VoIP 101: Voice over IP for Beginners

Written by Rich McIver

For those who have never heard aboutrepparttar potential of VoIP, be prepared to radically changerepparttar 133339 way you think about your current long-distance calling plan. VoIP (Voice over Internet Protocol) is very simply, a method for taking ordinary analog audio signals and turning them into digital signals that can be sent overrepparttar 133340 Internet.

So what? Well, for those of you who are already paying a monthly fee for an Internet connection, this means that you can use that same connection to place free long distance phone calls. This process works by using already available VoIP software to make phone calls overrepparttar 133341 Internet, essentially circumventing phone companies and their service charges.

Interestingly, VoIP is not an entirely new thing. In fact, a number of providing companies have been around for some time. But it has only been withrepparttar 133342 more recent explosion of high-speed internet access usage, that VoIP has gotten any attention. Nowrepparttar 133343 major telephone carriers are setting up their own VoIP calling plans throughoutrepparttar 133344 US, another testament torepparttar 133345 potential ofrepparttar 133346 technology.

How VoIP Is Used

While there are a number of ways that VoIP is currently being used, most individual callers fall into one of three categories: ATA, IP Phones, and Computer-to-Computer.

ATA or Analog Telephone Adaptor, isrepparttar 133347 most common way of using VoIP. This adaptor actually allows you to hook uprepparttar 133348 phone that is already in your house, to your computer, and then your Internet connection. Whatrepparttar 133349 ATA does, is turnrepparttar 133350 analog signals your phone sends out into digital signals that can be sent overrepparttar 133351 Internet. Setting up this system is quite simple. It simply requires that you order an ATA (its an adaptor remember), plugrepparttar 133352 cable from your phone which would normally go intorepparttar 133353 wall socket intorepparttar 133354 ATA, and thenrepparttar 133355 ATA gets plugged into your computer, which is connected torepparttar 133356 internet. Some ATAs include software that has to be installed on your computer before its ready, but basically it's quite a simple process. Then you are ready to make some calls.

The next type of VoIP usage utilizes IP Phones instead of your home phone. The IP Phone looks just like a normal phone, with allrepparttar 133357 same buttons and cradle,repparttar 133358 only difference is that instead of having a normal wall jack connector, it has an Ethernet connector. This means, that instead of plugging in your IP phone torepparttar 133359 wall jack like you would with a regular analog phone, it gets plugged directly into your router. This option allows you to circumvent your personal computer, and it also means that you will not have to install any software, because its all built in torepparttar 133360 handset. In addition,repparttar 133361 fact that Wi-Fi IP phones will soon be available, which will allow subscribing callers to make VoIP calls from any Wi-Fi hot spot, make this option an exciting possibility.

The simplest and cheapest way to use VoIP is through computer-to-computer calls. These calls are entirely free, meaning no calling plan whatsoever. The only thing you need, isrepparttar 133362 software which can be found for free onrepparttar 133363 internet, a good internet connection, a microphone, speakers, and a sound card. Except for your monthly internet service fee, there is literally no cost for making these calls, no matter how many you make.

For large companies, VoIP also offers some very unique possibilities. Some larger companies are already utilizingrepparttar 133364 technology by conducting all intra-office calls through a VoIP network. Becauserepparttar 133365 quality of sound is comparable to and in some cases surpasses that of analog service, some international companies are using VoIP to route international calls throughrepparttar 133366 branch of their company nearestrepparttar 133367 call's destination and then completing it on an analog system. This allows them to pay local rates internationally and still utilizerepparttar 133368 same intra-office VoIP network that they would if they were calling someone inrepparttar 133369 next cubicle over.

Other Advantages of VoIP

While your current long-distance plan covers you for only one location, say calls made from your office, with VoIP, you can make a call anywhere that you can get a broadband connection. That is because all three methods above, unlike analog calls, sendrepparttar 133370 call information viarepparttar 133371 Internet. This means you can make calls from home, on vacation, on business trips, and almost anywhere else. Anywhere you go, with VoIP you can bring your home phone along with you. Inrepparttar 133372 same way, computer-to-computer connections mean that as long as you have your laptop and a connection, you're ready to go.

VPN over Satellite: A comparison of approaches

Written by Richard McKinney and Russell Lambert

As awareness of VSAT Systems satellite Internet access (www.vsat-systems.com) becomes more wide spread, demand for secure connections from remote locations to corporate local area networks continues to increase. The high latency inherent in geo-synchronous satellite connections has presented a significant obstacle to efficient virtual private network (VPN) connections over satellite.

Various solutions to carrying IP traffic over satellite have been proposed, but each one has had some limitation that prevented it from becoming widely adopted. Recently Encore Networks released their VSR-30 3DES VPN device, which offersrepparttar most popular features of IPSEC appliances, but leavesrepparttar 133338 IP header unencrypted. This feature makesrepparttar 133339 VSR-30 attractive for satellite-based VPN applications because visible headers allow VSAT Systems to optimize throughput.

The Problem In order for a two-way satellite service to perform properly in conjunction with traditional terrestrial networks (Internet, Intranet), satellite data networks must employ special techniques to deal withrepparttar 133340 extra 44,600-mile space segment ofrepparttar 133341 connection. Without those steps,repparttar 133342 increased latency,repparttar 133343 time required to traverserepparttar 133344 extra distance, means that TCP severely limits performance.

The Internet relies onrepparttar 133345 Transmission Control Protocol (TCP) to ensure packet delivery without errors. TCP works by sending a certain amount of data,repparttar 133346 “window size,” then waiting forrepparttar 133347 receiver to send an acknowledgment of receipt. With TCP,repparttar 133348 sender cannot transmit more data until it has received an acknowledgment. If an acknowledgment does not arrive in a timely manner, TCP assumesrepparttar 133349 packet was lost (discarded due to network congestion) and resends it. When packets go unacknowledged, TCP also slowsrepparttar 133350 transmission rate to reduce congestion and to minimizerepparttar 133351 need for retransmissions.

TCP/IP sessions start out sending data slowly. Speed builds asrepparttar 133352 rate ofrepparttar 133353 acknowledgments verifiesrepparttar 133354 network’s capacity to carry more traffic. This is known as slow-start, followed by a ramp-up in speed. The speed ofrepparttar 133355 connection builds untilrepparttar 133356 sender detects packet loss from a lack of an acknowledgment. This allows TCP to achieverepparttar 133357 fastest practical data transfer rate forrepparttar 133358 conditions present onrepparttar 133359 network.

Terrestrial networks typically have round-trip latencies inrepparttar 133360 range of 35 to 100 ms. Satellite networks, due torepparttar 133361 distance of geo-synchronous satellites aboverepparttar 133362 equator, require 550 ms or more. Some satellite connections have much higher latencies. Depending uponrepparttar 133363 satellite hardware and subscription policy ofrepparttar 133364 service provider, latencies of 800 ms to as much at 2,000 ms or more can occur. TCP interpretsrepparttar 133365 additional satellite transit time as network congestion. If uncorrected, this effect causesrepparttar 133366 network to send all additional packets atrepparttar 133367 slow-start rate.

Current satellite data networks employ a technique referred to as TCP acceleration or IP spoofing to compensate forrepparttar 133368 extra time required to transitrepparttar 133369 space segment. Special equipment atrepparttar 133370 carrier’s main satellite hub appears to terminaterepparttar 133371 TCP session, so it appears torepparttar 133372 sender asrepparttar 133373 remote location. In actualityrepparttar 133374 device atrepparttar 133375 satellite hub acts as a relay or forwarder betweenrepparttar 133376 originating terrestrial location andrepparttar 133377 remote satellite unit. Whenrepparttar 133378 spoofing equipment receives Internet traffic destined for a remote satellite location, it immediately acknowledges receipt ofrepparttar 133379 packet torepparttar 133380 sender so more data packets will follow promptly. This wayrepparttar 133381 sender never experiencesrepparttar 133382 actual latency torepparttar 133383 remote site because acknowledgments return rapidly. As a result, TCP moves out of slow-start mode quickly and builds torepparttar 133384 highest practical speed.

To prevent packets from being acknowledged twice,repparttar 133385 spoofing equipment suppresses acknowledgments fromrepparttar 133386 remote site. In this way, computers behind a satellite link communicate seamlessly and efficiently with servers onrepparttar 133387 terrestrial Internet.

IPsec VPNs not only encryptrepparttar 133388 data portion of packets, they also encryptrepparttar 133389 TCP port number and IP address ofrepparttar 133390 sender’s computer. (Think of TCP port asrepparttar 133391 apartment number whilerepparttar 133392 IP address is that ofrepparttar 133393 building.) Consequently, onlyrepparttar 133394 VPN software atrepparttar 133395 remote site can decipher where packets originated and acknowledge receipt of data.

Popular IPsec VPNs, therefore, defeat TCP acceleration over satellite links because ground stations cannot adjustrepparttar 133396 fields inrepparttar 133397 header when those fields are encrypted. This situation requires that acknowledgments transitrepparttar 133398 space segment twice (over and back) and results in substantial performance degradation. The impact on performance increases asrepparttar 133399 latency rises. To determinerepparttar 133400 effect of latency on performance and to measurerepparttar 133401 effectiveness of an alternative VPN device, engineers at VSAT Systems transferred a variety of data files over a high-quality satellite link under controlled conditions and measuredrepparttar 133402 results.

Test Procedure The test compared transfer rates over a Cisco 1711 IPsec VPN and an Encore VSR-30 Selective Layer Encryption (SLE) appliance to each other and torepparttar 133403 speed of file transfers overrepparttar 133404 open Internet (unencrypted). The data moved from remote to server, then from server to remote using FTP. Transfer rates were measured in kilobits per second (Kbps). The test utilized six different files to measure data transfers rates: 500 kilobyte, 5 megabyte, and 10 megabyte files in both compressible (text) and non-compressible (binary)forms.

Bothrepparttar 133405 Cisco and Encore equipment used 3DES encryption. However,repparttar 133406 Encore unit’s SLE encrypted onlyrepparttar 133407 data, leavingrepparttar 133408 IP and TCP headers accessible. Withrepparttar 133409 headers accessible,repparttar 133410 encrypted packets are compatible with all types of satellite modems and all methods of TCP acceleration.

The test transferred files between two similarly configured Free BSD computers containing three identical network cards. With three cards in each system,repparttar 133411 computers could multi-home and physically separate data. The resulting three data paths facilitatedrepparttar 133412 near simultaneous testing ofrepparttar 133413 two VPN circuits andrepparttar 133414 unencrypted, clear connection.

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