hello
I have a query you make, not long ago that incursiene in DOCSIS.
I have a cisco CMTS IOS ubr7100-UBR7100-mz.123-9a.BC6.bin ik8s. and 12 Megabyte of my ISP.
My problem is I have is that my network is slow, my interface observed in a traffic Downstream of 8 megabytes Upstream interface but only 2 megabytes.
It strikes me atension Upstream interface is as applying rate-limit on the interface. My question is, should this be my problem of slowness.
I would be grateful if you could guide me in this regard. Thank you very much. my configurasion.
cable downstream annex B
cable downstream modulation 64qam
cable downstream interleave-depth 32
cable downstream frequency 501000000
cable downstream channel-id 0
no cable downstream rf-shutdown
cable downstream rf-power 61
cable upstream 0 frequency 30800000
cable upstream 0 power-level 0
cable upstream 0 channel-width 1600000
cable upstream 0 minislot-size 4
cable upstream 0 modulation-profile 1
no cable upstream 0 shutdown
cable upstream 1 frequency 30800000
cable upstream 1 power-level 0
cable upstream 1 channel-width 1600000
cable upstream 1 minislot-size 4
cable upstream 1 modulation-profile 1
no cable upstream 1 shutdown
cable upstream 2 channel-width 1600000
cable upstream 2 minislot-size 4
cable upstream 2 modulation-profile 1
cable upstream 2 shutdown
cable upstream 3 channel-width 1600000
cable upstream 3 minislot-size 4
cable upstream 3 modulation-profile 1
cable upstream 3 shutdown
cable helper-address x.x.x.x
show controllers cable 1/0 upstream 0
Cable1/0 Upstream 0 is up
Frequency 30.800 MHz, Channel Width 1.600 MHz, QPSK Symbol Rate 1.280 Msps
Spectrum Group is overridden
US phy SNR_estimate for good packets - 25.8856 dB
Nominal Input Power Level 0 dBmV, Tx Timing Offset 2227
Ranging Backoff automatic (Start 0, End 3)
Ranging Insertion Interval automatic (438 ms)
Tx Backoff Start 3, Tx Backoff End 5
Modulation Profile Group 1
Concatenation is enabled
Fragmentation is enabled
part_id=0x3137, rev_id=0x03, rev2_id=0xFF
nb_agc_thr=0x0000, nb_agc_nom=0x0000
Range Load Reg Size=0x58
Request Load Reg Size=0x0E
Minislot Size in number of Timebase Ticks is = 4
Minislot Size in Symbols = 32
Bandwidth Requests = 0x8AE77B78
Piggyback Requests = 0x66DEA93B
Invalid BW Requests= 0xBEC62
Minislots Requested= 0x5521609C
Minislots Granted = 0xF1A53D6A
Minislot Size in Bytes = 8
Map Advance (Dynamic) : 2397 usecs
UCD Count = 3447569
Atte.
Your upstreams are running 1.6mhz QPSK, that is all the bandwidth you're going to get out of those channels.
You will need to upgrade to a 3.2mhz channel and/or 16qam or better to get more upstream bandwidth.
Hi!
Do you have a uBR7111/7114? That's a DOCSIS 1.1 CMTS, so you can configure it to run 16QAM and 3.2 MHz bandwidth on the upstream(s). 16QAM does however require a rather clean (noise free) return path on your cable network. Signal quality is normally not affected by the bandwidth, so going to 3.2 MHz should be doable provided you have the upstream frequency space needed.
Going from QPSK to 16QAM doubles capacity, as does doubling the bandwidth from 1.6 to 3.2 MHz. 16QAM and 3.2 MHz gives 8.8 Mbps real IP-traffic throughput.
I also noted that you run 64QAM on the downstream. Unless your downstream (forward path) networks isn't really crappy, you could configure it to run 256QAM. If modems report 35 dB SNR on their RX (log in on one or more modems web pages to see this or read it using SNMP) you can do this easily. Just remember that upstream changes can be done with modems online (no service interruption) but downstream changes require a new ranging procedure for each modem, so this will mean a 10-60 second service interrupt.
If you have a DOCSIS 2.0 CMTS, you can even go to 64QAM (provided really noise-free upstream) and 6.4 MHz on the upstream, giving you 26 Mbps or so.
/Fredrik
hello
I have my cable upstream 0 modifiado channel-width to 3.2 MHz, only to see its impact, I saw my traffic improved, but my SNR was 31 dB, although the traffic was minimal variation, improved.
Thanks for the replies.
As you increase your channel width, your measured SNR will drop. Actually, if you look at a 1.6mhz channel and a 3.2 mhz channel, which are measured at the same channel power db, you'll see that the 3.2mhz channel is shorter. The signal level drops, but the channel power will remain the same because there is more carrier. Thus, your signal to noise drops. It'll drop another 3db if you go to a 6.4mhz channel. This is expected and normal.
At 31db, you might try 16QAM on that 3.2 and see if it works. I know a 3.2 64QAM will function well below 25snr, (though, you really wouldn't want to..)so I would think a 16qam should work for you at that level.