Cisco MC16S Bedienungsanleitung PDF herunterladen (Seite 8)

Spectrum Management Overview

12.0(7)XR2

For example, if the allocation is from 20.0 to 28.0 MHz and an upstream port has its channel width

set to 0.2 MHz, then there will be 40 possible slots for that channel width. Blind frequency hopping

may require quite a long time to ﬁnd the clean slot since it will try each available slot, one at a time

for several seconds each try.

Cable Modem Transmit Power Adjustment

In addition to frequency, the nominal input power level of the upstream receivers can be set at the

time of frequency hop. This allows the cable operator to perform minor equalization as a function of

frequency.

cable spectrum-group 1 frequency 21600000

cable spectrum-group 1 frequency 24800000 1

cable spectrum-group 1 frequency 28000000 2

In this example, the upstream port nominal receive power at 21.6 MHz is 0 dBmV, at 24.8 MHz is

1 dBmV, and at 28.0 MHz is 2 dBmV. At any time, the power level set in the interface conﬁguration

overrides the spectrum group power level.

Time-Scheduled Allocation

You can add spectrum on a weekly schedule by including an optional weekday and time:

cable spectrum-group 1 time Mon 08:00:00 frequency 21600000

Deletion is performed using the “delete” keyword:

cable spectrum-group 1 time Mon 18:00:00 delete frequency 21600000

If your cable plant has an upstream noise characteristic on a weekly cycle, use time-scheduled

spectrum allocation.

Upstream Frequency Migration

Per DOCSIS RFI speciﬁcation section 6.3.2.2, RF channel migration occurs by broadcasting a

change in the UCD message to all cable modems. The UCD message contains the upstream

frequency and transmission parameters associated with an upstream channel.

The speed of channel migration via the UCD message is typically less than 20 ms. During that period

of time, upstream transmission is interrupted until the cable modem transmitter adjusts to its new

frequency. Data is stored in the cable modem's buffers for this brief period of time and sent when the

frequency hop is complete.

Also, per the DOCSIS RFI, station maintenance intervals are used to perform per-modem keepalive

polling. The Cisco uBR7200 series routers poll each cable modem at least once every 30 seconds,

with the default polling count of once every 25 seconds. When there are fewer than 25 modems per

downstream, the default polling rate is every modem per second. The system takes the total number

of modems to be polled every 25 seconds, and evenly distributes the number of modems polled per

second.

When ingress noise or interference causes loss of keepalive messages from a conﬁgurable

percentage of all cable modems (resulting in missed polls) connected to an MC16S with Cisco IOS

Release 12.0(7)XR2, a new frequency is selected from the allocation table and an UCD update is

performed. But, the system must wait until a hop threshold time interval has elapsed before it can

act on that hop.

The migration time is 2 msec for any upstream UCD update. Once the UCD is updated, the hop has

occurred. The system must wait the hop period until it changes the UCD a second time.

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 33 34

Kommentare zu diesen Handbüchern

Keine Kommentare

Cisco MC16S Bedienungsanleitung Seite 8

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Vernetzung Cisco MC16S