The DOCSIS layers are briefly outlined as follows:
IP network layer
Data link layer comprising:
Logical Link Control (LLC) sublayer conforming to Ethernet standards
Link security sublayer for basic privacy, authorization, and authentication
Media Access Control (MAC) sublayer for operation supporting variable-length protocol data units (PDU)
Physical (PHY) layer comprising:
Downstream convergence layer conforming to MPEG-2 (Recommendation H.222.0)
Physical Media Dependent (PMD) sublayer for:
Downstream based on ITU-T Rec J.83 Annex B with either 64 or 256 quadrature amplitude modulation (QAM),
concatenation of Reed-Solomon and Trellis forward error correction (FEC), in addition to variable-depth
interleaving
Upstream employing Quadrature Phase Shift Keying (QPSK), 16, 64 or 128 QAM, support for multiple symbol
rates, cable modem controlled and programmable from the CMTS, frequency agility, fixed-frame and variable-
length PDU formats, Time-Division Multiple Access (TDMA), programmable Reed-Solomon FEC and
preambles and capability to support future physical layer technologies.
CX100/110/120/150/180 series e-Manual D07-00-002 Rev B01
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