablement of telecommunications for the grid. Telecommunications are not a simple add‐on over the grid, but a transformation vector. Whenever grid operations rely on telecommunications, telecommunications become as critical to the utility as any other resource.

Telecommunications private network design and/or third‐party TSP service selection must be performed to allow the provision of the Smart Grid needed services within the utility license conditions. When the utility operates a private network for this purpose, the performance responsibility is within its decision range. However, when third‐party TSP services are involved, Service‐Level Agreements (SLA) must be clearly defined to govern service delivery conditions.

ITU‐T E.860 provides a framework for SLAs, defined as “a formal agreement between two or more entities that is reached after a negotiating activity with the scope to assess service characteristics, responsibilities and priorities of every part. An SLA may include statements about performance, tariffing and billing, service delivery and compensations.” SLAs are based in some formal definitions that must be well known to both parties, especially when referred to the service characteristics that need to be expressed in telecommunication technical terms. However, they must also collate (see ITU‐T G.1000 and its reference to ETSI ETR 003) all different service functions (sales, service management, technical quality, billing processes, and network/service management by the customer) and quality criteria with each of them (speed, accuracy, availability, reliability, security, simplicity, and flexibility), to be consistent with the objective.

Smart Grid needs must be transformed into telecommunication technical parameter requirements that measure network performance. Network performance is defined as in ITU‐T Recommendation E.800, as “the ability of a network or network portion to provide the functions related to communications between users.” Performance is critical for applications to deliver their expected benefits and must be properly planned and controlled in networks that share resources among different users.

Two of the most important performance parameters in telecommunications are throughput and latency. These general parameters are included in the network performance objectives of different networks (e.g., ITU‐T I.350 and Y.1540 for digital and IP‐based networks):

 Throughput is the maximum data rate where no packet is discarded by a network. Throughput is usually measured as an average quantity, with control over the peak limits.

 Latency is the time it takes for a data packet to get from one point to another. Latency is usually defined as a requirement below a certain limit.

Service performance is assessed in terms of its Quality of Service (QoS). ISO 8402 defines QoS as “the totality of characteristics of an entity that bear on its ability to satisfy stated and implied needs.” ITU‐T E.800 defines it as “the collective effect of service performance which determine the degree of satisfaction of a user of the service.” Beyond QoS, QoE (Quality of Experience as in ITU‐T E.804) enters into the subjective domain of the service users' perception that cannot be neglected as it reflects previous experiences and expectations. Thus, SLA, QoS, and QoE go beyond the pure technical perspective.

Eventually, telecommunication systems must absorb all these service requirements and integrate them in their complex network structures. These networks will not only deliver them but also control and manage its performance in different circumstances. ITU‐T Study Group 12 “Performance, QoS and QoE” [60] is leading this work, as in ITU‐T E.804 “QoS aspects for popular services in mobile networks” and ITU‐T Y.3106 “Quality of service functional requirements for the IMT‐2020 network.”