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In a network all links are with limited bandwidth. The wise use of these bandwidths will be one of the main challenges in network communication. The wise use may depend on application. Those varieties applications are combine the several low-bandwidth channels into one large bandwidth channel and expand the bandwidth channel to achieve the goal.
We can develop the bandwidth utilization by two techniques such as multiplexing and spreading. we can achieve the efficiency of bandwidth utilization by multiplexing techniques. Similarly we can achieve the privacy and anti jamming of bandwidth by spreading technique.
Multiplexing is a set of technique that provides the simultaneous transmission of multiple signal across the single data link. Benefits of this technique is when we install the bandwidth of link is greater than the bandwidth needed for the device connected to it, the bandwidth will go waste. During the situation we can use this technique to maximize the utilization of the resources.
Multiplexing technique base on three techniques such as frequency-division multiplexing, wave length-division multiplexing, time division multiplexing. Here first two techniques use for analog signal and last one use for digital signal.
In spreading techniques, here also combine the signal which comes from different resources into larger bandwidth but goal is outweigh bandwidth efficiency. Spread spectrum techniques spread the original spectrum needed for each station by spreading code. There are two techniques to spread the bandwidth. First one is frequency hopping spread spectrum (FHSS) and second one is direct sequence spread spectrum (DSSS).
Switch is a small device to connect the couple of computers with in a network. Technically it operates at data link layer of the OSI model. Network switch has capable of inspecting data packets. So when the data transfer over the switch, it will determine the destination places of each data packets and forwarding them to correct destination places. So it generates less traffic in network. The switches are in different model according to concepts of support the difference no of connecting devices.
Hub is another multi computer connector with in a network. A hub includes series of ports which accept the RJ45 connector of standard Ethernet cables. Hubs donâ€™t inspect the data packets. So they will not know of destination place of data. So they will send the data to all computers which are connected with them. It will lead network conjunction. We can categorise the hubs into main three cases according to key features. Passive hubs, they do not amplify the signal before to transfer. Active hub, it do the amplification. Intelligence hubs, it contains remote management capabilities via SNMP, virtual LAN (VLAN).
Router is very important physical device in a network to join many wired or wireless networks. It operates at network layer of OSI model. It has ability of data filtering either incoming or out going, base on sender, receiver IP address. Routers work by accumulated routing table and use algorithm to find out the shortest route of individual devices in the network. In this way routers play main role to manage the traffic in a network.
Transmission medium use to carry information from source to destination. In data communication transmission medium is usually free space, cable or fiber optic cable. Those medium could be categorised into two boards. Those are guided medium, unguided medium. Twisted pair cable, coaxial cable and fiber optic cable are called guided medium and wireless is called unguided medium.
TWISTED PAIR CABLE
Twisted pair cable contains two main conductors, each conductor with its own plastic insulation. One of the conductor is used to carry the signal and other one is used as a ground reference. In a twisted pair cable can transmit wide range of frequencies. Those medium normally use on telephone lines to provide high data rate connection and in Local area networks such as 10 base T, 100 base T also use twisted pair cable.
Coaxial cable carries higher range frequency signal than twisted pair cable. It has central core conductor or standard wire and enclosed in an insulating sheath and also an outer conductor of metal foil turn around it. We need coaxial connector to connect coaxial cable. Usually it uses to telephone network where network could carry more than 10000 voice signal and also cable TV networks. Another common application is in traditional Ethernet LANs. Because of it has high bandwidth.
FIBER OPTIC CABLE
A fiber optic cable is made by class and transmit signal in light format. To connect fiber optic cable usually uses three type of fiber optic cable connector. Those are subscriber channel (SC) connector to use cable TV , straight-tip (ST) connector to connect network devices, MT-RJ connector to connect telephone lines. These type cable are very cost effective and has wide range bandwidth. So that SONET network and hybrid network are created by optical fiber cable.
In wireless communication signal are normally broadcast through the free space, so anyone who has a device capable of receiving them can access the signal. This unguided signal can travel from source to destination in several ways. Such as ground propagation, sky propagation and line of sight propagation.
Wireless transmissions are divided into three main board groups. Such as radio waves, micro waves, infrared waves.3 kHz to 1GHz frequency range waves is normally called radio waves. When we transmit radio waves it will propagate in all direction and it can receive by any receiving antenna. It use to AM, FM raid, television broad cast and cordless phones.
Micro waves having 1GHz to 300 GHz frequency range. When we transmit micro waves it focus narrowly so we need to align the sending, receiving antenna. Biggest advance is that waves travels without any interfering. This transmission medium use peer to peer communication Like as cell phones, satellite networks and wireless LANs.
The waves which have from 300 GHz to 400THz usually call Infrared waves. It could be used to short distance communication. It use for communication between devices such as keyboard ,mice, PCs, printer.