A network router is a small electronic device that allows you build a home network simply. The home router serves as the core or "centerpiece" of the network to which computers, printers and other devices can be connected. Networking with a router helps you to (for example):
*share files between computers
*share an Internet connection between computers
*share a printer
*connect your game console or other home entertainment equipment to the Internet
Routers are not necessarily required to build a network. For example, you can connect two computers directly to each other with just a cable (or without wires in some cases). Home
الخميس، 3 يونيو 2010
الأربعاء، 2 يونيو 2010
الأحد، 4 أبريل 2010
Networking Basics
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- Network - A network is a group of computers connected together in a way that allows information to be exchanged between the computers.
- Node - A node is anything that is connected to the network. While a node is typically a computer, it can also be something like a printer or CD-ROM tower.
- Segment - A segment is any portion of a network that is separated, by a switch, bridge or router, from other parts of the network.
- Backbone - The backbone is the main cabling of a network that all of the segments connect to. Typically, the backbone is capable of carrying more information than the individual segments. For example, each segment may have a transfer rate of 10 Mbps (megabits per second), while the backbone may operate at 100 Mbps.
- Topology - Topology is the way that each node is physically connected to the network (more on this in the next section).
- Local Area Network (LAN) - A LAN is a network of computers that are in the same general physical location, usually within a building or a campus. If the computers are far apart (such as across town or in different cities), then a Wide Area Network (WAN) is typically used.
- Network Interface Card (NIC) - Every computer (and most other devices) is connected to a network through an NIC. In most desktop computers, this is an Ethernet card (normally 10 or 100 Mbps) that is plugged into a slot on the computer's motherboard.
- Media Access Control (MAC) address - This is the physical address of any device -- such as the NIC in a computer -- on the network. The MAC address, which is made up of two equal parts, is 6 bytes long. The first 3 bytes identify the company that made the NIC. The second 3 bytes are the serial number of the NIC itself.
- Unicast - A unicast is a transmission from one node addressed specifically to another node.
- Multicast - In a multicast, a node sends a packet addressed to a special group address. Devices that are interested in this group register to receive packets addressed to the group. An example might be a Cisco router sending out an update to all of the other Cisco routers.
- Broadcast - In a broadcast, a node sends out a packet that is intended for transmission to all other nodes on the network.
What is Network Cabling?
Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.
The following sections discuss the types of cables used in networks and other related topics.
- Unshielded Twisted Pair (UTP) cable
- Shielded Twisted Pair (STP) Cable
- Coaxial Cable
- Fiber Optic Cable
- Cable Installation Guides
- Wireless LANs
Unshielded Twisted Pair (UTP) Cable
Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks
Categories of Unshielded Twisted
| Category | Speed | Use |
| 1 | 1 Mbps | Voice Only (Telephone Wire) |
| 2 | 4 Mbps | LocalTalk & Telephone (Rarely used) |
| 3 | 16 Mbps | 10BaseT Ethernet |
| 4 | 20 Mbps | Token Ring (Rarely used) |
| 5 | 100 Mbps (2 pair) 1000 Mbps (4 pair) | 100BaseT Ethernet Gigabit Ethernet |
| 5e | 1,000 Mbps | Gigabit Ethernet |
| 6 | 10,000 Mbps | Gigabit Ethernet |
Unshielded Twisted Pair Connector
The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig. 2). A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.
Shielded Twisted Pair (STP) Cable
Although UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.). If you must place cable in environments with lots of potential interference, or if you must place cable in extremely sensitive environments that may be susceptible to the electrical current in the UTP, shielded twisted pair may be the solution. Shielded cables can also help to extend the maximum distance of the cables.
Coaxial Cable
Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield (See fig. 3). The metal shield helps to block any outside interference from
Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial
Fiber Optic Cable
Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials (See fig. 5). It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between
Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is
The center core of fiber cables is made from glass or plastic fibers (see fig 5). A plastic coating then cushions the fiber center, and kevlar fibers help to strengthen the cables and prevent breakage. The outer insulating jacket made of teflon or PVC.
Wireless standards and speeds
The Wi-Fi Alliance is a global, non-profit organization that helps to ensure standards and interoperability for wireless networks, and wireless networks are often referred to as WiFi (Wireless Fidelity). The original Wi-Fi standard (IEEE 802.11) was adopted in 1997. Since then many variations have emerged (and will continue to emerge). Wi-Fi networks use the Ethernet protocol.
| Standard | Max Speed | Typical Range |
| 802.11a | 54 Mbps | 150 feet |
| 802.11b | 11 Mbps | 300 feet |
| 802.11g | 54 Mbps | 300 feet |
Java Read File Line by Line
learn how to write java program to read file line by line. We will use the DataInputStream class to Read text File Line by Line.
Here is the code of java program to Read text File Line by Line:
-------------------------------------------------------------------
-------------------------------------------------------------------
Here is the code of java program to Read text File Line by Line:
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import java.io.*;
class FileRead
{
public static void main(String args[])
{
try{
// Open the file that is the first
// command line parameter
FileInputStream fstream = new FileInputStream("textfile.txt");
// Get the object of DataInputStream
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine;
//Read File Line By Line
while ((strLine = br.readLine()) != null) {
// Print the content on the console
System.out.println (strLine);
}
//Close the input stream
in.close();
}catch (Exception e){//Catch exception if any
System.err.println("Error: " + e.getMessage());
}
}
}-------------------------------------------------------------------
الجمعة، 2 أبريل 2010
States and capitals
Argentina, Buenos Aires
Jordan, Oman
Ecuador, Quito
UAE, Abu Dhabi
Bahrain, Manama
Riyadh, Saudi Arabia
Kuwait, Kuwait
Brazil, Brasilia
Britain, London
Rome, Italy
Spain, Madrid
China, Beijing
Japan, Tokyo
South Korea, Seoul
Egypt, Cairo
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