client-server
multitier architecture
Peer-to-peer
By network topology
bus network
star network
ring network
grid network
toroidal networks and hypercubes
tree and hypertree networks
By specialized function
Storage area networks
Server farms
Process control networks
Value added network
SOHO network
Wireless community network
We're going to talk about three classifications. The first is based on host roles, second on geographic proximity and the third on signaling methods used.
Peer-to-Peer
The first type of network that we will consider is called peer-to-peer. In a peer-to-peer network, network hosts don't have a specific role. They provide network services and they also consume network services. In In a peer-to-peer network we can have hosts that will fulfill a variety of different roles. For example, one computer can have a printer connected to it which is shared on the network. Another computer can have a large hard drive installed and everyone is allowed to put files on that hard drive. So, in this situation we have hosts that both provide and consume network services. In essence, they function both as a client and as a server at the same time. The main benefit of peer-to-peer network is the ease of installation. All we have to do is share our resources on the network. It's also very inexpensive. Of course, there's some drawbacks to a peer-to-peer network. First of all, a peer-to-peer network is not very scalable which means that the bigger it gets, the harder it is to manage it. That's because they lack centralized control.
Client - Server
Another classification within the host roles category is a client server network. In a client server network, unlike a peer-to-peer network, network hosts have specific roles assigned to them. We have certain systems, certain hosts that are assigned to be servers. A server provides network resources. On a client server network we also have clients. A client does not provide network services, it only consumes network services. Clients will not have have, for instance, shared storage or printers. All those services are provided by the server. Server provides the resources, the client simply use the resources. With a peer-to-peer network everybody had the same operating system, but in a client server network client workstations have generic operating systems that provide functionality. For example, clients could have Windows XP or Windows 2000 installed. Servers would have some special optimized operating system like Server 2003. These operating systems are designed to provide these network resources and are not designed for client type tasks. The main benefit of this type of network is that it's very highly scalable. That means it's very easy to expand the size of the network, it's very easy to add more clients and it's very easy to add more servers. Client server networks are also much easier to support. That's because services are centralized. If we know where are all the services, we know where to look when we have some problems with them. Backup is also a lot easier. We can configure that users store their data on the server. That way,
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instead of having to back up individual workstations we only need to backup one location - the server. There are some drawbacks. Operating systems for servers are fairly expensive (the exception, of course, is Linux). The other thing is that this type of network takes a lot of planning. We have to decide which servers are going to host which services, where they're going to be placed on the network, etcetera.
LAN
Now, the first kind of network based on geography is the Local Area Network or LAN. Local area network resides within a small geographic area. An example of a local area network would be the network inside a particular company or the network at our home. It can have, for example, multiple floors but they would all be connected by a network medium in some way. It could also be multiple buildings and they could be interconnected in some way. We could have several buildings, like a campus for example. It's still a local area network because the geography separating the host is relatively small. This is called an internetwork, but it is still a local area network.
WAN
It's also possible to have a computer network where the networks and the hosts are very widely distributed geographically. In that case we are talking about a Wide Area Network or WAN. A wide area network is a group of interconnected LANs, Local Area Networks, that are separated geographically. For example, a company can have offices at different cities. Sometimes, user from one city needs to access some data that is located on a server in another city. To make that possible we've connected them in some way so that these local area networks are inter-networked together, making a very large internetwork, or a wide area network.
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1. What does the term Computer network wean?
2. Does a global computer network embrace hundreds of users all over the world?
3. What Computer network classification do you know?
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Metropolitan area network
1. A metropolitan area network (MAN) is a computer network that usually spans a city or a large campus. A MAN usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks (or WAN) and the Internet.
2. The IEEE 802-2002 standard describes a MAN as being[1]: A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of local networks.
3. Authors Kenneth C. Laudon and Jane P. Laudon (2001) of Management Information Systems: Managing the Digital Firm 10th ed. define a metropolitan area network as: A Metropolitan Area Network (MAN) is a large computer network that spans a metropolitan area or campus. Its geographic scope falls between a WAN and LAN. MANs provide Internet connectivity for LANs in a metropolitan region, and connect them to wider area networks like the Internet It can also be used in cable television.
Implementation
4. Some technologies used for this purpose are Asynchronous Transfer Mode (ATM), FDDI, and SMDS. These technologies are in the process of being displaced by Ethernet-based connections (e.g., Metro Ethernet) in most areas. MAN links between local area networks have been built without cables using either microwave, radio, or infra-red laser links. Most companies rent or lease circuits from common carriers because laying long stretches of cable can be expensive.
5. DQDB, Distributed-queue dual-bus, is the metropolitan area network standard for data communication. It is specified in the IEEE 802.6 standard. Using DQDB, networks can be up to 20 miles (30 km) long and operate at speeds of 34 to 155 Mbit/s.
6. Several notable networks started as MANs, such as the Internet peering points MAE-West, MAE-East, and the Sohonet media
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1. What is MAN?
2. What technologies are used for MAN?
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9 Steps to Protecting Your Computer from Viruses and Other Malware
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Security and safety standard
9 Steps to Protecting Your Computer from Viruses and Other Malware
Achieving good computer security can seem like a daunting task. Fortunately, following the few simple steps outlined below can provide a good measure of security in very little time.
1) Use antivirus software and keep it up-to-date. You should check for new definition updates daily. Most antivirus software can be configured to do this automatically.
2) Install security patches. Vulnerabilities in software are constantly being discovered and they don't discriminate by vendor or platform. It's not simply a matter of updating Windows; at least monthly, check for and apply updates for all software you use.
3) Use a firewall. No Internet connection is safe without one. Firewalls are necessary even if you have a dial-up Internet connection -- it takes only minutes for a a non-firewalled computer to be infected.
4) Secure your browser. Many labor under the dangerous misconception that only Internet Explorer is a problem. It's not the browser you need to be concerned about. Nor is it a matter of simply avoiding certain 'types' of sites. Known, legitimate websites are frequently being compromised and implanted with malicious javascript that foists malware onto visitors' computers. To ensure optimum browsing safety, the best tip is to disable javascript for all but the most essential of sites -- such as your banking or regular ecommerce sites. Not only will you enjoy safer browsing, you'll be able to eliminate unwanted pop-ups as well.
5) Take control of your email. Avoid opening email attachments received unexpectedly -- no matter who appears to have sent it. Remember that most worms and trojan-laden spam try to spoof the sender's name. And make sure your email client isn't leaving you open to infection. Reading email in plain text offers important security benefits that more than offset the loss of pretty colored fonts.
6) Treat IM suspiciously. Instant Messaging is a frequent target of worms and trojans. Treat it just as you would email.
7) Avoid P2P and distributed filesharing. Torrent, Kazaa, Gnutella, Morpheus and at least a dozen other filesharing networks exist. Most are free. And all are rife with trojans, viruses, worms, adware, spyware, and every other form of malicious code imaginable. There's no such thing as safe anonymous filesharing. Avoid it like the plague.
8) Keep abreast of Internet scams. Criminals think of clever ways to separate you from your hard earned cash. Don't get fooled by emails telling sad stories, or making unsolicited job offers, or promising lotto winnings. Likewise, beware of email masquerading as a security concern from your bank or other eCommerce site.
9) Don't fall victim to virus hoaxes. Dire-sounding email spreading fear, uncertainty and doubt about non-existent threats serve only to spread needless alarm and may even cause you to delete perfectly legitimate files in response.
Remember, there's far more good than bad on the Internet. The goal isn't to be paranoid. The goal is to be cautious, aware, and even suspicious. By following the tips above and becoming actively engaged in your own security, you'll not only be protecting yourself, you'll be contributing to the protection and betterment of the Internet as a whole.
Crime Prevention
Every business owner, manager and employee plays a part in making businesses safe. Here are some things you can do to help prevent robbery:
- Have at least two employees open and close the business.
- Do not release personal information to strangers.
- Keep purses and personal valuables locked in desks or lockers.
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- Install a robbery alarm.
- Place a surveillance camera behind the cash register facing the front counter. Replace videotapes regularly.
- Vary times and routes of travel for bank deposits.
- Don't use marked "moneybags" that make it obvious to would-be robbers you are carrying money for deposit.
- Keep a low balance in the cash register.
- Place excess money in a safe or deposit it as soon as possible.
- Cooperate with the robber for your own safety and the safety of others. Comply with a robber's demands. Remain calm and think clearly. Make mental notes of the robber's physical description and other observations important to law enforcement officers.
- If you have a silent alarm and can reach it without being noticed, use it. Otherwise, wait until the robber leaves.
- Be careful, most robbers are just as nervous as you are.
- Keep your business neat and clean. A tidy, orderly place of business is inviting to customers, but not to robbers. Dressing neatly also sends the right message.
- Stay alert! Know who is in your business and where they are. Watch for people who hang around without buying anything. Also, be aware of suspicious activity outside your place of business. Write down license numbers of suspicious vehicles if visible from the inside of your business.
- Make sure the sales counter can be seen clearly. Don't put up advertisements, flyers, displays, signs, posters or other items on windows or doors that might obstruct the view of the register from inside or outside your business. The police cruising by your store need to see in.
- Try to greet customers as they enter your business. Look them in the eye, and ask them if they need help. Your attention can discourage a robber.
- Keep your business well-lit, inside and outside. Employees should report any burned-out lights to the business owner or manager. Keep trees and bushes trimmed, so they don't block any outdoor lights.
- Encourage the police to stop by your business.
- Learn the names of the officers who patrol your business.
- Use care after dark. Be cautious when cleaning the parking lot or taking out the trash at night. Make sure another employee inside the business keeps you within eye contact while you are involved in work details outside of your building.
- If you see something suspicious, call the police. Never try to handle it yourself. It could cost you your life.
- Handle cash carefully. Avoid making your business a tempting target for robbers. Keep the amount of cash in registers low. Drop all large bills right away. If a customer tries to pay with a large bill, politely ask if he or she has a smaller one. Explain that you keep very little cash on hand.
- Use only one register at night. Leave other registers empty and open. Tilt the register drawer to show there is no money in it.
- Leave blinds and drapes partially open during closing hours.
- Make sure important signs stay posted. For example, the front door should bear signs that say, "Clerk Cannot Open the Time Lock Safe."
- If your business is robbed put your safety first. Your personal safety is more important than money or merchandise.
- Don't talk except to answer the robber's questions.
- Don't stare directly at the robber.
- Prevent surprises, keep your hands in sight at all times.
- Don't make any sudden moves.
- Tell the robber if someone is coming out of the back room or vault or working in another area of your business.
- Don't chase or follow the robber out of your place of business.
- Leave the job of catching the robber to the police.
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1. Is your computer connected to the Internet?
2. When does a PC become a target for criminals want to access your personal information and use it for their own purposes?
3. How safe is your computer?
4. Do you have anti-virus software installed on your computer to block email virus and worms?
5. Does your anti-virus software automatically update itself with current virus definitions?
6. Do you have a policy of never opening an email attachment even if it is from someone you know?
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To provide required level of system`s protection, to make datebase, to save time, to improve the employee work efficiency, the programme doesn`t require pre-installation, the theme of my course project is actual at present, the aim of economic part is, to display selected information in a form of graphics, the purpose of this diploma project creation is.
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