An identification of the protocol being used for the
application. For an OSI Application, this will be the
Application Context. For Internet applications, OID
values of the form {applTCPProtoID port} or {applUDPProtoID
port} are used for TCP-based and UDP-based protocols,
respectively. In either case 'port' corresponds to the
primary port number being used by the protocol. The
usual IANA procedures may be used to register ports for
new protocols.