# System Variants

There are three current variations of the system:

* **Mk II Autosync**. This unit automatically synchronizes the system timebases using GPS or GNSS. Synchronization requires both the transmitter and receiver to be (independently) exposed to GPS/GNSS signals at the start of the mission and periodically (every hour or two) during the mission. Additionally, Mk II Autosync units can operate on either of two channels allowing two independent ROV systems in the same operating area. The Autosync unit allows for multiple receivers to interoperate simultaneously with one transmitter on each channel. **This synchronization method is called "GNSS Sync".**
* **Mk III**. This system is similar to a traditional ultra-short baseline (USBL) system. The transceiver sends an interrogation pulse to the transponder, which returns an answer pulse. Slant range is calculated from time of flight, so no timebase synchronization is needed and thus the system can remain submerged indefinitely. Only one Mk III transceiver can operate in an area at one time. **This synchronization method is called "Acoustic Sync".**
* **Mk V**. This system uses a [network connection](/c/ethernet-rov-locator/system-variants/mk-v/connectivity-requirements-for-network-synchronization.md) (provided by you) between the Topside Transceiver and the ROV-mounted Transmitter to synchronize the system timebases. Only one Mk V system can operate in an area at one time. T**his synchronization method is called "Network Sync".**

## Summary of ROVLe Model Sync Method Compatibility

<table><thead><tr><th width="355.7159423828125"></th><th width="121.4075927734375">GNSS Sync</th><th width="131.69140625">Acoustic Sync</th><th>Network Sync</th></tr></thead><tbody><tr><td>Mk II Receiver (topside unit)</td><td>Yes</td><td></td><td></td></tr><tr><td>Mk II Transmitter (deepside unit)</td><td>Yes</td><td></td><td></td></tr><tr><td>Mk III Transceiver (topside unit)</td><td></td><td>Yes</td><td>Yes</td></tr><tr><td>Mk III Transponder (deepside unit) — <em>this unit is deprecated</em></td><td></td><td>Yes</td><td></td></tr><tr><td>Mk V Receiver (topside unit) </td><td></td><td></td><td>Yes</td></tr><tr><td>Mk V Transmitter / Transponder (deepside unit)</td><td></td><td>Yes</td><td>Yes</td></tr></tbody></table>

More details and trade-offs are here:

<table data-view="cards"><thead><tr><th></th><th data-type="content-ref"></th></tr></thead><tbody><tr><td></td><td><a href="/pages/6T0Eq7Re0f9PHb7J9Qnr">/pages/6T0Eq7Re0f9PHb7J9Qnr</a></td></tr><tr><td></td><td><a href="/pages/SGoEnTIA14ZclHm4Y9Pj">/pages/SGoEnTIA14ZclHm4Y9Pj</a></td></tr><tr><td></td><td><a href="/pages/F5ZV1tLaC8uhy9k13SWE">/pages/F5ZV1tLaC8uhy9k13SWE</a></td></tr></tbody></table>


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