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Is Dsl Shared?

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I'm having a slight debate. I always thought DSL was dedicated until it hit the nearest ISP CO.

Here's what he's telling me:

Dslam in your neighborhood distributes shared resource. Backbone to CO varies.

You still get shared scrock.

Even with the fiber.

DSlams and fiber NIU still share LIMITED bandwidth between geographically dispersed areas and the CO.

You may get a fixed speed to the DSLAM, but the shit is shared with the other dslams in your neighborhood.

look at hotels as an example, many older hotels dont have CAT5 to the rooms so they use a small dsl router in the room.

they will employ a dslam in the computer room that distributes several hundred dsl connections to the individual hotel rooms. Each at say 2.5megs each.

The Dslam is behind a router with a T1 to the ISP.

That T1 is 1.544meg to the ISP, if the hotel is empty you will be rockin. If the hotel is filled with porn gobbling knuckle shufflers than your shared resources are diminished.

but they advertised 2.5meg in the room.

There is not a direct link from a neighborhood dslam to the CO, many neighborhood dslams are combined at say a street corner, then banked onto slick to a nearby ATM before they hit the CO.

All those "pipes" have purposely capped bandwidth limits.

from wiki

The DSLAM equipment at the telephone company (telco) collects the digital signals from its many modem ports and combines them into one signal via multiplexing. Depending on the product being used, a DSLAM would aggregate the DSL lines with some combination of Asynchronous Transfer Mode (ATM), frame relay, or Internet Protocol networks (i.e., IP-DSLAM that uses the PTM-TC stack)(Packet Transfer Mode - Transmission Convergence).

The aggregated signal is then loaded onto the telco's backbone switching equipment, traveling through an access network (AN)—also known as a Network Service Provider (NSP)—at speeds of up to 10 Gbit/s and connecting to the Internet-backbone.

Most dslams are at the street corner, in some underground utility box thing, then they take a ride on an ATM or alternate in bold above, before they get to the CO.

Still using switches, still routing using measured resources.

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Maybe this will clear it up


DSL service was first provided over a dedicated "dry loop", but when the FCC required the incumbent local exchange carriers ILECs to lease their lines to competing providers such as Earthlink, shared-line DSL became common. Also known as DSL over Unbundled Network Element , this allows a single pair to carry data (via a digital subscriber line access multiplexer [DSLAM]) and analog voice (via a circuit switched telephone switch) at the same time. Inline low-pass filter/splitters keep the high frequency DSL signals out of the user's telephones. Although DSL avoids the voice frequency band, the nonlinear elements in the phone would otherwise generate audible intermodulation products and impair the operation of the data modem.

In the early days, when you had ISDN (Individual Subscriber Digital Network) you had one pair for the Digital traffic and a separate pair of copper wires for the voice.

DSLAM or digital subscriber line access multiplexer refers to using a single pair of copper wires to carry both your voice traffic and your digital stream. It does not refer to your sharing your connection (wire) with your neighbors. With DSL you have a dedicated copper wire connection to the Central Office or its equivalent (often an underground vault in your neighborhood).

It also refers to the ATM (Asynchronous Transfer Mode) connection from the central office to the ISP. Many DSL customers may be bundled together at this point from the Central Office or switch (where the voice and data streams are separated) to their specific ISP (IE over the Telephone companies data network ).

You have a dedicated line up until the point where they put in a splitter to separate the voice and data streams. Then the voice is connected to the appropriate Telco telephone network, and the data is sent over a data connection of the telephone companies data network ( generally fiber or coax , and generally shared by multiple users just like any other part of the internet) to your ISP.


Gotta include this link



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I mostly just copy and pasted what you said and this is his reply:

No. ISDN is a 2 wire trunk, both BRI and PRI. Bri has 2 64k channel and a data channel that you can use to carry things like x.25.- like all the 7-11's used to do with cc processing over x.25.

PRI is 23 64k channels and a data channel.

Let me make my point so as you can understand it,

All of your neighbors crap terminates in the underground vault at the dslam. The dslam does not have UNLIMITED bandwidth to the Central office. The carrier for the ATM from the underground vault to the CO may not even be the ISP, but a 3rd party who charges for access and leases rackspace to the carrier.

It may not even be ATM, but on aging slick that occasionally slips a time slot.

The point is this, they are all prone to imperfections (dsl, fiber, cable, microwave) and unless you live within a mile from a central office they dont terminate there.

Even if you live a mile from a co, you may be routed through some jerkoffs ATM because they own the access rights to your geographic area.

To conclude, you may have the wicked awesome fiber from your house to the underground vault, which is incredibly awesometastic. But, the vault to the internet is a bottleneck that provides you the same server response time as cable or dsl. Its not like getting your own private point to point fiber optic connection to an OC3 backbone. Its still broadband speeds, thats all they will guarantee.

Most ISPs dont own their entire network. They pay for traffic to localized areas, like your underground vault.

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Eventually everyone shares a connection. With DSL it isn't until you join the main pipeline. Cable you share immediately with your neighbor. DSL speeds are more consistent with better latency than cable.

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Yep and then your ISP pays for access to a backbone and that backbone provider pays for access to other backbones etc.

The whole internet is a shared network eventually so why worry about it?

You have choices: DSL, Cable, Fiber, Wireless, Satellite.

You weigh the cost versus performance and choose the one which meets your needs.

You hope that when they sell you a package that they have taken into account the other customers which will eventually be sharing the connection and that you will get what you thought you would and they do not try imposing bandwidth caps and filters to limit you.

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