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(56k) modems. Both connect to the Internet in different ways and with

different levels of connection speed.

2.Dial-up modems are the older of the two types of internal modems. They are often called 56k modems in reference to their maximum connection speed over a dial-up connection. These modems are either wired directly to the motherboard or are removable PCI cards that connect to a PCI card slot inside the computer.

3.Connection to the Internet is accomplished by connecting a standard telephone line to the modem's jack. The other end connects to a phone jack in a home or office. When connecting to the Internet, this modem dials out to a number issued by the Internet service provider. Data travels back and forth over the telephone line.

4.Wifi (wireless modems) are wireless cards built into a computer, commonly found in laptop computers. Older desktop computers may utilize a wireless network card installed in a PCI slot to access wireless networks.

5.Wireless modems connect to the Internet by picking up a signal from nearby wireless routers. These routers may be connected directly to a cable or DSL modem and allow computers with WiFi to connect through the router to the modem's Internet connection.

6.Sometimes an Internet service provider offers WiFi Internet on a larger scale, and the computer connects to a wireless network that is not linked directly to a cable or DSL modem.

7.WiFi modems connect to high-speed Internet connections provided by cable Internet, DSL Internet, Fios, or satellite connections. Dial-up modems provide access to slower connections that connect through telephone lines, linking them to nearby computer network centers.

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8.The time it takes to connect to a wireless network is generally quicker than a dial-up connection, and the data transfer time on a wireless modem is usually quicker than dial-up, depending on Internet traffic and network conditions.

9.WiFi modems can also connect to unsecured wireless networks that do not require an account or password to log on to the Internet. This allows users with a WiFi modem to potentially get free Internet access if an unsecured network is nearby.

10.Many computers today, both desktops and laptops, come equipped with Ethernet Network cards that allow them to be connected directly to Local Area Networks (LANs), such as those found in offices and dorm settings. These Ethernet cards also allow connections to wired routers in the home as well as a direct connection to a cable or DSL modem in the home or office.

11.When determining if a computer has an internal or internal modem, a computer owner may assume that their Ethernet card or port is an internal modem, when it is just a way to connect the computer to a high-speed external modem or network jack. (From www.eHow.com)

Differences Between an External & Internal Modem

A modem is a computer device that allows you to browse the Internet or a network. Modems can send or receive faxes and telephone calls. Most personal computers have an internal modem installed inside the computer case. External modems are portable devices that you can attach to a serial or USB (Universal Serial Bus) port on your computer. External modems can be disconnected from your computer and used with other computers.

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2.Internal modems are built into the motherboard or a circuit board that plugs into an expansion slot inside a computer. Internal modems are also known as analog or dial-up modems. Modern analog modems transfer information at about 56 kilobits per second (56K) over a telephone line.

3.Analog dial-up modems are susceptible to phone-line noise or interference from electrical devices and slower Internet connection speeds. However, 56K dial-up modems can be used anywhere a phone line is available.

4.Also, internal and external modems can be used to establish a wireless dial-up connection. With the support of special hardware, such as a Network Interface Card (NIC) and wireless router, several computers can share information on a network.

5.Today, several types of external modems are used for highspeed and broadband Internet connections. They are much faster than phone-line modems and you can receive information up to 100 times faster.

6.Cable modems allow you to connect to the Internet with a coaxial cable. Contact a cable company to find out if they provide this type of service for your area.

7.Digital-subscriber-line (DSL) modems allow you to connect to the Internet using a digital phone line. Contact your telephone company to find out if they provide high-speed digital phone-line service. Satellite modems allow you to connect to the Internet via satellite. They are most useful when you are unable to access the Internet from a phone line, cable or DSL connection.

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8.Wireless PC cards are external devices with modem capabilities. PC cards use radio signals to access the Internet by a wired or wireless network connection.

9.The advantage of high-speed and broadband connections is 24-hour Internet access. You won't receive a busy signal and don't have to wait to establish an Internet connection. Your standard phone line is available to accept or receive telephone calls. Web browsing is faster and significantly improved. Streaming videos and audio files download more smoothly with fewer interruptions.

10.Keep in mind, high-speed and broadband modems are always turned on, and over time, they can wear out. Typically, the lifetime of an external modem is about two to five years, depending upon the make and model. If your modem develops problems, you should contact your Internet service provider and ask for a replacement. (From www.eHow.com)

Wireless Modems

1. In the past, analog cellular phones used a landline modem for dial-up connection. This connection was as slow as 2.5 kb/second, and sometimes even slower. The generation of digital cellular phones offered faster connections, which improved up to 4 times faster during the 2G (Second Generation) era. After that, HSCSD (High-Speed CircuitSwitched Data) was developed to provide multiple GSM (Global System for Mobile) channel support. Because of this improvement, speed began ranging from 40 kb/sec to 45 kb/sec. However, these technologies required dial-up ISP (Internet Service Provider), which was provided by mobile phone networks.

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2.Shortly after the reign of 2G phones, 2.5G phones emerged. The latter had help options for packet data. It means that 2.5G networks split digital voice and other data into little amounts and they are mixed simultaneously in the network. This process of splitting and mixing is referred to as packet-switching. The technology permits the phone to have data and voice connection simultaneously.

3.This makes surfing the Internet using a mobile phone possible. A personal computer can even use that same mobile phone if it wishes to connect to the Internet. The PC just needs a special number, which it needs to “dial” before it gets admission with the packet data. The mobile phone, used as the wireless modem, now handles the data exchange in the network. Its speed can reach up to 50 kb/second.

4.The most common use of wireless modems are for an Internet connection arrangement you know as Wi-Fi. Contrary to popular belief, the term Wi-Fi does not mean “wireless fidelity”. Wi-Fi is simply a trademark name given by an alliance (Wi-Fi alliance) whose members are also part of the IEEE (Institute of Electrical and Electronics Engineers).

5.Wireless modems operate at very little frequencies, giving laptops, PDAs or personal computers access point towards a network. A lot of people prefer using wireless modems because the speeds by which they operate are exponentially greater than dial-up modems and

even broadband Internet. (From http://www.symatech.net/wireless-modem)

Mobile phones (Text 1)

1. A mobile phone (also called mobile, cellular telephone, cell

phone, handphone or handy) is an electronic device used for two-way

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radio telecommunication over a cellular network of base stations known as cell sites. Mobile phones differ from cordless telephones, which only offer telephone service within limited range through a single base station attached to a fixed land line, for example within a home or an office.

2.A mobile phone allows its user to make and receive telephone calls to and from the public telephone network which includes other mobiles and fixed-line phones across the world. It does this by connecting to a cellular network owned by a mobile network operator. A key feature of the cellular network is that it enables seamless telephone calls even when the user is moving around wide areas via a process known as handoff or handover.

3.In addition to being a telephone, modern mobile phones also support many additional services, and accessories, such as SMS (or text) messages, e-mail, Internet access, gaming, Bluetooth and infrared short range wireless communication, camera, MMS messaging, MP3 player, radio and GPS. Low-end mobile phones are often referred to as feature phones, whereas high-end mobile phones that offer more advanced computing ability are referred to as smartphones.

Mobile phones (Text 2)

1. The first handheld mobile phone was demonstrated by Dr. Martin Cooper of Motorola in 1973, using a handset weighing 2 kg (4.4 lb). Motorola released the first commercially available mobile phone, the DynaTAC 8000x, in 1983. In the year 1990, 12.4 million people worldwide had cellular subscriptions. By the end of 2009, only 20 years later, the number of mobile cellular subscriptions worldwide reached approximately 4.6 billion, 370 times the 1990 number, penetrating the

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developing economies and reaching the bottom of the economic pyramid.

2. The recently released 4th generation, also known as Beyond 3G, aims to provide broadband wireless access with nominal data rates of 100 Mbit/s to fast moving devices, and 1 Gbit/s to stationary devices defined by the ITU-R 4G systems may be based on the 3GPP LTE (Long Term Evolution) cellular standard, offering peak bit rates of 326.4 Mbit/s. It may perhaps also be based on WiMax or Flash-OFDM wireless metropolitan area network technologies that promise broadband wireless access with speeds that reaches 233 Mbit/s for mobile users. The radio interface in these systems is based on all-IP packet switching, MIMO diversity, multi-carrier modulation schemes, Dynamic Channel Assignment (DCA) and channel-dependent scheduling. A 4G system should be a complete replacement for current network infrastructure and is expected to be able to provide a comprehensive and secure IP solution where voice, data, and streamed multimedia can be given to users on a "Anytime, Anywhere" basis, and at much higher data rates than previous generations. Sprint in the US has claimed its WiMax network to be "4G network" which most cellular telecoms standardization experts dispute repeatedly around the world. Sprint's 4G is seen as a marketing gimmick as WiMax itself is part of the 3G air interface. The officially accepted, ITU ratified standards-based 4G networks are not expected to be commercially launched until 2011.

Serial Communications

1. Most digital messages are vastly longer than just a few bits. Because it is neither practical nor economic to transfer all bits of a long

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message simultaneously, the message is broken into smaller parts and transmitted sequentially. Bit-serial transmission conveys a message one bit at a time through a channel. Each bit represents a part of the message. The individual bits are then reassembled at the destination to compose the message. In general, one channel will pass only one bit at a time. Thus, bit-serial transmission is necessary in data communications if only a single channel is available. Bit-serial transmission is normally just called serial transmission and is the chosen communications method in many computer peripherals.

2.Byte-serial transmission conveys eight bits at a time through eight parallel channels. Although the raw transfer rate is eight times faster than in bit-serial transmission, eight channels are needed, and the cost may be as much as eight times higher to transmit the message. When distances are short, it may nonetheless be both feasible and economic to use parallel channels in return for high data rates. The popular Centronics printer interface is a case where byte-serial transmission is used. As another example, it is common practice to use a 16-bit-wide data bus to transfer data between a microprocessor and memory chips; this provides the equivalent of 16 parallel channels. On the other hand, when communicating with a timesharing system over a modem, only a single channel is available, and bit-serial transmission is required.

3.The baud rate refers to the signalling rate at which data is sent through a channel and is measured in electrical transitions per second. In the EIA232 serial interface standard, one signal transition, at most, occurs per bit, and the baud rate and bit rate are identical. In this case, a rate of 9600 baud corresponds to a transfer of 9,600 data bits per second with a bit period of 104 microseconds (1/9600 sec.). If two

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electrical transitions were required for each bit, as is the case in non- return-to-zero coding, then at a rate of 9600 baud, only 4800 bits per second could be conveyed. The channel efficiency is the number of bits of useful information passed through the channel per second. It does not include framing, formatting, and error detecting bits that may be added to the information bits before a message is transmitted, and will always be less than one.

4.The data rate of a channel is often specified by its bit rate (often thought erroneously to be the same as baud rate). However, an equivalent measure channel capacity is bandwidth. In general, the maximum data rate a channel can support is directly proportional to the channel's bandwidth and inversely proportional to the channel's noise level.

5.A communications protocol is an agreed-upon convention that defines the order and meaning of bits in a serial transmission. It may also specify a procedure for exchanging messages. A protocol will define how many data bits compose a message unit, the framing and formatting bits, any error-detecting bits that may be added, and other information that governs control of the communications hardware. Channel efficiency is determined by the protocol design rather than by digital hardware considerations. Note that there is a tradeoff between channel efficiency and reliability - protocols that provide greater immunity to noise by adding error-detecting and -correcting codes must necessarily become less efficient.

Asynchronous vs. Synchronous Transmission

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1. Serialized data is not generally sent at a uniform rate through a channel. Instead, there is usually a burst of regularly spaced binary data bits followed by a pause, after which the data flow resumes. Packets of binary data are sent in this manner, possibly with variable-length pauses between packets, until the message has been fully transmitted. In order for the receiving end to know the proper moment to read individual binary bits from the channel, it must know exactly when a packet begins and how much time elapses between bits. When this timing information is known, the receiver is said to be synchronized with the transmitter, and accurate data transfer becomes possible. Failure to remain synchronized throughout a transmission will cause data to be corrupted or lost.

2.Two basic techniques are employed to ensure correct synchronization. In synchronous systems, separate channels are used to transmit data and timing information. The timing channel transmits clock pulses to the receiver. Upon receipt of a clock pulse, the receiver reads the data channel and latches the bit value found on the channel at that moment. The data channel is not read again until the next clock pulse arrives. Because the transmitter originates both the data and the timing pulses, the receiver will read the data channel only when told to do so by the transmitter (via the clock pulse), and synchronization is guaranteed.

3.Techniques exist to merge the timing signal with the data so that only a single channel is required. This is especially useful when synchronous transmissions are to be sent through a modem. Two methods in which a data signal is self-timed are nonreturn-to-zero and biphase Manchester coding. These both refer to methods for encoding a data stream into an electrical waveform for transmission.

4.In asynchronous systems, a separate timing channel is not used. The transmitter and receiver must be preset in advance to an

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