All procedures transferring signalling information by using the protocol discriminator of Q.931 user-network call control messages are applicable only to those messages which pass the checks described in 5.8.1 through 5.8.7. The error handling procedures of 5.8.1 through 5.8.7 apply to messages using an ordinary call reference or the global call reference, except where otherwise noted.
Detailed error handling procedures are implementation dependent and may vary from network-to-network. However, capabilities facilitating the orderly treatment of error conditions are provided for in this subclause and shall be provided in each implementation.
Subclauses 5.8.1 through 5.8.7 are listed in order of precedence.