SDP[8] is an attempt to build a minimal protocol for experimentation with multicast resource discovery scenarios. The rationale behind this is discussed in detail in [9].
Version 1 of SDP uses unicast and multicast UDP[49]. All of the normal design issues which apply to UDP based protocols apply equally well to multicast UDP - in particular, there is no guarantee that packets will be delivered reliably. A future version of SDP is likely to incorporate a reliable multicast transport protocol such as RMP[50], in order that comparisons can be made with a purely UDP based approach.
This first version of SDP has been kept purposely simple, with the number of features limited to the minimal set of:
SDP does not require a request to result in any responses, and servers are free to ignore requests if they so choose. The quench request is essentially optional, in that a client need not send it. However, if caching is being used, quench messages are used to provide the cache server with details of the request and acceptable responses. SDP is an unusual protocol in that its design explicitly considers the role of caching.
Above and beyond these restrictions, the payload of each SDP packet is application dependent. It is envisaged that applications built with SDP would distinguish each other by the use of traditional mechanisms such as well-known port numbers.