Additionally, to increase upstream
capacity, the operator has the option of configuring the upstream channels with a higher
data rate (20.48 Mbps or 30.72 Mbps rather than 10.24 Mbps), although these higher
data rates require that the cable modems and CMTS be compliant with the DOCSIS 2.0
specification and that the upstream channel has sufficient signal-to-noise ratio to support
higher-order modulations.
Ongoing Developments
CableLabs has recently released specifications for a DOCSIS Modular-CMTS. The
M-CMTS architecture, shown in Figure 6.2, was designed as an extension to the DOCSIS
specifications to allow for flexibility and independent scaling of certain CMTS functions
and to allow operators to more efficiently use available network resources. One of the
key elements of the M-CMTS architecture is the separation of the downstream physical
layer QAM modulation and up-conversion functions from the CMTS and the placement
of that functionality into an edge-QAM (EQAM) device. This separation allows for the development
of EQAM products that support both video-on-demand services and DOCSIS
services, which in turn allow operators to use the same network resources to support
multiple types of services such as data, voice, and video.
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