ATM and xDSL

Chapter 16: Digital Subscriber Line


Digital Subscriber Line(xDSL)


     Is the term for the Broadband Access technologies based on Digital Subscriber Line (DSL) technology, "x" signifies that there are various flavors of DSL. It provides always-on, high speed data services over existing copper wires to residences and businesses.

Line-length limitations on DSL signal transmission from the telephone exchanges speeds have resulted in many types of DSLs.

Types of DSL

DSL Type	Description	Data Rate Downstream; Upstream	Distance Limit	Application
IDSL	ISDN Digital Subscriber Line	128 Kbps	18,000 feet on 24 gauge wire	Similar to the ISDN BRI service but data only (no voice on the same line)
CDSL	Consumer DSL	1 Mbps downstream; less upstream	18,000 feet on 24 gauge wire	Splitterless home and small business service; similar to DSL Lite
DSL Lite (same as G.Lite)	"Splitterless" DSL without the "truck roll"	From 1.544 Mbps to 6 Mbps downstream, depending on the subscribed service	18,000 feet on 24 gauge wire	The standard ADSL; sacrifices speed for not having to install a splitter at the user's home or business
G.Lite (same as DSL Lite)	"Splitterless" DSL without the "truck roll"	From 1.544 Mbps to 6 Mbps , depending on the subscribed service	18,000 feet on 24 gauge wire	The standard ADSL; sacrifices speed for not having to install a splitter at the user's home or business
HDSL	High bit-rate Digital Subscriber Line	1.544 Mbps duplex on two twisted-pair lines; 2.048 Mbps duplex on three twisted-pair lines	12,000 feet on 24 gauge wire	T1/E1 service between server and phone company or within a company; WAN, LAN, server access
SDSL	Symmetric DSL	1.544 Mbps duplex; 2.048 Mbps  on a single duplex line   downstream and upstream	12,000 feet on 24 gauge wire	Same as for HDSL but requiring only one line of twisted-pair
ADSL	Asymmetric Digital Subscriber Line	1.544 to 6.1 Mbps downstream; 16 to 640 Kbps upstream	1.544 Mbps at 18,000 feet; 2.048 Mbps at 16,000 feet; 6.312 Mpbs at 12,000 feet; 8.448 Mbps at 9,000 feet	Used for Internet and Web access, motion video, video on demand, remote LAN access
RADSL	Rate-Adaptive   DSL	Adapted to the line, 640 Kbps to 2.2 Mbps downstream; 272 Kbps to 1.088 Mbps upstream	Not provided	Similar to ADSL
UDSL	Unidirectional DSL	Not known	Not known	Similar to HDSL
VDSL	Very high Digital Subscriber Line	12.9 to 52.8 Mbps downstream; 1.5 to 2.3 Mbps upstream; 1.6 Mbps to 2.3 Mbps downstream	4,500 feet at 12.96 Mbps; 3,000 feet at 25.82 Mbps; 1,000 feet at 51.84 Mbps	ATM networks; Fiber to the Neighborhood

Asymmetric Digital Subscriber Line (ADSL)

is a technology for transmitting digital information at a high bandwidth on existing phone lines to homes and businesses. Unlike regular dial up phone service, ADSL provides continuously-available,"always on" connection. ADSL is asymmetric in that it uses most of the channel to transmit downstream to a user and only a small part to received information from the user.

ISDN Digital Subscriber Line (IDSL)

is a system in which digital data is transmitted at 128 Kbps on a regular copper telephone line from user to a destination using digital transmission, bypassing the telephone company's central office equipment that handles analog signals. IDSL uses the ISDN Basic rate Interface in ISDN code transmission.

High Bit-rate Digital Subscriber Line (HDSL)

One of the earliest form of DSL, is used for wideband digital transmission within a corporate site and between the telephone company and a customer. The main characteristic of HDSL is that it is symmetrical: an equal amount of bandwidth is available in both direction.

Symmetric Digital Subscriber Line (SDSL)

is similar to HDSL with a single twisted-pair line, carrying 1.544 Mbps or 2.048Mbps each direction on a duplex line. It's symmetric because the data rate is the same in both direction. 

Rate Adaptive Digital Subscriber Line (RADSL)

a technology in which software is able to determine the rate at which signal can be transmitted on a given customer phone line and adjust the delivery rate accordingly. RADSL delivers from 640 Kbps Downstream and from 272Kbps to 1.088Mbps upstream over an existing line.

Consumer Digital Subscriber Line (CDSL)

It is somewhat slower than ADSL (1Mbps downstream and less upstream) and has the advantage that a "splitter" does not need to be installed at the user's end.

Symmetric High-bit rate Digital Subscriber Line (SHDSL) or (G.lite DSL)

Provides for sending and receiving high-speed symmetrical data stream over a single pair of copper wires at rates between 192 Kbps and 2.31 Mbps.

Very High-bit rate Digital Subscriber Line (VDSL)

transmits data in 13Mbps - 55 Mbps range over short distance, usually between 1000 and 45000 feet, of twisted pair copper wire. the shorter distance, the faster the connection rate.