Overview of GB28181 National Video Surveillance Standard and Its SIP‑Based Implementation

GB28181, officially titled “Technical Requirements for Information Transmission, Exchange, and Control in Public Safety Video Surveillance Networking Systems,” is a Chinese national standard drafted by the Ministry of Public Security and related agencies to define the interconnection, communication protocols, and security requirements for city‑wide monitoring and alarm systems.

The standard adopts the Session Initiation Protocol (SIP) as the core signaling protocol, using SIP messages for device registration, session invitation, control, and status reporting. SIP, an application‑layer signaling protocol derived from HTTP and SMTP, supports request methods such as INVITE, ACK, PRACK, BYE, CANCEL, REGISTER, MESSAGE, and OPTIONS, each with specific roles in establishing and managing sessions.

SIP sessions in GB28181 rely on four main components: User Agents (UAs), Registration Servers, Proxy Servers, and Redirect Servers. These components exchange SDP‑described media information to set up RTP/RTCP streams for video transmission.

The standard defines a hierarchical deployment model: local surveillance domains (e.g., a community or factory) connect to county‑level platforms, which in turn connect to provincial platforms, enabling multi‑level cascading.

Key system elements include a central signaling server, a media server that handles RTP/RTSP streams, SIP‑compatible devices (IP cameras, NVRs), SIP clients for control, and a signaling security gateway for inter‑platform authentication. When interfacing with non‑GB28181 platforms, additional signaling and media gateways are required.

Device registration follows a SIP REGISTER flow where each device is assigned a globally unique 20‑digit identifier. The registration process records device IDs, IP addresses, and maintains periodic keep‑alive messages. Example SIP registration messages are shown below:

REGISTER sip: signaling_server@domain SIP/2.0
Via: SIP/2.0/UDP source_ip:port
From: <sip:device_id@source_domain>;tag=185326220
To: <sip:device_id@source_domain>
Call-ID: ...
CSeq: 1 REGISTER
Contact: <sip:device_id@source_ip:port>
Max-Forwards: 70
Expires: 3600
Content-Length: 0

Real‑time video streaming is achieved through a sequence of SIP INVITE, ACK, and BYE messages combined with SDP descriptions, while RTP/RTCP transports the media payload. The SIP server (central signaling server) mediates between the requesting client and the media server, negotiating ports and codecs before establishing the media path.

To develop a GB28181‑compliant solution, the following components are typically required: device‑side SDKs, a central signaling server implementation, SIP‑enabled media servers, and, if needed, signaling conversion and media gateways for non‑standard platforms.

For further details, the full GB28181 specification can be accessed at the official standards website.