DOCSIS Cable Modem Connection Process

DOCSIS Cable Modem

Connection Process

Objectives

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! Telco Return

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DOCSIS Block Diagram

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! Cable Modem Termination System (CMTS) located at the headed ! Cable Network

! Cable Modem (CM) located at the Customer Premise

Cable Network HFC Customer Cable Modem (CM) CMTS Network Side Interface Wide-Area Network Cable Modem Termination System (CMTS) _{CM Customer Premises} Equipment Interface

4

DOCSIS Support Devices

TOD: Time of Day; TFTP: Trivial File Transfer Protocol; DHCP: Dynamic Host Configuration Protocol

Home Subscriber Data Services - High Speed - Packet Data - IP Routing - IP Multicast - CM open Architecture Television PC or MAC Splitter HFC

COAX Cable Modem Headend or Central Office Local Programming Video Laser Combiner/ Splitter Fiber Node Satellite NM CMTS Internet On-line Services Local Server TFTP Server TOD Server DHCP Server

DOCSIS DHCP Server

!

DHCP Server

! Assigns IP addresses to client computers

" addresses are “leased” to clients (Cable Modems or CPE’s) for a period of time

" IP addresses can be reserved for specific clients or assigned from “pools”

" clients may be authenticated based on their MAC address

" address may be assigned from different “pools” based on extended options

DHCP Server

DHCP Process

!The following parameters will be requested by the Cable Modem (CM) from the DHCP server

" IP address of the CM

" IP address of the TFTP Server (for DOCSIS Configuration file) " IP address of the DHCP Relay Agent (if the DCHP server resides

on a different network than the CM) " TFTP/DOCSIS Configuration file name " Subnet Mask to be used by the CM

" Time offset of the CM from Universal Coordinated Time (UTC) " Default IP Gateway

" Time of Day Server IP address " SYSLOG Server IP address

DHCP Server

DOCSIS ToD Server

!

ToD Server

! Internet Time Protocol (ITP)

" RFC 868

! UDP and TCP requests honored on port 37

! 32-bit value defining the number of seconds since 00:00 (midnight January 1, 1900 GMT)

ToD Server

DOCSIS TFTP Server

!

TFTP Server

! Trivial File Transfer Protocol " (RFC 1350)

! UDP port 69

! Small and easy to implement

! Read and write to and from remote servers

TFTP Server

TFTP Process

!The following settings MUST be included in the configuration file:

" Network Access Configuration Setting " Class of Service Configuration Setting

!The following settings are optional: " Downstream Frequency

" Upstream Channel ID

" Vendor ID

" Baseline Privacy

" Software Upgrade filename

" SNMP Write-Access Control

" SNMP MIB Object

" Software Server IP Address

" CPE Ethernet MAC Address

" Maximum Number of CPE’s (32 Max)

" SNMP IP Address (if applicable)

TFTP Server

Cable Modem Architectures

RF Return

!

RF-Return

!Suited for CATV networks that have been fully upgraded for two-way communications

!Delivers high-speed data downstream and upstream over broadband network

!DOCSIS establishes standard specification for data communications over HFC network

Cable Modem Architectures

Telco Return

!

Telco-Return Suited for CATV networks without

two-way capability

!Delivers high-speed data downstream over broadband network

!Relies on dial-up networking technology for return data !Does not require HFC plant upgrade to two-way RF

!DOCSIS also specifies data communications using a telephone-return architecture

!Support for MMDS Wireless systems, DOCSIS does not support MMDS 2-Way

DOCSIS Protocol Signaling

!

Frames and Timing

!MPEG Frames

" 188 Bytes, 4 Byte header !Synchronous Transmission

" Clock Synch messages from head end (613 per second) " One source per downstream

" Multiple sources per upstream requiring time sharing " Cable Modems identified by 16 bit Service ID (SID)

DOCSIS Protocol and Signaling

contd.

!

Frames and Timing

!Upstream Time Sharing (TDMA)

!Time allocation MAP from head end (every 4 ms)

!Upstream time allocated for Cable Modems in mini slots " (Mini-slot = 8 ticks, Tick = 6.25 usec)

!Shared time slots for Maintenance & Requests (e.g. for new modems with no SID to come online)

DOCSIS Downstream Architecture

!

RF Channel Spacing

!88 - 860 MHz !6 MHz

» 64 QAM-Occupied bandwidth 5.057 MHz plus guard band » 256 QAM- Occupied bandwidth 5.4 MHz plus guard band

!

RF performance requirements

!CNR -- 23.5dB as measured for analog video performance. (assumes DOCSIS carrier at analog level and 64 QAM

downstream.)

!Amplitude ripple (response) -- 0.5 dB !Group delay -- 75ns

!Power levels – -15 dBmV to +15 dBmV

!

The DOCSIS Specification Uses a Modulation and

Coding Scheme Defined by ITU J.83 Annex-b, for the

Downstream:

!Modulation Type: 64-QAM or 256-QAM

!Maximum Data Rate: 27 Mbps at 64-QAM, 38 Mbps at 256-QAM

!Bandwidth: 6 MHz channel

!Frequency Range: 88 - 860 MHz !Transport Protocol: MPEG-2

!Forward Error Correction (FEC) encoding: outer Reed-Solomon and inner Trellis code

!1E-8 BER with a carrier to noise ratio (Es/No) of:

• 23.5 dB for 64-QAM • 30 dB for 256-QAM

!

Variable RF bandwidth and modulation.

!200 kHz,400 kHz, 800 kHz, 1600 kHz, and 3200 kHz

!QPSK ( Quadrature Phase Shift Key) or 16 QAM (Quadrature

Amplitude Modulation)

!

Frequency Range

!5 to 42 MHz (Edge to Edge)

!

RF Performance requirements

!CNR -- Not less than 25 dB

DOCSIS Upstream Architecture

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! Modulation Type: 16-QAM or QPSK ! Data Rates: 320Kbps - 10 Mbps

! Symbol Rates: 160, 320, 640, 1280 and 2560 ksym/s ! Bandwidth: 200, 400, 800, 1600 and 3200 kHz

! Frequency Range: 5 - 42 MHz (edge to edge)

!

U p s t r e a m S y m b o l R a t e ( k s p s ) B a n d w id t h U s e d ( K H z ) Q P S K D a t a R a t e ( k b p s ) 1 6 Q A M D a t a R a t e ( k b p s ) 1 6 0 2 0 0 3 2 0 6 4 0 3 2 0 4 0 0 6 4 0 1 2 8 0 6 4 0 8 0 0 1 2 8 0 2 5 6 0 1 2 8 0 1 6 0 0 2 5 6 0 5 1 2 0 2 5 6 0 3 2 0 0 5 1 2 0 1 0 2 4 0

CMTS and Cable Modem Startup

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HFC

CMTS

Downstream Channel Search

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HFC

CMTS

QAM Signal

Monitor for SYNC Message

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CMTS

SYNC Message

MODEM

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Obtain Upstream Parameters

!

! periodically transmitted by CMTS

! UCDs define characteristics of the upstream channel such as:

» mini-slot size » upstream channel ID » downstream channel ID » burst descriptors CMTS UCD Message

UCD: Upstream Channel Descriptor

MODEM

Initial Ranging

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! Initial Maintenance Interval (broadcast interval) with start and end of connection opportunity

!

CMTS

MAP Message

RNG-REQ

MODEM

Auto Adjustments

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! adjust power level, timing offset, and frequency adjustment ! Sets downstream and upstream channels

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CMTS

RNG-RSP

MODEM

Admission Control

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Bandwidth Requests

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MAPS

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! MAP is variable length, typically 5-15 ms

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! Set of all MAPs for a channel covers all minislots

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SID, Burst type, and Grant length

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IP Connectivity

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! IP address and Subnet Mask

! CM configuration file name and IP address of TFTP server

! UTC time offset to establish local time

! TOD Server IP address

DHCP-REQ

Server

MODEM

Time of Day

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CMTS ToD-RSP ToD-REQ Server MODEM HFC LAN/WAN

Transfer Operational Parameters

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Registration

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! Downstream frequency, Upstream channel ID

! Network access configuration settings

! Class of Service ! Modem Capabilities ! Modem IP address CMTS REG-REQ MODEM HFC

Registration

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! checks CM’s MAC address and authentication signature on the parameters

! assigns a SID

! provides bandwidth for CM requested Class of Service

! modifies forwarding table to allow full user data if the modem requested Network Access

! sends REG-RSP to CM (CM can pass unencrypted data)

REG-RSP

MODEM

Baseline Privacy

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! authentication: CM to CMTS and CMTS to CM

! key distribution: traffic keys and lifetimes

! data encryption applied to Sid's

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Security Association

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! CM sends Authorization Request

» Public key, MAC address, and SID’s

! CMTS responds with an Authorization Response

» Authorization Key (encrypted KEK)

» Key Sequence number and Lifetimes

» List of SID’s (for each requested Class of Service)

AUTH-REQ

MODEM

Security Association

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CMTS TEK

KEY-REQ

MODEM

DOCSIS Today

! DOCSIS 1.0

! Product Interoperability across available CMTS’s ! 64 and 256 QAM modulation (downstream) formats

! 6-MHz occupied spectrum coexists with all other signals on the cable plant

! Variabledepth interleaver supports both latencysensitive and -insensitive data.

! The features in the upstream direction are as follows:

• Flexible and programmable CM under control of the CMTS

• Frequency agility

• Time division multiple access

• QPSK and 16 QAM modulation formats

• Support of both fixed-frame and variable-length PDU formats

• Multiple symbol rates

DOCSIS 1.1 Enhancements

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! Multiple (dynamic) Service Flows and classifiers

! More upstream scheduling types (polling, periodic grants)

! Fragmentation

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DOCSIS 1.1 Enhancements

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! Authentication of CMs with digital certificates

! Longer keys and some new algorithms

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! Uses PKCS certificates and code image signing

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! SNMPv3

DOCSIS 1.1 Enhancements

! DOCSIS 1.1

! Packet Classification, based on fields in the Ethernet, IP, and UDP/TCP headers, into a Service Flow

! Service Flow association with a DOCSIS Service Identifier ! QoS MIB’s

! Fragmentation ! Concatenation

! Payload Header Suppression (for increased bandwidth efficiency,

particularly in the case of relatively small Voice-over-IP [VoIP] packets) ! Priority Queuing (e.g. Weighted Fair Queuing) at the CMTS

! BPI+ (Base Line Privacy - Plus)

DOCSIS 1.0 and 1.1

Interoperability

! Can DOCSIS 1.0 and 1.1 Modems Can Be Used in the Same System?

! DOCSIS 1.1 is backward compatible with DOCSIS 1.0

! DOCSIS 1.1 CMTS’s are required to to support both DOCSIS 1.0 and 1.1 cable modems

! DOCSIS 1.1 modems must be able to register as a DOCSIS 1.0 modem with a CMTS that only supports DOCSIS 1.0

! Can DOCSIS 1.0 and 1.1 Modems Used on the Same Upstream Channel?

! Yes.

! Managing 1.0 and 1.1 modems on the same upstream channel is a more complex task for the CMTS

DOCSIS 1.1 Overview

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Quality of Service

E-mail

Voice

file

In DOCSIS 1.0, all services compete for upstream

bandwidth on a best effort basis.

In DOCSIS 1.0, all services compete for upstream

bandwidth on a best effort basis.

In DOCSIS 1.1, each service can get performance

assurances based on QoS parameters (e.g. bandwidth, jitter)

In DOCSIS 1.1, each service can get performance

assurances based on QoS parameters (e.g. bandwidth, jitter)

CM CM

Packet Processing

•Max burst size

•Req/Transmission policy

•Max traffic rate

•Min reserved traffic rate

•Upstream scheduling type

•Grant/poll jitter

•Grant/poll interval

Upstream Scheduling

•Unsolicited Grant Service (UGS)

•UGS w/ Activity Detection

•Real-Time Polling

•Non-Real-Time Polling

•Best Effort

Service Flow Types

!

! Provisioned when the CM registers

! Defined in a CMs’ config file

!

! Created as needed, based on demand

! Dynamic service flow messages

» Dynamic Service Add (DSA)

» Dynamic Service Change (DSC)

» Dynamic Service Delete (DSD)

Service Flow States

!

! The CMTS has not yet reserved the resources in its MAC scheduler

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! The resources are reserved, but the flow is not active

!

! The resources are in use, data is actively being transmitted on the flow

Dynamic Service Flow Example

Two Phase Activation

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! Resources are admitted (phase 1)

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! DSC used to activate the resources (phase 2)

! Call in progress

Concatenation

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! Nominal latency for REQ/Grant sequence in idle network is ~2.5 msec, or ~400 Grants/sec for a single CM

! Operationally, ~150 grants/sec is typical

! Thus, transmission limited to ~150 bursts/sec

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Payload Header Suppression

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BPI+ Enhances BPI Capability

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Strong Authentication

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CM Authorization

CM

CMTS

Auth Request (CM-ID, CM-Certificate, Security-Capability, primary SAID)

Auth Reply (Auth-key, Key-Lifetime, Key-Sequence_Number, one or more SA-Descriptors)

CM-ID : serial number, manufacturer ID, MAC addr, & RSA public key CM Certificate : X.509 certificate

Security-Capability : crypto capability, BPI version Primary SAID : CM’s primary SID

Auth-Key : Authorization key encrypted with CM’s public key Key-Lifetime : remaining time that key is valid in secs

Key-Sequence-Number : Sequence number of Auth key

SA-Descriptors : Properties of the security association, including SAID, SA-type, & cyrpto-suite

Basic Authentication (1)

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– MAC addr, serial #, CM public key are correct

! Expiration okay

! CM cert issuer name matches manuf cert subject name

! CM cert signature is valid, using manuf cert public key

!

! Expiration okay

! Manuf cert issuer name is DOCSIS

! Manuf cert signature is valid, using DOCSIS root public key

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Basic Authentication (2)

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Dynamic Security Associations

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mechanism which triggers the establishment of dynamic SAs.

IGMP/SA-MAP Example

IGMP MR (Join) IGMP MR (Join)

SA-MAP Request

SA-MAP Reply

Key Req/Reply

Multicast Data Multicast Data

Encrypted Multicast Data

Secure Code Download

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Code Download Process

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DOCSIS Root CA

! Issues Manufacturer CVC

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Manufacturer

! Signs code file

! Send code file w/ CVC to MSO

!

MSO

! Verifies code file

! Optionally, adds MSO co-signature and MSO CVC to code file

! Send code file to CM on request

!

Cable Modem

! Download code file

! Verify manufacturer’s signature

! Verify MSO signature, if present

Dynamic Channel Change

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SNMPv3

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! Authorization

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Standardized Event Logging

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! ~250 standard event messages

! 16 DOCSIS-specific trap types

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! Common event message across CM products

References

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! Good overview article, available as PDF file

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! Video is of a presentation of the VG

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