High-bit-rate digital subscriber line 2

High-bit-rate digital subscriber line 2 (HDSL2) is a standard developed by the American National Standards Institute (ANSI) Committee T1E1.4 and published in 2000 as ANSI T1.418-2000.{{cite web |title=ATIS 0600418.2002(R2011): High bit rate Digital Subscriber Line - 2nd Generation (HDSL2/HDSL4) Issue 2|accessdate=2013-12-26 |publisher=ATIS |date=2002-01-05 |url=http://webstore.ansi.org/RecordDetail.aspx?sku=ATIS-0600418.2002%28R2011%29}}{{cite web |url=http://www.inf.puc-rio.br/~inf2056/inf2056_files/menu/trabalho/HDSL2-overview.pdf |title=HDSL2 Tutorial: Spectral Compatibility and Real-World Performance Advances | last=Zimmermann |first=George A. |publisher=PairGain Technologies |date=1998-06-25 |accessdate=2013-12-26}}{{cite web|url=http://misnt.indstate.edu/harper/HDSL2.htm |title=HDSL2 |last=Ferguson |first=Krista |date=1999 |accessdate=2013-12-26 |url-status=dead |archiveurl=https://web.archive.org/web/20100728162059/http://misnt.indstate.edu/harper/HDSL2.htm |archivedate=2010-07-28 }} Like its predecessor HDSL, HDSL2 provides a symmetric data rate of 1,544 kbit/s in both the upstream and downstream directions at a noise margin of 5-6 dB. Its primary purpose was also to provision a T-1 line, only this technology relies on fewer wires - two instead of four - and therefore costs less to set up. The modulation technique used in HDSL2 is TC-PAM, which is also used in G.SHDSL, as opposed to 2B1Q in HDSL. Spectral shaping is applied to increase compatibility with ADSL and HDSL2 on the same bundle.{{cite book |title=DSL Advances |year=2003 |editor1-last=Starr |editor1-first=Thomas |isbn=0-13-093810-6 |location=Upper Saddle River, NJ |publisher=Prentice Hall |url=https://books.google.com/books?id=VWaMdIq2w8QC}} HDSL4 provides the same bitrate as HDSL2, but uses four wires instead of two, to increase robustness. On an AWG26 local loop, the reach of HDSL2 is {{convert|9000|ft|km}}, while that of HDSL4 is {{convert|11000|ft|km}}.