Friday, September 11, 2009

Internet connectivity mechanisms

Internet connectivity mechanisms



Now anybody can access the Internet and get it's benefit. There are several ways to connect to the Internet.

Dial-UP

ISDN

DSL

Cable connections

Wireless connections

T-1, T-2 and T-3 lines

Satellite




Dial-UP

  • Dialup is simply the application of the Public Switched Telephone Network (PSTN) to carry data on behalf of the end user. It involves a customer premises equipment (CPE) device sending the telephone switch a phone number to direct a connection to.

  • Speed ranges from 2400 bps to 56 Kbps

  • Twisted pair (regular phone lines) is the physical medium.

  • Cheap but slow compared with other technologies.

  • Speed may degrade due to the amount of line noise



ISDN

  • Integrated Services Digital Network is a telephone system network. ISDN is integrates speech and data on the same lines, adding features that were not available in the classic telephone system. access interfaces

    • Basic Rate Interface (BRI)

    • Primary Rate Interface (PRI)

    • Broadband-ISDN (B-ISDN)

  • Dedicated telephone line and router required.

  • Speed ranges from 64 Kbps to 128 Kbps.

  • Physical medium is Twisted pair.

  • Not available everywhere but becoming more widespread.

  • An ISDN line costs slightly more than a regular telephone line, but you get 2 phone lines from it.

  • 56K ISDN is much faster than a 56K dialup line



Digital subscriber line ( DSL )

  • Digital subscriber line ( DSL ) is more expensive than dialup, but provides a faster connection. DSL also uses telephone lines, but unlike dialup access, DSL provides a continuous connection to the Internet.

  • This connection option uses a special high-speed modem that separates the DSL signal from the telephone signal and provides an Ethernet connection to a host computer or LAN.

  • Doesn’t interfere with normal telephone use.

  • Bandwidth is dedicated, not shared as with cable.

  • Bandwidth is affected by the distance from the network hubs. Must be within 5 km (3.1 miles) of telephone company switch.

  • Limited availability.

  • Not networkable


Cable Internet

  • A cable Internet is a connection option offered by cable television service providers. The Internet signal is carried on the same coaxial cable that delivers cable television to homes and businesses.

  • A special cable modem separates the Internet signal from the other signals carried on the cable and provides an Ethernet connection to a host computer or LAN.

  • CMTS is the equipments provides the Cable Internet service to the users. It provides the same service which DSLAM offers.

  • 512 Kbps to 20 Mbps

  • Coaxial cable and in some cases telephone lines used for upstream requests as physical medium


Wireless

  • Access is gained by connection to a high speed cellular like local multi-point communications system (LMCS) network via wireless transmitter/receiver.

  • Speed is 30 Mbps or more

  • Physical medium is Airwaves (antenna)

  • Can be used for high speed data, broadcast TV and wireless telephone service.

Satellite

  • Satellite connection is an option offered by satellite service providers.

  • The user's computer connects through Ethernet to a satellite modem that transmits radio signals to the nearest Point of Presence, or POP, within the satellite network.

  • Newer versions have two-way satellite access, removing need for phone line.

  • In older versions, the computer sends request for information to an ISP via normal phone dial-up communications and data is returned via high speed satellite to rooftop dish, which relays it to the computer via a decoder box.

  • Speed is 30 Mbps or more

  • Physical medium is Airwaves (antenna)

  • Bandwidth is not shared.

  • Satellite companies are set to join the fray soon which could lead to integrated TV and Internet service using the same equipment and WebTV like integrated services

  • Latency is typically high

  • Some connections require an existing Internet service account.


Frame Relay

  • Provides a type of "party line" connection to the Internet.

  • Requires a FRAD (Frame Relay Access Device) similar to a modem, or a DSU/CSU.

  • speed ranges from 56 Kbps to 1.544 Mbps (or more, depending on connection type)

  • Various physical mediums used

  • May cost less than ISDN in some locations.

  • Limited availability.

  • Uses one of the connection types below, fractional up to OC3


Fractional T1 (Flexible DS1)

  • Only a portion of the 23 channels available in a T1 line is actually used.

  • Speed ranges from 64 Kbps to 1.544 Mbps

  • Physical medium is Twisted-pair or coaxial cable

  • Cheaper than a full T1 line with growth options of 56 Kbps or 64 Kbps increments as required.



T1

  • Special lines and equipment (DSU/CSU and router) required.

  • Speed 1.544 Mbps

  • Physical medium is Twisted-pair, coaxial cable, or optical fiber

  • Typically used for high bandwidth demands such as videoconferencing and heavy graphic file transfers.

  • Minimum for large businesses and ISPs.

  • Expensive


T3

  • Typically used for ISP to Internet infrastructure.

  • Speed 44.736 Mbps

  • Physical medium is Optical fiber


OC-1

  • Typically used for ISP to Internet infrastructure within Internet infrastructure.

  • Speed 51.84 Mbps

  • Physical medium is Optical fiber


OC-3

  • Typically used for large company backbone or Internet backbone.

  • Speed 155.52 Mbps

  • Physical medium is Optical fiber

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