Cisco Systems UBR904 manual Interpret the MAC Log File and Take Action

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

communicates the same information. The field indicates that the scanning and synchronization was

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.

successful.

CMAC_LOG_DS_CHANNEL_SCAN_COMPLETED

CMAC_LOG_DS_64QAM_LOCK_ACQUIRED

Interpret the MAC Log File and Take Action

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

A frequency band is a group of adjacent channels. These bands are numbered from 88 to 99. Each band has starting and ending digital carrier frequencies and a 6 MHz step size. For example, a search of EIA channels 95-97 is specified using band 89. The starting frequency is 93 Mhz, the ending frequency is 105 Mhz.

The cable modem’s default frequency bands correspond to the North American EIA CATV channel plan for 6 MHz channel slots between 90 MHz and 858 MHz. For example, EIA channel 95 occupies the slot 90-96 MHz. The digital carrier frequency is specified as the center frequency of 93 MHz.

Channel 95 is usually specified using the analog video carrier frequency of 91.25 Mhz, which lies 1.75 Mhz below the center of the slot.

The search table is arranged so that the first frequencies tried are above 450 Mhz. Because many CATV systems have been upgraded from 450 MHz to 750 MHz coaxial cable, digital channels have a high chance of being assigned in the new spectrum. The search table omits channels below 90 MHz and above 860 MHz since the DOCSIS specification does not mandate their coverage.

Some CATV systems use alternative frequency plans such as the IRC (Incrementally Related Carrier) and HRC (Harmonically Related Carrier) plans. Most of the IRC channel slots overlap the EIA plan. The HRC plan is not supported by Cisco’s cable modems since so few cable plants are using this plan.

Troubleshooting Tips for the Cisco uBR904 Cable Modem 11