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received by all nodes and not just the intended recipient.
Historically, the main motive for purchasing hubs rather than switches was their price. This stimulus has largely been excluded by reductions in the price of switches, but hubs can still be useful in special and explicit circumstances
Switches
A network switch is a hardware device that joins multiple computers together within one local area network (LAN). Network switches may appear nearly identical to network hubs, but a switch generally contains more intelligence (and a slightly higher price tag) than a hub. Unlike hubs, network switches are capable of examining data packets as they are received, determining the source and destination device of each packet and forwarding them appropriately to that location only. By delivering messages only to the connected device intended, a network switch helps
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control network traffic and conserves network bandwidth, offerir generally superior performance than a hub. This feature also make switches more secure than hubs.,,Switch '
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Different models of network switches support differing nur connected devices. Most consumer-grade network switches either four or eight connections for network devices. Switches connected to each other, a so-called daisy chaining method progressively larger number of devices to a LAN.
Routers
Network routers are intelligent devices that forward and packets along networks. A network router connects at least twoi commonly two LANs or WANs or a LAN and its ISP network. A i located at a gateway (where one network meets another).Thei responsible for the delivery of packets across diverse net destination of the IP packet might be a web server in another* an e-mail server on the local area network. It is the respons router to deliver those packets in a timely manner. The effe internetwork communications depends, to a large degree, of routers to forward packets in the most
103 Information Technology in Financial Services | Reference
^tworking 104 A router has two crucial jobs:
■ The router confirms that information doesn't go where it's not needed. This is vital for keeping large volumes of data from jamming the network.
■ The router makes certain that information do make it to the intended destination.
In performing these two jobs, a router joins the two networks, passing information from one to the other and in some cases, performing conversions of various protocols between the two networks. It also protects the networks from one another, preventing the traffic on one from unnecessarily spilling over to the other. This process is known as routing.
A router may generate or/and maintain a routing table of the available routes and their conditions and use this information, along with distance and cost algorithms, to determine the best route for a given packet, i.e. shortest routes and/or with least traffic. Typically, a packet may travel through a number of network points with routers before arriving at its destination.
A router which connects end-users to the Internet is called an Edge router and a router which serves to transmit data between other routers is called a Core router.
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105 Information Technology in Financial Services | Reference
In addition to packet forwarding, a router provides further services as well. To meet the demands on today's networks, routers are also used
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■ To guarantee steady, reliance availability of network connectivity. Routers use substitute parts in cases where the primary component fails to achieve delivery of packets.
■ To provide integrated services of data, video and voice over wired and wireless networks.
■ For security, a router helps in mitigating the impact of worms, viruses and other attacks on the network by permitting or denying the forwarding of packets, thus performing the firewalling function.
Some other specialized network devices are Gateways, Bridges, Repeaters, etc.
Network Media Communication across networks is carried on a medium which provides the channel over which the message or data travel 什om source to destination. Modern networks primarily use three types of media to interconnect devices and to provide the pathway over which data can be transmitted. These media are
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■ Metallic wires within cables ■ Fiber optic cables
■ Wireless transmission
Choosing the cables necessary to make a successful LAN or WAN connection requires consideration of the different media types. Each media type has its advantages and disadvantages. Some of the factors to consider are
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cable length, cost, bandwidth, ease of installation, susceptibility to interferences and noise etc. It is also possible and very common to use different types of media in setting up of a network. For example, wire and wireless media may be used in a certain network. Also coaxial cables and fiber optic cables may be used in the same netw set-up.Metallic wires within cables
The most widely used network medium is copper wire. Since it is a conductor of electricity, the digital signals generated by the computer converted into electrical signals so that they can be sent over network. The disadvantage of copper wire is that there is too energy loss if the message is sent over long distances. The different of copper wires are described as follows
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UTP (Unshielded Twisted Pair)
Unshielded twisted pair cable is the most popular cable type today's networks. It consists of two or more pairs of unshielded copper wires. It is extensively used in telephone systems ar world and in computer networking due to its low cost, easy i and maintenance. UTP cables provide
^tworking 106 transmission speeds of 上
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(Megabits per second) to 100 Mbps, depending on the type and category of the cable used. The disadvantage of this cable is that it cannot be used for networks spread over long distances, as its runs are limited to 100 meters or less as after this length the signal strength weakens, a phenomenon called attenuation. Attenuation is a limitation in all metallic wires, ranging from mild to severe. As UTP is not shielded, it is more sensitive to electromagnetic interference.
STP (Shielded Twisted Pair)
Shielded twisted pair cable contains one or more pairs of twisted wires that are insulated with a metal foil to minimize electromagnetic interference. The metal shield is connected to the ground to prevent external signals from getting into and internal signals from getting out of the cable. Different types of STP cables with different characteristics are available. The right type is selected keeping in view the size of network, performance requirements and budget. These cables provide transmission speeds of up to 16 Mbps in Token rings and an overall speed of up to 155 Mbps. The maximum segment it provides is usually 100 meters, although a few hundred meters is also possible. The advantage of using the STP cable is that its ability to reduce the EMI (electromagnetic interference) is better than the UTP cable. Its disadvantages are that it is costly and provides less speed than the UTP cable.
Coaxial Cable:
Coaxial cables consist of an insulator that separates the braided inner conductor and the outer conductor, which is a woven copper braid. These cables are commonly used for cable TV connections in homes. Coaxial cable is of two types, namely the Thinnet and the Thicknet, depending on the thickness of the cable. Thinnet supports a maximum segment length of 185 meters and Thicknet can send signals up to 500 meters. The cost of the cable depends on which type of cable is used. Thinnet is less costly and easier to install, whereas Thicknet is costlier and demands more efforts in installation. The transmission speed these cables provide is between 2.5 Mbps and 10 Mbps. Coaxial cables are more resistant to electromagnetic interferences than UTP and STP cables, as they use insulators
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to minimize external interference.
Fiber Optic Cable
Fiber optic cables are made up of glass and they transmit data in the form of light, unlike the copper wire that uses electrical signals. A reflective coating that allows light beams to travel without outer interference covers the glass cable. The advantages of Fiber optic cables are that signals can be sent at a much higher speed and to very long distances without the risk of outer interference. Since no metallic conductor is used, attenuation is no longer a problem and even larger distances can be reached without losing signal power. This makes fiber optic cables the most suitable choice for establishing network backbones extending over very large distances.
Wireless (unguided) Transmission
Wireless transmission is the sending and receiving of data packets distance without the use of wires. Wireless network transmission is for locations where physical mediasuch as coaxial cables, UPT/SP fiber optic are not possible to deploy. The demand for communications is increasing exponentially.
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Types of Networks
Wireless communication can be performed in a variety of ways such as wireless Ethernet, GSM, Bluetooth, Infrared, Wi-Fi and Wi-Max. Similarly, broadband wireless is an emerging wireless technology that allows the concurrent delivery of voice, video and data signals. All these technologies are based on different standards and specifications.
Wireless transmission can provide special services and conveniences, such as connection to the Internet or other networks without connecting to a wire directly, hence giving mobility and ease of use. It can also facilitate the creation of networks in special situations, such as in terrain that is unfavorable to wired media.
There are various types of networks which are used world-wide these days, both domestically and commercially. These networks are used on the basis of their scale and scope, historical reasons and their design and implementation issues. LAN and WAN are mostly known and used widely. LAN, local area network, was first invented for communication between two computers. WAN emerged in due course of time with changing needs and as the technology became available.
LAN operates through cables and network cards. Later WLAN, Wireless local area network, was formed through the LAN concept.There are no wires involved in communication between computers. As mentioned already, LAN is the original network out of which other networks are formed according to requirements. Some popular types are as follows
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LAN - Local Area Network
A local area network (LAN) is a computer network that attaches computers and devices in a limited geographical area such as home, school, computer laboratory or office building. The defining features of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, lack of a need for leased telecommunication lines and moderate cost. Most local area networks are built with relatively economical hardware such as coaxial cables, network adapters and hubs. Wireless LAN and other more advanced LAN hardware options also exist.
Information Technology in Financial Services | Referencel WAN - Wide Area Network
A wide area network (WAN) is a telecommunications network, usually used for connecting computers, that spans a large geographical area. WANs can be used to connect cities, countries, or even continents. WANs are often used by large corporations or organizations to enable the exchange of data, and in a wide variety of industries. Corporations with facilities and offices/branches at multiple locations have embraced WANs with great enthusiasm. Increasingly, however, even small businesses are utilizing WANs as a way of increasing their communications competences. Although WANs serve a purpose similar to that of local area networks (LANs), WANs are structured and operated rather differently. The user of a WAN usually does not own the communications lines that connect the remote computer systems
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instead, the user subscribes to a service through a telecommunications provider. Unlike LANs, WANs typically do not link individual computers, but instead are used to link two or more LANs. WANs also transmit data at slower speeds than LANs. WANs are also structurally similar to metropolitan area networks (MANs), but provide communications links for distances greater than (approximately) 50 kilometers. The largest WAN in existence is the Internet.WANs have existed for decades, but new technologies, services, applications have developed over the years to dramatically increase efficacy for business. WANs were originally developed for di leased-line services carrying only voice, rather than data. Conseque they linked the private branch exchanges (PBXs) of distant offices branches of the same company. WANs are still used for voice services, today they are used more frequently for data and image transmi ' (such as video conferencing). These added applications have encou significant growth in WAN usage, primarily because of the surge in connections to the wider networks.
WANs can be used for almost any data sharing purpose for which can be used. Slower transmission speeds, however, may make applications less practical for WANs. Efforts are being made to over such shortcomings and there are noticeable successes. The most uses of WANs are for electronic mail and file transfer, but WANs can
permit users at remote sites to access and enter data on a central site's database, such as instantaneously updating accounting records. New types of network-based software that facilitate productivity and production tracking, such as groupware and work-flow automation software, can also be used over WANs. Using groupware, workers at dispersed locations can more easily collaborate on projects, sharing documents and designs. WANs also give remote offices access to a central office's other data communications services, including the Internet.
MAN - Metropolitan Area Network
A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. The latter usage is also sometimes referred to as a campus network. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations.
Network Topologies Topology is the network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.
Network topologies are categorized into the following basic types
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■ Bus ■ Ring ■ Star _ Tree _ Mesh
More complex networks can be built as hybrids of two or more of the above basic topologies.
Bus Topology
Bus networks use a common backbone to connect all computing devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector (e.g. NIC). A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. The term "broadcast
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is used because the message goes to all devices/computers connected to the bus. A terminator is required at each end of the bus cable to prevent the signal from bouncing back and forthInformation Technology in Financial Services | Referencel
iction to Networking
on the bus cable.
Bus topologies are relatively easy to install and don't require much cabling compared to the alternatives so there is generally a low upfront cost. However, there is a higher cost of managing the network. Bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result, including longer delays and greater collisions of data packets. In addition, if the backbone cable fails, the entire network effectively becomes unusable.
Ring Topology
In a ring network, each connected device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counter clockwise"). Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The basic problem of ring topology is that each workstation should participate actively in transfer of the information a failure in any cable or device breaks the loop and can take down the entire network - the network is dependent on the abilih of the signal to travel around the ring.
Star Topology
In networks with a star topology, each network host (for example a PC) is connected to a central hub with a point-to-point connection. The "hub" may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP). All traffic on the network passes through the central hub that acts as a signal booster or repeater.
The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire network. If the hub fails, however, the entire network also fails.
Tree Topology
Tree Topology is a combination of the bus and the star topology. Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.
A tree topology is supported by many network vendors and is the best topology for branched out networks. However, the tree topology network is entirely dependent on the trunk which is the main backbone of the network. If that were to fail, then the entire network would fail. A tree topology network can become complicated and difficult to manage after a certain point.
Mesh Topology
Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. The mesh network is based on a very practical concept and has red jced