Mainframe, MVS and zOS Discussion

What is the significance behindthe LU6.2? I mean, I try to understand the name. From manual I read that it's a communication protocol but if it's protocol why it's called as Logical unit? And what is 6.2? There are not much details on that. Can soemone please clarify what they might mean?

see
https://www.ibm.com/support/knowledgece ... rk/toc.htm

This will come as a shock to some of the younger readers of this forum, but TCP/IP was NOT the first computer communications protocol, and Ethernet was not the first networking medium. Systems Network Architecture (SNA) was published by IBM in 1974 as a standard way of connecting their computers to a network. SNA defined a number of logical units (LUs) and physical units (PUs):

LU0 provides for undefined devices, or build your own protocol. This is also used for non-SNA 3270 devices supported by TCAM or VTAM.
LU1 devices are printers or combinations of keyboards and printers.
LU2 devices are IBM 3270 display terminals.
LU3 devices are printers using 3270 protocols.
LU4 devices are batch terminals.
LU5 has never been defined.
LU6 provides for protocols between two applications.
LU7 provides for sessions with IBM 5250 terminals.

PU1 nodes are terminal controllers such as IBM 6670 or IBM 3767
PU2 nodes are cluster controllers running configuration support programs such as IBM 3174, IBM 3274, or the IBM 4701 or IBM 4702 Branch Controller
PU2.1 nodes are peer-to-peer (APPN) nodes
PU3 was never defined
PU4 nodes are front-end processors running the Network Control Program (NCP) such as the IBM 37xx series
PU5 nodes are host computer systems

LU6.2 is a variant of LU6 to communicate between two applications. Rather than attempting to research LU6.2, use IBM SNA as a search term (or systems network architecture) -- you'll get lots more results and hence more information.

Thansk a lot enrico and Robert. so LU and protocol can be used for each other. I asked that because protocol looks like a set of software rules while LU is physical entity...but they seem to be used an synonyms in the manuals.

LU6.2 is NOT a physical entity -- in CICS, for example, it is a set of commands in the API that allow two applications to communicate. LU6.2 is, however, a protocol as it is

A standard procedure for regulating data transmission between computers.

(per www.thefreedictionary.com).

Thanks Robert and all for the gyan.