**6.1 Guided media**

314 Advanced Topics in Measurements

communication network may cause huge problems in system operation and control, especially in operation of WAMS applications. Consequently, especial attention should be paid to communication infrastructure, which is as important as electrical infrastructure itself. These two infrastructures (communication and electrical) have become increasingly interdependent so that in the case of failure for each of them, another one may also become

New communication systems are designed based on open system interconnection (OSI) layer model. In this architecture, upper layers relay data, assuming that the lower layers work perfectly. In fact, this model is an effective architecture for explanation, designing, implementation, standardization and use of communications networks. The OSI reference model consists of seven layers: physical, data link, network, transport, session, presentation,

In wide area measurement systems, data resources and WAMS applications normally work at the upper layers of network models. Fig. 4 shows the map between OSI layers and three major blocks of WAMS shown in Fig. 1 i.e. data resources, WAMS applications and

out of service (Shahidehpour & Wang, 2003; Lukszo et al., 2010).

Data Resources ICT Applications

Fig. 4. Layering in WAMS based on OSI reference model (Shahraeini et al., 2010).

characterizing the limitations of transmission (Stallings, 1997).

The first layer of OSI model, referred to the physical layer, is a kind of medium that establishes the physical connection between transmitter and receiver. The characteristics of the communication systems will become seriously influenced by the characteristics of their media. Therefore, it can be concluded that the characteristics of the transmission media play an important role in communication infrastructure of WAMS. Some major characteristics of a medium are as follows: cost, bandwidth, propagation delay, security and reliability

Transmission media, as described below, can be classified as guided and unguided ones (Stallings, 1997). Guided media guides the waves through a solid medium. Twisted pair, coaxial cable, power transmission/distribution line and optical fiber are some examples of guided media. In the case of guided media, the media itself has the most important role in

and application (Shahraeini et al., 2010).

(Shahraeini et al., 2010).

communication system (Shahraeini et al., 2010).
