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Broadband Access Over CableBroadband Access Over Cable
Rolf Minder, SE CCIE #5972SP Broadband Solutionsrminder@cisco.com
September 19, 2001
2© 2001, Cisco Systems, Inc. www.cisco.com
AgendaAgenda
• DOCSIS Overview
• Cable Plant
• Cable Modem Provisioning
• DOCSIS 1.1 Key Features
3© 2001, Cisco Systems, Inc.
DOCSIS Overview
What you really need to know
DOCSIS OverviewDOCSIS Overview
What you really need to knowWhat you really need to know
4© 2001, Cisco Systems, Inc. www.cisco.com
IntroductionThe Underlying Technologies
IntroductionThe Underlying Technologies
• DOCSISData Over Cable Service Interface Specification
• DVB-RCDigital Video Broadcast, European answer to DOCSIS
• EuroDOCSISModified for the European 8MHz, AnnexA,5-65MHz upstream channel
5© 2001, Cisco Systems, Inc. www.cisco.com
DOCSIS Overview (What & Why)
DOCSIS Overview (What & Why)
• What is DOCSIS
DOCSIS (Data Over Cable System Interface Specification) is a standard developed under the guidance of MCNS (Multimedia Cable Network System) for the rapid deployment of Data over Cable.
6© 2001, Cisco Systems, Inc. www.cisco.com
• Why DOCSIS?
– Standards based
Standards based products bring more competition to the environment. Competition usually brings down the cost of products
– Feature richDOCSIS brings along with it the ability to add features to your network and differentiate service. The first example of this will be the Voice over IP on the CM
– Future Proof
With Standards brings in more avenues for others to get in the game. On demand video, IP video and a host of other possibilities
DOCSIS Overview (What & Why)
7© 2001, Cisco Systems, Inc. www.cisco.com
• Components of DOCSIS– Cable System
– CMTS (Cable Modem Termination System)
– CM (Cable Modem)
– “Back Office” Services
• DHCP
• TFTP
• ToD
DOCSIS Overview(Components of DOCSIS)
8© 2001, Cisco Systems, Inc. www.cisco.com
• CMTS (Cable Modem Termination System)— usually in the head end. It is the device that modulates the signal to the cable modem (CM) and demodulates the CM’s response.
• Cable modem—associated with customer premise equipment. The CM modulates and demodulates signals to and from the CMTS.
DOCSIS Overview(Components of DOCSIS)
9© 2001, Cisco Systems, Inc. www.cisco.com
• “Back Office” Services
– DHCP (Dynamic Host Configuration Protocol) Server
– RFC 2131—provides dynamically assigned IP addresses for modems and PC’s
– Allows re-use of assigned IP addresses
– TOD (Time Of Day) Server
– RFC 868—provides timestamps for logged events
– TFTP (Trivial File Transfer Protocol) Server
– RFC 1350—provides modem configuration files
– Bin File created with Configuration File Editor
DOCSIS Overview(Components of DOCSIS)
10© 2001, Cisco Systems, Inc. www.cisco.com
The Big Picture
• Components- CMTS, Line cards- IF to RF up converter- Cable ModemMCNS compliant
RHE(RegionalHead End)
OtherSources
LHE
LHE
FiberFiber
Tap
Distribution
HFC(Hybrid
Fiber Coax)
TrunksLocalLocalHead EndHead EndReceiver Modulator
and Scrambler
Receiver Modulatorand Scrambler
For EachChannel
Bi-directionalAmplifiers
FiberNode
Cable Cable ModemModem
UpConvertUpConvert
UpUpStreamStream
DownDownStreamStream
TV
LCLCuBRuBR 72467246
26
11© 2001, Cisco Systems, Inc.
DOCSIS
Cable Plant
DOCSISDOCSIS
Cable PlantCable Plant
12© 2001, Cisco Systems, Inc. www.cisco.com
Cable Plant ComponentsCable Plant Components
Head-End
COAXTap
Drop
Cable Modem PC
Broadband Router
uBR
InternetInternet
Node Node Node
Node
Node
Node
NodeNodeNode
PSTN
Lifetime VH-1
Packetized DataNICK
E!
Lifetime VH-1
Packetized DataNICK
E!
Hub
Hub
Hub
13© 2001, Cisco Systems, Inc. www.cisco.com
RF SpectrumRF Spectrum
• Radio Freq (RF)Above audio to infrared
• Down Stream (DS)Cable company to subscriber55–750 MHz
• Up Stream (US)Subscriber to cable company5–42 MHz
Frequency SpectrumFrequency Spectrum
X-Rays
Frequency
110/220 VElectrical Signal60 Hz
IFIF5–45 MHz5–45 MHz
Infrared Ultra Violet
GammaRays
CB 27 MHz
Channel 255 MHz
Satellite
VisibleLight
VisibleLight
RF (VHF and UHF) 55–750 MHz
RF (VHF and UHF) 55–750 MHz
MicrowaveAbove 1 GHzMicrowave
Above 1 GHz
14© 2001, Cisco Systems, Inc. www.cisco.com
Composite Downstream Spectrum
Composite Downstream Spectrum
• QAM
Quadrature Amplitude Modulation
AmplitudedBmV
Video
6.0 MHz
Multiple NTSC ChannelsMultiple NTSC Channels
Frequency MHz
0
-10
-20
-30
-40
-50
Down StreamQAM Data
Video
6.0 MHz 6.0 MHz
15© 2001, Cisco Systems, Inc. www.cisco.com
Basic RF and Multiplexing Concepts
Basic RF and Multiplexing Concepts
• MultiplexingTDM (Time Division Multiplexing)
TDMA (Time Division Multiple Access)
FDM (Frequency Division Multiplexing)
• ModulationQPSK (Quadrature Phase Shift Keying)
QAM (Quadrature Amplitude Modulation)
• FEC (Forward Error Correction)(Reed Solomon Coding Algorithm)
16© 2001, Cisco Systems, Inc. www.cisco.com
DOCSIS Modulation ModesDOCSIS Modulation Modes
• Downstream:
64 QAM; 256 QAM
• Upstream:
QPSK; 16 QAM
.. .... ..
.
16 QAM Constellation
.. ..
.. ..
17© 2001, Cisco Systems, Inc. www.cisco.com
Symbol MappingSymbol Mapping
Q1
I1
01
00
11
100111
0110
0101
0100
1101
1100
1111
1110
0010 0000
0011 0001
1000 1010
1001 1011
Q
I
QPSK Symbol Mapping
16QAM Gray-Coded Symbol mapping
18© 2001, Cisco Systems, Inc. www.cisco.com
Downstream Phase NoiseDownstream Phase Noise
19© 2001, Cisco Systems, Inc. www.cisco.com
Bit Error Rate
• BERErred bits among total transmitted payload
BER of 1 in 10 million pay load bits acceptable
Main cause is low C/N
Sharp threshold
BER
QPSKQPSK
QAMQAM--256256QAMQAM--6464
Bit Error RateBit Error Rate
C/N dB
10
10 20 30 400
QAMQAM--1616
10
10
10
0
-5
-10
-20
1010--77
20© 2001, Cisco Systems, Inc. www.cisco.com
Data Rates
FreqFreqRange MHzRange MHz
TDMATDMACarrierCarrier
QAMQAM--2562568 b/Sym8 b/Sym
QAMQAM--64646 b/Sym6 b/Sym
QAMQAM--16164 b/Sym4 b/Sym
QPSKQPSK2 b/Sym2 b/Sym
54-860
54-860
5454--860860
54-860
5-42
5-42
55--4242
5-42
ChannelChannelWidth MHzWidth MHz
6
8
66
8
1.6
3.2
1.61.6
3.2
BaudBaudRate Rate MSpsMSps
5.3605
7.15
5.0575.057
6.74
1.28
2.56
1.281.28
2.56
Raw BitRaw BitRate MbpsRate Mbps
42.88
57.2
30.3430.34
40.44
5.12
10.24
2.562.56
5.12
PayloadPayloadRate MbpsRate Mbps
38
51
2727
36
4.6
9
2.32.3
4.638
21© 2001, Cisco Systems, Inc.
DOCSIS
Cable Modem Provisioning
DOCSISDOCSIS
Cable Modem ProvisioningCable Modem Provisioning
22© 2001, Cisco Systems, Inc. www.cisco.com
MCNS Data over CableMCNS Data over Cable
Protocols
OSIOSITransportTransport
Data LinkData Link
PhysicalPhysical
NetworkNetwork
TCP or UDP
IPMCNS Control
Messages
IEEE 802.2
MCNS MAC (MPEG Frames)
HFCHFC
Up StreamUp StreamTDMA
Digital IF Modulation(QPSK or QAM-16)
Down StreamDown StreamTDM
Digital RF Modulation(QAM-64 or QAM-256)
23© 2001, Cisco Systems, Inc. www.cisco.com
DOCSIS CM Self Provisioning Process
(Downstream Scan)
DOCSIS CM Self Provisioning Process
(Downstream Scan)
Head End InterfaceHead End Interface Cable ModemCable ModemClock Synch B’cast(One per 1.63 msec)Clock Synch B’cast(One per 1.63 msec)
UCD B’castUS Channel Descriptor,DS channel ID and Minislot Size(One per Second per US Channel)
UCD B’castUS Channel Descriptor,DS channel ID and Minislot Size(One per Second per US Channel)
MAP B’castContains US Time sharing Information(One per 4 ms per US Channel)
MAP B’castContains US Time sharing Information(One per 4 ms per US Channel)
Wait for MAPLook for Shared Request Slots(Available Every 2 Seconds)
Wait for MAPLook for Shared Request Slots(Available Every 2 Seconds)
Wait for UCDSet US Channel FrequencyWait for UCDSet US Channel Frequency
Scan DS for QAMWait for Clock SynchSet Signaling Clock
Fails if No/Bad DS
Scan DS for QAMWait for Clock SynchSet Signaling Clock
Fails if No/Bad DS
24© 2001, Cisco Systems, Inc. www.cisco.com
Head End InterfaceHead End Interface Cable ModemCable Modem
Link EstablishmentLink Establishment
Ranging Response(Can Be Sent as Needed)US/DS frequency Can Be ChangedContains Temp SID
Fails if No/Bad USOr Too Many Modems
Ranging Response(Can Be Sent as Needed)US/DS frequency Can Be ChangedContains Temp SID
Fails if No/Bad USOr Too Many Modems
Keep Alive(One per 30 Second per Modem)Keep Alive(One per 30 Second per Modem)
Ranging Response(Can Be Sent As Needed)US?DS Frequency Can Be Changed)
Ranging Response(Can Be Sent As Needed)US?DS Frequency Can Be Changed)
Ranging ResponseOnly in Shared Request SlotsUse USE = 0 (Service ID)
Ranging ResponseOnly in Shared Request SlotsUse USE = 0 (Service ID)
Wait for Ranging ResponseAdjust Clock (in 6.25 US Ticks)Adjust Power (in 0.25 dB Steps)
Wait for Ranging ResponseAdjust Clock (in 6.25 US Ticks)Adjust Power (in 0.25 dB Steps)
Wait for 1st Keep Alive
Ranging RequestNow in AllocatedMaintenance Slot
Wait for 1st Keep Alive
Ranging RequestNow in AllocatedMaintenance Slot
(Cable Modem HFC Interface Line Protocol Up, Not Online Yet)Maintain Station Link Using Periodic Keep Alives
Link Broken if Missed 16 Keep Alives
(Cable Modem HFC Interface Line Protocol Up, Not Online Yet)Maintain Station Link Using Periodic Keep Alives
Link Broken if Missed 16 Keep Alives
DOCSIS CM Self Provisioning Process(Power Ranging)
25© 2001, Cisco Systems, Inc. www.cisco.com
Head End InterfaceHead End Interface Cable ModemCable Modem
Map B’CastContains US Time Sharing Info(One per Four ms per US Channel
Map B’CastContains US Time Sharing Info(One per Four ms per US Channel
DHCP ResponseContains ID Addr, Default GW, ToD Server, TFTP Server Addr and TFTP Boot Config File NameFrom a DHCP Server
DHCP ResponseContains ID Addr, Default GW, ToD Server, TFTP Server Addr and TFTP Boot Config File NameFrom a DHCP Server
ToD ResponseContains Time of DayRFC 868, not NTPFrom a ToD Server
ToD ResponseContains Time of DayRFC 868, not NTPFrom a ToD Server
Bandwidth RequestOnly in Shared Request SlotsUse Temp SID (Service ID)(Needed for Every Use of US)
Bandwidth RequestOnly in Shared Request SlotsUse Temp SID (Service ID)(Needed for Every Use of US)
ToD RequestNow in Allocated SlotsToD RequestNow in Allocated Slots
DHCP RequestNow in Allocated SlotsDHCP RequestNow in Allocated Slots
DOCSIS CM Self Provisioning Process
(IP / TOD Registration)
26© 2001, Cisco Systems, Inc. www.cisco.com
Head End InterfaceHead End Interface Cable ModemCable Modem
TFTP Boot File TransferContains QoS ParametersSpecifies Privacy, New Software Downloads, etc.From an TFTP Server
TFTP Boot File TransferContains QoS ParametersSpecifies Privacy, New Software Downloads, etc.From an TFTP Server
Registration ResponseContains Assigned SIDModem Registered
Fail if QoS not AvailableOr Authentication Failed
Registration ResponseContains Assigned SIDModem Registered
Fail if QoS not AvailableOr Authentication Failed
TFTP Boot RequestSend TFTP Boot File NameNow in Allocated Slots
TFTP Boot RequestSend TFTP Boot File NameNow in Allocated Slots
Registration RequestSend QoS ParametersNow in Allocated Slots
Registration RequestSend QoS ParametersNow in Allocated Slots
Cable Modem OnlineCable Modem OnlineMaintain Station Link Using Periodic Keep Alives
May Need to Hop Upstream Frequency Due to Noise (Means Link Reset)Maintain Station Link Using Periodic Keep Alives
May Need to Hop Upstream Frequency Due to Noise (Means Link Reset)
DOCSIS CM Self Provisioning Process
(Authentication / QoS Configuration)
27© 2001, Cisco Systems, Inc. www.cisco.com
Head End InterfaceHead End Interface Cable ModemCable Modem
Encrypted Data Flow EnabledEncrypted Data Flow Enabled
Generate Private KEK
Key Encryption KeyEncrypt KEK by Public Key
Generate Private KEK
Key Encryption KeyEncrypt KEK by Public Key
Send Public KeyRequest KEKSend Public KeyRequest KEK
Decrypt KEK Using Public KeyKEK Life Is Seven Days(Configurable One to 70 Days)Request TEK
Decrypt KEK Using Public KeyKEK Life Is Seven Days(Configurable One to 70 Days)Request TEK
Only Data inside IEEE 802.2 Frame is Encrypted Using TEK40/56 Bit DES Encryption Supported
Must re-establish Keys within configured Grace Period before Life Expiry
Only Data inside IEEE 802.2 Frame is Encrypted Using TEK40/56 Bit DES Encryption Supported
Must re-establish Keys within configured Grace Period before Life Expiry
Generate Private TEK
Traffic Encryption KeyEncrypt TEK by KEK
Generate Private TEK
Traffic Encryption KeyEncrypt TEK by KEK
Decrypt TEK Using KEKTEK Life Is 12 Hours(Configurable 30 Min. toSeven Days)
Decrypt TEK Using KEKTEK Life Is 12 Hours(Configurable 30 Min. toSeven Days)
DOCSIS CM Self Provisioning Process (Baseline Privacy)
28© 2001, Cisco Systems, Inc. www.cisco.com
offline—modem considered offlineinit(r1)—modem sent initial ranginginit(r2)—modem is ranginginit(rc)—ranging completeinit(d)—dhcp request receivedinit(i)—dhcp reply received; IP address assignedinit(t)—TOD request received.init(o)—TFTP request was received.Online—modem registered, enabled for dataonline(d)—modem registered, but network access is disabledonline(pk)—modem registered, BPI enabled and KEK assignedonline(pt)—modem registered, BPI enabled and TEK assignedreject(m)—registration refused due to bad MICreject(c)—registration refused due to bad COSreject(pk)—KEK modem key assignment rejectedreject(pt)—TEK modem key assignment rejected
Show Cable Modem StatesShow Cable Modem States
29© 2001, Cisco Systems, Inc.
DOCSIS
DOCSIS 1.1 Key Features
DOCSISDOCSIS
DOCSIS 1.1 Key Features DOCSIS 1.1 Key Features
30© 2001, Cisco Systems, Inc. www.cisco.com
DOCSIS 1.0 QoS LimitationsDOCSIS 1.0 QoS Limitations
• Per CM QoS
• Based on SID and QoS Profile
• No means to distinguish different types of CM traffic
• All CM traffic is treated equal
• Unsuitable for simultaneous Data/Voice/Video traffic
31© 2001, Cisco Systems, Inc. www.cisco.com
DOCSIS 1.1 Key FeaturesDOCSIS 1.1 Key Features
• Flow based QoS for multiple simultaneous traffic streams to a CM
• Advanced upstream scheduling services for different traffic types
• Flexible signaling model for “on-demand” QoS
• Improved provisioning and authorization
• Features for improved bandwidth utilization
• Extra “security” features (BPI+)
32© 2001, Cisco Systems, Inc. www.cisco.com
Key Features OverviewKey Features Overview
• Best Effort
• CIR
data with rate guarantees
• Real Time Polling (RTPS)periodic contention free request slots
• Unsolicited Grants (UGS)
CBR like - fixed size slots at fixed interval
• Unsolicited Grants with Activity Detection UGS-AD)
combination of UGS and RTPS
• Non Real Time Polling (nRTPS)
33© 2001, Cisco Systems, Inc. www.cisco.com
Key Features continuedKey Features continued
• QoS can be setup on-demand using Dynamic Service MAC Messages
DSA (Dynamic Service Add)
Add a new service flow
DSC (Dynamic Service Change)
Modify existing service flow parameters
DSD (Dynamic Service Delete)
Delete a service flow
• Geared towards VoIP style applications
34© 2001, Cisco Systems, Inc. www.cisco.com
Key Features continuedKey Features continued
• FragmentationAllows grants to be fragmented to improve scheduling
efficiency
Improves MAC latency characteristics
• Payload Header SuppressionAllows for suppression of constant header fields and
transmission of variable payloads
Especially useful in VoIP type applications where header size is comparable to payload size
35© 2001, Cisco Systems, Inc. www.cisco.com
Other Sources of InformationOther Sources of Information
• QoS in Cable Data Networkshttp://www.cisco.com/warp/public/cc/pd/rt/ub7200/ub7246/tech/caqos_wp.htm
• IP Quality of Servicehttp://www.ciscopress.com/ book.cfm?series=1&book=173
• Configuring Head-End Broadband Access Router Features http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/multi_c/mcprt3/mcdhubr.htm
• Data Over Cable Services Interface Specification http://www.cablelabs.com
• Configuring Voice over IP (VoIP) http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/multi_c/mcprt1/mcdvoip.htm
36© 2001, Cisco Systems, Inc. www.cisco.com
• You need a CMTS, DHCP, TFTP, TOD, and CM along with the cable plant to make a DOCSIS system
• DOCSIS is a standard based system that provides data over cable
DOCSIS Summary
37© 2000, Cisco Systems, Inc.