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SNA Commands
This section describes the format of SNA commands and describes how the 3708
processes these commands.
Transmission Formats
The host program and the 3708 communicate using half-duplex/flip-flop or
contention send/receive protocols. When the host program or the 3708 is
transmitting data, it assumes the role of
the~Sending
LU. The LU to which the
transmission is directed is the receiving LU An LU is the logical entity that
communicates on behalf of an end user (such as a terminal or application program).
The term outbound refers to transmissions from the host to the 3708. The term
inbound refers to transmissions from the 3708 to the host.
The portions of an SNA transmission between the host and the 3708 are:
Transmission Header (TH)
This header contains format identification, mapping fields, an
expedited flow indicator, the destination address (OAF'), the origin
address (OAF'), and a sequence number.
Request/Response Header (RH)
This header describes the type of message being transmitted and
contains indicators that control SNA protocols.
Request/Response Unit (RU)
This unit contains the data or commands that flow in the transmission.
A Null RU is an RU that contains no data.
The 3708 communicates with an SNA host system by means of a teleprocessing
network that uses the synchronous data link control (SOLC) transmission format.
See "SDLC Transmission Frames" on page 3-2 for information about SOLC.
Transmission Header
The 3708 supports FI02 transmission headers (TH). The transmission header
consists of 6 bytes. The following table describes the transmission header.
THByte
Bits
Description
0
0-3
Format Identification (FlO)
4-5
Mapping Field (MPF)
6
Reserved
7
Expedited Flow Indicator (EFI)
1
0-7
Reserved
2
0-7
Destination Address Field (OAF')
3
0-7
Origin Address Field (OAF')
4-5
Sequence Number; 10 number on expedited flow
request and responses
Chapter 3. SOLC and SNA Communication
3-15
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