Technology - Infrastructure - Last Mile 6 - Symmetrical SHDSL, VoDSL

Synopsis

The symmetrical data rates of BR-ISDN, HDSL, SDSL and most importantly SHDSL G.991.2 are of special importance for business customers. We discuss their technical characteristics, improved latency and their advantages over ADSL. Voice over Digital Subscriber Line (VoDSL) and the new Channelised VoDSLC are two different approaches to carrying multiple voice circuits over symmetrical and asymmetrical DSL services. We explain and compare these to see which situations each is most appropriate for.

Table of Contents

• 1. Synopsis
• 2. Symmetrical DSL
  • 2.1 Less widely used than ADSL
  • 2.2 DSLAM location
  • 2.3 Future of symmetrical DSL
• 3. T1 and E1
  • 3.1 PABX applications
  • 3.2 Bit stuffing
  • 3.3 Interference problems
• 4. BR-ISDN and IDSL
  • 4.1 Basic rate ISDN
  • 4.2 IDSL
• 5. HDSL
  • 5.1 Replacement for T1 and E1
  • 5.2 Unconditioned copper pair
  • 5.3 HDSL-2
• 6. SDSL
• 7. SHDSL G.991.2
  • 7.1 Pulse Amplitude Modulation (PAM)
  • 7.2 Compatibility with ADSL and VDSL
  • 7.3 Low latency
  • 7.4 Repeaters
  • 7.5 Extensions to basic SHDSL standards
    • 7.5.1 Amendment 1
    • 7.5.2 Amendment 2 - faster data rates
    • 7.5.3 Amendment 3 - Ethernet encapsulation
    • 7.5.4 ETSI TS 101 524
    • 7.5.5 ATIS/ANSI T1.426 E-SHDSL
• 8. Voice over broadband (VoBB)
• 9. Latency and delay
• 10. VoDSL - Voice over DSL
  • 10.1 Limitations
  • 10.2 Voice traffic in ATM cells
  • 10.3 VoDSL standards
  • 10.4 Compression algorithms
• 11. CVoDSL - Channelised Voice over DSL
  • 11.1 Using 64Kb/s
  • 11.2 ‘Robbed bit’ approach
  • 11.3 Still early days
  • 11.4 Interfacing technology
• 12. Related reports

• Table 1 – HDSL reach (km) vs. wire gauge