In small installations, whether a camera talks to a recorder often depends on a vendor's proprietary protocol. In city-scale and campus-scale projects, GB/T 28181 and ONVIF support has become a mandatory clause in the tender documents.

GB/T 28181 defines how devices register with and are managed by Chinese networking and management platforms — registration, heartbeat, device directories, live audio and video on demand, playback and PTZ control. ONVIF focuses more on device discovery, media configuration and event subscription. The two serve different purposes, and real projects usually need both.

Three suggestions for buyers. First, verify integration against the actual platform during sample testing rather than trusting a protocol list on a datasheet. Second, look at consistency of implementation, especially for playback and PTZ control, which are the two areas where problems surface most often. Third, favour vendors that keep shipping firmware updates and can supply a protocol conformance statement.

Protocol support looks like a software detail, but it determines how expandable the system is three to five years out. Cameras can be replaced; platforms and cabling tend to stay.