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Chapter 2
Cisco CMTS Configuration Commands
Increasing the Minislot Size for High Bandwidth Users
The DOCSIS specifications allow a maximum burst limit of 255 minislots, which could require
increasing the minislot size from the default values if you are offering service level agreements (SLAs)
that offer guaranteed upstream speeds of 2 Mbps or greater, or if you are allowing maximum
concatenation bursts greater than 2000 bytes. This is because the default minislot sizes might not
accommodate the largest bursts that are possible with these configurations.
The default minislot sizes provide for 8 or 16 bytes per minislot, depending on Cisco IOS release. If the
default setting provides 8 bytes per minislot, then the maximum possible burst is 8 bytes * 255 minislots,
or 2040 total bytes, which might not be sufficient for certain users with high guaranteed upstream speeds.
You should increase the minislot size to accommodate the expected maximum burst transmissions,
adding in approximately 10 percent for overhead.
Using values of 64 or 128 for higher symbol rates such as 1280 kilosymbols/second or
Caution
2560 kilosymbols/second can cause performance problems. Depending on your current setting's symbol
rate, you should select the minislot size (in ticks) that yields a minislot size of 32 or 64 symbols.
Examples
The following example shows how to set the minislot size on upstream port 4 to 16:
Router# configure terminal
Router(config)# interface cable 3/0
Router(config-if)# cable upstream 4 minislot-size 16
Router(config-if)# exit
Router(config)# exit
Router#
Related Commands
cable modulation-profile
cable upstream channel-
width
cable upstream docsis-
mode
cable upstream
equalization-coefficient
cable upstream
modulation-profile
show cable hop
show cable modulation-
profile
show interface cable mac-
schedule
show interface cable sid
OL-1581-08
Defines a modulation profile for use on the router.
Specifies an upstream channel width for an upstream port.
Configures an upstream to use either DOCSIS 1.x or DOCSIS 2.0
modulation profiles.
Enables the use of a DOCSIS 1.1 pre-equalization coefficient on an
upstream.
Assigns one or two modulation profiles to an upstream port.
Displays CM configuration settings.
Displays the modulation profile information for a Cisco CMTS.
Displays the current time-slot scheduling state and statistics.
Displays cable interface information.
Cisco Broadband Cable Command Reference Guide
cable upstream minislot-size
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