Introduction

Accurate time synchronization between all access points (APs) on your Celona private cellular network is critical because time is used by each AP to schedule when connected devices can transmit.

Celona APs use time-division duplexing (TDD), which uses the same frequency block for upload and download traffic. Since each direction must only transmit at specific times, the current time must be precisely synchronized between an AP and its connected devices.

Indoor networks with multiple APs are designed to take advantage of overlapping coverage.

If the APs are not accurately time synchronized, they could transmit at the same time, interfering with signals from nearby APs in the coverage area.

To synchronize time between APs, Celona uses the Precision Time Protocol (PTP), which works similarly to Network Time Protocol (NTP). PTP relies on a Grandmaster, a network-connected appliance with a GPS/GNSS receiver, to act as the network time source.

Depending on the size of your Celona deployment, you will receive a GPS antenna or a PTP Grandmaster appliance to serve as the timing synchronization source for APs on your Celona network.

Time Sync Configuration Options

Each Celona AP can synchronize its time using one of four options:

  • Free Running. The AP syncs to its own internal clock set by an NTP server.

  • GNSS. The AP syncs time using a directly-connected GPS (GNSS) antenna.

    • An AP in GNSS mode is considered a PTP leader. Up to ten APs can be followers of a time sync leader AP.

  • Internal (PTP). The AP syncs with a Leader AP in GNSS mode (that has a connected GPS antenna).

    • APs in Internal mode are considered PTP followers.

  • External (PTP). The AP syncs with a local PTP server (Grandmaster).

    • You may designate a primary and secondary PTP server(s). Secondary PTP server(s) are used as fallback if the primary server fails.

Configuring Time Sync in Celona Orchestrator

To change the time sync configuration for a single AP, open its Access Point Details page. In the Configuration Details card, click the pencil icon next to Time Sync Configuration.

To change time sync configuration for multiple APs at once (in bulk), open the Site page of the Site at which the relevant APs are located. In the Access Points card, click the checkbox next to each AP you'd like to modify, and click Edit Time Sync Configuration in the upper-right corner.

Either of these methods will open the Time Sync Configuration window.

First, determine which time sync configuration option each of your Celona APs will use. Then, follow the relevant section below.

Note that any time sync configuration change will immediately reboot the AP, resulting in temporary network downtime.

Free Running

To set an AP to Free Running mode, click the Free Running button in the Time Sync Configuration window. Acknowledge that the AP will reboot as a result of this change and click Save.

Celona does not recommend Free Running mode in production deployments because of the possibility of time drift between APs.

Free Running APs cannot act as PTP leaders.

GNSS

Before modifying time sync configuration to GNSS mode, ensure a GPS antenna is directly connected to the AP.

To set an AP to GNSS mode, click the GNSS Time Sync button in the Time Sync Configuration window. Acknowledge that the AP will reboot as a result of this change and click Save.

An AP in GNSS mode is automatically designated as a PTP leader. A PTP leader AP can have up to 10 follower APs that synchronize their time with the leader.

Internal (PTP)

Before modifying time sync configuration to Internal mode, ensure there is another AP in GNSS mode at the same Site. This leader AP must have fewer than 10 followers.

To set an AP to Internal mode, click the Internal Time Sync (PTP) button in the Time Sync Configuration window.

Select a Primary Leader AP. The AP set to Internal will use this Primary Leader as its first source of truth for time.

Optionally, select a Secondary PTP Leader(s). If the AP set to Internal encounters an error when synchronizing time with the Primary Leader AP (e.g., the Primary AP is down), it will attempt to synchronize with each Secondary Leader until it successfully does so.

When the Primary Leader AP comes back online, PTP will automatically switch back to synchronizing with the Primary Leader AP.

Acknowledge that the AP will reboot as a result of this change and click Save.

External (PTP)

Before configuring APs to sync with an external PTP server, you must add the PTP server's configuration information (i.e., the Grandmaster) to a site in Celona Orchestrator.

If you have not yet configured your PTP Grandmaster, start here. Otherwise, skip directly to the AP External Time Sync Configuration section below.

PTP Grandmaster Configuration

How the PTP Grandmaster is Deployed

The PTP Grandmaster appliance must be deployed in a suitable physical location that allows connection to your network and the placement of an outdoor antenna to receive GPS signals.

If your Celona deployment includes a PTP Grandmaster, you will receive a Trimble Thunderbolt GM200. The The Thunderbolt Grandmaster must be installed and synchronized prior to integration with your Celona network.

Configuring the PTP Grandmaster (Trimble Thunderbolt GM200)

Before starting the configuration of the GM200, connect the GPS antenna, which must have a clear, uninterrupted, view of the open sky.

By default, the GM200 will ship with the Management port (Eth2) set to IPv4 address 192.168.2.250.

  • Set a static IP on your computer (e.g. 192.168.2.10) and connect to port Eth2 on the GM200.

  • Open a web browser session to 192.168.2.250. Log in with:

    • Username trimblesuper

    • Password Tbolt_<serial number>

  • Configure Port IP addresses. Note that the Management Port and the PTP Port must be on different subnets, or the GM200 will trigger an alarm.

  • Click the gear icon (top-right menu) to enter edit mode.

  • Select the preferred IP mode, Static or DHCP.

  • Enter static IP info if required.

  • Click the wrench icon to save these settings.

  • Update your computer's IP address settings and reconnect to the GM200 web interface.

With the management interface settings complete, you may move on to set Ethernet Port 1, which is the port used for PTP network traffic. Once configured and saved, connect Ethernet Port 1 to your LAN.

Next, select Synchronization Management from the left-hand menu.

  • Click the gear icon to enable editing.

  • Select Ethernet Port 1

  • Set the following;

    • PTP Port Status: Enabled

    • PTP Profile: G8275.2

    • Sync Mode: One-Step

    • Transport Protocol: IPV4

    • IP Mode: Unicast

    • Delay Mechanism: E2E

    • Domain Number: 44

    • Clock Class: blank

    • Announce Interval: 0

    • Announce Timeout: 3

    • Sync Interval -7

    • Delay Request Interval: -7

    • Priority 1: 128

    • Priority 2: 128

    • P2P Delay Request Interval: 0

    • DiffServ Code Point 0

  • Click the download icon (top-right menu) to save the config.

Once all your settings are saved you can check the status of GPS Synchronization by selecting System Status > GNSS from the left-hand menu. The image below shows a successful synchronization.

Your Trimble Thunderbolt is now ready for use with your Celona network.

Configuring Celona for PTP

The first step is to add the PTP Grandmaster information to a Site. Log in to your Celona Orchestrator account, and select Sites from the left-hand menu.

Open the Site at which the Grandmaster is located, and click the plus sign in the upper-right of the External PTP Time Sync Servers card.

The External Time Sync Configuration window opens.

Enter the PTP server's:

  • Name (arbitrary)

  • IP address

  • PTP domain

    • A PTP domain is a logical grouping of device clocks that synchronize time over PTP. All device clocks in one PTP domain are synced. If you are unsure about this value, leave it at the default.

    • The default PTP domain number is 44. The range of allowed PTP domain numbers is 44 - 63.

  • Packet rate

    • The packet rate refers to the number of PTP packets per second (pps) the PTP server will send.

    • Available options:

      • 128 pps (up to 16 APs supported per PTP server)

      • 64 pps (up to 32 APs supported per PTP server)

      • 32 pps (up to 64 APs supported per PTP server)

    • Celona recommends selecting 128 pps for optimal network performance.

Click Save, then select the Access Points menu to begin configuring your APs to use the PTP Grandmaster.

IMPORTANT: Any changes to Time Sync settings will cause all APs using that time sync source to reboot and begin the synchronization process again. This can take up to 30 minutes, during which the APs will be offline. Celona suggests that any updates to timing sync settings are conducted outside of normal operating hours.

Multiple PTP Grandmasters can be added to the network for redundancy. Follow the same process to add each PTP device. Once your PTP devices are added to the system, configure each AP with the appropriate PTP servers.

AP External Time Sync Configuration

Before modifying time sync configuration to External mode, ensure you have configured a PTP Grandmaster appliance on the network.

To set an AP to External mode, click the External Time Sync (PTP) button in the Time Sync Configuration window.

Click Time Sync Configuration for each AP, selecting the primary and secondary PTP sources as shown in the screenshot below.

Acknowledge that the AP will reboot as a result of this change and click Save.

Once time sync servers has been selected the AP will reboot and begin the time synchronization process, which can take up to 30 minutes.

Monitoring the PTP Sync Status

Monitor status of PTP sync directly from the Devices page as shown above.

Status message definitions are listed below.

  • Initializing: waiting for time-of-day sync to complete.

  • Acquiring: frequency sync in progress.

  • FREQ_LOCK: frequency is synchronized. Phrase is synchronizing.

  • Synced: frequency and phase are synchronized.

  • Failed: either frequency is uncertain, no reports have been received, or no PTP server has been found.

  • Unknown: either initializing the sync or PTP is in an unknown state.

You may also confirm PTP client status via the Trimble GM200 web interface by selecting System Status > Timing from the left-hand menu.

The PTP client IP addresses should reflect those of your Celona APs.

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