MORE ABOUT LAN

BicneT Network Planning Guide

LAN COMPONENTS 

A typical local area network  has four basic components that make up the network. These are:
1. FILE SERVER
2. PERSONAL COMPUTERS, WORK STATIONS OR NODES
3. NETWORK INTERFACE CARDS
4. CABLING

FILE SERVER

A network file server is a computer system used for the purpose of managing the file system, servicing the network printer, handling network communication, and other function. A server may be dedicated in which case all of its processing power is allocated to network functions, or it may be nondedicated in which case a part of the server's function may be allocated as a work station or DOS based system. The network operating system is loaded into the servers hard disk along with the system management tools and users utilities. When the system is restarted, Netware boots and the server comes under its control. At this point, DOS is no longer valid on the network drive, since it is running the netware operating system or Netware; however most DOS programs can be run as normal. No processing is done on the server, and hence it is called a PASSIVE DEVICE. The choice of a dedicated or nondedicated network servers is basically a trade odd between the cost and the performance, and the operation of the network. The larger the network, the more important it becomes to have a high performance server. Larger amounts of RAM are required to support disk caches and printer queues. The server should be matched with anticipated throughput as closely as possible.

WORKSTATIONS

Work stations are attached to the server through the network interface card and cables. The DUMB terminal on mainframes and minicomputers systems are not supported on networks because they are not capable of processing on their own. Workstations are normally intelligent systems, such as the IBM PC, XT and PCAT. The concept of distributed processing relies on the fact that personal computers attached to the networks perform their own processing after loading programs and data from the server. Hence, a workstation is called an ACTIVE DEVICE on the network. After processing, files are stored back on the server.

The workstation can also be a diskless PC, where in booting takes from the file server. In short, PC + LAN card = Workstation

NETWORK INTERFACE CARD

Network interface card provides the connection for network cabling to servers and workstations. An NIC first of all, provides the connector to attach the network cable to a server or a workstation. The on board circuitry than provides the protocol required to support this type of network card. An NIC has additional memory for buffering, incoming and outgoing data packets, thus improving the network throughput. A slot may also be available for remote boot PROM, permitting the board to be mounted in a diskless workstation. Network interface cards are in 8-bits or 16-bit standards.

NETWORK TOPOLOGIES

These are many ways in which the nodes can be arranged in a network, these are commonly referred as topologies.
The popular topologies that are run in India are STAR, BUS and RING topologies.

STAR TOPOLOGY

Under star topology a central switching system is used to connect all the nodes in the network. A node that has to send data sends a request to the central switch for a connection to the destination node, and the central node uses circuit switching to establish a dedicated path between the two stations. Once the circuit is setup, data is exchanged between the two stations.

RING TOPOLOGY

The ring topology consists of a closed loop with each mode attached on a loop. Data circulates around the ring on a series of point to point data links. A node that wishes to transmit data waits for its turn and then sends the data out onto the ring in the form of a packet, which contains both the source and the destination of the data. As the packet circulates, the destination node copies the data into a local buffer. The packet continues to circulate until it goes back to the source node in the form of acknowledgment.

BUS TOPOLOGY

Bus topology has a multipoint configuration ( multiple access broadcast ). It allows more than two devices, at a time , to be connected to and capable of transmitting on the medium. Like the ring topology, here also a packet is transmitted.

NETWORK CABLING

Once the server, workstations and network interface cards are in place, Network cabling is done to connect everything together. The most popular type of cabling is the fire optic cabling.
The typical cable types and the topologies for a computer network are as follows:

CO-AXIAL CABLE

A co-axial cable consists of a single wire conductor surrounded by an insulating core, then a moven ground wire and finally an insulating jacket to protect the whole assembly. It passes digital signals from one workstation to the next at a speed of 10 MB/sec, to distances upto 600 feet. It is commonly used on Ethernet network.

TWISTED-PAIR CABLE

Twisted-pair cabling is one of the most common types of cabling used in telephone system. The twisting in the cables helps eliminate a lot of the noise and interference associated with the cabling system. Much of the cabling installed for telephones systems is a 25-pair cable in which only a few pairs are in actual use. In most cases, unused pair can taken advantage of to establish a network cabling system. It is important to check the specification of the network interface board to make sure that the cable is of sufficient quality for transmission.

FIBRE OPTIC CABLE

Fibre optic cables transmit signals over glass-threaded wire using lights beams. The light signals are immune to outside interference and didn't emanate a signal beyond the cable itself. Hence the fibre optic cable is excellent for long runs and also excellent for high security use. What's really different about fibre optic cable and what makes it so attractive ; is its security potential and the fact that data transfer speed can be increased without decreasing the reliability of the signal at the other end of the cable. Fibre optic cable standards specify a data transmission rate of 100MB/sec, but it is possible to transmit upto 1 GB/sec. It is the ideal medium for high volume generated by Multimedia and Video Conferencing applications.

NETWORK TYPES

The most popular network types :
ETHERNET
ARCNET AND
TOKEN RING

ETHERNET

Ethernet was originally developed by Xerox and DEC, and has been available for over 10 years as a way to cable networks. The system was originally designed to use co-axial cable, but other cabling systems are now available. Ethernet has a throughput of 10MB/sec. The topology of a Ethernet cable system is a linear bus with CSMA/CD (Carrier Sense Multiple Access/ Collision Detection) access method. Workstations are connected to the trunk segment of the cable that is terminated on both ends. There are two types of Ethernet cable connections referred to as
THIN ETHERNET CABLE NETWORK
THICK ETHERNET CABLE NETWORKS.
It is possible to combine the thick and thin Ethernet cabling systems. This is usually done to save money on cables. Since thin Ethernet is usually cheaper than thick, the thick cable may be used to extend the distance between two thin Ethernet cable trunks by using repeater.
THIN CO-AXIAL ETHERNET
The thin Ethernet is physically easier to handle and does not require the use of transreceivers at the workstations. It is used most commonly for routine applications

The following rules and limitations apply:

CABLING COMPONENTS FOR THE THIN CO-AXIAL ETHERNET:

The following components are normally used in this type of cabling :
NETWORK INTERFACE CARD :
Most Ethernet cards will support either thick or thin Ethernet cabling. The board should have a BNC-type connector attached to the back. A BNC T-connector will be attached to a BNC connector on the back of the board to accommodate in and out of the cable run.
REPEATER :
Repeater is an optional device used to join two Ethernet trunks together and to strengthen the signals between them.
BNC T-CONNECTORS :
T-connector are attached to the BNC connector on the back of the Ethernet interface card. The T-connectors provides two cable connections for signal IN and signal OUT.
BNC-BARREL CONNECTORS :
These are used to join the two cable segments together.
BNC-TERMINATORS :
Each cable segment must be terminated at both ends with a 50 ohm BNC terminator.

THICK COAXIAL ETHERNET

The following rules and limitations apply:

CABLING COMPONENT FOR THICK CO-AXIAL ETHERNET

The following types of components are normally used in this type of cabling :
NETWORK INTERFACE BOARD :
Most Ethernet boards will support either thick or thin Ethernet cabling. The boards should have a female DIX-type connector for the attachment of the tranreceiver cable. A BNC connector for thin Ethernet connection is also on the board, but it is not used.
REPEATER :
The repeater is an optional device used to join two Ethernet trunks together and to strengthen the signal between them.
TRANSRECEIVER :
The transreceiver is a junction box on the thick Ethernet cable where workstations can be attached. It has three connectors. Two are thick Ethernet IN and OUT connectors, and the third connector is used to attach the workstation to the transreceiver using the transreceiver cable.
TRANSRECEIVER CABLE :
Transreceiver cable usually come with the transreceiver unit. Male and female DIX-type connectors are mounted on either end, along with the slide locks to lock the cable.
SN-SERIES TERMINATORS :
Each cable segments must be terminated at both the ends with a 50 ohm n-series terminator.

UTP ETHERNET

Its main feature is that it combines the advantages of both the BUS and STAR topologies. It makes use of micro HUBS that are connected in the common Bus topology(using co-axial cables) to the main server and the various workstations are connected to each of the hubs in the star topology(using special UTP cables).

ADVANTAGE of Ethernet e.g. HIGH SPEED of 10MB/sec, LOW COST as well as the RELIABILITY of the star topology can be achieved.

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Last updated on July 01, 1996