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
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Cisco IOS Release 12.2(15)CZ
The Cisco uBR905 and Cisco uBR925 cable access routers and the Cisco CVA122 Cable Voice Adapter
automatically support DCC requests when running Cisco IOS Release 12.2(15)CZ.
Dynamic Quality-of-Service
DOCSIS 1.1 adds support Dynamic Services MAC-layer messages that provide for Dynamic QoS
(DQoS) between the cable modem and the CMTS. These messages are DOCSIS link-layer equivalents
of the higher-layer messages that create, tear down, and modify a service flow. These messages are
collectively known as DSX messages to represent the three types of dynamic service messages:
• Dynamic Service Add (DSA)—Creates a new service flow.
• Dynamic Service Change (DSC)—Changes the attributes of an existing service flow. These changes
can include the following:
–
Adding, replacing, or deleting a classifier from the service flow.
–
Changing the flow’s Admitted and Active QoS parameter sets.
–
Adding, setting, or deleting payload header suppression (PHS) rules for the service flow.
• Dynamic Service Deletion (DSD)—Deletes an existing service flow.
The DSX state machine module on the cable modem manages the several concurrent dynamic service
transactions between cable modems and the CMTS. The DSX state machine supports all three
DOCSIS1.1 DSX MAC messages (DSA, DSC, DSD).
Provisioned QoS
Provisioned QoS (PQoS) allows the cable modem to create the service flows it needs for voice calls and
other real-time traffic at the time it registers with the CMTS, without actually using the bandwidth for
those flows. The service flow is kept in the admitted state and is activated only when the cable modem
signals a voice call using the DOCSIS 1.1 Dynamic Service Request (DSC-REQ) message. Bandwidth
is used only when the voice call is actually in progress.
To use PQoS services, you must configure the cable modem with secondary service flows for VoIP calls.
(If you do not define any secondary service flows, DQoS is used instead of PQoS). You can use any voice
signaling that is supported by the cable modem for VoIP traffic.
Table 1 compares how the router sets up and tears down VoIP calls when using DQoS and PQoS:
Table 1 Comparison of DQoS and PQoS Call Setup and Teardown Operation
Quality-of-Service Type VoIP Signaling Type Call Setup Description
Dynamic QoS
H.323 Sends DSA at off-hook and DSD at on-hook.
SGCP/MGCP/SIP Sends DSA at off-hook, DSC when the call setup
parameters are received from the gateway, and
DSD at on-hook.
Provisioned QoS
H.323 Sends DSC at off-hook to activate the provisioned
service flows and DSD at on-hook.
SGCP/MGCP/SIP Sends DSC at off-hook to activate the provisioned
service flows, a second DSC when the call setup
parameters are received from the gateway, and
DSD at on-hook.