Specifications

DOCSIS 1.1 for Cisco uBR905 and Cisco uBR925 Cable Access Routers and Cisco CVA122 Cable Voice Adapters
Information About DOCSIS 1.1 Support
14
Cisco IOS Release 12.2(15)CZ
Service Flow Manager
The Service Flow Manager is a new module that manages different activities related to service flows on
a cable interface. Typical events include the creation of new DOCSIS service flows, modification of the
attributes of existing service flows, and the deletion of service flows.
Quality-of-Service Comparison
Quality-of-service (QoS) is a measure of performance for a transmission system that reflects its
transmission quality and service availability. This section describes the differences in QoS between
DOCSIS 1.1 and DOCSIS 1.0 and 1.0+.
DOCSIS 1.0
DOCSIS 1.0 uses a static QoS model that is based on a class of service (CoS) that is preprovisioned in
the TFTP configuration file for the cable modem. The CoS is a bidirectional QoS profile that has limited
control, such as peak rate limits in either direction and relative priority on the upstream.
DOCSIS 1.0 defines the concept of a service identifier (SID), which specifies the devices allowed to
transmit and which provides device identification and CoS. In DOCSIS 1.0, each cable modem is
assigned only one SID, creating a one-to-one correspondence between a cable modem and the SID. All
traffic originating from, or destined for, a cable modem is mapped to that cable modem’s SID.
Typically, a DOCSIS 1.0 cable modem has one CoS and treats all traffic the same, which means that data
traffic on a cable modem can interfere with the quality of a voice call in progress. The CMTS, however,
can prioritize downstream traffic based on IP precedent type-of-service (ToS) bits. For example, voice
calls using higher IP precedence bits receive a higher queueing priority (but without a guaranteed
bandwidth or rate of service). A DOCSIS 1.0 cable modem could increase voice call quality by
permanently reserving bandwidth for voice calls, but then that bandwidth would be wasted whenever a
voice call is not in progress.
DOCSIS 1.0+ Extensions
In response to the limitations of DOCSIS 1.0 in handling real-time traffic, such as voice calls, Cisco
created the DOCSIS 1.0+ extensions to provide the more important QoS enhancements that were
expected in DOCSIS 1.1. In particular, the DOCSIS 1.0+ enhancements provide basic Voice-over-IP
(VoIP) service over the DOCSIS link.
Cisco DOCSIS 1.0+ extensions include the following DOCSIS 1.1 features:
• Multiple SIDs per cable modem, creating separate service flows for voice and data traffic. This
allows the CMTS and cable modem to give higher priority for voice traffic, preventing the data
traffic from affecting the quality of the voice calls.
• Cable modem-initiated dynamic MAC messages—Dynamic Service Addition (DSA) and Dynamic
Service Deletion (DSD). These messages allow dynamic SIDs to be created and deleted on demand,
so that the bandwidth required for a voice call can be allocated at the time a call is placed and then
freed up for other uses when the call is over.
• Unsolicited grant service (CBR-scheduling) on the upstream—This helps provide a higher-quality
channel for upstream VoIP packets from an Integrated Telephony Cable Modem (ITCM) such as the
Cisco uBR924 cable access router.