network topologies

What is network topologies
Network Topology refers to layout of a network and how different nodes in a network are connected to each other and how they communicate. This slideshow describes five of the most common network topologies.


  

1. Mesh Topology:
In a mesh network, devices are connected with many redundant interconnections between network nodes. In a true mesh topology every node has a connection to every other node in the network. There are two types of mesh topologies:
 Full mesh topology occurs when every node has a circuit connecting it to every other node in a network. Full mesh is very expensive to implement but yields the greatest amount of redundancy, so in the event that one of those nodes fails, network traffic can be directed to any of the other nodes. Full mesh is usually reserved for backbone networks.
 Partial mesh topology is less expensive to implement and yields less redundancy than full mesh topology. With partial mesh, some nodes are organized in a full mesh scheme but others are only connected to one or two in the network. Partial mesh topology is commonly found in peripheral networks connected to a full meshed backbone.

2. Star Topology:
In a star network devices are connected to a central computer, called a hub. Nodes communicate across the network by passing data through the hub.
Main Advantage:
In a star network, one malfunctioning node doesn't affect the rest of the network.
Main Disadvantage:
If the central computer fails, the entire network becomes unusable.

  


3. Bus Topology:
 In networking a bus is the central cable -- the main wire -- that connects all devices on a local-area network (LAN). It is also called the backbone. This is often used to describe the main network connections composing the Internet.  Bus networks are relatively inexpensive and easy to install for small networks. Ethernet systems use a bus topology.
Main Advantage:
 It’s easy to connect a computer or device and typically it requires less cable than a star topology.
Main Disadvantage:
The entire network shuts down if there is a break in the main wire and it can be difficult to identify the problem if the network shuts down.

                                      

4. Ring Topology:
 A local-area network (LAN) whose topology is a ring. That is, all of the nodes are connected in a closed loop. Messages travel around the ring, with each node reading those messages addressed to it. One main advantage to a ring network is that it can span larger distances than other types of networks, such as bus networks, because each node regenerates messages as they pass through it.

5. Tree Topology:
 This is a "hybrid" topology that combines characteristics of linear bus and star topologies. In a tree network, groups of star-configured networks are connected to a linear bus backbone cable.
Main Advantage:
A Tree topology is a good choice for large computer networks as the tree topology "divides" the whole network into parts that are more easily manageable.
Main Disadvantage:
The entire network depends on a central hub and a failure of the central hub can cripple the whole network.

            

Network Adapters & Interfaces, NIC
A network card (also called network adapter, network interface card, NIC, etc.) is a piece of computer hardware designed to provide for computer communication over a computer network.


Network cards used to be expansion cards to plug into a computer bus, most newer computers have a network interface built into the motherboard, so a separate network card is not required unless multiple interfaces are needed or some other type of network is used.


The card implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as ethernet or token ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP.


A network card typically has a twisted pair, BNC, or AUI socket where the network cable is connected, and a few LEDs to inform the user of whether the network is active, and whether or not there is data being transmitted on it. The Network Cards are typically available in 10/100/1000 Mbit/s. This means they can support a transfer rate of 10 or 100 or 1000 Mbit/s




What Is a Computer Operating System?
Computers use low-level software called an operating system (O/S) to help people build and run their own programs. Operating system software runs not just on laptop computers but also on cell phones, network routers and other so-called embedded devices.


Concentrator
As generally used, a concentrator is a device that acts as an efficient forwarder of data transmission signals. A remote access hub is sometimes referred to as a concentrator. The term aggregator is also frequently used with approximately the same meaning. A typical concentrator or remote access hub is a device that handles incoming dial-up calls for an Internet (or other network) point-of-presence and performs other services. A concentrator or hub may be able to handle up to 100 dial-up modem calls, support a certain number of ISDN connections, and support leased line and frame relay traffic while also functioning as a router.


Repeater
Network repeaters regenerate incoming electrical, wireless or optical signals. With physical media like Ethernet or Wi-Fi, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel.
Actual network devices that serve as repeaters usually have some other name. Active hubs, for example, are repeaters. Active hubs are sometimes also called "multiport repeaters," but more commonly they are just "hubs." Other types of "passive hubs" are not repeaters. In Wi-Fi, access points function as repeaters only when operating in so-called "repeater mode."




What is Ethernet?
Basically, Ethernet is both the name for the cable that enables network devices to connect to one another, and the name for the communication protocol that these cables use. When you refer to an Ethernet port, for example, you're referring to the physical port to which the Ethernet cable connects, but you're also referring to the method of communication that the cable uses; it networks via Ethernet protocols. Most modern Ethernet networks consist of Ethernet cards that contain the Ethernet port, Ethernet cables to connect devices and Ethernet routers or hubs to help regulate traffic.

What is localTalk
The cabling scheme supported by the AppleTalk network protocol for Macintosh computers. Most local-area networks that use AppleTalk, such as TOPS, also conform to the LocalTalk cable system. Such networks are sometimes called LocalTalk networks .
Although LocalTalk networks are relatively slow, they are popular because they are easy and inexpensive to install and maintain. An alternative cabling scheme that is faster is Ethernet.


What is terminator
(1) A device attached to the end-points of a bus network or daisy-chain. The purpose of the terminator is to absorb signals so that they do not reflect back down the line. Ethernet networks require a terminator at both ends of the bus, and SCSI chains require a single terminator at the end of the chain.
(2) A character that indicates the end of a string. In the C programming language, the null character serves as a terminator.