Juniper G10 CMTS, Руководство по оборудованию

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DOCSIS Module
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JUNOSg 3.0 G10 CMTS Hardware Guide 34
MAC Layer Functions
The DOCSIS Module provides the following MAC layer functions:
!
Classifier—Classifies upstream data frames into higher layer packet flows; classifies
downstream frames into corresponding service flows using service flow IDs (SFIDs).
!
Frame generator—Encapsulates downstream packets into DOCSIS frames.
!
Encryption—Encrypts downstream data frames in accordance with the DOCSIS Baseline
Privacy and Baseline Privacy Plus standards.
!
Decryption—Decrypts upstream data.
!
Fragmentation/concatenation—Reassembles upstream fragmented MAC frames and
deconcatenates concatenated MAC frames.
!
Frame parser—Parses DOCSIS MAC header, identifies packet as data or management,
and routes accordingly. Verifies header checksum (HCS) and cyclical redundancy
checking (CRC).
!
MAC management—Provides cable modem, service flow, and RF management
functions. Performs resource allocation scheduling of requests, service flows, QoS, and
other items. Handles cable modem and service flow admission control.
Physical Layer Functions
The DOCSIS Module provides the following physical layer functions:
!
Downstream transmission convergence (DTC) sublayer:
! Manages the use of internal or external clock in MPEG transport stream; inserts
timestamp.
!
Examines packets for DOCSIS PID (packet identifier) and MPEG null PID and
multiplexes queued data packets into available MPEG packets.
! Re-stamps DOCSIS PID with MPEG null PID if no data is queued for transmission.
!
Physical media dependent (PMD) sublayer:
! Frames downstream MPEG packets by substituting synchronization byte with parity
checksum.
!
Implements FEC (forward error correction) and interleaving downstream;
descrambles data and decodes FEC upstream.
! Modulates to IF baseband and upconverts to RF for downstream traffic;
demodulates upstream traffic.
!
Monitors upstream performance characteristics such as timing, frequency offset,
BER (bit error rate), and RF spectrum.