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Troubleshooting Tips for the
Cisco uBR904 Cable Modem
The following sections are provided:
• Feature Summary on page 1
� Prerequisites on page 3
� Supported MIBs and RFCs on page 3
� CMTS to Cable Modem Network Topology on page 4
� Troubleshooting Tips on page 5
� Command Reference on page 16
� Debug Commands on page 42
� What to do Next on page 54
Feature Summary
This document provides MSOs (multiple service operators) with a set of software tools for
troubleshooting a cable modem for data-ov
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Feature Summary List of Terms CATV—Originally stood for Community Antenna Television. CATV now refers to any cable (coaxial/fiber) based system that provides television services. Cable modem—Any device that modulates and demodulates digital data onto a CATV plant. Cable router—A modular chassis-based router optimized for the data over CATV HFC applications. Channel—A specific frequency allocation and bandwidth. Downstream channels used for television in the U. S. are 6 MHz wide. CM—Cable mode
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List of Terms Prerequisites Cisco IOS Release 11.3(4)NA or later must be running inside the cable modem. Enter the show version EXEC command to display the software version level. Supported MIBs and RFCs The Cisco uBR904 cable modem supports the following: � Radio Frequency Interface Specification—This specification is developed by the Multimedia Cable Network System (MCNS) corsortium. It defines the radio-frequency interface specification for high-speed data-over-cable systems. � Cisco Stand
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CMTS to Cable Modem Network Topology 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 ISP IP-related WAN ATM, FDDI, 100BT... 100BT 100BT 100BT ISP @ home... Proxy server Cisco uBR7246 CMTS 100BT MSD: Maintenance Service Organization, Cable companies Upconvertor Analog TV DS-RF 54-860 Mhz Digital TV Fiber Transceiver 80 km 1000 ft Fiber node (Telephone pole, underground box) Drop
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Understand How Basic Initialization Works Troubleshooting Tips Perform the following steps to troubleshoot a cable modem: � 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 � Step 5—(Optional) Use Additional Troubleshooting Commands Understand How Basic Initialization Works Before you troubleshoot a cable modem, you should be familiar with the cable modem initia
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Troubleshooting Tips Figure 2 Cable Modem Initialization Flowchart Power on Scan for Establish downstream 1 6 security channel Downstream Security sync established established Obtain Transfer upstream operational 2 7 parameters parameters Upstream Transfer parameter complete acquired Register with Start the Cisco 3 8 Ranging uBR7246 Ranging and Registration auto adjust complete completed Establish Baseline IP privacy 4 9 connectivety initialization Baseline IP privacy complete initialized Es
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Connect to the Cable Modem . Table 1 Cable Modem Initialization Sequences and Events Sequence Event Description 1 Scan for a downstream channel and The cable modem acquires a downstream channel from the establish synchronization with the headend, saves the last operational frequency in non-volatile headend Cisco uBR7246. 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 fram
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Troubleshooting Tips Display the Cable Modem’s MAC Log File A MAC layer circular log file is inside the cable modem. This file contains a history of log messages, such as state event activities and timestamps, which are used for troubleshooting purposes. This log file contains the most valuable information for a cable technician or engineer to debug the cable interface. The MAC log file is displayed by entering the show controller cable-modem 0 mac log EXEC command. The most useful display
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Display the Cable Modem’s MAC Log File 508146.122 CMAC_LOG_DS_CHANNEL_SCAN_COMPLETED 508146.124 CMAC_LOG_STATE_CHANGE wait_ucd_state 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_RC
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Troubleshooting Tips You can display other aspects of the MAC layer by using variations of the show controller cable-modem 0 mac command: uBR904# show controller 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 on how to use these keywords, see the show controller cable-modem mac command reference page. Interpret the MAC Log File and Tak
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Interpret the MAC Log File and Take Action 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_
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Troubleshooting Tips Event 3—Obtain Upstream Parameters The cable modem waits for an upstream channel descriptor messages (UCD) from the headend Cisco uBR7246. This is done to retrieve transmission parameters for the upstream channel. 508146.124 CMAC_LOG_STATE_CHANGE wait_ucd_state 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 CMA
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Interpret the MAC Log File and Take Action Event 5—Establish IP Connectivity After ranging is complete, the cable interface on the cable modem is up. Now the cable modem accesses a remote DHCP server to get an IP address. 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. The field CMAC_LOG_DHCP_ASSIGNED_IP_ADDRESS indicates the IP address assigned from the DHCP server t
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Troubleshooting Tips Event 8—Transfer Operational Parameters After the DHCP and security operations are successful, the cable modem downloads operational parameters from a cable company’s TFTP server. These parameters are transferred via a configuration file. The field CMAC_LOG_DHCP_CONFIG_FILE_NAME shows the filename containing the transmission parameters. 508177.164 CMAC_LOG_STATE_CHANGE configuration_file_state 508177.166 CMAC_LOG_LOADING_CONFIG_FILE p
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Use Additional Troubleshooting Commands Event 11—Enter the Maintenance State As soon as the cable modem is completely up and running, it enters the operational maintenance state. 508178.322 CMAC_LOG_STATE_CHANGE maintenance_state Use Additional Troubleshooting Commands You can use other show controller and debug cable modem commands to troubleshoot different aspects of a cable modem. However, the most useful command is the show controller cable-modem 0 mac command. To
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Command Reference Command Reference This section provides new commands for troubleshooting the Cisco uBR904 cable modem. All other commands used with this feature are documented in the Cisco IOS Release 11.3 command references. � show controller cable-modem � show controller cable-modem bpkm � show controller cable-modem mac � show controller cable-modem phy � show controller cable-modem des � show controller cable-modem filters � show controller cable-modem lookup-table � show controller cabl
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show controller cable-modem show controller cable-modem To display high-level controller information about a cable modem, use the show controller cable-modem Privileged EXEC command. Syntax Description number Controller number inside the cable modem. Command Mode Privileged EXEC Usage Guidelines This command first appeared in Cisco IOS Release 11.3 NA. Sample Display Following is a sample output for this command: uBR904# show controller cable-modem 0 BCM Cable interface 0: CM unit 0, idb 0x200
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Command Reference Global control and status: global_ctrl_status=0x00 interrupts: irq_pend=0x0008, irq_mask=0x00F7 Related Commands show controller cable-modem bpkm show controller cable-modem des show controller cable-modem filters show controller cable-modem lookup-table show controller cable-modem mac show controller cable-modem phy show controller cable-modem tuner show interface cable-modem Release 11.3(4)NA 18
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show controller cable-modem bpkm show controller cable-modem bpkm To display information about the baseline privacy key management exchange between the cable modem and the headend CMTS, use the show controller cable-modem bpkm Privileged EXEC command. show controller cable-modem number bpkm Syntax Description number Controller number inside the cable modem. Command Mode Privileged EXEC Usage Guidelines This command first appeared in Cisco IOS Release 11.3 NA. Sample Display The following outpu
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Command Reference show controller cable-modem des To display information about the Data Encryption Standard (DES) engine registers, use the show controller cable-modem des Privileged EXEC command. show controller cable-modem des Syntax Description This command has no key words or arguments. Command Mode Privileged EXEC Usage Guidelines This command first appeared in Cisco IOS Release 11.3 NA. Sample Display DES engine registers are displayed in the following example: uBR904# show controller cab
