Access Technologies xDSL and FTTx

1
Access Technologies xDSL and FTTx

• Chuck Storry
• January 25, 2007

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Objectives

• Statistics Terminology
• Evolution of DSLs the loops they run on
• xDSL - definition and taxonomy
• What people are doing with DSL
• ADSL - some details
• Evolution from copper to fiber
• FTTx and xPON more alphabet soup
• Fiber deployment models
• GPON nuts and bolts
• Summary

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Terminology

• Telco Access Subscriber Loop
• Legacy -gt twisted copper pair -gt DSL
• New to access -gt optical fiber -gt PON
• Emerging -gt wireless -gt WiFI/WiMAX (pt-mpt vs
  mesh-gt not discussed here)

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Statistics broadband is definitely mass market

• Internet is now gt 1 Billion users worldwide
  (http//www.internetworldstats.com/stats.htm)
• World-wide broadband statistics (as of Q3-2006)
• Broadband Subs worldwide 263 Million
• DSL Subs worldwide 173 M
• gt 66 of broadband subs worldwide are DSL (22
  cable, 10 are FTTx, wireless lt 2)
• Phone Lines worldwide 900 Million ( copper
  lines not growing)
• 19 phone lines worldwide have DSL
• IPTV subs 3M
• Canadian broadband statistics
• 32 Million people in Canada, 21.9M Internet
  users
• 7.6 Million broadband subs (4.1 Million DSL
  subs / 3.9 Million cable)
• 9 worldwide by number of broadband subs USA 1
• 69 of Canadians use the Internet and about 1 in
  3 access via broadband
• Source DSL Forum (www.dslforum.org), Point topic
  (www.point-topic.com) and Statscan
  (www.statcan.ca)

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Broadband High speed Internet and more
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(No Transcript)
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Growth in Access Loop Capability
Fiber
Digital Modems
Kbps Bandwidth to Residence
1,000,000
PON
Analog Modems
VDSL
100,000
Cable Modem
ISDN
56 Kbps Modem
ADSL
10,000
38.4 Kbps Modem
9.6 Kbps Modem
28.8 Kbps Modem
1,000
2.4 Kbps Modem
100
1.2 Kbps Modem
10
300 bps Modem
1
1975
1980
1985
1990
1995
2000
2005
Year
8
Todays Copper Access Loop Topology
Carrier Serving Area (CSA)
Serving AreaInterface
Distribution Area (DA)
Out
In
Out
Terminals
Central Office
Lateral
IW

• Phone
• PC
• TV

Switch
NID
MDF
Distribution
Copper Feeder
GR-303 GR-008
There are usually 2 to 5 DAs in a carrier
serving area (CSA), the limits of which can
extend 9-12 Kft beyond the RT

• POTS, ISDN
• COIN, PBX, FXS
• 2W/4W Specials
• DS1, DS3, OC-3c
• HDSL, IDSL, HDSL2,
• ADSL, SHDSL

Fiber
DLC RT
The RT must at least support all services the SP
delivers on copper.
DLC COT
Outside Plant
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DSL Performance vs Loop topology
75 of FDI loops lt 3 kft (1 km)
Downstream rate of 30 Mbps is achievable with
either VDSL or pair bonded ADSL2
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A Taxonomy of DSLs

• DSL is Digital Subscriber Line
• A .. Z DSL
• How many are there really ?
• Arent they really all the same ?
• How do I decide which to use ?

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DSLs and their characteristics
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DSLs deJour

• Todays most popular DSLs include
• ADSL/ADSL2/ADSL2plus and Reach-extended ADSL for
  residential
• ESHDSL for business
• VDSL2

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What are people doing with DSL ?

• 1st Wave residential high speed Internet
• 2nd Wave - business services
• 3rd Wave residential triple play
• Canada leads the way - PC and/or TV triple play
• Triple Play Voice / Video / Data
• ADSL(2) Sask Tel (MAX), Telus TV, Aliant (TV
  on My PC)
• VDSL Bell Canada (ExpressVu TV for condos), MTS
  (MTS-TV)
• Developing Applications
• On-line gaming
• Software on-demand
• Video on Demand

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ADSL - an example

• Described by ITU G.992.1 (G.99x series)
• Single pair All digital loop, over POTS or ISDN
  (start frequency)
• works like 256 V.34 modems spread apart every 4.3
  khz (frequency separation)
• total bandwidth to 1.1 Mhz (or 2.2 for ADSL2plus)
  (end frequency)
• variable bit rate, up to 10 Mbps, based on loop
  conditions (startup)
• can adapt to changing line conditions (showtime)
• forward error correction
• multiple latency paths
• ATM transport (although single PVC is becoming
  popular, Ethernet transport is an option but not
  popular til VDSL)
• VDSL by comparison is
• 4096 carriers up to 12 Mhz (16 x complexity of
  ADSL but remember Moores law)
• Variable bit rate, up to 50 Mbps, dependant upon
  loop length

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Three Information Channels

• High Speed Downstream (1.5 - 12 Mbps)
• Uses upper end of loop spectral bandwidth
• Bandwidth drops off quickest on long loops
• Medium Speed Upstream (64 - 640 kbps)
• Uses low end of loop spectrum
• Most reliable
• Analog POTS
• 0 - 4 KHz
• Low pass filters required to split POTS at each
  end

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DSL Spectrum
DMT Discrete Multi Tone modulation based on
multiple carriers ADSL2 straightforward
extension of ADSL QAM Quadrature Amplitude
Modulation based on single carrier
138 kHz or 276 kHz
lt 8/1 Mbps
ADSL
0.138 to 1.1 MHz
U.S.
lt 3/1 Mbps
0.138 to 0.5 MHz
ADSL-Lite
Optional U.S.
DS
lt 16/1 Mbps
0.138 to 2.2 MHz
ADSL2
Spectrally Compatible
lt 12/1 Mbps
0.5 to 2.2 MHz
Remote ADSL2
lt 23/8 Mbps
1.1 or 2.2 to 12 MHz
VDSL (DMT /QAM)
1.1
12 MHz
100 Mbps 200 Mbps (Japan)
VDSL2 (DMT)
2.2
12 MHz
17 MHz
30 MHz
U0
D1
U1
D2
U2
D3
U3
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DMT - Discreet Multitone Transmission

• DMT functions by dividing the available bandwidth
  into a multitude of sub-channels. The bandwidth
  available to ADSL DMT linecoding is 26kHz to
  1.1MHz.
• DMT technology can be thought of as 256
  consecutive v.90 modems

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Conceptual ADSL Modem
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Loop Length distribution in some countries
4.5 Km (ADSL reach)
1 Km (VDSL reach)
Fiber
Subscribers that require higher speeds need DSLs
that have shorter reach so fiber is deployed to
push the DSL modem closer to the customer
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Evolution from copper to fiber
Bandwith / Service Capability
FTTx
P-P Optics
CO
FTTNode Electronics at the Copper Cross Connect
(FDI)
FTTArea Electronics at Centralized Remote
Location (CSA)
FTTExchange Electronics at CO
VDSL
CO
RT
ADSL2
CO




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FTTx Alternatives

• FTTU - Fiber to the User (residential ONT)
• FTTPremises
• FTTHome
• FTTSuite
• FTTB Fiber to the Business (business ONT)
• FTTBuilding
• FTTCampus
• FTTC Fiber to the Curb (transport ONT)
• FTTCabinet
• FTTArea

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FTTx Technology Options
OLT Optical Line Termination

• Shared Fiber
• PON (Passive Optical Network)
• Passive and flexible cable plant
• Optimum sharing of bandwidth
• Low cost
• Security
• WDM (Wavelength Division Multiplexing)
• High sharing of bandwidth over single fiber
• High cost (WDM/DWDM components)
• Dedicated Fiber
• Point to point
• High bandwidth flexibility
• High cost (fiber and equipment)
• Active Star
• Flexible in feeder range
• Ethernet widely accepted technology
• Active node in the field (high Cost of Ownership)

ONT Optical Network Termination
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Why PON

• Higher bit rates (than copper)
• option to use additional wavelengths in the
  future
• Longer reach (than copper)
• 2 to 4 times longer spans possible
• Lower cost (than point to point fiber)
• Shared feeder fiber and termination in the CO
• Low cost passive splitters in the field (not
  active electronics)
• Retains reliability (of fiber rings)
• Optional ring feeder support (including fast
  protection switching)

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xPON comparison

• Passive Optical Network
• Standardized at ITU, IEEE (requirements from
  FSAN)
• Multiple span length options depending upon
  optics category, topology, number of splits,
  optical loss, etc.)
• Multiple split configurations 1n
• Single fiber used bidirectionally (multiple light
  wavelengths)

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Comparison of PON Technologies
Line Rate
Throughput
Line Rate
Line Rate
Throughput
Throughput
GPON
Active Ethernet
Gigabit EPON
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FTTU PON Deployment Model
Splits
Span
CPE Customer Premises Equipment
PON Passive Optical Network
Central Office
1490 nm
OLT
Single mode fiber
14 splitters
1310 nm
ONT
Data / voice
WDM
Video Overlay
RF Video
DIPLEXER
TRIPLEXER
Video overlay being discouraged in favor of IPTV
1550 nm
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GPON an example

• Described by ITU G.984.1- G.984.4 (G.984.x
  series)
• High re-use of G.983 ( trend at standards)
• Single fiber with 2 wavelengths (can use 2
  fibers)
• Up to 64 ONTs per PON (addressing for 128) -gt
  usually 32
• Typically deployed as 2.4/1.2 Gbps (symmetrical
  rates allowed)
• Downstream encryption
• Multiple native transport options GEM GPON
  Encapsulation Mode (TDM, Ethernet or ATM) -gt
  usually Ethernet
• OMCI ONU Management and Control Interface for
  easy ONT management

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PON Data Transport
ONT - A
1490 nm
C B A
C B A
OLT
ONT - B
B
A B C
C B A
1310 nm
ONT - C
C

• TDM downstream (point to multipoint)
• Downstream needs security
• ONTs process only cells with their GEM ID
  address
• churning used to ensure privacy
• TDMA upstream (4 Kbps increments) (multipoint to
  point)
• Who can talk next ? Upstream needs access
  mechanism
• DBA (dynamic bandwidth allocation makes TDMA
  work- conserving)

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Transport (cont)

• Downstream
• Data is visible by all ONUs
• Scrambling or churning of data is employed
  (Advanced Encryption Standard (AES) encryption is
  mandatory in GPON))
• Upstream
• access mechanism (Dynamic Bandwidth Allocation
  DBA)
• Downstream grants assign slots for ONT upstream
  (see PON frame)
• synchronization
• Ranging ensures ONU US bursts are aligned to US
  frame (accounts for differences in propagation
  delay between ONUs to OLT)
• Each ONU applies equalization delay as defined by
  OLT via Ranging protocol
• During Ranging, ONU is assigned ONU-ID

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GPON Frame Format
Downstream Frame Format
PCBd n
Payload n
PCBd n1
Payload n 1

• - SYNC
• - PLOAM
• US B/W MAP
• (slotpointers)

ATM
TDM Frame (over GEM)
ATM
ATM
ATM
GEM hdr
Frame data
GEM hdr
Frame data

• OLT assigns slots to ONTs to allocate bandwidth
  (see DBA)
• Uses pointers to allocate upstream bandwidth

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DBA
OLT
ONT
request
data
User data report
Report updates b/w
request
data
User data report
B/W continues to be allocated
request
report
B/W updated

• ONT indicates need for upstream b/w
• OLT assigns slot as available

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Summary - Access Technologies

• Both copper and fiber can offer triple-play
  alternatives
• Copper will typically be used for existing
  installations
• Fiber will enhance the bandwidth capabilities of
  copper
• Deploy DSL technology close to customer
• Modern version of HFC (hybrid fiber coax)
• Amazing how difficult/costly/irritating it is to
  dig up peoples yards
• Fiber will start being deployed all the way to
  the residence for new neighborhood construction
• PON is lowest cost option for FTTH
• Some new construction is being subsidized by
  other than traditional ILECs (incumbent telephone
  company)

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References

• Walter Goralski, ADSL and DSL Technologies,
  McGraw-Hill, ISBN 0-07-024679-3, 1998
• Charles K. Summers, ADSL Standards,
  Implementation, and Architecture, CRC Press,
  ISBN 0-8493-9595-X, 1999
• and more
• Tom Starr, et al, Understanding Digital
  Subscriber Line Technology, Prentice Hall, ISBN
  0137805454, 1998
• Tom Starr, et al, DSL Advances, Prentice Hall,
  ISBN 0130938106, 2002
• Michael Beck, Ethernet in the First Mile,
  Mcgraw-Hill, ISBN 0071469915 , 2005
• Note EFM encompasses Ethernet over both GPON and
  VDSL