ch03.htm

this describes managing multivendor networks

when it is running. In the simplest of applications, each user might have a copy
of the program running out of the user's portion of the system's memory. From a programmer's
perspective, this can ease the pain of program development because there is no need
to take into consideration the complications caused by multi-user, multithreaded
access (multiple users accessing the same program at the same time but at a different
logical point in the program).</P>
<P>But reality dictates that large multi-user computers cannot truly give each user
program and memory space. At a minimum, there must be a standard or interface that
allows multiple programs to share data in a file. (After all, if everyone lived in
their own little world and never needed to share or integrate information, they might
as well each have stand-alone PCs and throw away the minicomputers and mainframes.)</P>
<P>To address these real-world, multi-user interfaces, HP uses layers of programs
and provides central, shared resources to back them up. For example, while each user
might have a copy of the portion of the program that is processing the screen, each
copy of this program might in turn pass the data to another common program that coordinates
all the input and output from all of the user programs. This arrangement ensures
that Person A does not obliterate the information Person B is working on.</P>
<P>While it is probably unreasonable to go into further detail regarding how application
programs are layered within the system, the availability and function of the central
application resources are noteworthy. One of the key functions of any computer system
is the database. To address this key area, HP provides a product called TurboIMAGE--a
proprietary database package for its entire computer line (HP 1000, 3000, and 9000).</P>
<P>TurboIMAGE enables multiple programs to access and retrieve information based
on a wide variety of selection criteria. It supports its own interface with programs
and the Structured Query Language (SQL) interface. But TurboIMAGE is unique because
it is one of the few databases developed by a computer manufacturer. Although end
users do not see TurboIMAGE directly, the way that TurboIMAGE stores and retrieves
information significantly controls what the users do see.</P>
<P>In contrast to TurboIMAGE's transparency is the physical appearance of the operating
system. Until the late 1980s and early 1990s, the user saw a character-based (nongraphical)
interface that prompted for action and then read back the typed response. In the
late 1980s, HP adopted a graphics-based interface it termed NewWave. Although initially
implemented on PCs with Microsoft Windows, NewWave was intended to also serve as
an interface for graphics-based terminals. Furthermore, HP's experience developing
NewWave greatly influenced its role in the development of the OSF/Motif graphic interface.</P>
<P>Following NewWave was HP-VUE, which ultimately formed the basis of the Common
Desktop Environment (CDE), a standard GUI for all UNIX and X-based systems. CDE,
a joint project led by HP and other prominent vendors, establishes a common look
and feel for all UNIX systems, including workstations, X terminals and PCs, and provides
for easier portability between UNIX-based operating systems. CDE does not actually
represent any new technology, but instead incorporates existing technology from several
vendors into a single, common standard. CDE includes HP's Visual User Environment
(VUE), and is available on HP-UX and several other UNIX operating systems. Besides
HP-VUE, CDE also includes elements of IBM's Common User Access Model.</P>
<P>In many respects, HP's approach to the user/application interface combines the
best of both worlds. The user and the program appear to have a relatively simple
one-to-one relationship while, in reality, these seemingly separate tasks are being
centrally coordinated. The downside of this approach is the overhead and resources
used to maintain the separate user identities and work areas.
<H3><A NAME="Heading10"></A><FONT COLOR="#000077">Terminal Attachment Philosophy</FONT></H3>
<P>Before HP's pervasive changes in its networking strategy, the relationship between
an HP terminal and a computer was so straightforward that it bordered on boring.
In the majority of installations, HP terminals were directly attached to the main
computer via simple asynchronous connections. One terminal was attached to one port
on the computer using one line.</P>
<P>These attachments generally used standard RS-232C connections (although options
for RS-422 were also supported). Of the 25 supported RS-232C leads, direct-connected
terminals can be configured to only three required lines: reference ground (7), transmit
(2), and receive (3). An optional fourth line for frame ground (1) was more often
ignored than used. Remote (modem) connections followed the more-or-less standard
RS-232C asynchronous signals (pins 2-7, 20, and 22).</P>
<P>With this limited number of signals, the flow of data between the terminal and
the computer is controlled through software--specifically, HP's proprietary, point-to-point
terminal control protocol. Like the HP terminals and their multifaceted capabilities,
the terminal protocol is also multilayered. Essentially, the flow control options
can be lumped into the following groups:

<UL>
	<LI><I>DC1 handshaking.</I> This option, which regulates when the terminal can transmit
	data to the computer, has two different (and mutually exclusive) implementations.
	DC1 trigger is the simpler option; it specifies that the terminal can transmit after
	receipt of a DC1 control character. With the other option, DC1/DC2 handshake, the
	computer sends a DC1 character, the terminal responds with a DC2 acknowledgment,
	the computer sends a second DC1, and then the terminal can transmit.<BR>
	<BR>
	
	<LI><I>ENQ/ACK pacing.</I> This option ensures that the data is received correctly
	by the terminal and gives the terminal sufficient time to keep up with the computer.
	When ENQ/ACK is enabled, the computer breaks up a large transmission into small groups
	and terminates each group with the ENQ control character. When the terminal sees
	the ENQ, it responds to the computer with an ACK, thereby indicating it is ready
	for the next block of data.<BR>
	<BR>
	
	<LI><I>XON/XOFF pacing.</I> XON/XOFF pacing also ensures that the side receiving
	the data is keeping up with the side transmitting the data. The XON and XOFF signals
	are the DC1 and DC3 control characters. XON/XOFF pacing has two implementations:<BR>
	<BR>
	
	<UL>
		<LI><I>XOFF transmitted by the terminal.</I> This implementation enables the terminal
		to terminate transmission, giving it time to process the data in its local buffer.
		When the terminal has caught up with the computer, it sends an XON, signal- ing the
		computer to resume transmission. (Also note that the user can perform this function
		by pressing Ctrl+S for XOFF and Ctrl+Q for XON, providing an opportunity to pause
		and review lengthy displays.)<BR>
		<BR>
		
		<LI><I>XOFF transmitted by the computer.</I> Here the perspective is reversed. The
		computer sends an XOFF to pause a transmission from the terminal and then sends an
		XON to resume it. Because the XON and XOFF characters are DC1 and DC3, this op- tion
		cannot be used if either of the DC1 handshakes is enabled.
	</UL>
</UL>

<P>Of course, to make life complicated, any of these options can be used alone or,
more likely, in a combination. Like the functional capabilities of the terminals,
the flexibility of the data communications options can be overwhelming.</P>
<P>Even when HP made a major commitment to redevelop its LAN architecture along the
lines of IEEE 802.3, terminal computer communications were not affected. Not until
the introduction of the RISC-based HP 3000 Series 900 did HP change the way that
terminals connected to computers; and even then, HP's changes affected only the HP
3000 RISC machines.</P>
<P>Given the general nature of IEEE 802.3 as a relatively high-speed (10 Mbps) coaxial-type
of LAN, HP borrowed a page from the book of Digital Equipment and developed its own
type of terminal servers, Distributed Terminal Controllers (DTCs). These DTCs took
the place of asynchronous ports; in fact, each DTC interfaced up to 48 lines (terminals)
to the IEEE 802.3 network, and consequently into the computer (see Figure 3.3).</P>
<P><A HREF="javascript:if(confirm('http://docs.rinet.ru:8080/MuNet/ch03/03fig03.gif  \n\nThis file was not retrieved by Teleport Pro, because it was redirected to an invalid location.  You should report this problem to the site\'s webmaster.  \n\nDo you want to open it from the server?'))window.location='http://docs.rinet.ru:8080/MuNet/ch03/03fig03.gif'" tppabs="http://docs.rinet.ru:8080/MuNet/ch03/03fig03.gif"><B>FIG. 3.3</B></A> <I>HP 3000 Series 900 Attachments</I></P>
<P>While the DTCs introduced some new functions to HP's networking architecture (such
as the ability for one terminal to connect to different hosts--a tough trick when
they are hard-wired), the basic data communications flow between the terminal and
the computer remained (for the most part) unchanged.
<H3><A NAME="Heading11"></A><FONT COLOR="#000077">Peer-to-Peer Relationships</FONT></H3>
<P>In HP's pre-NS days, establishing communications paths between programs (or even
systems) was not a pretty sight. Within a machine, HP offered memory- and disk-based
mailboxes to facilitate interprocess communications. This technique, however, required
a great deal of standardization and cooperation from the programmers developing such
applications.</P>
<P>On a larger scale, the Data Services (DS) family of products provided system-to-system
communications. The physical communications between systems was typically HP's imple-mentation
of a High-Level Data Link Control (HDLC) protocol, although support for X.25 connectivity
was also permitted. Essentially, DS allowed terminals on one system to log onto other
systems, files to be exchanged, and programs to open and access remote databases.
But in comparison to NS, DS was a dinosaur waiting for a comet.</P>
<P>Because NS was modeled in many ways after the TCP/IP standard, its interprocess
commun-ications (IPC) methodology also follows the TCP/IP IPC standards. Much like
Digital's task-to-task programmatic access, HP's NetIPC interface allows programs
on the HP NS system to exchange information without requiring the programming gyrations
necessary under the mailbox approach.</P>
<P>Furthermore, HP's acquisition of Apollo greatly enhanced its offering in this
area. Apollo's own implementation of program-to-program communications--here, Apollo
used the term remote procedure calls (RPCs)--was part of its overall Network Computing
System (NCS). Apollo's approach to the matter became a subject of great interest
to the computer industry as a whole, and the marriage of the two represented a new
and significant standard to peer- to-peer processing.
<H3><A NAME="Heading12"></A><FONT COLOR="#000077">PC Integration Strategy</FONT></H3>
<P>Having chosen the IEEE 802.3 standard to implement its systemwide communications,
HP borrowed its PC networking strategy from AT&amp;T's StarLAN network. Integration
of this separate network strategy with the backbone 802.3 computer system is handled
through the use of a bridge.</P>
<P>With HP StarLAN, each PC is connected to a central hub using 1 Mbps thin wire
(or optional twisted pair) cables (see Figure 3.4). Such systems as the HP 3000 can
be connected directly to the same hub, or a node on the hub can be connected to an
HP bridge that connects that hub to the backbone of the main 802.3 network.</P>
<P>A high-performance version of this basic network architecture is also available
in the form of HP's StarLAN-10. StarLAN-10 differs from the original StarLAN in that
it is based on a 10 Mbps coaxial medium and does not require a bridge to link with
the main backbone (see Figure 3.5). Also note that either HP StarLAN or StarLAN-10
can be implemented as a stand-alone PC network--larger systems (HP 3000) need not
be connected.</P>
<P><A HREF="javascript:if(confirm('http://docs.rinet.ru:8080/MuNet/ch03/03fig04.gif  \n\nThis file was not retrieved by Teleport Pro, because it was redirected to an invalid location.  You should report this problem to the site\'s webmaster.  \n\nDo you want to open it from the server?'))window.location='http://docs.rinet.ru:8080/MuNet/ch03/03fig04.gif'" tppabs="http://docs.rinet.ru:8080/MuNet/ch03/03fig04.gif"><B>FIG. 3.4</B></A> <I>HP StarLAN Network</I></P>
<P>Although this PC networking strategy might seem somewhat less than awe inspiring,
HP's advances in the area of user interfaces are noteworthy. Specifically, HP's NewWave,
a graphical user interface for the PC environment, and the subsequent HP-VUE interface,
provide an alternative to the IBM Presentation Manager (note that the release of
NewWave preceded the final release of Presentation Manager).</P>
<P>NewWave, working with Microsoft Windows, provided a graphical interface that enables
the user to select from programs and applications, regardless of where the applications
reside or the information is located. VUE continued this functionality, and with
the establishment of CDE, provided a single set of interfaces for HP-UX, IBM AIX,
Solaris, UnixWare, and other UNIX platforms. This enabled users to access data and
applications from anywhere in the network, regardless of physical location or hardware
platform.</P>
<P><A HREF="javascript:if(confirm('http://docs.rinet.ru:8080/MuNet/ch03/03fig05.gif  \n\nThis file was not retrieved by Teleport Pro, because it was redirected to an invalid location.  You should report this problem to the site\'s webmaster.  \n\nDo you want to open it from the server?'))window.location='http://docs.rinet.ru:8080/MuNet/ch03/03fig05.gif'" tppabs="http://docs.rinet.ru:8080/MuNet/ch03/03fig05.gif"><B>FIG. 3.5</B></A><B> </B><I>HP StarLAN-10 Architecture</I></P>
<P>NewWave, although it was a significant development, was also important in that
it paved the road for other developments, including VUE and CDE. Within a year of
NewWave's formal release, HP released NewWave Office. Whereas NewWave focused on
bringing a better, graphical interface to the PC, NewWave Office is the first application
implemented under the NewWave architecture. Under NewWave Office, the PC user selects
an application whose core service (HP DeskManager) resides on an HP 3000 under the