By Yair Neugeboren, Greg Cyr & Chris Zettinger, CommScope
The ability to support the transport of accurate timing information over DOCSIS networks has become an important and urgent need for both cable and telco operators as mobile backhaul becomes a key service offering of the future.
The DOCSIS network (without any modifications) is not an appropriate access infrastructure for delivering accurate timing information for both frequency and phase. The latency asymmetry between the DOCSIS upstream (US) and downstream (DS) and the large packet delay variation (PDV) in upstream grant cycles cannot guarantee the timing requirements of LTE; 16 ppb of frequency accuracy for LTE-FDD and 1.5 microsecond of phase accuracy for LTE-TDD and 5G.
There is active research on-going within the cable industry to define the requirements needed for the DOCSIS network to support these stringent mobile backhaul requirements. Much of this work is based on the DOCSIS Timing Protocol (DTP), which was previously defined within DOCSIS 3.1 and the CableLabs MBH (Mobile Backhaul) Synchronization Techniques specification.
This paper will describe modeling and experimental results for accurate phase and frequency delivery over DOCSIS, covering multiple different use cases as LTE-FDD, LTE-TDD, and 5G. Some approaches require minimal changes to the current DOCSIS implementations, while others require incorporating the DOCSIS 3.1 DOCSIS Timing Protocol (DTP). This paper will show how the experiments results prove that DOCSIS Distributed Access Architecture (DAA) and Centralized Access Architecture (CAA) could support the MBH requirements for the various use cases.
In this paper we will focus on two use cases, one for frequency delivery and one for phase delivery. We will describe the mobile sync accuracy requirements in general from 3GPP and ITU-T and the proposed solutions for those use cases over DOCSIS.
Following that, we will describe in detail the MBH over DOCSIS setups we used to explore the performance and show the results for each use case.