Digital Hierarchy

Committee T1
Sponsored by the Alliance for Telecommunications Industry Solutions and accredited by ANSI for interoperability standards.
http://www.t1.org/

DCB's T1 Info
All you wanted to know about T1's but were afraid to ask.
http://www.dcbnet.com/notes/9611t1.html

EverythingT1.com
Offering T-1/T-3 information, glossary, FAQs, reference, Technical reports, news, messageboard, ISP lists and links.
http://www.everythingt1.com/

SONET/SDH Technical Summary
Defines SONET and SDH, and provides references to appropriate standards organizations.
http://www.techfest.com/networking/wan/sonet.htm

T-1 Carrier
Webopedia definition and links about T1.
http://webopedia.com/TERM/T/T_1_carrier.html

T1 T-extender
DCB's T1 repeater for customer-owned cable.
http://www.dcbnet.com/datasheet/textds.html