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low power level reception , negociated

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rainbow
low power level reception , negociated

Hello , can someone help me with this ... , I am working with a BSR 64000 Motorola BSR, I am aware the Power RX is negociated between the CM and the CMTS , at current configuration I have it set in the CMTS to be 14dBmV, I have some CM registered with low power level reception , - 0.5 , 8 , 10 dBmV , it happens with some CMs in different Upstream channels , so I dont think it is a plant problem, can be the wire instalation at clients home ? or a problem with the CMTS in the process of negociating the power level , how can this low power level affect the service being provided ? ... another question ... when I analyze the cable flap list output , some rng flap are registered, as far as I am concerned it means the the CM send a RNG-req after being given a rng-response by the CMTS, is the CM trying to get restarted by itself ? , the SNR y power level are okay, i suspect is a device fabric problem .... I appreciate any response you guys can give me. Regards.

cmcaldas
rx levels

The receive level of 14 is bit high. most have it set to 0. what version sw are you running? can you check the modem's receive and transmit power levels? with any cmts, modems receive of zero and transmit of around 45 is good. I'm thinking you've got modems in the 50 plus and that could be the problem.
how many nodes are combined per receiver? are there other services on the return?

~Carl

rainbow
hello , thanks for the

hello , thanks for the answer , I think I dont express myself correctly, when I mean power level reception I am talking about the power level received in the CMTS from CMs , this level is set up in the CMTS configuration to be 14dBmV and it´is negociated between the two entities, some CMs are registered with low levels for instance 8, 10 dBmV, contrary to other CMs which register in the CMTS with 14 or around 14 dBmV, however they all share the same Upstrem channel .... can be this a wire problem on the clients ? ...... plus ... what do you know about the rng flaps ?, I want to be sure what it means . Thank you.

cmcaldas
receive level

yes, I understand the level into the cmts receiver is configured for 14 and recommend you lower it to 5.
when you say you have modems reporting an 8 or 10 (show cable modem for example). that tells me the modem is at it's max transmit level and still can't reach the 14 that the receiver port is configured for. a few problems. with modems at max transmit you'll have a ton from that flap list, your laser in the node will start to clip because of too much power and with more than one node combined ( not confirmed if that's the case ) more customers will have service problems.
why I asked what the average registered cable modem's receive and transmit levels are. thinking you'll find too many in 50's.
that that modem that you said was registered with an 8. the ipaddress of the modem, say 10.20.20.213 and snmp to the modem to get it's transmit level and thinking you'll see it at 55
why I recommend you lower the receive level and double check again. your head end and cale plant tech should let you know what to expect into the receiver.
please let me know what you get from the modems

~Carl

rainbow
hello , I am sorry for the

hello , I am sorry for the delay, I wasn´t able to get the information from the responsible area, finally I got it, the CMs with low power level rx in the CMTS are transmiting at 54dBmV, however the level of 14dBmV is being defined because of design made by Motorola, in this case , which can be the consequences of reaching the CMTS with a lower power level than the defined one?,

cmcaldas
receive level

When you say design by Motorola, do you mean a Motorola field engineer recommended the 14 dbmv level or that's what you seen as a sample config?
I recommend modems transmit in the mid 40's. example 45 dbmv. reason is it gives the modem room to increase level if needed to compensate for changes in the cable plant. the return doesn't have auto gain control, so the modem needs to raise or lower it's level because the loss will change due to temp. metal will expand in the summer and shrink in the winter. so your return loss will be higher in the summer than the winter. in general, 20 dbmv into the receiver of the node should get you more than enough signal at the head end to split it to feed your services. let's say there's a 20 tap on the pole, 150 foot drop and a 3 way splitter. the modem would need to transmit enough signal to reach the receiver with 20. so 20 for the tap loss, about 7 for drop and splitter and 20 to hit the receiver adds up to 47 and that's average with enough to hit the cmts with a 4 depending on the combining at the head end. but most receivers are configured for zero.
the consequences of reaching the CMTS with a lower power level than the defined one.....
lowering the receive level on the cmts will have the modems transmit at a lower level. pros and conns are the modem can stay registered even though return loss increases. those modems that are running at 54 dbmv now will have problems staying online in the middle of the summer. as you add more modems to the node, the total high power going into the receiver will cause it to go into distortion because levels going in are too high.
the draw back to lowering the transmit levels is the snr will be lower. for an snr of 18 or higher qpsk, 22 and higher for 16qam and 28 for atdma is what I would consider as min. for return modulation.
Hope this helps

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