low-cost systems are STARLAN, ARCnet, 10Net,
and LANtastic.
Zero-Slot Network Operating Systems
Zero-slot network operating systems are
appropriate only for networks with very few users and
light usage.
They are an inexpensive and simple
alternative to the NOSs that require expensive
network interface cards. Rather than requiring each
workstation computer to have a NIC, the computer’s
RS-232 serial communications port and twisted-pair
cables are used. Because of this, they are very slow
and offer limited file transfer abilities. They may not
provide disk sharing.
An example of a zero-slot
system is LANLink.
SUMMARY—LOCAL-AREA NETWORKS
This chapter introduced you to local-area
networks. The following information summarizes the
important points you should have learned.
LOCAL-AREA NETWORKS— LANs are a
combination of hardware and software which allows
personal computers to share information. The total
number of computers and the total distance the
network can cover are determined by several factors,
including the type of cable used and the network
operating system software.
CABLES— Several types of cables can be used to
create a local-area network. They are twisted-pair,
shielded twisted-pair, coaxial, and fiber-optic. The
type of cable used determines maximum data transfer
rates and can be a factor when the number of nodes in
the network is determined.
NETWORK INTERFACE CARD— The
network interface card attaches the PC to the network.
Most network interface cards have built-in
microprocessors
that
control
network
communications. This frees the PC’s main processor
of time-consuming I/O operations.
NETWORK SERVERS— The modern network
server controls all operations of the network. These
operations
include
controlling
network
communications, storing and retrieving files from
shared memory resources, and controlling common
printers. In older systems, each of these functions
required a separate server.
WORKSTATIONS— Workstations are the
personal computers connected to the network. Even
if a PC is part of a network, it can still be used in a
stand-alone configuration.
OPEN SYSTEM INTERCONNECTION
OSI REFERENCE MODEL— The open systems
interconnection reference model defines the protocols
network hardware and software manufacturers use to
create a network operating system. There are seven
layers in the OSI model. These layers are contained
in the five levels.
HARDWARE LEVEL— The hardware level
contains the first two layers of the OSI reference
model. These are the physical layer and the data link
layer. The physical layer defines the electrical,
mechanical, and functional interfaces for the
transmission of data through the cable. The data link
layer is responsible for error detection and correction
of the transmitted data.
TRANSPORT LEVEL— The next three layers of
the OSI reference model are contained in the transport
level, also referred to as the subnet. The three layers
of the transport level are the network layer, the
transport layer, and the session layer.
The network layer monitors network activity and
controls which path the data is to be transmitted over.
The software, controlling the network interface card,
stores the data to be transmitted, builds the data
packets, and routes the data to the correct destination.
The transport layer ensures the integrity of the
data packets.
The session layer provides for the
interface between two or more applications to
communicate across the network.
PRESENTATION
LEVEL/LAYER— The
presentation level contains the presentation layer. The
presentation layer formats the data presented to the
application level. The presentation layer provides
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