# Industrial NTP Time Server — Selection Sheet (Reference · Policy · Capacity)

| Item | Content |
|------|---------|
| **Audience** | Agents / end customers / tender package |
| **Document title** | Selection Sheet (Reference · Policy · Capacity) |
| **Doc No.** | `DOC-Q3000-SEL-EN-011` |
| **Model** | **QYTS-3000-BG-T-S** |
| **Document version** | 1.0 |
| **Firmware** | V4.9.0-b139+ (see device Web / label) |
| **Use** | Selection / bid / acceptance (status — policy — capacity one-pager) |
| **Companion** | Shipping Product Specification Product Specification (Shipping) in this folder |

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## 1. Reference source status

Time reference = **GNSS 1PPS + disciplined local clock** (not PTP; not dual-clock failover).

| Device state (Web / LCD) | Meaning | NTP under factory policy |
|--------------------------|---------|----------------------------|
| **LINK up** | Ethernet link OK | NTP / Web possible |
| **GNSS fix / satellites** | Module positioning valid | Discipline in progress |
| **Warm-up** (synced + PPS, not yet LOCK) | Cold-start converge | May reply **Stratum 2** |
| **LOCK** | Reference ready | **Stratum 1** |
| **Brief PPS loss** (after LOCK) | PPS blip window (~≤10 s) | May still reply |
| **Unlock / holdover** | GNSS or discipline lost | See §2 |
| **No LINK** | Cable / switch fault | **No** NTP |

**Do not mix layers:** internal/1PPS are hardware-edge metrics; **Ethernet NTP is typically millisecond-class on LAN** (measure at the client); Modbus resolution **1 ms**.

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## 2. NTP serve policy (Web)

| Web name | LCD `Pol` | Warm-up | After LOCK | After GNSS unlock |
|----------|-----------|---------|------------|-------------------|
| **Lock-based (factory default)** | `LCK` | May **S2** | **S1** | **Stop** (except brief PPS blip) |
| **Lock + timed hold** | `TIM` | Same | **S1** | Still **S2** for ~**≤5 min** (preferred for Web export / soak) |
| **Holdover serve** | `HLD` | Sync → reply, usually **S2** | Usually **S2** | Continues (legacy “always need packets”) |

- Saved on **Network** page; persists across reboot.  
- Prefer **Lock + timed hold** during large Web CSV/HTML exports.  
- Optional **NTP ACL** is independent of the table above.

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## 3. Capacity boundaries (contract numbers)

| Boundary | Spec | Note |
|----------|------|------|
| **Recommended clients** | ≤ **60** on LAN | Default commitment; slow poll typical |
| **Per-source IP** | ≤ **8** replies/s | Anti-abuse |
| **Global overload protect** | ≈ ≤ **1024** replies/s | Adaptive: no low hard cap in normal load |
| **During large Web export** | Global cap further derated | Shared single port with NTP |
| **Not included** | PTP, dual-port failover, IPv6, NTP broadcast/multicast, NTS, **HTTPS**, SNMPv3 | Entry industrial NTP; on-device SNMP is v2c **read-only** only |

**Acceptance:** After LOCK, LAN `w32tm` / `sntp` OK; Web **NTP Served** increases; do **not** accept “module ns” as “client ns”.

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## 4. Quick answers

| Question | Answer |
|----------|--------|
| When is official Stratum 1? | **LOCK** under lock-class policy |
| Cold start with no time for clients? | Default allows warm-up **S2**; use **timed hold** for unlock behavior |
| How many clients? | **≤60 recommended** — not a 10k+ req/s appliance |
| Market segment | **Entry industrial LAN NTP** — not modular high-end / PTP-first platforms |

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*Filename Selection Sheet. Interfaces: Industrial IF Protocol; operations: User Guide. Firmware as shown on device.*