Hi,
I have configured my all 4 upstream ports channel-width to 3.2 MHz.Since I am using QPSK modulation for upstream,I can get maximum upstream bit rate 5.12 mbps.
As I have 4 upstream ports for one downstream, will I get 5.12 mbps upstream separate throughput across all upstreams? or 5.12 will be aggregate for all upstreams? Pls suggest
Robart
Hello,
You will get 5.12 Mbps for each upstream.
all 4 upstreams together will be 20Mbps.
Using QAM 64 with 5.03 symbol rate,i can get max ~ 30 mbps down stream data rate.If I have 1x4 downstream card, it means i can get 30 mbps in D/S and 20 mbps in U/S?
Rgds,
DOCSIS has some overheads so you real world throughput wont be as high as you say
Example upstream settings for DOCSIS 1.x :
1.6Mhz at QPSK = 2.56M less overheads = 2.2M usable
1.6Mhz at 16QAM = 5.12M less overheads = 4.4M usable
3.2Mhz at QPSK = 5.12M less overheads = 4.4M usable
3.2Mhz at 16QAM = 10.24M less overheads = 8.9M usable
Example upstream settings for DOCSIS 2.0 :
3.2Mhz at 64QAM = 15.36M less overheads = 13.3M usable
6.4MHz at 16QAM = 20.48M less overheads = 17.8M usable
6.4Mhz at 32QAM = 25.60M less overheads = 22.2M usable
6.4Mhz at 64QAM = 30.72M less overheads = 26.7M usable
Example downstream settings :
6MHz at 64QAM = 30.34M less overheads = approx 27M usable
6MHz at 256QAM = 42.88M less overheads = approx 38M usable
If your card is 1x4, it means you have one downstream, and 4 upstreams
You can wire this up in differnet ways.
For example configure your network as 1 node that contains 1 downstream and 4 upstreams. First modem that boots up will grab the downstream plus one of the upstream. Next modem will grab the same downstream but may pick a different upstream.
Or you might configure 2 nodes, each sharing the same downstream, and having 2 upstreams each
Or you might configure 4 nodes, each sharing the same downstream, and having 1 upstream each.
Or you might configure 8 nodes, each sharing the same downstream, and 1 upstream being shared per 2 nodes.
etc
It's up to you to decide how to wire it.
But yes as you say the aggregate output of the card is going to be capped at eg 27Mbps down and 16Mbps or so up if everything is running flat out. Peak speed for any given modem would be 27Mbps down and about 4Mbps up in best case (because D1/D2 modems are 1x1 tuner, they will grab 1 downstream and 1 upstream. D3 gear goes faster by having 4x4 or 8x4 tuners where the modem can grab multiple downstreams and upstreams - you need a D3 CMTS as well as D3 modems though for this to work).
Hope that helps!