More Wi-Fi terms and definitions
Industrial wireless tutorials: We've recently received correspondence asking about several terms that were left out of our previous article dealing with Wi-Fi terms. Following are several terms for which a definition was specifically requested by a reader. Thanks for writing in.
Access point (AP): This device is the heart of a wireless network; when an AP powers up and begins transmitting, a wireless network exists. An access point is the portal by which a wireless device, or client, can access the network resources. A wireless router is an AP; however, an AP is not necessarily a router. An AP can also be a very simple radio transceiver that is either wired into the backbone or is meshed to other APs. An AP can be classified as thin or fat: in the former, the AP is just a radio transceiver, usually under the control of a centralized wireless network controller; in the latter, the AP contains considerable intelligence and can perform routing and security functions independently and autonomously.
Bridge: A device used to connect two networks or network segments, that is, a wireless to wired network. A bridge is also used to perform a protocol translation and allow seamless communication between the two network segments. Another type of bridge is called a "translational bridge" because it will translate from one type of protocol to another within the same network, such as would be the case of translating 802.15 data streams to 802.11 data streams. This is commonly done with WiHART based wireless instruments. Note that bridging is different from routing.
Cellular router: A specialized device that operates in the cellular bands to allow data traffic to associated devices. Typically, a cellular modem is some sort of dongle, which plugs into a USB or PCM port on a computer to allow wireless connectivity with a cellular network, or it can be a stand-alone unit. These devices work on different frequencies than Wi-Fi.
Gateway: A gateway is a device that connects a private network, such as your office or factory network, to an outside network such as the Internet; a gateway connects a local area network (LAN) to a wide area network (WAN). A gateway can combine several functions into one device, such as wireless and/or router functionality, and provide firewall protection, as well.
Industrial wireless routers, or industrial wireless access points, are generic terms. These devices are used to describe enterprise grade devices that may or may not be hardened to function in harsh environments, such as NEMA 4X or 7 rated areas. Any wireless router can be used for industrial purposes if it is capable of handling the type and amount of data you are trying to move around. Typically, an industrial grade access point can also function as a router, repeater, or a client.
Repeater: This device is used to extend the range of an access point, increasing the size of the basic service set, or BSS. A repeater works by associating with an AP on the same channel and simply repeating the transmissions. Repeaters should be used only when absolutely necessary for several reasons: because of the increased traffic between the AP and its repeater, data throughput becomes very slow; also, each time data is repeated, it experiences diminished throughput-typically, the limit is three repeats, or hops.
Wireless radios: This term is not used because radios are, by definition, wireless devices. As you can see, it is redundant. Every Wi-Fi device contains at least one radio.
Wireless client: This is the mobile device (actually any other wireless device) that is connected to a wireless network through an access point in order to access the network resources.
Wireless modem: Again, this term is really not used unless you are referring to a cellular modem. Modem is a contraction of the terms MODulate/DEModulate. All radio systems modulate data onto a carrier signal and then apply that modulated signal to an antenna; on the receiving end, the signal is captured by the antenna and demodulated. In a sense, any AP is a wireless modem. I will be explaining modulation techniques in a future article.
– Daniel E. Capano, owner and president, Diversified Technical Services Inc. of Stamford, Conn., is a certified wireless network administrator (CWNA). Edited by Chris Vavra, production editor, CFE Media, Control Engineering, firstname.lastname@example.org.
www.controleng.com/blogs has other wireless tutorials from Capano on the following topics:
Wi-Fi acronyms, wireless buzzwords, WLAN nomenclature, wireless terms
www.controleng.com/webcasts has wireless webcasts, some for PDH credit.
Control Engineering has a wireless page.