The following functions are not currently supported by Interon SNA:

Interon SNA comprises the following components: The Interon PU_T2 SNA Engine (the SNA Server), a TN3270 Server (optional), and Interon SDLC. All three of these components can co-reside on the same machine or can reside on separate machines.

The SDLC component resides on an off-the-shelf intelligent communications adapter, offloading the main CPU of the link-layer activity. The SDLC component provides reliable, connection-oriented transmssion services for the upper layers of SNA; it is responsible for insuring successful and orderly transmission of data.

The SNA component implements the following SNA Layers (analogous OSI layers are shown in parentheses): SNA Path Control (OSI Network Layer), SNA Transmission Control (OSI Transport Layer), SNA Data Flow Control (OSI Session Layer), and the SNA Presentation Layer/Logical Unit Services (OSI Presentation Layer).

This section provides a detailed description of Interon SNA features.

LOGICAL UNIT TYPE 0. Interon SNA supports Type 0 logical units. An LU Type 0 can use any format or protocol defined by SNA. It can also supplement SNA formats and protocols with implementation-specific formats and protocols.

A typical LU Type 0 session is known as SNA Pipeline, which is often used financial and credit transactions. Half-session characteristics for the LU Type 0 Pipeline session are TS Profile 4, FM Profile 4, full-duplex send/receive protocol, no FM headers, and a maximum RU size of 256 bytes.

See the "SNA Reference Summary," GA27-3136, for a more detailed description of an LU Type 0 session.

LOGICAL UNIT TYPE 2. Interon SNA supports Type 2 logical units. An LU Type 2 comprises a subset of SNA functions that facilitate interactive communication between an application program and a single display terminal. For example, a 3278 display terminal uses LU Type 0 to interact with a CICS application running on an IBM host.

Half-session characteristics for a type 2 LU-LU Session are TS Profile 3, FM Profile 3, SNA 3270 data stream, no FM headers, and a limited set of sense (error) codes. See the "SNA Reference Summary," GA27-3136, for a more detailed description of an LU Type 2 session.

LOGICAL UNIT TYPE 3. Interon SNA supports Type 2 logical units. An LU Type 3 comprises a subset of SNA functions that facilitate communication between an application program and a printer, using the SNA 3270 data stream.

TS PROFILE 3. Transmission services Profile 3 allows session-level pacing in both directions, enforced sequencing on normal flows, and support of the Session Control commands, CLEAR and SDT. The following TS usage specifications are in the BIND:

- Pacing counts

- Maximum RU size on normal flow

TS PROFILE 4. Transmission Services Profile 4 allows session-level pacing in both directions, sequencing on normal flows, and support of the Session Control commands, SDT, CLEAR, RQR, and STSN. TS usage specifications are:

- Pacing counts

- Maximum RU sizes on normal flow

FM PROFILE 3. Function Management Profile 3 implies immediate response mode and the following DFC commands: CANCEL, SIGNAL, LUSTAT (Secondary Logical Unit to Primary Logical Unit--SLU to PLU--only), CHASE, SHUTD, RSHUTD, SHUTC, BID, and RTR. FM usage specifications in the BIND are:

• Chaining use (single or multiple RU chain)
• Request control mode specification
• Chain response protocol (definite and exception response)
• Compression support (not supported)
• Send EB indicator (PLU only);
• FM Header use (not supported)
• Brackets use and reset state (brackets are used and reset state is between brackets, BETB)
• Bracket termination rule (Bracket Termination Rule 1)
• Alternate code set (not used)
• Normal flow send/receive mode (half-duplex flip-flop)
• Recovery responsibility (PLU)
• Contention winner/loser (SLU is contention winner and PLU is contention loser)

FM PROFILE 4. Function Management 4 is the same as FM3, with the exception that SNA commands QEC, OC, and RELQ are also allowed.

SESSION-LEVEL PACING. Session-level pacing is a method of data flow control between half-session partners; it prevents one half-session from over-running its partner half-session with data requests.

SEGMENTATION. Segmenting is the fragmenting of an RU to fit the specified maximum size of the network layer. Segmentation is performed by Interon SNA.

SEND/RECEIVE MODE PROTOCOL. The send/receive mode provides a means by which two half-sessions can coordinate when they send and receive messages. If the mode is Half-Duplex Flip-Flop, the sending half-session must own the Change Direction Indicator (CDI). If the mode is Full Duplex, both half-sessions may transmit and receive data simultaneously.

SEQUENCING ENFORCED ON NORMAL FLOWS. Sequencing guarantees orderly, sequential communication between half-sessions. Sequence numbers can be initialized with the CLEAR or STSN commands.

IMMEDIATE REQUEST MODE. Immediate request mode is enforced in both directions, meaning that an RU cannot be sent on a session if a previous RU chain requires a definite response which has not yet been received.

IMMEDIATE RESPONSE MODE. Immediate response mode is enforced in both directions, meaning that RU chains must be responded to in the order in which they were received.

DEFINITE AND EXCEPTION RESPONSE SUPPORTED. Definite response (DR) mode requires a response at the end of every chain. Exception response (ER) responds only in the case of an error situation.

SINGLE OR MULTIPLE ELEMENT CHAINS. Chaining provides a means whereby a sequence of messages can be related for the purpose of error recover. For instance, if a chain of message elements requires a definite response, one response may be sent after the entire chain has been received to acknowledge its reception. If a particular message in a chain is negatively reponded to, the already received elements of the chain are discarded along with those that are forthcoming. Currently, only single element chains can be sent or received by Interon SNA, except in the case of TN3270.

BRACKETS. "A sequence of RU chains transmitted on the normal flow may be grouped in an entity called a bracket. This can be done to associate together the RUs pertaining to a particular transaction (unit of work) and prevent other, unrelated requests and responses transmitted during the session from appearing within that transaction." (GC30-3073, Page 5-13)

Brackets are used LU Types 2 and 3, and optional for LU Type 0.

SNA COMMAND SUPPORT. The following table indicates which SNA commands are supported for LU Types 2 and 3: