VoIP 101: Voice over IP for Beginners

Written by Rich McIver

Continued from page 1

There are also some nifty benefits to having your calls transmitted overrepparttar Internet. For example, some VoIP service providers allow you to check your voicemail via your e-mail, while others allow you to attach voice messages to your e-mails. How VoIP Works

The current phone system relies on a reliable but largely inefficient method for connecting calls known as circuit switching. This technique, which has been used for over 100 years, means that when a call is made between two people a connection is maintained in both directions between callers forrepparttar 133339 duration ofrepparttar 133340 call. This dual directional characteristic givesrepparttar 133341 systemrepparttar 133342 name circuit.

If, for example, you made a 30-minute callrepparttar 133343 circuit would be continuously open, and thus used, betweenrepparttar 133344 two phones. Up until about 1960, this meant that every call had to have an actual dedicated wire connectingrepparttar 133345 two phones. Thus a long distance call cost so much, because you were paying for pieces of copper wire to be connected allrepparttar 133346 way from your phone torepparttar 133347 destination phone, and for that connection to remain constant throughoutrepparttar 133348 call. Today, however, your analog call is converted after leaving your house to a digital signal, where your call can be combined with many others on a single fiber optic cable. While this system is certainly an improvement overrepparttar 133349 past copper wire system, it is still quite inefficient. This inefficiency is due in part torepparttar 133350 fact thatrepparttar 133351 telephone line can't distinguish between useful talking and unneeded silences. For example, in a typical conversation while one person is talkingrepparttar 133352 other person is listening. Thusrepparttar 133353 current analog system uses roughly half its space sending useless messages like this silence. But there is also more information, even down to pauses in speech, which under a more efficient system can be effectively cut out rather than wastingrepparttar 133354 circuit space. This idea of only transmittingrepparttar 133355 noisy bits of a telephone call and saving a great deal on circuit space, isrepparttar 133356 basis of Packet-Switching,repparttar 133357 alternative method to circuit switching thatrepparttar 133358 VoIP phone system uses.

Packet-Switching isrepparttar 133359 same method that you use when you view a website. For example, as you read this website, your computer is not maintaining a constant connection torepparttar 133360 site, but rather making connections to send and receive information only on an as needed basis (such as when you click on a link). Just as this system allowsrepparttar 133361 transfer of information overrepparttar 133362 Internet to work so quickly, so also does it work inrepparttar 133363 VoIP system. While circuit switching maintains a constant and open connection, packet switching opens connections just long enough to send bits of data called packets from one computer to another. This allowsrepparttar 133364 network to send your call (in packets) alongrepparttar 133365 least congested and cheapest lines available, while also keeping your computer or IP phone, free to send and receive messages and calls with other computers. This way of sending information, not to mention data compression, makesrepparttar 133366 amount of information which must be transmitted for every call at least 3-4 times less for VoIP thanrepparttar 133367 exact same call in a conventional telephone system. For this reason, VoIP is so much cheaper than conventional calling plans.

The Future of VoIP

While most analysts believe it will be at least a decade before companies and telephone providers makerepparttar 133368 full switch to VoIP,repparttar 133369 potential forrepparttar 133370 technology's use today is already quite astounding. A report byrepparttar 133371 Forrester Research Group predicts that byrepparttar 133372 end of 2006, nearly 5 million U.S. households will be using VoIP phone service. Withrepparttar 133373 savings and flexibility thatrepparttar 133374 technology already offers, and new advances just ahead onrepparttar 133375 horizon, we can expect those numbers will only increase inrepparttar 133376 future.

Rich McIver is a contributing writer for VoIP Now: Voice over IP News. Learn more at http://www.voipnow.org .

VPN over Satellite: A comparison of approaches

Written by Richard McKinney and Russell Lambert

Continued from page 1

The remote connection utilized VSAT Systems NetModem II (www.vsat-systems.com/satellite-internet/hardware.html) commissioned for 512 Kbps/512 Kbps service torepparttar Internet. The host side had a cable modem connection running at 3 Mbps/384 Kbps. The 384 Kbps outbound connection limitedrepparttar 133338 ability to testrepparttar 133339 full 512 Kbps download capability ofrepparttar 133340 satellite modem, but it did provide adequate results to compare relative speeds of encrypted and unencrypted data coming fromrepparttar 133341 host.

The latency ofrepparttar 133342 VSAT Systems satellite link (www.vsat-systems.com) used in these tests ranged from approximately 550 ms to 625 ms. Some satellite connections (www.skycasters.com) have much higher latencies. Depending uponrepparttar 133343 satellite hardware and subscription policy ofrepparttar 133344 service provider, latencies of 800 ms to as much at 2,000 ms have been observed.

The performance of any shared bandwidth system varies throughoutrepparttar 133345 day. To minimize bandwidth effects on results, five iterations of each test ran at different times. To further reducerepparttar 133346 influence of bandwidth fluctuations,repparttar 133347 testing sequence progressed through all six files, once in each direction, before repeatingrepparttar 133348 transfer of any one file. For example,repparttar 133349 500 K text file ran throughrepparttar 133350 SLE tunnel, thenrepparttar 133351 IPsec circuit, and finally inrepparttar 133352 clear.

Next a 500 K binary file passed through each circuit, and so on. Each interleaved sequence of transfers repeated five times. An efficient VPN solution must do more than simply transfer files proficiently. The time to establish a TCP/IP session can significantly impact how applications run across a high-latency connection. To gain an indication ofrepparttar 133353 rate at whichrepparttar 133354 connections could establish TCP/IP sessions,repparttar 133355 test procedure transferred a directory file and a group of web pages back and forth.

The time required to establish a TCP/IP session can have a noticeable impact onrepparttar 133356 performance of some web-enabled applications. Since each file included in a web page requiresrepparttar 133357 browser to start a new HTTP connection torepparttar 133358 server, a page with multiple graphics, framed text, or media in external files will cause a delay as multiple connections open and close. Similar circumstances occur in FTP connections as a client traversesrepparttar 133359 serverís file structure if that action involves multiple files.

To illustrate TCP/IP session initiation efficiency,repparttar 133360 test protocol included two additional procedures. First, each server transferred a directory containing files of different sizes and composition over and back acrossrepparttar 133361 connections using FTP. Second,repparttar 133362 servers moved a series of web pages to and fromrepparttar 133363 remote site using HTTP. Since both FTP and HTTP must establish a new connection for each file, this procedure provided a method to assess start/restart timing issues associated with VPN tunnels extended across satellite links. For convenience,repparttar 133364 FTP and HTTP tests measuredrepparttar 133365 total time required to transferrepparttar 133366 respective data from one side to another, notrepparttar 133367 time to reestablish each individual connection.

Results The 3DES Selective Layer Encryption technology proved consistently faster than IPsec encryption in all three categories: FTP file transfer, FTP directory transfer, and HTTP web page downloads. This is as expected because SLE leavesrepparttar 133368 TCP/IP headers inrepparttar 133369 clear which allowsrepparttar 133370 satellite operator to perform IP spoofing or TCP acceleration.

In half ofrepparttar 133371 FTP file transfers, Selective Layer Encryption attained higher data transfer rates thanrepparttar 133372 unencrypted circuit. Data moved 20% slower overrepparttar 133373 IPsec connection than it did overrepparttar 133374 unencrypted channel when moving from host to remote and 38% slower going fromrepparttar 133375 remote torepparttar 133376 host. Bothrepparttar 133377 graph on page 3 entitled FTP to Remote Site andrepparttar 133378 one above labeled FTP from Remote Site presentrepparttar 133379 mean values for five iterations of each file type.

Selective Layer Encryption also performed well inrepparttar 133380 TCP/IP intensive tests involving directories and web pages. When downloadingrepparttar 133381 directory information torepparttar 133382 remote site, SLE performed only 7% slower thanrepparttar 133383 unencrypted connection compared with 25% forrepparttar 133384 slower IPsec protocol. Inrepparttar 133385 opposite direction,repparttar 133386 SLE connection completedrepparttar 133387 task only 3% behindrepparttar 133388 unencrypted connection whilerepparttar 133389 IPsec circuit ran 14% slower.

Inrepparttar 133390 web page test, SLE completedrepparttar 133391 task 0.5% faster thanrepparttar 133392 unencrypted circuit when moving data fromrepparttar 133393 host torepparttar 133394 remote site. Reversing direction reducedrepparttar 133395 SLE performance relative torepparttar 133396 clear channel: SLE took 6% longer. The IPsec connection pulled downrepparttar 133397 web pages 5% slower thanrepparttar 133398 unencrypted circuit going from host to remote and 66% slower when run fromrepparttar 133399 remote site.

As mentioned earlier, satellite latency varies with equipment and service quality. Longer latencies, while affecting allrepparttar 133400 results, will have a more severe impact onrepparttar 133401 IPsec connection than either ofrepparttar 133402 other two protocols in this test.

Conclusions Any encryption technique over any connection imposes some performance loss. Performance also suffers as a function of increased latency. Some ofrepparttar 133403 geo-synchronous satellite services available today, however, have sufficiently low latencies (550 to 625 ms) that even an IPsec VPN becomes practical.

But asrepparttar 133404 results of these tests clearly indicate, IPsec encryption significantly reducesrepparttar 133405 performance of TCP/IP over a high latency connection. The Encore VSR-30 with Selective Layer Encryption technology combines with VSAT Systems high-end satellite equipment (www.vsat-systems.com) offers an efficient method to achieve fast, secure 3DES encryption when using a satellite link to accessrepparttar 133406 public Internet.


    <Back to Page 1
ImproveHomeLife.com © 2005
Terms of Use