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Active Hub a network device used to amplify signals when extending or bridging. It is active because it has its own power supply. otherwise it would be passive.
Alternative routing when information travelling along the normal route between two nodes is made to take another route. Probably caused by network over loading
Application Layer the highest level of the OSI model which describes the way that programmes interact with the network operating system
Asynchronous a type of communication between independant devices, distinguished by the lack of a set of strict timing arrangement between them (some-times called start-stop as seperate signals are included in the data stream to indicate the beginning and end rather than a strictly timed sequence such as synchronous systems) Serial communications between microprocessors, printers and modems are asynchronous)
Attenuation is the difference between the transmitted and receive power of a signal when affected by various transmission losses in a media.
Bandwidth the difference between the highest and the lowest possible frequencies that are available for signalling over a channel.
Bridge a device that links two similar LANs so that the facilities of one are available to the other.
Bus topology all nodes share
a single cable. Data is broadcast in either direction on the network
and because there is no control a sytem has to be organised that deides
who can transmit. A popular system called Ethernet
uses a contention method of control. One such control is CSMS/CD.
Client go
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Any device which request services from a server is called
a client. A client may be a workstation, a printer, another server,
an ATM or EPOST terminal.
Client Server Networks
These networks have a dedicated computer called the server
which provides file services and manages shared resources. Client
computers get services from the server.
Client-server networks use their own Network Operating System (NOS). Novell Netware is an example of the client-server model, where the workstations (clients) communicate with the server to get services. All communications on the network is through the server.
Client - Server Networks provide:
Examples of client server networks operating systems are:
CSMA/CD (Carrier Sensing Multiple Access/Collision Detection) Before transmission begins each station checks to see if the channel is busy. If no carrier is sensed the station starts to transmit else it waits and tries later. Once it begins to transmit it listens to check that no other transmissions start. If messages do collide then both stations will stop transmission, and random timer will run in each station to ensure that they both do not attempt to start transmission agin at the same time.
Dumb terminals are used on mini or mainframe computers, do not have RAM and usually have no processing power.
NetWare workstations may be IBM PCs, IBM P/S2s, Apple Macintosh, or UNIX based computers.
Ethernet go
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Ethernet (IEEE 802.3 standard) is one of the most
common networks using CSMA/CD protocol
to control data flow.
Currently Ethernet supports 10Mbps and three common types are 10BASE-2 (thin ethernet), 10BASE-5 (thick ethernet) and 10BASE-T (UTP).
Ethernet is a branching, bus topology in which each adapter attaches to a central cable segment. Cable segments can be connected to each other with MAUs, repeaters or concentrators to form longer segments or to branch existing segments.
The segments follow a wiring rule known as 5, 4, 3 rule, where no more than 5 segments can separate any two work stations on the network, no more than four repeaters between any two workstations and no more than three populated segments can separate any two workstations.
A H/W driver is a software program which provides interface between specific H/W device and S/W programs. In other words S/W programs need H/W or device driver programs to communicate with a device. For instance, the DOS must use a mouse driver to talk to a mouse.
Two important network H/W drivers are LAN drivers to communicate with the network Interface card (NIC) and the disk driver to communicate with the file server’s hard disk.
see also hardware drivers network
components Netware network
operating system installing a LAN work
station SW software installation
Local Area Network (LAN) go
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A LAN connects devices that are relatively close to each
other, typically within a single building or campus. A LAN can provide
communication speeds up to 100 megabytes per second (Mbps). Some
common LAN speeds are:
ARC Net 2.5Mbps
Ethernet 10Mbps
Token Ring 16Mbps
FDDI (Fibre Distributed
Data Interface) 100Mbps
Local Area Networks are also categorised according to the way they exchange data and services. The two major categories are,Client-Serverand Peer-to-Peer.
LAN Components go
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Basic components of a LAN are:
H/W installation
S/W installation
H/W Installation
A NIC is installed in the file server computer and in
each workstation’s available slot (expansion bus) and then connected via
a cable. The manner in which you connect all these computers is called
the topology or physical layout of the network.
S/W Installation
After the H/W installation, the NOS is installed on the
file server computer. To connect a workstation to the file server
the following workstation files are executed.
IPX
NETX
or
LSL
NE2000 (or other LAN driver)
IPXODI
VLM (or NETX.EXE)
The above files establish a connection with the file server. The next step is to login and configure the file server.
see also hardware drivers network components Netware network operating system installing a LAN work station SW software installation
How Applications Run a Network
All user applications and data are installed (copied)
onto the server’s hard disk from a workstation. Once installed, users
can access these applications and data as if they were installed on their
own local hard disk. When a user requests (executes) an application
file, or data from the file server, it is loaded on the workstation’s memory
(RAM) and processed there in the same way as if loaded from a local hard
disk. This is called DISTRIBUTED PROCESSING
Note: In the case of mini or mainframe systems, all processing is done on the main computer. Users use a "dumb" terminal (or PC terminal mode) which usually does not have any processing power or RAM. This is called CENTRALISED PROCESSING
LAN Software Components go
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Basic S/W components of a LAN are:
Municipal Area Network (MAN) go
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A MAN occupies a middle ground between LAN’s
and WAN’s. A MAN covers a larger geographical
area than a LAN, ranging from several blocks of buildings to a good sized
metropolitan area. It provides high speed (100Mbps), and supports
both data and voice.
It has mainly come about by the introduction of fibre optic and it’s greater signalling properties.
MEDIA Copper circuits provide data communication using electrical signals; optic fibre uses light signals and infra red and microwave provide wireless transmission of data. see transmission media
Network Interface Cards (NICs) go
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Computers need communication H/W to talk to each other.
The main communications H/W component is a circuit board bearing the components
necessary for sending/receiving messages. This board is called a
NIC and is plugged into a spare available slots on the PC expansion bus.
A transmission cable is then attached to the connector on the NIC (coax
etc)
Examples for NICs are:
Network
Operating System (NOS) Software
The network operating software is installed on a file
server computer to manage network resources.
see also hardware drivers network components Netware network operating system installing a LAN work station SW software installation
NOVELLE NETWARE 3.11 and Earlier
Versions Version 4 is now in common use.
To connect a DOS workstation to a Netware 3.11 server,
boot the workstation with DOS then load the workstation files as follows.
see also hardware driversnetwork
components Netwarenetwork
operating system installing a LAN
work station SW software
installation
Peer-to-Peer go to top
Peer-to-Peer networks share computer resources without the help of a control server. Any two computers in the network can communicate and share resources directly. NOS software is located in each computer. Each computer can be set up as a server, client or both.
Although a peer-to-peer network does not have a file server one or more of the computers can be allocated to control tasks such as printing (printer server). The computer often controls a locally configured printer and other workstations access the printer via the print server, which controls the print queue.
Peer-to-Peer networks are less expensive, easier to install/manage. However, they provide poor throughput and security, supporting a limited number of workstations.
Examples:
Advantages
A server is a combination of Hardware and Software which manages shared resources, and provides services to other devices (clients) on the network. In a Novell Network, a computer running the Netware operating system is a server.
There may be other types of server in a network but each network must have at least one server.
The file server stores all of the networks shared files:
Star network Each node in a star network is connected to a central controlling computer. In a typical star network a polling system is commonly used. (ie. the file server polls each station in turn to see whether it is ready to transmit)
Advantages
Topology Network topology is the physical layout of a network. There are several basic layouts, ring, bus, star and mesh.
Each device on a network is connected to a transmission cable to allow messages to be sent from one device to another.
LANs typically use:
The differences between these media relate to:
Wide Area Network (WAN) go
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A WAN connects computer networks or devices that are
located in different geographical areas. A WAN uses world-wide communications
usually telephone lines, to connect computer resources. A WAN may
connect similar computer systems (LANs to LANs) or dissimilar systems (LANs
to mini computers or mainframes)
A WAN provides communication speeds at usually less than
2Mbps (a common communication line is called T1 that gives 1.544Mbps) Higher
speed lines are available for WANs but those are provided by the telephone
companies at a very high price. Workstations on a LAN are
PCs. LANs do not support dumb terminals.
Workstation Software
Loading Workstation S/W
To connect a DOS workstation to a Netware server, boot
the workstation with DOS, then load the workstation files in the following
order
see also hardware
drivers network components Netware
network operating system installing
a LAN work station SW software
installation
Wireless LAN: Workstations on a network can be connected via physical media such as copper or fibre cable, but they can also be connected by wireless means such as infr-red and micro-wave (i.e. similar to the controls on a TV) WAN systems can be connected by radio, micro-wave and satellite.
Wireles systems are being developed to allow all of the electrical machines in a household to be interconnected. It is called "Home Networking"
Networking standards in the home will break away from traditional networking features. New technology is aimed at complete integration of home appliances on a local network. It is envisaged that all computers in a home will be able to share resources and communicate in the near future. It will also allow people to communicate, programme and control household apliances (TV, telephones, washers, cookers etc) as well as heating.
Control of 25 appliances up to 500ft apart are envisaged as initial signalling standards. Players include Advanced Power Components (APC using standard telephone sockets), Tut Systems (produced HomeRun plug-in boxes), Compaq, Intel (Anypoint) and home networking kits are to be launched summer 1999 by Microsoft, who plan to make it part of Windows 2000).
Although referred to as wireless, some of these systems will use the power-point and electrical cabling within a house as the media. The problems that are needed to be overcome are how to seperate the communication signal from the 240V electrical supply (possible using filters) and how to filter out and prevent noise being generated which would make the signalling unstable. Once stable systems have been developed each powerpoint in a house can be set up as a node on a LAN and with interface cards being inserted in workstations and appliances integrated household sytems will be possible. A major difficulty to be overcome with this and other public utility systems is that the media (power feed cables) is shared with everyone else and therefore security could be a problem.
Workstation S/W connects the workstation to the
file server and lets application S/W at the workstations communicate with
the NOS. After the workstation is physically connected to the network
then two types of S/W are required. Communication protocol to
manage communication (transfer data) between workstation and file server
and the NetWare shell to provide network access to get network services.
Examples of workstation files are:
The above files establish the connection with the server
and provide transparent access to network resources. Transparent
access means a user accesses the network resources as if they were local
NetWare 3.12 / 4.x
You will now be attached to the server. Now you can
change to the F: network drive and login as follows:
or
The DOS Requester installation process creates a directory
C:\NWCLIENT to store the executable files. A batch file named STARTNET.BAT
is created to automatically load these files. The AUTOEXEC.BAT file
is modified to call STARNET.BAT file.
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