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WISP Terminology: Understanding the Basics

Learn the essential terms used in the wireless internet service provider (WISP) industry. From access points to customer premises equipment, this guide will help you navigate the jargon.

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WISP Terminology: Understanding the Basics

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  1. Say What?????Defining WISP termsThe Basics Marlon K. Schafer Owner Odessa Office Equipment Box 489 Odessa Wa. 99159 Marlon K. Schafer (509-982-2181)

  2. Bio, Marlon K. Schafer Born and raised in the farming community of Odessa, WA.  After high school he entered the United States Air Force and became a Linesman. During his stint in the Air Force Marlon worked on overhead and under ground high voltage electrical distribution systems, security lighting, and runway lighting. Upon his Honorable Discharge in 1988 he returned to Odessa to help with the family specialty foods business.  In 1989 he and his wife moved to Spokane where Carr Sales, an electrical supply store, hired him.  Marlon went from delivery driver to rec. clerk to warehouse manager over the next couple of years, while also taking electronics classes. In 1991 he went to workfor a copier repair company where he serviced copiers, printers, faxes etc. until 1995. In1995 he and his family moved back to Odessa and launched Odessa Office Equipment. In 1998 he bought his second largest local copier competitor. In 1997 Odessa Office Equipment formed an Internet division offering local dialup services.  As a pioneer in the High-Speed Fixed Wireless Industry, Marlon designed and installed one of the first High-Speed Wireless DSL systems in the country and authored the Homebrew DSL page www.odessaoffice.com/sdsl.htm.  Since that time in early 2000 he's built 7 broadcast sites in 4 markets.  As CTO and part owner of KMS Wireless, Marlon has helped hundreds of other Internet Providers break into the WDSL game.  Marlon markets a wide range of wireless equipment and also provides design, installation, and troubleshooting services for most types of wireless systems. Marlon K. Schafer (509-982-2181)

  3. What’d he just say? • WISP: wireless internet service provider • That’s you! • AP: access pointAU: access unit (same as above) BU: base unit (same as above) • These are the broadcast or WISP side radios. • CPE: customer premises equipment • SU: subscriber unit, WB: Wireless Bridge, SA : Station Adapter (same as above, kinda) • This is the radio (and accessories) that the people paying you get. • EC : Ethernet converter • A device that turns an ethernet connection into a wireless one, usually associated with a particular Orinoco/Agere device. • OR: Outdoor Router, ROR: Remote Outdoor Router, COR: Central Outdoor Router • More Orinoco/Agere/Lucent specific nomenclatures. • LOS: Line of sight • This means that the two antennas can be seen visually from each end and have proper fresnel clearence. • NLOS: Near/non LOS • This means that even though you can’t see the other antenna the signal is bouncing around or penetrating well enough to get through in a usable form. • Mostly marketing drivel. • QAM: quadrature amplitude modulation • This deals with how the RF section of the radio deals with the packaging of the bit within a single 360* sine wave cycle. The higher the number the more data that can be sent and the more complex the transmission is. Marlon K. Schafer (509-982-2181)

  4. DefinitionsContinued • BWA: broadband wireless access • The correct term for what we do. We’re not just wireless (like the Cell phone guys are trying to be) and we’re not always fixed (see my t-1 to the cop car installs!). • PtMP: point-to-multipointPMP: Point-Multipoint • Any AP that talks to more than one remote radio. • PtP: Point-to-point • Any radio that talks to only one other radio (this includes the client side of a PTMP system). • DS (or DSSS): direct sequence spread spectrum • This refers to radio systems that use a set channel and are always on that channel (actually, multiple channels). • FH (or FHSS): frequency hopping spread spectrum • Radios that hop from channel to channel normally in a random pattern (can we even say that???). • RSSI: receive(r) signal strength index/indication • Indication of how much energy is making it from the remote end to the local end. This is normally listed as dB and will be a negative (-) number. Marlon K. Schafer (509-982-2181)

  5. DefinitionsContinued • WEP: wired equivalent privacy • Encryption mechanism for wireless networks. Long since hacked to death and almost totally insecure in relation to what it was designed to do. There are several other methods of doing this that work better and those mechanisms are moving into the main stream at this time. • WLL: wireless local loop (traditionally used for telephony voice circuits) • A local data circuit that uses Wireless rather than a t-1 or some such. • Backhaul/backbone • The system used to get your data from point A to point B. • Very closely related to WLL in most cases. • OFDM: orthonagol frequency division multiplexing • According to Mike Wollebin with Wi-Lan: OFDM is a way of using many carrier waves instead of using one, and using each carrier wave for only part of the message.  OFDM is also known as Multi-Carrier modulation.  Remember OFDM as a transmission scheme not a modulation technique.  Good analogy is the road Tollway.  Many lanes will allow more traffic to get through.  Also if some lanes are blocked traffic will still get through on the other lanes.  • VOFDM: vector OFDM • Ummmmm. Yeah. Marlon K. Schafer (509-982-2181)

  6. DefinitionsContinued • PAN: personal area network • VERY short range networks. Think Bluetooth. • IF: intermediate frequency • Carrier frequency used between the indoor and outdoor parts of a two piece radio system. • TDD: time division duplex • Typical WISP type radios. They use one channel for both sending and receiving. The two way conversation (duplex) part is done with time slots. • FDD: frequency division duplex • Typical backhaul radios. They transmit on one channel and receive on another one, at the same time. These make for very robust and very low latency links. • TDMA: time division multiple access • Polling mechanism. Each client gets a pre-determined time slot whether he’s got something to say or not. • CSMA/CA: carrier sense multiple access/collision avoidance • Each client hollers “listen to me” when he has something to say. • Sometimes this causes problems because too many clients try to get the Aps attention all at once. Marlon K. Schafer (509-982-2181)

  7. DefinitionsContinued • ISM: Industrial, Scientific, and Medical • That’s the FCC’s name for part of the radio spectrum that we work in. • Covers 902-928MHz, 2400-2483MHz (2.4 GHz), and 5725-5850 MHz (5.8 GHz). • There are several other frequencies allowed, you can get info on them at the GPO site: http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=47&PART=18&SECTION=301&YEAR=2001&TYPE=TEXT • UNII: Unlicensed-National Information Infrastructure • The other part of the radio spectrum we normally work with. • 5.15-5.35 GHz and 5.725-5.825 GHz bands • CDMA: code division multiple access • A protocol used by the cell phone industry. • GFSK: Gausian frequency shift keying • Most of what I found about this was related to Bluetooth. • It’s a modulation technique designed to help minimize interference, some kind of frequency hopping it looks like. Marlon K. Schafer (509-982-2181)

  8. DefinitionsContinued • BSS: basic service set • Network identifier. • ESSID: extended service set ID • More network identifier stuff, kinda like the workgroup name. • CIR: committed information rate • The minimum data rate promised by a provider. • MIR: maximum information rate • The maximum data rate allowed by a provider • ARQ: automatic retransmission queing • Automatically retransmits after an error. • This is (ideally) done before TCP/IP knows about the error. • ARS: automatic rate switching • See above. • I’m *guessing* that it’s the method of switching from one speed to another based on the success (or lack there of) of the last transmission. Marlon K. Schafer (509-982-2181)

  9. DefinitionsContinued • QoS: quality of service • A guarantee of service. Usually with a monetary penalty against the provider if the promise is not kept. • Like we’re going to offer a guarantee when using non-licensed radios! hehehe • CoS: class of service • Residential, business, old family friend etc. • EMI: electromagnetic interference • Energy that interrupts your signal. • Generic name for anything that messes with your system! • RFI: radio frequency interference • RF energy that interrupts your signal (see above). • IDU: indoor unit • The indoor half of a two part radio. • ODU: outdoor unit • Do you REALLY need me for this one????? Marlon K. Schafer (509-982-2181)

  10. DefinitionsContinued • dB: Decibel • The dB convention is an abbreviation for decibels. It is a mathematical expression showing the relationship between two values. • From Alexander Gram Bell. • RF Power Level • RF power level at either transmitter output or receiver input is expressed in Watts. • It can also be expressed in dBm. • The relation between dBm and Watts can be expressed as follows: PdBm = 10 x Log Pmw. For example: 1 Watt = 1000 mW; PdBm = 10 x Log 1000 = 30 dBm 100 mW;PdBm = 10 x Log 100 = 20 dBm. For link budget calculations, the dBm convention is more convenient than the Watts convention. • Got all that? • PoE: Power over Ethernet • A method of running power up an ethernet cable so that the radio can be mounted up by the antenna. Usually cheaper than running bigger coax. • PSU: Power Supply Unit • Any device that converts the building electrical power to the voltage needed for the device (in our case, radio). Marlon K. Schafer (509-982-2181)

  11. DefinitionsContinued • Attenuation: Loss of power • Expressed in dB. Attenuation is expressed in dB as follows:PdB = 10 x Log (Pout/Pin). For example: If, due to attenuation, half the power is lost (Pout/Pin = 2), attenuation in dB is 10 x Log (2) = 3dB. • Path Loss: Amount of signal that will be lost to attenuation on a given link. • Path loss is the loss of power of an RF signal travelling (propagating) through space (air or other objects). It is expressed in dB. • Path loss depends on: • 1. The distance between transmitting and receiving antennas. • 2. Line of sight clearance between the receiving and transmitting antennas. • 3. Antenna height. • Free Space Loss: Attenuation of the electromagnetic wave while propagating through space (that’s air in our case). • This attenuation is calculated using the following formula: Free space loss = 32.4 + 20xLog F(MHz) + 20xLog R(Km) F is the RF frequency expressed in MHz. R is the distance between the transmitting and receiving antennas. At 2.4 Ghz, this formula is: 100+20xLog R(Km). Marlon K. Schafer (509-982-2181)

  12. DefinitionsContinued • Isotropic Radiator: Theoretical antenna • A hypothetical, lossless antenna having equal radiation intensity in all directions. • Used as a zero dB gain reference in directivity calculation (gain). • The sun is often given as an example of an isotropic radiator. • Gain: The result of an antennas focusing of RF energy • Antenna gain is a measure of directivity. • It is defined as the ratio of the radiation intensity in a given direction to the radiation intensity that would be obtained if the power accepted by the antenna was radiated equally in all directions (isotropically). • Antenna gain is expressed in dBi. • Radiation Pattern: Where the antenna is going to make the RF go • The radiation pattern is a graphical representation in either polar or rectangular coordinates of the spatial energy distribution of an antenna. • Side Lobes: Radiation patterns that we wish weren’t here. • The radiation lobes in any direction other than that of the main lobe. Marlon K. Schafer (509-982-2181)

  13. DefinitionsContinued • Omni-directional Antenna: Omni = all • This antenna radiates and receives equally in all directions in azimuth. • Azimuth is toward the horizon. • Directional Antenna: Directional = less than all • This antenna radiates and receives most of the signal power in one direction. • Antenna Beamwidth: How much area will this antenna cover • The directiveness of a directional antenna. Defined as the angle between two half-power (-3 dB) points on either side of the main lobe of radiation. • Receiver Sensitivity: How well does that radio hear • The minimum RF signal power level required at the input of a receiver for certain performance (e.g. > BER). • EIRP: effective isotropic radiated power • This is the total output of a system/device. • It can be measured as dBm, dBd, or dBi depending on what you are measuring. Marlon K. Schafer (509-982-2181)

  14. DefinitionsContinued • EIRP: Effective Isotropic Radiated Power • The antenna transmitted power. • Equal to the transmitted output power minus cable loss plus the transmitting antenna gain. • EIRP = Pout - Ct + Gt Pout = Output power of transmitted in dBm Ct = Transmitter cable attenuation in dB Gt = Transmitting antenna gain in dBi Gr = Receiving antenna gain in dBi Pl = Path loss in dB Cr = Receiver cable attenuation is dB Si = Received power level at receiver input in dBm Ps = Receiver sensitivity is dBm Si = Pout - Ct + Gt - Pl + Gr - Cr Example: Link Parameters: Frequency: 2.4 Ghz Pout = 4 dBm (2.5 mW) Tx and Rx cable length (Ct and Cr) = 10 m. cable type RG214 (0.6 dB/meter) Tx and Rx antenna gain (Gt and Gr) = 18 dBi Distance between sites = 3 Km Receiver sensitivity (Ps) = -84 dBm. • Link Budget Calculation EIRP = Pout - Ct + Gt = 16 dBm Pl = 32.4 + 20xLog F(MHz) + 20xLog R(Km) @ 110 dB Si = EIRP - Pl + Gr - Cr = -82 dBm • In conclusion, the received signal power is above the sensitivity threshold, so the link should work. The problem is that there is only a 2 dB difference between received signal power and sensitivity. Normally, a higher margin is desirable due to fluctuation in received power as a result of signal fading. Marlon K. Schafer (509-982-2181)

  15. DefinitionsContinued • Signal Fading: Fading of the RF signal • Caused by several factors: • 1. Multipath: The transmitted signal arrives at the receiver from different directions, with different path lengths, attenuation and delays. The summed signal at the receiver may result in an attenuated signal. • 2. Bad Line of Sight: An optical line of sight exists if an imaginary straight line can connect the antennas on either side of the link. Radio wave clear line of sight exists if a certain area around the optical line of sight (Fresnel zone) is clear of obstacles. A bad line of sight exists if the first Fresnel zone is obscured. • 3. Link Budget Calculations (too little signal to start with). • 4. Weather conditions (Rain, wind, etc.) At high rain intensity (150 mm/hr that’s 6 inches per hour!), the fading of an RF signal at 2.4 Ghz may reach a maximum of 0.02 dB/Km. • 5. Wind may cause fading due to antenna motion. • 6. Interference: Interference may be caused by another system on the same frequency range, external noise, or some other co-located system. • The Line of Sight Concept: • An optical line of sight exists if an imaginary straight line can be drawn connecting the antennas on either side of the link. Clear Line of Sight: A clear line of sight exists when no physical objects obstruct viewing one antenna from the location of the other antenna. A radio wave clear line of sight exists if a defined area around the optical line of sight (Fresnel Zone)is clear of obstacles. Marlon K. Schafer (509-982-2181)

  16. DefinitionsContinued • Fresnel Zone: pronounced: fruh nell • The Fresnel zone is the area of a circle around the line of sight. • The Fresnel Zone is defined as follows: R1 = ½ square root of (lxD) R: radius of the first fresnel zone l: wavelength D: distance between sites. • FSO: Free Space Optical • Laser or infrared systems Marlon K. Schafer (509-982-2181)

  17. DefinitionsContinued I didn’t have time or energy to get into more general networking terms. I’ll work on that someday and get the whole list posted to www.odessaoffice.com/wireless (DHCP, PPP,PPPoE,RIP,BGP,OSPF,etc) SNMP: Simple Network Management Protocol  ( Security Not My Problem :-)MIB: Management Information Base Marlon K. Schafer (509-982-2181)

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