NETWORK COMPONENTS
1. NIC (Network Interface Card)
A network interface card (NIC) is a computer circuit board or card that is installed in a computer so that it can be connected to a network. Personal computers and workstations on a local area network (LAN) typically contain a network interface card specifically designed for the LAN transmission technology, such as Ethernet or token ring. Network interface cards provide a dedicated, full-time connection to a network.
Function of NIC The NIC card has one or more user-accessible ports to which the network cabling medium is connected. Adapter card drivers inhabit the Data Link layer of the OSl model or, more specifically, the Media Access Control (MAC) sub layer of the Data Link layer. A network adapter card driver is sometimes called a MAC driver.
The network adapter card and its accompanying software and firmware perform several roles.
Microsoft identifies the following roles for the network adapter card:
(a) Preparing data for the transmission medium
(b) Sending data
(c) Controlling the flow of data
Preparing Data for the Transmission Medium The data travels on the network in serial form. Inside the PC, however, data moves along the data bus in parallel form (8, 16, or 32 bits at a time). The network adapter card, therefore, must convert the parallel data from the bus into the serial form required for network transmission.
Switch -
In a telecommunications network, a switch is a device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination. In local area network (LAN), a switch determines from the physical device (Media Access Control or MAC) address in each incoming message frame which output port to forward it to and out of.
In a wide area packet-switched network such as the Internet, a switch determines from the IP address in each packet which output port to use for the next part of its trip to the intended destination.
In the Open Systems Interconnection (OSI) communications model, a switch performs the Layer 2 or Data-link layer function. That is, it simply looks at each packet or data unit and determines from a physical address (the "MAC address") which device a data unit is intended for and switches it out toward that device.
There are two types of switches-
(a) Layer2 switch
(b) Layer3 switch
1- Layer 2 switch Layer 2 refers to the Data Link layer of the commonly-referenced multilayered communication model, Open Systems Interconnection (OSI). The Data Link layer is concerned with moving data across the physical links in the network. In a network, the switch is a device that redirects data messages at the layer 2 level, using the destination Media Access Control (MAC) address to determine where to direct the message.
The Data-Link layer contains two sub layers that are described in the IEEE-802 LAN standards:
* Logical Link Control (LLC) sub layer
The Data Link layer ensures that an initial connection has been set up, divides output data into data frames, and handles the acknowledgements from a receiver that the data arrived successfully. It also ensures that incoming data has been received successfully by analysing bit patterns at special places in the frames.
2- Layer3switch A network device that forwards traffic based on layer 3 information at very high speeds. Traditionally, routers, which inspect layer 3, were considerably slower than layer 2 switches. In order to increase routing speeds, many "cut-through" techniques were used, which perform an "inspect the first packet at layer 3 and send the rest at layer 2" type of processing.
The switching technique are as under
* Cut -Through Switch Cut-through switches read the MAC address as soon as a packet is detected by the switch. After storing the 6 bytes that make up the address information, they immediately begin sending the packet to the destination node, even as the rest of the packet is coming into the switch.
* Store and Forward A switch using store-and-forward will save the entire packet to the buffer and check it for CRC errors or other problems before sending. If the packet has an error, it is discarded. Otherwise, the switch looks up the MAC address and sends the packet on to the destination node. Many switches combine the two methods, using cut-through until a certain error level is reached and then changing over to store-and-forward. Very few switches are strictly cut-through, since this provides no error correction.
* Fragment-Free A less common method is fragment-free. It works like cut-through except that it stores the first 64 bytes of the packet before sending it on. The reason for this is that most errors, and all collisions, occur during the initial 64 bytes of a packet.
3- Difference between layer 2 &Layer 3 Switch
Layer 2 switch
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Layer 3 switch
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a) Layer 2 is for peer to peer communication.
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a) Layer 3 is for process to process communication.
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b) Routing in inter network with Layer 2 switches is not possible.
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b) Routing in inter network with Layer 3 switches.
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c) Layer 2 switch can only do switching.
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c) Layer 3 can do switching as well as routing.
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d) Layer 2 uses the Mac address for switching.
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d) layer 3 uses the IP address for routing.
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e) Layer 2 in the header portion contains source and destination physical addresses.
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e) layer 3 in the header portion contains logical IP of the source and in the destination portion it contains logical IP of gateway of that(of source) network.
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f) L2 Switch, restrict only collision.
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f) L3 Switch, enable to restrict broadcast.
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g) Peer is identified by MAC address.
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g) Process is identified by Socket.
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| h) Layer 2 switch has multi collision and single broadcast domain. | h) Layer 3 switch has multi collision and multi broadcast domain. |
Repeater
A network device used to regenerate or replicate a signal. Repeaters are used in transmission systems to regenerate analog or digital signals distorted by transmission loss. Analog repeaters frequently can only amplify the signal while digital repeaters can reconstruct a signal to near its original quality.
In a data network, a repeater can relay messages between subnets that use different protocols or cable types. Hubs can operate as repeaters by relaying messages to all connected computers. A repeater cannot do the intelligent routing performed by bridges and routers.
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.
Bridges operate at the data link layer (Layer 2) of the OSI model. Bridges inspect incoming traffic and decide whether to forward or discard it. An Ethernet bridge, for example, inspects each incoming Ethernet frame - including the source and destination MAC addresses, and sometimes the frame size - in making individual forwarding decisions.
Bridges serve a similar function as switches that also operate at Layer 2. Traditional bridges, though, support one network boundary, whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.
Router
A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs network. Routers are located at gateways, the places where two or more networks connect.
Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP (Internet Control Message Protocol) to communicate with each other and configure the best route between any two hosts. Router links dissimilar networks which are not transparent to end stations. Router acts on a network layer frame.
Hubs
A hub is a repeater with multiple ports. Hubs operate at physical layer of the OSI reference model. Hubs are used to connect computers to a server in Networks that use the star topology. Hubs can also be used to connect multiple segments of the same network, and transfer data from one segment to another. In a network, a hub acts as a central point for devices such as computers, printers, and routers. If a node sends data to any one of the other node, hub receives the data and transmits the signal to all the ports. This increases the Network traffic.
Hubs can be classified as follows
*Active Hub An active hub is usually powered and it amplifies the signal to its original strength. Active hubs are the most common type of hubs used in Networks. They are useful when the segments of the networks are not close to one another and the signal may require amplification.
*Passive Hub A passive hub is typically unpowered and makes only physical electrical connections. It does not regenerate or amplify the signal.
*Intelligent Hub An intelligent hub is an active hub with additional features such as Network monitoring capabilities.
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COMPUTING KNOWLEDGE
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