Device Servers
A device server is defined
as a specialized, network-based hardware device designed to perform a
single or specialized set of server functions. It is characterized by a
minimal operating architecture that requires no per seat network
operating system license, and client access that is independent of any
operating system or proprietary protocol. In addition the device server
is a "closed box," delivering extreme ease of installation, minimal
maintenance, and can be managed by the client remotely via a Web
browser.
Print servers, terminal
servers, remote access servers and network time servers are examples of
device servers which are specialized for particular functions. Each of
these types of servers have unique configuration attributes in hardware
or software that help them to perform best in their particular arena.
Print Servers
Print servers allow printers
to be shared by other users on the network. Supporting either parallel
and/or serial interfaces, a print server accepts print jobs from any
person on the network using supported protocols and manages those jobs
on each appropriate printer.
The earliest print servers
were external devices, which supported printing via parallel or serial
ports on the device. Typically, only one or two protocols were
supported. The latest generation of print servers support multiple
protocols, have multiple parallel and serial connection options and, in
some cases, are small enough to fit directly on the parallel port of the
printer itself. Some printers have embedded or internal print servers.
This design has an integral communication benefit between printer and
print server, but lacks flexibility if the printer has physical
problems.
Print servers generally do
not contain a large amount of memory; printers simply store information
in a queue. When the desired printer becomes available, they allow the
host to transmit the data to the appropriate printer port on the server.
The print server can then simply queue and print each job in the order
in which print requests are received, regardless of protocol used or the
size of the job.
Multiport Device Servers
The ancestor of today's
multiport device server was a "Terminal Server", used to enable
terminals to transmit data to and from host computers across LANs,
without requiring each terminal to have its own direct connection. And
while the terminal server's existence is still justified by convenience
and cost considerations, its inherent intelligence provides many more
advantages. Among these is enhanced remote monitoring and control.
Multiport Device Servers that support protocols like SNMP make networks
easier to manage.
Devices that are attached to
a network through a multiport device server can be shared between
terminals and hosts at both the local site and throughout the network. A
single terminal may be connected to several hosts at the same time (in
multiple concurrent sessions), and can switch between them. Multiport
device servers are also used to network devices that have only serial
outputs. A connection between serial ports on different servers is
opened, allowing data to move between the two devices.
Given its natural
translation ability, a multi-protocol multiport device server can
perform conversions between the protocols it knows, like LAT and TCP/IP.
While server bandwidth is not adequate for large file transfers, it can
easily handle host-to-host inquiry/response applications, electronic
mailbox checking, etc. And it is far more economical than the
alternatives of acquiring expensive host software and special-purpose
converters. Multiport device and print servers give their users greater
flexibility in configuring and managing their networks.
Whether it is moving
printers and other peripherals from one network to another, expanding
the dimensions of interoperability or preparing for growth, multiport
device servers can fulfill your needs, all without major rewiring.
Access Servers
While Ethernet is limited to
a geographic area, remote users such as traveling sales people need
access to network-based resources. Remote LAN access, or remote access,
is a popular way to provide this connectivity. Access servers use
telephone services to link a user or office with an office network.
Dial-up remote access solutions such as ISDN or asynchronous dial
introduce more flexibility. Dial-up remote access offers both the remote
office and the remote user the economy and flexibility of "pay as you
go" telephone services. ISDN is a special telephone service that offers
three channels, two 64 Kbps "B" channels for user data and a "D" channel
for setting up the connection. With ISDN, the B channels can be combined
for double bandwidth or separated for different applications or users.
With asynchronous remote access, regular telephone lines are combined
with modems and remote access servers to allow users and networks to
dial anywhere in the world and have data access. Remote access servers
provide connection points for both dial-in and dial-out applications on
the network to which they are attached. These hybrid devices route and
filter protocols and offer other services such as modem pooling and
terminal/printer services. For the remote PC user, one can connect from
any available telephone jack (RJ45), including those in a hotel rooms or
on most airplanes.
Network Time Servers
As organizations become
global in their scope, they can begin to encounter problems which never
before affected them. Time is one of these problems. How does one begin
to coordinate activities in several sites that require precise timing of
events when network traffic between those sites is subject to delays or
inconsistencies? The answer to this question is to obtain timing
information in all locations from a single source.
A network time server
is a server specialized in the handling of timing information from
sources such as satellites or radio broadcasts and is capable of
providing this timing data to its attached network. Specialized
protocols such as NTP or udp/time allow a time server to communicate to
other network nodes ensuring that activities that must be coordinated
according to their time of execution are synchronized correctly. GPS
satellites are one source of information that can allow global
installations to achieve constant timing.
Device Servers
A Device Server is
an appliance that network-enables any device with a serial
communications port. By virtue of its independent operating system,
protocol independence, small size and flexibility, Device Servers are
able to meet the demands of virtually any network-enabling application.
The demand for Device Servers is rapidly increasing because
organizations need to leverage their networking infrastructure
investment across all of their resources. Many currently installed
devices lack network ports or require dedicated serial connections for
management -- Device Servers allow those devices to become connected to
the network.
Device Servers are currently
used in a wide variety of environments in which machinery, instruments,
sensors and other discrete devices generate data that was previously
inaccessible through enterprise networks. Device Servers are also used
for security systems, point-of-sale applications, network management and
many other applications where network access to a device is required.
As Device Servers become
more widely adopted and implemented into specialized applications, we
can expect to see variations in size, mounting capabilities and
enclosures. Device Servers are also available as embedded devices,
capable of providing instant networking support for builders of future
products where connectivity will be required.
Conclusion
We hope this introduction to
networking has been helpful and informative. However, we cannot explain
everything there is to know about planning, installing, administering
and troubleshooting a network in this short tutorial. There are many
Internet websites, books and magazines available that explain all
aspects of computer networks, from LANs to WANs, network hardware to
running cable. Check your local bookstore, software retailer or
newsstand for more detailed information.
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