Simple Service Discovery Protocol

The Simple Service Discovery Protocol ( SSDP ) is a network protocol that is used to find UPnP devices on the network. SSDP normally uses port 1900 UDP. The company Microsoft has introduced it along with their operating system Microsoft Windows ME.

On the UPnP page, we read:

" As soon as a UPnP device has an IP address, it must report to the control points of its existence in the network. This is done via UDP on the multicast address based on the 239.255.255.250:1900 SSDP protocol. Also, search the network control points for UPnP devices. In both cases, the "discovery message" contains only the most important information about the device and its services, such as the device name, device type and a URL to the detailed description of the device. "

Packet structure

A SSDP packet is a HTTP request using the " NOTIFY " (or " M- SEARCH" ) which is sent over UDP. The HTTP body is empty, the HTTP header must be terminated with a blank line anyway. In the HTTP header UPnP -specific attributes are set:

  • NTS ( Notification Sub Type) has the value " ssdp: alive" to login or " ssdp: byebye " to log out of a device.
  • NT ( Notification Type) determines the property of the device.
  • USN (Unique Service Name ) contains a unique ID of the device.
  • LOCATION contains a URL to the description ( Description)

Example:

NOTIFY * HTTP/1.1 SERVER: Linux/2.6.15.2 UPnP/1.0 Mediaserver/1.0 CACHE -CONTROL: max-age = 1800 LOCATION: http://192.168.0.10:8080/description.xml NTS: ssdp: alive NT: urn: schemas- upnp -org: service: ConnectionManager: 1 USN: uuid: 550e8400 - e29b - 11d4- A716 - 446 655 440 000 :: urn: schemas- upnp -org: service: ConnectionManager: 1 HOST: 239.255.255.250:1900   see also

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