PDF《故障排除 UBR 电缆调制解调器不上线的问题》

5 offline

2290 0.00

2 0 10.1.1.25 0050.7366.2223 Cable2/0/U0

6 offline

2811 0.00

2 0 10.1.1.22 0050.7366.1e01 Cable2/0/U0

7 offline

2810 -0.50

2 0 10.1.1.20 0030.96f9.65d9 Cable2/0/U0

8 offline

2810 -0.25

2 0 10.1.1.21 0030.96f9.6605 从上面输出Show Cable Modem显示命令我们有四调制解调器在.有时调制解调器可能通过其他状 态循环然后回到.以下列表给出不能的调制解调器的多数常见原因达到求积分法振幅 modulation(QAM)锁定: 有线调制解调器没有连接对网络或没有打开 q 微弱的载波信号(许多个噪声) q 不正确的下行中心频率 q 在DOCSIS文件指定的错误频率 q 缺乏下行数字QAM调整的信号 q 在CMTS路由器的cable modem change-frequency指定的错误频率 q 在MCxx卡的不正确的填充 q 下面是show controllers cable-modem 0被裁减的输出显示如被采取从有线调制解调器(Kuffing)端: kuffing# show controllers cable-modem

0 BCM Cable interface 0: CM unit 0, idb 0x8086C88C, ds 0x8086E460, regaddr = 0x2700000, reset_mask 0x80 station address 0030.96f9.65d9 default station address 0030.96f9.65d9 PLD VERSION:

1 Concatenation: ON Max bytes Q0:

2000 Q1:

2000 Q2:

2000 Q3:

2000 MAC State is ds_channel_scanning_state, Prev States =

3 MAC mcfilter 01E02F00 data mcfilter

00000000 MAC extended header ON DS: BCM

3300 Receiver: Chip id = BCM3300 US: BCM

3300 Transmitter: Chip id =

3300 Tuner: status=0x00 Rx: tuner_freq 529776400, symbol_rate 5361000, local_freq

11520000 snr_estimate 166(TenthdB), ber_estimate 0, lock_threshold

26000 QAM not in lock, FEC not in lock, qam_mode QAM_64 (Annex B) Tx: tx_freq 27984000, symbol rate

8 (1280000 sym/sec) power_level: 6.0 dBmV (commanded)

7 (gain in US AMP units)

63 (BCM3300 attenuation in .4 dB units)Rest of display omitted. 自上我们能看到信噪比估计是16.6 dB.理论上来讲这应该是至少30dB为了CM能正常运行为64个QAM.有线数据业务接口规范(DOCSIS)下行与上行说明的参考的RF规格,并且关于正在验证下行 信号.有时您可以有好信噪比(SNR)说34dB,但是仍然有噪声现在例如脉冲噪声.这经常是由有的 正向通路扫描发射机导致的干涉调制解调器信号的信号.这可能由操作在零的间距模式的光谱分析 程序只检测. 关于调查的更多信息噪声问题使用光谱分析程序参考连接Cisco ubr7200系列路由器对电缆头端.脉 冲噪声的一个征兆是在输出看到的无法修复的错误show interfaces cable 2/0 upstream中0如下所示 : sydney# show interfaces cable 2/0 upstream

0 Cable2/0: Upstream

0 is up Received

46942 broadcasts,

0 multicasts,

205903 unicasts

0 discards,

12874 errors,

0 unknown protocol

252845 packets input,

1 uncorrectable

12871 noise,

0 microreflections Total Modems On This Upstream Channel :

3 (3 active) Default MAC scheduler Queue[Rng Polls] 0/64, fifo queueing,

0 drops Queue[Cont Mslots] 0/104, fifo queueing,

0 drops Queue[CIR Grants] 0/64, fair queueing,

0 drops Queue[BE Grants] 0/64, fair queueing,

0 drops Queue[Grant Shpr] 0/64, calendar queueing,

0 drops Reserved slot table currently has

0 CBR entries Req IEs 77057520, Req/Data IEs

0 Init Mtn IEs 1194343, Stn Mtn IEs

117174 Long Grant IEs 46953, Short Grant IEs

70448 Avg upstream channel utilization : 1% Avg percent contention slots : 96% Avg percent initial ranging slots : 4% Avg percent minislots lost on late MAPs : 0% Total channel bw reserved

0 bps CIR admission control not enforced Current minislot count :