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Cisco uBR10012 Universal Broadband Router Software Configuration Guide
OL-1520-08
Chapter1 Overview of CiscouBR10012 Universal Broadband Router Software Supported Software Features for the CiscouBR10012 Router
DOCSIS 1.1 Fragmentation and Reassembly
The MAC scheduler fragments data slots to fill the gaps in-between Unsolicited Grant Service (UGS)
slots. Fragmentation reduces the jitter experienced by voice packets when large data packets are
transmitted on the shared upstream channel and preempt the UGS slots used for voice. Fragmentation
splits the large data packets so that they fit into the smaller timeslots available around the UGS slots.
The grant fragmentation gets triggered in the MAC scheduler, and fragment reassembly happens in the
upstream receive driver.
Note DOCSIS fragmentation should not be confused with the fragmentation of IP packets, which is done
to fit the packets on network segments with smaller maximum transmission unit (MTU) size.
DOCSIS fragmentation is Layer 2 fragmentation that is primarily concerned with efficiently
transmitting lower-priority packets without interfering with high-priority real-time traffic, such as
voice calls. IP fragmentation is done at Layer 3 and is primarily intended to accommodate routers
that use different maximum packet sizes.
Commands
Router# show interface cable x/y sid [n] counters [verbose]
Router(config-if)# [no] cable upstream n fragmentation
Router# debug cable errors
DOCSIS 1.1 Layer 2 Fragmentation
Layer 2 fragmentation on the upstream prevents large data packets from affecting real-time traffic, such
as voice and video. Large data packets are fragmented and then transmitted in the time slots that are
available between the time slots used for the real-time traffic.
DOCSIS 1.1 MAC Scheduler
The MAC scheduler controls all time-slot assignment on the shared upstream channel. This block has
been redesigned to support several new scheduling disciplines of DOCSIS1.1. Important enhancements
include:
•Support for grant fragmentation.
•Support for multiple unsolicited grants per service ID (SID).
•Support for Unsolicited Grant Service with Activity Detection (UGS-AD) and Real-Time Polling
Service (RTPS) slot scheduling mechanisms besides Unsolicited Grant Service (UGS), best effort
(BE), and Committed Information Rate (CIR) service of DOCSIS1.0+.
•Enhanced per SID minimum or maximum rate shaping.
All old Cisco features, such as dynamic contention control are supported in the new design.

MAC Scheduler Commands

Router# show interface cable x/y mac-scheduler n
Router(config-if)# [no] cable upstream n fragmentation
Router(config-if)# [no] cable upstream n unfrag-slot-jitter
Router# cable service flow inactivity-threshold n
Router# debug cable mac-scheduler
DOCSIS 1.1 Payload Header Suppression and Restoration
The Payload Header Suppression (PHS) feature is used to suppress repetitive or redundant portions in packet
headers before transmission on the DOCSIS link. This is a new feature in the DOCSIS1.1 MAC driver. The
upstream receive driver is now capable of restoring headers suppressed by CMs, and the downstream driver
is capable of suppressing specific fields in packet headers before forwarding frames to the CM.