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Internet service provider (abbr. ISP, also called Internet access provider or IAP) is a

 business or organization that sells to consumers access to the Internet and related

services. In the past, most ISPs were run by the phone company. Now, ISPs can be

started by just about any individual or group with sufficient money and expertise. In

addition to Internet access via various technologies such as dial-up and DSL, they may

 provide a combination of services including Internet transit, domain name registration

and hosting, web hosting, and colocation.

Contents

[hide]

• 1 ISP connection options

• 2 How ISPs connect to the Internet

• 3 Virtual ISP

• 4 Related services

• 5 See also

[edit] ISP connection options

ISPs employ a range of technologies to enable customers to connect to their network. For 

"home users", the most popular options include dial-up, DSL (typically ADSL),

Broadband wireless access, Cable modem, and ISDN (typically BRI). For customers who

have more demanding requirements, such as medium-to-large businesses, or other ISPs,

DSL (often SHDSL), Ethernet, Metro Ethernet, Gigabit Ethernet, Frame Relay, ISDN

(BRI or PRI), ATM, satellite internet access and SONET are more likely.

With the increasing popularity of downloading music and online video and the general

demand for faster page loads, higher bandwidth connections are becoming more popular.

[edit] How ISPs connect to the Internet

Just as their customers pay them for Internet access, ISPs themselves pay upstream ISPs

for Internet access. In the simplest case, a single connection is established to an upstream

ISP using one of the technologies described earlier in this article, and the ISP uses this

connection to send or receive any data to or from parts of the Internet beyond its own

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network; in turn, the upstream ISP uses its own upstream connections, or connections to

its other customers to allow the data to travel from source to destination.

In reality, the situation is often more complicated. For example, ISPs with more than one

Point of Presence (PoP) may have separate connections to an upstream ISP at multiplePoPs, or they may be customers of multiple upstream ISPs and have connections to each

one at one or more of their PoPs. ISPs may engage in peering, where multiple ISPs

interconnect with one another at a "peering point" or "Internet exchange" (IX), allowing

the routing of data between their networks, without charging one another for that data -

data that would otherwise have passed through their upstream ISPs, incurring charges

from the upstream ISP. ISPs who require no upstream, and have only customers and/or 

 peers, are called Tier 1 ISPs, indicating their status as ISPs at the top of the Internet

hierarchy. Routers, switches, Internet routing protocols, and the expertise of network 

administrators all have a role to play in ensuring that data follows the best available route

and that ISPs can "see" one another on the Internet.

[edit] Virtual ISP

virtual ISP (virtual Internet service provider, sometimes abbreviated as VISP or

vISP ) is a company that offers Internet services under its own company or

brand name, while actually using the equipment and facilities of another ISP 

to provide those services. A virtual ISP typically offers the all same services as

a regular ISP, such as Web hosting, e-mail, newsgroup access, domain name 

provision, and support. A number of real ISPs specialize in providing a virtual

ISP setup on a local or wider geographic basis. In some cases, the ISP offering

the virtual ISP setup can also handle billing and answer support calls for the

virtual ISP company under the virtual ISP name.

A Virtual ISP (vISP) purchases services from another ISP (sometimes called a wholesaleISP or similar within this context) that allow the vISP's customers to access the Internet

via one or more Points of Prescence (PoPs) that are owned and operated by the wholesale

ISP. There are various models for the delivery of this type of service, for example, the

wholesale ISP could provide network access to end users via its dial-up modem PoPs or 

DSLAMs(Digital Subscriber Line Access Multiplexer (DSLAM) is a network device,

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usually located at a telephone company central office, or within a neighborhood Serving

Area Interface (SAI) as part of a digital loop carrier , that receives signals from multiple

customer Digital Subscriber Line (DSL) installed in telephone exchanges, and route,

switch, and/or tunnel the end user traffic) to the vISP's network, whereupon they may

route the traffic toward its destination. In another model, the wholesale ISP does not route

any end user traffic, and needs only provide AAA (Authentication, Authorization and

Accounting) functions, as well as any "value-add" services like email or web hosting.

Any given ISP may use their own PoPs to deliver one service, and use a vISP model to

deliver another service, or, use a combination to deliver a service in different areas. The

service provided by a wholesale ISP in a vISP model is distinct from that of an upstream

ISP, even though in some cases, they may both be one and the same company. The

former provides connectivity from the end user's premises to the Internet or to the end

user's ISP, the latter provides connectivity from the end user's ISP to all or parts of therest of the Internet.

A vISP can also refer to a completely automated white label service offered to anyone at

no cost or for a minimal set-up fee. The actual ISP providing the service generates

revenue from the calls and may also share a percentage of that revenue with the owner of 

the vISP. All technical aspects are dealt with leaving the owner of vISP with the task of 

 promoting the service. This sort of service is however declining due to the popularity of 

unmetered internet access.

[edit] Related services

• Broadband access

o DSL

o Fixed wireless access

o Cable

o Triple play

DIAL_UP

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Refers to connecting a device to a network  via a modem and a public telephone network.

Dial-up access is really just like a phone connection, except that the parties at the two ends

are computer devices rather than people. Because dial-up access uses normal telephone

lines, the quality of the connection is not always good and data rates are limited. In the past,

the maximum data rate with dial-up access was 56 Kbps (56,000 bits per second), but new

An alternative way to connect two computers is through a leased line, which is a permanent

connection between two devices. Leased lines provide faster throughput and better

quality connections, but they are also more expensive.

Dial-up access is a form of data access (mainly used for  Internet access) in which the

client uses a modem to connect a computer to a telephone line and dials into an Internetservice provider 's (ISP) node to establish a modem-to-modem link, which is then routed 

to the Internet.

Modern dial-up modems typically have a maximum theoretical speed of 56 kbit/s

WIRELESS BROADBAND

Broadband wireless access is a technology aimed at providing high-speed wireless

access over a wide area from devices such as personal computers to data networks.According to the 802.16-2004 standard, broadband means 'having instantaneous

 bandwidth greater than around 1 MHz

DSL

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Here are some advantages of DSL:

• You can leave your Internet connection open and still use the phone line for voice calls.

• The speed is much higher than a regular modem

• DSL doesn't necessarily require new wiring; it can use the phone line you already have.

• The company that offers DSL will usually provide the modem as part of the installation.

Other types of DSL include:

• Very high bit-rate DSL (VDSL) - This is a fast connection, but works only over a short distance.

• Symmetric DSL (SDSL) - This connection, used mainly by small businesses, doesn't allow you to use the

phone at the same time, but the speed of receiving and sending data is the same.

• Rate-adaptive DSL (RADSL) - This is a variation of ADSL, but the modem can adjust the speed of the

connection depending on the length and quality of the line.

If you have read How Telephones Work, then you know that a standard telephone installation in the United Statesconsists of a pair of copper wires that the phone company installs in your home. The copper wires have lots of room for carrying more than your phone conversations -- they are capable of handling a much greater bandwidth, or range of frequencies, than that demanded for voice. DSL exploits this "extra capacity" to carry information on the wire withoutdisturbing the line's ability to carry conversations. The entire plan is based on matching particular frequencies to specifictasks.

To understand DSL, you first need to know a couple of things about a normal telephone line -- the kind that telephoneprofessionals call POTS, for Plain Old Telephone Service. One of the ways that POTS makes the most of the telephonecompany's wires and equipment is by limiting the frequencies that the switches, telephones and other equipment willcarry. Human voices, speaking in normal conversational tones, can be carried in a frequency range of 0 to 3,400 Hertz(cycles per second -- see How Telephones Work for a great demonstration of this). This range of frequencies is tiny. For example, compare this to the range of most stereo speakers, which cover from roughly 20 Hertz to 20,000 Hertz. And thewires themselves have the potential to handle frequencies up to several million Hertz in most cases.

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ISDN

Integrated Services Digital Network (ISDN) is a type of circuit switched telephone 

network system, designed to allow digital transmission of voice and data over ordinary

telephone copper wires, resulting in better quality and higher speeds than available with

analog systems. More broadly, ISDN is a set of  protocols for establishing and breaking

circuit switched connections, and for advanced call features for the user 

 Integrated Services refers to ISDN's ability to deliver at minimum two simultaneous

connections, in any combination of data, voice, video, and fax, over a single line.

Multiple devices can be attached to the line, and used as needed. That means an ISDN

line can take care of most people's complete communications needs, without forcing the

 purchase of multiple analog phone lines at a much higher transmission rate

Services Offered By ISDN

Normal Telephone & Fax (G3)

Digital Telephone -with a facility to identify the calling subscriber number and otherfacilities.

G4 FaxData Transmission at 64 Kbps with ISDN controller card

Video Conferencing at 128 KbpsVideo Conferencing at 384 Kbps (Possible with 3 ISDN lines)

Types of Accesses

There are two types of "accesses" (connections) for ISDN.

o Basic Rate Access(BRA): 2B+D2 Channels of 64 Kbps for Speech And Data.

1 Channel of 16 Kbps for Signalling

o Primary Rate Access (PRA): 30 B+D

30 Channels of 64 Kbps for speech and data.1 Channel of 64 Kbps for signalling.

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ISDN

ISDN Has emerged as a pow

worldwide for provisioning ofservices like voice, data and transmission over the teleph

through the telephone netwobeing viewed as the logical e

digitalization of telecommuniand most developed countrie

different stages of implemen

An ISDN subscriber can establish two simultaneous independent calls (except when the termina

such that it occupies two 'B' channels for one call itself like in video conferencing etc.) on existinthe telephone line (Basic rate ISDN) where as only one call is possible at present on the analog connection. The two simultaneous calls in ISDN can be of any type like speech, data, image etc.

time for a call between two ISDN subscribers is very short, of the order of 1 to 2 seconds. ISDN whole new set of additional facilities, called Supplementary Services.

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DIIFERENCE BETWEEN ISDN AND DSL

ISDN- ISDN generally comes in two flavors, 64 Kbps and 128 Kbps.

DSL- DSL is a scalable technology, with speeds ranging from 128Kbps to 1.5 Mbps

Second, ISDN can be more expensive than DSL

DSL utilizes the standard copper wiring already installed into businesses and homes,requiring no special line installation for service

ISDN utilizes copper wiring as well, but a special ISDN line must be installed at thecustomer’s location.

 Then ISDN connection charges vary, depending upon whether or not the customerrequires a dedicated, “always on” connection. Dedicated connections can get priceyas many ISDN packages are billed at a per-minute cost.

Special “dial-up ISDN” packages are available in most areas at a much lower cost and

can be a reasonable alternative in areas where DSL is not yet available

many DSL customers had problems with “cross-talk

And DSL still suffers from a distance limitation

In order to receive Asynchronous DSL (ADSL) service, a customer’s location must bewithin 18,000 feet (3 miles) of a central office (CO) of their local telephone serviceprovider