SNA-SDLC Abbreviations

AID

Attention Identifier.

BB,EB

Begin Bracket, End Bracket.

SNA Brackets are used to delimit transactions. In the HSM environment they can be used to carry-out a change of direction (CD) on the link. Bracketing is only of limited use with HSMs.

BC,EC

Beginning of Chain and End of Chain Bits:

 

00

:

Middle in Chain

:

MIC.

 

01

:

End of Chain

:

LIC.

 

10

:

Beginning of Chain

:

FIC.

 

11

:

Only in Chain

:

OIC.

BETB

3274 "Between Bracket" State.

After EB and before BB (i.e., ]..here..[ ).

CD

Change Direction so that the other LU has control.

CSI

Bit in RH defining "Code Selection Indicator".

DFC

Data Flow Control command.

SNA command to control the flow of data in LU-LU sessions.

FIC

First in Chain.

Position of a request (RU) in an SNA Chain.

FMD

Function Management Data command.

SNA Command for Data transfer between LUs (LU-LU).

INB

3274 "In Bracket" State.

After BB and before EB (i.e., [..here..] ).

IPR

Isolated Pacing Response.

LIC

Last in Chain.

Position of a request (RU) in an SNA Chain.

LU

SNA Logical Unit, entity which partakes in SNA sessions.

MIC

Middle in Chain.

Position of a request (RU) in an SNA Chain.

OIC

Only in Chain.

PEND.BB

3274 "Pending Begin Bracket" State.

A 3270 Terminal user has started to type but has not yet pressed <Enter>.

PLU

SNA Primary Logical Unit; normally the application program in the Host computer.

PU

SNA Physical Unit, can contain several LUs (e.g., a 3274 Cluster Controller).

RCV

Receive state.

RH

Request/Response Header (3 bytes).

RQD

Definite Request/Response.

The recipient must reply to this message.

RQE

Exception Request/Response.

The sender does not expect a reply unless there is a problem.

+RSP

A positive (affirmative) response to an SNA request.

RU

Request/Response Unit.

SBA

Set Buffer Address.

SDT

Start Data Traffic.

SLU

SNA Secondary Logical Unit; normally a terminal or the HSM.

SSCP

SNA System Services Control Point; normally resides in the Communications Controller (37x5) and responsible for controlling access to the PU and SLU.

TH

Transmission Header (6 bytes).

WCC

Write Control Character (3270).

WSF

Write Structured Field.

X'NNNN

A 4-digit hexadecimal value.