saddison@ca.excelan.com (Skip Addison) (03/16/91)
The News Manager)
Nntp-Posting-Host: ca
Organization: Novell Inc., Open Systems Div., San Jose CA.
Date: Sat, 16 Mar 1991 02:28:51 GMT
Note: The following was written during 9-10/90. At that time the Ethernet
interface was very new and not much was known about it.
-- Skip
saddison@novell.com
---------------------------------------------------------------------------
HOW TO HOOK A NETWARE LAN TO AN AS/400?
by Skip Addison
Director, Consultant Relations
Novell Communications Products Division
INTRODUCTION
The AS/400 supports numerous connectivity options including twinaxial
cabling, SDLC (Synchronous Data LinkControl) lines, ethernet and token ring
connections. Novell has received numerous requests for information onhow
best to tie a NetWare network to an AS/400. This paper outlines the
connectivity strategy that will best integrate the capabilities of the LAN
and the AS/400 into one system providing access to LAN applications, AS/400
(and S/3x) applications and to new client/server applications using IBM's
System Application Architecture (SAA). We assume that while the reader may
be familiar with 3270 communications, 5250 communications or NetWare, they
may not be familiar with all three. We also assume that the reader has
a passing familiarity with LAN technology.
BACKGROUND
Today, the IBM mid range product line consists of the older System 3X
(S/34, S/36, and S/38) series and newer AS/400 series of minicomputers.
The S/3X products were very successful when they were introduced in the mid
1970s. However, sales began to level in the early 1980s with the
increasing popularity of Personal Computers and Local Area Networks. In
addition, 5250 terminal sales declined as PC terminal emulation replaced
many terminals. Although by 1988 there were 300,000 IBM S/3Xs installed
worldwide, it was rumored that IBM might abandon the mid range market.
This rumor was dispelled when in June 1988, IBM announced the AS/400.
There are nine models of the AS/400, providing from 4 to 96MB of memory and
up to 38GB of disk storage.
AS/400 Configurations
C04 C06 C10 C20 C25
Main Storage, MB 8-12 8-16 8-20 8-32 8-40
Max DASD, GB .96 1.28 1.28 2.56 3.84
Comm Lines 5 5 8 14 14
LAN Interfaces 1 1 1 2 2
Local Devices (twinax) 14 54 40 80 80
B35 B45 B50 B60 B70
Main Storage, MB 8-40 8-40 16-48 32-96 32-196
Max DASD, GB 13.7 13.7 27.4 54.8 54.8
Comm Lines 16 32 32 32 48
LAN Interfaces 4 4 4 4 4
Local Devices (twinax) 160 240 400 600 800
At this time there are over 50,000 AS/400s installed, split roughly equally
between the US and the rest of the world. The key features of the AS/400
are a high-level machine interface, an object-oriented design, single-level
storage with relational database capabilities, and highly integrated
systems functions. Although there are office, electronic mail, and query
applications available for the AS/400, the most common applications are
industry specific such as accounting and manufacturing software packages.
COMMUNICATIONS
The AS/400 supports several communications options over several different
types of media as shown below:
SDLC Twinax Token Ring
5250 (LU 4 & 7) yes yes no
3270 (LU 1, 2, 3) yes no yes
APPC (LU 6.2) yes yes yes
A REVIEW OF THE TERMINAL TYPES
> 3270
For reasons unknown outside IBM, mainframe computers based on the 370
architecture do not share common communications with the S/3x
minicomputers. IBM mainframes were designed to work with the 3270 family
of terminals. 3270 terminals can talk to a mainframe via either an SDLC
line or a Token Ring. Additionally, the IBM 3270 terminal controller can
attach directly to a mainframe's I/O channel. SNA's LU type 1 printer,
type 2 display, and type 3 printer describe the 3270 terminals.
The 3270 system was designed with an eye towards large installations. Up
to 128 terminal sessions can use a single terminal controller. By
emulating a controller, a single LAN-to-host gateway can represent up to
255 users. Moreover, multiple gateways can share a single attachment to
the mainframe.
> 5250
The System/3x machines from which the AS/400 is descended were designed to
use the 5250 family of displays and printers. These communicate with the
minicomputer via either SDLC or Twinax hardware.
In IBM's System Network Architecture (SNA), each type of terminal or
printer has its own Logical Unit (LU) type. The LU type number defines the
communication protocol, or language, that the device "knows how to speak."
The 5250 terminals are LU types 4 and 7.
Only up to 7 terminals are allowed to connect to a single twinax interface.
For single user terminals this was not a limitation. In the world of LAN
gateways, however, only 7 connections is a distinct limitation.
A 5250 terminal can not talk to a mainframe; and until the AS/400 came out,
a 3270 terminal could not talk to a minicomputer. The differences in the
protocols have caused significant problems.
AS/400 COMMUNICATIONS
Both the 5250 and 3270 protocols are based on a master-slave relationship.
The minicomputer or mainframe is the master and the terminal is the slave.
As desktop devices grew more sophisticated, however, IBM needed to develop
a communication mechanism which would let an application on a desktop
computer talk to an application on a mainframe as peers. IBM called this
Advanced Program-to-Program Communications or APPC. APPC uses the LU 6.2
communications protocol. APPC is available on the AS/400 via twinax, SDLC
and token ring connections.
APPC is the primary backbone of future SAA-compliant networks. Using
APPC/LU 6.2, desktop applications can share data in a cooperative
processing environment with the mainframe, sending updates and queries to
host transaction databases.
Because of APPC's ability to provide highly functional sessions, whether
for terminal service or client server applications, IBM has put most of its
long term strategic emphasis on APPC for connections from desktop
computers. However, the 3270 and 5250 communication protocols will still
be used for many years, because of their support for nonprogrammable
terminals and a large installed base.
Because of the communication differences between different terminal
systems, IBM encourages developers to develop their applications in such a
way that either 5250 or 3270 terminal users can use them. The long term
direction from IBM is to use APPC/LU 6.2 for all SAA compliant
applications.
Also, the AS/400 provides no documented method of supporting
non-programmable terminals and APPC from the same gateway. Therefore,
whether using 3270 or 5250 terminal emulation, a separate gateway will be
required for SAA compliant client/server applications.
> 3270 SNA for AS/400
When IBM introduced the AS/400, they reduced its dependency on 5250
terminals by allowing 3270 terminals to run applications that had
heretofore required 5250 terminals. This is made possible by transparently
translating between the 3270 and 5250 data streams "on the fly". That is,
the application running "sees" a 5250 terminal although the user may
actually be using a 3270 terminal.
The translation is not perfect, however. The principal difference is that
the 3270 keyboard is missing three keys that exist on the 5250 keyboard
("Field +", "Field -" and "Field Exit").
"PC SUPPORT"
IBM's AS/400 PC Support program allows PCs to connect to an AS/400 via
token ring, ethernet or twinax. In this case, the PC is emulating a 5250
terminal, but the 5250 information is "buried" in LU 6.2 packets for
transmission across the token ring. (Note that the chart above indicates
that 5250 communications can not be sent directly over the token ring.)
Unfortunately, IBM's AS/400 PC Support program degrades performance of the
AS/400 and consumes a sizeable portion of the PC's RAM. The determination
of whether these detractions are prohibitive or not must be made by the
customer.
There is no support from IBM for third-party equivalents to AS/400 PC
Support. The method used by AS/400 PC Support to encapsulate the 5250 data
stream in APPC/LU 6.2 is not documented publicly.
NOVELL AS/400 COMPATIBLE COMMUNICATION PRODUCTS
LAN to mainframe and LAN to minicomputer products are a major part of
Novell's communication product line. We have products for all three
communication protocols (3270, 5250 and APPC). These are described below.
3270 and APPC Communications.
There are two products which provide 3270 and APPC communication protocols,
the NetWare 3270 SNA Gateway and NetWare 386 Communication Services for SAA
(which will begin shiping later this year). In the SNA Gateway and
Communication Services for SAA, a PC on the LAN emulates an IBM cluster
controller. This gateway PC can attach to the AS/400 using either SDLC or
token ring. Other PCs on the LAN run the NetWare 3270 LAN Workstation
software to emulate 3270 terminals and use APPC.
Novell's 3270 LAN Workstation has always included a keyboard definition
utility permitting users to permit users to redefine the keyboard for 5250
emulation. On October 18th we will begin shipping our SNA product with
5250 keyboard emulation as an option (but the 3 "missing keys" will still
be missing.
The gateway plays a central role in the interaction between users and the
AS/400. It performs the low level interaction with the AS/400, freeing up
memory and processing power in the workstation. The high level interaction
is handled at the workstation. In SNA terms, the gateway emulates a PU,
the workstation a LU.
Due to limitations in the AS/400, one gateway can not support both 3270 and
APPC simultaneously. This limitation does not exist in the mainframe
world.
5250 Communications.
The NetWare 5250 Gateway, Version 2 emulates a 5250 terminal controller
(IBM 5251 Model 12, 5294, or 5394) so that up to 7 or 9 workstations
(depending on configuration) on the LAN can function as 5250 terminals on a
System/34, System/36, System/38 or AS/400. The gateway connects to the
AS/400 via either twinax or SDLC lines. In concept, it is identical to the
NetWare SNA Gateway except that it facilitates emulation of 5250 terminals
rather than 3270.
STRATEGIC DIRECTION
As we have seen above, in connecting NetWare to an IBM mainframe there is
little question about how to proceed. NetWare SNA Gateways provide highly
reliable, fully functional 3270 terminal emulation, the same type of
communications mainframe applications expect in normal day-to-day
operation, with or without a LAN. There has been some confusion, however,
in the area of connectivity to the AS/400. This confusion has arisen, in
part, because of the dependence of many System/3x applications on 5250
communications on the one hand, and the historically poor industry support
(including support from IBM) for 5250 communications.
One can see, however, that IBM's trategic direction is to provide the
broadest level of support to 3270 and APPC communications. While the
AS/400 can support 3270, there is no support for 5250 terminals on
mainframes. While the token ring can support 3270 controllers, there is no
direct 5250 terminal support on token ring, except for AS/400 PC Support.
It is clear that IBM's primary strategic direction is focused on APPC and
cooperative processing. Novell is supporting this direction and increasing
NetWare's connectivity to the AS/400.
RECOMMENDATION
1. All new applications being developed for use by non-programmable
terminals should support 3270 terminals as an option.
2. All cooperative processing applications for the IBM environment should
use APPC/LU 6.2.
3. Users should look to 5250 gateways and terminal emulation (including
AS/400 PC Support) as a migration strategy for existing applications.
By following these recommendations users can expect the following benefits:
>Support for existing applications
>Positioning the network for future enhancements
>Better support for advanced communications
Existing applications have largely been written to use the 5250 data
stream.
For many users, 5250 gateways are the preferable choice to ease the
transition to LAN based systems without retraining.
While providing support for these existing applications, MIS staff and
application developers can best position themselves and the corporate
network to take advantage of future communication enhancements by
developing all new applications in such a way that they can be used by
either 5250 or 3270 users. Applications to be used by PC users (ie. no
nonprogrammable terminals) should be written to use APPC/LU 6.2.
Micro to AS/400 applications which are implemented using APPC in compliance
with SAA provide the highest level of functionality today and are in the
best position to support all the features of the network of the future.
CONCLUSION
The changing world of data communications offers ever better means of
communicating between the desktop and the minicomputers and mainframes.
Today's changes, however, must preserve yesterday's investments. So when
it comes time to determine the best strategy for tying the AS/400 to a LAN,
the recommendation is: APPC for the long term strategy; 3270 and 5250 as a
migration tool and for support of existing applications.