ANSI SCTE 137-1:2017 pdf download.Modular Headend Architecture Part 1: DOCSIS Timing Interface.
Introduction and Overview
The requirements for timing and synchronization of the DOCSIS system come from the following areas:
• Existing DOCSIS Specification & ATP Requirements
• Remote PRY System Requirements
• Implementation Requirements
• Emerging Services like T-Services and wireless
These requirements place definitions and constraints on the use of the 10.24 MHz DOCSIS master clock and the DOCSIS timestamp, which is delivered in the SYNC message. The DOCSIS standard [RFI2I originally envisioned the M-CMTS Core. EQAMs, and upstream receive functions on one assembly. fed with a common clock. The timestamp counter resided in the M-CMTS Core function.
The M-CMTS Remote PHY architecture may result in three components: the M-CMTS CORE. the upstream receiver, and the EQAM being located in a different chassis, and potentially at different physical locations. As a system. the three components comply with the DOCSIS standard IRFI2I and any existing CMTS equipment.
The DOCSIS Timing Protocol (DTI) defined in this document supports the accurate and robust transport of the DTI server 10.24 MHz master clock, 32-hit DOCSIS timestamp, and Time of Day, to the DTI client within the DOCSIS M-CMTS cable network. The DTI protocol is structured to minimize the complexity and cost of the DTI client clocks, and the per port cost of the shared server function while supporting all S-CDMA and TDMA timing requirements.
1.1.1 System Requirements
The DTI system requirements refer to the DOCSIS timing requirements as outlined in the DOCSIS standard [RFI2J. These requirements are presented independent of the CMTS architecture.
The sections of the DOCSIS standard fRFI2] that are of interest are:
6.2.11.2 Mini-slot Numbering
6.2.21.8.2 Chip Timing Jitter for Synchronous Operation
6.3.7 CMTS Timestamp Jitter
6.3.8 CMTS Clock Generation
6.3.9 CMTS Downstream Symbol Clock Jitter for Synchronous Operation
6.3.10 CMTS Downstream Symbol Clock Drift fhr Synchronous Operation
9.3 Timing and Synchronization
1.1.2 T-Services Consideration
To maintain compatibility with the T-Service synchronization hierarchy, the DTI Server clock operates with the specifications detailed in section 7.1, which integrate both the DOCSIS timing system requirements and the existing legacy synchronization network clock consistent with IG.8 121 and ITI.lOlI. This is done to ensure that the CM supporting T-Services can derive its clocking and meet IG.8231 or [G.8241 jitter and wander requirements for both traffic bearing and synchronization bearing transport clock sources.
Support of T—Services will require that the master clock and the downstream symbol clock he locked and upstream and downstream clocks be coherent.
1.1.3 Modular Implementation Requirements
The M-CMTS CORE element:
• Uses the DTI server master clock for creating a timestamp
• Uses the timestamp for MAP generation The Edge QAM element:
• Uses the DTI server master clock for symbol rate generation
• Uses the timestamp for inserting and/or correcting SYNC messages.ANSI SCTE 137-1 pdf download.