cnp3-ebook/protocols/lan — English @ Weblate

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126 ../../protocols/ethernet.rst:404

	English Another important advantage of Ethernet switches is the ability to create Virtual Local Area Networks (VLANs). A virtual LAN can be defined as a `set of ports attached to one or more Ethernet switches`. A switch can support several VLANs and it runs one MAC learning algorithm for each Virtual LAN. When a switch receives a frame with an unknown or a multicast destination, it forwards it over all the ports that belong to the same Virtual LAN but not over the ports that belong to other Virtual LANs. Similarly, when a switch learns a source address on a port, it associates it to the Virtual LAN of this port and uses this information only when forwarding frames on this Virtual LAN. 685/10000 · 685
127 ../../protocols/ethernet.rst:406

	English The figure below illustrates a switched Ethernet network with three Virtual LANs. `VLAN2` and `VLAN3` only require a local configuration of switch `S1`. Host `C` can exchange frames with host `D`, but not with hosts that are outside of its VLAN. `VLAN1` is more complex as there are ports of this VLAN on several switches. To support such VLANs, local configuration is not sufficient anymore. When a switch receives a frame from another switch, it must be able to determine the VLAN in which the frame originated to use the correct MAC table to forward the frame. This is done by assigning an identifier to each Virtual LAN and placing this identifier inside the headers of the frames that are exchanged between switches. 721/10000 · 721
128 ../../protocols/ethernet.rst:413

	English Virtual Local Area Networks in a switched Ethernet network 58/10000 · 58
129 ../../protocols/ethernet.rst:415

	English IEEE defined in the [IEEE802.1q]_ standard a special header to encode the VLAN identifiers. This 32 bit header includes a 12 bit VLAN field that contains the VLAN identifier of each frame. The format of the [IEEE802.1q]_ header is described below. 247/10000 · 247
130 ../../protocols/ethernet.rst:421

	English Format of the 802.1q header 27/10000 · 27
131 ../../protocols/ethernet.rst:423

	English The [IEEE802.1q]_ header is inserted immediately after the source MAC address in the Ethernet frame (i.e. before the EtherType field). The maximum frame size is increased by 4 bytes. It is encoded in 32 bits and contains four fields. The Tag Protocol Identifier is set to `0x8100` to allow the receiver to detect the presence of this additional header. The `Priority Code Point` (PCP) is a three bit field that is used to support different transmission priorities for the frame. Value `0` is the lowest priority and value `7` the highest. Frames with a higher priority can expect to be forwarded earlier than frames having a lower priority. The `C` bit is used for compatibility between Ethernet and Token Ring networks. The last 12 bits of the 802.1q header contain the VLAN identifier. Value `0` indicates that the frame does not belong to any VLAN while value `0xFFF` is reserved. This implies that 4094 different VLAN identifiers can be used in an Ethernet network. 969/10000 · 969
132 ../../protocols/wifi.rst:5

	English 802.11 wireless networks 24/10000 · 24
133 ../../protocols/wifi.rst:7

	English The radio spectrum is a limited resource that must be shared by everyone. During most of the twentieth century, governments and international organizations have regulated most of the radio spectrum. This regulation controls the utilization of the radio spectrum, in order to prevent interference among different users. A company that wants to use a frequency range in a given region must apply for a license from the regulator. Most regulators charge a fee for the utilization of the radio spectrum and some governments have encouraged competition among companies bidding for the same frequency to increase the license fees. 624/10000 · 624
134 ../../protocols/wifi.rst:9

	English In the 1970s, after the first experiments with ALOHANet, interest in wireless networks grew. Many experiments were done on and outside the ARPANet. One of these experiments was the `first mobile phone <http://news.bbc.co.uk/2/hi/programmes/click_online/8639590.stm>`_ , which was developed and tested in 1973. This experimental mobile phone was the starting point for the first generation analog mobile phones. Given the growing demand for mobile phones, it was clear that the analog mobile phone technology was not sufficient to support a large number of users. To support more users and new services, researchers in several countries worked on the development of digital mobile telephones. In 1987, several European countries decided to develop the standards for a common cellular telephone system across Europe : the `Global System for Mobile Communications` (GSM). Since then, the standards have evolved and more than three billion users are connected to GSM networks today. 979/10000 · 979
135 ../../protocols/wifi.rst:13

	English While most of the frequency ranges of the radio spectrum are reserved for specific applications and require a special license, there are a few exceptions. These exceptions are known as the `Industrial, Scientific and Medical <http://en.wikipedia.org/wiki/ISM_band>`_ (ISM) radio bands. These bands can be used for industrial, scientific and medical applications without requiring a license from the regulator. For example, some radio-controlled models use the 27 MHz ISM band and some cordless telephones operate in the 915 MHz ISM. In 1985, the 2.400-2.500 GHz band was added to the list of ISM bands. This frequency range corresponds to the frequencies that are emitted by microwave ovens. Sharing this band with licensed applications would have likely caused interference, given the large number of microwave ovens that are used. Despite the risk of interference with microwave ovens, the opening of the 2.400-2.500 GHz allowed the networking industry to develop several wireless network techniques to allow computers to exchange data without using cables. In this section, we discuss in more detail the most popular one, i.e. the WiFi [IEEE802.11]_ family of wireless networks. Other wireless networking techniques such as `BlueTooth <http://en.wikipedia.org/wiki/BlueTooth>`_ or `HiperLAN <http://en.wikipedia.org/wiki/HiperLAN>`_ use the same frequency range. 1365/10000 · 1365
136 ../../protocols/wifi.rst:15

	English Today, WiFi is a very popular wireless networking technology. There are more than several hundreds of millions of WiFi devices. The development of this technology started in the late 1980s with the `WaveLAN <http://en.wikipedia.org/wiki/WaveLAN>`_ proprietary wireless network. WaveLAN operated at 2 Mbps and used different frequency bands in different regions of the world. In the early 1990s, the IEEE_ created the `802.11 working group <http://www.ieee802.org/11/>`_ to standardize a family of wireless network technologies. This working group was very prolific and produced several wireless networking standards that use different frequency ranges and different physical layers. The table below provides a summary of the main 802.11 standards. 747/10000 · 747
137 ../../protocols/wifi.rst:19

	English Frequency 9/10000 · 9
138 ../../protocols/wifi.rst:19

	English Typical throughput 18/10000 · 18
139 ../../protocols/wifi.rst:19

	English Max bandwidth 13/10000 · 13
140 ../../protocols/wifi.rst:19

	English Range (m) indoor/outdoor 24/10000 · 24
141 ../../protocols/wifi.rst:22

	English 802.11 6/10000 · 6
142 ../../protocols/wifi.rst:22 • ../../protocols/wifi.rst:24 • ../../protocols/wifi.rst:25

	English 2.4 GHz 7/10000 · 7
143 ../../protocols/wifi.rst:22

	English 0.9 Mbps 8/10000 · 8
144 ../../protocols/wifi.rst:22

	English 2 Mbps 6/10000 · 6
145 ../../protocols/wifi.rst:22

	English 20/100 6/10000 · 6

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