Intro to xdsl part 1

xDSL types

T1 service

• 1963: Coax deployment of T1
• 2 groups in digital TDM
• RZ-AMI line code
• Beyond CSA range should use DLC (direct loop carrier)
• Repeaters every 6 Kft
• Made possible by Bell Labs invention of the transistor
• 1971: UTP deployment of T1
• Bring 1.544 Mbps to customer private lines
• Use two UTP in half duplex
• Requires expensive line conditioning
• One T1 per binder group

T1 line conditioning

• In order for a subscriber’s line to carry T1
• Single gauge
• CSA range
• No loading coils
• No bridged taps
• Repeaters every 6 Kft (starting 3 Kft)
• One T1 per binder group
• Labor intensive (expensive) process
• Need something better … (DSL)
• Europeans already found something better

The first xDSL!

• 1984,88: IDSL
• BRI access for ISDN
• 2B1Q (4 level PAM) modulation
• Prevalent in Europe, never really caught on in US
• 144 Kbps over CSA range
• 1991: HDSL
• Replace T1 line code with IDSL line code (2B1Q)
• 1 UTP (3 in Europe for E1 rates)
• Full CSA distance without line conditioning
• Requires DSP

HDSL

• Replace T1/E1 DS1 service
• Use 2B1Q line code, DFE
• Full duplex on each pair with echo cancellation
• CSA reach w/o conditioning/repeaters
• more complex DSP
• ANSI: 2 pairs for T1 (each 784 Kbps)
• ETSI: 1, 2, 3 or 4 pairs
• Most mature of DSL technologies

HDSL2

• Customers request HDSL service that is
• single UTP HDSL
• at least full CSA reach
• spectrally compatible w/
• HDSL, T1, ADSL, etc.
• Variously called
• HDSL2 (ANSI)
• SDSL Symmetric DSL (ETSI)
• Now called
• SHDSL Single pair HDSL (ITU)