Cisco Headend System Release 2.5 Notas de publicación
4001703 Rev B
Why Choose System Release 4.0?
1-5
DSG: New DOCSIS Option Can Consolidate Administration of the Data Network,
Continued
Editing the Time-to-Live Parameter for Multicasting
An IP multicast packet must “hop” or traverse routers to reach its final destination of
a CMTS device. SR 4.0 adds a default Time-To-Live (TTL) parameter of 10 for IP
multicast packets that are generated by the DNCS. This TTL parameter decrements
by 1 each time the IP multicast packet traverses a router. Whenever the TTL
parameter reaches 0, the packet is discarded. Without TTL, an IP multicast packet
could exist in an endless loop—never reaching its destination and never being
discarded by the system.
If the system administrator for your DBDS network concludes it takes more than 10
If the system administrator for your DBDS network concludes it takes more than 10
hops for an IP multicast packet to reach a CMTS device, the administrator can
increase the TTL parameter by changing all of the following environment variables
in the .profile file:
•
•
COMM_MULTICAST_TTL
•
HCTM_MULTICAST_TTL
•
BFS_MULTICAST_TTL
Each of these variables must be set to the same value in the .profile file. For
assistance on determining the number of hops required for a packet of data to reach
a CMTS and setting environment variables to alter the TTL parameter if necessary,
contact Cisco Services.
Which Set-Top Models Can I Use?
You can use the Explorer 8300
™
and Explorer 8300HD
™
Set-Top in a DOCSIS
network to deliver digital broadcast video and support real-time, two-way
interactive applications. In addition, the 8300 models include a digital video recorder
(DVR) with picture-in-picture (PIP) control.
The 8300 models can use either a DOCSIS or DAVIC channel depending upon the
The 8300 models can use either a DOCSIS or DAVIC channel depending upon the
communication mode of the set-top. In DOCSIS mode, the set-top receives both OOB
data and unicast data on a DOCSIS channel. In DAVIC mode, it receives both OOB
data and unicast data on the DAVIC channel.