There are various ways in which digital networks can be classified, for example, by the services they offer (fixed and mobile telephony, television, information exchange); for its function in the network architecture (access networks, transport networks); by the population of users who use them (public, private, corporate, home networks); due to its geographical coverage. This last classification is very common in the literature, so it will be briefly presented.
Body Area Networks (BANs)
It is a recent concept in which devices use the human body as the transmission medium. Devices transmit information to each other simply by touching them. This technology must use low-power signals to reduce interference between devices and, above all, to avoid harmful effects on health. An advantage of the body as a means of transmission is that the information is not radiated into the environment. The Electronics and Telecommunications Research Institute of South Korea has developed a prototype that allows data to be exchanged at 5kb/s (IIET, 2005). This class of devices could be used to offer authentication services, electronic payment or clinical monitoring of patients. Its coverage area is a couple of meters.
Personal Area Networks (PANs)
They are typically wireless networks that interconnect computing devices in a small coverage area, around 10 meters. The first PAN networks used infrared links for interconnection, offering speeds of 2.4kb/s up to 16Mb/s in a range of up to one meter, but the devices had to have a direct path between them, that is, without objects obstructing it. This is known in telecommunications as line of sight (LOS).
Current standards, including IEEE 802.15.1, better known as Bluetooth, IEEE 802.15.4, called ZigBee 6, and Wireless USB7, do not require LOS. Bluetooth 2.0 offers speeds of 3Mb/s while WUSB reaches 110Mb/s over distances of 10 meters. ZigBee, more focused on device interconnection, is a very simple, low-cost, low-speed (up to 250 kb/s) and relatively secure network. All of them are designed to operate in ad-hoc mode, in which electronic devices connect to each other without user intervention. That is, the devices identify themselves to the network, request to join, receive an address, and establish communication on their own.
Local Area Networks (LANs)
They are the best known in organizations and, increasingly, in homes. They allow you to connect devices with a coverage of hundreds of meters up to a couple of kilometers. Historically, the dominant technology in these networks has been Ethernet, created by Robert Metcalfe at Xerox PARC laboratories in the mid-1970s (Metcalfe and Boggs, 1976), and standardized by the IEEE under the 802.38 working group.
In its first versions, the devices are connected to a shared medium (a coaxial cable, or a hub) in which the transmitted signal is broadcast, which can be heard by everyone. When a device wants to send information, it verifies that the medium is free and transmits it in a frame that has, among other fields, sender and receiver identifiers. The latter takes the middle plot; the others ignore her.
There is a possibility that two devices that want to transmit almost at the same time, listen to the medium, find it free and start their transmission, distorting the other’s signal. Senders are required to detect this phenomenon, called a collision, and should it occur, they abort the transmission and try again at a later time.
Campus Area Networks (CAN)
As local networks spread, the need arose to connect them to each other efficiently in areas that could span a few kilometers, such as hospitals, airports, university campuses, and corporate buildings. This interconnection could be done by means of ATM switches, or by means of specific technologies for this, such as FDDI (Fiber Distributed Data Interface). Currently, interconnection is usually through point-to-point links (typically optical links) between Ethernet switches or IP routers, so for many researchers this category is no longer relevant.
Wide Area Networks (WANs)
This category, which also includes Regional Area Networks (RANs), covers large areas, including several countries. Most of these networks are integrated into the transport infrastructure (wired) of the large operators. They typically consist of high-speed switching nodes interconnected with each other with fiber optic links using technologies such as ATM, SONET/SDH, and WDM.
The recently approved IEEE 802.22 standard (Cordeiro et. al., 2005), aims to provide fixed wireless access to regions with a radius of up to 100 km in areas with low population density. It uses unlicensed frequencies in the band originally established for television broadcasting. The standard makes use of cognitive spokes. It has the great advantage of not interfering with devices using licensed frequencies. This technology is of particular interest in developing countries and in rural areas.
Global Area Networks (GANs)
Global area networks cover an unlimited geographic area by interconnecting a large number of networks. This is the case of fixed telephone networks on a global scale, and almost fully integrated with their cellular counterparts. Another obvious example is the Internet, the great “network of networks”, which has gone beyond the borders of the earth with initiatives to launch space probes that use routers with the IP protocol to send information to the earth.
