Technology

Switched vs. Leased Connections
  Switched-A switched connection is used on an as needed basis.   Either the user or the equipment must dial a number to connect to another user or equipment on the other end.  When the user or equipment is done exchanging information, the connection is terminated.
  Leased-A leased connection is always connected.  Once a leased connection is established, it stays connected until it is told to do otherwise.   Rather than the connection being determined by dialing, a leased connection is only between two predefined points.

Analog vs. Digital Connections
  Before you can understand how connections work, you must understand the difference between an analog signal vs. a digital signal. Traditional phone service was created to let you exchange voice information with other phone users and the type of signal used for this kind of transmission is called an analog signal. An input device such as a phone set takes an acoustic signal (which is a natural analog signal) and converts it into an electrical equivalent in terms of volume (signal amplitude) and pitch (frequency of wave change).  Since the telephone company's signaling is already set up for this analog wave transmission, it's easier for it to use that as the way to get information back and forth between your telephone and the telephone company. That's why your computer has to have a modem - so that it can demodulate the analog signal and turn its values into a string of 0 and 1 values that is called digital information.
  The ability of your computer to receive information quickly is constrained by the fact that regular modems put digital data into analog form for your telephone line and it requires your modem to change received data back into digital. In other words, the analog transmission between your home or business and the phone company is a bandwidth bottleneck. However, if the connections can be kept on digital signaling the entire way, it opens up the way for much higher connection speeds.

Switched Services

Analog Dial-up Access
  Dial-up access is the most common way for users to connect to other users anywhere in the world.  Nearly everything in the telecommunications industry uses some form of analog dial-up access, including cellular phones, voice mail, and Internet access.

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Switched 56
  Switched 56 is a digital 56K connection that can be used to connect to the Internet or to connect to corporate networks.  Switched 56 requires a special phone line and hardware at both ends of the connection.  Switched 56 is often used as a backup to leased line systems.

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ISDN
  ISDN stands for Integrated Services Digital Network and it allows for digital transmission over ordinary telephone copper wire. Home and business users who install ISDN adapters (in place of their modems) can see highly-graphic web pages arriving very quickly (up to128 Kbps). ISDN requires adapters at both ends of the transmission so your access provider also needs an ISDN adapter.  ISDN allows for simultaneous data and voice over one line, eliminating the need for two separate phone lines.

  Available now?    Call for availability at your location.

Leased Services

T-Carrier
  The T-carrier system is entirely digital, using pulse code modulation and time-division multiplexing. The system uses four wires and provides full-duplex capability (two wires for receiving and two for sending at the same time). The T-1 digital stream consists of 24 64-Kbps channels that are multiplexed. (The standardized 64 Kbps channel is based on the bandwidth required for a voice conversation.) The four wires were originally a pair of twisted-pair copper wires, but can now also include coaxial cable, optical fiber, digital microwave, and other media. A number of variations on the number and use of channels are possible.
  In the T-1 system, voice signals are sampled 8,000 times a second and each sample is digitized into an 8-bit word. With 24 channels being digitized at the same time, a 192-bit frame (24 channels each with an 8-bit word) is thus being transmitted 8,000 times a second. Each frame is separated from the next by a single bit, making a 193-bit block. The 192 bit frame multiplied by 8,000 and the additional 8,000 framing bits make up the T-1's 1.544 Mbps data rate. The signaling bits are the least significant bits per frame.

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Hybrid Services

DSL
  DSL (Digital Subscriber Line) is considered a hybrid service because it allows for switched analog dial-up access and it is also a leased line data service.   It is a technology for bringing high-bandwidth information to homes and small businesses over ordinary copper telephone lines.  The Delhi Telephone Company uses a variant of DSL called ADSL (Asymmetric Digital Subscriber Line).  ADSL is called "asymmetric" because most of its two-way or duplex bandwidth is devoted to the downstream direction, sending data to the user. Only a small portion of bandwidth is available for upstream or user-interaction messages. However, most Internet and especially graphics- or multi-media intensive Web data needs lots of downstream bandwidth, but user requests and responses are small and require little upstream bandwidth. Using ADSL, up to 6.1 megabits per second of data can be sent downstream and up to 640 Kbps upstream. The high downstream bandwidth means that your telephone line will be able to bring motion video, audio, and 3-D images to your computer or hooked-in TV set. In addition, a small portion of the downstream bandwidth can be devoted to voice rather data, and you can hold phone conversations without requiring a separate line.
  Unlike a similar service over your cable TV line, using ADSL, you won't be competing for bandwidth with neighbors in your area. In many cases, your existing telephone lines will work with ADSL.
  ADSL is coming soon to The Delhi Telephone Company.

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