Internet access technology
Internet access technology is techniques that provide the connection types between user and internet service providers. The rapid growth of the Internet available to people has placed an increasing demand on telecommunications providers to supply faster data rates for private use. One of the currently popular solutions is Digital Subscriber Line (DSL) technology. These standards are often called xDSL because of many variations, permit rapid data communications over common telephone lines, often simultaneously permitting voice conversations.
DSL is one of the most important internet access technology. A major network company Aber, 2001 defines xDSL as the dedicated, point-to-point, public network access technologies which allow multiple forms of data, voice, and video to be carried over the twisted-pair copper wire on the local loop between a network service provider’s central office and the customer site.
The different types of Internet access technology are as below-
Public Switched Telephone System (PSTN / POTS) – Internet access technology
PSTN (Public Switched Telephone System) refers to the entire collection of voice-oriented circuit-switched telephone networks. The PSTN standards are governed by ITU-T (International Telecommunication Union-Telecommunication) standardization sector. PSTN provided a bi-directional or a two-way path to carry voice signals on a pair of copper wires. In the introductory phases of a PSTN, an operator used to manually connect the telephone wires to a switch and establish a connection between the telephone users.
PSTN gradually evolved into digital technology, except for the final link from the telephone office to the end-user. Manual switchboards were replaced by the automated telephone exchange. Mobile phones were also added to the PSTN network. Additional features like Voice mail, Caller ID, Call Waiting, and speed dialing were incorporated. Digitizing PSTN allows more voice calls over the same cable and reduces the per-minute cost for a telephone call. PSTN is also called POTS (Plain Old Telephone Service); largely due to the advent of newer telephony technologies like the VoIP and ISDN. PSTN or POTS is an important method of Internet access technology.
PSTN uses a 64 Kbps channel using an 8-bit Pulse Code Modulation of 8 kHz voice signals. PSTN provides the groundwork needed for long-distance internet infrastructure. The ISPS (Internet Service Provider) uses the copper wires to provide internet to the internet user by charging them on a monthly or hourly basis. In turn, ISPS Local Phone companies for using their infrastructure. The mode of internet access where the user uses a telephone to connect to the internet is known as Dial-up Access. Dial-up needs no other additional infrastructure other than the voice-carrying copper wires.
Dial-up connectivity is a slower mode of internet connectivity as compared to broadband. It uses a modem to establish connectivity between the user’s computer and the ISP through the telephone line. It is very similar to a voice-call phone connection, except that the sender and the receiver have a computer rather than a person. Once the connection is established and a ‘handshake’ between the two modems takes place, the data transmission and reception begin.
The dial-up connections have a speed limit of 56 Kbps, however, practically only 53 Kbps speed can be achieved. It also has several data communication standards like the V.34. V.90 and V.92. These standards the data transfer speeds of the dial-up connection. The V..34 limits the speeds to 33.6 Kbps, the V.90 modem to 49 Kbps, and the V.92 modem reduces the time required to connect to the internet by 50% and limits the speed to 49 Kbps.
xDSL- Digital Subscriber Line – Internet access technology
Digital Subscriber Line or DSL was started as a part of Integrated Services Digital Network or ISDN. The ISDN provides connectivity for all communication devices. As the name of Integrated Services Digital Network suggests the connectivity provided is completely digital in nature. DSL provides internet at high speed. Thus, it allows easy transfer of data over the internet. It also allows the user to utilize the phone and internet services simultaneously.
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Asymmetric Digital Subscriber Line (ADSL) – Internet access technology
The Asymmetric DSL provides an internet service that is asymmetric because it has different download and upload speeds. As mentioned in DSL, the ADSL may provide around 9 Mbps of download speed and 1 Mbps of upload speed. The download speed is the speed from NSP Central Office to the user’s computer. The upload speed is the speed from the user’s computer to the NSP Central Office. Thus, the users can download a lot of data in less time, but sending data is not so fast. ADSL technology is one of the most important Internet access technology.
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Broadband cable (Cable Modem)
Broadband means transmitting several data channels in one stream. Internet through cable is one of the most popular means of internet access today. Here ‘Cable’ refers to cable television. Broadband cable internet access utilizes the existing cable TV infrastructure. The unused bandwidth in the cable TV is used to deliver high-speed internet access through cable modems. The downstream speeds can range between 1 Mbps to 30 Mbps depending on whether the connection is a residential or a business connection. Hence the speed is more than 20 times of a dial-up connection. The upstream speeds can range up to 6 Mbps. The downstream data channel is 6 MHz and the upstream data channel is 2 MHz. The following figure shows the allocation of internet data channels in a cable wire.
The cable internet needs a cable modem at the customer’s end and a CMTS (Cable Modem Termination System) at the service provider’s end. The cable modem connects to the cable network using a standard coaxial cable. This cable is then connected to an Ethernet interface on the computer. CMTS is similar to the DSLAM in the DSL circuitry. CMTS routes the internet traffic between the internet users and the ISP. CMTS collects the data from all the users through a single channel and routes it to an ISP. The total available bandwidth is divided into time slices measured in milliseconds. CMTS enables more than 1000 users to receive data through a 6 MHz channel.
A cable modem consists of five blocks; Tuner, Modulator, Demodulator, MAC, and a Microprocessor. The tuner receives the modulated digital signal and passes it to the Demodulator. A tuner also contains a Diplexer which switches between Upstream and Downstream data transfer. A Modulator converts the digital signals from the computer to analog RF signals for transmission. At the receiving end or in the downstream mode, the Demodulator converts the analog signals to digital using an A/D converter.
The MẠC is an interface between the hardware and the software portions of the network protocols. It facilitates the upstream and downstream data transfer of the cable modem. The Microprocessor manages the MAC functions of a cable modem. To ensure compatibility and data security, the cable modems are subjected to a rigorous testing procedure to ensure the DOCSIS (Data over Cable Service Interface Standard). Once the DOCSIS is met, the products are CableLabs Certified.
Satellite internet access is one form of wireless internet access. It is preferred in locations where internet data cannot be delivered through the terrestrial lines; very useful for a customer who is staying too far or on the edge of the 18000 ft radius of DSL service and does not have a cable TV in the locality. Some investment in satellite internet equipment will eliminate the necessity of a wired internet connection. The satellite internet does not use telephone lines or cable systems but instead uses a satellite dish for two-way data communications.
Internet is provided directly from a Broadband IP uplink station to the internet user through a Satellite. Equipment at the user’s location consists of a dish antenna, a microwave receiver, and a digital decoder card which is plugged into the PC Computer Bus. The following figure gives an idea of internet access through satellite. Dish antennas are placed both on the reception and transmission end. The user sends the data from the computer to the dish antenna through a coaxial cable. The antenna then transmits the data to an Uplink station. The Uplink station then transmits the data to the satellite.
On the receiving end, the satellite sends the data to the Downlink station. The downlink station then sends the data to different dish antennas placed at the customer premises. The speeds delivered by the satellite internet may differ anywhere from 64 Kbps to 45Mbps. The satellites used for internet delivery can either be a single fixed-position satellite or clusters of satellites.