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.
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Parameter
Description
IUC
Interval Usage Code. The IUC typically has an assigned numeric value. It defines what kind of Information Element
(IE) is being sent from the CMTS to the cable modems:
• 1 =Request
• 2 =Request/Data
• 3 =Initial Ranging
• 9 =Advanced PHY Short Data Grant
• 4 =Periodic Ranging
• 10 =Advanced PHY Long Data Grant
• 5 =Short Data Grants
• 11 =Advanced PHY Unsolicited Grant
• 6 =Long Data Grants
1 Request This portion of the upstream map interval is used by cable modems to request bandwidth for data
transmission. If the class of the SID associated with the request IE is broadcast, then cable modems must contend
with each other for upstream bandwidth. If the class of the SID associated with the request IE is unicast, then this is
an opportunity for a single cable modem to request additional bandwidth.
2 Request/Data Either data requests or short data messages can be sent in this portion of the upstream map
interval. A multicast SID must be used to indicate the size of the data message that can be sent. This IE is not used by
the CMTS map algorithm and as such changes made to this IE will have no affect on upstream data transmissions.
3 Initial Ranging (Also called Initial Maintenance). This IE allows cable modems a method to adjust their timing,
frequency, and transmit power so that they can reliably communicate with the CMTS. The timing adjustments allow
for the round trip delay of the fiber optic/coax plant plus the time to transmit the range request message. A DOCSIS
1.X cable modem can send a range request message only during this IE. A DOCSIS 2.0 cable modem can send a range
request message or an initial range request message depending upon the type of the upstream channel. Normally,
range request messages are sent in this IE when it contains a broadcast SID, meaning cable modems must contend
with each other when transmitting. An initial range request message can be sent either with a broadcast SID or with
a unicast SID depending upon the situation.