but it allows networking over greater distances with
more users. Twisted-pair EtherNet uses a distributed
star topology with wiring concentrator hubs, not the
bus topology characterizing standard EtherNet and
ThinNet. Connecting more than 100 users on a
standard EtherNet trunk or on a series of twisted-pair
concentrators is not uncommon, while ThinNet LANs
usually support less than 50 users.
All versions of EtherNet create a LAN with high
interconnectivity options. A number of products are
available for connecting EtherNet LANs to
minicomputers and mainframe computers and for
bridging to other LANs; examples are STARLAN,
ARCnet, and IBM Token Ring Network.
STARLAN
STARLAN uses a star topology with a CSMA/CD
protocol. Its throughput speed is 1Mb per second
over twisted-pair cable. If buildings are already wired
with twisted-pair cable meeting AT&T premise
cabling specifications, STARLAN can be installed
easily. It is considered to be a low cost-per-user
network and its star topology makes it a flexible
network.
ARCnet
ARCnet is a distributed star topology that uses a
token passing protocol and either twisted-pair or
coaxial cabling. Its throughput speed is 2.5Mb per
second. Although ARCnet does not conform to an
IEEE standard, it closely resembles the 802.4 standard
for a token bus system. It can easily handle up to 75
users. If user demand is low, it can handle additional
users. It is considered an extremely reliable network
and is easy to install, expand, and modify.
IBM Token Ring Network
The IBM Token Ring Network uses a star ring
topology, and is defined by the IEEE 802.5
specification. It has a throughput speed of 4 Mbits
per second and 16 Mbit per second. This allows for
flexible expansion of very large networks. Because of
its speed and token passing protocol, it is a good
choice to meet high-volume requirements. It is a
6-12
sophisticated LAN technology developed by IBM to
be used with an IBM cabling system and is currently
the fastest growing installed network base. The star
ring topology also makes use of redundant circuits
and loopbacks to handle breaks in the ring and results
in high-fault tolerance on the network.
NETWORK OPERATING SYSTEMS
Network operating system software is necessary
to control the overall operations of the network.
Careful consideration must be given to the various
packages on the market to ensure the operating
software is fully compatible with your system,
topology, and needs.
NETWORK OPERATING SYSTEM BASICS
The two basic components of the network
operating system are the network operating system
server and the workstation. The network server is
usually a dedicated computer that runs the operating
system software and processes all requests for
services.
The workstation computer runs the
application software needed by the workstation user
and establishes communications with the network
server.
The network server operating system consists of
the following five subsystems: the control kernel,
the network interfaces, the file systems, the system
extensions, and the system services.
Control Kernel
The control kernel is the main subsystem of the
network operating software.
The control kernel
coordinates the various processes of the other
subsystems. Some of the functions performed by the
control kernel are as follows:
Optimizing access to services by users
Maintaining status information of many of the
processes
Error reporting
