Assisted Partial Timing Support (APTS)
Assisted Partial Timing Support (APTS)
What Is APTS?
APTS operation is a simple concept. In this scenario, both the core PRTC and edge PRTC have a GNSS input referenced to UTC time. The core PRTC Server delivers PTP time stamps to the downstream edge PRTC clock using a PTP profile. The edge PRTC compares the PTP time stamp to the local GNSS time. The edge PRTC accumulates information about the PTP flow from the PTP time stamps and from message exchanges with the Core PRTC. Consequently, it understands the actual overall delay and time error on that specific PTP path. The edge PRTC adjusts the PTP flow information and calibrates the incoming PTP flow by compensating for the measured time error so that it is now equivalent to the local GNSS time.
![APTS graphic APTS graphic](https://i0.wp.com/davidb7201.wpengine.com/wp-content/uploads/2023/05/APTS-graphic.jpg?resize=811%2C307&ssl=1)
APTS synchronizes the core PRTC with the edge PRTC using PTP. The PTP flow into the edge PRTC is calibrated using the local GNSS, which is the same time reference (UTC) as the core GNSS.
GPS Protection
This calibration process improves the performance of the edge PRTC in the event of a GPS loss of signal at this site. With APTS, the time error on a single PTP input path is removed. Once the APTS algorithm is operating, the incoming PTP flow can be used as a proxy for the GNSS. If the GNSS on the local PRTC is lost, then the system will use the calibrated incoming APTS flow as the reference clock. As mobile networks evolve from frequency-based networks to dense, highly distributed radio heads that require phase alignment to provide advanced 4G/5G services, it will be increasingly necessary to deploy PRTC clocks around the edge of the network. These PRTC can be protected by implementing assisted partial timing support, G.8273.4, an engineering tool that can be used to back up the PRTC at the edge from a core PRTC clock.
Assisted Partial Timing Support (APTS) is a method to improve the synchronization of communication networks. It uses the Precision Time Protocol (PTP) to synchronize clocks throughout a computer network. APTS is a special case of Partial Timing Support (PTS) networks.
APTS is suitable for:
- Small, indoor, last-mile deployments where the network has limited or no timing support
- Bridging between areas of FTS as a cost-effective option
In APTS, the GNSS receiver acts as the primary source providing time synchronization. The core PRTC T-GM delivers PTP time stamps to the downstream edge PRTC/GM clock using a PTP profile. When the GNSS/GPS reference is lost, the slave will fall back to the backup PTP session.
PTP is specified in the IEEE 1588 standard. It offers a level of accuracy and precision that NTP cannot achieve. It can significantly reduce the chance of network delays and errors.