PC to UNIX Connectivity

Introduction
Today�s GIS computing environment is both exciting and 
challenging.  Never before has there been so much in the way
of computing at such low costs for performing GIS analysis
or building GIS databases.  In tandum with all this power and 
affordability has been the continued growth of GIS�s use and its 
rapid deployment to the corporate masses.  This is an exciting time
for GIS because the technology and the computing environment are
finally being accepted as legitimate tools and necessary resources.  

At the same time though, it is also a challenging time.  The �open 
computing� model poses a special set of considerations which 
complicate connectivity.  Never before has it been possible to 
internetwork so many different types of platforms together.  
Consequently, connectivity for a GIS potentially involves a number 
of issues.  It is these issues this paper addresses.

To illustrate and provide a context for certain examples, this paper 
will make reference to the operational GIS program at Baltimore 
County, Maryland.  In brief, the computing environment consists of 
a WAN in which several campus buildings are interconnected with 
a fiber backbone and all remote sites are connected via T-1 or 
other dedicated line based services.  The hardware consists of a 
collection of IBM mainframes and AS/400�s, PC�s and IBM 
RS/6000�s.  Networking operations consist of TCP/IP, IPX and SNA 
with Token Ring being the primary transport and Ethernet running 
on many subnets.  The enterprise GIS solution is the Esri 
combination of ArcInfo and ARCVIEW (MS Windows) with 
Oracle RDBMS support.

Issues
The arrival of affordable and extremely powerful PC�s now enables 
enterprise GIS�s like never before.  These slick little computers can 
now process like the their midrange counterparts (workstations) 
running UNIX.  However, like their midrange counterparts they present
issues to be dealt with.  In some respects they carry more issues 
since their function can often serve multiple purposes.  In other 
words, the more applications they can run, the more trouble they 
can cause.  Therefore, to provide an intelligible solution to the 
connectivity challenge, three inter-related and complex issues must 
first be addressed.  The issues consist of Operational issues, 
Physical Issues and Logical Issues.  

The  Operational Issue
This issue centers around the answer to three basic questions.  
First, what do the users expect?  Second, what is the primary role 
of the PC at a particular site?  Third, how is the PC to interact with 
the network?  The answers to the questions of this issue very much 
set the stage for what would be expected of the remaining two 
issues.  Remember, the reason a computer would be deployed is 
to serve a function.

What do users expect?
This is an interview activity in which the GIS management and 
systems staff obtain some insight into a users current technical 
ability and provides an opportunity to clarify any misconceptions.  
This activity also makes the user feel part of the GIS process 
instead of just being a number.  Very often, users can be helpful in 
identifying problems or limitations not otherwise considered.

What is the primary role of the PC at a particular site?
The question attempts to clarify the intended purpose of the 
PC�s existence at a particular location.  This is important so that 
management and users know the line of priority for a PC�s use.  In 
addition, it clarifies why a PC may be configured a particular way.  
If all the parties involved are clear on why things are the way they 
are, higher degrees of cooperation will exist.

How is the PC to interact with the network?
The answer here will define the required networking functionality.  
Although this may seem very basic it is an interaction which is at 
times only loosely defined or not at all.   It is important 
to specify the required connectivity in order to provide the best 
solution and understand the context of the PC�s role within the 
network.  

Baltimore County�s Experience
As ARCVIEW was deployed on the PC platform it quickly became 
painfully obvious that every new site was it's own set of problems.  
Many sites had inadequate PC�s, and no existing network to 
connect to.  Some sites which got a new PC for GIS looked to 
monopolize its use for other applications, while others were 
disappointed with what was included.  In some instances where an 
existing network was in place the local LAN administrator was less 
then pleased that a foreign connection was required.  All of these 
differences made for uneasy installations.  Therefore, the GIS Unit 
developed a set of standards which addressed the operational 
issues presented here in order to deal with any problems before an 
install would be underway.

The Physical Issue
The physical issue is concerned with all of the physical aspects 
which will involve the connectivity task.  Often many people are 
surprised just how much there is to consider when providing a 
network hookup.  Dependent on the existing network and currently 
enforced design and management, an additional hookup can range 
widely in price and the amount of equipment.  Essentially, the 
physical components for attaching the PC to the network entail the 
following:

Define the Network Connection
By today�s definitions a network connection is one of the following: 
WAN, LAN or PPP/SLIP (dial-up).  A Wide Area Network (WAN) is 
generally referred to as a set of remote LANs which are 
internetworked.  WAN connections are usually the most expensive 
and pose the most number of technical problems because they 
involve remote signal transmission issues.  A Local Area Network 
(LAN) is generally a site network which may contain several sub-
networks for performance and/or security issues.  LANs are usually 
easily tapped into via a hub or direct bus attachment.  Point-to-
Point Protocol/Serial Line Internet Protocol (PPP/SLIP) connections 
are dial-up serial connections.   PPP/SLIP connections can be 
complicated to administer and keep secure but also usually offers 
cheap connectivity from a remote location.

Network Interface Card (NIC)
The NIC, referred to as the network adapter, defines what transport 
protocol the PC must have in order to route its communications on 
the network.  The typical adapter protocols are Ethernet and Token 
Ring, and in the case of PPP/SLIP connections, a modem.  The 
correct adapter is required for the PC to be networked, there is no 
substitution.  NIC adapters, as do modems, require a separate 
level of configuration to themselves aside from the operating 
system.  Many of today�s adapters however are virtually self 
configuring.

Network Transmission Speed
The network transmission speed is also important to know as it 
affects the physical settings of the NIC�s and even modems.  For 
example, a properly configured adapter to a Token Ring network 
running at 16mbs will not properly tap a Token Ring network 
running at 4 mbs.  Similarly, modems already configured at 
particular speed may not ever connect or hang if speeds between 
them are not the same.

PC bus type for NIC (ISA-PCI)
This is important only if the devices to be used by the PC are 
internal.  The bus slot type of the PC to be hooked up dictates the 
NIC or modem �plug� type.  These devices have to be correct and 
plug into the PC or they are useless.  Most PC�s today come with a 
combination of PCI/ISA slots.

Network Topology (Routed-bridged-gateways)
It is crucial to understand the network topology through which the 
PC will communicate.  Dependent on the network design and 
setup, several configuration parameters may need to be given to 
the individual hooking up the PC by a network administrator.  
Conversely, the network administrator involved may need to make 
several new modifications to components which run the network.  
For example, several routers may need to be programmed to 
permit traffic to and from a given PC to other destinations on the 
network.  Without this programmed permission, traffic flow could be 
denied.   Failure to grasp the topology and/or talk to the 
administrators of the network will result in failure to communicate.  

Cabling (CAT-5, Coaxial, UTP)
Oddly enough, all this high-tech equipment is useless without 
some sort of transmission conduit.  It is important to acquire the 
correct cabling for the type of applications being run and to have 
an understanding of its limitations.  For example, Category-5 UTP 
cable is certified to carry a digital signal no more than 300 feet.  
Running a connection longer than this without repeating the signal 
risks inconsistencies in the signal.  Understanding cabling needs 
and designing appropriate wiring schemes is basic, but necessary.

Baltimore County�s Experience
The physical issue experience is perhaps the hardest and most 
complex problem constantly faced.  As was true for Operational 
Issue, most every site posed its own special set of connectivity 
circumstances.  Therefore, in order to provide a solution, a 
standard approach was developed whereby each perspective 
deployment got the Physical Issue investigated completely via a 
checklist.  Once investigated, the necessary parties required to 
decide on a solution met and discussed what items to buy and the 
best way to proceed.  Admittedly, a couple of disorganized
installations led to this arrangement.

The Logical Issue
The logical issue refers to the software required for the physical 
network connection to work and for application software to transmit 
and receive data.  Unfortunately, what is required is largely 
dependent on the existing network and currently enforced design 
and management.   In general, the components which comprise the 
logical issue are the following:

Drivers and Utilities
Several pieces of the physical network connection will require 
software (drivers ) in order to bring the connection to life.  As a rule 
of thumb, most any component which has a printed circuit board in 
it will require software on how to behave.  A review of the 
components listed in the Physical Issues section identifies most of 
the items which require drivers.  In many instances the physical 
devices need to be specifically configured to act a certain way.  
This need is usually addedressed with a manufacturer's s software
utility.

Network Protocol (TCP/IP & IPX)
It is imperative to know what the required protocol of the network 
being connected to requires.  In addition, if communication with 
another computer on another network is required, then that 
protocol must also be in order to communicate.  Essentially, the 
Network protocol is the particular methodology of how data pieces 
are structured and routed for network transport.  In the UNIX world 
Transmission Control Protocol/Internet Protocol (TCP/IP) is the 
standard.  However, in the PC world Internetwork Packet Exchange 
(IPX) is the defacto standard as judged by Novell Corporations 
market share.  Consequently, a PC running IPX will need a TCP/IP 
stack in order to address a UNIX computer.

Operating Systems (OS) of the PC�s
The specific OS of the PC�s to be brought on-line play an important 
role as to what software will work with what software.  It is not 
uncommon to find in a large organization several different revisions 
of MS Windows and/or DOS as well as the applications running 
under the OS.  Keep in mind that software upgrades and new 
software solutions have to be reviewed for their migration impacts.  
It is quite possible to buy an upgrade to an OS only to ruin the 
existing connection with the network.   

Baltimore County�s Experience
Similarly to the Physical Issue, almost every site was unique in one 
way or another.  Therefore, the Logical Issue was handled the 
same way as the Physical Issue.  After a couple of difficult 
installations,  it became necessary to devise a standard way of 
operating to put together a total solution for any given site.  Like 
any corporation, different divisions perform different tasks and 
therefore have different software requirements.  Consequently, GIS 
which threads several divisions poses this Issue in the worst way.

Connectivity Solution
Once all the issues concerning the connectivity problem are 
understood and addressed it is time to employ a solution.  Thanks 
to the explosive growth of the Internet and corporate Intranets, a 
myriad of potential solutions now exist as a viable connectivity 
solution.  However, this paper will address the specific software 
solution developed by SUN Microsystems called PC-NFS pro.

PC-NFS pro is one of the first windows based program suites 
which provide LAN based connectivity to UNIX platforms.  The 
product is called a suite because it is a collection of individual 
programs which can be used at the users discretion.  The specific 
connectivity provided is TCP/IP and a variety of UNIX based 
daemons for the PC which are Winsocked.  For example, Network
File System (NFS) daemons are provided in order to let the PC 
actually mount exported UNIX filesystems just like any other UNIX 
computer.  Complete support for Name Information Service (NIS) and
Domain Name Service (DNS) and remote printing is included 
so that the PC plays by the same rules as any UNIX station would.  
In fact, certain server services like print serving can be setup 
through the LPD daemon to use the PC as a print server.

The package features a full logon and session control interface by 
which several different users can use the same PC via logons, set 
filesystems mounts and add/change file permissions.  Since users 
profiles and groups are controlled via the UNIX system, particularly 
when NIS and DNS are running, the PC poses no security 
problems.  All operations are integrated into the Windows 
operating system when running for easy use.  For example, when a 
filesystem is mounted, it will now appear as an additional 
selectable drive in the Program Manager or Windows Explorer 
window.  This in turn means that these resources will now be seen 
and made available to the PC applications running like ARCVIEW.

The PC-NFS pro suite also has a variety of utilities which may be 
of use dependent on the site.  Programs like Ping, FTP, Telnet, e-
mail client, Finger and a SNMP agent are included.  For the most 
part these programs are not necessary for GIS operations and 
would only be useful to Systems and Network Administrators.

Summary
Keep in mind that computers exist to serve a function.  Typically, 
that function is to make the worker more efficient by providing a 
better tool.  This basic definition holds true also for GIS users.  In 
the case of GIS on PC, users are becoming more and more varied.  
Consequently, close attention needs to be given to the functions 
desired and required within the context of the connectivity issues 
presented herein.  With a good handle on what the problem to 
solve is and an inventory of the existing operational constraints 
and an eye to the future the connectivity solution path will be clear.

In the case of Baltimore County, the PC-NFS pro 
product proved to be a perfect fit for most cases.  In 
the one year of use with the product few problems 
have been encountered and I would recommend the 
product as an affordable and comprehensive solution.