Bra att veta om trådlöst PDF generated using the open source mwlib toolkit. See http://code.pediapress.com/ for more information. PDF generated at: Mon, 03 Jan 2011 16:47:12 UTC Contents Articles Comparison of mobile phone standards 1 3G 6 CDMA2000 11 3GPP Long Term Evolution 13 Router 24 Machine-to-Machine 29 Input/output 32 RS-232 33 RS-422 42 EIA-485 44 Modbus 48 Virtual private network 53 Layer 2 Tunneling Protocol 58 Network address translation 63 Wi-Fi 70 Service set (802.11 network) 80 Wireless access point 82 Wired Equivalent Privacy 84 Wi-Fi Protected Access 88 Power over Ethernet 91 Antenna (radio) 98 References Article Sources and Contributors 114 Image Sources, Licenses and Contributors 118 Article Licenses License 120 Comparison of mobile phone standards 1 Comparison of mobile phone standards Global System for Mobile Communications (GSM, around 80–85 % market share) and IS-95 (around 10–15 % market share[1] ) are the two most prevalent mobile communication technologies. Both technologies have to solve the same problem: to divide the finite RF spectrum among multiple users. TDMA (Time Division Multiple Access—underlying technology used in GSM's 2G) does it by chopping up the channel into sequential time slices. Each user of the channel takes turns to transmit and receive signals. In reality, only one person is actually using the channel at a specific moment. This is analogous to time-sharing on a large computer server. CDMA (Code Division Multiple Access Underlying technology used in GSM's 3G and IS-95's 2G) on the other hand, uses a special type of digital modulation called spread spectrum which spreads the voice data over a very wide channel in pseudorandom fashion. The receiver undoes the randomization to collect the bits together and produce the sound. For comparison, imagine a cocktail party, where couples are talking to each other in a single room. The room represents the available bandwidth. In GSM, a speaker takes turns talking to a listener. The speaker talks for a short time and then stops to let another pair talk. There is never more than one speaker talking in the room, no one has to worry about two conversations mixing. In CDMA, any speaker can talk at any time; however each uses a different language. Each listener can only understand the language of their partner. As more and more couples talk, the background noise (representing the noise floor) gets louder, but because of the difference in languages, conversations do not mix. Comparison table Feature NMT GSM UMTS (3GSM) IS-95 (CDMA CDMA 2000 one) Technology FDMA TDMA W-CDMA CDMA CDMA Generation 1G 2G 3G 2G 3G Digital No Yes Yes Yes Yes Year of First Use 1981 1991 2001 1995 2000 / 2002 Worldwide market 0% 72% 12% 0.6% 12% share *Valid non-biased source still required Roaming Scandinavia Worldwide, 200+ Worldwide Limited Limited countries Handset None SIM card SIM card None RUIM (not interoperability commonly implemented) Operator locking Monopoly Unlockable Unlockable ESN ESN Common Interference None Interferes with some None None None electronics, such as amplifiers Comparison of mobile phone standards 2 Signal Good coverage Good coverage indoors Smaller cells and lower Unlimited cell Unlimited cell size, quality/coverage area due to low on 850/900 MHz. indoors coverage on size, low low transmitter power frequencies Repeaters possible. 2100 MHz; equivalent transmitter power permits large cells 35 km hard limit. coverage indoors and superior permits large cells range to GSM on 850/900 MHz. Frequency Very low density 0.2 MHz = 8 timeslots. 5 MHz = 2 Mbit/s. Each call ? Comparable to ? Comparable to utilization/Call density Each timeslot can hold uses 1.8-12 kbit/s depending UMTS UMTS up to 2 calls through on chosen quality and audio interleaving. complexity. Battery life Low, due to high Very good due to simple Lower due to high demands Lower due to high Lower due to high transmitter protocol, good coverage of WCDMA power control demands of demands of CDMA power (1 watt) and mature, and young chipsets. CDMA power power control and power-efficient chipsets. control. young chipsets. Handoff Hard Hard Soft Soft Soft Breathing No No Yes Yes Yes Intellectual property Scandinavian Concentrated among a Concentrated among a few Qualcomm Qualcomm telecom few manufacturers manufacturers operators Advantages of 2G GSM • GSM is mature; this maturity means a more stable network with robust features. • Less signal deterioration inside buildings. • Ability to use repeaters. • Talktime is generally higher in GSM phones due to the pulse nature of transmission. • The availability of Subscriber Identity Modules allows users to switch networks and handsets at will, aside from a subsidy lock. • GSM covers virtually all parts of the world so international roaming is not a problem. • The much bigger number of subscribers globally creates a better network effect for GSM handset makers, carriers and end users. Disadvantages of 2G GSM • Pulse nature of TDMA transmission used in 2G interferes with some electronics, especially certain audio amplifiers. 3G uses W-CDMA now. • Intellectual property is concentrated among a few industry participants, creating barriers to entry for new entrants and limiting competition among phone manufacturers. • GSM has a fixed maximum cell site range of 35 km, which is imposed by technical limitations.[2] Comparison of mobile phone standards 3 Advantages of IS-95 • Capacity is IS-95's biggest asset; it can accommodate more users per MHz of bandwidth than any other technology. • Has no built-in limit to the number of concurrent users. • Uses precise clocks that do not limit the distance a tower can cover.[3] • Consumes less power and covers large areas so cell size in IS-95 is larger. • Able to produce a reasonable call with lower signal (cell phone reception) levels. • Uses soft handoff, reducing the likelihood of dropped calls. • IS-95's variable rate voice coders reduce the rate being transmitted when speaker is not talking, which allows the channel to be packed more efficiently. • Has a well-defined path to higher data rates. Disadvantages of IS-95 • Most technologies are patented and must be licensed from Qualcomm. • Breathing of base stations, where coverage area shrinks under load. As the number of subscribers using a particular site goes up, the range of that site goes down. • Because IS-95 towers interfere with each other, they are normally installed on much shorter towers. Because of this, IS-95 may not perform well in hilly terrain. • IS-95 covers a smaller portion of the world, and IS-95 phones are generally unable to roam internationally. • Manufacturers are often hesitant to release IS-95 devices due to the smaller market, so features are sometimes late in coming to IS-95 devices. • Even barring subsidy locks, CDMA phones are linked by ESN to a specific network, thus phones are typically not portable across providers. Development of the Market Share of Mobile Standards This graphic compares the market shares of the different mobile standards. Cellphone subscribers by technology (left Y axis) and total number of subscribers globally (right Y axis) In a fast growing market, GSM/3GSM (red) grows faster than the market and is gaining market share, the CDMA family (blue) grows at about the same rate as the market, while other technologies (grey) are being phased out. Comparison of mobile phone standards 4 Comparison of wireless Internet standards As a reference, a comparison of mobile and non-mobile wireless Internet standards follows. Comparison of Mobile Internet Access methods ( ) Standard Family Primary Use Radio Tech Downlink Uplink Notes (Mbit/s) (Mbit/s) LTE UMTS/4GSM General 4G OFDMA/MIMO/SC-FDMA 100 (in 50 (in 20 LTE-Advanced update expected 20MHz MHz to offer peak rates of at least 1 bandwidth) bandwidth) Gbit/s fixed speeds and 100 Mbit/s to mobile users. WiMAX 802.16 Mobile Internet MIMO-SOFDMA 128 (in 56 (in WiMAX update IEEE 802.16m 20MHz 20MHz expected to offer peak rates of at bandwidth) bandwidth) least 1 Gbit/s fixed speeds and 100Mbit/s to mobile users. Flash-OFDM Flash-OFDM Mobile Internet Flash-OFDM 5.3 1.8 Mobile range 18miles (30km) mobility up to 10.6 3.6 extended range 34 miles (55km) 200mph 15.9 5.4 (350km/h) HIPERMAN HIPERMAN Mobile Internet OFDM 56.9 56.9 Wi-Fi 802.11 Mobile Internet OFDM/MIMO 288.9* Antenna, RF front end (11n) enhancements and minor protocol timer tweaks have helped deploy long range P2P networks compromising on radial coverage, throughput and/or spectra efficiency (310km [4] [5] & 382km ) (*can support 600 when set at 40MHz channel width). iBurst 802.20 Mobile Internet HC-SDMA/TDD/MIMO 95 36 Cell Radius: 3–12 km Speed: 250kmph Spectral Efficiency: 13 bits/s/Hz/cell Spectrum Reuse Factor: "1" EDGE Evolution GSM Mobile Internet TDMA/FDD 1.9 0.9 3GPP Release 7 UMTS UMTS/3GSM General 3G CDMA/FDD 0.384 0.384 HSDPA widely deployed. W-CDMA CDMA/FDD/MIMO 14.4 5.76 Typical downlink rates today 2 HSDPA+HSUPA 56 22 Mbit/s, ~200 kbit/s uplink; HSPA+ HSPA+ downlink up to 56 Mbit/s. UMTS-TDD UMTS/3GSM Mobile Internet CDMA/TDD 16 16 Reported speeds according to [6] IPWireless using 16QAM modulation similar to HSDPA+HSUPA 1xRTT CDMA2000 Mobile phone CDMA 0.144 0.144 Succeeded by EV-DO for data use, but still is used for voice and as a failover for EV-DO Comparison of mobile phone standards 5 EV-DO 1x Rev. 0 CDMA2000 Mobile Internet CDMA/FDD 2.45 0.15 Rev B note: N is the number of EV-DO 1x Rev.A 3.1 1.8 1.25 MHz chunks of spectrum EV-DO Rev.B 4.9xN 1.8xN used.