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
12
Cisco IOS Release 12.2(15)CZ
Each service flow has a set of QoS attributes associated with it. These QoS attributes define a particular
class of service and determine characteristics such as the maximum bandwidth for the service flow and
the priority of its traffic. The class of service attributes can be inherited from a preconfigured CMTS
local service class (class-based flows), or they can be individually specified at the time of the creation
of the service flow.
Every service flow also has a unique (unique per DOCSIS MAC domain) identifier called the service
flow identifier (SFID). The upstream flows in the admitted and active state have an extra Layer 2 SID
associated with them. The SID is the identifier used by the MAC scheduler when specifying time-slot
scheduling for different service flows.
Each service flow has multiple packet classifiers associated with it, which determine the type of
application traffic allowed to be sent on that service flow. Each service flow can also have a payload
header suppression (PHS) rule associated with it to determine which portion of the packet header will
be suppressed when packets are transmitted on the flow.
Figure 1 illustrates the mapping of packet classifiers.
Figure 1 Classification Within the MAC Layer
Dynamic Channel Change
DOCSIS 1.1 supports Dynamic Channel Change (DCC) requests, which allow the CMTS to change the
upstream or downstream frequency that the cable modem is using. This allows the CMTS to move cable
modems to another channel when the current one is either becoming congested or is encountering
growing noise problems that could eventually force the cable modems offline.
RF
Upstream service
flows
Downstream
service flows
CMTS CM
Upstream
classifier
MAC
Mgmt
Msgs
Primary SID
SID 2
SID n
Upstream
classifier
Downstream
Downstream
classifier
MAC
mgmt
msgs
Primary DSFID
DSFID 2
DSFID n
(Optional)
Ingress classifier
Upper layer entity
(bridge, router)
Upper layer entity
(bridge, router, client)
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