Cisco Cisco IOS Software Release 12.2(4)XF Release Notes

Cisco IOS Release 12.2(4)XF1 provides support for the new DOCSIS 1.1 standard for the Cisco Release 
12.2(4)XF1 series routers. DOCSIS 1.1 modifies the DOCSIS 1.0 specification to provide better 
performance, in particular for real-time traffic such as voice calls. 

The DOCSIS 1.1 specification provides the following functional enhancements over DOCSIS 1.0 
coaxial cable networks:

Enhanced Quality of Service (QoS) to give priority for real-time traffic such as voice and video 

The DOCSIS 1.0 QoS model (a Service IDs (SID) associated with a QoS profile) has been 
replaced with a service flow model that allows greater flexibility in assigning QoS parameters 
to different types of traffic and in responding to changing bandwidth conditions 

Multiple service flows per CM in either direction due to packet classifiers

Support for multiple service flows per cable modem allows a single cable modem to support a 
combination of data, voice, and video traffic 

Greater granularity in QoS per cable modem in either direction, using unidirectional service 
flows 

Dynamic MAC messages that can create, modify, and tear-down QoS service flows dynamically 
when requested by a DOCSIS 1.1 cable modem

Supported QoS models for the upstream are: 

Best effort-Data traffic sent on a non-guaranteed best-effort basis 

Committed Information Rate (CIR)—Guaranteed minimum bandwidth for data traffic 

Unsolicited Grants (UGS)—Constant bit rate (CBR) traffic, such as voice, that is characterized 
by fixed size packets at fixed intervals 

Real Time Polling (rtPS)—Real Time service flows, such as video, that produce unicast, 
variable size packets at fixed intervals 

Unsolicited Grants with Activity Detection (USG-AD)—Combination of UGS and RTPS, to 
accommodate real time traffic that might have periods of inactivity (such as voice using silence 
suppression). The service flow uses UGS fixed grants while active, but switches to RTPS polling 
during periods of inactivity to avoid wasting unused bandwidth. 

Enhanced time-slot scheduling mechanisms to support guaranteed delay/jitter sensitive traffic on the 
shared multiple access upstream link 

Payload Header Suppression (PHS) conserves link-layer bandwidth by suppressing unnecessary 
packet headers on both upstream and downstream traffic flows 

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 timeslots that 
are available between the timeslots used for the real-time traffic. 

Concatenation allows a cable modem to send multiple MAC frames in the same timeslot, as opposed 
to making an individual grant request for each frame. This avoids wasting upstream bandwidth when 
sending a number of very small packets, such as TCP acknowledgement packets. 

DOCSIS 1.1 cable modems can coexist with DOCSIS 1.0 and 1.0+ cable modems in the same 
network—the Cisco Release 12.2(4)XF1 series provides the levels of service that are appropriate for 
each cable modem