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Here we have collected some answers to commonly asked questions about the Hikari Telephone JJY service.


Operation of Hikari Telephone JJY
Since when is the Hikari Telephone JJY service in operation and how long will the previous Telephone JJY service continue?

The Hikari Telephone JJY service was developed in joint research with commercial manufacturers. Experimental operation started in May 2016. After confirming the effectiveness of the system, official service began on February 1, 2019.

The previous Telephone JJY service is planned to remain active until the end of March 2024. We expect that this five year period is sufficient to complete the transition to Hikari Telephone JJY.

Overview of Hikari Telephone JJY
What is the reference for the time delivered by Hikari Telephone JJY?

The Hikari Telephone JJY service distributes the Japan Standard Time provided by NICT.

What information does Hikari Telephone JJY distribute?

We provide data packets according to an extended version of the NTP protocol used for time synchronization over the internet. These packets contain additional information such as the time difference between Japan Standard Time (JST) and Coordinated Universal Time (UTC).

How accurate is the time synchronization by Hikari Telephone JJY?

Experiments performed by NICT using an actual optical communications line over up to about 900 km have confirmed that time can be synchronized to within an error of 1 ms or less. One millisecond is 1/1000s of a second. The accuracy can usually be improved further by averaging the results of multiple synchronizations.

How secure are the communications used by Hikari Telephone JJY?

All communication is performed privately over the one-to-one connection provided by a telephone line.

Will access to the Hikari Telephone JJY service be limited during times of intense use?

NICT provides a line capacity that is expected to be sufficient even in the future. No access restrictions are planned, but we continuously monitor usage and will take actions as necessary.

The limited bandwidth of the user’s communication line may lead to degraded performance if NTP packets are sent at a continuous high rate. We request that users do not send more packets than necessary and limit the connection time to less than 3 minutes.

Is Hikari Telephone JJY free to use?

The Hikari Telephone JJY service can be used free of charge. However, the user is responsible for the cost of equipment and any connection charges. We will provide advance notice if there are any changes to the service or its terms of use.

Can I access Hikari Telephone JJY with multiple devices at the same time?

Although the Hikari Telephone JJY service supports multiple simultaneous requests, the number of lines and system capacity is limited. We therefore request not to use the system in this way.

Requirements for using Hikari Telephone JJY
I am looking for specific instructions for how to use Hikari Telephone JJY. Where can I find them?

NICT publishes this information on the same website that hosts this FAQ. You can find it at:
www.nict.go.jp/sts/hikari_tel_jjy.html

Our website also provides a wide range of other information about Japan Standard Time.

Can Hikari Telephone JJY be used with a different communication line than NTT’s Hikari Telephone “Data Connect”?

The Hikari Telephone JJY service

  • is intended to meet the synchronization needs of systems that cannot be connected to the internet due to security concerns.
  • requires end-to-end communication with high stability to perform delay compensation and time synchronization with high accuracy.

We recommend the “Data Connect” service using NTT’s optical telephone line because it is routed directly over NGN, NTT’s own “Next Generation Network” and its QoS functions ensure sufficient bandwidth. In this way, packets are never routed over the internet, and are not affected by other traffic.

What equipment is required to use Hikari Telephone JJY?

In addition to a communications line such as NTT’s optical telephone “Data Connect” (see above), you will need a suitable router for communication, and a receiving device, typically a computer, for time synchronization.

You also need to register for the use of the service. As a registered user you will be able to contact us by email and to inquire about the current access status.

What kind of router is required?

Any router that can provide an IP UDP tunnel connection via “Data Connect” can be used.

Telephone JJY and Hikari Telephone JJY
Can equipment for the Telephone JJY service be converted to use Hikari Telephone JJY?

Several manufacturers are currently (as of December 2020) offering devices that connect to the Hikari Telephone JJY service and provide a Telephone JJY connection for a user system. In this way an existing system can continue operation with minimal modification.

Known sources:
  Seiko Time Systems Inc.
  E3 Design, Inc. / E3 Technology, Inc.

What kind of system are Telephone JJY and Hikari Telephone JJY and where are they needed?

Both services provide accurate time to systems that require it, but can neither be connected to the internet (typically due to security concerns) nor rely on the reception of GPS or standard radio time and frequency signals (JJY). Hikari Telephone JJY provides this service over a modern, optical telephone line that is digital and packet-based, while the earlier Telephone JJY system required a direct analog connection.

What are the technical differences between Hikari Telephone JJY and Telephone JJY?

The differences are the following:

  • Where Telephone JJY sends data over a low-level serial protocol, Hikari Telephone JJY communicates according to the Network Time Protocol (NTP).
  • Where Telephone JJY achieves a synchronization error of less than 1 ms (1/1000s) only under the best circumstances, Hikari Telephone JJY reaches an error below 1 ms routinely.
  • The communication speed of Hikari Telephone JJY is at least 64 kbit/s (64,000 bits of data per second), 26 to 52 times more than Telephone JJY.