Installation guide

6: Programming Considerations

DC 900-1564A 85

refer to the International Air Transport Association (IATA) document referenced on

page 13 of the Preface.

6.4.1 SS

This level of SLC service provides transparent transmission and reception of SLC blocks

without regard for content. This service requires that the client application provide the

content of the SLC frame excluding the leading SYN and DLE control characters, the

trailing ETB control character and the Block Check Character (BCC).

The SLC protocol service is not content-sensitive. The client application can send and

receive SLC Link Control Blocks (LCBs) and/or Information Blocks directly using

DLI_PROT_SEND_TRANS_DATA commands and responses. However, the content of each

speciﬁed block must exclude control characters such as SYN, DLE and/or ETB.

6.4.2 SS

This level of SLC service performs message segmentation and reconstruction opera-

tions for low-level network format messages. This requires that the SLC service control

the construction of the Transmission Sequence Identiﬁer and the Message Block Iden-

tiﬁer ﬁelds within each transmitted SLC block.

At the client interface, the

usProtCommand ﬁeld determines the message priority indica-

tion in the constructed Transmission Sequence Identiﬁer ﬁeld. The

DLI_PROT_SEND_NORM_DATA command is associated with a Transmission Sequence Iden-

tiﬁer ﬁeld that contains a low-priority indicator. The

DLI_PROT_SEND_PRIOR_DATA com-

mand is associated with a Transmission Sequence Identiﬁer ﬁeld that contains a high-

priority indicator.

The

iProtModifier ﬁeld determines the Acknowledge Message Label portion of the

Message Block Identiﬁer series for the message. The

DLI_PROT_SEND_NORM_DATA com-

mand allows

iProtModifier ﬁeld values of SLC_AML_A_ND through SLC_AML_G_ND for all

message lengths, and restricts

SLC_AML_H_ND_SBM to single block messages. The