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									                                                           DOCSIS Test Challenges

      Testing Challenges

High-speed Internet service is being enabled with new, broadband technology for
cable TV networks, which are being upgraded with digital cable modems and cable-
modem termination systems. These high-technology devices provide two-way data
traffic between the internet service provider and the customers, and they must
conform to the DOCSIS standard. Assuring equipment conformance to the standard
is a formidable challenge for design engineers and managers who must subject their
products to complex testing required for certification. This paper discusses those
challenges and provides insights for success. It also introduces Agilent
Technologies' DOCSIS test solutions, which provide protocol analysis and design
verification testing.

                                DOCSIS Test Challenges

• Introduction
• Testing Challenges
• Testing Solutions
• Conclusion

                                                               DOCSIS Test Challenges

          DOCSIS Service

                                                        Cable Modem
        Internet             CMTS

                                                        Cable Modem
                    Server                                              PC

       • Transfer bidirectional data traffic between service provider’s headend
         (CMTS) and customer’s cable modem
       • CATV tree-and-branch infrastructure provides data conduit: fiber and
         coax cables with amplifiers -- hybrid-fiber/coax (HFC)
       • Wide BW and fast data rate for DS
       • Allocated BW and lower data rate for US

The data-over-cable-service interface specification (DOCSIS) defines system
operation and specifications for high-speed, two-way data in a cable network. The
DOCSIS service transfers bidirectional Ethernet or asynchronous transfer mode
(ATM) traffic over hybrid-fiber/coax (HFC) cable between the service provider’s
headend equipment, or cable-modem termination system (CMTS), and customer
cable modems (CM). The service is supported on a cable TV (CATV) network with a
tree-and-branch architecture.
The DOCSIS system is composed of downstream (DS) and upstream (US) paths. The
DS is the connection from the CMTS to the CM located in the subscriber’s home or
business. This path is a wide-bandwidth, high-data-rate connection. The US
connection is the path from the subscriber back to the CMTS. This path is lower
bandwidth and uses lower data rates than the DS.

                                                               DOCSIS Test Challenges

          RFI, PICS, and ATP
          Radio Frequency Interface (RFI)
          • Document defines interface specifications for CM and CMTS
          Protocol Implementation Conformance Statements (PICS)
          • Industry selected all “must”, “must not”, “should”, and “should not”
            statements in the RFI
          • PICS document defines CM/CMTS characteristics needed to meet
            DOCSIS requirements
          Acceptance Test Plan (ATP)
          • Addresses test methods for PICS requirements
          • Defines DOCSIS test procedures: PHY, MAC, MP (PHY & MAC),
            BPI, Eth, and OSS

The DOCSIS radio frequency interface (RFI) specification, published in 1997,
describes the DOCSIS technology. This document defines interface specifications
needed for developing high-speed data-over-cable systems, which include DOCSIS
CMs and CMTS headend equipment.
The cable industry developed a checklist summary from the very large RFI
document. The checklist includes hundreds of protocol implementation
conformance statements (PICS) -- all the "must", "must not", "should", and "should
not" statements in the RFI. With the PICS document, vendors can more easily
determine if CM and CMTS designs meet all of the requirements for DOCSIS
Because the PICS list does not include specific testing for RFI conformance, the
DOCSIS acceptance test plan (ATP) was developed to address testing. The ATP
includes over fifty performance verification tests grouped into several DOCSIS
categories: physical (PHY), media-access control (MAC), MAC and PHY (MP)
interaction, baseline privacy interface (BPI), Ethernet (Eth), and operation support
system (OSS).
This paper focuses on PHY and MAC testing. The PHY section of the ATP addresses
testing analog radio-frequency (RF) signals that travel between the CMTS and CM.
The MAC portion of the ATP focuses on the messaging protocol that is required
between the CMTS and CM. The MP tests verify the MAC and PHY interaction.

                                                             DOCSIS Test Challenges

       DOCSIS Testing Goals

       • Product quality and DOCSIS conformance
       • Passing the CableLabs or tComLabs DOCSIS testing waves
          – CM certification
          – CMTS qualification

       • Answering testing issues
          – PICS coverage
          – ATP measurements

       • Being prepared with test data and product confidence is key
         to success -- thorough DV testing

CM certification is desirable for vendors because it provides product-quality
assurance and DOCSIS proof-of-conformance for the retail customer. Cable
Television Laboratories, or CableLabs (a non-profit research organization for the
cable industry) administers North American DOCSIS testing in certification waves
held several times annually. For the European DOCSIS (Euro-DOCSIS) standard,
tComLabs administers certification waves. CMTS qualification provides the same
product assurance to cable operators and service providers.
Strictly following the DOCSIS documents for CM/CMTS testing has some issues. For
example, some PICS cover multiple requirements, which complicate test setups and
procedures. Another example is that some ATP measurements go beyond test-
equipment capabilities such as noise-floor limits and signal-triggering ability. Test
solutions should provide practical measurements that verify PICS compliance.
The key to successfully passing certification or qualification is being prepared with
product test data and design confidence, acquired with thorough design-verification
(DV) testing to the DOCSIS PICS list.

                                DOCSIS Test Challenges

• Introduction
> Testing Challenges
• Testing Solutions
• Conclusion

                                                               DOCSIS Test Challenges

       DOCSIS Testing Challenges

       Biggest Challenge -- passing certification
       • Verifying design covers all PICS items
       • Test repeatability between design and manufacturing
       Critical Testing Challenges
       • Flexible triggering for upstream burst testing
       • Analyze MAC protocol conformance
       • Calibrated active impairments for CM and CMTS tests

Perhaps the greatest challenge to passing DOCSIS certification is the design of
comprehensive, realizable test methods that cover all the requirements in the PICS
list. Many PICS are covered by the ATP tests, but some have no associated ATP test.
Other PICS are difficult to test if the CM or CMTS is not yet 100% functional or if
cable-system components cannot be simulated. Many PICS require extensive testing
that can consume significant time and resources. Also, developing repeatable
measurements that provide correlated results between the design and
manufacturing phases can be a challenge for product release.
We will focus now on three critical test challenges:
• Finding test methods that offer flexible triggering for US burst-signal testing
• Finding test methods that can analyze MAC protocol layer conformance
• Providing calibrated active impairments for both CM and CMTS testing

                                                              DOCSIS Test Challenges

       US Burst Triggering Challenges

       • Providing repeatable triggering
       • Making accurate measurements on burst signals
       • Triggering on desired burst with multiple burst types present

We will address three US burst triggering challenges for measurement equipment:
• Test equipment must provide repeatable triggering on burst signals.
• When triggering is achieved, the burst-signal measurement must be accurate.
• Under the presence of multiple burst types (five are available), the trigger must
select the desired burst signal.

                                                              DOCSIS Test Challenges

       Reliable Burst-Signal Triggering

       • US burst types: BW request, initial & station maintenance, and
         short & long data
       • Bursts distinguished by width (duration)

Spectrum analyzers can trigger on time-burst signals using frequency-selective and
amplitude-selective methods. But spectrum-analyzer triggering cannot distinguish
between burst types:
• Bandwidth (BW) request burst precedes a data burst and asks for US BW for
• Initial-maintenance (or initial ranging) burst is part of the CM power-up
initialization process.
• Station-maintenance (or periodic ranging) burst updates the CM-CMTS physical-
layer settings (frequency, power, timing) during defined intervals.
• Short- and long-data bursts contain the US data for communication.
The burst-time width (or duration) is determined by modulation type and the US
channel descriptor (UCD) parameters: preamble length, forward error-correction
(FEC) bytes, FEC codeword length, and others. Triggering on burst signals with
different durations and intervals is a DOCSIS testing challenge.
The diagram shows an example of US burst signals displayed by a digital
oscilloscope. The bursts from left to right are station maintenance, BW request, and
long data.

                                                                    DOCSIS Test Challenges

       Accurate Burst Measurements

              VSA Measurement Table
                                                 Spectrum Display

       Example: PHY-10 for frequency range
       • Trigger on station-maintenance burst and measure frequency
       • Spectrum-analyzer frequency accuracy is issue
       • VSA demodulates burst and displays frequency error

A spectrum analyzer can trigger on the station-maintenance burst and measure the
US frequency range as specified by PHY-10 of the ATP. The carrier frequency is
measured by assuming it is the center of the spectrum bandwidth displayed, but
determining the center of a modulated signal is difficult. Also, the spectrum analyzer
center-frequency accuracy can exceed the 50 ppm required for the test.
A vector signal analyzer (VSA) provides a more accurate measurement in which the
burst signal is demodulated and the frequency-error result is displayed in the
measurement-summary table.
The diagram shows the spectrum analyzer display for an US station-maintenance
burst with quadrature phase-shift-keying (QPSK) modulation. The VSA frequency-
error result is -267 Hz as displayed in the measurement table.

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                                                              DOCSIS Test Challenges

       Triggering on Desired Burst

       Example: PHY-17 for spectral shape
       • Trigger on data burst in presence of BW-REQ and RNG-REQ
       • Trigger point within random-data portion of burst

An US-test example that requires more than one burst type is the spectral-shape
measurement of PHY-17. This test verifies that the filter alpha factor is equal to 0.25
and the burst frequency response meets limits under varying conditions of
modulation, format, and symbol rate. The payload data must be random to achieve a
true filter-shape representation. With non-random data, the repeating data periods
cause frequency spikes, which corrupt the flatness measurement. The diagram
shows the measured flatness of a US data burst.
This test presents two triggering challenges. First, the measurement must trigger on
the long-data burst instead of the BW-request or station-maintenance burst. The
long-data burst is available only after the CM has registered with and is transmitting
data to the CMTS. Second, a trigger point must be provided that coincides with the
random portion of the burst.

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                                                                          DOCSIS Test Challenges

      Burst Trigger Timing
                            Non-Random Data                Random Data
                                                                           Trigger Point

                            MAC E-Net   IP               PDU
                      Pre                                             R
                            Hdr Hdr     Hdr            “Random”

                                               VSA Time Measurement

      Measure Random PDU Data
      • Trigger at end of burst
      • Negative delay into burst with time-record data
      • Position time-measurement window within PDU

      Measure Non-Random PDU Data
      • Enable US phase-noise measurement

The diagram shows the US-burst-packet construction: preamble, MAC header,
Ethernet header, IP header, payload-data unit (PDU), and cyclical-redundancy
check (CRC). (The CRC is a parity check for the burst data.) The VSA can make a
burst-signal measurement during the PDU where random data occurs.
For example, the VSA can receive an end-of-burst trigger from external burst-
width-trigger circuits. Because of its stored time-record data, the VSA can
negatively delay its measurement into the PDU. Then, the VSA can select a time-
measurement window that is within the PDU, which eliminates measurements on
undesired non-random data in the header.
US-signal phase-noise measurements can be made by setting the PDU to all zeros
instead of random data. This eliminates modulation and creates a CW signal on
which the VSA can measure phase noise.

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                                                            DOCSIS Test Challenges

      MAC Analysis Challenge

       Validate CMTS and CM MAC Operation
       • MAC management messages in DS and US
       • DS MAC messages
          – Embedded in MPEG-2 frames -- one or span across many
          – SYNC, MAP, UCD, other

       • US MAC messages
          – Embedded in US bursts
          – REQ-BW sent with BW-request burst
          – RNG-REQ sent with initial- or station-maintenance burst
          – RNG-REQ messages sent with short- or long-data burst

The ability to measure the MAC management messages is important for validating
CMTS and CM operation. The management messages are sent in both the DS and
In the DS, the MAC messages are embedded in the Motion Picture Experts Group
(MPEG) frames, version-two standard or MPEG-2. The messages can be in one
frame or spread across multiple frames. The DS MAC messages include time
synchronization (SYNC), bandwidth-allocation map (MAP), UCD, and others.
In the US, the MAC messages are transmitted in different burst types. For example,
the request-BW (REQ-BW) message is sent with the BW-request burst. The range-
request (RNG-REQ) message is sent with either the initial- or station-maintenance
burst. The registration-request (REG-REQ) message is sent with either the short- or
long-data burst. REG-REQ is included also in the CM initialization process.

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                                                                                      DOCSIS Test Challenges

       Testing MAC at Physical Layer
       Example: MPEG-01 sub-layer test of ATP
       • Verify MPEG frame construction, including header
       • Verify MAC messages within frame

       MPEG Frame                                                 MAC Messages
       D:/docsis/bin tsh> dsmpeg                                  D:/docsis/bin tsh> dsmac
       {Timestamp is OFF                                          { 219 MAC frames were found:
       } {5318 frames contained SYNC bytes                        }{     6 SYNC messages
       } { 221 frames contained DOCSIS PID                        } { 213 other MAC messages
       } {5097 frames contained NULL PID                          }{     0 Packet PDU frames
       } { 0 frames contained other PID                           } { 0 frames contained pointer errors
       } { 0 frames contained errors                              } { 0 frames contained HCS errors
       } { 0 DOCSIS frames contained errors                       } { 0 frames contained SYNC overrun errors
       } { 1 DOCSIS frames contained header errors} {:            } { 0 frames contained bad message types
       }{     1 CC errors                                         } { 0 frames contained non-null DSAPs
       } { 220 DOCSIS frames had the PUSI bit set                 } { 0 frames contained non-null SSAPs
       } { 0 DOCSIS frames contained all-ones payload

To verify that the CMTS or CM is fully operational, MAC management messages
should be measured at the physical layer after they have modulated the RF signal.
CM- or CMTS-specific messages can be measured separately to isolate CM or CMTS
As a CMTS example, the ATP MPEG-01 sub-layer test verifies that MPEG frames are
correctly constructed and the MAC messages are correctly placed within the MPEG
frames. This test also verifies that the MPEG header is correct, including the pointer
usage indicator (PUSI) bit and pointer byte.
In the table, the MAC message list on the left verifies the MPEG frame construction:
• 5318 frames contain SYNC bytes “47”, the first two header bytes.
• Of the total frames, 221 contain the DOCSIS program identification (PID) “1ffe”,
and 5097 contain the NULL PID “1fff”.
• No frames contain other PIDs or frame errors.
• One DOCSIS frame had a header error.
• 220 DOCSIS frames contain the PUSI.
• No DOCSIS frames contain all ones in the payload.
The MAC message list on the right verifies MAC messages within frames:
• Of the 219 MAC frames found, six were SYNC messages and 213 were MAC
• No PDU frames were found -- no data, only messages.

                                                         2 - 14
                                                                              DOCSIS Test Challenges

       Correlate MAC with US Bursts
       Example: MP-01 US transmit-power test of ATP
       • Validates interaction between DS and US messages for setting
         CM transmit power
       • DS MPEG data demodulated, and MAC messages for MAP
         and RNG-RSP decoded
       • Validate US RNG-REQ message by triggering on station-
         maintenance burst
                     CMTS              CM

                                             200 µsec Min.
                                             MAP In Effect
                            RNG-REQ            Initial Maint. Opportunities

                                              50 msec Min.
                                            200 msec. Max.
                                            CM Adjustments

The MAC messages sent to and from the CM can be correlated with the US bursts.
For example, the ATP MP-01 US transmit-power test measures the CMTS ability
to adjust the CM transmit power after the initialization process has been completed.
The CM must set its output-power level accurately to compensate for line losses
between itself and the headend. This test validates the interaction between the DS
and US messages for setting the CM output power. The process includes
demodulating the DS MPEG data and decoding the MAC messages for MAP and
range response (RNG-RSP) sent by the CMTS. In the US, the RNG-REQ message
sent by the CM can be validated by triggering on the station maintenance burst
through use of burst-width triggering.
The CMTS-CM message interaction shown in the diagram is as follows:
• The CMTS sends the CM a MAP message -- a contended-and-granted time-slot
(TS) table.
• When the CM finds a granted TS, it sends the CMTS a RNG-REQ message.
• The CMTS responds with a RNG-RSP message that includes settings for
frequency, power, and timing.

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                                                              DOCSIS Test Challenges

       Calibrated Impairments Challenge

       Active Impairments to CMTS-CM Communication
       • US ingress degrades SNR
       • DS adjacent channels and noise
       • DOCSIS tests done under active impairments
       • US burst Impairments

CMs must share a spectrum crowded with other transmissions such as analog or
digital television channels in an environment that is susceptible to noise and other
interference. Also, CMs and CMTSs must not cause interference to the other
services on the cable network.
In the US band, CMTS-CM communication can be impaired by random noise, signal
intermodulation products, external electrical interference, off-air signals, and many
other interfering sources. These impairments are called ingress, and they affect the
entire cable system by reducing signal-to-noise ratio (SNR). Adding more cable
subscribers increases ingress, which mostly occurs at subscriber sites. In the DS
band, CMTS-CM interference can result from adjacent TV channels and
intermodulation products caused by all the communications channels (sometimes
greater than 100).
Many DOCSIS tests, for example the ATP PHY-07 bit-error-rate (BER) test, require
measurements under active-impairment conditions. US burst impairments are useful
for testing CMTS-CM communication. An example is testing the FEC response to
corrupted data.

                                        2 - 16
                                                           DOCSIS Test Challenges

      Active Impairments for DOCSIS Tests

       Verify CMTS and CM Performance in Presence of Impairments
       • Adjacent-channel interference
       • In-band and out-of-band noise
       • Burst-signal interference

Some DOCSIS tests require measurements in the presence of active impairments
such as adjacent-channel interference, in-band and out-of-band noise, and burst
signals. These tests verify that CMTS and CM receivers perform correctly under
stressful conditions.
The diagram shows two signals above and below a DOCSIS DS carrier. These
adjacent-channel interfering signals are CATV video channels, with National
Television Standards Committee (NTSC) formatting, that are 10 dB higher than the
DOCSIS channel power.

                                      2 - 17
                                                           DOCSIS Test Challenges

      Generating In-Band Impairments

       DS-Impairment Example
       • Separate signal source summed into DS
       • Same frequency as DS DOCSIS channel
       • Acts as noise to reduce SNR

A separate signal source, summed into the DS DOCSIS channel, can simulate in-
band impairments by reducing the DS SNR. The source modulation is the same type
as the DS signal and appears like noise. Because source symbol rate has a wider BW
than and is uncorrelated with the DS signal, it appears like noise. The combined
source-and-DS signals are calibrated for the correct impairment power by adjusting
the source power level. Then, an error-vector-magnitude (EVM) measurement is
made with the VSA.
The VSA display shows a 64 quadrature-amplitude-modulation (QAM) constellation
with degraded SNR. The DS channel measures 1.5% EVM for normal operation; with
in-band impairments, the EVM can be much higher such as the 4% shown in the

                                      2 - 18
                                                                              DOCSIS Test Challenges

      Generating US Burst Impairments
                             Arm on Burst Width       Trigger on Burst Edge

                US Bursts      Req.                        Long Data


                VSA Arb

       Example: Breaking bytes in US data
       • Generate interfering US signal with VSA Arb
       • Arm DPA with BW-request burst width
       • Trigger VSA at long-data leading edge
       • Delay Arb signal, and sum into long-data burst

Other impairments are useful for testing CMTS-CM communication such as
disrupting the MAC header or PDU data. For example, an impairment that breaks an
integer number of US bytes is useful for checking the FEC and codeword for US
data. A US impairment can be generated by a modulated-burst signal with a time
duration equal to an integer number of bytes in the US data burst. When the
interfering signal is summed into a US burst signal, different FEC modes can be
checked to determine if the correction process is working.
The diagram shows how the VSA, with the help of a DOCSIS protocol analyzer
(DPA), can break a controlled number of bytes in US bursts. First, the VSA stores an
interfering burst signal in its arbitrary waveform generator (Arb). The time record
can be varied to control the impairment length, which determines the number of
bytes that will be impaired. Then, the DPA senses the BW-request burst width and
arms its trigger. The DPA then detects the rising edge of the long-data burst and
triggers the VSA, which delays its Arb output to coincide with the MAC header
and/or the PDU. Finally, the impairment is summed with the long-data burst.

                                                  2 - 19
                                                              DOCSIS Test Challenges

       US Burst Impairments

        • Burst impairment inserted in long-data burst
        • Break MAC header and/or PDU bytes

The display shows the result of the previous test setup for breaking a controlled
number of bytes in an US burst. The narrow burst on the left is the BW-request
burst, and the wide burst on the right is the long-data burst. The burst impairment in
the center can be positioned with 1 µs resolution within the long-data burst.

                                        2 - 20
                                                            DOCSIS Test Challenges

       Modified Initial Maintenance Burst
          US Burst         Initial    Attenuation
                        Maintenance     (81 dB)

         VSA Arb         Captured
         Substitution      Initial                  CMTS

       Example: Control CMTS RNG-RSP message
       • VSA captures initial-maintenance burst
           – VSA Arb plays back burst
           – CM US signal attenuated
       • Arb replaces CM burst and controls power, frequency, timing
       • Modify RNG-RSP and test CM & CMTS responses

Another useful impairment is a modified initial-maintenance burst that can test the
CM initialization process after the CM is turned on. The initial-maintenance burst
from the CM can be modified for frequency, power, and timing. Then, the affect on
the RNG-RSP message returned by the CMTS can be tested. The offsets sent in the
MAC message can be evaluated in relation to the amount of impairment that has
been added to the initial-maintenance burst.
The test starts with the VSA capturing the burst and using its Arb to duplicate the
signal. Then, the CM US signal is highly attenuated (81 dB), and the initial-
maintenance burst is replaced by the Arb signal. By modifying the Arb signal in
frequency, power and time, different CMTS RNG-RSP messages can be generated.
The CM response to those messages is analyzed; for example, the CM frequency
and power can be measured.

                                          2 - 21
                                 DOCSIS Test Challenges

• Introduction
• Testing Challenges
> Testing Solutions
• Conclusion

                        2 - 22
                                                             DOCSIS Test Challenges

       E1371A DOCSIS Test System
      • System test strategies provide
        CM/CMTS design verification
        testing to DOCSIS 1.0
          – DOCSIS 1.1 enhancement
          – Euro-DOCSOS enhancement

      • Automated testing for PHY/MAC
         – Open software platform

      • Includes DOCSIS protocol analyzer
          – US triggering and DS data
            capture and analysis
          – Upgrade for US data capture
            and analysis

Agilent has developed a DOCSIS test solution based upon the PHY and MAC PICS
items for both the CMTS and CM. Compliance test procedures have been written to
test as many PICS as possible before products are submitted for certification. The
E1371A DOCSIS test system maximizes test-instrument use and provides effective
testing for both CMTS and CM. The system is a DV tool and pre-certification tester
with the following characteristics:
• The system design is based on DOCSIS 1.0 ATP, PICS, RFI and Agilent’s test
technology. Enhancements are planned for DOCSIS 1.1 and Euro-DOCSIS.
• The system provides automatic testing for PHY and MAC protocol layers. The
software platform is open at the application layer, allowing users to modify or add
tool-command-language (Tcl) test scripts.
• The system includes a specialized DPA, designed for the E1371A, with US
triggering and DS data capture and analysis. An upgrade is planned for US data
capture and analysis.

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                                                             DOCSIS Test Challenges

       DOCSIS Test Strategies

       • PHY and MAC testing based on industry references
          – ATP test conditions
          – PICS list
          – RFI specifications

       • Four test-strategy groups
           – DS and US PHY
           – Basic and operational MAC

       • Efficient testing
           – Verify CMTS and CM conformance
           – Minimize test equipment and time
           – Other uses for DV test methods

The E1371A creates a DOCSIS test environment for the PHY and MAC protocol
layers. The E1371A provides CM and CMTS test coverage that is traceable to the
industry testing guidelines: ATP, PICS, and RFI. Test strategies, which are structured
plans for PICS testing, are organized into four groups: downstream PHY, upstream
PHY, basic MAC, and operational MAC. (See the following test-strategy tables.)
The system platform is an efficient design that supports both CM and CMTS
conformance testing with a minimum equipment set (only five instruments are
needed). Test time has been minimized by using individual measurement
configurations for testing multiple PICS. Also, the DV test methods can be leveraged
for other uses such as manufacturing troubleshooting and process analysis.

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                                                                                                 DOCSIS Test Challenges

       PHY Test Strategies
               Test Type                          Description               Test DUT          ATP Coverage
             Downstream PHY 4-1-1 DS Frequency & Power (CMTS)               CMTS        PHY-01
                            4-1-2 DS Spurs and Noise                        CMTS        PHY-03, PHY Vendor
                            4-1-3 DS Spectral Mask                          CMTS        PHY-06
                            4-1-4 DS Modulation Char                        CMTS        PHY-04, PHY-06
                            4-1-5 DS In-Band Noise                          CMTS        PHY Vendor
                            4-2-1 CMTS DS Return Loss                       CMTS        PHY Vendor
                            4-3-1 Interleaver Depth                         CMTS   CM   PHY-05
                            4-3-2 MPEG-MAC Alignment                        CMTS   CM   MPEG-01 (partial)
                            4-4-1 DS Frequency and AGC (CM)                 CM          PHY-01
                            4-4-2 DS Adjacent Channel Interference          CM          PHY-07
                            4-4-3 DS Noise Impairment and BER               CM          PHY-07
                            4-5 CMTS Master Clock Characteristics           CMTS        PHY-Vendor
             Upstream PHY   5-1-1 Upstream Frequency Range                  CMTS   CM   PHY-10 (except CmPhTx.30)
                            5-1-2 CMTS RF Input Power                       CMTS        PHY-13
                            5-1-3 US Coding and Scrambler                   CMTS   CM   PHY-16
                            5-1-4 US FEC and Codeword Length                CMTS   CM   MP-03, MAC-Vendor
                            5-1-5 US Adjacent Channel Interference          CMTS
                            5-1-6 US Power Range and Modulation             CM          PHY-12, PHY-Vendor
                            5-1-7 CMTS Rx Threshold Range                   CMTS
                            5-2-1 CMTS US Return Loss                       CMTS
                            5-3-1-1 US Burst Flatness                       CM          PHY-15
                            5-3-1-2 US Burst Transients                     CM          PHY-Vendor
                            5-3-2-1 US Spurs and Noise – Adjacent Channel   CM          PHY-17, PHY-18, PHY-Vend
                            5-3-2-2 US Spurs and Noise -- US Band Scan      CM          PHY-17, PHY-18, PHY-Vend
                            5-3-3-1 US Spurs and Noise – Out of Band        CM          PHY-17, PHY-18(partial)
                            5-3-3-2 US Spurs and Noise – Crossover Band     CM          PHY-17, PHY-18(partial)
                            5-3-4 US Spectral Shape                         CM          PHY-17
                            5-3-5 US Noise Impairment and BER               CMTS
                            5-3-6 US In-Band Noise                          CM          PHY-14
                            5-4-1 CM CATV Return Loss                       CM          PHY-Vendor

The table lists the E1371A DS and US PHY test strategies, and correlation is shown
between the strategies and the PICS covered by the ATP. The E1371A test strategies
were written for PICS coverage, and individual strategies may cover PICS from
different ATP sections. For example, when "US Spurs and Noise - In Band” is
selected from the US PHY test-strategy group, the resultant testing covers the ATP
for PHY-17, PHY-18, and PHY-Vendor. To give vendors more DV testing capability,
some test strategies go beyond the ATP PICS coverage. An example from the US
PHY group is the "CMTS Rx Threshold Range” test strategy, which verifies that the
CM US power is set to the level commanded by the CMTS. This strategy covers five
PICS not included in the ATP.

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                                                                                                 DOCSIS Test Challenges

       MAC Test Strategies
               Test Type                            Description            Test DUT            ATP Coverage
             Basic MAC       7-1-1 MPEG and MAC Framing                    CMTS        MPEG-01(partial)
                             7-1-2 SYNC Message                            CMTS
                             7-1-3 UCD Message                             CMTS
                             7-1-4-1 MAP Message Format and Content        CMTS
                             7-1-4-2 MAP Message Timing                    CMTS
             Operational MAC 6-1-1-1 Initial Ranging Power                 CMTS   CM MP-01(partial), MP-02
                             6-1-1-2 Initial Ranging Backoff               CMTS   CM MAC-06(Int Ranging Only)
                             6-1-1-3 Initial Ranging Forced Contention     CMTS
                             6-1-2-1 RNG-RESP Message                      CMTS   CM   MP-01
                             6-1-2-2 Ranging Timing Adjust                 CMTS   CM
                             6-1-2-3 Ranging Frequency Adjust              CMTS   CM
                             6-1-3 Power Level Corrections                 CMTS   CM   MP-01
                             6-2-1 DHCP Offer Message                      CMTS   CM
                             6-2-2 CMTS MIB Parameters                     CMTS   CM   p/o MAC-01
                             6-2-3 CM MIB Parameters                       CMTS   CM   p/o MAC-01
                             6-2-4 Invalid CMTS MIC Config File            CMTS   CM   p/o MAC-05
                             6-3-1-1 DS Channel Change – Config. File      CMTS   CM   MP-05
                             6-3-2-1 US Channel Change – Config. File      CMTS   CM
                             6-3-2-3 US Channel Frequency Change           CMTS   CM   MP-04
                             6-3-2-4 US Channel Change - Impairment        CMTS   CM   MP-04
                             6-4-1 BW Req Contention Backoff               CMTS   CM   MAC-06
                             6-4-2 REQ-Data Contention Backoff             CMTS   CM   MAC-06
                             6-4-3 Piggyback BW Request                    CMTS   CM   MAC-02
                             6-4-4 Short & Long Data Intervals             CMTS   CM   MAC-12
                             6-4-5 MAC Concatenation                       CMTS   CM
                             6-4-6 Baseline Privacy Mode                   CMTS   CM
                             6-5-1 Extended Duration Operation             CMTS   CM
                             6-5-2 COS Test Scenarios                      CMTS   CM

The table lists the E1371A basic and operational MAC test strategies, and correlation
is shown between test strategies and the PICS covered by the ATP.

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                                                                                             DOCSIS Test Challenges

       Spreadsheet Test-Results Example
             Downstream Frequency and Power
             PHY-01    CmtsPhTx.7,9-11,13,14
             CmtsPhTx4.3.4 CMTS Output Electrical (Center Frequency, Level)
             4.3.4 CMTS Output Electrical (Center Frequency, Level)
             Strategy Date     28 January 2000
             Test Date
             Unit ID

             64 QAM
                           Xm it    Meas     Corrected                                Carrier
              DS Freq     Pow er    Pow er     Pow er     Lim it         Low Lim it Freq Error High Lim it
               (MHz)      Setting   (dBm )    (dBm V)    (dBm V)   P/F     (Hz)        (Hz)       (Hz)     P/F
                     93     Min       0.4       49.2      50.25     F     -30000        314      30000      P
                    153     Min       1.4       50.2      50.25     F     -30000        455      30000      P
                    213     Min       1.6       50.4      50.25     P     -30000        422      30000      P
                    273     Min       1.7       50.5      50.25     P     -30000        600      30000      P
                    333     Min       1.7       50.5      50.25     P     -30000        640      30000      P
                    393     Min       1.8       50.6      50.25     P     -30000        678      30000      P
                    453     Min       1.9       50.7      50.25     P     -30000        708      30000      P
                    513     Min       1.8       50.6      50.25     P     -30000       1208      30000      P
                    573     Min       1.8       50.6      50.25     P     -30000       1280      30000      P
                    633     Min       1.7       50.5      50.25     P     -30000       1509      30000      P
                    693     Min       1.6       50.4      50.25     P     -30000       1777      30000      P
                    753     Min       1.6       50.4      50.25     P     -30000       2087      30000      P
                    813     Min       1.5       50.3      50.25     P     -30000       2208      30000      P
                    855     Min       1.6       50.4      50.25     P     -30000       2400      30000      P

The E1371A stores test data for each test strategy in a text file according to the
American Standard Code for Information Technology (ASCII). Because of the data
organization for each test strategy, test results can be easily exported to a
spreadsheet as shown in the table (a sample of a much larger table). Collecting test
results in this manner is a convenient way of presenting the large amount of DV data
required for certification.

                                                          2 - 27
                                                             DOCSIS Test Challenges

      E1371A Platform Architecture

                            DS                                          Port
                                    Impairments            DS/US
               DOCSIS                                                 DOCSIS
                CMTS                                                   CMs
       NSI                            Passive
       Port                         Impairments

              Impairments         Measurement

       Closed-loop design with five test instruments:
       VSA, ESG, DSO, DPA, LAN Gen/Rx

The DOCSIS test system is a closed-loop architecture in which the CM and CMTS
are connected through the system hardware and communicate as they would in a
cable plant – the CMTS at the headend and the CM at the subscriber premises. Local-
area-network (LAN) equipment establishes data traffic that flows between the CM
and CMTS, and the test system performs automatic measurements on the DS and US
signals. The system also inserts passive and active impairments in the
communications path to test the affect on signal quality and data protocol. Both PHY
and MAC testing can be performed with the same system architecture.
The E1371A test system minimizes test equipment needed by assigning different
roles to each instrument while running a test strategy. The test system is composed
of five primary instruments:
• Agilent 89441A VSA
• Agilent E4430B analog and digital RF signal generator (ESG series)
• Agilent 54810A digital storage oscilloscope (DSO, Infiniium series)
• Agilent downstream DPA
• LAN protocol analyzer (Ethernet generator/receiver)

                                        2 - 28
                                                             DOCSIS Test Challenges

       Triggering Solutions

       • VSA external trigger and delay
       • DSO external triggering
          – US signal coupled to DSO through burst detector
          – DSO triggers on > or < burst width
          – Trigger generation: DSO ---> DPA ---> VSA

       • DPA specialized triggering
          – Burst-width discriminator: trigger on > and < burst width
          – Trigger arming and delay for burst sorting

The E1371A solves the burst-selective triggering challenge with the VSA external
trigger and delay capabilities.
The external trigger is generated by an external burst detector and the DSO. The US
signal is coupled first to the detector and then to the DSO, which can trigger from
bursts that are either greater-than or less-than a designated burst-width value. With
this triggering capability, the DSO can easily distinguish between two burst widths,
such as BW-request and long-data bursts, and trigger on either one.
After triggering on a selected burst, the DSO sends a trigger through the DPA to the
VSA, which uses its negative-delay feature to position the pulse for demodulation in
time. The burst must be positioned correctly in the time domain for the VSA to
demodulate the burst signal.
For more sophisticated triggering, the DPA has a burst-width discriminator that
allows triggering from a burst width that is both greater-than and less-than a
designated value. The DPA also provides trigger-arming and delay capabilities that
provide burst sorting with microsecond resolution and accurate US-triggering-event
correlation in the DS signals.

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                                                           DOCSIS Test Challenges

      MAC Analysis Solutions
       DPA Captures and Analyzes DS MPEG & MAC
       • Filter data by PID and time-stamp each packet
       • MPEG-2 frame analysis
          – Sync-byte count
          – PID frame count
          – Incorrect frame count
          – Display frames in hex or decoded MAC (TLV)

       • MAC frame analysis
          – Total SYNC message count
          – Pointer-error count
          – Incorrect-message types

       • Trigger on US bursts and demodulate DS data

Agilent’s DPA captures and analyzes DS data for MPEG and MAC framing, MAC
messages, and MAC timing.
The DPA demodulates the MPEG data, filters it by the PID in the header, and time
stamps each packet with arrival time. Time stamping is important because the
MPEG-2 frames with DOCSIS MAC messages are not necessarily contiguous.
MPEG-2 frame analysis can be done for parameters that include number of MPEG
sync bytes, number of frames with DOCSIS PID or other PID, and erred DOCSIS
frames. The DPA can display DS MPEG-2 frames in either hex format or as decoded
MAC messages, which are in hex or type-length value (TLV) format. (TLV
determines information encoding in MAC messages.)
MAC frame analysis is done for total SYNC message count, pointer error count,
incorrect DOCSIS message types, and more.
By using its DS MPEG analysis and triggering subsystems together, the DPA can
perform high-level analysis. As an example, the DPA develops a trigger signal from
the US station-maintenance burst. The trigger is routed simultaneously to the VSA
for burst capture and the DPA demodulator for synchronous capture of DS MPEG-2

                                          2 - 30
                                                             DOCSIS Test Challenges

       E7333A DOCSIS Protocol Analyzer
       • 19” rack-mountable 1U chassis
       • PC-controlled via 10/100Base-T interface
       • Upstream and downstream RF inputs

       • Windows NT® software with GUI for control and analysis
       • Platform-independent Tcl API

The DOCSIS 1.0 DPA in the E1371A is not available as a stand-alone product.
However, a new DOCSIS 1.0/1.1 DPA is available for independent protocol testing.
The E7333A DOCSIS protocol analyzer is packaged in a 19” chassis that can be rack
mounted or used on a bench. The control interface uses 10/100Base-T Ethernet to
connect to the controlling PC or workstation. The E7333A software runs on
Windows NT® and comes with a graphical user-interface (GUI) that controls the
DPA and provides off-line protocol analysis.
A Tcl application-program interface (API) is provided for controlling the DPA from
any platform such as PC or UNIX. The instrument has separate US and DS RF
inputs (shown on the right side) and several trigger inputs and outputs (left side).

Windows NT® is a U.S. registered trademark of Microsoft Corporation.

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                                                                      DOCSIS Test Challenges

      CM and CMTS Protocol Testing
      for DOCSIS 1.0 and 1.1
       E7333A Characteristics
                                                                 RF Interface
       • Capture, decode, and                         CMTS                                 CM
         analyze data streams                                           Clk In   Clk Out

       • Correlate DS and US data                                         DPA
         with precision time stamping
       • Decode and error check                                           10/100Base-T
         MAC and MPEG protocols
                                                         PC or UNIX
       • Filtering and triggering features
         and SYNC jitter analysis
       • Windows NT® based analysis software
       • Tcl scripting interface supports automation

The DPA supports both DOCSIS 1.0 and 1.1 for CM and CMTS testing, and the
interface provides simultaneous DS and US analysis. DS and US data are captured
and correlated, which is important for analyzing the interaction between DS and US
MAC protocols. Triggering features allow capture of specific protocol events, for
example certain kinds of MAC messages. Planned enhancements include real-time
filtering on MAC headers.
The downstream SYNC message contains a 10.24 MHz reference-clock timestamp
from the CMTS. All CMs must synchronize to this, so analyzing the jitter is an
important measurement (required for DOCSIS 1.0 testing) provided by the DPA.
The DPA provides a Tcl scripting interface, which can be useful for automated and
pre-certification testing.

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                                                                DOCSIS Test Challenges

       Active Impairment Solutions

       • Noise impairments
          – VSA calibrates DS and US SNR for BER measurement
          – ESG creates in-band noise

       • Signal impairments
           – Video gen and modulators create adjacent NTSC channels
           – ESG generates QAM carrier signal

       • US burst impairments
          – VSA Arb replays burst signals in US
          – DPA provides trigger timing

For noise impairments, the E1371A uses the VSA in vector-demodulation mode to
calibrate the DS/US channel SNR. Then, it measures the EVM and SNR needed to
predict FEC BER. The ESG generates in-band noise by modifying the DS modulation
parameters for symbol rate and alpha factor. This results in a signal that is
uncorrelated (noise-like) when combined with the main DS/US channel.
For signal impairments, a baseband video generator and two video modulators
create adjacent NTSC channels. And, the ESG generates a QAM carrier as an
interfering digital signal.
For some tests, the US burst must be impaired to verify that the US FEC works
correctly. To perform this test, the E1371A uses the VSA Arb to regenerate captured
US signals at three defined burst widths and replay them in the US.

In generating the burst impairment, the DPA provides a trigger for the VSA Arb so
that it can insert the interfering burst signal into the US long-data burst. By using the
DPA trigger delay, the impairing burst is placed in either the MAC header or payload
portion of the US burst so that one or more bytes can be corrupted. A data generator
is used to produce the traffic and make packet-loss measurements.

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                                                            DOCSIS Test Challenges


       • Passing certification starts with effective DV testing
       • Vendors are faced with DOCSIS testing challenges:
           –   Testing to DOCSIS PICS
           –   Reliable US triggering
           –   MAC protocol analysis
           –   Calibrated impairments
       • Agilent test solutions answer the challenges
           –   DOCSIS DV test system
           –   DOCSIS protocol analyzer

Passing CM certification and CMTS qualification starts with effective DV and pre-
certification testing. But, CM and CMTS vendors must overcome DOCSIS testing
• Test methods that comply with the DOCSIS PICS list
• Reliable US triggering needed for US and DS measurements
• Specialized testing and analysis for the MAC protocol
• Calibrated physical-layer impairments for PHY and MAC testing
Agilent’s answer to the DOCSIS test challenges is a DOCSIS system for DV and pre-
certification testing. A key system component is the DOCSIS protocol analyzer, and
a stand-alone DPA is useful for independent protocol measurements.

                                        2 - 34
                                      DOCSIS Test Challenges

DOCSIS Information

E1371A DOCSIS Test System
Product Overview #5988-1245EN

E7333A DOCSIS Protocol Analyzer
Data Sheet #5980-2143E

Agilent Web Site for DOCSIS

                          2 - 35
                                                       DOCSIS Test Challenges

Agilent Business Contacts
E1371A DOCSIS Test System
Steve Karakitsios -- Solution Specialist (West US & International)
  Phone: 303-662-4325 (Denver, CO)
  E-Mail: steve_karakitsios@agilent.com
Clark Braud -- Solution Specialist (East US)
 Phone: 504-461-3148 (New Orleans, LA)
 E-Mail: clark_braud@agilent.com
E7333A DOCSIS Protocol Analyzer
Trevor Dyck -- Product Manager
  Phone: 604-454-3500 (Vancouver, BC)
  E-Mail: trevor_dyck@agilent.com

                                2 - 36

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