ECN specification for Bluetooth SDP

​The Bluetooth "Service Discovery Protocol" (SDP) can reasonably be described as the heart of the Bluetooth protocol suite. It enables any Bluetooth-enabled system to discover the presence in the local environment of other Bluetooth-enabled systems, either in general, of a specific type (offering a specific service), or of a specific type with a given name.The protocol uses a mixture of TLV-encoded types and fixed-length fields. 

One of the key features of this protocol is its open-ended nature. It allows suppliers of Bluetooth-enabled equipment to define new types of service, and the parameters associated with that service. 

Encoding of such information is always of a Type-Length-Value (TLV) form, so a receiver who does not understand some particular service type and parameters can easily skip such material and ignore that service.