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Configuring Subscriber-End Broadband Access Router Features
Subscriber-End Broadband Access Router Data Operations
MC-611
Cisco IOS Multiservice Applications Configuration Guide
Note End-to-end throughput varies based on the design and loading of network components, the
mix of traffic, the processing speed and interface of the host server(s), the processing speed
and local Ethernet performance of the subscriber computer, and other parameters. Because
the network can be configured to support multiple levels of service to meet differing market
price/performance requirements, the subscriber service-level agreement also affects
throughput. DOCSIS further contains some fundamental performance limitations because
standards are designed to give a larger number of customers good performance, rather than
permitting a few users to consume the entire capacity.
Figure 110 Typical Cisco Broadband Data Cable System
Operating Modes
The broadband data cable system uses multiple types of access control to ensure efficient use of
bandwidth over a wide range of loading conditions. Advanced queueing techniques and service
algorithms are used to define the acquisition and release of channels.
Cisco uBR900 series cable access routers support 64 or 256 Quadrature Amplitude Modulation (QAM)
downstream, and Quadrature Phase Shift Keying (QPSK) or 16 QAM upstream transmission. The CMTS
system administrator can set the preferred modulation scheme based on the quality of the cable plant.
Note In noisy plant environments, 16 QAM upstream and 256 QAM downstream modulation
may not be viable. In high-quality HFC networks capable of supporting 16 QAM formats
in the upstream direction, we recommend using QPSK for fixed-slot short packets like
maintenance or data requests, and 16 QAM for variable-length data packets. This results in
the most efficient use of the available upstream timeslots or minislots.
Cisco uBR900 series
cable access router
18197
HFC
cable
plant
Internal backbone
and
worldwide internet
Cable System Headend
Upstream and downstream data interfaces
Operation support system interface
Downstream RF interface
Upstream RF interface
Residence or SOHO
subscriber site:
subscriber RF interface
Ethernet interface
Fiber
WAN
Switch/router
Servers
CMTS
rack equipment
Combiner
Tx
Rx