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Routing table is actually a electronics table that shows you the routes that you have set on the Windows OS, network routers or other network devices. The computer or network devices will know how to do routing based on this routing table.
The Routing Table is usually stored in a router or networked computer in the form of a database or file. When data needs to be sent from one node to another on the network, the routing table is referred to in order to find the best possible route for the transfer of information.
Here is an example of routing table in Windows OS by just opening the command prompt and then type netstat –r or route print. Quite simple to understand it, the computer will send the network packets to the Gateway that tie to particular Network Destination. Example again, the computer will send the network packets to 192.168.1.250 if the destination is in 224.0.0.0 multicast network. Please note the gateway shown with network destination 0.0.0.0 is default gateway. If no specific route found, all the network traffic will be sent to default gateway for routing.
Hop-by-hop Routing is a common routing method used in networks wherein for each node in the network, the address of the next node leading to the destination is listed. So when a data packet arrives at a particular node, it then refers to the routing table to find the address of the next hop destination. Once it reaches that node, it again refers to the routing table for the address of the next hop and so on, until it reaches the final destination.
For a large network consisting of a number of nodes and routers, the routing tables in all the routers need to be consistent, failing which, routing loops can often develop. This can create problems especially in networks that use the hop-by-hop routing model in which the data packets can end up being sent in an endless loop. Routing loops have always been a recurring problem in networks and one of the major goals of designing routing protocols is the careful avoidance of these routing loops.
Routing tables can generally be maintained manually when the network is small and static. The routing tables for all static network devices never change unless and until the administrator of the network changes them manually. In dynamic routing, the devices themselves automatically build and maintain their own routing tables. They do this by exchanging information regarding the network topology using routing protocols. This enables the devices in the network to automatically adapt to the changes in the network like device failures and network congestion as and when they occur.
TCP (Transmission Control Protocol) is a set of rules (protocol) used along with the Internet Protocol (IP) to send data in the form of message units between computers over the Internet. While IP takes care of handling the actual lower-level delivery of the data from computer to computer as a message makes its way across the Internet, TCP at a higher level, concerned only with the two end systems and takes care of keeping track of the individual units of data (called packets) that a message is divided into for efficient routing through the Internet.
For example, when an HTML file is sent to you from a Web server, the Transmission Control Protocol (TCP) program layer in that server divides the file into one or more packets, numbers the packets, and then forwards them individually to the IP program layer. Although each packet has the same destination IP address, it may get routed differently through the network. At the other end (the client program in your computer), TCP reassembles the individual packets and waits until they have arrived to forward them to you as a single file.
TCP is known as a connection-oriented protocol, which means that a connection is established and maintained until such time as the message or messages to be exchanged by the application programs at each end have been exchanged. TCP is responsible for ensuring that a message is divided into the packets that IP manages and for reassembling the packets back into the complete message at the other end. In the Open Systems Interconnection (OSI) communication model, TCP is in layer 4, the Transport Layer.
Hub
In general, a hub is the central part of a wheel where the spokes come together. The term is familiar to frequent fliers who travel through airport "hubs" to make connecting flights from one point to another. In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. A hub usually includes a switch of some kind. (And a product that is called a "switch" could usually be considered a hub as well.) The distinction seems to be that the hub is the place where data comes together and the switch is what determines how and where data is forwarded from the place where data comes together. Regarded in its switching aspects, a hub can also include a router.
1. In describing network topologies, a hub topology consists of a backbone (main circuit) to which a number of outgoing lines can be attached ("dropped"), each providing one or more connection port for device to attach to. For Internet users not connected to a local area network, this is the general topology used by your access provider. Other common network topologies are the bus network and the ring network. (Either of these could possibly feed into a hub network, using a bridge.)
2. As a network product, a hub may include a group of modem cards for dial-in users, a gateway card for connections to a local area network (for example, an Ethernet or a token ring), and a connection to a line (the main line in this example).
Switch
In telecommunications, a switch is a network device that selects a path or circuit for sending a unit of data to its next destination. A switch may also include the function of the router, a device or program that can determine the route and specifically what adjacent network point the data should be sent to. In general, a switch is a simpler and faster mechanism than a router, which requires knowledge about the network and how to determine the route.
Relative to the layered Open Systems Interconnection (OSI) communication model, a switch is usually associated with layer 2, the Data-Link layer. However, some newer switches also perform the routing functions of layer 3, the Network layer. Layer 3 switches are also sometimes called IP switches.
On larger networks, the trip from one switch point to another in the network is called a hop. The time a switch takes to figure out where to forward a data unit is called its latency. The price paid for having the flexibility that switches provide in a network is this latency. Switches are found at the backbone and gateway levels of a network where one network connects with another and at the subnetwork level where data is being forwarded close to its destination or origin. The former are often known as core switches and the latter as desktop switches.
In the simplest networks, a switch is not required for messages that are sent and received within the network. For example, a local area network may be organized in a token ring or bus arrangement in which each possible destination inspects each message and reads any message with its address.
Switch
In a telecommunications network, a switch is a device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination. In the traditional circuit-switched telephone network, one or more switches are used to set up a dedicated though temporary connection or circuit for an exchange between two or more parties. On an Ethernet local area network (LAN), a switch determines from the physical device (Media Access Control or MAC) address in each incoming message frame which output port to forward it to and out of. In a wide area packet-switched network such as the Internet, a switch determines from the IP address in each packet which output port to use for the next part of its trip to the intended destination.
In the Open Systems Interconnection (OSI) communications model, a switch performs the layer 2 or Data-Link layer function. That is, it simply looks at each packet or data unit and determines from a physical address (the "MAC address") which device a data unit is intended for and switches it out toward that device. However, in wide area networks such as the Internet, the destination address requires a look-up in a routing table by a device known as a router. Some newer switches also perform routing functions (layer 3 or the Network layer functions in OSI) and are sometimes called IP switches.
On larger networks, the trip from one switch point to another in the network is called a hop. The time a switch takes to figure out where to forward a data unit is called its latency. The price paid for having the flexibility that switches provide in a network is this latency. Switches are found at the backbone and gateway levels of a network where one network connects with another and at the subnetwork level where data is being forwarded close to its destination or origin. The former are often known as core switches and the latter as desktop switches.
In the simplest networks, a switch is not required for messages that are sent and received within the network. For example, a local area network may be organized in a Token Ring or bus arrangement in which each possible destination inspects each message and reads any message with its address.
Circuit-Switching version Packet-Switching
A network's paths can be used exclusively for a certain duration by two or more parties and then switched for use to another set of parties. This type of "switching" is known as circuit-switching and is really a dedicated and continuously connected path for its duration. Today, an ordinary voice phone call generally uses circuit-switching.
Most data today is sent, using digital signals, over networks that use packet-switching. Using packet-switching, all network users can share the same paths at the same time and the particular route a data unit travels can be varied as conditions change. In packet-switching, a message is divided into packets, which are units of a certain number of bytes. The network addresses of the sender and of the destination are added to the packet. Each network point looks at the packet to see where to send it next. Packets in the same message may travel different routes and may not arrive in the same order that they were sent. At the destination, the packets in a message are collected and reassembled into the original message.
Packet
A packet is the unit of data that is routed between an origin and a destination on the Internet or any other packet-switched network. When any file (e-mail message, HTML file, Graphics Interchange Format file, Uniform Resource Locator request, and so forth) is sent from one place to another on the Internet, the Transmission Control Protocol (TCP) layer of TCP/IP divides the file into "chunks" of an efficient size for routing. Each of these packets is separately numbered and includes the Internet address of the destination. The individual packets for a given file may travel different routes through the Internet. When they have all arrived, they are reassembled into the original file (by the TCP layer at the receiving end).
A packet-switching scheme is an efficient way to handle transmissions on a connectionless network such as the Internet. An alternative scheme, circuit-switched, is used for networks allocated for voice connections. In circuit-switching, lines in the network are shared among many users as with packet-switching, but each connection requires the dedication of a particular path for the duration of the connection.
"Packet" and "datagram" are similar in meaning. A protocol similar to TCP, the User Datagram Protocol(UDP) uses the term datagram.
Router
In packet-switched networks such as the Internet, a router is a device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any gateway (where one network meets another), including each point-of-presence on the Internet. A router is often included as part of a network switch.
A router may create or maintain a 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. Typically, a packet may travel through a number of network points with routers before arriving at its destination. Routing is a function associated with the Network layer (layer 3) in the standard model of network programming, the Open Systems Interconnection (OSI) model. A layer-3 switch is a switch that can perform routing functions.
An edge router is a router that interfaces with an asynchronous transfer mode (ATM) network. A brouter is a network bridge combined with a router.
For home and business computer users who have high-speed Internet connections such as cable, satellite, or DSL, a router can act as a hardware firewall. This is true even if the home or business has only one computer. Many engineers believe that the use of a router provides better protection against hacking than a software firewall, because no computer Internet Protocol address are directly exposed to the Internet. This makes port scans (a technique for exploring weaknesses) essentially impossible. In addition, a router does not consume computer resources as a software firewall does. Commercially manufactured routers are easy to install, reasonably priced, and available for hard-wired or wireless networks.
Hub
In general, a hub is the central part of a wheel where the spokes come together. The term is familiar to frequent fliers who travel through airport "hubs" to make connecting flights from one point to another. In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. A hub usually includes a switch of some kind. (And a product that is called a "switch" could usually be considered a hub as well.) The distinction seems to be that the hub is the place where data comes together and the switch is what determines how and where data is forwarded from the place where data comes together. Regarded in its switching aspects, a hub can also include a router.
1) In describing network topologies, a hub topology consists of a backbone (main circuit) to which a number of outgoing lines can be attached ("dropped"), each providing one or more connection port for device to attach to. For Internet users not connected to a local area network, this is the general topology used by your access provider. Other common network topologies are the bus network and the ring network. (Either of these could possibly feed into a hub network, using a bridge.)
2) As a network product, a hub may include a group of modem cards for dial-in users, a gateway card for connections to a local area network (for example, an Ethernet or a Token Ring), and a connection to a line (the main line in this example).
Gateway
A gateway is a network point that acts as an entrance to another network. On the Internet, a node or stopping point can be either a gateway node or a host (end-point) node. Both the computers of Internet users and the computers that serve pages to users are host nodes. The computers that control traffic within your company's network or at your local Internet service provider (ISP) are gateway nodes.
In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy server and a firewall server. A gateway is often associated with both a router, which knows where to direct a given packet of data that arrives at the gateway, and a switch, which furnishes the actual path in and out of the gateway for a given packet.
Wi-Fi products are used to build WLANs, while WiMAX products are used to build WMANs
A Wireless Local Area Network (WLAN) is a group of devices linked together by wireless within a relatively small space like a single office building or home. Three WLAN technologies were included in the original 802.11 standard: Infrared, Frequency Hopping Spread Spectrum (FHSS), and Direct Sequence Spread Spectrum (DSSS). 802.11b focused exclusively on DSSS; 802.11a/g/n also used Orthogonal Frequency Division Multiplexing (OFDM).
Wi-Fi is a certification applied to 802.11a/b/g/n products tested by the Wi-Fi Alliance, an industry consortium that promotes interoperability in heterogeneous WLANs. For example, all 802.11g products implement standard OFDM and DSSS, but only Wi-Fi certified products have proven that they correctly support a mandatory subset of features and options.
To create a WLAN, enterprises, small businesses, and home owners can purchase Wi-Fi certified Access Points (APs) and clients (laptops, phones, printers). Clients must be no more than a few hundred feet from the closest AP. Larger buildings can be covered by installing multiple APs that are connected to each other. Most WLANs are deployed indoors, but WLANs can also cover parking lots or courtyards or other local outdoor areas.
Wireless Metropolitan Area Networks (WMANs) use wireless "last mile" technologies to connect subscriber stations (customer premise equipment) to base stations (carrier network infrastructure), providing a wireless alternative to wireline Internet access technologies like DSL, cable, or fiber.
802.16 standards define several WMAN technologies that operate at various frequencies, distances, and speeds to deliver Broadband Wireless Access (BWA). The original 802.16 focused on Fixed BWA, using point to point wireless uplinks to connect subscriber networks to carrier networks and the Internet. More recently, the 802.16e amendment defined Mobile BWA to serve subscriber stations that are not fixed in place, like laptops used in cars and trains.
WiMax is a certification applied to 802.16 products tested by the WiMAX Forum. Carriers build and operate WMANs by purchasing licensed spectrum and then deploying WiMAX base stations throughout a city, region, or other designated coverage area. To use the WMAN, subscribers must purchase wireless services from a carrier.
Here are some key differences between WLANs and WMANs, supported by Wi-Fi and WiMAX products:
* It's possible to use WMAN technology indoors, but 802.16 protocols are optimized for outdoor operation. It's possible to use WLAN technology outside, but 802.11 protocols were primarily designed for indoor networks.
* Larger WLANs can be constructed using many densely-spaced Wi-Fi APs, but to blanket miles of territory with wireless, you really want to create a WMAN technology. On the other hand, using WiMAX products for communication between PCs inside the same building would be pricey and impractical -- that's precisely what WLAN technologies were created for.
* Most office and home WLANs are composed of Wi-Fi products operating in unlicensed spectrum -- channels freely available for use by anyone. WiMAX products most often operate in spectrum licensed to wireless carriers who use them to deliver commercial BWA services.
For nuts-and-bolts differences, check out Michael Finneran's excellent paper on WiMax versus Wi-Fi.
The bottom line is that WLANs and WMANs are complementary network architectures, supported by standard technologies that were designed for very different environments and purposes. This is why your next laptop may well include both Wi-Fi and Mobile WiMAX adapters. Use the Wi-Fi adapter to connect to your office or home WLAN free-of-charge, but use the WiMAX adapter when you're on the go to reach the Internet through a carrier's WMAN.
