About SNA Logical Units › Parts of an SNA Network › LUs › LU Types

LU Types

IBM classifies LUs into roughly seven different types (LU 6.2 is a subset of LU 6). The products that support each of these LU types will continue to be supported in future years and the 3270 data stream will also be preserved, but not in its current form.

The following list shows all of the LU types that are in use today to differing degrees.

0

Denotes a flexible protocol, which eliminates standardization beyond layers of SNA. This was commonly used in the late 1970s (before the advent of LU 6.2).

1

Specifies the protocol used as early as the 1960s by remote job entry (RJE) devices such as the 3770 RJE terminal. Designed for use with printers and card readers, this protocol is most typically used in asymmetrical links where one node is a slave to the host.

2

Specifies the protocol for 3270 video display stations. It defines the data streams used by dumb terminals to communicate with the host.

3

Specifies a variant subset of 3270 protocol that was used to drive printers attached to 3274 cluster controllers. Today it is still used to support old hardware.

4

Specifies a protocol that was intended for use on word processors attached to a host network. You can still see it on old IBM word processors.

6.1

Specifies SNA's prototype protocol defined for program-to-program communication that was developed during the late 1970s. It was a first attempt to provide a standardized mechanism for communication between intelligent peer systems.

6.2

Alternatively referred to by the marketing title Advanced Program-to-Program Communications (APPC), this used to be called the Convergent LU, or the LU type around which the entire IBM product line would converge. LU 6.2 defines standard functions or verbs such as SEND, RECEIVE, and CONFIRM that simplify the work of making two different programs on two different kinds of system talk to each other. This is the only LU type supported by CA XCOM Data Transport.

7

Specifies the data stream of the 5250 video display stations commonly used with the IBM midrange systems.