Broadband Access Networks and Services

1
Broadband Access Networks and Services
EE4541.759 Spring 2003

• Chapter 3
• Cable based Access Networks
• Byeong Gi Lee
• Seoul National University

2
3. Cable-based Access Network

• Conventional CATV Network
• Cable based broadband Access
• Hybrid Fiber Coax (HFC)
• Digital Video Services
• Data Services
• Integration of Video and Data Services
• Penetration of Cable based Access Network

3
Structure of Access Network

• ADSL Asymmetric Digital Subscriber Line
• DBS Direct Broadcast Satellite
• FTTC Fiber To The Curb
• HFC Hybrid Fiber Coaxial
• LMDS Local Multipoint Distribution System
• MMDS Multi-channel Multipoint Distribution
  System
• MSO Multiple Service Operator

Cable-based AN
Digital DBS
Fiber or Wireless
MMDS/LMDS
LMDS only
Hub Station
DBS STB/ MMDS/LMDS STB
64Kbps
ISDN Adaptor
ISDN Line
MSO /CO
Analog Modem
56Kbps
ADSL Modem
6Mbps
Home Terminal
640Kbps
30Mbps
Coax
Cable Modem
Fiber
HFC
3Mbps
ONU
Coax or Copper
VDSL Modem
Fiber
52Mbps
FTTC/FTTO
3Mbps
4
Access and Backbone Infrastructure
5
Conventional CATV Network (1)

• Initially community antenna based TV(CATV) signal
  distribution, expanded to general services
• Coaxial cable based, tree branch architecture
  with headend and subscribers equipment at both
  ends
• Unidirectional video signal distribution
• 450 MHz band in 50 - 550 MHz range, carrying NTSC
  TV signals that occupies 6 MHz band each

6
Conventional CATV Network (2)

• Conventional Cable System Schematic

7
Conventional CATV Network (3)

• Spectrum of NTSC Television Signal

8
Conventional CATV Network (4)

• Architecture
• A tree and branch topology with the headend as
  the root and the subscribers as leaves
• Consists of headend, trunk cable, amplifiers,
  splitters, feeder cable, taps, and drop cable
  (see the figure)
• Video traffic emanates from headend downstream
  and is boosted by amplifiers to maintain the
  strength
• Signal strength attenuates by square root of
  frequency
• Pad, a passive attenuation device, is placed when
  needed to avoid too much signal strength of
  amplifiers

9
Conventional CATV Network (5)

• Headend
• Receives programs from contents providers
• Converts each channel to the channel frequency
  desired, and scrambles the channels as needed
• Combines all the frequencies onto a single
  broadband analog channel (FDM)
• Broadcasts the combined analog stream downstream
  to subscribers

10
Conventional CATV Network (6)

• Drawbacks of Pure Cable System
• Still insufficient channel capacity (roughly 40)
• Lack of robustness amplifier malfunction near
  headend affects the subscribers all the way down
• Insufficient signal quality for large number of
  users
• Very complicated to design and operate dozens of
  amplifiers, splitters, taps, cables of various
  different impedances
• Complicated ongoing operational network design

11
Conventional CATV Network (7)

• Adding Fiber to CATV Network

12
Conventional CATV Network (8)

• Adding Fiber to CATV Network (contd)

Core Network
Core Network
13
Cable based Broadband Access (1)

• Business Rationale
• Cable modems over cable TV systems
• High-speed alternative to xDSL and analog modems
• Large base of over 68.8 million cable-wired homes
  and over 70 million home PCs in US (as of June
  2002)
• Actively involved in developing cable data
  network standards, upgrading the cable plant to
  handle two-way digital connectivity
• Only about 15-20 of cable distribution plant is
  two-way-capable

14
Cable based Broadband Access (2)

• Business Rationale (contd)
• Speed Comparable to xDSL and wireless access
• Reduced Signaling always on, no need of call
  setup
• Tariffing no time dependent pricing (always on)
• Port Conservation shared medium
• Only a single physical port at the carrier
  premises to support hundreds or thousands of
  users
• Vertical Integration
• Content providers own cable properties

15
Cable based Broadband Access (3)

• Characteristics of Cable based systems
• Operation at 27 Mbps downstream, 2 Mbps upstream
• Shared LAN-like architecture
• user receives unguaranteed bandwidth depending on
  the number of users at an instant of time
• Issues of security and privacy
• problems in return path due to electromagnetic
  interference and sharing of the bus (tree and
  branch)
• Rapidly dropping prices of modems compared to
  ADSL modems

16
Hybrid Fiber Coax (HFC) (1)

• Chracteristics
• Hybrid Fiber and Coaxial cable network
• Bidirectional, digital interactive services added
  by upgrading transmission equipment, amplifiers,
  and repeaters
• Hybrid of analog CATV services (broadcasting)
  and digital interactive services
• VOD, POTS, Internet services
• Upstream telephony and set-top control at low
  frequency band (5-30 MHz)

17
Hybrid Fiber Coax (HFC) (2)

• HFC Network Architecture

Program provider
FTTLA
Microwave/ optical link
Core Network
Head- end
ONU
Optical Unit
B
STU
Tree branch
PSTN
BISDN
Fiber to the last amplifier
(Core Network)
18
Hybrid Fiber Coax (HFC) (3)

• Mapping of HFC to DAVIC Ref Model

A9
A4
A2
A1
A0
Fiber
Video
Cable
Server
Modem
Coax
Fiber
ATM
Transport
Terminal
NT
NIU
STU
Node
Network
Server
(ONU)
PC
Web
(AN, HE)
Internet
Cable
Server
Modem
10BT
Core Network
Access Network
Server
Cache
19

Hybrid Fiber Coax (HFC) (4)

• HFC Frequency Allocation
• A representative in US

Control Upstream telephony
Upstream Return path
Digital interactive services
Analog CATV services
MHz
5 42 54 350
750 1000
20

Hybrid Fiber Coax (HFC) (5)

• HFC Frequency Allocation

21

Hybrid Fiber Coax (HFC) (6)

• Modulation Techniques

22
Hybrid Fiber Coax (HFC) (7)

• Illustration of Service Integration (1)

23
Hybrid Fiber Coax (HFC) (8)

• Illustration of Service Integration (2)

DS
US
24
Hybrid Fiber Coax (HFC) (9)

• Upstream Transmission
• Cable return channel
• Low split 542 MHz frequency range
• Mid split 5108(up)/ 174450(down) MHz
• High split 5150(up)/ 174750(down) MHz
• Channels 2-6 are sacrificed.
• Telephone based return
• Some cable operators choice due to return path
  impairment problems
• Phone based connection for the return information
  
• For an interim period use

25
Hybrid Fiber Coax (HFC) (10)

• Advantage
• Utilizes existing coax cables
• set-top box cost relatively cheap
• accepts digital and analog video streams
• Technical Issues
• Carrier serving area
• ONU serves 200-600 homes (2000 homes
  conventionally)
• Frequency plan
• RF modulation technology (QAM vs. VSB)

26
Hybrid Fiber Coax (HFC) (11)

• Cable Modem
• Very competitive Internet access means currently
• Multimedia cable network system (MCNS) spec.
• Enables combined provision of TV and Internet
  services

27
Hybrid Fiber Coax (HFC) (12)

• Cable Modem Schematic

Cable Operator
Diplex Filter
Demodulate
Modulator
Memory
FEC
FEC
Deinterleave
Interleaver
CPU
Data
Framing
MAC
Processor
PC
Network
Data
Encoder
Interfc card
28
Digital Video Services (1)

• MPEG-2 encoded digital TV over HFC
• 750 MHz of forward bandwidth offering 110 or more
  passbands of 6 MHz each
• Each 6 MHz passband is MPEG-2 encoded to yield
  four to six digital channels
• QAM modulation
• Reed-Solomon forward error correction (FEC)
• Sharing of 750 MHz among 500 to 2000 households
• Legacy analog TV, nVoD, VoD, Internet access..

29
Digital Video Services (2)

• Principles of operation
• Analog channels are received from satellite or
  terrestrial over-the-air means, which are passed
  along transparently to the viewers
• Digital channels can be handled in a variety of
  ways
• 8-VSB modulation in over-the-air
• QAM-64 or QAM-256 modulation in cable digital TV
• FDM of analog and digital channels from 54MHz to
  750 MHz

30
Digital Video Services (3)

• Digital Set-Top Box basic functions
• Diplex filters to separate upstream form
  downstream traffic
• Handle modulation/demodulation of traffic to/from
  the HFC
• Create an electronic program guide
• Perform MPEG-2 PID selection and decoding
• Manage analog interfaces outlets to analog TV
  controls
• Descramble analog TV broadcasts
• Manage infrared controls and VCR controls
• Transmit return path signals
• Encrypt/de-encrypt upstream/downstream traffic
• Authenticate
• Manage separate, or out of band, control channel
• Perform IP stack and IP address filtering

31
Digital Video Services (4)

• OpenCable Initiative
• Standardization of key elements of a digital set
  top for digital TV over HFC
• Common spec agreed by General Instrument,
  Scientific Atlanta
• Creation of new functionality for digital TV,
  VCRs, DVD players, and personal computer NICs
• Key elements
• Consistent services (from different
  manufacturers)
• Backward compatibility (compatible with existing
  ones)
• Portability (consumer may move from system to
  system)
• Conditional access (security system)
• Software development environment for navigation
  tools
• Platform independence

32
Digital Video Services (5)

• Security and the Point of Deployment Module
• Point of Deployment (PoD) module
• Smart card that plugs into the set-top box
• Contains keys to view premium programs
• Repository for billing information for e-commerce
  transactions
• Basic programs without PoD and premium channel
  requiring PoD
• Emergency alerts preemt programming
• Challenges to Digital Video Service
• Competition from satellite
• Copy protection
• Must Carry (analog channels) rules for digital
  TV
• Viruses and Bugs
• Set-top boxes subject to computer hacks, viruses,
  bugs, etc.

33
Data Services (1)

• Principles of Operation (1)
• DOCSIS1.1 Specification
• Data-Over-Cable Service Interface Specification
• Channelization and modulation (downstream)
• Modulated with QAM-64 or QAM-256
• 6MHz increments anywhere from 50 to 860MHz
• QAM-64 5.057Msps or 30.3 Mbps
• QAM-256 5.361 Msps or 42.9Mbps
• MPEC-2 Transport Framing as framing protocol
• Interleaving applied
• Latency of 0.22 to 4.0ms depending on burst
  protection

34
Data Services (2)

• Principles of Operation (2)
• Channelization and modulation (upstream)
• Return paths vary according to bandwidth anywhere
  542MHz
• Center frequencies located with 32KHz precision
• QPSK or QAM-16 modulated

35
Data Services (3)

• Principles of Operation (3)
• Startup user-friendly installation process of
  cable modem
• Obtain physical-layer information, such as which
  downstream to use, which upstream frequencies to
  use, modulation scheme, and symbol rate
• Obtain network-layer information, such as IP
  address and access list filters
• Authenticate the cable modem and establish an
  encryption

36
Data Services (4)

• Principles of Operation (4)
• Continuing Operations Forward path
• data received at cable modem terminal server
  (CMTS) from the Internet,
• modulated, up-converted to the proper frequency,
• multiplexed with standard video traffic in the
  analog domain,
• and transmitted through the distribution plant

37
Data Services (5)

• Principles of Operation (5)
• Continuing OperationsReturn path
• traffic is received at the head-end,
• some data split off (pay-per-view, telephony,
  monitoring)
• the remaining data traffic is sent to a QPSK or
  QAM-16 demodulator, which then sends bits to a
  terminal server,
• traffic is then sent to a local router or switch
  for transmission to a local server, the Internet.

38
Data Services (6)

• Principles of Operation (6)

39
Data Services (7)

• Principles of Operation (7)
• Return path bandwidth arbitration (1)
• Bandwidth arbitration i.e., MAC protocol needed
  for multiple customers to request use of return
  bandwidth on return path
• Objectives of MAC
• Support of the maximum number of possible users
  per cluster
• Minimize latency on data transfer
• Provide fairness so that all users get some
  access
• Achieve maximum bandwidth utilization of the
  return path
• Support multiple classes of service

40
Data Services (8)

• Principles of Operation (8)
• Return path bandwidth arbitration (2)
• Collision-avoidance or credit-allocation scheme
  instead of using standard Ethernet techniques
• Key features
• User data, requests to transmit user data sent
  in fixed-length increments, or time slots
• Variable-length packets sent by multiple time
  slots per request
• Mechanisms exits to provide for QoS
• CRC checksums to detect errored packets, not to
  correct
• Requests to transmit occur in special packets or
  may be piggybacked inside user data packets

41
Data Services (9)

• Principles of Operation (9)
• Return path bandwidth arbitration (3)
• Normally, only one request may be outstanding
  form a single subscribe at a time
• When subscribers collide, they are unaware of the
  event unless informed by the head-end
• When informed of a collision, cable modem
  performs a backoff and tries again
• High level of ongoing management
• Power management
• Changing upstream channels
• Changing upstream parameters

42
Data Services (10)

• Summary of Data Services

43
Data Services (11)

• Challenges to Data over Cable
• Competition from xDSL and other services
• Big telephone companies
• New generation carriers
• Wireless carriers using various technologies
• Return Path Problems
• Frequency range limited 5 42 MHz
• Shared nature creates a funneling effect
• Impairments and noises at home funneled together
  while moving upstream

44
Data Services (12)

• Challenges to Data over Cable (2)
• Sources of Ingress
• Ham radio and citizens band(CB) radio
• Poorly insulated equipment in the home
• Emission from outside the home
• Output of digital signals from the home terminal
• Tampering and malice
• Loose or poor quality F-connectors and bad cable
  quality and installation in the home
• Corrosion

45
Data Services (13)

• Challenges to Data over Cable (3)
• Scaling Techniques
• Multiple return paths per forward channels
• Multiple paths prevents traffic collision caused
  by path traffic increase
• Having multiple return paths potentially
  complicates the MAC design
• Additional Forward Channels
• Convert a forward channel of 27 Mbps for return
  path
• Smaller Clusters
• Extend fiber closer to the user, reducing user
  cluster smaller
• Equal Access
• Local telephone companies are required to offer
  equal access to any long-distance telephone
  service provider.
• MSOs offering data service are not required to
  offer equal access to ISPs but changes are being
  sought for.

46
Integration of Video-Data Units (1)

• The differences between video and data
• Tradeoff between latency and high-integrity bit
  rate
• Data can withstand relatively higher bit error
  rate (higher layer proc)
• Video requires more interleaving, so generates
  more latency
• Common hardware/software in TV and DOCSIS
• Use of MPEG framing
• Use of QAM(QPSK) modulation on the
  forward(return) path
• Use of concatenated Reed-Solomon forward error
  correction
• Requirement for a MAC protocol for the return
  path
• Requirement for local processing to manipulate
  digital content

47
Integration of Video-Data Units (2)

• Convergence of digital TV set tops with cable
  modems
• Encouraged since set tops are likely to have a
  built-in IP stack
• Beneficial to users as two STBs will be needed
  otherwise.
• Possible by having a combined OpenCable and
  DOCSIS STB.
• Then data collection (for ppv) can be done any
  time without phone call.
• The MAC block must comply with the DOCSIS
  standard, as well as comply with raging and
  control.
• Combined OpenCable/DVB set-top for use in Europe.
  
• DVB is used as the DAVIC data standard in
  parallel with DOCSIS.
• Control information sent to subscriber in
  separate data channel(OOB)

48
Digital CATV (1)

• Faster developing of digital modulation-related
  parts than analog parts
• SDH/SONET-based digital optical networks motivate
  strongly digitalization of CATV network
• Digital CATV makes sense
• From the signal compression point of view
• Video signals of NTSC broadcast quality
  compression of 3-6Mbps
• MPEG-2 compression of HDTV into normal 6MHz TV
  channel

49
Digital CATV (2)

• HFC-FTTC combination network
• Overlaid digital-analog network
• Digital ATM channel overlaid over analog CATV
  network to ONU by fiber, where two channels split
  
• Digital ATM channel delivered over VDSL TP to
  home for broadband conversational services
• Analog CATV channel loaded on coaxial cable for
  entertainment video services
• Could evolve to FTTH, competing with FTTC

50
Standards for Cable Modem (1)

• DOCSIS
• Data-Over-Cable Service Interface Specifications
• CableLabs, MCNS(Mulimedia Cable Network System )
  partners
• Late 1996
• Downstream passband 50MHz750MHz (system
  dependent upper limit)
• Upstream passband 542MHz
• Downstream data rates 27Mbps
• Upstream data rates 10Mbps provided by FR
  return path on cable or telephone return channel

51
Standards for Cable Modem (2)

• DOCSIS1.1
• Functional enhancement over DOCSIS1.0
• Completed in 2000
• Dynamic QoS and hardware fragmentation to reduce
  application specific transport latency
• Enabling multimedia services including voice
• CableLabs to develop open standards for
  delivering IP telecommunications and multimedia
  services through PacketCable initiative
• PakcetCable1.3 issued in 2002

52
Standards for Cable Modem (3)

• DOCSIS2.0
• 3rd generation spec. ITU approved in Dec. 2002
• Focuses on increasing upstream capacity and
  reliability
• Advanced physical layer implementation
• S-CDMA (synchronous CDMA) and A-TDMA (advanced
  frequency agile TDMA) operating simultaneously in
  530.72MHz
• All versions of Cable Modems can co-exist on the
  same CMTS
• Higher data rates (30Mbps) in very noisy upstream
  channels

53
Standards for Cable Modem (4)

• EuroDOCSIS
• Essentially the same as DOCSIS apart from the
  physical layer which is DVB-compliant
• ETSI adopted DVB2.0 as ETS 300 800
• Out-of-band and in-band transmission options
  applicable to interactive set-top boxes and cable
  modems
• ETS 300 800 selected by DAVIC to be DAVIC 1.5
  spec for cable modems

54
Standards for Cable Modem (5)

• DAVIC
• Digital Audio-Visual Council
• Industry organization focusing on developing
  specifications for supporting digital audiovisual
  applications and services over different physical
  medium (ADSL, HFC, HTTC, wireless)
• DAVIC1.1 digital video over HFC and SDV using
  ATM
• DAVIC1.2 support of high-speed data and Internet
  access
• DAVIC1.5 DAVIC intranet for QoS management of
  audio-visual services over IP

55
Cable Penetration Worldwide (1)

• US

56
Cable Penetration in Korea (1)

• 11 million broadband access subscribers (Jun.
  2003)
• 6.2 million xDSL (56.5), 3.8 million Cable
  (34.5)

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57
Cable Penetration in Korea (2)

• Service Providers and Base Technologies

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58
Cost Comparison - xDSL vs Cable
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