Lan In Star

STAR NETWORK

The concept of a StarLAN network is the same as an Arcnet network or the Novell star network with the following characteristics:

· Peripherals installed on the server are shared.

· The connection is made through a Central Distributor (HUB) with 12 ports each, and has interconnection with other Central Distributors in order to be able to connect up to 3 levels of them.

· The network server can be an 80386 processor-based computer, such as the RS model or a Hewlette-Packard mini 3000 or micro XE.

· It has the possibility of connection with other computers of the HP 9000, HP 1000 family or with the VAX family of Digital Equipment Corp. (DEC)

To connect a star-type network, there are rules based on the management of the Central Distributor, which is responsible for making the communication between the workstations and the selected server.

This configuration presents good flexibility when it comes to increasing the number of teams; In addition, the failure of one of the peripheral computers does not affect the general behavior of the network. However, if the failure occurs in the central computer, the result affects all stations. Diagnosing network problems is simple, since all computers are connected to a central computer. It is not a suitable topology for large installations, since when the cables are grouped in the central unit, it creates situations prone to management errors, also requiring large amounts of expensive cables. This configuration is fast in communications between the peripheral computers and the central one, but slow in communications between peripheral computers. On the other hand, the capacity of the network is high if the flow of information is between peripheral and central computers, the speed of the network depending very little on the flow of information that circulates through it. ATT's STARLAN or SNeT networks are star networks.

The star type network is composed of the following devices:

· Interface card.
· Two-wire unshielded cable.
· Central Distributor (HUB).

In order to carry out installation tests, the StarLAN network has a feedback connector (Loop-Back) to check the operation of the network cards.

This network cannot be connected directly between mini computers for data exchange, it can be done through another HP network, THIN-LAN, in order to connect against any model of the HP 3000 family, the HP 9000, the HP 1000 and DECVAX.

The network connection starts from the installation of the interface card in each of the computers of the network itself, once this is done they are connected to the Central Distributor in some of the free connectors. The distance to any of the workstations cannot be greater than 250 meters and the distance between two workstations cannot be greater than 1000 meters.

The Central Distributor has 12 free ports to make the connection; ports 1 through 11 can connect any workstation, and port 12, labeled Upper Central Distributor, is used to connect two network levels.

The intermediate Central Distributor is connected to the superior one through this port and the main Central Distributor is left empty, StarLAN only uses two levels of interconnection, as can be seen in the figure. By using the two levels of the Central Distributor we can connect up to 50 workstations.

Elements of a Network

A computer network consists of both hardware and software. Hardware includes: workstations, servers, network interface card, cabling, and connectivity equipment. The software contains the Network Operating System (NOS).

Work stations

Each computer connected to the network retains the ability to function independently, performing its own processes. Likewise, the computers become network workstations, with access to the information and resources contained in the network's file server. A workstation does not share its own resources with other computers. This can be from a PC XT to a Pentium, equipped according to the needs of the user; or also from a different architecture such as Macintosh, Silicon Graphics, Sun, etc.

Servers

They are those computers capable of sharing their resources with others. Shares can include printers, disk drives, CD-ROMs, hard drive directories, and even individual files.

Network Interface Card

To communicate with the rest of the network, each computer must have a Network Interface Card (NIC) installed. They are also called network adapters or just network cards. In most cases, the card fits into the computer's expansion slot, although some are external drives that connect to the computer through a serial or parallel port. Internal cards are almost always used for PC's, PS/2 and workstations like SUN's. Interface cards can also be used in minicomputers and mainframes. External cases are often used for Mac's and for some laptops. The interface card gets the information from the PC, converts it to the proper format, and sends it over the cable to another interface card on the local network. This card receives the information, translates it so that the PC can understand it, and sends it to the PC.

Wiring

The LAN must have a cabling system that connects individual workstations to file servers and other peripherals. If there was only one type of wiring available, the decision would be easy. The truth is that there are many types of cabling, each with its own proponents, and since there is such a wide variety in cost and capacity, selection should not be a trivial matter.

Twisted Pair Cable: This is by far the least expensive and most common type of network medium.

Coaxial cable: It is as easy to install and maintain as twisted pair cable, and is the preferred medium for large LANs.

Fiber optic cable: It has a higher transmission speed than the previous ones, it is immune to radio frequency interference and capable of sending signals over considerable distances without losing its strength. It has a higher cost.

connectivity team

In general, for small networks, the length of the cable is not a limitation for its performance; but if the network grows, it may be necessary to extend the cable length further or exceed the specified number of nodes. There are several devices that extend the length of the network, each of which has a specific purpose. However, many devices incorporate the features of another type of device to increase flexibility and value. Hubs or concentrators: They are a central point of connection for network nodes that are arranged according to a physical star topology.

Repeaters: A repeater is a device that allows you to extend the length of the network; amplifies and retransmits the network signal.

Bridges: A bridge is a device that connects two separate LANs to create what appears to be a single LAN.

Routers: Routers are similar to bridges, only they operate at a different level. They generally require each network to have the same network operating system, in order to connect networks based on completely different logical topologies such as Ethernet and Token Ring.

Gateways: A gateway allows nodes on a network to communicate with different types of networks or with other devices. You might have, for example, a LAN consisting of IBM-compatible computers and one Macintosh-compatible computer.

Operating system

After meeting all the hardware requirements to install a LAN, you need to install a Network Operating System (NOS), which manages and coordinates all the operations of said network. Network operating systems come in a wide variety of shapes and sizes, because each organization that employs them has different needs. Some operating systems do very well on small networks, while others specialize in connecting many small networks over fairly large areas.

The services that NOS performs are:

File support: This is creating, sharing, storing and retrieving files, essential activities in which the NOS specializes in providing a fast and secure method.

Communications: Refers to everything that is sent through the cable. Communication takes place when, for example, someone logs onto the network, copies a file, sends email, or prints.

Services for equipment support: This includes all special services such as printing, tape backups, network virus detection, etc.

Talking Ethernet

Ethernet, also known as IEEE 802.3, is the most popular standard for LANs in use today. The 802.3 standard employs a logical bus topology and a physical star or bus topology. At first, it was thought of using coaxial cable for wiring this type of network, although today other types of cables can be used. The transmission speed of the information through the cable is 10 Mbps.

If thick coaxial cable is used, up to 4 sections of cables can be made (joined with repeaters) of a maximum of 560 meters each. The computers are connected to the cable through transceivers, with a maximum distance between the transceiver and the computer of 15 meters. There can only be computers in three of the four sections, with the maximum number of workstations being 100 per section.

If fine coaxial cable is used, no transceiver devices are needed, and the computer cable can be connected to the network cable with simple T-connectors. The maximum number of sections in this case is 5, with the maximum length of each section being 305 meters. The sections are joined through the use of signal repeaters. There can only be computers in three of the sections, with the maximum number of workstations being 30 per section.

Ethernet networks use a bus topology with the CSMA/CD method (Carrier Sense Multiple Access with Collision Detection) to access the medium. That means that any station can try to transmit data at any time, but since they are all connected to a single common cable, only one station can be transmitting on the cable (bus) at any given time. To solve the problems of collisions in the transmission there are a series of rules such as: before transmitting check that there is no other station transmitting, or in case of collision make a station wait a random time margin before trying again sending data.