Access to Bandwidth Spectrum Management in the Access Network

1
Access to BandwidthSpectrum Management in the
Access Network

• David Davies
• NICC DSL Task Group Chairman

acd
NICC Open Forum - 18 November 1999
2
Agenda

• The need for Spectrum Management
• Developing Spectrum Management Plan
• implementation issues
• customers terminal equipment (CPE)
• EMC
• current activities outside UK
• status of work in NICC DSL TG

3
Need for Spectrum Management

• Standards define PSD of xDSL system
• Standards do not ensure spectrum compatibility
  between different xDSL system
• compatibility is dependent on location of xDSL
  transceivers
• xDSL system performance dependent on noise level
• spectrum management plan needed

4
Aim of Spectrum Management Plan

• Prevent interference between different systems in
  cable
• maximise use of cable capacity
• minimise deployment risks
• protect working systems from degradation/failure
• protect external environment from interference

5
Spectrum Management for Access Cable
ISDN- BA
ADSL over POTS
POTS
VDSL
ADSL over ISDN
SDSL
6
Maximising the capacity of the network
ISDN- BA
ADSL over POTS
POTS
VDSL
ADSL over ISDN
SDSL
Access Cable
7
Capacity of Access Cable affected by

• Physical cable characteristics
• composition, length, construction, installation
• Noise environment
• extrinsic (RFI, lightening)
• intrinsic (crosstalk, attenuation, thermal noise,
  echoes)
• spectrum management plan is network
• specific

8
Crosstalk
Customer transceivers
Exchange transceivers
transmitted signal
NEXT - independent of line length FEXT -
attenuated by line (as is the transmitted signal)
RX
TX
Near end crosstalk signal (NEXT)
TX
RX
Far end crosstalk signal (FEXT)
TX
RX
RX
TX

• ISDN, HDSL are NEXT limited
• ADSL, VDSL are FEXT limited

9
Interference Management Issues

• frequency transmit power
• defined by standards (PSD mask)
• usable margin between standard PSD mask and
  actual PSD
• location - both within and outside (ie CPE)
  network
• orientation eg reverse ADSL
• Interference can be
• fatal eg POTS ADSL vs ISDN ADSL normal
  ADSL vs reverse ADSL
• seen as reduced performance ie reach/data rates

10
Spectrum Overlap
HPNA
VDSL
ADSL over ISDN
ADSL over POTS
DSL-Lite
ISDN
POTS
Frequency
11
Interference from Terminal Equipment

• Currently terminal equipment subject to testing
  approval
• Approval for voiceband CPE tests to 200kHz
  (CTR21)
• RTTE Directive (99/5/EC) applies from 8/4/2000
• Terminal equipment only subject to safety EMC
  requirements
• RTTE has provision for network harm
  requirements - unlikely to be used
• interference from analogue baseband leased lines?

12

Typical Home Networking (HPN)
HPN/ Ethernet
PC HPN
HPN could use a b pair or spare pair
PC

POTS NTP

Key
Phone wiring - arbitrary topology - carries POTS
Home Phoneline Network (HPN)
10 Base-T Ethernet
13
Home Networking

• Specifications produced by HPNA (Home Phone
  Networking Alliance
• New work item in ITU-T SG15
• uses frequencies compatible with ADSL but not
  VDSL
• HPN signals radiate into access network and via
  crosstalk into other pairs
• HPN not seen as telecoms terminal equipment

14
Use of cable capacity

• maximising use of cable capacity is
• a commercial decision
• maximise reach/data rate of ADSL, or
• maximise use of HDSL/SDSL, or
• allow reverse ADSL
• dependent on deployment risk margins

15
Deployment Risks
?Broken Promise
?No Opportunity
No
Could line actual support DSL?
?Earn Money
? Lost Opportunity
YES
YES
No
Deployment Decision
16
Protecting future opportunities

• DSL technology continues to develop
• need to protect unused spectrum
• once defined, very difficult to change spectrum
  management plan

17
Development of Spectrum Management Plan
Spectrum Management Plan
Transmission PSDs Allowed
Deployment Rules
18
Enforcement

• Spectrum Management benefits all users of access
  network
• Is it enforceable?
• Detection process is intrusive
• non-conformant system may have be working for a
  long time
• legal commercial issues (proof on
  non-conformance)
• installation validation testing ? - cant cover
  location user configuration
• Who does the enforcement? Who pays?
• Need to try to prevent accidental
  non-conformance

19
EMC Issues

• xDSL systems use RF frequencies
• balanced cable does not radiate (but access
  customer cabling not perfectly balanced)
• DTI/RA drafting EMC limits (MPT 1570)
• limits very low (too low?)
• need balance between protecting RF spectrum and
  exploiting access cable
• Allocating responsibility in ULL environment

20
Spectrum Management Activities

• ANSI T1E1
• started work Oct 98
• many world experts on DSL participated
• draft specification produced
• received many NO votes and a large number of
  comments
• EC have asked ETP to produce guidelines
• ETSI about to start work (spring 2000)

21
NICC DSL Task Group

• Re-convened 8/99
• ToR agreed
• Spectrum Management Plan - Rob Kirkby, BT
• PBLC Rules - Richard Sheard, Racal Telecom
• SPM User Guide - Peter Page, Marconi
  Communications
• 2 Phases
• Phase 1 (lt 1.1 MHz) - 6/00
• Phase 2 (lt 30 MHz) - 9/00

• Reviewed T1E1 work
• BT Option 2 design needs SPM by end 99
• Basic principles discussed and partly agreed
• Co-ordination with RA WLT/EMC OPF Option 2
  Implementation
• BT to present its Spectrum Management Plan at
  next DSL TG meeting (17 Dec)

22
Spectrum Management Plan - Principles

• Agreed
• No pair segregation management
• Any system on any pair
• Defined change control
• Includes existing BT transmission systems
• technology independent

• Protection of working systems
• Protect safety
• Supports POTS ADSL (not ISDN ADSL)
• Not Agreed
• Maximise ADSL reach

23
Conclusions

• Spectrum Management Plan is essential for all
  users of the access network (and RF spectrum)
• In ULL environment, much more complex
• conflicting commercial objectives
• increased use of different DSL systems/manufacture
  rs
• management more difficult
• enforcement impossible?