Cisco DNCS System Release 2.8 3.8 4.3 Design Guide
4000358 Rev B
Introducing DOCSIS
1-27
DHCT Response to System Interruptions
Introduction
This section describes how system interruptions affect a DOCSIS-capable DHCT. For
each of the three DHCT Communication Modes, interruption of critical downstream
and upstream communication is considered.
Important: After the DHCT establishes an interactive connection, it ignores any
Important: After the DHCT establishes an interactive connection, it ignores any
mode changes that are in DCM messages. The DHCT will act on changes in the DCM
message only if it receives a DCM Updated message.
How a DHCT Operating in DAVIC Mode Responds to the Loss of the DAVIC Channel
This section describes how a DHCT operating in DAVIC mode responds when it
loses the DAVIC channel.
Loss of the DAVIC Channel
A DHCT operating in DAVIC mode responds to the loss of the downstream DAVIC
Loss of the DAVIC Channel
A DHCT operating in DAVIC mode responds to the loss of the downstream DAVIC
out-of-band QPSK signal in the following ways:
•
•
After a timeout period, the DHCT attempts to find DBDS broadcast data on
another downstream DAVIC out-of-band channel by scanning the DAVIC QPSK
spectrum.
•
The DHCT maintains audiovisual services, and does not disrupt these services
when the downstream DAVIC out-of-band QPSK signal is recovered and the
interactive connection is restored.
If a DHCT that boots in DAVIC mode loses the DAVIC forward channel, then all
broadcast and unicast communications with the DHCT are interrupted. However,
analog, clear digital, and subscription services continue to function. For example, all
purchased IPPV events already in progress will continue without interruption. Any
new IPPV event purchases can only succeed if the appropriate GBAMs were cached
by the DHCT prior to the interruption of the DAVIC channel. VOD events that are
already in progress will continue without interruption only if the interactive session
timeout value is longer than the DAVIC channel interruption. The ability to fast-
forward, pause, and rewind (trick modes) will be lost during the loss of the
interactive channel.
While the DAVIC channel is unavailable, RPPV event purchases, interactive
While the DAVIC channel is unavailable, RPPV event purchases, interactive
applications (Web browsing, e-mail, and so forth), new VOD event purchases, out-
of-band System Information (SI) updates, Service Application Manager (SAM)
updates, and out-of-band IPG updates will not function.