Installation guide

DC 900-1564A 21

Chapter

SLC Protocol

Theory of Operation

Simpact’s SLC protocol software running on the ICP provides the application with sig-

niﬁcant control over SLC operations while reducing the overall processing burden on

the application. This chapter identiﬁes the principal features of the SLC protocol that

are under application control.

2.1 SLC Envelope Service

An SLC envelope consists of leading SYN characters, the DLE control character, the

ETB control character and the trailing block check character (BCC) for each SLC block.

The SLC software on the ICP always provides the SLC envelope for frames transmitted

and removes the SLC envelope from frames received. The ICP generates the BCC for

frames transmitted and checks the BCC in frames received.

When the application conﬁgures an ICP link for SLC envelope service, the application

assumes full responsibility for SLC frame content between the DLE and ETB control

characters provided by the SLC envelope. In this case, the application must implement

all message handling procedures, block handling procedures, and link control proce-

dures of the SLC protocol.

2.2 SLC Protocol Service

When the application conﬁgures an ICP link for SLC protocol service, the ICP enhances

the basic SLC envelope service to provide additional SLC protocol support. These addi-

tional services include network-level support, message blocking support, multi-chan-

nel support, retransmission support, safe store support, and stop/resume ﬂow support.