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Remote Access
means users can use system
resources from locations outside the control room. In the broadest sense one of
the following two cases is possible:
- One is accessing NTMC via a homogeneous network where all of
the computers involved are IBM PC compatible, and they are all running one
version of Microsoft's Windows or another. LANs
and telephone dialup are examples of this situation. WANs
(excluding the internet) may fall into this category
- Access is being done via the internet, where there are many different
kinds of computers running different kinds of operating systems, such as
MAC-OS, VMS, and the various flavors of UNIX, for example.
Compatibility
is a major issue. In case
#1 above one can more or less count on being able to run the same software on
all machines. Not so in case #2.
Security
is also very important. The
larger the network being used, the more chance there is for abuse. A simple peer
to peer telephone dialup situation is the simplest of all, while the internet is
the most complex. Files resident on computers accessible via the internet need
to be encrypted. Computers accessible via the internet need to be protected with
passwords, firewalls, virus cleaners, etc. Control system components need to
have authentication (secure log-on), and authorization (security profiles)
mechanisms. Communications between all software components (browser - server,
and control system - server) need to go via secure, encrypted channels. NTMC
uses 128 bit SSL (Secure Socket Layer), the same technology that most banks use.
Complexity
- Bandwidth - the faster the network the better. Unfortunately not
all networks are fast. Clients need to be able to see changes in the system
in a reasonable time. While this is not a problem on a fast T1 line, or a
100baseT LAN, it does become an issue when working over slow telephone
lines. NTMC users report that speeds down to about 24.4K Baud
are still tolerable, while speeds slower than that become a problem.
Fortunately most long distance telephone lines are at least that fast, while
DSL, cable modems, and LANS are much faster.
- Network architecture - networks come in all shapes and sizes. Once
again, the larger networks are more complex than the smaller ones. The
largest of them all, the internet, is very large indeed. It not only
consists of millions of computers, but also servers, proxies, switches,
routers, etc. NTMC was designed to work around these.
Implementation
- More on how NTMC
can be accessed via homogeneous networks and dialup (case #1 above) can be
found here.
- More on how NTMC
can be accessed via heterogeneous networks (internet and large WANs) can be
found here.
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