Network Connectivity: –
To expand a network without breaking it into new parts for connecting it to other networks are have to use devices like,
All networks require a central location to bring media segments together. These central locations are called hub. They are also called multipart repeaters or connectors.
We should keep our attention on following points,
- There is a limit to the number of hub; maximum 4 hubs can be connected together.
- Connect each hub directly to a server network card rather than to another hub.
- We should label the connection on the hub. By this way we can save number of hours for trouble shooting.
- The more hubs data passes through, the slower the connection could be.
There are three types of hubs available,
- Passive Hub
- Active Hub
- Intelligent Hub
- Passive Hub: –
A hub which simply combines the signals of network segment is called passive hub. There is no signal processing or regeneration because it does not bouts the signal. It reduces the maximum cabling, distance, permitted to half.
If a segment normally allows a reliable transmission distance of 200 meters, the distance between a passive hub & a device can be only 100 meters.
- Active Hub: –
Hubs which have electronic components that regenerate or amplify signals are called active hub. Using these hubs the distance between devices can be increased.
The active hub amplifies signal as well as noise too, depending on whether it functions as simple amplifier or signal generator. It is much more expensive than passive hub.
- Intelligent Hub: –
Hubs which provide network management and intelligent path selection in addition to signal regeneration are called intelligent hubs.
All transmission media alternate the electromagnetic waves that travel through them. In this way attenuation limits the distance in any medium that carry data. Adding a device that amplifies a signal can allow it to travel further increasing the size of the network.
If we are connecting computers those are more than 100 meters away, using a 10 base T – Ethernet cable. When we will need a device that amplifies signal to ensure data transmission.
Devices which amplify the signals during data transmission are called repeaters which have two categories.
- Amplifier Repeaters
- Signal Regenerating Repeaters
- Amplifier Repeaters: –
An amplifier repeater amplifies the entire incoming signal. It amplifies the noise too along with the signals.
- Signal Representing Repeaters: –
It creates an extra duplicate of incoming data by identifying it among the noise, reconstructing it and transmitting only the desired information. In this way, it reduces the noise.
In this repeater, the original signal is duplicated, boosted to its original strength and sent.
Normally repeaters simply deal with the actual, physical signal on a repeater and therefore they operate at the physical layer of the open system interconnection model.
Repeaters can be used to combine an unlimited number of transmission media segments but for proper design, networks limit the number of repeaters.
The connect network segment avoid regenerated signals in order to extend network length, bridges re used.
Bridges connect network segments and increase the maximum possible size of our network. A bridge selectively determines the appropriate segment to which it should pass a signal. It does this work by reading the address of all the signals it receives.
The bridge reads the physical location of the source & destination computers from the address. E.g. if we have following two segments, “A” and “B” bridges, follow the following procedure.
- It receives all the signals from both segments “A” & “B”.
- It reads the addresses and filters all signals from segment “A”, that are address to segment “A” because they do not need to cross the bridge.
- Signals from segment “A” addressed to a computer on segment “B” are retransmitted to segment “B”.
- The signals from segment “B” are treated in the same way.
Bridges first filters the addresses so that it can divide busy network information segment & reduce network traffic. Network traffic will be reduced if most of signals are addressed to same segment and do not cross the bridge. To use a bridge effectively, networks are divided into groups by physical location and shared resources.
A bridge is capable of Ethernet segment and token ring segment. Translation Bridge allows us to connect different type with different physical addressing.
There are four different types of bridges, source route transparent bridging, transparent bridges, Source routing bridges and Translation bridging.
- Transparent bridges keep a table of addresses in memory to determine where to send data.
- Source routing bridges require the entire route to be included in the transmission & do not route packets intelligently. IBM token ring network uses this type of bridge.
Routers are packet forwarding device just like switches & bridges. However routers allow transmission data between network segments. Unlike switches which forward packets based on physical node address, routers, operate at the network layer of the open system interconnection reference model. Routers forward packets based on a network ID.
A collection of interconnected network is referred to as an internetwork. Routers provide the connectivity within an internetwork.
Routers are simply specialized computers concerned with getting packets from point A to point B when a route receives a packet defined for its network interface; it examines the destination address to determine the best way to get in there. It makes the decision based on information contained within its own routing tables. Routing tables are association for network IDs and interfaces that know how to get to that network. If a router can resolve a means to get the packet from A to B, it forwards it to either the intended recipient or to the next router in the chain otherwise the route informs the sender that it doesn’t know how to reach the destination network.
Routers enabled with the TCP/IP protocol and all networking devices configured to use TCP/IP, make some sort of routing decision. All decision occurs within the IP protocol framework.
There are two types of routing methods, distance vector routing and link state routing.
A switch is the next rung up the evolutionary blabber from bridges. In modern star topology networking when you need bridging functionality you often buy a switch, but bridging is not the only benefit of switch implementation. Switches also provide the benefit of micro-LAN segmentation. Micro-LAN segment means that every node connected to a switched port receives its own dedicated bandwidth with layer 3 switching. You can further segment the network into virtual local area network.
Like, bridges and switches also operate at the link layer of open system interconnection reference model and in the case of layer 3 switches, sometimes extend into network layer. The same mechanism is used to build dynamic tables that associated MAC addresses with switched port. However bridges implement, store and forward bridging via software, whereas switches implement either store, forward or cut through switching via hardware, with a marked improvement of speed. Micro-LAN segmentation is the key benefit & switches.
Primary Network Components: –
Networks consist of three primary components, servers, clients / workstations and resources.
Servers come in many shapes and sizes. They are a core component of network, providing a link to perform any task. The link it provides could be to a resource existing on the server it self or a resource on a client pc.
Servers perform several task servers that provide files to the user on the network are called file servers. Servers that host printing services for users are called print servers. Servers can be multipurpose or single purpose.
Server offers network the capability of centralizing the control and resources & can reduce administrative difficulties. They can be used to distribute processes for balancing the load on the computer and can increase speed & performance. They can also offer departmentalizing of files for improved reliability.
- Dedicated Server: –
These are assigned to provide specific application or services for the network because a dedicated server is specializing in only a few tasks. It requires fewer resources then non-dedicated server.
- Non-dedicated Server: –
These are assigned to provide one or more network services and local access. A non-dedicated server is expected to be slightly more flexible than a dedicated server.
Workstations are computers that the user on a network does their work on, performing activities such as database design, graphic design or other computers. As client they are allowed to communicate with the server in order to use the network resources.
It takes several items to make a workstation into a client. You must install a network interface card, a special expansion card that allows a pc to talk on a network. You must connect it to a cabling system and you must install some special software called client software which allow the computer to talk to the server.
Network Resources: –
The servers are used to share the resources among other computers on the network. The workstations use the resources from the servers. A resource is any item that can be used on a network. Resources can include a broad range of items including following.
- Printers and other peripherals.
- Disk storage.
Network Interface Card: –
The network interface card provides the physical interface between computer & cabling. It prepares data, sends data & control the flow of data. It can also receive and translate data into bytes for the CPU to understand.
The following factors should be taken into consideration when choosing of network interface card, Preparing data, sending and controlling data, configuration, drivers, compatibility and performance.
Preparing Data: –
On a network cable, data travel in a single stream, as on a one-lane highway. It is the network interface card’s job to translate the data from the computers into signals. It does this by translating digital signals into electrical signals.
Sending and Controlling Data: –
In order to successfully send data on the network, you need to make sure that the network cards are of the same type and they are connected to the same piece of cable. If you use card & different types, neigh additionally, network card can send data in either full duplex or half duplex modes.
The network interface card’s configuration includes manufactures hardware address, IRQ address, base I/O port address and base memory address. Some may also use DMA channels.
Each card must have a unique hardware address. Configuring on network interface card is similar to configuring any other type of expansion card. The network interface card usually needs a unique IRQ channels & I/O address & possibly a DMA channel.
For computer to use the network interface card it is very important to install the proper device drivers. These drivers communicate directly with the network radiator & adaptor.
PC Bus Type: –
When choosing a network interface card, use one that files the bus type of your PC. If you have move than one type of bus in your PC, use a network interface card that fits into the fastest type.
The most important goal of the network interface card is to optimize network performance and minimize the amount of time needed to transfer data packets. There are several ways of doing this. If the network card can use DMA channels than data can move directly from card’s buffer to the computers memory, by passing the CPU, thus the performance is increased.
Types of Networks: –
Based on the role of the computer attached to them, networks are divided into three types. Server based network, peer network and hybrid network.
Server Based Network (Client/Server Network): –
Server based networks are also called client/server network. Server based networks are defined by the presence of dedicated server on a network that provide security & resources. It divide processing task between clients and servers. In windows 2000 server based networks are organized into what are called active directory domains. Domains are collections of network and clients that share security information.
Special server called domain controllers control domain security & logon permission. Computer users cannot access the resources of servers in a domain until a domain controller has authenticated them. User information is stored centrally so users only need to logon once.
- Advantages: –
- Strong central security.
- Central file storage.
- They have ability to pool available hardware and software with low cost.
- They also have the ability to share expensive equipment.
- They include optimized dedicated servers which are faster at sharing network resources.
- It needs less intrusive security since a single password allow access to all shared resources on the network.
- Large number of users can be managed easily.
- Disadvantages: –
- Expensive dedicated hardware.
- Expensive network operating system software & client licenses.
- A dedicated network administrator.
Peer Networks: –
Peer networks are defined by a lock of central control over the network. There are no servers in peer network. Users simply share disk space & resources such as printer & faxes. Peer networks are organized into workgroups. There is not central login process. If you have logged into one peer, you will able to use only resource on the network that are not controlled by a specific password because there is not central security. You will have to know the individual password for each secured shared resources. This can be quite inconvenient.
Peers cannot be optimized peers generally have licensing limitations that prevent more than a small number of from simultaneously accessing resources.
- Advantages: –
- No extra investment in server where hardware, software are required.
- Easy setup.
- Little network administration required.
- Ability of users to control resource sharing.
- Lower cost for small network.
- Disadvantages: –
- Additional load on computer because of resource sharing.
- Inability of peers to handle as many network connections as servers.
- Lock of central organization.
- No central point of storage.
- Weak and intrusive security.
- Lock and central management.
Hybrid Networks: –
Hybrid networks have all three types of computers operating on them and generally have active directory domain and workgroups. This means while most shared resources are located on servers, network user still have access to any resources. It also means that network users do not have to logon to the domain controller to access workgroup resources being shared by peers.
- Advantages: –
- Advantages of server based network.
- Many of the advantages of peer based network.
- Ability of user and network administrator to control security based on the important of the shared resources.
- Disadvantages: –
- Expensive dedicated hardware.
- A dedicated network administrator.
Server Types: –
A server in a network is dedicated for performing specific task of other computers on the network. Common server types include following. File servers, print servers, application servers, message servers, database servers.
File Servers: –
File servers offer services that allow network users to share files. File servers are network application that store, retrieve and move data. This type of service is probably the most important reasons companies invest in a network. There are several popular types of file servers such as Windows NT, Netware and apple share.
Following are the services provided by file servers.
- File Transfer: –
To transfer a file from one computer to another computer, you could save the file to a floppy disk, put on your sneakers and wait it over to other computer. Fortunately networks become more sophisticated and began to offer file transfer services. Every network operating system has its own level of file security. File security level is needed when all these files transferring taking place.
- File Storage & Data Migration: –
Information explosion is a huge amount of data that must be stored somewhere. File server provide three categories of file storage – online storage, offline storage and near-line storage.
The process by which data is moved from online to offline or near-line is called data migration. Files are selected for migration based on factors such as the last time the file was accessed, the file owner or the file size.
- File Update Synchronization: –
File update synchronization ensures that each user of a file has the latest version. File synchronization works to ensure that changes made to files are organized in the chronological order in which they take place and those files are properly updated.
Print Servers: –
Another important factor of computer networking was the demand for the ability to share printers. The advent of networking represented a whole new level of computer printing because a network can allow users to share printers. It allows you to place printer where convenient. It achieves better workstation performance by using high speed network data transfer.
Print services manage and control printing on a network allowing multiple & simultaneous access to printing facilities. Network operating system achieves this by using print queues. Printing on a network with queues can be more efficient way for users to work. Network printing also cost’s by allowing shared access to printing devices. Another print service is fax service.
Application Servers: –
Application services allow client PCs to access & use extra computing power & expensive software applications that reside on a shared computer. You can add specialized server to provide specific applications on a network. Application servers can be dedicated computers setup specifically for the purpose of providing application services. Although in the earlier days of networking, application services were not often found on networks they have recently become more popular.
Message Servers: –
Message servers provide message services in a wide verity of communication methods that go far beyond simple file servers with message services, data can take the form of graphics, digitized video or audio as well as text and binary data.
Message services must coordinate the complex interactions between users, documents and applications. Message servers provide four main services as follow – electrical mail, workgroup applications, object oriented applications and directory services.
Database Servers: –
Database services can provide a network with powerful database capabilities that are available for use on relatively weak PCs most database systems are client server based. The client end portion of the application runs on the client providing an interface and handling less intensive functions. The server end portion of application handles the intensive performance of database operations.
Database servers are becoming increasingly powerful providing complex services including security, database optimization & data distribution.
Network Media: –
Media are what the message is transmitted over different media have different properties and are most effectively used in different environments for different purposes.
TV is a good medium for quick coverage. Media in network determines how quickly and to change a computer can talk and how expensive the process is! Following are the most common network medium.
Copper is the most common network medium. This metal has served over communications need for over a century and will likely be widely used for another century. Engineers have become very good at sending electrical signals over copper wires and detecting them with a great deal of identity at the other hand fidelity is how precisely the signal that is received corresponds to the signal that was sent.
Photons are the basic particles of light, photons are not affected by interference from electrical devices or radio waves. Fiber optics is a network technology developed to exploit the communications medium of light in long strands & glass.
Unfortunately, properly installing fiber optics requires more skill than installing copper wires and an adapter card for a computer to send data at several gigabytes is very expensive. Fiber optic is used mainly in environment where copper will not work and where the faster speed is really needed.
Both fiber optics and copper cabling have the drawback that you a need a cable to connect the computers. Infrared technology can send the data right through the air. Infrared provide an effective solution for temporary or hard to cable environments. Infrared is a line of sigh technology. The photons will not go through the walls, which limit the usefulness of infrared in office environment.
Infrared is not a very high speed network when compared to copper and fiber optics networks. Most local area networks today operate speed of 10 MBPS. Infrared adapter operate at speeds ranging from 3 MBPS to 4 MBPS. Some infrared equipment operate at data rates of 100 MBPS, but the cost and complexity of such specialized hardware make it impractical to use.
Another through the air method is via radio. Engineers have been sending information over electro magnetic waves for almost as long as they have over copper wires. Radio waves will also reach places, it is difficult to get a network cable to one problem with radio is that there is only so much electro magnetic spectrum to go around.