SSDP, the Simple Service Discovery Protocol (SSDP), is an application layer protocol and one of the core protocols that constitute the Universal Plug and Play (UPnP) technology.
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Simple Service Discovery Protocol is a protocol implemented on the basis of HTTPU and HTTPMU.
According to the protocol, when a control point (client) accesses the network, it can send an "ssdp:discover" message to the SSDP port of a specific multicast address using the M-SEARCH method. When the device listens to the message sent by the control point on the reserved multicast address, the device will analyze the service requested by the control point. If it provides the service requested by the control point, the device will directly respond to the control point by unicast. request.
Similarly, when a device is connected to the network, it should send an "ssdp:alive" message using the NOTIFY method to the SSDP port of a specific multicast address. The control point processes the monitored messages according to its own policy. Considering that the device may stop the service or be uninstalled from the network without notification, the "ssdp:alive" message must specify a timeout value in the HTTP protocol header CACHE-CONTROL, and the device must resend the "ssdp" before the agreed timeout value is reached. :alive" message. If the control point does not receive the "ssdp:alive" message sent by the device again within the specified timeout value, the control point will consider the device to be invalid.
When a device is scheduled to be offloaded from the network, it should also send a "ssdp:byebye" message to the SSDP port on a specific multicast address using the NOTIFY method. However, even if the "ssdp:byebye" message is not sent, the control point will consider the device corresponding to the "ssdp:alive" message that times out and does not receive again as a failed device according to the timeout value specified by the "ssdp:alive" message. .
In the IPv4 environment, SSDP generally uses the multicast address 239.255.255.250 and the UDP port number 1900 when it is necessary to transmit related messages by multicast.
According to the assignment of the Internet Address Assignment Authority, SSDP uses the multicast address FF0x::C in the IPv6 environment, where X can have different values depending on the scope.
