Chapter 9: Upstream Cable Access Modules (UCAMs)
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
299
Table 52.
Recommended Settings as Cable Modem Scaling Increases
CMs per CAM
Ranging
Backoff
Insertion
Interval
Centisecs
Ranging
Interval
Centisecs
BPI ?
CAM
Sparing
Service Flow
US Priority
Bandwidth
Data Rate
Restrictions
Up to 1000 (b)
2-5
10-40
2400
OK
Yes
Any
None
1000-2000 (c)
3-7
20-40
1500-2400
OK
Yes
Any
None
2000-4500 (12U only)
2000-660024U only)
5-9
20-40
1500
OK
Yes
Any
None
(a) If CAM Sparing is not configured, the Ranging Interval can be left at the default value of 2400 centiseconds.
Reducing the Ranging Interval is done for the purpose of improving CAM Sparing results on larger scale systems.
(b) If BPI+ is enabled on modems, use 40 centisecond insertion interval when supporting 500-1000 modems.
(c) If BPI+ is enabled on modems, use 40 centisecond insertion interval.
Explanation of Upstream Parameters
Modulation profiles are pre-defined sets of upstream channel parameters which make it easier to configure or reconfigure
upstream channels. This document describes the parameters used in modulation profiles. Where possible, it lists the
default values of these parameters. For greater technical detail on these parameters and their functions, see the DOCSIS
Radio Frequency Interface Specification.
In order to understand all of the parameters used in modulation profiles, some terms must be defined:
IE — Information Element — portions of the allocation MAP used to define transmission opportunities for cable modems.
Each IE is a 32-bit quantity, of which the most significant 14 bits represent the Service ID (SID), the middle 4 bits represent
the Interval Usage Code (IUC), and the low-order 14 bits represent the minislot offset.
SID — Service ID. SIDs are assigned to upstream Service Flows. The CMTS allocates upstream bandwidth to SIDs, therefore
to the cable modems served by the SIDs. SIDs are also used in Quality of Service functions. Certain values of SIDs are
defined in the RFI specification and convey specific meanings for the service flows they represent: