**2. State of the art in railway communications**

Railway communications emerged almost exclusively from the communication between fixed elements to carry out traffic management and circulation regulation. The technologies that communicate fixed elements with mobile elements (trains) are relatively recent, and they have contributed to improve and simplify the work required for rail service exploitation. Therefore, focusing on the network topology, two categories can be identified within the field of railway communications: a first one involving only fixed elements, and a second one involving both, fixed and mobile elements (called "train-to-earth" communications) (Salaberria et al., 2009). For the former, the most efficient solutions are based on wired systems. The latter has undergone great change in recent years, requiring wireless and mobile communications (Laplante & Woolsey, 2003).

Traditionally, the communication between fixed elements and trains has been established using analogical communication systems, such as the traditional telephone or PMR (Private Mobile Radio) based on radio systems (ETSI, 2008). These analogical systems are still used for voice communications and issues related with signalling. However, their important limitations in terms of bandwidth are causing the migration to digital systems, which offer a higher bandwidth.

Among the technologies of communication "train-to-earth", one of the most important advances of the last decade has been the GSM-R (Global System for Mobile Communications - Railway) (International Union of Railways, 2011). This system is based on the GSM telephony, but has been adapted to the field of railways. GSM-R is designed to exchange information between trains and control centres, and has as key advantages its low cost, and worldwide support.

Another technology that provides a wide circulation in the rail sector is the radio system TETRA (Terrestrial Trunked Radio) (ETSI, 2011). TETRA is a standard for digital mobile voice communications and data communication for closed user groups. The system includes a series of mobile terminals, similar to walkie-talkies, which allow establishing direct communication between control centres, train drivers and maintenance personnel, in addition to being able to establish communications with earthlines and mobile phones. Being a private mobile telephone system, its deployment in the rail sector is very simple, because it is based on the placement of a series of antennas at stations or control centres along the route.

In addition, the special-purpose technologies mentioned so far include the growing use of wireless communication technologies based on conventional mobile telephony (GSM, GPRS

The second section of this chapter includes a brief description of the state of art in railway communications. The third one describes a specific train-to-earth wireless communication architecture. The fourth section describes the main challenges concerning with the management of the quality of service in train-to-earth communications. The fifth identifies some services that are arising as result of using this connectivity architecture and the way in which they interoperate. The sixth section shows the future lines of work oriented to improve the proposed communication channel. Finally, the seventh section of the chapter

Railway communications emerged almost exclusively from the communication between fixed elements to carry out traffic management and circulation regulation. The technologies that communicate fixed elements with mobile elements (trains) are relatively recent, and they have contributed to improve and simplify the work required for rail service exploitation. Therefore, focusing on the network topology, two categories can be identified within the field of railway communications: a first one involving only fixed elements, and a second one involving both, fixed and mobile elements (called "train-to-earth" communications) (Salaberria et al., 2009). For the former, the most efficient solutions are based on wired systems. The latter has undergone great change in recent years, requiring

Traditionally, the communication between fixed elements and trains has been established using analogical communication systems, such as the traditional telephone or PMR (Private Mobile Radio) based on radio systems (ETSI, 2008). These analogical systems are still used for voice communications and issues related with signalling. However, their important limitations in terms of bandwidth are causing the migration to digital systems, which offer a

Among the technologies of communication "train-to-earth", one of the most important advances of the last decade has been the GSM-R (Global System for Mobile Communications - Railway) (International Union of Railways, 2011). This system is based on the GSM telephony, but has been adapted to the field of railways. GSM-R is designed to exchange information between trains and control centres, and has as key advantages its low

Another technology that provides a wide circulation in the rail sector is the radio system TETRA (Terrestrial Trunked Radio) (ETSI, 2011). TETRA is a standard for digital mobile voice communications and data communication for closed user groups. The system includes a series of mobile terminals, similar to walkie-talkies, which allow establishing direct communication between control centres, train drivers and maintenance personnel, in addition to being able to establish communications with earthlines and mobile phones. Being a private mobile telephone system, its deployment in the rail sector is very simple, because it is based on the placement of a series of antennas at stations or control centres

In addition, the special-purpose technologies mentioned so far include the growing use of wireless communication technologies based on conventional mobile telephony (GSM, GPRS

establishes the main conclusions of this work.

higher bandwidth.

along the route.

cost, and worldwide support.

**2. State of the art in railway communications** 

wireless and mobile communications (Laplante & Woolsey, 2003).

and UMTS) and broadband solutions such as WiFi (IEEE 802.11, 2007) or WiMax (IEEE 802.16.2, 2004). The wireless local area networks WiFi enable the exchange of information, at much higher speeds and bandwidths than with other technologies. The cost of deployment of such networks is very low, but these are limited in terms of coverage or distance they cover. To address this limitation, the WiMax technology has emerged extending the reach of WiFi, and is a very suitable technology to establish radio links, given its potential and high-capacity at a very competitive cost when compared with other alternatives (Aguado et al, 2008).

All technologies discussed so far aim to establish a wireless communication channel between fixed elements and mobile elements of the railway field, but what happens with the services offered by means of this communication channel?, how can they have access to the channel?, how can they share it?. To address these questions, a categorization of railway services is necessary. Traditional applications or services of the railway can be classified into two major groups: (1) services related with signalling and traffic control; and (2) services oriented to train state monitoring.

The first group of services is based on the exchange of information between infrastructure elements (tracks, signals, level crossings, and so on) and control centres, all of them fixed elements. Additionally, it uses voice communication between train drivers and operators in the control centres. Therefore, for this type of service, traditional communication systems based on analogical technology remain significant.

The second group of services requires the exchange of information in the form of "data" between the trains and the control centres. In this case, the new services use any of the wireless technologies mentioned so far, but on an exclusive basis, which means that each application deployed on the train must be equipped with its own wireless communications hardware. This leads to have an excessive number of communications devices, often underused. In addition, there are still many applications that require a physical connection "through a wire" between the train devices and a computer for information retrieval and updating tasks.

On the other hand, a new set of services around the end user (passenger, or companies who need to transport some goods) is emerging. These services are oriented to providing a transport service of higher quality that not only is safe, but provides additional benefits such as: detailed information about the location of trains and schedules, contextual advertising services, video on demand, and so on. All these services are characterized by their need of a wireless communication channel with high bandwidth and extensive coverage (Garstenauer & Pocuca, 2011). As a result, the following needs are identified: (1) to standardize the way to exchange train state information between the trains and the control centres; and (2) to define a wireless communications architecture suitable for the new 'end user'-oriented services (Aguado et al., 2005).

In this chapter, a specific communications architecture based on standard technologies and protocols; that is designed to manage train-to-earth connectivity at application layer, will be presented in order to fulfil such needs.
