Cisco Broadband Cable, Справочное руководство

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Cisco Broadband Cable Command Reference Guide
OL-1581-08
Chapter 2 Cisco CMTS Configuration Commands
cable upstream minislot-size
Usage Guidelines
The minislot size determines the minimum amount of information that can be transmitted on the
upstream. How much a particular minislot size can contain depends on the modulation profile and
channel width being used, with higher-bandwidth settings allowing larger amounts of data.
Because DOCSIS specifications require that the minislot size contain at least 32 symbols, you might
need to change the minislot size whenever you change the channel width or modulation of an upstream,
to meet the DOCSIS requirements.
Note
In Cisco IOS Release 12.2(15)CX, Cisco IOS Release 12.2(15)BC2, and later releases, manually
changing the minislot size is not needed on the Cisco uBR-MC16U/X, Cisco uBR-MC28C, and
Cisco uBR-MC28U/X cards, because these cards automatically change the minislot size when the
channel width is changed, to produce 32 symbols per minislot, as required by the DOCSIS
specifications.
Table 2-12 lists the default minislot sizes for each channel width for Cisco IOS releases before and after
Cisco IOS Release 12.2(15)BC1.
12.2(15)BC1 The default minislot size was reduced to optimize the upstream for data and
Voice-over-IP (VoIP) traffic. The previous defaults produced 16 bytes per
minislot when using QPSK modulation and a 1.6 MHz channel width, and
the new defaults produce 8 bytes per minislot with the same configuration.
12.2(15)BC2 Support was added for the minislot size of 1 to support DOCSIS 2.0
A-TDMA and mixed modulation profiles on the Cisco uBR-MC5X20S/U
cable interface line cards.
Release Modification
Table 2-12 Default Minislot Sizes
Releases Earlier than Cisco IOS Release
12.2(15)BC1 (creates 64 symbols and 16 bytes
per minislot) Cisco IOS Release 12.2(15)BC1 and Later
Releases (creates 32 symbols and 8 bytes per
minislot)
Channel Width
Default Minislot Size (in
Ticks)
Channel Width
Default Minislot Size (in
Ticks)
0.2 MHz 64 0.2 MHz 32
0.4 MHz 32 0.4 MHz 16
0.8 MHz 16 0.8 MHz 8
1.6 MHz 8 1.6 MHz 4
3.2 MHz 4 3.2 MHz 2
6.4 MHz
(DOCSIS 2.0 only) 1
1
1. You must be using a 6.4 MHz channel width if using a minislot size of 1 tick. Otherwise, you will violate the DOCSIS
requirements that each minislot should contain 32 symbols.