Cisco Systems UBR900 User Manual
Data Operations
Configuring the Cisco uBR900 Series Cable Access Routers 7
Service Assignments
Each Cisco uBR900 series cable access router on the network is configured to receive data on a
particular downstream channel. A downstream channel contains upstream segment(s). Each
upstream segment typically serves more than one fiber node.
particular downstream channel. A downstream channel contains upstream segment(s). Each
upstream segment typically serves more than one fiber node.
Partitioning the upstream plant into smaller segments significantly reduces the number of potential
ingress sources and failure points. The CMTS divides the cable plant into downstream channels and
upstream segments or clusters of nodes.
ingress sources and failure points. The CMTS divides the cable plant into downstream channels and
upstream segments or clusters of nodes.
Downstream and Upstream Data Transfer
When operating normally, the Cisco uBR900 series cable access router receives data addressed to it
from the CMTS. The router reads the address in the header of the message, filters the message and
forwards it to the appropriate device at the subscriber site.
from the CMTS. The router reads the address in the header of the message, filters the message and
forwards it to the appropriate device at the subscriber site.
Note
Bandwidth at the subscriber site is shared by the active data users connected to the network
segment.
For upstream data transfer, the Cisco cable access router uses a request/grant mechanism to obtain
upstream bandwidth. The CMTS configures, via MAC messages, upstream parameters associated
with transmissions from all Cisco cable access routers on the system. Service class registration is
granted based on class assignment and load provisioning. Upstream channels are time slotted and
divided into basic scheduling time units.
upstream bandwidth. The CMTS configures, via MAC messages, upstream parameters associated
with transmissions from all Cisco cable access routers on the system. Service class registration is
granted based on class assignment and load provisioning. Upstream channels are time slotted and
divided into basic scheduling time units.
The CMTS informs the Cisco cable access router of minislot structures on the upstream channel.
Some minislots are marked as contention-based—shared by routers to make bandwidth (timeslot)
requests with the CMTS. Others are grouped together into unicast grants for specific routers to send
their data bursts. Yet others are grouped together into maintenance slots for “keep alive” messages
from routers to the CMTS.
Some minislots are marked as contention-based—shared by routers to make bandwidth (timeslot)
requests with the CMTS. Others are grouped together into unicast grants for specific routers to send
their data bursts. Yet others are grouped together into maintenance slots for “keep alive” messages
from routers to the CMTS.
Bridging Applications
In bridging applications, the Cisco uBR900 series cable access router acts as a transparent bridge for
up to 254 devices depending on the version of Cisco IOS software you are using. Older versions of
software allow a maximum of 3 CPE devices to be bridged. The cable access router is connected to
the Internet through the coaxial cable interface. All four 10BaseT Ethernet ports are treated as one
Ethernet interface by the Cisco IOS software. The IP addresses for the CPE devices and the coaxial
cable interface are typically in the same subnet, although this is not a requirement.
up to 254 devices depending on the version of Cisco IOS software you are using. Older versions of
software allow a maximum of 3 CPE devices to be bridged. The cable access router is connected to
the Internet through the coaxial cable interface. All four 10BaseT Ethernet ports are treated as one
Ethernet interface by the Cisco IOS software. The IP addresses for the CPE devices and the coaxial
cable interface are typically in the same subnet, although this is not a requirement.
Security
DES decryption: DOCSIS Baseline Privacy
(BPI), 40 bit-, 56 bit- and 168 bit DES
encryption, as controlled by the headend and
configuration files.
(BPI), 40 bit-, 56 bit- and 168 bit DES
encryption, as controlled by the headend and
configuration files.
Note
Cisco IOS images must contain
encryption software at both the CMTS and the
Cisco uBR900 series. Both routers must be
enabled and properly configured to support
encryption.
Cisco uBR900 series. Both routers must be
enabled and properly configured to support
encryption.
DES encryption
Table 1
Cisco uBR900 Series Cable Access Router Data Specifications (continued)
Description
Downstream Values
Upstream Values