Operating System Networking Technology Computer Science Essay

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A simple network can consist on two computers by connecting them with each other. There are different mediums such as cable; air waves, fiber optics etc are used to send data from one machine to another. In a network as many computer can connected with the respect of need. In a network two machines or more than two machines can send or receive data from one end to other at same time. Many different devices are used to send make a quick and efficient network. A network can be established anywhere like at home, office, company etc according to the requirements.

Local area network is known as LAN. This network is used for small networks such as in building, schools, a few kilometers or in a company. This network is commonly used to connect personal computers in an office or a small company to share different resources such as printer, scanner etc. LAN is a restricted or its transmission time is very limited, that's why it is known as Local area network. In LAN a cable is used as a resource to establish this network. All the computers and devices are connected with a cable. Earlier the LAN run speed was 10Mbps (mega bits per second) to 100Mbps. Now a day it can run up to 100Gbps and it is a high speed data network.

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Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN).

Most LANs connect workstations and personal computers. Each node (individual computer) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions

Local-area networking has been revolutionized by the exploding use of LAN switching at Layer 2 (the data link layer) to increase performance and to provide more bandwidth to meet new data networking applications. LAN switches provide this performance benefit by increasing bandwidth and throughput for workgroups and local servers. Network designers are deploying LAN switches out toward the network's edge in wiring closets. These switches are usually installed to replace shared concentrator hubs and give higher-bandwidth connections to the end user.

Layer 3 networking is required in the network to interconnect the switched workgroups and to provide services that include security, quality of service, and traffic management. Routing integrates these switched networks, and provides the security, stability, and control needed to build functional and scalable networks.

Traditionally, Layer 2 switching has been provided by LAN switches, and Layer 3 networking has been provided by routers. Increasingly, these two networking functions are being integrated into common platforms. Multilayer switches that provide Layer 2 and 3 functionality, for example, are now appearing in the marketplace. [3]

ETHERNET:

Ethernet and its newer sibling Fast Ethernet are the LAN technologies most commonly used today. Ethernet has become popular because of its modest price; Ethernet cable is inexpensive and easily installed. Ethernet network adapters and Ethernet hardware components are also relatively inexpensive.

On Ethernet networks, all computers share a common transmission medium. Ethernet uses an access method called Carrier Sense Multiple Access with Collision Detect (CSMA/CD) for determining when a computer is free to transmit data on to the access medium. Using CSMA/CD, all computers monitor the transmission medium and wait until the line is available before transmitting. If two computers try to transmit at the same time, a collision occurs. The computers then stop, wait for a random time interval, and attempt to transmit again.

CSMA/CD can be compared to the protocol followed by a room full of polite people. Someone who wants to speak first listens to determine whether anybody else is currently speaking (this is the Carrier Sense). If two people start speaking at the same moment, both people will detect the problem, stop speaking, and wait before speaking again (this is Collision Detect).

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Traditional Ethernet works well under light-to-moderate use but suffers from high collision rates under heavy use. Some of the newer ethernet variants, which might include intelligent hubs or switches, support higher traffic levels. You'll learn more about hubs and switches in Hour 9, "Network Hardware."

There are many different types of LANs Ethernets being the most common for PCs. Most Apple Macintosh networks are based on Apple's AppleTalk network system, which is built into Macintosh computers.

There are many network operating systems (NOS) introduced TCP/IP is one of them. A twisted pair cable is used for this purpose.

Fig. 2 [4]

3.1 FEATURES OF LAN:

Some of the advantages of LAN are given below. (a) Workstations can share different devices like printers, scanner, fax machine. This is cheaper than buying these devices for every workstation.

(b) Workstations do not necessarily need their own hard disk or CD-ROM drives which make them cheaper to buy than stand-alone PCs.

(c) Users can communicate with each other and transfer data between workstations very easy.

(d) One copy of each application package such as a word processor, spreadsheet etc. can be loaded onto the file and shared by all users. When a new version comes out, it only has to be loaded onto the server instead of onto every workstation.

Fig. 7 [11]

3. WAN (WIDE AREA NETWORK):

As its name shows it is used for large geographical area. This area could be a country or continent. A huge collection of machines and devices are interconnected in this network. Those machines are known as "hosts". These hosts are connected in LAN and LAN connects to a "router". These routers are arranged inside the "subnet". The subnet carries messages from host to host.

CIRCUIT SWITCHING:

A type of communications in which a dedicated channel (or circuit) is established for the duration of a transmission. The most ubiquitous circuit-switching network is the telephone system, which links together wire segments to create a single unbroken line for each telephone call.

The other common communications method is packet switching, which divides messages into packets and sends each packet individually. The Internet is based on a packet-switching protocol, TCP/IP.

Circuit-switching systems are ideal for communications that require data to be transmitted in real-time. Packet-switching networks are more efficient if some amount of delay is acceptable.

Circuit-switching networks are sometimes called connection-oriented networks. Note, however, that although packet switching is essentially connectionless, a packet switching network can be made connection-oriented by using a higher-level protocol. TCP, for example, makes IP networks connection-oriented. [12]

Fig 8. [13]

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PACKET SWITCHING:

Packet switching refers to protocols in which messages are divided into packets before they are sent. Each packet is then transmitted individually and can even follow different routes to its destination. Once all the packets forming a message arrive at the destination, they are recompiled into the original message.

Most modern Wide Area Network (WAN) protocols, including TCP/IP, X.25, and Frame Relay, are based on packet-switching technologies. In contrastnormal telephone service is based on a circuit-switching technology, in which a dedicated line is allocated for transmission between two parties. Circuit-switching is ideal when data must be transmitted quickly and must arrive in the same order in which it's sent. This is the case with most real-time data, such as live audio and video. Packet switching is more efficient and robust for data that can withstand some delays in transmission, such as e-mail messages and Web pages.

A new technology, ATM, attempts to combine the best of both worlds -- the guaranteed delivery of circuit-switched networks and the robustness and efficiency of packet-switching networks. [14]

Fig 9. [15]

WAN Dialup Services

Tripod said in his website that Dialup services offer cost-effective methods for connectivity across WANs. Two popular dialup implementations are dial-on-demand routing (DDR) and dial backup.

DDR is a technique whereby a router can dynamically initiate and close a circuit-switched session as transmitting end station demand. A router is configured to consider certain traffic interesting and other traffic uninteresting. When the router receives interesting traffic destined for a remote network, a circuit is established and the traffic is transmitted normally.

WAN Switch

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A WAN switch is a multi-port internetworking device used in carrier networks. These devices typically switch such traffic as Frame Relay, X.25, and SMDS and operate at the data link layer of the OSI reference model. Following figure illustrates two routers at remote ends of a WAN that are connected by WAN switches.

REMOTE CONNECTION NETWORK.

David says in his article (networking & connectivity) that Remote connections link single users (mobile users and/or telecommuters) and branch offices to a local campus or the Internet. Typically, a remote site is a small site that has few users and therefore needs a smaller-size WAN connection. The remote requirements of a network, however, usually involve a large number of remote single users or sites, which causes the aggregate WAN charge to be exaggerated.

Consequently, network designers typically choose between dialup and dedicated WAN options for remote connections. Remote connections generally run at speeds of 128 kbps or lower. A network designer might also employ bridges in a remote site for their ease of implementation, simple topology, and low traffic requirements.

Trends in Remote Connections

Today, there is a large selection of remote WAN media that includes the following:

Analogue modem

Asymmetric Digital Subscriber Line

Leased line

Frame Relay

X.25

ISDN

EXPLANATION:

In this diagram a wide area network is shown which having all the types of networking (LAN, MAN WAN and wireless network). In this network 2 LAN (Ethernet) are connected to WAN through WAN router by using their IP addresses. Below that a wireless network and wide area network is shown. A satellite is transmitting signals to the base station and from base station they are converted to other networks. Through wide area network they are transmitted in all over the world.

IP Addresses :

Defination

An identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route messages based on the IP address of the destination. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 1.160.10.240 could be an IP address.

Within an isolated network, you can assign IP addresses at random as long as each one is unique. However, connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates.

The four numbers in an IP address are used in different ways to identify a particular network and a host on that network used . Four regional Internet registries -- ARIN, RIPE NCC, LACNIC and APNIC -- assign Internet addresses from the following three classes.

Class A - supports 16 million hosts on each of 126 networks

Class B - supports 65,000 hosts on each of 16,000 networks

Class C - supports 254 hosts on each of 2 million networks

The number of unassigned Internet addresses is running out, so a new classless scheme called CIDR is gradually replacing the system based on classes A, B, and C and is tied to adoption of IPv6.

Subnet mask:

A subnet mask is a mechanism used to split a network into subnetworks; it can be used to reduce the traffic on each subnetwork by confining traffic to only the subnetwork(s) for which it is intended, thereby eliminating the issues of associated congestion on other subnetwork(s) and reducing congestion in the network as a whole. Each subnet functions as though it were independent, keeping traffic local and forwarding traffic to another subnetwork only if the address of the data is external to the subnetwork.

Subnetting Concept .

Subnetting an IP network allows for the flow of network traffic to be segregated based on a network configuration. It essentially organizes the hosts into logical groups, and provides for improving network security and performance. The most common reason for subnetting IP networks is to control network traffic. Traditionally, in an Ethernet network, it is very common for all nodes on a segment to see all the packets transmitted by all the other nodes on that segment, which introduces collisions, and the resulting retransmissions under heavy traffic loads. For additional information on subnetting, see RFC 1817, and RFC 1812.

Class Address Ranges

ClassA- 1.0.0.0 to 126.0.0.0

ClassB- 128.0.0.0 to 191.255.0.0

ClassC- 192.0.1.0 to 223.255.255.0

ClassD- 224.0.0.0 to 239.255.255.255

ClassE- 240.0.0.0 to 255.255.255.255

Class A, Class B, and Class C are the three classes of addresses used on IP networks in common practice. Class D addresses are reserved for multicast. Class E addresses are simply reserved, meaning they should not be used on IP networks (used on a limited basis by some research organizations for experimental purposes).

Reserved Address Ranges

Address ranges below are reserved by IANA for private intranets, and not routable to the Internet. For additional information, see RFC 1918.

10.0.0.0 10.255.255.255(10/8prefix)

172.16.0.0 - 172.31.255.255(172.16/12prefix)

192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

Other reserved addresses:

127.0.0.0 is reserved for loopback and IPC on the localhost.

224.0.0.0 - 239.255.255.255 is reserved for multicast addresses.

255.255.255.255 is the limited broadcast address (limited to all other nodes on the LAN)

Subnet Calculator Explanation(Example)

This calculator will calculate the subnet mask to use, given a TCP/IP network address and the number of subnets or nodes per subnet required.

To create the subnet mask, first remember that the purpose of the subnet mask is to separate the (32 bit) ip address into the network prefix and the host number. If a bit in the subnet mask is 1, the corresponding bit in the IP address is part of the network address; if the bit in the subnet mask is 0, the corresponding bit in the IP address is part of the host address.

First depict the ip address in binary. Take 61.246.19.18 and convert to binary:

ip address: 00111101.11110110.00010011.00010010

First we determine what class of address it is:

If the first bit is 0 it is a Class A address If the first two bits are 10 it is a Class B address If the first three bits are 110 it is a Class C address If the first four bits are 1110 it is a Class D multicast address If the first four bits are 1111 it is a Class E experimental address

Your example is a Class A address. The default subnet mask for a Class A address is:

subnet mask: 11111111.00000000.00000000.00000000

The formula for figuring out the number of 'host' bits in a subnet mask is

2^n=(number of nodes ) (2^n means '2' to the power of 'n')

Since you know the number of nodes, you need to find 'n'.

Because you want 64 node(s), you want to leave 6 - '0' bits in the subnet mask since 64 = 2 ^ 6.

This will give you the following subnet mask:

subnet mask: 11111111.11111111.11111111.11000000

Which is referred to as /26 or in dotted decimal notation as 255.255.255.192