What is the difference between Wired Sync and OptiSync?

Wired Sync and OptiSync are the synchronization protocols utilized in USB camera systems. 

Wired Sync

Wired Sync provides camera-to-camera synchronization using RCA cables in a daisy chain arrangement. With a master RCA sync cable connecting the master camera to the OptiHub, each camera in the system needs to be connected in series via RCA sync cables and splitters. 

V100:R1 (Legacy) and Slim 3U cameras utilize Wired Sync only, and therefore any OptiTrack system containing these cameras need to be synchronized through Wired Sync.

Wired Sync is optionally available for Flex 3 cameras. 

Wired Sync between Flex 3 cameras. From Flex 3 QuickStart Guide

OptiSync

OptiSync is a custom synchronization protocol designed for our Flex series cameras. OptiSync sends and receives sync signals over the USB cable, without the need for RCA sync cables. This sync method is only available when using Flex 3 or Flex 13 cameras connected to the OptiHub.

OptiSync in Flex 3 camera system. From Flex 3 QuickStart Guide