Dual-tone multi-frequency signaling (DTMF)

Dual-tone multi-frequency signaling (DTMF) is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communications devices and the switching center.

When we consider dialing numbers in the telephone now days commonly uses DTMF. Using DTMF (dual tone multi frequency) when we press a key on our phone, it generates two tones of specific frequencies. Then the signal is encoded as a pair of sinusoidal (sine wave) tones from the table below which are mixed with each other. The mixed frequency is traveled to the exchange.

DTMF

Advantages of DTMF compare to Rotary Dialing 

The main advantage is easy to access the phone when we are taking a call. But using rotary dialing hard to make a call.

When we are taking a call, in rotary dialing we have to rotate the numbers. Rotary dial pulses cannot pass through a central exchange. It is time consuming. Normally it takes an average of about 1.5 seconds per digit, or 15 seconds for dialing a 10-digit number. But DTMF tones can pass through a central exchange. It is recognized by the register at the central exchange. A DTMF tone must be present for a minimum of 40 ms. Between two consecutive digits, a pause of 60 ms is required. Total time needed for transmission of one digit is about 100 ms. Compare to rotary dialing it takes very much low of time .It is more efficient than rotary dialing.

WAN Technologies

Features of WAN

WAN is a network that spread over large geographical area. It uses several technologies to get that connectivity over vast area. From that connectivity we can have lot features in WAN. They are,

Circuit switching

Packet switching

Lease line

X.25

Frame relay

ATM

Circuit switching

Circuit switching involves creating a direct physical connection between sender and receiver. The connection must be set up before any communication can occur. A circuit-switched network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. 

Circuit switching

The sender and receiver can count on "owning" the bandwidth allotted to them for as long as they remain connected.

Packet switching

Packet switching is a WAN technology in which users share common carrier resources. Packet-switched describes the type of network in which relatively small units of data called packets are routed through a network based on the destination address contained within each packet. Packet Switching allows the same data path to be shared among many users in the network.

 

Packet Switching

 

The packet passes from exchange to exchange for delivery through the provider network. This data packets change the path dynamically. According to the traffic it changes the path.

Lease line

Lease line is used to provide point-to-point dedicated network connectivity. Analog leased line can provide maximum bandwidth of 9.6 Kbps. Digital leased lines can provide bandwidths: 64 Kbps, 2 Mbps (E1), 8 Mbps (E2), 34 Mbps (E3) ... Internet lease line is used to access internet with dedicate bandwidth.

X.25

X.25 Defines a telephone network for data communications. It provides users with WAN connectivity across public data networks (TELENET, TYMNET). Developed by common carriers to increase subscription to PDNs. Specification defines a point-to-point interaction between DTEs and DCEs for remote access terminals and computers.

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Usage of Microwave frequency & Wave length

Usage of Microwave frequency & Wave length

• Microwaves are electromagnetic waves with wavelengths ranging from 1 m down to 1 mm, or equivalently, with frequencies between 0.3 GHz and 300 GHz.
• The microwave range includes ultra-high frequency (UHF) (0.3–3 GHz), super high frequency (SHF) (3–30 GHz), and extremely high frequency (EHF) (30–300 GHz) signals.
• Wireless LAN protocols, such as Bluetooth and the IEEE 802.11 specifications, also use microwaves in the 2.4 GHz ISM band, although 802.11a uses ISM band and U-NII frequencies in the 5 GHz range.
• Cable TV and Internet access on coaxial cable as well as broadcast television use some of the lower microwave frequencies. Some mobile phone networks, like GSM, also use the lower microwave frequencies.
• Microwave radio is used in broadcasting and telecommunication transmissions because, due to their short wavelength, highly directive antennas are smaller and therefore more practical than they would be at longer wavelengths (lower frequencies). There is also more bandwidth in the microwave spectrum than in the rest of the radio spectrum; the usable bandwidth below 300 MHz is less than 300 MHz while many GHz can be used above 300 MHz.
• Most satellite communications systems operate in the C, X, Ka, or Ku Bands of the microwave spectrum. These frequencies allow large bandwidth while avoiding the crowded UHF frequencies and staying below the atmospheric absorption of EHF frequencies

Micro wave frequency ra