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Managing Multivendor Networks
  
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International Business Machines
Company Background
BM's origin is rooted in a company that incorporated in 1911 as the Computing-Tabulating-Recording
Company. Tom Watson acquired this company in 1914. Ten years later, in 1924, Watson
opened a new chapter in the history of corporate America when he changed the name
of his business automation company to International Business Machines (IBM) Corporation.
During its early years (1920 through the 1940s), the company produced and marketed
a variety of office automation equipment such as punch-card tabulators and electric
typewriters. In 1964, IBM released a computer that was destined to become the definition
of a mainframe system--the IBM System/360. The System/360 was actually a third-generation
computer, and the hardware/software design that enabled it to handle multiple tasks
(programs) concurrently set new standards in the emerging computer industry.
IBM released the System/370 computer in 1970 as a follow-up to the System/360.
Improvements in the mem-ory and storage devices, coupled with a multiprocess- ing
hardware architecture, enabled the System/370 to offer substantial performance improvements
over its predecessor. The System/370's popularity continued where the System/360
left off, spawning two additional lines: the 9370, a scaled-down System/370 released
in 1986; and the System/390, the ultramodern mainframe architecture released in 1990.
Even though IBM achieved market dominance on the high (mainframe) end of the market,
it continued to expand its overall computer line to provide midrange and low-end
solutions. In the midrange, small business market, IBM offered a series of computers,
with the best known models of this era being the System/38 (released in 1978) and
the System/36 (released in 1983). Then, in 1988, IBM released its Application System/400
(AS/400) computer.
In the low-end of the market, IBM set most of the standards for today's PCs. The
success of the PC led IBM to develop and release the PC/XT (short for Extended Technology)
in 1983 and the PC/AT (short for Advanced Technology) in 1984. These models, in turn,
were replaced with the Personal System/2 (PS/2) line (introduced in 1987) and the
Personal System/1 (PS/1) line (released in 1990).
Product Line Overview
IBM manufactures its own products in various plants around the globe and also
has agreements with other companies to produce products for them. IBM is the largest
U.S. computer manufacturer, measured by both sales and output. It not only produces
computers, but also designs and manufactures terminals, printers, disk drives and
more.
PowerPC
The RISC-based PowerPC platform is deployed throughout the IBM product family,
from laptops to parallel processing supercomputers. PowerPC, an open standard, is
the result of an alliance between Apple, IBM, and Motorola, and is not tied to any
single operating system or hardware configuration. The PowerPC family contains multiple
execution units for symmetrical superscalar operation, cache memory, and a multiprocessing
interface.
The PowerPC architecture is based on reduced instruction set computing (RISC)
technology. RISC differs substantially from complex instruction set computing (CISC),
which is typically used in lower-end machines. In releasing its PowerPC product line,
however, IBM is one of the first vendors to offer RISC-based PCs. The difference
between CISC and RISC is that CISC processors contain several instructions to handle
a variety of processing tasks; RISC processors contain only those instructions that
are used most often, and when a complex instruction is required, the RISC processor
will build it from a combination of its basic instructions.
IBM has also introduced its new line of PC 300 Pentium Pro systems, running at
speeds of up to 200 MHz. The availability of the PC 330 and PC 350 might actually
reflect an eventual shift away from the PowerPC platform. The systems can run Microsoftís
Windows 95 or IBMís own Warp Connect operating system, and are well-suited for
power-hungry multimedia applications.
Before the PowerPC architecture was designed, RISC designs were used only in high-end
engineering workstations and servers. IBM and the PowerPC Alliance, however, hold
the view that RISC technology is the next step in personal computing.
The alliance designed the first four members of the PowerPC family simultaneously.
These four processors include the following:
- PowerPC 601. A 32-bit implementation that provides high performance for
computer systems.
- PowerPC 602. A lower-power implementation of the PowerPC architecture,
meant for use in home entertainment or commercial business devices.
- PowerPC 603 and 603e. Also low-power implementations, used in desktop
computers and entry-level systems.
- PowerPC 604 and 604e. 32-bit implementations used in high-end workstations
and SMP computer systems. The 604 and 604e are software- and bus-compatible with
the 601 and 603 and 603e microprocessors.
The PowerPC Platform (PowerPC Microprocessor Common Hardware Reference Platform)
is a set of specifications that defines a unified personal computer, combining the
advantages of the Power Macintosh and the PC environment. Computers made to this
open standard can run operating systems from either Apple, Microsoft, Novell, or
SunSoft. The PowerPC Platform is an open reference architecture that is publicly
available.
IBM Terminals
IBM has two mainstream terminal lines--one for the mainframe (System/390-architecture)
computers and one for the midrange (System/3X-related) computers. The mainframe terminal
line comprises the 3270 family of devices. The midrange computers, on the other hand,
normally use the 5250 line of terminals.
Both terminals share a block orientation that lets the operator enter information
into fields and correct the data at the terminal before transmitting it to the mainframe.
Both terminals have models that support wide text (132 columns) and graphics displays.
They also share a general connectivity philosophy that supports the attachment of
multiple terminals to a computer using one or more lines (the connectivity aspect
of IBM terminals will be addressed later in this chapter).
The 3270 family of terminals includes the 3178, 3270 PC, 3276, 3277, 3278, and
3279 color terminal. The 3270 family supports two types of function keys. One type
is referred to as the Program Attention (PA) keys, and the other is the more standard
Program Function (PF) keys. The 3270 family supports up to four PA keys (PA1 through
PA4) and up to 24 PF keys (PF1 through PF24). Please note, however, that a variety
of keyboards are available for each 3270 model, and some do not contain all 24 function
keys.
The 5250 family is the terminal of choice for the System/36, System/38 and AS/400
systems (although they also have special provisions for supporting 3270 terminals).
The modern 5250 family is composed of the 5251, 5291, 5292 (color), 3197 (color),
3180, and the 3196 terminals.
In contrast to the 3270's support of PA and PF keys, the 5250 family supports
up to 24 Command Function (CF) keys. Please note, however, that different keyboards
for the different 5250 models might not contain all 24 CF keys.
Like the hosting computers, the two families of terminals are oriented toward
their respective markets. The 3270 is a more generalized workstation, suitable for
a wide variety of applications. The 5250, on the other hand, is tailored for the
menu orientation of the midrange systems and is better suited for general business
applications (although the issue is certainly arguable).
Some fundamental operational differences between the 5250 family and the 3270
family are the following:
- In certain configurations, the 5250 has special capabilities that work with midrange
software to perform such advanced word processing functions as word wrap and dual
cursor operations. This feature is most notable under the AS/400 Office system.
- The 5250 has three special field operation keys:
- The field exit key clears the contents of an alphanumeric field to the right
of the cursor and then advances to the next field.
- The field + and field exit keys are used to right-justify numbers in a numeric
field, adding the appropriate sign (blank for positive or "-" for negative)
at the right side of the number.
- The 5250 supports roll-up and roll-down keys that enable the terminal to scroll
through multipage screens offered by the host.
The first position of a 5250 display (line 1, column 1) is reserved in most operations.
Most of these differences are minor, and simply serve to illustrate how each line
of terminal is oriented toward a specific host line (mainframe or midrange). To a
certain extent, this is one of the most unique features of the IBM terminal line--IBM
is one of the few full-line manufacturers that does not offer a single line of terminals
applicable across the entire computer line (like DEC's VT offerings or HP's terminal
line).
Personal Computers
Having stayed out the personal computer market for so long, when IBM decided to
jump, it decided to go in headfirst--and in a real hurry. Certainly its product,
the Personal Computer (PC), was no technological powerhouse.
Before IBM's entry in 1981, the personal computer market was loaded with products
from every manufacturer even remotely involved with electronics. Virtually every
watchmaker, TV manufacturer, or major chip vendor had a product offering in this
area. Most of these forgettable products used the CP/M operating system, and those
that did not favored proprietary operating systems that have not seen the light of
day since. The industry sadly lacked microcomputer standards.
Rumor has it that when IBM went shopping for an operating system, it first turned
to Digital Research. Digital Research, however, was sitting happily on what it believed
to be the top of the microcomputer heap, so it did not agree to the terms IBM offered.
Much to its surprise, IBM then went to Bill Gates at Microsoft Corporation. Mr. Gates,
in turn, went out and purchased ownership of another company's operating system.
Thus, PC-DOS--and MS-DOS--was born.
The IBM PC included up to 640K (kilobytes) of memory, which was ten times the
memory offered by most of the 64K CP/M machines. For storage, it featured a 5.25-inch
floppy disk drive and the inevitable interface to a cassette tape recorder. To hurry
the product to the market, IBM even turned to the Far East to supply some of the
components. To increase the availability of applications, IBM appealed to key software
companies to develop or port their products to the IBM PC.
IBM followed up on its original PC design with the PC/XT (Extended Technology)
in 1983. The PC/XT introduced some relatively minor design changes in the original
PC board but served to bring hard disk technology to the PC through the inclusion
of a full-height (but slow at 85 ms) 10M hard disk drive. In the same year IBM released
the scaled-down version of its the PC, called the PCjr.
In 1984, IBM released the IBM PC/AT (Advanced Technology). While the changes between
the original PC and PC/XT were relatively small, the changes between the PC/XT and
PC/AT were relatively large. First and foremost, the IBM PC/AT used the Intel 80286
processor instead of the PC/XT's 8088 processor. Second, the input/output bus (used
for such option boards as the display adapter and disk controller) was improved to
contain both 8-bit and 16-bit slots (the PC and PC/XT contained only 8-bit slots).
By 1987, the PC market had grown to unbelievable proportions, and IBM was quickly
losing market share. IBM's market was being eroded by American manufacturers such
as Compaq Computer Corp. and AT&T; by a massive number of off-shore (Taiwanese
and Korean) manufacturers marketing through large companies, such as Leading Edge
Hardware Products Inc.; and by small, garage-type operations. IBM sought to retrench
its position by redesigning the architecture of the PCs, using a closed architecture
that would force other manufacturers to sign license agreements with IBM if they
wanted to use the same technology.
The result of IBM's research was announced in 1987 as the Micro Channel Architecture
of IBM's Personal System/2 (PS/2) line--the replacement to the PC line. Shortly after
the announcement of the PS/2 series, IBM discontinued the PC/XT and PC/AT models.
Despite this discontinuation, the ISA Bus, (based on the AT bus) is still the most
common PC bus design. The Micro Channel Architecture offers many advantages over
the ISA Bus design. It provides for a large channel bandwidth, and includes an arbitration
mechanism to prevent a single adapter from taking over the system. Other features
of the Micro Channel Architecture include automatic configuration and a streaming
technique that allows an address line to be used as an additional data line, effectively
doubling channel throughput.
In addition to the change in hardware architecture, the PS/2 also served as the
launching platform for a new multitasking operating system, Operating System/2 (OS/2).
Despite the announcement of OS/2, however, IBM has continued to offer the popular
PC-DOS operating system. In fact, when IBM introduced the PS/1 home computer in 1990,
PC-DOS was the only operating system option.
There are two families of PCs now offered by IBM--the 300 and the 700 family.
The high-end systems have a Pentium or Pentium Pro processor, PCI busmaster device
controller, 6X CD-ROM, and 4M of Video memory. Networkable with optional Ethernet
and Token Ring cards, the 700 provides networking and communications features and
enhanced graphics.
Engineering Workstations
Engineering workstations are the weakest area of the IBM product line. IBM's initial
RISC-based offering, the RT-System, was introduced in 1986 in the wake of IBM's sweeping
success in the PC market. To a certain extent, IBM was hoping that the RT would ride
on the coattails of the PC and become a success by association. The RT's alignment
with the PC family is evident in its capability to use PC/AT adapter cards. As with
many other engineering workstations, a co-processor option enables the RT to run
PC-DOS concurrently with its native operating system, AIX. Unfortunately, the RT-System
lacked sufficient innovation or price/performance advantage to rise to the top of
the heap, and it never became a commercial success.
The RT line used a RISC architecture. As noted, the entire line ran the AIX operating
system, IBM's version of UNIX. IBM's enhancements to AIX include support for up to
one terabyte (one trillion bytes) of virtual memory and up to 16M of real memory.
IBM has also addressed connectivity of the RT to other systems by including the SNA
Logical Unit 6.2 (LU 6.2) interface and support for both IBM Token Ring and TCP/IP
over Ethernet.
In early 1990, IBM totally revamped its engineering workstation line with the
introduction of the RISC System/6000 (RS/6000) family of workstations and servers.
Modern developments in RISC technology enabled the RS/6000 line to offer a dramatic
performance increase over the older RT technology. The RS/6000 family runs the AIX
operating system and is divided into two lines: Powerstation and Powerserver models.
Powerstation models are targeted at individual workstation users, while the Powerserver
models are intended to serve multiple users.
The Future of the RS/6000
New offerings in the RS/6000 line include a PowerPC-based workgroup and Internet
server, and the introduction of multiple operating system options. Other new announcements
include a multimedia software offering, which delivers multiple audio and video streams
from the RS/6000 server to a variety of desktop clients over LANs and internetworks.
IBM is also planning to incorporate Sun Microsystems' Java technology with the AIX
operating system, so Java applets can be sent to clients across the corporate intranet
or the public Internet. Another new feature will provide access to tape devices,
and consolidate tape operations across a network of RS/6000 workstations. This creates
a pool of tape resources, and facilitates centralized tape management.
The RS/6000 family runs from low-end ThinkPads, to workstations, to the high-end
symmetric multiprocessor and parallel processing computers (all running the same
version of AIX), making it one of the most scalable lines of RISC-based systems available.
The RS/6000 supports multiple operating systems, including IBM AIX, Windows NT, and
SunSoft Solaris. At the high end, the RS/6000 can function as an application or data
server, and can be optimized for transaction-oriented applications; or for graphics-intensive
workstation usage such as CAD or scientific visualization. It may also be applied
to OnLine Transaction Processing (OLTP) applications, which process transactions
in real time as they are received by the system.
Midrange Offerings
If you liked the television series M*A*S*H, then you'll love the AS/400--or so
thought IBM when they used Alan Alda in prime-time commercials and high-visibility
print ads as they brought the AS/400 to market. The early and overt commercialization
of the AS/400 shows clearly that IBM is targeting the product toward the general
business community. The emphasis is on multi-user business solutions and upward growth
(or the perception of it, anyway).
Understanding this orientation is significant when you evaluate IBM's midrange
offerings against Digital's and HP's. While HP and Digital offer products focused
toward the technical environment, IBM offers products focused on the business environment.
Given the scale of these types of systems, it is not at all unusual to find an IBM
midrange processor in the front office and a DEC VAX in the lab, even in smaller
businesses. Of course, the coexistence of VAX computers with IBM mainframes is commonplace
in larger businesses.
In those dinosaur days before the AS/400, IBM offered two lines of midrange systems--the
System/36 and the System/38. The System/36 ran an operating system called System
Support Program (SSP) that featured, among other things, a menu-driven user interface
that was simple and straightforward to use. Additionally, the System/36 featured
connectivity options specifically geared toward the integration of PC networks with
the System/36.
The System/38, on the other hand, was more upscale. It ran the Control Program
Facility (CPF) operating system, which featured an extensive programming environment
and an integrated relational database. The System/38 was geared for connectivity
to mainframe systems.
All things considered, the two offerings were very similar in many categories,
but not similar enough overall. For example, although IBM offered migration provisions
to facilitate a move from a System/36 to a System/38, this migration was just painful
enough to be avoided. To make the jump, you had to modify and recompile programs;
and worse, the two systems' databases were not totally compatible. These differences
formed a chasm wide enough to keep both product lines on the market simultaneously
(much to IBM's chagrin).
The AS/400 was created to provide easy migration for all midrange users. The AS/400
borrowed more from the System/38 design than it did from the System/36, although
many areas (like connectivity) are supersets of both capabilities. In a nutshell,
the AS/400 combines the easy-to-use menu-orientation of the System/36 with the programming
and database environment of the System/38.
Programs from the System/38 can run as is on the AS/400 (again attesting to the
closeness between the AS/400 and System/38). IBM implemented improved migration aides
for the operating system, OS/400, to enable System/36 programs to move to the AS/400
but, at a minimum, the programs have to be recompiled (and in some cases, rewritten)
first. To further garner support for the AS/400, IBM offered third-party software
developers AS/400 access and technical assistance to move their programs to the AS/400
before its official release. As a result of this effort, the 1988 AS/400 announcement
included support for thousands of ready-to-run business applications.
The new AS/400 Advanced 36 (See Figure 4.1) offers a gradual migration path for
S/36 users by enabling up to three System/36 configurations to run with an AS/400.
Under this configuration, System/36 users can use their existing applications while
still accessing the advanced features of the AS/400 operating system.
FIG. 4.1 IBM AS/400 Advanced 36
After a seemingly successful two-and-one-half years with the AS/400, IBM revamped
the product line and made the first major version change in the OS/400 operating
system. Announced in April 1991, the D-series AS/400 models offer dramatic improvements
in price/performance ratios, and high-end D-series models cross over into the domain
of mainframe computing power. Beyond the feature content, IBM's marketing program
behind this new lineup clearly was oriented at moving any remaining System/36 and
System/38 users over to the AS/400 architecture, as well as extending the AS/400's
reach into other midrange environments.
The System/3X products and the AS/400 support the 5250 terminal family as the
preferred workstation line. However, the System/36, System/38 and AS/400 all have
special provisions built into their operating systems to handle 3270-type terminals.
The newest incarnation of the AS/400, the AS/400 Advanced System, supports high-speed
communications and includes support for wireless LANs and an Integrated Fax Adapter.
The Advanced System now runs the powerful 64-bit RISC PowerPC AS microprocessor.
Existing applications can run unchanged on the Advanced System. The AS/400 includes
IBM's AnyNet architecture, which permits communications over several public and private
networks. It supports SNA, TCP/IP, IPX, Token ring, Ethernet, and other protocols.
Some other additions include:
- Web connection for OS/400. Permits the AS/400 to function as a Web server
on the Internet, and function as a repository for images and other data.
- Support for high-speed communications. Includes network adapters for 16/4
Mbps token ring Ethernet II or IEEE 802.3, FDDI, and Shielded Twisted Pair Distributed
Data Interface. In addition, the High Speed Communications Adapter can support T1/J1
or E1 communication over Frame Relay, or point-to-point SDLC lines.
There are a number of models in the Advanced Series, including:
- Model 300, 310, and 320. These models include the System Power Control
Network (SPCN) and Redundant Array of Inexpensive Disks (RAID-5) storage capability.
All three have multiple processor options and modular designs.
- Model 400. This high-performance machine boasts 32M of main storage and
1.96G of DASD (Direct Access Storage Device) in the base configuration.
- Models 500, 510, and 530. These models support higher main storage and
DASD, and can accommodate up to 200 communications lines.
- Models 20S and 30S, 40S, 50S, 53S. These are used primarily as departmental
servers. Under the client/server strategy, the processing is shared between the AS/400
and intelligent clients. With Client Access/400 (formerly PC Support), client/server
and traditional AS/400 applications can run side by side. The AS/400 is easy to install
in an existing SNA or TCP/IP network, and can be used to manage a distributed client/server
network. Supports a LAN Server/400 option for high-performance file serving to connected
PCs. Since this service is tied to the operating system, one administrator can manage
multiple LAN services from a central location. When deployed on a client/server network,
it can be an application server, database, communications, print, or network management
server for OS/2, Windows, DOS, UNIX, AIX, and Macintosh workstations.
- Model P03. This 22 pound, entry-level system has connections for up to
16 workstations. It is available for Token Ring or Ethernet LAN configurations supporting
16 workstations, or twinax configurations supporting 14 workstations.
Top-end Offerings
IBM's mainframe history began with the System/360 line; the success of the System/360
line led to the development and release of the System/370 in 1970. The System/370
introduced virtual storage to the IBM mainframe lineup. Its architecture became the
foundation for the high-end 3030, 3080, and 3090 lines, as well as the lower-end
4300 and 9370 lines.
The 20-year dynasty of the System/370 architecture ended in 1990 when IBM introduced
its System/390 architecture. The System/390 offered dramatic improvements in performance
from improved processor technology and the use of fiber optic links for high-speed
channel communications. At the same time it made the introduction, IBM unveiled a
new family of mainframes under the name ES/9000. The ES/9000 is a broad line targeted
to replace the older 9370, 4300 and 3090 lines. When IBM released the ES/9000 line
in 1990, the initial models did not feature the improved processor technology but
did offer fiber optic channels.
IBM shipped more large system processors in 1995 than ever before, primarily due
to a surge in S/390 shipments. IBM was the first to adopt complementary metal oxide
semiconductor (CMOS) technology for its large commercial computers. CMOS-based machines
are less expensive to make and more efficient than the older bipolar mainframe technology.
It requires less system cooling and takes up about 75 percent less floor space compared
to the bipolar technology. The S/390's Coupling Facility can link two or more CMOS
servers to form an IBM Parallel Sysplex environment, a large system image that can
combine up to 32 servers, each running 10 CMOS microprocessors.
The OS/390 operating system includes products for systems management and distributed
computing. The integration of VTAM, AnyNet and TCP/IP provide added flexibility,
and enable the S/390 server to manage information across a multivendor network. OS/390
has an optional Security Server to prevent unauthorized access and ensure data integrity.
Multiple S/390 processors can be coupled as a single system, with data sharing
and workload balancing. This method ensures a high uptime because there is no single
point of failure.
Efficient backup is facilitated through its massive data storage capability, and
users can dynamically add storage and processing without having to shut down the
server. Print jobs can be distributed from NetWare LANs to S/390 printers, so the
host system can access attached LAN printer resources.
IBM first started experimenting with CMOS in its laboratory in Germany in 1983
and first deployed it in its S/370 air-cooled mainframes in 1986. In 1990, CMOS technology
broke into the ES/9000 line. In 1994, IBM introduced its Parallel Enterprise Servers,
Parallel Transaction Servers, and Parallel Query Servers--all based on the CMOS technology.
Initially, CMOS technology complemented bipolar technology in the entry-level and
midrange arena, and it later moved to the high-end mainframe market. The older bipolar
technology had been used for more than 25 years; CMOS can either replace or coexist
with bipolar technology. CMOS uses far fewer parts than bipolar technology, which
lowers the cost of computing. The S/390 CMOS microprocessors are compatible with
existing systems and use up to 97 percent less energy--about the amount of electricity
used by a household refrigerator. CMOS is more reliable than bipolar--the S/390 Parallel
Enterprise Server, for example, has a failure rate of less than once every 20 years.
Also, unlike the older machines, no raised floors are required, and it uses significantly
less floor space.
The three operating systems most prevalent on the IBM mainframes are the following:
- Virtual Storage Extended (DOS/VSE). The oldest of the three operating
systems, DOS/VSE is most often found on 4300 Series machines. DOS/VSE supports a
suite of subsystems similar to those of MVS.
- Multiple Virtual Storage (MVS). Usually found in business environments
at the top end of the line. MVS is a direct descendent of the OS/VS2 originally released
with the System/370. The popularity of MVS stems primarily from its suitability for
running business applications.
- Virtual Machine (VM). VM is unique in its capability to host other operating
systems (thus, MVS can run underneath VM).
Each operating system has, in turn, its own set of variations. For example, MVS/Extended
System Architecture (MVS/ESA) is different from MVS/Extended Architecture (MVS/XA)
and both are, in turn, quite different from MVS/System Products (MVS/SP). The differences
in the versions rest in the capacities of the virtual storage environments they can
manage and therefore the size and number of programs they can run. The bottom line
is that two machines running MVS might not be equivalent.
Both VSE and MVS share the same basic operating philosophy and architecture (see
Figure 4.2).
FIG. 4.2 Traditional IBM O/S Environment
Running underneath the operating system are the following major subsystems:
- Virtual Telecommunications Access Method (VTAM). VTAM controls the flow
of information from the terminal network to the programs. It also plays a major role
in sites that use IBM's Systems Network Architecture (SNA). The packages that existed
before VTAM and provided similar functions include Basic Telecommunications Access
Method (BTAM), Remote Telecommunications Access Method (RTAM) and Telecommunications
Access Method (TCAM). IBM is planning to add TCP/IP features to VTAM, enabling it
to control multivendor traffic.
- Job Entry System (JES). JES is responsible for the batch environment of
the mainframe. It processes jobs submitted from local terminals or Remote Job Entry
(RJE) workstations (specialized devices that have their own input and output capabilities).
For example, JES can be used to receive the day's transactions from a remote bank,
update the information on the central files, and then send a printed report of the
activities back to the remote bank. In MVS environments, JES might be known as JES2
or JES3 (for Releases 2 and 3). Under VSE, the job environment is handled by Priority
Output Writers, Executions Processors and Input Readers (POWER). Other memorable
implementations of job-handling packages include Attached Support Processor (ASP)
and Houston Automatic Spooling Program (HASP).
- Time Sharing Option (TSO). TSO provides an interface to terminals to enable
program development and data file management. TSO is one of the most widely recognized
ways of interfacing with a mainframe. Furthermore, within TSO is a menu-oriented
utility named Interactive System Productivity Facility (ISPF) that provides a simple
and easy- to-understand way of accessing TSO functions. Also note that TSO is capable
of submitting jobs to the JES and monitoring their progress.
- Customer Information Control System (CICS). CICS implements transaction-based
routing between the terminal network and the application programs. Essentially, CICS
receives input from terminal users and then decides which application program is
responsible for processing each user's transaction. Once determined, CICS delivers
the transaction to the program. A program must be written specifically to run under
CICS. CICS has become a de facto industry standard, and because several vendors write
applications to CICS, it can be used to share information with non-IBM systems.
The VM operating system, on the other hand, carves the mainframe into multiple,
virtual machines. Each user sees his or her own virtual machine and, more important,
virtual machines can support other operating systems, such as VSE and MVS (see Figure
4.3).
FIG. 4.3 IBM VM Environment The subsystems
that work under VM include:
- Control Program (CP). CP is a central management facility for system resources.
- Conversational Monitor System (CMS). CMS provides the communications between
the user and CP. CMS is responsible for managing a user's virtual machine (or hosting
another operating system). Multiple copies of CMS facilitate multiple virtual machines.
- Group Control System (GCS). GCS is similar to CMS in that it is a virtual
machine supervisor. GCS is used normally to host SNA-oriented subsystems, such as
the Advanced Communications Function for VTAM (ACF/VTAM). This is the preferred methodology
for implementing SNA in VM environments.
- Remote Spooling Communications System (RSCS). This is VM's job entry facility.
RSCS runs in conjunction with the GCS.
In terms of terminal support, all of these mainframe systems are normally used
with the IBM 3270 line of terminals.
Strategy for Connectivity
IBM unleashed its Systems Network Architecture (SNA) on the public in 1974. Before
this occasion, the IBM world of data communications was filled with byte-oriented,
synchronous protocols, such as the now-classic bisynchronous 3270-terminal protocol
and the bisynchronous 2780 and 3780 RJE protocols. With the introduction of SNA,
however, IBM replaced these protocols with bit-oriented Synchronous Data Link Control
(SDLC) protocol variations, and the relationships between the various communications
devices became more strict and formal.
In terms of topology, SNA was originally a networking architecture that featured
a central host as the control point. It was continually refined and expanded in subsequent
releases to support networks with multiple hosts and to facilitate host-to-host communications.
Under SNA, each participating device is given a physical unit (PU) definition that
establishes its role in the hierarchical relationship between the terminal and the
host (see Figure 4.4).
The PU definitions are as follows:
- Physical Unit Type 2. PU 2 defines a device that controls workstations.
This includes the traditional IBM cluster controllers (for example, 3274 and 3174)
as well as the System/3X and AS/400 midrange systems.
- Physical Unit Type 2.1. PU 2.1 is a refinement to SNA that was added to
enable peer-to-peer communications between intelligent PU 2 devices, such as midrange
systems, PCs and PS/2s. This is an integral part of the Advanced Peer-to-Peer Networking
(APPN) aspect of SNA.
- Physical Unit Type 4. A PU 4 device is a communications controller or
front-end processor (for example, 3705 and 3725). This is a mainframe-oriented device
that interfaces with the PU 2 and PU 2.1 devices which, in turn, interface with the
actual terminals and workstations.
- Physical Unit Type 5. A PU 5 device is a host (mainframe) processor that
provides global services to the SNA network. These devices sponsor the System Services
Control Points (SSCPs).
NOTE: Physical Unit Type 1 and Physical Unit Type 3 have no validity
in the modern SNA architecture. n
While PUs describe network devices that provide physical services, SNA logical
units (LUs) define the contents of the data stream (information flow) between the
PUs. LU definitions include the following:
- Logical Unit Type 0. LU 0 is used for unregulated, direct-link communications
between two entities in the network (typically two programs). Any two programs using
the LU 0 information flow must be programmed to define and use the same format for
the information.
- Logical Unit Type 1. LU 1 refers to the format of data sent to and received
from specialized data processing workstations (such as RJE stations).
FIG. 4.4 SNA Physical Units
- Logical Unit Type 2. LU 2 defines the format of data sent to and received
from the 3270 family of workstations.
- Logical Unit Type 3. LU 3 describes the format of data sent to the 3270
family of printers.
- Logical Unit Type 4. LU 4 refers to the format of data sent to and received
from dedicated word processing workstations.
- Logical Unit Type 6.1. LU 6.1 is for program-to-program communications
using one of the following SNA data formats: character string, 3270 workstation,
logical message services, or user-defined.
- Logical Unit Type 6.2. LU 6.2 is also for program-to-program communications.
Programs using the LU 6.2 definition can use either an SNA general data format or
can define and use their own data format.
- Logical Unit Type 7. LU 7 defines the format of data sent to and received
from the 5250 family of workstations.
NOTE: The Logical Unit Type 6.2 is often used with Physical Unit
Type 2.1 for Advanced Program-to-Program Communications (APPC). Under this approach,
the PU 2.1 devices establish a peer-to-peer connection and then a program running
on each device initiates an LU 6.2 conversation. In support of this, IBM supplies
a library of LU 6.2 calls to facilitate programming the LU 6.2 interface. n
Beyond the introduction of many new concepts and terminology, the biggest immediate
change that SNA posed to IBM customers was the switch from the well-understood, byte-oriented
protocols to the bit-oriented Synchronous Data Link Control (SDLC) protocol and its
variations.
Under the older bisynchronous formats, the information physically transmitted
and received was relatively easy to understand because at its core was the actual
data being transferred in its native character format. Surrounding that basic data
were additional control characters that signaled the start of data, start of field,
the field attributes, end of field, end of data, and so on. By sitting at a simple
line monitor, a technician could see and identify the data itself.
Unfortunately, this approach has severe limitations. For example, if the information
being sent is binary, it might turn into control characters when it is prepared for
transmission. Because it is inappropriate to have an end-of-data control character
in the middle of the data, additional structures and control characters must be inserted
to handle these special cases. This need for special processing often greatly increases
the amount of data transmitted and also requires an additional amount of processing
overhead before transmission.
To address these and other concerns, IBM developed the bit-oriented SDLC protocol.
Under SDLC, data is not interpreted on a byte-by-byte basis; rather, it is interpreted
as a series of bits, with control bits at the beginning indicating the size and length
of the bit patterns to follow. This bit-level approach to data communications easily
handles standard terminal input/output information as well as the special problems
posed by binary data.
In fact, IBM was so pleased with its SDLC implementation that it submitted SDLC
to the ANSI and ISO standards organizations for their approval. ANSI modified the
basic SDLC definition and called it Advanced Data Communications Control Procedure
(ADCCP), which is used today by many government organizations. ISO changed it into
High-level Data Link Control (HDLC) and it is a model for many other computer manufacturers'
communications protocols. Finally, the Consultative Committee for International Telegraphy
and Telephony (CCITT) further modified HDLC into Link Access Procedure (LAP) and
then into LAP-B (LAP-Balanced) as part of its X.25 network definition.
In SNA, SDLC is the main communications protocol used by workstations, controllers,
and front-end processors alike. To accommodate the variety of devices (3270 versus
5250, for example), SDLC then carries the LU and PU assignments of the transmitting
and receiving devices. Thus, an SDLC transmission can be identified as coming from
a 3270 (LU 2) on a cluster controller (PU 2).
Another connectivity strategy is IBM's MQSeries, a messaging middleware that is
used to connect applications across dissimilar environments. Different programs are
capable of communicating with the MQSeries API, a high-level interface that shields
developers from the various complexities of the different operating systems. MQSeries
is often used by institutions, such as banks, that need to handle large numbers of
transactions. Messages can be placed on queues and retrieved from queues instantly,
and delivery is registered to ensure reliability.
APPN (Advanced Peer-to-Peer Networking)
APPN is a creation of IBM, which it originally positioned as the successor to
SNA. APPN is used mostly in AS/400 environments, although it can support a mainframe
network in a limited fashion. However, APPN is not able to provide native support
for SNA 3270 datastreams, which makes up most mission-critical traffic.
Cisco Systems and Bay Networks, two major router vendors, both managed to overcome
this limitation by enabling a routed APPN network to support SNA traffic from any
SNA device. Without this solution, each device must contain its own dependent LU
Requestor (dLUR) software. dLUR software is not widely available--it is offered only
for 3174 controllers and OS/2 PCs. Cisco's and Bay's approach provides support for
any SNA device, regardless of whether it possesses the dLUR software. With Cisco
and Bay bridge/routers, it will be possible to run an APPN-based multiprotocol system
that can support SNA traffic.
APPN has a number of strengths. It offers peer-to-peer networking, it can dynamically
discover remote destinations, and it has a traffic prioritization mechanism. However,
APPN does not support dynamic alternate routing. APPN might still be a good solution
for complex networks because of its dynamic destination discovery service.
High-Speed Networking
IBM is working towards supporting Asynchronous Transfer Mode (ATM) in LAN/WAN
environments. Price is one major barrier to wide area ATM, but another is the amount
of work required to interface ATM with legacy networks.
IBM's solution for joining ATM with its SNA/APPN installed base uses the High
Performance Routing (HPR) feature to provide native access to wide-area ATM networks
for SNA/APPN. SNA is well suited for interfacing with ATM because of its service
features. However, SNA routing is less suited to high-speed networking. HPR fills
in for this area. IBM proposes that the native interface to ATM be through the HPR
feature. Mainframe SNA and APPN would connect directly to ATM using either LAN emulation
or Frame Relay emulation.
HPR is an open technology for routing data quickly and efficiently. The technology
combines some features of APPN, frame relay, IP, and SNA. In case of a link failure,
HPR's built-in rerouting capabilities relieves network managers from having to physically
reroute sessions . In addition, HPR supports SNA priority and class-of-service features.
HPR can run on existing hardware, and interoperates with existing SNA and APPN products.
HPR uses three separate techniques to improve data routing: Rapid Transport Protocol
(RTP), Automatic Network Routing (ANR), and Adaptive Rate-Based (ARB) congestion
control. RTP, a connection protocol, supports data transfer over a high-speed network.
RTP automatically establishes end-to-end connections and generates the appropriate
routing information. In the event of failure, RTP will detect the failure, and recalculate
the path dynamically and automatically. Data that was sent at the time of failure
will be automatically recovered.
ANR is a connectionless protocol used in the intermediate nodes of the HPR subnet.
The ANR technology helps to control congestion between the various RTP endpoints
by monitoring the amount of data flowing between the endpoints, and making adjustments
to ensure against overload. ARB also guards against congestion by sending data only
in measured amounts, as opposed to uncontrolled bursts.
Application/User Relationship
From the simplest of perspectives, the relationship between IBM users and applications
is highly structured, highly controlled and menu-oriented. This is true of both the
midrange (System/3X and AS/400) and the System/390 environments because both types
of terminals (5250 and 3270) are block-oriented. Typically, users access the system
and run the program they desire. Although accessing the program can be done in a
conversational manner (as with TSO), the actual application program or utility normally
uses some type of full-screen input/output.
Although IBM's environment is multiuser, each user's activities should not be
construed as sessions, such as those with HP and DEC architectures. With sessions,
users perceive that they have the computer to themselves and that their applications
seem to function independently from other activities. In a multiuser environment
like IBM's, each user accesses the system and then is given a controlled set of choices--
the system guides the user through the selection process based on the user's profile.
Another key difference between the session-oriented computers and IBM computers
is the level at which shared access to a program or system service occurs. With DEC
and HP computers, each person runs, in effect, an individual copy of the program
that shares system resources at a level typically below the visibility of the user.
With IBM, this sharing occurs on a higher plane. In most cases, in fact, programs
on IBM systems are written to accommodate concurrent access from multiple users.
The actual appearance of the user interface and the development of programs are
disparate among the IBM platforms. Developing a program on an AS/400, for example,
has a dramatically different approach and appearance than developing the same program
on a 3090. These differences pose a real problem to IBM because it often prohibits
an AS/400 customer, for example, from upgrading to a 9370, because the customer's
AS/400 programs would not be compatible with the 9370 architecture (nor would the
user's programming staff be competent with the new system).
To address this issue and to provide IBM-wide standards for programming and the
program's appearance to the user, IBM introduced its Systems Application Architecture
(SAA). SAA is a set of routines and transport mechanisms that (theoretically) makes
it possible to develop and implement a program on one platform--a PS/2, for example--and
then move that program to another platform--say, a 9370--with minimal effort. SAA
programming routines perform the following functions:
- Provide a common means of accessing files and database information (regardless
of where they reside).
- Supply a consistent way to access a terminal (regardless of the terminal's location).
- Define and implement both a universal character (workstation) and window-based
(graphics) appearance to the user.
The full definition of SAA specifies and defines the underlying formats and transport
mechanisms upon which these three higher-level functions rely. The term SAA-compliant
indicates that a particular feature or function is included in the SAA definition.
For example, the LU 6.2 interface is deemed SAA-compliant but LU 0 is not. Also note
that the actual implementation of SAA is a long-term strategy that involves releasing
pieces of SAA as time progresses.
Terminal Attachment Philosophy
IBM uses a hierarchical architecture between terminals and computers. This architecture
is similar in the midrange systems and mainframes, although the midrange implementation
cannot accommodate the large numbers of terminals supported by the mainframe architecture.
In the mainframes, the 3270 family of terminals and printers is the backbone of
the user interface. In Figure 4.5, terminals attach to a cluster controller (also
known as a remote control unit) via coaxial cable. Some example workstation controllers
include the 3174, 3274, and the 3276 (which also features a built-in terminal). Each
cluster controller can support multiple terminals and printers (typical numbers include
8, 16, and 32, although cluster controllers can be configured to support larger numbers).
FIG. 4.5 IBM 3270 Connectivity
Each cluster controller interfaces to the central mainframe (or a remote front-end
processor). At the central site, the actual interface can be an Integrated Communications
Adapter (ICA) for smaller networks or a front-end processor in larger networks. With
the exception of small 4300 sites, the interface is normally to a front-end controller
such as a 3705, 3720, 3725, or 3745.
The front-end communications controller is in itself an intelligent device. The
front end runs software called the Network Control Program (NCP), which defines and
controls the network. The NCP interfaces with VTAM (or some communications access
method subsystem) in the host. The attachment between the front-end processor and
the mainframe is a high-speed channel that facilitates a larger volume of high-speed
data.
For the 5250 family of terminals and printers used with midrange systems, the
architecture is similar but not identical. Like the 3270s, the 5250 terminals attach
to a controller, but they use a twinaxial cable connection that daisy-chains the
terminals on the cable to the controller (see Figure 4.6). In smaller networks, the
controller is integrated directly into the midrange computer. In larger networks,
remote controllers (5294 or 5394) serve to funnel the terminals back to the midrange
host.
FIG. 4.6 IBM 5250 Connectivity
The critical difference between the midrange and mainframe terminal architectures,
however, is the midrange's lack of a front-end communications processor. This device
enables mainframes to handle large terminal networks.
NOTE: Both product families use SDLC as their communications methodology.
Messages from the 3270 family are carried in the LU 2 and LU 3 formats, while messages
from the 5250 family are carried in LU 7 format. n
Peer-to-Peer Relationships
Given the hierarchical nature of SNA and its structured PU layout, it is sometimes
difficult to determine what is a peer to what else, let alone what relationship those
two peers can have. Previously in this chapter, the fundamental concepts of PU 2.1,
APPN, LU 6.2, and APPC were presented. However, it is often unclear how (or if) these
topics are related.
Recall that a Physical Unit Type 2.1 device is an intelligent device capable of
conversing with other PU 2.1 devices and is also capable of routing or rerouting
messages through other PU 2.1 devices. Application Peer-to-Peer Networking (APPN)
describes the interaction between PU 2.1 devices. A Logical Unit Type 6.2 is a data
format that enables two programs to communicate across SNA. A program implementing
the LU 6.2 interface must reside on a system that is operating at either the PU 2.1
or PU 5 level. Application Program-to-Program Communications (APPC) describes LU
2 conversations.
In addition to these concepts and implementations, SNA also supports the following
interactions, which can be considered peer-to-peer:
- SNA Distribution Services (SNADS). As the name implies, SNADS is a distribution
service used to move information, such as documents, electronic mail, and files,
throughout the SNA physical network. Please note, however, that the information sent
through SNADS must be selected for distribution and that the distribution does not
occur on demand (like the U.S. mail, things get there when they get there). SNADS
uses both APPC and APPN as part of the delivery mechanism.
- Network Job Entry (NJE). NJE exists above the Job Entry System (JES) and
is used to distribute the processing aspects of batch jobs among systems. In other
words, NJE links JES processing systems to form a loosely coupled batch system. With
NJE, a job can be submitted on System A, processed on System B, and printed at System
C. NJE uses bisynchronous links, SDLC links or direct channel-to-channel attachment
to facilitate the communications between systems.
- Distributed Data Management (DDM). DDM is used primarily in the midrange
systems. DDM is a shared-file product that enables midrange systems to share access
to data files on a file or record basis. DDM can be run over a Token-Ring network
or over SDLC lines. Support for DDM is also available for versions of CICS, thus
enabling mainframes and midrange system to share file-based information using DDM.
Again, given the size and complexity of SNA, other peer-to-peer facilities are
available. The capabilities presented herein, however, are the most commonly used.
PC Integration Strategy
IBM has adopted the IEEE 802.5 Token-Ring specification as the basis for its PC
and PS/2 LAN implementation. This ring topology features a central ring from which
devices (such as PCs and PS/2s) are attached (see Figure 4.7). In this LAN architecture,
a token is passed along the ring. When a unit stops transmitting or has nothing to
transmit, it relinquishes the token to the next unit on the ring.
FIG. 4.7 Token-Ring Topology
The original IBM Token-Ring implementation operated at a rate of 4 Mbps. A higher
data rate, 16 Mbps, was made available in the late 1980s. To make the physical attachments
to the ring easier, additional concentrators and attachment units were released.
Two common units are the eight-port medium access unit (MAU) and the two-port hub;
these units extend the ring without corrupting its fundamental topology. Gateways
and bridges can be used to tie two or more Token-Ring networks together.
With the physical Token-Ring LAN, stand-alone PC networks can be implemented using
IBM's network software or other network software such as Novell's NetWare. To incorporate
a Token-Ring LAN into a global SNA network, however, IBM's networking software must
be implemented with attachments to the SNA network. The nature of this attachment
depends on the processor or terminal types closest to the LAN.
For example, in a small midrange environment, a Token-Ring LAN can be connected
to the midrange via a midrange interface controller. In this case, the midrange system
actually participates in the Token-Ring LAN; a PC product named PC Support is available
to enable the PCs or PS/2s to access the midrange applications and files. (Moreover,
when multiple midrange processors are present on a Token-Ring LAN, special peer-to-peer
capabilities are available to share files and log on to the various systems.)
In larger SNA networks, however, the attachment of the LAN to the network depends
on the location of the Token-Ring LAN. If the Token-Ring LAN is remote to the central
mainframe, it can be attached to the remote cluster controller, which acts as a gateway
to the SNA network. If, however, the LAN is near the central processor, it might
also be connected to the front-end communications processor, which serves this gateway
function.
For a more detailed comparison of the Token-Ring topology to other topologies
(such as CSMA/CD), refer to Chapter 7, "LANs and WANs" (p. 139).
Office Automation
IBM offers several products to address the area of office automation. Its two
basic products that offer office functions (a calendar, electronic mail, information
management, and so on) are the following:
- PROFS (PRofessional OFfice System). PROFS is a software package available
for the VM operating system. Because PROFs depends on VM and because VM is not usually
implemented on larger mainframes, the 9370 is often the host of choice. PROFS exchanges
messages with other mail systems through SNA Distribution Services (SNADS) or DISOSS.
- AS/400 Office. AS/400 Office is a software package for the AS/400. AS/400
Office exchanges messages with PROFS or through SNADS or DISOSS (Distributed Office
Support System).
To provide an office automation solution that integrates PC and PS/2 functions
with the PROFS and AS/400 Office products, IBM developed OfficeVision. Like HP's
NewWave Office, OfficeVision is a distributed solution that integrates the core services
of PROFS or AS/400 Office with a network of PCs or PS/2s. OfficeVision was introduced
as the first SAA-compliant IBM solution.
While both PROFS and AS/400 Office provide office automation features, the Distributed
Office Support System (DISOSS) is also important to IBM's office automation strategy
and its capability to interface with other non-IBM systems. DISOSS enables you to
tie together a wide variety of word processing packages, office automation software,
and non-IBM products. In a nutshell, it provides distribution and library services
specifically for handling documents. DISOSS is not an electronic mail facility like
PROFS and AS/400 Office; it is a network-wide document management facility.
DISOSS, AS/400 Office, and PROFS support a document format known as the Document
Content Architecture (DCA). DCA defines the structure for revisable documents (documents
that contain the entire editing history) and final-form documents (documents that
are the final result of all edits). DCA establishes a common ground that most word
processing systems can use. When DCA is coupled with DISOSS, documents can be imported
and exported from virtually any source. For example, both HP and DEC support DCA
document conversion in their word processors and also support DISOSS document exchange.
Also note that the term Document Interchange Architecture (DIA) is often used
with DCA and DISOSS. DIA is the least known of IBM's three major distribution services
(SNADS, DDM, and DIA). Whereas SNADS is a general-purpose distribution service and
DDM is oriented toward record-level and file-level access in midrange systems networks,
DIA is oriented toward the distribution and systematic storage of documents.
In most cases, SNADS is the facility through which electronic mail is distributed
between systems. For example, if a PROFS message is sent to AS/400 Office, SNADS
usually provides the delivery mechanism.
FIG. 4.8 Typical IBM SNA Network
Network Architecture
A typical SNA physical network might contains a mainframe (3090 or 4300), a 9370,
two AS/400s and some PS/2s or PCs. Each of these types of systems supports direct
or indirect attachments to an SDLC-based SNA network, a Token-Ring LAN and an Ethernet
(or IEEE 802.3) LAN. Standard SNA supports SDLC, X.25 and Token-Ring. The Ethernet/802.3
connections, in turn, can be used to implement IBM's variation of TCP/IP for multivendor
connectivity (see Figure 4.8).
The mainframe supports connectivity to the terminal network via a front-end processor
(the 3725 in Figure 4.8). From the 3725, connections can be made to the following:
- An X.25 network.
- Multiple, remote cluster controllers (the 3174 in Figure 4.8) that attach via
coaxial cable to the 3270 family of terminals and printers.
- A second, remote front-end processor (the 3725) that interfaces with additional
cluster controllers.
Connectivity between the mainframe and the Token-Ring LAN is shown at the cluster
controller (3174) level, although that connection can also be made at the front-end
communications processor. Because the mainframe does not support direct connection
to Ethernet/802.3, a special device (the 8232 LAN/channel adapter) connects the mainframe
to the LAN via a mainframe channel.
The ES/9370 uses the same general terminal network architecture as the mainframe,
with the notable exception of no front-end processor. The 9370 interfaces with cluster
controllers that in turn interface with the physical terminals via coaxial connections.
Figure 4.8 also shows a single SDLC line from the 9370 to the front-end communications
processor of the mainframe. This connection enables the 9370 to participate in peer-to-peer
interactions with the mainframe, and it also allows its own terminal network to access
the mainframe.
The ES/9370 supports direct attachment to both the Ethernet/802.3 LAN and the
Token-Ring network. Similarly, attachment to an X.25 network is made using an integrated
controller.
The AS/400 supports attachment to both 3270 and 5250 terminals. Attachment to
the 3270 terminal is made with a cluster controller (3174) that interfaces to an
integrated controller in the AS/400. The native 5250 terminals can be directly connected
to an integrated controller via twinaxial cable or through a remote cluster controller
(the 5394 in Figure 4.8).
The AS/400 offers an integrated controller for connection to a Token Ring or Ethernet
network. As shown, however, connectivity from Token Ring to an Ethernet/802.3 network
can also be provided through an 8209 LAN bridge that converts Token Ring packets
into either Ethernet or 802.3 packets.
Figure 4.8 also shows two additional SDLC links originating from the AS/400. One
is routed to the front-end communications processor of the mainframe, and the other
is routed to another AS/400. The link to the mainframe enables the AS/400 to participate
in the SNA network with the mainframe; it also enables the local AS/400 terminals
to access the mainframe via 3270 emulation.
The second SDLC link to the other AS/400 is typically for peer-to-peer relationships
(PU 2.1/LU 6.2). This connection enables the two AS/400s to establish a direct link
with one another (using APPN) and exchange program-to-program information (using
APPC) without involving the mainframe. In effect, this link is independent from the
main SNA physical network when used for this purpose.
Finally, the AS/400 supports an integrated adapter, enabling it to connect to
an X.25 network.
The last elements in the network diagram are PS/2s or PCs. These devices can exist
on a Token Ring network independent of the SNA network, or they can use the links
available on the ring to access any of the processors via SNA.
Storage
The IBM Network Tape Access and Control System for AIX (NetTape) simplifies tape
management and access in RS/6000 networks, and is capable of consolidating tape operations
for all tape devices from a single GUI. With this system, you are able to transfer
data between tape servers and clients over a high-speed TCP/IP network, such as FDDI,
Fibre Channel, ATM, or High Performance Parallel interface (HiPPI).
ADSTAR Distributed Storage Manager (ASDM), a client/server storage management
tool, provides disaster recovery support and more client capabilities. The Disaster
Recovery Manager feature of ASDM can automatically generate a disaster recovery plan,
manages off-site recovery media, and keeps an inventory of client and server systems
for restoration of systems and data.
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