VIA PÚBLICA, SEGURETAT, MOBILITAT I SERVEIS

As opposed to wired networks, wireless systems are far easier to deploy. Already widely deployed in Europe is the well-known DECT technology, notably for voice communication. For services other than voice, they can be divided into two categories: Wireless PANs and LANs.

Wireless Personal Area Networks (PANs) typically have a short range-of-use (10-100 meters), and are intended to set up connections between personal devices. The most widely

deployed standard in this class is Bluetooth. Its capability is providing 1 Mbit/s for few connected devices in a small network, called piconet. Its range is between 10 and 100 meters depending on the transmission power. The used transmission-band for Bluetooth lies in the 2.4 GHz ISM band (license-free).

The IEEE 802.15 standard is intended to go a step further. It integrates the Bluetooth standard and harmonizes it with the IEEE 802 family, such that it is IP and Ethernet compatible. The objectives are a high-bit rate solution (IEEE 802.15.3) providing up to 20 Mbit/s, and a low bit-rate one (IEEE 802.15.4, also known as ZigBee).

The HomeRF standard, like Bluetooth, also works in the 2.4 GHz ISM band. From an initial maximum data rate of 1.6 Mbit/s, it has been extended to 10 Mbit/s. HomeRF has a range of 50 meters at this speed. It is not interoperable with its strongest competitor, IEEE 802.11b (see below), however.

Wireless local area networks (LANs) have a broader application area: their purpose is to provide a wireless connection for networked devices like laptops or even handheld devices, not restricted to one person. The IEEE 802.11 series of standards are leading in this area: The IEEE 802.11b (WiFi) standard uses the 2.4 GHz band, and the IEEE 802.11a standard the 5 GHz band. Notably the 802.11b standard is gaining market share. Capabilities of 802.11 are to provide up to 54 Mbit/s over 300 meters distance. ETSI former Hiperlan2 standard has now merged with 802.11a, giving some features that were already considered like power control and QoS.

Concerning wireless networks to the home, the driving and most deployed systems are DVB- based access networks. Currently, they are mainly deployed through satellite transmission, for Digital TV broadcasting services. Interactive services are provided through the use of eg. telephone-lines for the (narrow-band) return channels. The technology has the main

characteristic to be a broadcast and reliable (with very low error rate) link supporting around 1Gbit/s in total, and thereby able to transport hundreds of compressed TV programs. In parallel, some data-based services can be carried, adding extra features around the TV programs, such as electronic program guides (EPGs) and encryption keys. For terrestrial transmission of digital TV, the DVB-T standard has been standardised and will be deployed in the near future progressively. Its purpose is the same, but the number of carried TV programs will be limited to about 40.

Some wireless fixed broadband-access solutions have also been standardised, with relatively poor success. The local multipoint distribution service (LMDS) is being used for point-to- multipoint applications, like Internet access and telephony. It only has a 3-mile coverage radius, however. The multichannel multipoint distribution service (MMDS) was initially used to distribute cable television service. Currently it is being developed for residential Internet service. However, installations have not been profitable and service delays have been widespread. Currently, new standards have being defined: e.g. the IEEE 802.16

(WirelessMAN) standard addresses metropolitan-area networks; amendment 802.16a expands the scope to licensed and license-exempt bands from 2 to 11 GHz. ETSI is following a similar track for Europe.

The following challenges can be seen for wireless home networks:

- To deal with governmental regulations that vary widely throughout the world, and prevent interference, especially in the license-free spectrum bands, to ensure optimal network performance.

- Power consumption for mobile devices: since wireless networks enable mobile applications, their success relies on the duration and limited weight of the devices

batteries. One of the requirements driving the development of Bluetooth was to have low- cost, low power consumption devices.

- To enable the use of wireless networks in consumer applications of every day life,

seamless integration of new devices is critical. This involves interoperability for both low level protocols (plug-and-play devices) as well as higher-level functionality.

- Wireless networks have specific features such as loss of packets and bit rate modifications that have a significant impact on some applications requiring a constant QoS such as video. Adaptation of data transport to the constraints of wireless networks with techniques such as error resilience, scalability or joint source-channel coding is therefore critical. Interworking and interoperability, as well as the seamless provision of services, independent of the underlying networks is the most challenging topic to be addressed in the access and home network environments. The standards arena of home networks is another area, which is currently too diversified and hence there is a number of proprietary technologies and

interfaces. This is not a cost-effective solution that can exist in the long term. 6.1.3.2.1 Heterogeneous in-home networks

From the previous sections it is clear that several technologies for in-home networking exist. These standards and technologies differ in:

- Application domain (home control, communication, infotainment, entertainment) - Middleware technology (HAVi, UPnP, Jini, etc.)

- Connection technology (based on new wiring (coax, twisted-pair, fibre), on existing wiring like power-line and phone-line, or wireless).

At least for the coming years, but even in the long run, there will not be a clear winner, and it is expected that several technologies will co-exist. Moreover, since there is no main player dominating the home infrastructure, all kind of technology combinations will co-exist within a single home network making it fully heterogeneous. This implies that networked devices, services and applications will only be successful, if they are prepared to run within a

heterogeneous environment. Therefore, a strong research need arises to develop bridges and gateways that can couple the different clusters in a heterogeneous home network.

The heterogeneity can appear both at the lower (data transport focused) and higher (middleware) layers of the ISO OSI protocol stack.

An overview of the various wired and wireless data transport focused standards we provided before. Here we focus on heterogeneity at the middleware layer, which means that different middleware standards are present dealing diversely with fundamental issues like:

- Device models and definitions - Resource management

- Event management - Stream management - Plug-and-Play mechanism - User-interface concepts

The available (combinations of) middleware standards heavily influence both the architecture of the devices, as well as the architecture of services and applications in the network.

To make a proper architectures for devices and applications it is essential to have adequate knowledge of the various middleware technologies they may end up working on. The state-of- the-art middleware technologies for entertainment/infotainment are: HAVi, UPnP, Jini, Bluetooth, WAP. They vary in the protocol stack, some of them like UPnP or Jini, are bound to a specific layer (network, eg. IP) in the OSI stack. Others, like HAVi, Bluetooth and WAP, are tightly coupled to a specific communication medium but stretch out far into the

application layers.

There is a pervasive use of sensors in all areas of our lives, and these will be increasingly miniaturised, equipped with embedded intelligence and capabilities for being networked so that they can communicate with other devices.

Besides the in-home networks, there are the various access networks to the outside world, via telephone, cable, satellite, etc. These will have different characteristics and have an impact on the provided external services. To make good architectures for devices and applications it is essential to have good knowledge of the properties from the different access networks and the services offered through them.

The following challenges can be seen for heterogeneous in-home networks:

- To deal with heterogeneity at lower layers requires development of bridging solutions, or a common network abstraction layer like IP

- To deal with heterogeneity at higher layers requires development of gateways coupling different middleware standards