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Understanding SDSL and the
Chapter 1
Express L768
SDSL OVERVIEW
Symmetrical Digital Subscriber Loop (SDSL) is high bit rate Digital
Subscriber Loop (HDSL) running at half its full rate, using only two
wires instead of four. HDSL is rapidly becoming the service providers'
technology of choice for the deployment of T1 services: according to
recent estimates, over 60% of today's T1 installations use HDSL tech-
nology. Instead of traditional methods requiring multiple T1 repeat-
ers, HDSL allows the telephone companies to quickly deploy a T1
circuit over Carrier Serving Area (CSA) loops (9,000 feet on 26 AWG
wire or 12,000 feet on 24 AWG wire) without loop conditioning or re-
peater installation. SDSL offers higher bandwidth, using the same two
wires that are traditionally used for DDS and ISDN technology.
ADTRAN provides a full line of HDSL and SDSL products that are the
price/performance leaders in the industry.
THE EXPRESS L768
The Express L768 is a standalone device that links two Local Area
Networks (LANs) using a high-speed DSL two-wire line. The Express
L768 has a two-wire interface and operates up to 768 kbits per second.
See Figure 1-1 for an illustration of the Express L768. The 10BaseT con-
nector operates at 10 Mbits per second half duplex and accepts stan-
dard ethernet packets encapsulated using IEEE 802.3 or Ethernet II
(DIX). Because the 10BaseT is a four-wire interface, a crossover switch
permits the user to connect to either a hub-concentrator or network in-
terface card without the need for special cabling. The maintenance
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Express L768 User Manual
1-1
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