DSL Variants Examples


- Key feature: Slow travel upstream (from subscriber to CO), fast travel downstream (from CO to subscriber)

- Key feature: Upstream and downstream speeds are the same

- Key feature: G.SHDSL is a new standard that was developed by the International Telecommunications Union (ITU) that addresses the worldwide SDSL market.

• Integrated Services Digital Network DSL (IDSL)

- Key feature: No call setup

- Key feature: Very high speed with shorter reach

- Key feature: Used to replace T1 or E1 service

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DSL variants include the following:

■ ADSL: With ADSL, the connection speed for downloading data is faster than the connection speed for uploading data. This type of DSL service is geared more toward a residential application, where the typical end user is not concerned with being able to send large amounts of data to the Internet. ADSL is perfect for common residential high-speed requirements, such as downloading music or movies, playing online games, surfing the Internet, or receiving large e-mail messages. ADSL provides slow upstream speed for uploading (sending) low-data-rate requests and fast downstream speed for downloading bursts of rich graphics and multimedia content

SDSL: With SDSL, the connection speed for downloading data is exactly the same as the connection speed for uploading data. This type of DSL service is ideal for a commercial application where the end user must send large amounts of data over the Internet. SDSL is perfect for applications such as sending large e-mail messages with attachments to customers, uploading information to a company or corporate server, or updating web pages.

■ G.SHDSL: A new standard, G.SHDSL, is a symmetric high-data-rate digital subscriber line, was developed by the International Telecommunication Union (ITU) that addresses the worldwide SDSL market. G.SHDSL is multirate, multiservice, extended reach, and repeatable. Supporting data rates from 192 kbps to 2.3 Mbps, G.SHDSL delivers approximately 30 percent greater reach than currently deployed DSL technologies and is expected to rapidly replace the proprietary SDSL implementations of today.

■ ISDN DSL (IDSL): IDSL is a cross between ISDN and DSL. Like ISDN, it uses a single wire pair to transmit full-duplex data up to 144 kbps. IDSL also uses a 2B1Q line code to enable transparent operation through the ISDN U interface. IDSL is essentially a leasedline ISDN BRI, or an ISDN BRI that is not switched and does not contain signaling (a data [D] channel). The line can be configured for a speed of 64 kbps, 128 kbps, or 144 kbps. IDSL carries only data, but is ideal for remote users because the signals can be repeated, as with ISDN, and because it is billed at a flat rate, thus avoiding per-call fees.

■ Very-high-data-rate digital subscriber line (VDSL): VDSL delivers 13 to 52 Mbps downstream and 1.5 to 2.3 Mbps upstream over a single-twisted copper pair. The operating range of VDSL is limited to 1,000 to 4,500 feet (304.8 to 1,372 meters). The Cisco Long Reach Ethernet (LRE) solution is based on Ethernet over VDSL.

High-data-rate digital subscriber line (HDSL): HDSL is commonly used as a T1 or E1

replacement. Because HDSL provides T1 or E1 speed, telephone companies have been using HDSL to provision local access to T1 or E1 services whenever possible. The operating range of HDSL is limited to 12,000 feet (3658.5 meters), so signal repeaters are installed to extend the reach.

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