Mobile modems and routers

Modems which use mobile phone lines (GPRS, UMTS, HSPA, EVDO, WiMax, etc.), are known as cellular modems. Cellular modems can be embedded inside a laptop or appliance, or they can be external to it. External cellular modems are datacards and cellular routers. The datacard is a PC card or ExpressCard which slides into a PCMCIA/PC card/ExpressCard slot on a computer. The best known brand of cellular modem datacards is the AirCard made by Sierra Wireless.[citation needed] (Many people just refer to all makes and models as AirCards, when in fact this is a trademarked brand name.)[citation needed] Nowadays, there are USB cellular modems as well that use a USB port on the laptop instead of a PC card or ExpressCard slot. A cellular router may or may not have an external datacard (AirCard) that slides into it. Most cellular routers do allow such datacards or USB modems, except for the WAAV, Inc. CM3 mobile broadband cellular router. Cellular Routers may not be modems per se, but they contain modems or allow modems to be slid into them. The difference between a cellular router and a cellular modem is that a cellular router normally allows multiple people to connect to it (since it can route, or support multipoint to multipoint connections), while the modem is made for one connection.

Most of the GSM cellular modems come with an integrated SIM cardholder (i.e., Huawei E220, Sierra 881, etc.) The CDMA (EVDO) versions do not use SIM cards, but use Electronic Serial Number (ESN) instead.

The cost of using a cellular modem varies from country to country. Some carriers implement flat rate plans for unlimited data transfers. Some have caps (or maximum limits) on the amount of data that can be transferred per month. Other countries have plans that charge a fixed rate per data transferred—per megabyte or even kilobyte of data downloaded; this tends to add up quickly in today's content-filled world, which is why many people are pushing for flat data rates.

The faster data rates of the newest cellular modem technologies (UMTS, HSPA, EVDO, WiMax) are also considered to be broadband cellular modems and compete with other broadband modems below.

RS-232

In telecommunications, RS-232 (Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). It is commonly used in computer serial ports. A similar ITU-T standard is V.24.



The standard does not define a maximum cable length but instead defines the maximum capacitance that a compliant drive circuit must tolerate. A widely-used rule-of-thumb indicates that cables more than 50 feet (15 metres) long will have too much capacitance, unless special cables are used. By using low-capacitance cables, full speed communication can be maintained over larger distances up to about 1,000 feet. For longer distances, other signal standards are better suited to maintain high speed.

Since the standard definitions are not always correctly applied, it is often necessary to consult documentation, test connections with a breakout box, or use trial and error to find a cable that works when interconnecting two devices. Connecting a fully-standard-compliant DCE device and DTE device would use a cable that connects identical pin numbers in each connector (a so-called "straight cable"). "Gender changers" are available to solve gender mismatches between cables and connectors. Connecting devices with different types of connectors requires a cable that connects the corresponding pins according to the table above. Cables with 9 pins on one end and 25 on the other are common. Manufacturers of equipment with 8P8C connectors usually provide a cable with either a DB-25 or DE-9 connector (or sometimes interchangeable connectors so they can work with multiple devices). Poor-quality cables can cause false signals by crosstalk between data and control lines (such as Ring Indicator).

Wi-Fi Card

PCI Card WiFi

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Wi-Fi is a trademark of the Wi-Fi Alliance for certified products based on the IEEE 802.11 standards. This certification warrants interoperability between different wireless devices.

In some countries (and in this article) the term Wi-Fi is often used by the public as a synonym for IEEE 802.11-wireless LAN (WLAN).

Not every IEEE 802.11 compliant device is certified by the Wi-Fi Alliance, which may be because of certification costs that must be paid for each certified device type. The lack of the Wi-Fi logo does not imply that a WLAN-device is incompatible to certified Wi-Fi-devices.

Wi-Fi is supported by most personal computer operating systems, many game consoles, laptops, smartphones, printers, and other peripherals.

Network card

Network card


PCI Wireles Network Card

Modem

Example image: Internal modem


Example image: External modem (Conexant V.9)

Modem (from modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data.