Download May – Greg White, Lead Architect

Overview of Cable Data Networks
—
DOCSIS Technology Primer
May 16, 2006
Greg White
Lead Architect - Broadband Access
Cable Television Laboratories, Inc.
www.cablelabs.com
Topics
• Overview of the cable data network
• DOCSIS Technical Overview
– Basics
– Physical (PHY) layer technology
– Media Access Control (MAC) layer technology
• Future Developments
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Overview of the
Cable Data Network
Broadband Trends
• IP-based broadband networks have revolutionized wireline communications
– Number of U.S. broadband subscribers expected to hit 80M by 2009 (Sanford &
Bernstein)
• Customers value broadband for a wide range of real-time communication and
entertainment services
–
–
–
–
–
VoIP and video telephony
Online-gaming
Music and content acquisition and distribution
Instant Messaging
Video content delivery (IPTV)
• Cable operators, telephone companies, and independent service providers are
competing to offer new services to broadband customers
• VoIP has become a ‘killer’ application and created a multibillion dollar market
opportunity
• Many MSOs are dabbling in IPTV types of video services.
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Over 64 Million DOCSIS® Modems
Shipped Worldwide
Cumulative DOCSIS Modem Shipments
80
Million
60
40
Rest of World
North America
20
0
2000
2001
2002
2003
2004
2005
(2Q)
Source: Cable Datacom News, Kinetic Strategies, September 2005
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Terms
• DOCSIS – Data-Over-Cable Service Interface Specification
– Set of standardized protocol specifications that allow multi-vendor
interoperability for CM & CMTS
• CM – Cable Modem
– Device at the customer’s premises
• CMTS – Cable Modem Termination System
– Device at the operator’s headend
• HFC – Hybrid-Fiber Coax
– The physical media that separates the CM & CMTS
• MSO – Multiple System Operator
– Synonymous with cable operator
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Cable Architecture
PacketCable
Services
MPEG Services
DOCSIS
•HVAC control
•Fire sense & control
•Security
•Air quality monitoring
•Child monitoring
•Energy management, etc.
CableHome
CM
CMTS
CM
CM
CM
CM
Operator Core
Backbone
IP Services
•Remote file sharing
•Shared calendar
•Unified messaging
•Managed services
Core Network
Operator
Aggregation
network
CM
CMTS
CM
CM
CMTS
Aggregation Network
CM
CM
CM
Access Network
Operator administered
Backend
Headend
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
CPE
Modern Cable Data Network
(Aggregation Network)
Distribution
Hub
Interne
t
mux
mux
Regional Data Network
DWDM
DWDM
Master Headend
DWDM
Distribution Hub
GigE/IP
PSTN
Regional Content Servers
Distribution
Hub
DOCSIS CMTS
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
HFC
(access
network)
Hybrid Fiber-Coaxial Network
(Access Network)
Coax
Fiber Node
Fiber
Modem
Fiber Tx
Modem
CMTS
Modem
Fiber Rx
Fiber Node
Modem
Modem
Modem
Modem
Bi-Directional Amp
High-Pass (50-860MHz)
H
H
L
L
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Low-Pass (5-42MHz)
Extending into the home network
Entertainment
Device
Printer
PC
Mobile Device
Coax
Cable
Residential
Gateway
IP Audio
MP3 Player
Home Security
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
DOCSIS®
Technical Overview
What is DOCSIS ?
• DOCSIS defines the PHY & MAC layer protocol for
communication and Ethernet frame carriage between the
CMTS and the CM.
• DOCSIS also defines a provisioning and management
framework
• Three published versions:*
– DOCSIS 1.0 (ca. 1996) (ITU-T J.112-B (3/98))
– DOCSIS 1.1 (ca. 1999) (ITU-T J.112-B (3/04))
– DOCSIS 2.0 (ca. 2001) (ITU-T J.122 (12/02))
• Next generation in progress:
– DOCSIS 3.0 (ca. 2006)
*available at www.cablemodem.com
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Cable Modem Protocol Stack
Application Layer
SNMP, TFTP, DHCP, ToD, IGMP
Presentation Layer
Session Layer
Transport Layer
TCP/UDP
Network Layer
IP, ICMP, ARP
Link Layer
Control
802.2 LLC
Media Access
Control
DOCSIS MAC
802.3 MAC
Physical Layer
DOCSIS PHY
10/100Base-T, USB
OSI Ref. Model
Cable Interface
Customer Interface
Data
Link
Layer
802.1d Bridge
802.2 LLC
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
DOCSIS Physical Layer
HFC Spectrum Allocation
AWGN (~1/f)
Downstream
…
~
~
DOCSIS
…
DOCSIS
~
~
Upstream
5
42 54
Analog Video
Digital Video
(NTSC/PAL)
(MPEG/DVB)
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
860
f (MHz)
Downstream Physical Layer
Region
Standard
North America
Europe
ITU-T J.83-B
ETSI EN 300 429 (DVB)
Modulation
64QAM
256QAM
64QAM
256QAM
Channel Spacing
6 MHz
6 MHz
8 MHz
8 MHz
Symbol Rate (Mbaud)
5.057
5.361
6.952
6.952
Raw Data Rate (Mbps)
30.34
42.88
41.71
55.62
TCM rate
14/15
19/20
N/A
N/A
(128,122)
(128,122)
(204,188)
(204,188)
26.97
38.80
38.44
51.25
Reed-Solomon FEC
Post-FEC Data Rate (Mbps)
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Upstream Physical Layer
Version
DOCSIS 1.x
DOCSIS 2.0
Format
Bursted F/TDMA
Bursted F/TDMA, F/S-CDMA
QPSK, 16QAM
QPSK, 8QAM, 16QAM,
32QAM, 64QAM, 128QAM
Channel Width (MHz)
0.2, 0.4, 0.8, 1.6, 3.2
0.2, 0.4, 0.8, 1.6, 3.2, 6.4
Symbol Rate (Mbaud)
0.16, 0.32, 0.64, 1.28,
2.56
0.16, 0.32, 0.64, 1.28, 2.56,
5.12
Raw Data Rate (Mbps)
0.32 – 10.24
0.32 – 35.84
Pre-Equalization
8-tap FIR (opt. in 1.0)
24-tap FIR
Trellis Coded
Modulation Rate
N/A
Optional: n/n+1
Reed-Solomon FEC
T=0-10; k=16-253
T=0-16; k=16-253
Post-FEC Data Rate
(Mbps)
0.14 – 10.24
0.11 – 30.72
Modulation
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
DOCSIS Upstream PHY Modes
• Time Division Multiple Access (TDMA)
– CMs take turns transmitting, one at a time, each occupies the
entire upstream channel during transmission.
– Tranmissions consist of: preamble, data burst, guard time
– Better immunity to narrowband interferers
• Synchronous Code Division Mult. Access (S-CDMA)
–
–
–
–
–
DOCSIS 2.0 only
Direct Sequence Spread Spectrum
Multiple CMs can transmit simultaneously
Much shorter preamble, no guard time
Slightly more efficient, better immunity to burst noise
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
S-CDMA Basics
•
S-CDMA is a multiple access modulation technique
which uses direct-sequence spread-spectrum and a set of
128 orthogonal codes.
•
Orthogonality is maintained by aligning and
synchronizing the transmitted waveforms.
•
Multiple access is supported through both time and code
domain allocation (more than one CM can transmit at a
time).
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
S-CDMA System
Code 1
Code 1
Spreading
De-spreading
Data stream 1
Data stream 1
Code 2
+
Data stream 2
RF
Channel
Code 2
Data stream 2
Spreading
De-spreading
Code N
Code N
Spreading
De-spreading
Data stream N
Data stream N
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Ranging
• Ranging is used to synchronize CMs and align them with
the CMTS receiver.
–
–
–
–
TDMA requires coarse alignment (±800 nsec)
S-CDMA requires accurate alignment (±1 nsec).
CM sends a RNG-REQ message
CMTS responds with a RNG-RSP message
• Contains Timing Adjust (Resolution = 0.3815 nsec.)
• also Power adjust, Frequency adjust, Pre-EQ params.
• Ranging is a two-step process:
– Initial maintenance (coarse time alignment).
– Periodic station maintenance (fine time alignment).
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
DOCSIS MAC Layer
DOCSIS MAC
• Media Access Control (MAC) Sub-Layer
– Controls access to the Physical Layer (the channel)
– Allows multiple users to share a communications channel
• One-to-many architecture
• Two physical channels (upstream/downstream) both
controlled by the CMTS
• No direct peer-to-peer (CM-to-CM) communication
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
DOCSIS Downstream MAC
•
•
•
•
Only one transmitter - the CMTS
Multiple receivers - the CMs
CMTS manages its own transmissions.
Quality of Service can be assured by:
– Token bucket rate limiting
– Reserved data rates
– Traffic Priority
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
DOCSIS Upstream MAC
• Multiple transmitters - the CMs
• One receiver - the CMTS
• The CMTS arbitrates access to the channel
– Upstream channel is described in minislots
• 2n*6.25µs in TDMA mode
– “MAP” messages are broadcast downstream to describe who
gets to transmit and when
– One MAP message per upstream channel per MAP interval
(chosen by CMTS, 2-5ms typical)
• Access Control is Reservation based
– Reservation requests are sent in contention (“Slotted-Aloha”)
– Reservations can also be pre-scheduled at periodic intervals
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
MAPs are broadcast by the CMTS on the downstream channel
Downstream Channel
MAP
MAP
Upstream Channel (TDMA)
Transmit Opportunities
mini-slots
CM tx opportunity
previous map
request contention area
CM tx opportunity
ranging
minislots described by the current map
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
as-yet
unmapped
minislots
S-CDMA Mini-slot Mapping
• Mini-slots are one-dimensional (transmission in
time only).
• S-CDMA transmissions are two-dimensional
(transmissions in time and code domains).
– S-CDMA frame is up to 128 codes by K spreading
intervals.
– Frame size parameters are configurable.
• The PHY layer maps the mini-slots to frames.
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
S-CDMA Framing Structure
K spreading intervals
K spreading intervals
K spreading intervals
...
...
...
codes
code 127
code 126
code 3
code 2
code 1
code 0
frame f
frame f+1
frame f+2
time
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Mini-slot Numbering and Timestamp Snapshot
K spreading intervals
K spreading intervals
K spreading intervals
Mini-slot m+62
Mini-slot m+125
Mini-slot m+188
code 127
code 126
...
...
...
code 3
Mini-slot m
Mini-slot m+63
Mini-slot m+126
code 2
code 1
code 0
t
frame f
timestamp counts
In this example, 126
codes are active.
frame f+1
t1
t2
t3
frame f+2
t4
timestamp count
minislot number
frame
number
32 bits
32 bits
8 bits
timestamp snapshot
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Included
in UCD
Ranging, again
• Initial Ranging
–First upstream transmission by CM
–To lock-in time sync, frequency, and power
• Periodic Ranging
–a.k.a. Periodic Maintenance, Station Maintenance
–CMTS must offer to each CM at least once every 35 seconds
•generally much more often
•If not offered by CMTS (or missed by CM), CM declares T4 timeout
–To maintain sync, frequency, and power settings over daily plant
variations
•Temperature change
•Cable stretch, etc.
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
The Reservation Mechanism –
Requests and Grants
• When a CM has data to send, it:
– Waits for a Request contention interval in downstream MAP messages
– Randomly selects a sub-interval
– Transmits a 6-byte REQ message to the CMTS, which:
• identifies the CM (via Service ID)
• specifies the number of minislots needed
– Retransmits its request, if no response from the CMTS
• The CMTS then:
– Queues/prioritizes REQs
– Reserves future minislots for the requesting CMs
– Communicates the “Grants” to the CMs via MAP messages.
• The CM can have only one request outstanding at a time (per SID)
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Piggybacking
• Suppose the CM has sent a REQ to transmit Pkt #1.
• Before the grant time arrives, Pkt #2 is enqueued.
• The CM can “piggyback” a REQ for Pkt #2 in the
MAC header of Pkt #1.
• Avoids delay/backoff waiting for a contention interval,
and possibility of collision.
DOCSIS MAC
Header
FC
(1 byte)
REQ for
Pkt #2
EHDR Len
(1 byte)
0x13
Pkt #1
PDU #1
Length
(2 bytes)
EHDR
(4 bytes)
#minislots
HCS
(2 bytes)
SID
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Concatenation
• Suppose the CM has multiple small packets waiting in
the queue.
• The CM can pack them together into a large frame, and
send one REQ to transmit the concatenated frame
• CMTS unpacks the concatenated frame and forwards the
individual packets normally
• Avoids multiple REQ-grant latency cycles, collisions,
minimizes PHY overhead.
Concat
Header
Pkt#1
Pkt#2
Pkt#3
Pkt#4
Concatenation Frame
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
CM Provisioning
• During initialization, the CM downloads (via TFTP) a
configuration file from the cable operator
• Config file defines:
– Quality of Service (QoS) Parameters
• Rate limiting, bandwidth guarantees, etc.
– Filters
• e.g. block Windows file sharing (netBIOS, SMB, CIFS)
– Privacy (encryption) parameters
• The CM then sends a Registration Request message to
the CMTS containing the QoS parameters, and begins a
key exchange to initialize encryption.
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
CM Initialization Sequence
1. Downstream Channel Acquisition
– Scan for digital channels, acquire QAM,FEC,MPEG lock, identify DOCSIS
PID (program ID)
2. Upstream Channel Acquisition
– Select upstream channel based on Upstream Channel Descriptor messages
– Initial Ranging
• Find Initial Maintenance interval in MAP messages
• Send RNG-REQ, receive RNG-RSP, adjust transmitter, repeat if necessary
3. Establish IP Communications (DHCP)
4. Download Configuration File (TFTP)
5. Registration
– Send REG-REQ, receive REG-RSP, send REG-ACK
6. Initialize Encryption
– CM Authentication & Key exchange with CMTS
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
Future Developments
DOCSIS 3.0 Features
• Much higher bandwidth through channel bonding
– Starts at 160 Mbps Downstream, 120 Mbps Upstream & goes up from there
– Multiple physical channels are bound, treating them logically as one
– Channel bonding in both upstream and downstream
• IPv6 for advanced networking capabilities
– Expanded address space
• 667,000 per square nanometer of the earth’s surface vs. 22 per sq. mile today
– Improved operational capabilities
• IP Multicast to support IPTV-type applications
– Use existing standard protocols to manage IP video service
– Efficient “switched-video-like” bandwidth usage
• Programs are only delivered when viewers are present.
– Quality-of-Service so network congestion doesn’t impact video quality
• Stronger Traffic Encryption (128bit-AES instead of 56bit-DES)
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.
DOCSIS Roadmap
DOCSIS Version
DOCSIS 1.0
DOCSIS 1.1
DOCSIS 2.0
DOCSIS 3.0
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
40
5[1]
40
5[1]
40
5[1]
160 minimum[2]
5[1]
10
80[3]
10
80[3]
30
170[4]
120 minimum[5]
170[4]
Services
Broadband Internet
Tiered Services
VoIP
Video Conferencing
Commercial Services
Entertainment Video
Consumer Devices
Cable Modem
VoIP Phone (MTA)
Residential Gateway
Video Phone
Mobile Devices
IP Set-top Box
Downstream Bandwidth
Mbps/channel
Gbps/node
Upstream Bandwidth
Mbps/channel
Mbps/node
[1]
[2]
[3]
[4]
[5]
Assumes 750MHz of available downstream spectrum (125 channels)
Aggregation of four 6MHz channels. With 256QAM = 160 Mbps
Assumes ~25MHz of useable upstream spectrum
© Cable
Television
Laboratories,
Inc. 2006.
Assumes ~35MHz
of useable
upstream
spectrum
Aggregation of four 6.4 MHz channels
All Rights Reserved.
Thank You!
CableLabs
®
Cable Television Laboratories, Inc.
Greg C. White
Lead Architect
Broadband Access
858 Coal Creek Circle
Louisville, Colorado 80027-1266
Phone: 303-661-9100
Direct: 303-661-3822
Fax: 303-664-8192
Email: [email protected]
http://www.cablelabs.com
© Cable Television Laboratories, Inc. 2006. All Rights Reserved.