⁷ ITU-T Recommendation Q.703 (03/93) 

⁶ Geoffrey Gerrien, "CDI - Application Program Interface Guide," Gcom, Inc., March 1999. 

¹Brian F. G. Bidulock <bidulock@openss7.org> 

²OpenSS7 Web Site: <http://www.openss7.org/> 

³SDLI is different in one respect than the remainder of the protocol modules defined in OpenSS7. At the time of writing, few user-space programs have sufficient peformance to meet the thight timing requirements placed my the SS7 specifications on the SDLI. As a result, this interface is not normally used by user-level programs, but is used as a STREAMS interface to higher-level modules within a STREAMS protocol stack. 

⁴For the SDLI it is advised that the SDL user wait for a transmit wakeup indication from the SDL provider before transmitting data to avoid aging of the transmit data in the SDL provider's internal queues. This ensures that SS7 Level 2 Forwards and Backwards Indicator Bits and Sequence Numbers in the transmitted message are timely. Also, the SDLI provider is not required to transmit all but the first of a group of identical Fill-In Signal Units (FISUs) or Link Service Signal Units (LSSUs). On the receiving end of the signalling data link, the SDL user will receive data indications as quickly as they arrive, but will only receive on indication for a group of identical and repeating FISUs or LSSUs. 

⁵I should fix this and make it more consistent with the CD_INFO_ACK and the DL_INFO_ACK in that they indicate the offset and length of the addresses so that the messages can be extended without affecting previous implementations (i.e. sustaining backwards compatibility).