Troubleshooting guide

5-3
Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 5 Troubleshooting DOCSIS Networks
Understanding Initialization States
Understanding Initialization States
The following sections review each of the initialization states, including any problems that may occur in
that state.
Before discussing the initialization process in detail, following is a summary of the process as displayed
on a Killerbee RDCM console:
Example output from Killerbee initialization:
Found DS frequency (64 QAM): 651000000 Hz
MAC State --->>> 'wait_ucd_state'
Found US channel: 1 6 5 4 3 2
MAC State --->>> 'wait_map_state'
Trying Upstream Channel 6 (41200000 Hz)
MAC State --->>> 'ranging_broadcast_state'
MAC State --->>> 'ranging_unicast_state'
MAC State --->>> 'establish_dhcp_state'
cmWriteFlashFile("CM_MACCONFIG", 0x8313d54, 0x136) by TID 0x82eb558 (tConfigNV)
cmWriteFlashFile("CM_DHCPLEASE", 0x81162c0, 0x24) by TID 0x82d7d90 (tLease-0)
MAC State --->>> 'establish_tod_state'
MAC State --->>> 'security_association_state'
MAC State --->>> 'configuration_file_state'
MAC State --->>> 'registration_state'
MAC State --->>> 'establish_privacy_state'
MAC State --->>> 'operational_state'
cmWriteFlashFile("CM_MACCONFIG", 0x8313d54, 0x136) by TID 0x82eac00 (tConfigNV)
cmWriteFlashFile("CM_BOOT_BK", 0x8313e8a, 0x13e) by TID 0x82eac00 (tConfigNV)
cmWriteFlashFile("CM_BOOT", 0x8313e8a, 0x13e) by TID 0x82eac00 (tConfigNV)
Physical and MAC Configuration
The first few states involve configurations at the Physical and Data Link (Media Access) levels.
Scanning Downstream Channel
Scanning Downstream Channel...
lower_limit upper_limit step_size valid
BAND 0: 855000000 855000000 6000000 yes Trying: 855000000 2
The first stage of MTA bring-up is downstream channel acquisition. The tuner scans the downstream
spectrum until a digital QAM signal is encountered. When a channel with QAM is found, the receiver
listens for SYNC messages from the CMTS (the Cisco uBR7246vxr). SYNC messages are CMTS
timestamps that the MTA needs in order to synchronize with the CMTS to calculate latency — how much
time it takes for messages to travel in the HFC network.
If a modem is stuck in this state, or comes back to this state quite frequently, this is an indication of a
less than adequate physical setup. Difficulty in acquiring sync can be caused by a weak carrier signal (or
lots of noise). Since noise is random, the downstream channel has a carrier signal that must have enough
power for the modem to discern the carrier from the noise. This carrier is the QAM symbols representing
the bits of the SYNC messages (and all other messages and data). The signal power can also be too strong
for the receiver to discern the symbols in the carrier.
Another problem to check for with failure to sync is the center frequency. If the center frequency of the
carrier is not a standard channel center frequency, the receiver may not discern all the symbols, or more
likely will not achieve QAM lock at all.