This is a collection point for pointers to Interface Engineering and other nuts&bolts documents available on the web. These documents describe things like; how ADSI works, how the different Voice Message Waiting indicators are supposed to act, what 'Feature Group D' really is and so on.

It is all pretty heavy reading, but:

• AT&T Network Services Interfaces Testlab
  • AT&T PRI Services Note: Section 3 of this document contains detailed information on ISDN call control, including command sequence diagrams
  • AT&T BRI Services

• Canadian Telecom Information
  • Aliant Technical Disclosures
  • Bell Canada Technical Disclosures
  • MTS Technical Disclosures
  • SaskTel Technical Disclosures
  • Interface Documents pertaining to TELUS
    • NI-2 based PRI (Telus)

• QWEST Technical Publications
  • QWEST PRI Service

• Defense Information Systems Agency index to Q-series ITU-T recommendations
  • Q.850 through Q.999

• ANSI/TIA/EIA standards
  • ANSI/TIA/EIA-464-C Standard - 5th draft
  • Analog DID access using Loop Reverse-Battery Signalling
  • Voice Gateway Transmission Requirements

• Cisco Telephony Signalling whitepaper library
  • Voice Network Signaling and Control - a particularly good resource

Also the United Kingdom (GB) Public Switching Telephone Network Interopabillity Standards, courtesy of 'Anonymous'.