12 hours Beginners
Network means when two or more computers are connected using a transmission media for sharing resources(e.gprinter,scanner,cdrom etc.) and transfer data. Or network is collection of computers and devices which are connected to each other through transmission media for sharing resources and information. Computer Network can be classified according to the hardware and software technology which are used to interconnecting the individual devices in the network,such as hub, switch, router, cable etc.
Why we use computer network or what is the advantages of networking of computer ?
We use network because of following reasons
Resourse Sharing-This is main reason for using networking. Resourse sharing means a single device used by multiple computers within the network. Ex-Use of network printe, i.e A single printer used by many computers in one network. This save our money.
Reliability : Copies of a file may be maintained on two or more different machines such that if one of the copies becomes un-accessible due to a hardware crash, the other copies may be used.
Data Sharing-Same data can be shared by multiple computers.
High Speed-The information can be synchronized by different computers at high speed. If any change made in online document,this changed can seen immediately.
Cost Factor : The Personal Computers have a better price / performance ratio than other types of computer systems. Thus, it is better to have PCs, one per user, with data stored on a shared “file – server” machine.
Before we go further let us know the some basic fact of network devices.Simplex,Full and Half Duplex
Simplex- In simplex transmission, one of the communcating devices can only send data, wheras the other can only receive it. the communication is unidirection. Full duplex-The device which can send and receive data simultaneously.ex- Telephone, Mobile etc. Half duplex-The device which transmit and receive data but only one at a time,i.e either device can send data or receive data but not both.ex:: walkie-talkies Broadband and Base band
Broadband-In broadband transmissions share medium’s bandwidth into multiple analog channel unidirectionally. This transmission work well over long distance,WAN Communications uses this feature .
Base band- It uses the entire medium’s capacity for a single channel over digital signaling. Since only one signal at a time can occupy a channel, the use of MUX(multiplexer) will allow multiple devices to send multiple signal using a single transmission media.
Hub- A “hub” is a device which is used to connect input connections with multiple output connections. A “hub” is basically a place of convergence where data arriving from one or more directions is forwarded out in one or more other directions. Hubs are multiport repeaters which work at the Physical Layer of the OSI model. The hubs are used to provide a physical “Star” topology. Hub is called dump devices because when it receive data from a port , it broadcast to its all port except receiving port this create unwanted traffic and data collosion. Ethernet hubs vary in the speed (network data rate or bandwidth) they support. Some years ago, Ethernet hubs offered only 10 Mbps rated speeds. Newer types of hubs offer 100 Mbps Ethernet. Some support both 10 Mbps and 100 Mbps (so-called dual-speed or 10/100 hubs).Hub is two types:- Active hub-hub which amplify signal and broadcast it. Passive hub- hub which only broadcast the signal.
Switch- A “switch” is a device that incorporates bridge functions as well as point – to – point dedicated connections. Switches connect devices or networks and forward frames based on the MAC destination addresses of each frame. Switches operate at the Data – Link Layer of the OSI model. Network switches nearly identical to network hubs, but a switch generally contains more intelligence than a hub. Unlike hubs, network switches are capable of inspecting data pakets as they are received, determining the source and destination device of each packet, and forwarding them appropriately. By delivering messages only to the connected device intended, a network switch conserves bandwith and offers generally better performance than a hub.
Hubs” and “Switches” may be further compared as under :-
|Hubs are collision domain devices.||Switches are broadcast domain devices.|
|All the parts of a hub are part of the same Ethernet.||Each part of a switch may be regarded as a separate Ethernet but all are part of the same LAN.|
|All ports of a hub share the same bandwidth.||Each port on a switch has it’s own bandwidth.|
|In a hub, a frame appearing on any port is repeated to all the other ports.||In a switch, a frame appearing on a particular port is repeated only to the specified destination port.|
|A “sniffer” on any hub port can see the traffic of the entire network.||A switched network is difficult to “sniff”.|
|A hub repeats any defective incoming frame.||A switch does not repeat defective frames.|
Router A router is used to route data packets between two ore more different networks. When a data packet comes in on one of the network lines, the router reads the address information in the packet to determine its ultimate destination. Then, using information in its routing table, it directs the packet to the next network on its journey. A data packet is typically passed from router to router through the networks of the Internet until it gets to its destination computer.
Routers also perform other tasks such as translating the data transmission protocol of the packet to the appropriate protocol of the next network, and preventing unauthorized access to a network by the use of a firewall. The section on routing explains the theory behind this and how routing tables are used to help determine packet destinations. Routing occurs at the network layer of the OSI model. They can connect networks with different architectures such as Token Ring and Ethernet. Although they can transform information at the data link level, routers cannot transform information from one data format such as TCP/IP to another such as IPX/SPX.
Routers do not send broadcast packets or corrupted packets. If the routing table does not indicate the proper address of a packet, the packet is discarded. When multiple router are connected to each other they exchange the routing tables information, by using a dynamic routing protocol(Eigrp,Ospf,).
A router has interfaces for different physical types of network connections, (such as copper cables, fiber optic, or wireless transmission). It also contains firmware for different networking protocols standards. Each network interface uses this specialized computer software to enable data packets to be forwarded from one protocol transmission system to another.
Bridge A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments. It reduces the traffic on other network segments, since it does not send all packets.
Bridge operate at the data link layer of the OSI model, which means the bridge cannot read IP addresses, but only the outermost hardware address of the packet. In our case the bridge can read the ethernet data which gives the hardware address of the destination address, not the IP address.Bridges inspect incoming traffic and decide whether to forward or discard it.
Bridges forward all broadcast messages. Only a special bridge called a translation bridge will allow two networks of different architectures to be connected. Bridges do not normally allow connection of networks with different architectures. The hardware address is also called the MAC (media access control) address. To determine the network segment a MAC address belongs to, bridges use one of:
Transparent bridge Derives its name from the fact that the devices on the network are unaware of its existence. A transparent bridge does nothing except block or forward data based on the MAC address.Most of today's transparent bridges are more commonly called "Learning Bridges" because, in addition to buffering the packets at the port, they also examine information the source address field of a data packet. When a packet arrives at a port on a learning bridge, the bridge looks for its source address in its FDB (filtering database), an internal database. If the source address is not in the FDB, it simply adds that source address and the bridge port number on which it arrived to the FDB. Then the bridge looks for the packet's destination in the FDB,
If the destination exists in the FDB, the packet is sent to the bridge port associated with the destination address.
If the destination does NOT exist in the FDB, the packet is sent out all of the bridge ports except for the port on which it arrived.
A Learning bridge learns from a packets source address and forwards it on the packets destination address.
Source route bridge(SRT) examine the packet for a special field that indicates the path the packet should take through the network. If a path between the source and destination device is unknown, an "Explorer" packet is transmitted and it collects the IDs of the bridges and LANs as it progresses through the network between the source and destination devices. The Explorer packet is then returned to the transmitting station with a sequential listing (map) of the LAN(s) and bridges ID's between the source and destination devices. A SRT bridge relies on the intelligence in the data packet to make decisions how where the packet should be sent.
SRT (Source Routing Transparent Bridge) is a hybrid of both a Source Routing bridge and a Transparent bridge and is capable of supporting packets with or without the source routing information.
Gateway A node on a network that serves as an entrance to another network. In enterprises, the gateway is the computer that routes the traffic from a workstation to the outside network that is serving the Web pages. In homes, the gateway is the ISP that connects the user to the internet. A network gateway is an internetworking system capable of joining together two networks that use different base protocols. A network gateway can be implemented completely in software, completely in hardware, or as a combination of both. Depending on the types of protocols they support, network gateways can operate at any level of the OSI model.
Thanks for reading this article. We believe that every article always has a scope for improvement. Your little effort and time will make this article more useful for other users. Share your tips in the comments, and I’ll use the best ones in a future post.
Please like and share this page.