Cisco Ubr904 Assembly instructions

Troubleshooting Tips for the Cisco uBR904 Cable Modem 1

Troubleshooting Tips for the

Cisco uBR904 Cable Modem

The following sections are provided:

•Feature Summary on page 1

•Platforms on page 3

•Supported MIBs and RFCs on page 3

•CMTS to Cable Modem Network Topology on page 4

•Troubleshooting Steps on page 5

•Command Reference on page 16

•Debug Commands on page 49

•What to do Next on page 61

Feature Summary

This document describes the set of Cisco IOS troubleshooting commands that may be used by

multiple service operators (MSOs) to verify communication between a Cisco uBR904 cable modem

and other peripheral devices installed in the HFC network such as the headend Cisco uBR7246

router, a DHCP server, and a TFTP server.

Note For an explanation of error messages displayed by the uBR904, see Cisco Cable CPE Error

Messages, viewable online at

www.cisco.com/univercd/cc/td/doc/product/cable/cab_modm/ubcmerrs.pdf .

Benefits The uBR904 troubleshooting system provides the following benefits:

•A MAC-layer system log file exists which provides a snapshot of detailed reasons why an

interface might reset, along with all the negotiations that occurred between the uBR904 cable

modem and the CMTS (a Cisco uBR7246 positioned at the headend). Over 220 possible

description fields exist in this log, which is displayed using the show controllers cable-modem

0 mac log command from privileged EXEC mode.

•Debug does not need to be turned on to troubleshoot a uBR904 cable modem.

Feature Summary

2Cisco IOS Release 12.0(3)T

•The progression of normal data-over-cable communication events is clearly explained,

simplifying the resolution of faulty system connections.

•A cable technician can remotely telnet into a Cisco uBR904 cable modem, which could be

installed in a customer’s home, and perform simple diagnostic tasks.

List of Terms

CATV—Originally stood for Community Antenna Television. Now refers to any coaxial or fiber

cable-based system that provides television services.

Cable modem (CM)—Any device that modulates and demodulates digital data onto a CATV plant.

Cable router—A modular chassis-based router optimized for data-over-CATV hybrid fiber-coaxial

(HFC) applications.

Channel—Aspecificfrequency allocation and bandwidth.Downstreamchannelsusedfortelevision

in the United States are 6 MHz wide.

CM—Cable modem.

CMTS—Cable Modem Termination System. Any DOCSIS-compliant headend cable router, such

as the Cisco uBR7246.

DHCP—Dynamic Host Configuration Protocol. This protocol provides a mechanism for allocating

IP addresses dynamically so that addresses can be reused when hosts no longer need them.

DOCSIS—Data Over Cable Service Interface Specification. Defines technical specifications for

equipment at both subscriber locations and cable operators’ headends.

Downstream—The set of frequencies used to send data from a headend to a subscriber.

Headend—Central distribution point for a CATV system. Video signals are received here from

satellite (either co-located or remote), frequency converted to the appropriate channels, combined

with locally originated signals, and rebroadcast onto the HFC plant. For a CATV data system, the

headend is the typical place to create a link between the HFC system and any external data networks.

HFC—Hybrid fiber-coaxial (cable network). Older CATV systems were provisioned using only

coaxial cable. Modern systems use fiber transport from the headend to an optical node located in the

neighborhood to reduce system noise. Coaxial cable runs from the node to the subscriber. The fiber

plant is generally a star configuration with all optical node fibers terminating at a headend. The

coaxial cable part of the system is generally a trunk-and-branch configuration.

Host—Any end-user computer system that connects to a network. In this document, the term host

refers to the computer system connected to the LAN interface of the cable modem.

MAC layer—Media Access Control sublayer. Controls access by the cable modem to the CMTS

and to the upstream data slots.

MCNS—Multimedia Cable Network System Partners Ltd. A consortium of cable companies

providing service to the majority of homes in the United States and Canada. This consortium has

decided to drive a standard with the goal of having interoperable cable modems.

MSO—Multiple Service Operator. A cable service provider that also provides other services such

as data and/or voice telephony.

QAM—Quadrature Amplitude Modulation. A method of modulating digital signals onto a

radio-frequency carrier signal involving both amplitude and phase coding. QAM is a modulation

scheme mostly used in the downstream direction (QAM-64, QAM-256). QAM-16 is expected to be

List of Terms

Troubleshooting Tips for the Cisco uBR904 Cable Modem 3

usable in the upstream direction. Numbers indicate number of code points per symbol. The QAM

rate or the number of points in the QAM constellation can be computed by 2 raised to the power of

<number of bits/symbol>.

QPSK—Quadrature Phase-Shift Keying. A method of modulating digital signals onto a

radio-frequency carrier signal using four phase states to code two digital bits.

Ranging—The process of acquiring the correct timing offset such that the transmissions of a cable

modem are aligned with the correct mini-slot boundary.

SID (Service ID)—A number that defines (at the MAC sublayer) a particular mapping between a

cable modem (CM) and the CMTS. The SID is used for the purpose of upstream bandwidth

allocation and class-of-service management.

Subscriber Unit (SU)—An alternate term for cable modem. See cable modem.

Upstream—The set of frequencies used to send data from a subscriber to the headend.

PlatformsThe uBR904 cable modem is a standalone device; it works in conjunction with the Cisco uBR7246

universal broadband router.

Prerequisites

Seethe companiontothisdocument,“BridgingandRoutingFeatures for theCisco uBR904Cable Modem”

for information regarding prerequisites.

Supported MIBs and RFCs

See the companion tothis document, “Bridging andRouting FeaturesfortheCisco uBR904Cable Modem”

for information regarding supported MIBs and RFCs.

CMTS to Cable Modem Network Topology

4Cisco IOS Release 12.0(3)T

CMTS to Cable Modem Network Topology

Figure 1 shows the physical relationship between the devices in the HFC network and the cable

modem.

Figure 1 Sample Topology

IP-related

ATM, FDDI, 100BT...

100BT

Analog TV

Digital TV

Upconvertor

ISP @ home...

DS-RF 54-860 Mhz

Fiber

Transceiver

80 km

Fiber node

(Telephone pole,

underground box)

Distribution

amplifier Top

amplifier

1000 ft

Drop box

Cisco u BR904

cable modem

100BT

Proxy server

ISP

WAN

Cisco

uBR7246

CMTS MSD: Maintenance Service

Organization, Cable companies

13304

Step 1—Understand How Basic Initialization Works

Troubleshooting Tips for the Cisco uBR904 Cable Modem 5

Troubleshooting Steps

To troubleshoot a malfunctioning cable modem, perform the following tasks:

•Step 1—Understand How Basic Initialization Works

•Step 2—Connect to the Cable Modem

•Step 3—Display the Cable Modem’s MAC Log File

•Step 4—Interpret the MAC Log File and Take Action

•(Optional) Step 5—Use Additional Troubleshooting Commands

Step 1—Understand How Basic Initialization Works

Before you troubleshoot a Cisco uBR904 cable modem, you should be familiar with the cable

modem initialization process. See Figure 2 and Table 1. Understanding this flowchart and sequence

of events will help you determine where and why connections fail.

The sequence numbers shown in Figure 2 are explained in Table 1, which appears after the

illustration. The cable modem will complete all the steps in this flowchart each time it needs to

reestablish ranging and registration with the CMTS.

Troubleshooting Steps

6Cisco IOS Release 12.0(3)T

Figure 2 Cable Modem Initialization Flowchart

the Cisco

uBR7246

Registration

complete

Power

Scan for

downstream

channel

Obtain

upstream

parameters

Upstream

parameter

acquired

Start

Ranging

Ranging and

auto adjust

completed

Establish

connectivety

complete

Establish

time of

day

Time of day

established

Establish

security

Transfer

operational

parameters

Transfer

complete

Baseline

privacy

initialization

Baseline

privacy

initialized

Operational

2960

Downstream

sync

established Security

established

Step 2—Connect to the Cable Modem

Troubleshooting Tips for the Cisco uBR904 Cable Modem 7

Step 2—Connect to the Cable Modem

Telnet to the IP address assigned to the cable interface or Ethernet interface. If the interface is not

up, you need to access the Cisco IOS software via the RJ-45 console port, which is a physical port

on the back of the cable modem.

Because the MAC log file only holds a snapshot of 1023 entries at a time, you should try to display

the cable modem’s log file within 5 minutes after the reset or problem occurs.

Table 1 Cable Modem Initialization Sequences and Events

Sequence Event Description

1Scan for a downstream channel and

establish synchronization with the

headend Cisco uBR7246.

The cable modem acquires a downstream channel from the

headend, saves the last operational frequency in non-volatile

memory, and tries to reacquire the saved downstream channel

the next time a request is made.

An ideal downstream signal is one that synchronizes QAM

symbol timing, FEC framing, MPEG packetization, and

recognizes downstream sync MAC layer messages.

2Obtain upsteam channel parameters. The cable modem waits for an upstream channel descriptor

(UCD) message from the headend Cisco uBR7246. This is

done to retrieve transmission parameters for the upstream

channel.

3Start ranging for power adjustments. The ranging process adjusts the cable modem’s transmit

power. The cable modem performs ranging in two stages:

ranging state 1 and ranging state 2.

4Establish IP connectivity. The cable modem invokes DHCP requests to obtain an IP

address, which is needed for IP connectivity. The DHCP

request also includes the name of a file that contains additional

configuration parameters, the TFTP server’s address, and the

Time of Day (TOD) server’s address.

5Establish the time of day. The cable modem accesses the TOD server for the current date

and time, which is used to create time stamps for logged events

(such as those displayed in the MAC log file).

6Establish security. Keys for privacy are exchanged between the cable modem and

the headend Cisco uBR7246.

7Transfer operational parameters. After the DHCP and security operations are successful, the

cable modem downloads operational parameters from a

configuration file stored on the cable company’s TFTP server.

8Perform registration. The cable modem registers with the headend Cisco uBR7246.

The cable modem is authorized to forward trafficinto thecable

network after the cable modem is initialized, authenticated,

and configured.

Note The Cisco uBR904 cable modem supports baseline

privacy in Cisco IOS Release 11.3(5)NA and later,andin Cisco

IOS Release 12.0(2)XC and later.

9Comply with baseline privacy. Link level encryption keys are exchanged between the

headend and the cable modem.

10 Enter the operational maintenance

state. As soon as the cable modem has successfully completed the

above sequence, it enters operational maintenance state.

Troubleshooting Steps

8Cisco IOS Release 12.0(3)T

Step 3—Display the Cable Modem’s MAC Log File

A MAC-layer circular log file is stored inside the cable modem. This file contains the most valuable

information for troubleshooting the cable interface: a history of the log messages such as state event

activities and timestamps.

The MAC log file is displayed by entering the show controllers cable-modem 0 mac log command

from privileged EXEC mode.

The most useful display fields in this log file arethe reported state changes. These fields are preceded

by the message CMAC_LOG_STATE_CHANGE. These fields show how the cable modem progresses

through the various processes involved in establishing communication and registration with the

CMTS. The maintenance_state is the normal operational state, and the wait_for_link_up_state

is the normal state when the interface is shut down.

The following is the normal progression of states as displayed by the MAC log:

wait_for_link_up_state

ds_channel_scanning_state

wait_ucd_state

wait_map_state

ranging_1_state

ranging_2_state

dhcp_state

establish_tod_state

security_association_state

configuration_file_state

registration_state

establish_privacy_state

maintenance_state

Note To translate this output into more meaningful information, see “Step 4—Interpret the MAC

Log File and Take Action” on page 10.

Following is an example of what the MAC log file looks like when the cable modem interface

successfully comes up and registers with the CMTS. The output you see is directly related to the

messages that are exchanged between the cable modem and the headend Cisco uBR7246.

uBR904# show controllers cable-modem 0 mac log

508144.340 CMAC_LOG_DRIVER_INIT_IDB_RESET 0x08098FEA

508144.342 CMAC_LOG_LINK_DOWN

508144.344 CMAC_LOG_LINK_UP

508144.348 CMAC_LOG_STATE_CHANGE ds_channel_scanning_state

508144.350 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 88/453000000/855000000/6000000

508144.354 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 89/93000000/105000000/6000000

508144.356 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 90/111250000/117250000/6000000

508144.360 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 91/231012500/327012500/6000000

508144.362 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 92/333015000/333015000/6000000

508144.366 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 93/339012500/399012500/6000000

508144.370 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 94/405000000/447000000/6000000

508144.372 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 95/123015000/129015000/6000000

508144.376 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 96/135012500/135012500/6000000

508144.380 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 97/141000000/171000000/6000000

508144.382 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 98/219000000/225000000/6000000

508144.386 CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND 99/177000000/213000000/6000000

508144.390 CMAC_LOG_WILL_SEARCH_SAVED_DS_FREQUENCY 699000000

508145.540 CMAC_LOG_UCD_MSG_RCVD 3

508146.120 CMAC_LOG_DS_64QAM_LOCK_ACQUIRED 699000000

508146.122 CMAC_LOG_DS_CHANNEL_SCAN_COMPLETED

508146.124 CMAC_LOG_STATE_CHANGE wait_ucd_state

Step 3—Display the Cable Modem’s MAC Log File

Troubleshooting Tips for the Cisco uBR904 Cable Modem 9

508147.554 CMAC_LOG_UCD_MSG_RCVD 3

508147.558 CMAC_LOG_UCD_NEW_US_FREQUENCY 20000000

508147.558 CMAC_LOG_SLOT_SIZE_CHANGED 8

508147.622 CMAC_LOG_FOUND_US_CHANNEL 1

508147.624 CMAC_LOG_STATE_CHANGE wait_map_state

508148.058 CMAC_LOG_MAP_MSG_RCVD

508148.060 CMAC_LOG_INITIAL_RANGING_MINISLOTS 40

508148.062 CMAC_LOG_STATE_CHANGE ranging_1_state

508148.064 CMAC_LOG_RANGING_OFFSET_SET_TO 9610

508148.066 CMAC_LOG_POWER_LEVEL_IS 28.0 dBmV (commanded)

508148.068 CMAC_LOG_STARTING_RANGING

508148.070 CMAC_LOG_RANGING_BACKOFF_SET 0

508148.072 CMAC_LOG_RNG_REQ_QUEUED 0

508148.562 CMAC_LOG_RNG_REQ_TRANSMITTED

508148.566 CMAC_LOG_RNG_RSP_MSG_RCVD

508148.568 CMAC_LOG_RNG_RSP_SID_ASSIGNED 2

508148.570 CMAC_LOG_ADJUST_RANGING_OFFSET 2408

508148.572 CMAC_LOG_RANGING_OFFSET_SET_TO 12018

508148.574 CMAC_LOG_ADJUST_TX_POWER 20

508148.576 CMAC_LOG_POWER_LEVEL_IS 33.0 dBmV (commanded)

508148.578 CMAC_LOG_STATE_CHANGE ranging_2_state

508148.580 CMAC_LOG_RNG_REQ_QUEUED 2

508155.820 CMAC_LOG_RNG_REQ_TRANSMITTED

508155.824 CMAC_LOG_RNG_RSP_MSG_RCVD

508155.826 CMAC_LOG_ADJUST_RANGING_OFFSET -64

508155.826 CMAC_LOG_RANGING_OFFSET_SET_TO 11954

508155.828 CMAC_LOG_RANGING_CONTINUE

508165.892 CMAC_LOG_RNG_REQ_TRANSMITTED

508165.894 CMAC_LOG_RNG_RSP_MSG_RCVD

508165.896 CMAC_LOG_ADJUST_TX_POWER -9

508165.898 CMAC_LOG_POWER_LEVEL_IS 31.0 dBmV (commanded)

508165.900 CMAC_LOG_RANGING_CONTINUE

508175.962 CMAC_LOG_RNG_REQ_TRANSMITTED

508175.964 CMAC_LOG_RNG_RSP_MSG_RCVD

508175.966 CMAC_LOG_RANGING_SUCCESS

508175.968 CMAC_LOG_STATE_CHANGE dhcp_state

508176.982 CMAC_LOG_DHCP_ASSIGNED_IP_ADDRESS 188.188.1.62

508176.984 CMAC_LOG_DHCP_TFTP_SERVER_ADDRESS 4.0.0.1

508176.986 CMAC_LOG_DHCP_TOD_SERVER_ADDRESS 4.0.0.32

508176.988 CMAC_LOG_DHCP_SET_GATEWAY_ADDRESS

508176.988 CMAC_LOG_DHCP_TZ_OFFSET 360

508176.990 CMAC_LOG_DHCP_CONFIG_FILE_NAME platinum.cm

508176.992 CMAC_LOG_DHCP_ERROR_ACQUIRING_SEC_SVR_ADDR

508176.996 CMAC_LOG_DHCP_COMPLETE

508177.120 CMAC_LOG_STATE_CHANGE establish_tod_state

508177.126 CMAC_LOG_TOD_REQUEST_SENT

508177.154 CMAC_LOG_TOD_REPLY_RECEIVED 3107617539

508177.158 CMAC_LOG_TOD_COMPLETE

508177.160 CMAC_LOG_STATE_CHANGE security_association_state

508177.162 CMAC_LOG_SECURITY_BYPASSED

508177.164 CMAC_LOG_STATE_CHANGE configuration_file_state

508177.166 CMAC_LOG_LOADING_CONFIG_FILE platinum.cm

508178.280 CMAC_LOG_CONFIG_FILE_PROCESS_COMPLETE

508178.300 CMAC_LOG_STATE_CHANGE registration_state

508178.302 CMAC_LOG_REG_REQ_MSG_QUEUED

508178.306 CMAC_LOG_REG_REQ_TRANSMITTED

508178.310 CMAC_LOG_REG_RSP_MSG_RCVD

508178.312 CMAC_LOG_COS_ASSIGNED_SID 1/2

508178.314 CMAC_LOG_RNG_REQ_QUEUED 2

508178.316 CMAC_LOG_REGISTRATION_OK

508178.318 CMAC_LOG_STATE_CHANGE establish_privacy_state

508178.320 CMAC_LOG_NO_PRIVACY

508178.322 CMAC_LOG_STATE_CHANGE maintenance_state

Troubleshooting Steps

10 Cisco IOS Release 12.0(3)T

You can display other aspects of the MAC layer by using variations of the show controllers

cable-modem 0 mac command:

uBR904# show controllers cable-modem 0 mac ?

errors Mac Error Log data

hardware All CM Mac Hardware registers

log Mac log data

resets Resets of the MAC

state Current MAC state

For examples and descriptions of how to use these keywords, see the show controllers

cable-modem mac command reference page.

Step 4—Interpret the MAC Log File and Take Action

The MAC log file gives a detailed history of initialization events that occurred in the cable modem.

All pertinent troubleshooting information is stored here.

The following sample log file is broken down into the chronological sequence of events listed below.

Sample comments are also included in the log file.

•Event 1—Wait for the Link to Come Up

•Event 2—Scan for a Downstream Channel, then Synchronize

•Event 3—Obtain Upstream Parameters

•Event 4—Start Ranging for Power Adjustments

•Event 5—Establish IP Connectivity

•Event 6—Establish the Time of Day

•Event 7—Establish Security

•Event 8—Transfer Operational Parameters

•Event 9—Perform Registration

•Event 10—Comply with Baseline Privacy

•Event 11—Enter the Maintenance State

Event 1—Wait for the Link to Come Up

The MAC layer informs the cable modem’s drivers that it needs to reset. This is the first event that

happens after the modem powers up and begins initialization. The fields LINK_DOWN and LINK_UP are

similar to the shut and no shut conditions on a standard Cisco interface.

uBR904# show controllers cable-modem 0 mac log

528302.040 CMAC_LOG_LINK_DOWN

528302.042 CMAC_LOG_RESET_FROM_DRIVER

528302.044 CMAC_LOG_STATE_CHANGE wait_for_link_up_state

528302.046 CMAC_LOG_DRIVER_INIT_IDB_SHUTDOWN 0x08098D02

528302.048 CMAC_LOG_LINK_DOWN

528308.428 CMAC_LOG_DRIVER_INIT_IDB_RESET 0x08098E5E

528308.432 CMAC_LOG_LINK_DOWN

528308.434 CMAC_LOG_LINK_UP

Step 4—Interpret the MAC Log File and Take Action

Troubleshooting Tips for the Cisco uBR904 Cable Modem 11

Event 2—Scan for a Downstream Channel, then Synchronize

Different geographical regions and different cable plants use different frequency bands. The

Cisco uBR904 cable modem uses a built-in default frequency scanning feature to address this issue.

After the cable modem finds a successful downstream frequency channel, it saves the channel to

NVRAM. The cable modem recalls this value the next time it needs to synchronize its frequency.

The field CMAC_LOG_WILL_SEARCH_DS_FREQUENCY_BAND tells you what frequency the cable modem

will scan for. The field CMAC_LOG_WILL_SEARCH_SAVED_DS_FREQUENCY tells you the frequency the

cable modem locked onto and saved to NVRAM for future recall. The field

CMAC_LOG_DS_64QAM_LOCK_ACQUIRED communicates the same information. The field

CMAC_LOG_DS_CHANNEL_SCAN_COMPLETED indicates that the scanning and synchronization was

successful.