Ideal HFC Plant Configuration Issues
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JUNOSg 3.0 G10 CMTS Hardware Guide
154
8. You can compute the approximate upstream channel utilization by dividing the
measured bandwidth calculated in ste p 5 by the derated maximum bandwidth
calculated in step 7: (4,384,549 / 4,710,400)=93 percent. This represent s a highly
utilized interface.
Congestion might be attributed to one or more of the following:
!An excessive number of cable modems are attached to a DOCSIS Module in the
return path of the HFC plant. Review your corporate guidelines to ensure you have
not exceeded the maximum number of cable modems per DOCSIS Module for the
modulation profiles being used. If necessary, install additional DOCSIS Modules.
!An excessive number of cable modems are assigned to the upstream inte rface in
which the cable modem transmits. Issue the show cable modem command as
follows to determine the number of cable modems with in an upstream interface:
user@host> show cable modem summary total interface
cu-virtual-slot/docsis-slot/upstream-interface
---Cable Mod em Operational States---
Interface Us CM Dstry Dclr R ng Rng Rng IP Reg Acce ss
Qty Abort Compl Compl Deni ed
ca-0/2/0 0 5 0 0 0 5 0 0 0 0
total 5 0 0 0 5 0 0 0 0
An excessive number of cable modems on an upstream interface can be addressed
by the following:
!Enable load balancing in the CMTS by including the load-balance statement at
the [edit services cable upstream] hierarchy level. The CMTS attempts to
assign a cable modem to an upstream channel based on channel width and
utilization.
!Provision one or more additional upstream interfaces in the cable interface in
which the cable modem resides. The logical allocation of up to 16 upstream
interfaces to any of the upstream ports on a DOCSIS Module allows you to
provision interfaces without the need for physical node recombining.
!Increase the upstream channel width.
!The cable modem is transmitting using QPSK modulation. The all-digital processing of
the Broadband Cable Processor ASIC, along with its advanced noi se cancellation and
equalization algorithms, might allow the cable modems on an upstream channel to
operate at 16QAM. To change the modulation of an upstream channel, assign a new
modulation profile to that channel.