Routers are physical devices* that join multiple wired or wireless networks together
Technically, a wired or wireless router is a Layer 3 gateway*, meaning that the wired/wireless router connects networks (as gateways* do), and that the router operates at the network layer of the OSI model
Home networkers often use an Internet Protocol (IP) wired or wireless router, IP being the most common OSI network layer* protocol*. An IP router such as a DSL or cable modem broadband router joins the home's local area network (LAN*) to the wide-area network (WAN*) of the Internet
By maintaining configuration information in a piece of storage called the "routing table," wired or wireless routers also have the ability to filter traffic, either incoming or outgoing, based on the IP addresses of senders and receivers. Some routers allow the home networker to update the routing table from a Web browser interface. Broadband routers combine the functions of a router with those of a network switch and a firewall in a single unit
In other words, it is
A device* that forwards data packets* along networks
A router is connected to at least two networks, commonly two LANs* or WANs* or a LAN and its ISP’s* network
Routers are located at gateways*, the places where two or more networks connect
Routers use headers* and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP* to communicate with each other and configure the best route between any two hosts
Very little filtering of data is done through routers
Explanation of some words - with asterix *
Any machine or component that attaches to a computer.
Examples of devices include disk drives, printers, mice, and modems.
These particular devices fall into the category of peripheral devices because they are separate from the main computer
Most devices, whether peripheral or not, require a program called a device driver that acts as a translator, converting general commands from an application into specific commands that the device understands
A piece of a message transmitted over a packet-switching network.
One of the key features of a packet is that it contains the destination address in addition to the data.
In IP networks, packets are often called datagrams
LAN* : Local-Area Network
A computer network that spans a relatively small area. 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
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
The following characteristics differentiate one LAN from another
topology : The geometric arrangement of devices on the network. For example, devices can be arranged in a ring or in a straight line.
protocols : The rules and encoding specifications for sending data. The protocols also determine whether the network uses a peer-to-peer or client/server architecture.
media : Devices can be connected by twisted-pair wire, coaxial cables, or fiber optic cables. Some networks do without connecting media altogether, communicating instead via radio waves
LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN
Short for wide-area network
Short for Internet Service Provider, a company that provides access to the Internet. For a monthly fee, the service provider gives you a software package, username, password and access phone number. Equipped with a modem, you can then log on to the Internet and browse the World Wide Web and USENET, and send and receive e-mail.
In addition to serving individuals, ISPs also serve large companies, providing a direct connection from the company's networks to the Internet. ISPs themselves are connected to one another through Network Access Points (NAPs)
ISPs are also called IAPs (Internet Access Providers)
1. In many disciplines of computer science, a header is a unit of information that precedes a data object. In a network transmission, a header is part of the data packet and contains transparent information about the file or the transmission. In file management, a header is a region at the beginning of each file where bookkeeping information is kept. The file header may contain the date the file was created, the date it was last updated, and the file's size. The header can be accessed only by the operating system or by specialized programs.
In e-mail, the first part of an e-mail message containing controlling and ****-data such as the Subject, origin and destination e-mail addresses, the path an e-mail takes, or its priority. The header will contain information about the e-mail client, and as the e-mail travels to its destination information about the path it took will be appended to the header
2. In word processing, one or more lines of text that appears at the top of each page of a ********. Once you specify the text that should appear in the header, the word processor automatically inserts it
Most word processors allow you to use special symbols in the header that represent changing values. For example, you can enter a symbol for the page number, and the word processor will automatically replace the symbol with the correct number on each page. If you enter the date symbol, the word processor will insert the current date, which will change if necessary each time you print the ********
Most word processors allow you to specify different headers, for example, one for odd-numbered pages (odd headers) and another for even-numbered pages (even headers). Headers are also called running heads
1. A node on a network that serves as an entrance to another network. In enterprises, the gateway is the computer that routes the traffic from a workstation to the outside network that is serving the Web pages. In homes, the gateway is the ISP that connects the user to the internet
In enterprises, the gateway node often acts as a proxy server and a firewall. The gateway is also associated with both a router, which use headers and forwarding tables to determine where packets are sent, and a switch, which provides the actual path for the packet in and out of the gateway
2. A computer system located on earth that switches data signals and voice signals between satellites and terrestrial networks
3. An earlier term for router, though now obsolete in this sense as router is commonly used
An agreed-upon format for transmitting data between two devices. The protocol determines the following:
the type of error checking to be used
data compression method, if any
how the sending device will indicate that it has finished sending a message
how the receiving device will indicate that it has received a message
There are a variety of standard protocols from which programmers can choose. Each has particular advantages and disadvantages; for example, some are simpler than others, some are more reliable, and some are faster
From a user's point of view, the only interesting aspect about protocols is that your computer or device must support the right ones if you want to communicate with other computers. The protocol can be implemented either in hardware or in software
Short for Internet Control Message Protocol, an extension to the Internet Protocol (IP) defined by RFC 792. ICMP supports packets containing error, control, and informational messages. The PING command, for example, uses ICMP to test an Internet connection