VoIP services convert your voice into a digital signal that travels over the Internet. If we are calling a regular phone number, the signal is converted to a regular telephone signal before it reaches the destination. VoIP can allow you to make a call directly from a computer, a special VoIP phone, or a traditional phone connected to a special adapter. In addition, wireless "hot spots" in locations such as airports, parks, and cafes allow you to connect to the Internet and may enable you to use VoIP service wirelessly
Although progressing rapidly, Internet telephony still has some problems with reliability and sound quality, due primarily to limitations both in Internet bandwidth and current compression technology. As a result, most corporations looking to reduce their phone bills today confine their Internet-telephony applications to their intranets. With more predictable bandwidth available than the public Internet, intranets can support full-duplex, real-time voice communications. Corporations generally limit their Internet voice traffic to half-duplex asynchronous applications (e.g., voice messaging). Internet telephony within an intranet enables users to save on long-distance bills between sites; they can make point-to-point calls via gateway servers attached to the local-area network (LAN). No PC–based telephony software or Internet account is required.
Duplex" simply means to send and receive data (the human voice) from the same device whether that be with phone, 2-way radio, or Computer.
Half-duplex devices let you send and receive, but only one-way at a time. If you've ever used a walkie-talkie, then you know what half-duplex conversations sound like. You have to push the TALK button to send your message. But as long as you are holding the TALK key, you can't hear what anyone else is saying. You must release the button to receive.
Enter full duplex Actually, full duplex is nothing new. In fact, you already know exactly what it sounds like. Your corded or cordless phones are full-duplex devices letting you and your caller speak simultaneously without any dropouts in either one of your voices.
It's when you use a hands-free speakerphone that you really appreciate full duplex. Conventional speakerphones must shut the speaker off when the mic is activated so as not to pick up your caller's voice and transmit it along with yours causing an echo effect. When you speak, you can't hear what your caller is saying. This problem is really compounded if both of you are using conventional speakerphones. A full-duplex device digitizes the signal coming out of its speaker (your caller's voice). It then edits this info out of the signal it's transmitting (your voice) using a built-in digital processor similar to those found in PCs. This eliminates echo effect and more importantly, does away with the on-off mic/speaker dilemma. Full-duplex devices do all of this virtually instantaneously so your calls sound natural and free-flowing. It's this technology that differentiates high-end conferencing systems from ordinary, half-duplex speakerphones.
What's "digital duplex"? Panasonic is trying to rectify the sometimes awful, always annoying half-duplex sound quality typical of conventional speakerphones by using what they call Digital Duplex technology. While it doesn't quite deliver the same sound quality as full duplex, the special digital circuitry does help reduce the echo and dropout effects.
What about talking on the internet? If you're using your PC to talk on the internet, it's best to install a full-duplex sound card in your PC. Because internet talk has a host of obstacles specific to the medium it must overcome—bandwidth, internet traffic, connection speed—why add the frustration of stop-start, half-duplex conversations? The time and cost of a full-duplex sound card are worth it.
Network Topologies The term "topology" refers to the layout of connected devices on a network. Topology in Network Design
A topology can be consider as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be unlikely to have ring topology.
Network topologies are categorized into the following basic types: 1. Bus 2. Ring 3. Star 4. Tree 5. Mesh
Bus Topology Bus networks use a single cable to connect all devices. A single cable functions as a shared communication medium that devices attached with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. Bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance will decrease. And if the cable fails, the entire network effectively becomes unusable.
Ring Topology In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network. Ring topologies are found in some office buildings or school campuses.
Star Topology Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet. Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN.
Tree Topology Tree topologies integrate multiple star topologies together onto a bus. Only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus or a star.
Mesh Topology Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. Some WANs, like the Internet, employ mesh routing.
More complex networks can be built as hybrids of two or more of the above basic topologies.
Registry Editor is a tool for viewing and changing settings in your system registry, which contains information about how your computer runs. Almost the entire settings are stored in the registry.Although Registry Editor enables you to inspect and modify the registry, it's advisable to use Registry Editor only if the GUI does not provide the option you're looking for. Making incorrect changes in the registry can break your system. It's highly advisable to backup the registry before editing any portion of it.One way to backup the registry is to create a System Restore snapshot. System Restore returns your computer to a previous snapshot without losing recent personal information, such as documents, history lists, favorites, or e-mail. It monitors the computer and many applications for changes and creates restore points. You restore these snapshots when your configuration isn't working. This method is unreliable in case you want to rollback the registry changes made a longtime ago, in which case the System Restore might have purged that particular restore point - due to space constraints or due to a recent system restore point or even a Restore point corruption. Please remember, System Restore points get deleted for many reasons, making it unreliable, especially in the long run.This method is preferred if you're making changes to a specific key/area of the registry. To backup a selected branch/key in the registry
Click Start, and then click Run. In the Open box, type regedit, and then click OK Locate and then click the key that contains the value that you want to editOn the File menu, click Export. In the Save in box, select a location where you want to save the Registration Entries (.reg) In the File name box, type a file name, and then click Save.
Now that you've created a Registry backup for that particular key. Save the REG file in a safer location in case you want to undo the registry changes made. You can restore the settings by just double-clicking the REG file. It automatically merges the contents to the Registry.
For backing up the whole registry, use the NTBackup utility to back up the System State. The System State includes the registry, the COM+ Class Registration Database, and your boot files.
A network consists of two or more computers that are linked in order to share resources (such as printers and CD-ROMs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.
The two basic types of networks include: * Local Area Network (LAN) * Wide Area Network (WAN)
Local Area Network
A Local Area Network (LAN) is a network that is confined to a relatively small area. It is generally limited to a geographic area such as a writing lab, school, or building. Rarely are LAN computers more than a mile apart. In a typical LAN configuration, one computer is designated as the file server. It stores all of the software that controls the network, as well as the software that can be shared by the computers attached to the network. Computers connected to the file server are called workstations. The workstations can be less powerful than the file server, and they may have additional software on their hard drives. On most LANs, cables are used to connect the network interface cards in each computer.
Wide Area Network
Wide Area Networks (WANs) connect larger geographic areas, such as Florida, the United States, or the world. Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of network.
Using a WAN, schools in Florida can communicate with places like Tokyo in a matter of minutes, without paying enormous phone bills. A WAN is complicated. It uses multiplexers to connect local and metropolitan networks to global communications networks like the Internet. To users, however, a WAN will not appear to be much different than a LAN or a MAN.
