New Technology Reviews!.: Explained

Explained: How MP3 compression works

<img src="http://cdn.mos.techradar.com//Review%20images/PC%20Plus/PCP%20302/PCP302.theory.opener-200-200.jpg"> Ask us to name a universally known file format, and it would probably be a toss-up between MP3 and JPG. Simply put, if you're a fully paid up member of the digital multimedia revolution, you will have thousands of these files on your computer's hard drive – music you listen to and photos you look at – both of which have been compressed to cram as much information as possible into the minimum of space. What is an MP3? The MP3 is a fairly recent invention in digital music and sound. Before that, there was the compact disc, or CD. The audio on a CD is converted from an analog source, such as the master tape (although these days, most audio is recorded directly as digital). The analogue wave can't be recorded digitally as it is, so a digital audio processor is used to sample the analogue audio wave 44,100 times a second. This means, at every tick, the digital audio processor works out the amplitude of the original very complex audio wave. It records this as a two-byte value, so there are 65,536 possible values for this amplitude: 32,767 values above zero and 32,767 below. It does this sampling for the two channels of stereo as well. For a CD, the values of the amplitudes are stored directly onto the CD as a series of pits that the laser in your optical drive can read and interpret. No compression is done on the data stream. Since a CD can store up to 74 minutes of music, we can calculate the storage capacity of a CD: 74 minutes ˜ 60 seconds per minute ˜ 44,100 samples per second ˜ two bytes per sample ˜ two channels = 783,216,000 bytes or 747MB. Furthermore, the I/O channel that the CD uses needs to be able to transfer 176kB of data per second to the digital audio processor (the one that reconstructs the analogue audio wave from the digital data and then feeds it through the amplifier to the speakers). Recording soundwaves The reason for the sample rate and the amplitude measurement is fairly mundane. Suppose we're sampling the waveform shown in Figure 1. <img alt="Figure 1" src="http://mos.futurenet.com/techradar/Review%20images/PC%20Plus/PCP%20302/PCP302.theory.figure1_pos-420-90.jpg" width="420"></IMG> If we sample at too low a rate, we may miss some peaks and troughs in the original audio and so the resulting waveform may sound completely different and muddy. <img alt="figure 2" src="http://mos.futurenet.com/techradar/Review%20images/PC%20Plus/PCP%20302/PCP302.theory.figure2_pos-420-90.jpg" width="420"></IMG> Figure 2 shows this scenario, where the resulting waveform in red looks quite different from the original. We therefore need to sample much more often. Given that the human ear (in general) only hears a tone up to about 20kHz in frequency, we should therefore sample at least twice that rate in order to properly capture the highs and lows of the audio wave at that frequency. With a fudge factor added just in case, the rate settled on was 44,100Hz. <img alt="Figure 3" src="http://mos.futurenet.com/techradar/Review%20images/PC%20Plus/PCP%20302/PCP302.theory.figure3_pos-420-90.jpg" width="420"></IMG> Figure 3 shows a different problem: the number of possible values for the amplitude is fairly small. From the original measured amplitude, the processor must choose the closest value it can record. Here we've got a fairly high sample rate, but the measurements of the amplitude are pretty coarse. Again, the resulting waveform looks different from the original – a little more subtle perhaps, but it could still alter the sound pretty badly (highs might be higher than the original, for example, making the result more shrill and meaning that subtle nuances in the music are lost). Here, a different criterion comes into play: making the sample values fit into a whole number of bytes to help make the output DAC's job easier. One byte would be far too small for this (with only 256 different values for the amplitude), so the original designers decided on two bytes per sample. There things stood until the age of the personal computer and the internet. A three-minute track on a CD (which is the length of a typical pop song) occupies 31,752,000 bytes, or just over 30MB. Downloading a CD track using a 9,600 baud modem would take hours, and would still take well over an hour on a 56K dialup modem (the fastest retail modem before broadband became mainstream). On a typical broadband connection (12mbit/s download, for example), that track would take under three minutes to download, meaning you could just about stream it while listening to it. The solution would seem to be to compress the digital audio data. As it happens, compressing a typical CD track with something like the Deflate algorithm in Zip doesn't actually give many space savings. The reason is the data stream exhibits randomness: the two-byte accuracy of the sampling means that even similar pieces of music encode slightly differently, negating the benefits of dictionary compression algorithms such as Deflate. Random data doesn't compress, so CD tracks don't compress terribly well at all. Trimming the edges The next solution is to use a lossy compression scheme. Such a scheme essentially throws away unimportant data in order to make the result more compressible. On decompressing the data, the algorithm doesn't produce exactly the same output as the original input, but we don't notice the difference. This kind of algorithm is therefore only of any real use for things such as images, video, and audio. For images and photos, the archetypal lossy compression algorithm is the JPG file format. The vast majority of lower-end digital cameras produce JPG images as a matter of course. The reasons are primarily to do with smaller file sizes: more photos can be stored on the camera's internal flash storage, and transferring photos to a computer takes less time. Of course, the fact that the vast majority of digital photos are only viewed on a computer screen (sometimes as thumbnails more often than full size) and never digitally manipulated that much means that JPGs are more than sufficient. High-end DSLRs and professional cameras use a RAW format, which, although it may be compressed, isn't lossy-compressed. We don't usually notice that JPG is a lossy compression format because the algorithm only discards information that the human eye would have difficultly perceiving when viewed alongside other parts of the photo. With audio compression, we take advantage of the imperfect nature of the human ear to help us identify (and discard) unimportant parts of the music: there are frequencies we can't hear, there are frequencies we distinguish better than others, and when two sounds play at the same time, we hear the louder sound rather than the softer one. Why use MP3? The MP3 algorithm uses these details to remove those sounds we can't hear (or have difficulty in perceiving among the rest of the audio) to simplify the data stream to make it more compressible. The idea is to tweak things so that the removed data does not hurt the quality of the audio for the eventual listener. Nevertheless, to make things plain, MP3 cannot produce CD quality audio since it eliminates information from the data stream; instead we call the result near-CD quality or even FM quality. However, the compression ratio we obtain is truly remarkable: three minute MP3 tracks are typically between 3MB and 5MB in size – about an order of magnitude smaller than the original CD track. The MP3 algorithm has a single tuning knob that enables us to determine how much information is thrown away. Some people will be fine with increasing the lossy part of the compression algorithm because they only listen to MP3s in a noisy environment – in a car or a busy office, for example. Within a noisy environment, you won't hear the most subtle sounds, so it makes sense to optimise for file size rather than audio quality. If you're listening to music in a quieter environment, such as at home in your living room, you may be more aware of the loss of quality and not so bothered by file size. The lossy algorithm tuning knob is known as the bit rate. Bit rates are measured in bits per second; MP3 varies from 96kbps to 320kbps. At the low end of the scale, 96kbps or 128kbps is equivalent to FM radio. At the high end of the scale – say 256kbps to 320kbps – the sound quality is comparable to that of a CD. The speed of sound Remember that a CD delivers data at a rate of 176KB/s, or 1,400kbps. This means that a song saved at the 96kbps bit rate is roughly 1/14 of the size of a CD track. At the 256kbps bit rate, files are about a fifth of the size. So, for example, if your car's CD player can play MP3 CDs (that is, data CDs containing MP3s), you'll be able to put five times as many 256kbps bit rate MP3 tracks on the CD as you could on a standard audio CD. The burning question then is: which bit rate do you go for when you want the best sound you can get for the smallest file size? The only subjective variable here is quality: what I might deem as acceptable quality, you might cringe at, or vice versa. Various experiments have been conducted and it's been discovered that, in general, people can't tell the difference between an audio track encoded as a 256kbps MP3 and one from a CD. The only significant statistic is that if you know a particular track very well from CD, you're more likely to spot an MP3-encoded version of it than if you're listening to a track you've never heard before. The MP3 file format was designed to contain more than just the lossy-compressed audio data. The file consists of a set of MP3 frames, each comprising a header and corresponding data. A set of frames may be enclosed inside a tag to indicate that the frames are describing something special, such as metadata about the MP3 track (the artist's name, title, album, track number, musical genre, album art and so on). Add your own data Although the MP3 standard doesn't define its own standards for these metadata tags, there are two that have grown into standards through being recognised by several audio players. These are the ID3v1 and ID3v2 tags – although there's also a new one called APEv2, which is gaining familiarity and approval. On playback, the metadata tags are generally read by the audio player, so that relevant information can be displayed for the user. Although many CD rippers create metadata for your tracks and embed them in the MP3 files (and programs such as iTunes enable you to edit the metadata for your tracks), there are MP3 tag editors that allow you to manipulate the metadata at a finer level, or in block mode. All in all, MP3s have changed the music environment for good. Although you can still buy CDs – or if you're really old-school, vinyl – most people consume their music through MP3 or AAC. Online retailers such as Amazon and iTunes help you buy MP3s for immediate download and gratification. Online radio stations, including Pandora and Spotify, enable you to listen to lossy-compressed streamed tracks without the need for purchase. Programs like iTunes and Windows Media Player enable you to rip your CDs as MP3s onto your hard disk for later listening. Audio players such as the iPod and Zune let you to listen to your MP3-encoded music wherever you want to. In short, MP3s are here to stay.

Explained: How MP3 compression works

Ask us to name a universally known file format, and it would probably be a toss-up between MP3 and JPG. Simply put, if you're a fully pa...

In Depth: AMD Fusion APU explained

<div style="text-align: center;"><img src="http://img17.imageshack.us/img17/4851/pcf247wtechchip20020029.jpg" /></div>Zacate is a Spanish noun that means grasses, generally those used for grazing animals. It is used chiefly in Mexico. It's also the code name for AMD's new wunderkind. 
 
 
This Zacate is a little low-power number aimed at notebooks, and is more than a straight Intel Atom rival, it's a bit beefier than that. Zacate is the first of AMD's two new cores and reflects its new design philosophy; and shows the direction AMD is going, so take note. 
Zacate is a twin-core chip (well, one version is), and these cores are the completely new Bobcat design. Sitting next to these on the die are integrated graphics. Zacate is the first of what AMD has dubbed Fusion APUs. 
APU (Accelerated Processor Unit) is AMD's term for bunging graphics onto the die and Fusion is AMD's name for its new approach at doing this. Fusion is the coming together of processor and graphics in a single chip in co-operative manner, hence the name 'fusion' [I think everyone gets it now, move on – Ed]. 
Integrated and okay? 
The basic block diagram of a Fusion APU puts a graphics engine on one side, a processor, or processors, on the other and between them a bus and memory controller. Both sides share the system resources depending on the job in hand. 
<div style="text-align: center;"><a href="http://img412.imageshack.us/img412/8398/pcf247wtechtestrig24209.jpg" style="margin-left: 1em; margin-right: 1em;"><img alt="test rig 1" border="0" src="http://img412.imageshack.us/img412/8398/pcf247wtechtestrig24209.jpg" width="420" /></a> </div><div style="text-align: center;"> 
</div>Instead of thinking of two discrete data processors doing two jobs, we have a single unit programmed as one, with operations piped down the most suitable route. GPUs are only specialised CPUs after all. 
It was the Fusion programme that drove AMD to buy ATI in 2006, as it needed the company's GPU expertise. PCs boasting integrated graphics have only really been tolerable in laptops out of necessity. Any desktop listing such a feature is rightly shunned by any right-thinking person. Fusion should bring us on-board graphics that we might actually be pleased about. 
Okay, that might be going a bit far, we may not run away in horror though. The concept is due to creep up the form factors, from netbooks and thin laptops through to mini-PCs and onwards. 
Refreshing re-think 
The blurb from AMD talks big. Fusion is "a new approach to processor design", and is "ushering in a new era of visual computing experiences". It takes on an epic biblical air in places, but all cynicism aside, Fusion is a refreshing re-think, especially if the SDKs get a good airing and code is written with them in mind. 
The aim is a decent graphical punch in a small system – what's not to like? Along with the nice new Bobcat cores the new GPU is DX11 capable and has 80 stream processors. If this were a new desktop graphics card we might pause and cogitate here as that's not a lot of stream processors, but putting it into context of a tiny low-power chip that's not half bad. 
Do you want high definition video? Of course you do and there is a unified video decoder specifically for the job. 
<div style="text-align: center;"><img alt="Test rig 2" src="http://img571.imageshack.us/img571/1894/pcf247wtechtestrig14209.jpg" width="420" /> </div>Zacate's processor cores and GPU are clocked differently, the later being a fair bit slower (current estimates reckon on 500MHz maximum). The whole package comes in with a TDP of 18W. Low, but not ultra low enough for really small packages where Atom has been pitching its tent. 
Zacate comes on a tiny 40nm die and is a BGA package (that means soldered directly on to boards). Memory consists of a single channel of DDR3-1333. 
There will be two initial flavours: the twin core E350 and the single core E240, which will be the same, but one core is zapped. 
To go with the new chip, we have a new hub chip, the Hudson DI. This connects to Zacate via a PCI-e 2.0 x4 bus (fast enough for now). Hudson will carry SATA 300 and USB 2.0, but no Ethernet (huh?). 
<div class="separator" style="clear: both; text-align: center;"><a href="http://img412.imageshack.us/img412/8398/pcf247wtechtestrig24209.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"> 
</a></div>First public run 
At the unveiling of Zacate (held at the same time as Intel's IDF – just for kicks) AMD pitted a Zacate development rig against a mainstream laptop running an Intel i5 520, which also boasted integrated graphics, of course. 
<div style="text-align: center;"></div>Running City of Heroes at 1,024 x 769 pixels, the Intel-powered notebook managed around 16 to 17fps. The Zacate board trotted along at a more acceptable 30fps. That's nearly twice as fast, folks. 
Some questions were raised about drivers and whether or not it was a level playing field, but honestly can't you lot be impressed for a change? No, suspect everyone, it's the only way to be sure. 
Some fiddling about with drivers and the use of other games and benchmarks followed. It transpires that while some results are only on a par with the 520 (the IE9 benchmark is as near as makes no odds), it is still a highly impressive games chip. 
Reportedly Batman Arkham Asylum ran at 16.5 fps as against 11.3fps and City of Heroes 39.6fps against 25.5fps. That's still half as fast again – tasty. 
The killer is that Zacate is doing this with a TDP of 18W, while the Intel i5 520 takes a more substantial 35W, which translates into mucho battery life. This means they won't be direct rivals as such, which is all the more impressive. 
All in all, Zacate looks to be a very good thing. Obviously AMD has spent a small fortune developing it and so it jolly well better had be. What we will get is faster portables with better gaming – no complaints there. 
Does this mean we can live in a world where real high-power gaming is properly portable and we can finally do what we always dreamed of? Playing proper butt-clenching 3D games while sat anywhere we like. No. Desktops will remain gaming kings and always will. There is just no getting around the fact that your desktop PC can put 300W through a graphics card. 
Are we nearly there yet? 
We should see Zacate-powered hardware early next year. Initially, it'll be machines in the lower half of the portable market. Mini-ATX boards will follow, so we can expect other formats. There are Atom-powered servers around, so perhaps we will see Zacate or something very similar. 
Bang per watt is attractive in all form factors. What have we missed? Oh yeah, clock speeds. Nothing official on this at the time of writing, although 1.6GHz has been touted. The days when it was all about frequencies are over (unless it makes you look especially good, of course). 
Also, don't expect to see the names Zacate and Bobcat splashed about when the hardware arrives. These are just code names and branding will be under a different banner. 
AMD has the Vision brand all ready and waiting as well as the Fusion name. The world of netbooks and laptops is going to get a lot more competitive and capable. Zacate is just AMD's vanguard too, there's a lot more to come. 
 
<a href="http://www.techradar.com%20/">Source.</a>

In Depth: AMD Fusion APU explained

Zacate is a Spanish noun that means grasses, generally those used for grazing animals. It is used chiefly in Mexico. It's also the code ...

Tutorial: OS X networking explained

<img src="http://cdn.mos.techradar.com//Review%20images/MacFormat/MAC%20228/MAC228.main_feat.grab6-200-200.jpg"> Networks can be complex. They are much better than they were, but they are always the most complicated part of your Mac. When you send a document to a network printer, it is transmitted from one protocol to another, broken into pieces, each with their own addressing system, until finally it is transmitted as radio signals represent the bits and bytes. As your print job flies through the air, it encounters interference and interference from cell phones, microwaves and power tools. Your Wi-Fi access point plucks this signal from the air and reassembles the scrambled mess. Small errors are corrected, large errors are replaced with valid data, patiently re-sent. Your router reads the address on each packet and chooses the best way to pass it to its destination. At the printer, the packets of data are placed in the correct order, the envelopes are opened and the wrappers discarded. As your document is finally translated from electricity to ink, the printer sends you a confirmation message that this miraculous endeavour has succeeded. And to get to you, that message makes the same incredible journey back through the protocol layers and across the airwaves to reach your Mac. At least, that's what you hope happens. With so many different steps, it's no wonder that things sometimes go wrong. Network problems can feel daunting, with intermittent faults and error messages. But we're going to put a stop to all that. With our guide, we'll show you how your network is put together and where the choke points are. We'll cover how to set up a new network and why some networks are more error-prone than others. We'll tell you what kit to buy and what to avoid. Despite all this, your network may still sometimes break. Long after death and taxes have both been abolished, network problems will remain. Home networking is a rough neighbourhood and you're always going to get shot at. But armed with the next few pages, you'll be able to roll for cover and return fire. Networking basics When you get broadband, your internet service provider (ISP) normally supplies you with a broadband modem. This, plus your Mac, is the simplest network you can have, and for lots of people it's all the network they need. If you have ADSL broadband – the most common kind – it's delivered to your house through the phone line. At the phone socket, you plug in a filter that splits the frequency range, so that the lower 4KHz is used by voice phone calls and the rest is sent to the modem. The modem takes the analogue electrical signal from the phone line and extracts the digital data stream encoded within it. This data takes the form of network 'packets' that are wrapped up using an addressing protocol called TCP/IP. (This is a fairly meaningless acronym, so don't bother trying to remember what it stands for.) Each TCP/IP packet contains a small piece of a website, or a graphic, or a downloaded file, or whatever is being sent from the internet. And every packet has a number, called an IP address, which identifies which computer or device it's intended for. Your broadband modem has an IP address assigned to it by your ISP and, if you have a modem that plugs into a USB port on your Mac, then this IP address is available exclusively for the use of that Mac. But if you want to connect more than one computer through the same broadband connection, you need a router – if you're not sure where yours is, that's because most modern broadband modems have a router built-in. If your modem has sockets for Ethernet cables, then it is actually a modem/router. Router vs modem The router is like a telephone exchange; it assigns separate IP addresses to all the computers connected to it and acts as a single point of contact for the wider network beyond it. When an incoming TCP/IP packet arrives from the internet, the router opens it and re-addresses it using the local IP addresses of your home network. This process is called Network Address Translation, or NAT. As well as enabling your broadband connection to be shared among many computers, NAT provides a measure of security from hackers, as the IP address of your Mac is never exposed to the wider internet. Only the router uses the external IP address provided by your ISP. <img alt="BT router" src="http://mos.futurenet.com/techradar/Review%20images/MacFormat/MAC%20228/MAC228.main_feat.grab1-420-90.jpg" width="420"></IMG> This anti-hacking function is called a firewall. By itself, NAT already does quite a good job, but almost all routers nowadays have much more sophisticated hardware firewalls that actively block probing attacks and make it hard for a hacker to tell that you're actually connected to the internet at all. Going wireless A broadband/router with a Mac connected via an Ethernet cable is the simplest configuration. But your phone socket doesn't generally come into the house right next to the Mac and most of us would rather not have to start tacking Ethernet cable around the skirting board. The solution is wireless networking, also called Wi-Fi or AirPort. A Wi-Fi connection is provided using a wireless access point and, again, most broadband modems include this in the same device. Instead of converting the TCP/IP packet into an electrical signal to transmit it along an Ethernet cable, a wireless access point broadcasts it as a radio signal. This is received by the Wi-Fi antenna in your Mac. There are several international standards for Wi-Fi devices. They are cryptically labelled as 802.11a, 802.11b and so on, but they are usually just referred to by the last letter – as 'wireless b', for example. The most widely used systems are b, g and n. The later letters are faster, or more reliable, or both, but they are backwards-compatible with earlier Wi-Fi standards. Generally, the slowest point in your network is your broadband connection, so unless you do a lot of transfers between devices on your network (to and from a networked disk, for example) it's a non-issue. If you want to print across your network, you can always connect the printer to one of your computers and share it from there. But this only works when that computer is running. Some printers are network-aware and can be connected to your router directly. Otherwise, you can use a print server. Your printer is served This device connects to your router with a wired or wireless connection and lets you plug in one or more printers. It keeps its own queue of print jobs and makes sure they go to the right printer. Apple's own-brand network devices are the AirPort Extreme Base Station, the Airport Express and the Time Capsule. An AirPort Extreme is a router with a wireless access point built-in. This is the same as the Wi-Fi router/modem from your ISP, except that it doesn't have the modem part. There are still some reasons why you might want to add an AirPort Extreme though. It has a USB port that you can use to add an external hard disk or a printer (or both if you use a USB hub); these will then be accessible across the network, from your Mac. The AirPort Express is a cut-down version of the Extreme. It only supports 10 simultaneous wireless devices instead of 50, and only one wired connection instead of three. The USB port on the Express can only be used to network a printer, not a hard disk, but it does include a stereo speaker jack that you can use to connect speakers or an amplifier and stream your music wirelessly from your iTunes library on your Mac. Time Capsule is an AirPort Extreme with a hard disk actually built-in. You can use the disk for overflow storage or you can allocate it for use with Time Machine backups. You can also do this with a USB drive plugged into an Airport Extreme, but it's a setup that isn't officially supported by Apple, and using a Time Capsule is a little tidier. When a network problem strikes, it isn't always immediately obvious. It's rare to get a clear message on the screen and it's easy to imagine that your Facebook app has simply crashed or a website is temporarily offline. A good first check is to open a new window in Safari and try pointing at www.google.com. The web requires the least complicated protocols of any of the services that run over the internet, and Google has a nice fast web page that is always up. <img alt="internet fail" src="http://mos.futurenet.com/techradar/Review%20images/MacFormat/MAC%20228/MAC228.main_feat.grab2-420-90.jpg" width="420"></IMG> The front page itself could be loading from Safari's internal cache, of course, so test your live connection to the internet by typing something random into the search box to force it to query the server. If you get a page of results, then you have an internet connection, at least. If you get a progress bar that goes nowhere, followed by a 'Safari can't find the server' page, you've got problems. If you have a wireless connection to your broadband router, cast a glance up at the menu bar on your Mac. The 'stripy slice of pie' icon on the right-hand side should be black. If it's greyed out, right-click it and see if you're connected to the right network. Sometimes you'll see your Wi-Fi network listed in the 'available' section, but it won't have a tick against it to show that it's selected. This is because the network briefly disappeared from the radar and OS X hasn't automatically reconnected when it came back up. Just click it on the list to reconnect. <img alt="network list" src="http://mos.futurenet.com/techradar/Review%20images/MacFormat/MAC%20228/MAC228.main_feat.grab3-420-90.jpg" width="420"></IMG> If your Wi-Fi link looks okay but you still have no internet connection, it's time to take a look at the router. Broadband modem/routers are little computers running an embedded operating system and they can crash just like any other computer. If none of the lights on the front are flickering – either because they are all stuck on or they are all switched off – turn the modem off at the wall. Actually, do this even if your modem lights look normal – different modems use different light sequences to indicate problems and rebooting the modem is an easy and quick way to rule out a crash. Light show When your modem starts up it will begin with a power-on self-test, which is normally indicated by the power light flashing steadily. After about five seconds of this, the power light will change to steady. Next to light up will be the LAN lights for any wired Ethernet connections that are active, closely followed by the WLAN light, which should start blinking away. <img alt="router" src="http://mos.futurenet.com/techradar/Review%20images/MacFormat/MAC%20228/MAC228.main_feat.grab4-420-90.jpg" width="420"></IMG> After that there will be a pause as your modem logs in to your ISP and then the light labelled 'broadband', 'ADSL' or just 'DSL' will come on. After that, there should be another pause before the internet light comes on to indicate that the router has been allocated an external IP address from the ISP. If all the lights come on in more or less this sequence, then you can be confident that the broadband modem is working fine. If any of the lights are yellow or red, or if the broadband or internet lights don't come on at all, then it could be that your modem is damaged. This can happen if the modem isn't ventilated and has overheated, or if the phone lines near your house are struck by lightning, sending a power surge to the modem. (This is why it's a good idea to disconnect the phone line from the modem if you have a big thunderstorm nearby.) Alternatively, your ISP may be having technical problems at your exchange. Try calling their support hotline to check this. Simplify, simplify Assuming that the modem restarts correctly but your network problems remain, the next step is to take as much complexity out of your network as you can. This will help you identify which link in the chain is failing. Does your iPod touch or iPad still connect through Wi-Fi? If so, it's a sign that the problem lies with your Mac. If none of them can connect, try a wired connection. There are lots of things that can cause Wi-Fi networks to suddenly break, but most of them boil down to either incompatibility with another network device or problems with wireless security. If you have recently changed broadband provider your wireless security key will have changed, but the new modem/router might also be using a different wireless security protocol. Some older network devices and computers have problems with the newer WPA2 protocol. Try temporarily turning security off and see if that makes a difference. It's possible you might need to fall back to the older WEP protocol. This is less secure than WPA or WPA2, but it's still better than nothing. Wireless security is only to protect yourself from hackers within physical wireless range of your network, so depending on your neighbours you might not really need more than WEP. Every device on your network must have a unique IP address. These take the form 192.168.1.n, where n is a number between 0 and 255. When you install a device, you can either choose a number for it yourself or you can let the router allocate one automatically, using a service called DHCP. <img alt="DHCP" src="http://mos.futurenet.com/techradar/Review%20images/MacFormat/MAC%20228/MAC228.main_feat.grab5a-420-90.jpg" width="420"></IMG> Using DHCP for all devices is usually the easiest option, but some devices do not support or behave oddly with her. If you assign static IP addresses to some of your network devices, make sure you restrict the range of addresses that the DHCP server on your router may use, and assign static IP addresses that do not reside in this range .

Tutorial: OS X networking explained

Networks can be complex. They are much better than they were, but they are always the most complicated part of your Mac. When you send a do...

In Depth: 3D TV without glasses explained

<img src="http://cdn.mos.techradar.com//classifications/home-entertainment/tv/images/3d_without_glasses/Philips%20IFA%203D%20pic-200-200.jpg"> Ever wish you could lose the specs and watch a 3D TV without those annoying glasses? Analysts at Futuresource Consulting predict that by 2011 the UK will have more 3D TVs than the current front-runners, France and Germany, with one in three homes 3D Ready by 2014 - and a staggering 50 per cent by 2015. That's an awful lot of 3D glasses - and at £100 a pop, it's a serious complaint about the 3D home experience. The solution, of course, is a 3D TV without glasses. So-called auto stereoscopic prototypes have existed for yonks, but now <a href="http://www.techradar.com/news/television/toshiba-gl1-brings-glasses-less-3d-tvs-to-the-mass-market-720737">Toshiba has started selling the first such TVs in Japan</A>, albeit in tiny sizes. Its 12-inch and 20-inch GL1 panels may be small, but they have huge prices at ¥120,000 (£914) and ¥240,000 (£1,828) respectively. Both include Toshiba's Cell Regza chipsets, though resolutions differ; the 12GL1 uses a 466 x 350 resolution panel, while the 20GL1 achieves 3840 x 2160 pixels. <img alt="Toshiba cell tv" src="http://mos.futurenet.com/techradar/classifications/home-entertainment/tv/images/3d_without_glasses/Toshiba%20Glasses-less%203DTV-420-90.jpg" width="420"></IMG> That makes it a 4k2k panel, as <a href="http://www.techradar.com/news/television/hdtv/stand-back-panasonic-unveils-the-worlds-largest-full-hd-3d-tv-662138">used increasingly on monster screens</A>, though here it serves a crucial purpose. Lenticular lens Effectively replacing glasses is a lenticular lens across the front, which refracts the light so a different image is seen by each eye. Unfortunately, this also lessens the visible resolution. "The resolution is 1280 x 720 pixels when it transmits the final 3D image," a Toshiba spokesperson told TechRadar. A Full HD final image would require an 8k4k screen, better know as <a href="http://www.techradar.com/news/television/bbc-delivers-long-distance-super-hi-vision-broadcast-720223">Super HiVision</A>. "Multiple viewing capability is necessary for larger format screens to enable multiple viewers to experience 3D," says James Bower, president and chief operating officer at glasses-free 3D TV developer Master Image. "In order to technically achieve this, resolution is greatly reduced. We will begin to see more commercially viable 3D TVs without glasses when 8k4k resolution screens become standard in the market." Meanwhile, Toshiba's 3D TVs have a very small viewing zone. "There is an ideal viewing zone, and this is best at a 40 degree viewing angle," said the Toshiba spokesperson, adding, "the suggested viewing distance is 90cm for the 20GL, and 65cm for the 12GL." So it's case of sit close and don't move; in other words, these glasses-free 3D TVs are effectively 'personal use' 3D screens. "It's a novelty item like the <a href="http://www.techradar.com/reviews/audio-visual/televisions/plasma-and-lcd-tvs/sony-xel-1-440032/review">Sony 11-inch OLED</A>," says Bill Foster, senior technology consultant at Futuresource Consulting. "I don't think Toshiba has any plans to sell it outside Japan." Multiview The present glasses-free tech - adding a lenticular lens to the front of the screen - is all about multiview; as you walk in front of an auto stereoscopic TV your viewpoint changes, so the screen must provide as many 3D views - or 'sweet spots' - as possible, other you'll see a double image or, worse, a reverse 3D image. "In order to format multiview content correctly, multiple perspectives are necessary," says Bower. "This is easily achieved with 3D animation, but for live action content it is much more difficult and is currently not commercially viable - eight or nine camera viewpoints are needed per stereo image." "Nine views is the current standard, but coming down the pike is 15 views, though that will require more processing and a meaty chip," says Foster. "It has been suggested that a large screen auto stereoscopic 3D TV could need up to 100 views." Exactly how camera rigs would be able to film from that many viewpoints is anyone's guess. Larger screens So will we see the big brands issuing large auto stereoscopic 3D TVs anytime soon? "It will take not less than four years for 32, 42 and 50-inch screens at consumer pricing - i.e. under £2,000," says Foster. "We might see auto stereoscopic TVs for £4,000, but they won't be in Currys. It may need an entirely new approach to make auto stereoscopic TVs viable, rather than trying to develop on from nine-view and lenticular lens system." Not that people aren't trying. It may be distant dream in the living room, but the wholly commercial digital signage market is pushing on with auto stereoscopic 3D TV using this lenticular lens system. Four ex-employees of Philips 3D labs have licensed the Dutch giant's never-got-past-the-prototype (ie not good enough for the home) WOWvx technology and formed Dimenco, which showed a prototype 56-inch 4K panel with 15 views at IFA. <img alt="Philips at ifa" src="http://mos.futurenet.com/techradar/classifications/home-entertainment/tv/images/3d_without_glasses/Philips%20IFA%203D%20pic-420-90.jpg" width="420"></IMG> Aiming its €40,000+ screens at casinos, advertising agencies and cinemas, CEO Dimenco Maarten Tobias says: "We expect consumers to experience 3D digital photo frames without the need to wear glasses soon. For other consumer markets, such as 3D game consoles and 3D TV, this will take a couple of years to further optimise the technology." Licensing the same technology from Philips is 3DFusion, which has added its own picture processing to create what its president Stephen Blumenthal calls "a new dimension in mastering, interacting, and optimizing the 3D video signal." 3D Fusion's 42-inch 3DFMax display is commercially available, but strictly for the B2B market. <img alt="3Dfusion" src="http://mos.futurenet.com/techradar/classifications/home-entertainment/tv/images/3d_without_glasses/3DFusion-420-90.jpg" width="420"></IMG> Another leading light in lenticular lens TVs is <a href="http://www.alioscopyusa.com/">Alioscopy</A>, whose 3D screens have been installed at one of the most famous retailers in the world, SAKS Fifth Avenue in New York, and used several World cities to launch the Lexus CT-200h. We asked Pia Maffei, Chief Operating Officer at Alioscopy USA in San Diego, when auto stereoscopic 3D screens will be available for the home. "Everyone has a different answer, buy my guess is within five years," she said. 3D gaming without glasses Much closer is 3D gaming - and we're not talking <a href="http://3dradar.techradar.com/3d-tech/depth-3d-console-gaming-test-gran-turismo-5-3d-01-12-2010">Gran Turismo 5 in 3D on a PlayStation </A>3. Foster thinks that we could see a 24-inch gaming panel and a new generation of games and consoles in the not-too-distant future, but the immediate glasses-free future is for now restricted to handhelds. First up in the UK is 2011's <a href="http://www.techradar.com/news/gaming/handhelds/hands-on-nintendo-3ds-review-697325">Nintendo 3DS</A>, which sources tell us is using a 3.53-inch auto stereoscopic display developed by Sharp, though that's not confirmed. Meanwhile, <a href="http://masterimage3d.com/products/3d-lcd">Master Image</A>'s slightly smaller 3.1-inch 3D screen has already found a commercial application in Hitachi's <a href="http://k-tai.hitachi.jp/h001/index.html">WOO H001 3D phone</A> in Japan, which was launched in 2009 for around £500. <img alt="Hitachi woo" src="http://mos.futurenet.com/techradar/classifications/home-entertainment/tv/images/3d_without_glasses/Hitachi%20WOO%203D%20phone-420-90.jpg" width="420"></IMG> Master Image's Bower thinks the market for 3D handhelds is about to explode. "We will see millions of 3D smartphones and tablets in the second half of 2011 - and tens of millions in 2012," he told us. However thrilling 3D phones, tablets and consoles turn out to be, it's on the bigscreen where 3D without glasses will have the greatest impact. So if not on TVs in the immediate future, could we ditch the specs in cinemas before long? "It's not coming to your local Odeon anytime soon," says Foster, who then gives a glimpse of just how exciting it will be when it does eventually arrive. "Watch My Bloody Valentine in 3D and the machete comes straight at you. In the next generation of 'multiview' glasses-free 3D, it will go straight down the middle of the cinema." Tantalisingly just beyond our reach, the future of 3D isn't just about ditching the specs. It's a whole new era of holographic imagery - and it's bound to make cinema-goers go wild in the aisles.

In Depth: 3D TV without glasses explained

Ever wish you could lose the specs and watch a 3D TV without those annoying glasses? Analysts at Futuresource Consulting predict that by 201...

Explained: QuickPath Interconnect vs HyperTransport

<img src="http://cdn.mos.techradar.com//Review%20images/PC%20Format/PCF%20246/PCF240.w_rev6.rampage3-200-200.jpg"> Due to your insatiable appetite for ever-faster PCs, the poor old Front Side Bus has had its chips. It just can't cope any more. Since the FSB sits between the processor and the northbridge chip, all the data the processor worked on passed through it. Hanging off the northbridge chip were the memory, hard drive, graphics card and just about everything else. Increased frequencies and clever tech such as double and quad data rates have helped, but what with multi-core processors, insanely powerful graphics cards and everything else, it's just become flooded. Data rates have topped out at 12,800 MB/s at best, which is just not fast enough. So it's out with the old and in with the new. Two high-speed bus standards with more serious capabilities take the place of the old FSB: Intel's QuickPath Interconnect and AMD's HyperTransport. Both involve processors with onboard memory controllers. No longer will the processor have to funnel data from the main memory down the same bus its trying to access the hard drive through and send data through to the graphics card. Moving the memory controller off the FSB means the old limitations on memory speed have been removed too – it's no longer limited to the speed of the FSB, so dual or triple channel starts to make real sense. Dual channel DDR3-2000, for example, can deliver a maximum (on paper) of 32GB/s, considerably more than the FSB would ever be able to handle. The second aspect of these new architectures is the bus itself, which sits between the processor and the northbridge chip (or what was the northbridge chip). Strictly speaking, both QPI and HT are not buses, but point-to-point connections. A bus is a set of wires that can be used to connect a number of devices, while point-to-point, as you might have guessed, is just for connecting two devices. We'll still call them buses though, because it's a set of wires on the motherboard transferring data, which to most of us means it's a bus. Both systems use similar methods and have similar sets of features, although the technical implementations are different. HyperTransport AMD was first of the big two to replace the FSB with its HyperTransport, released in 2003 with its Athlon 64 processors coupled to Nvidia nForce chipsets. Bundled together it's called the Direct Connect Architecture. HyperTransport is an open standard and has its own .org site to prove it. It was first announced to the world in 2001 and was originally called the Lightning Data Transport (super hero names appear to be de rigueur for high-speed connections). HyperTransport has separate data paths for input and output, enabling the processor to read and write at the same time. It also employs double data rate technology to squeeze two transfers per clock, and has a variable bit-width between two and 32 bits. Thus 3.2GHz double data rate by 32 bits gives us 3.2 x 2 x 32 bits per second in each direction, which when divided by 8 to convert into bytes, reaches the headline 51.2GB/s maximum figure, 25.6GB/s in each direction. However, AMD processors use a 16-bit wide HyperTransport, and the best of them are running HyperTransport at 2GHz, which gives us 16GB/s. HyperTransport isn't limited to PCs. It's being developed to be used on much more complex server systems, and as a bus in high-speed routers. There are even HyperTransport expansion cards. The idea of HyperTransport-enabled expansion cards is an interesting one. It might not mean much for desktops, but for servers it opens all sorts of possibilities. Version 3.0 even supports hot plugging. QuickPath Interconnect Five years after AMD released its high-speed bus on the PC, Intel responded with QuickPath Interconnect. It was developed by a team that used to be part of Digital Equipment Corporation, and was originally called the Common Systems Interface. As with HyperTransport, it's a point-to-point connection, and offers similar speeds. Of course, the two systems are completely incompatible with each other. QPI first appeared in 2008 on the X58 motherboard chipset and the Xeon 5500 processor. QPI currently features on the top end of Intel's Nehalem range. Taken together with the integrated memory controller, it forms the QuickPath Architecture. The physical structure consists of two sets of 20 data links, one set going in one direction, and one set going in the other. As with HyperTransport, it employs low-voltage differential signalling, which uses two signals on separate lines to transmit data, reading the difference between the two. It's a method used on PCs and many other electronic devices to combat electromagnetic interference. Add in a pair of clock lines, and the total pin count is 84. QPI transmits data in flits (yes, that's what Intel calls them) of 80 bits, which takes two clock cycles. Each flit has 8 bits of error detection, 8 bits of header, leaving 64 bits of data. The bus is divided into quadrants, each with five data links, and each can be used independently. QPI runs off a multiplier of the base clock (133MHz for Intel), currently either x18 or x24, giving us speeds of 2.4 or 3.2GHz. All this boils down to theoretical maximum transfer rates of 19.2GB/s for the 2.4GHz version, and 25.6GB/s for the 3.2GHz. The industry likes to employ the term, 'Gigatransfer GT/s'. This is double the frequency, as it includes the double data tech (transferring two bits per clock), thus 6.4GT/s equates to 3.2GHz. Since it's bi-directional, you might prefer to halve those figures, though. Only Intel's top dogs get QPI, and even pretty tasty i7s have to struggle on with the FSB and DMI bus instead. (Direct Media Interface is another point-to-point bus that sits between the northbridge and southbridge chips.) You'll find the 2.4GHz version of QPI on Intel i7-920 through to the 970. The faster version graces the i7-975X, 980X and 990X. Can I overclock QPI? You've just read about how fast these systems are, and you want to overclock them already? Typical. Basically, it's not such a good idea, since you're better off trying to squeeze more performance out of your system elsewhere. Since QPI runs off the base clock (like everything else), adjusting the base clock will overclock QPI. It isn't advised though, as it also overclocks the Uncore (so called because it isn't part of the core). The Uncore controls the L3 cache and the memory bus. This must be clocked at twice the memory clock, and doesn't react well to being played around with. Your best bet is sticking to the simple stuff, such as experimenting with the CPU multiplier. The only time you might want to mess with QPI speeds is if your processor has a locked multiplier. This means you'll have to resort to playing with the base clock. Your best bet here is to drop the QPI multiplier to 18 if it isn't there already and then start increasing the base clock and vCore by little steps until it all stops working. HyperTransport then? It's a similar story with HyperTransport, which can be a sensitive beast if you play with the multiplier or hike the base clock up too much. You'll get more tangible gains elsewhere. The gains that were once had by playing with the FSB speed are gone. We know this won't stop you from trying though. As you might have spotted, the replacement of the FSB with something faster gives your graphics card more breathing space, too. For a start it doesn't have to share the processor's attention with the main memory. The current top spec for connection is PCIe 2.0, which is another high-speed point-to-point system, and can theoretically shift 8GB/s. The next step, PCIe 3.0, is due to be finalised in November, and will be able to shift 32GB/s. We won't see cards until next year though. Which system is faster? There are a lot of numbers thrown about, and to be frank they really don't matter. QPI is currently faster, but HyperTransport is ultimately more flexible. Both are extremely capable, and can quite happily handle a single-processor desktop PC with room to spare. It's still fairly early days too, and both will get faster. Where this tech really flies is in multi-processor systems, connecting each processor to each other processor in a little net of connections, enabling high-speed non-uniform shared memory access. These boys are so capable that on the average desktop you're laughing. That said, you can be sure that if there is bandwidth available, somebody will find a way to use it all up, and it all starts again…

Explained: QuickPath Interconnect vs HyperTransport

Due to your insatiable appetite for ever-faster PCs, the poor old Front Side Bus has had its chips. It just can't cope any more. Since t...

Explained: Windows Phone 7 microSD card: why you can't change it

<img src="http://cdn.mos.techradar.com//classifications/Mobile%20Phones/Hands%20on%20pictures/Samsung/Samsung%20Omnia%207/Samsung_Omnia_7_01-200-200.jpg"> Microsoft has been saying all along that even if you can get at the microSD slot in a Windows Phone that the point isn't to be able to swap cards. As general manager Charlie Kindel told TechRadar: "It is possible for the manufacturer to put a microSDcard in the phone - but that memory is not user serviceable, you can't pull it out or replace it." The quick start guide tells you that if you do take the card out, the phone will reset itself and you won't be able to use the card in other devices. That's because the OS pairs the card to the phone by locking it with an automatically generated password and checksum - which means it can recognise the card and be sure the content hasn't changed. Why does Windows Phone 7 do that? "We use the built-in flash memory on the phone and the flash on the microSD as a single file system," Kindel told us: "if the user were to pull it out, it would break that file system." Your music, pictures, apps and everything else will be spread across both areas of storage and the phone has no way of knowing what's on the microSD card so it can't just tell you something is missing - it has to reset the phone to make sure you don't try to use something that's no longer available. Setting the password isn't permanent - but the vast majority of devices don't implement passwords for SD cards so they won't even recognise the card to format it (some Nokia phones support this part of the SD card standard). Windows Phone 7 microSD expansion Suppose you want to replace a low capacity microSD with a larger one and you don't mind resetting your phone? After all you can get your apps back from the marketplace and your media from the Zune software. The problem is, according to Charlie Kindel, "these memory cards have very different speed characteristics and if the user is willy-nilly putting in different memory cards that would hurt the phone experience." Having a slow SD card in your camera will mean it takes slightly longer to save a photo but you might never notice; having apps launching from a slow SD card could make your Windows Phone feel very sluggish. Why can't you just buy a fast microSD card of the right class? "Yes, it's about read write speeds [which is what the SD class number indicates]," senior product manager Greg Sullivan told us. "The IO rate is part of it but actually what's equally important are the bit error rates. That will impact the speed of the checksum rewrite." Microsoft was hoping that the issue wouldn't come up for most users (and we agree that the majority of mainstream users will never open up their phone to change the memory card). "Most of the microSD slots are not user accessible for that very reason," Sullivan told us. When they are, as with the Samsung Focus, "there's a big sticker that asks you to read the Quick Start guide before changing the microSD". Larger Windows Phone 7 microSD cards The obvious answer is for Microsoft or the handset manufacturers to test and certify memory cards. But the Windows Phone team told us they didn't have the time or resources to do this before launch, that manufacturers tested only the microSD cards they buy in bulk, which aren't available in retail - and that just going by what the chassis specification for the handset says (or even the class of the microSD card) isn't enough to guarantee good performance and performance varies between vendors and even between different cards from the same manufacturer. The same member of the Windows phone team told us they're now busily buying every microSD card they can get their hands on and testing it in their phones, and when they have a list of which cards perform well enough to recommend they'll be distributing the information. But for now, the <a href="http://support.microsoft.com/kb/2450831">official Microsoft line</A> is still not to swap out your microSD card for a new one.

Explained: Windows Phone 7 microSD card: why you can't change it

Microsoft has been saying all along that even if you can get at the microSD slot in a Windows Phone that the point isn't to be able to s...

Explained: Windows Phone 7 microSD card: why you can't change it

<img src="http://cdn.mos.techradar.com//classifications/Mobile%20Phones/Hands%20on%20pictures/Samsung/Samsung%20Omnia%207/Samsung_Omnia_7_01-200-200.jpg"> 
Microsoft has been saying all along that even if you can get at the microSD slot in a Windows Phone that the point isn't to be able to swap cards. As general manager Charlie Kindel told TechRadar: "It is possible for the manufacturer to put a microSDcard in the phone - but that memory is not user serviceable, you can't pull it out or replace it." The quick start guide tells you that if you do take the card out, the phone will reset itself and you won't be able to use the card in other devices. That's because the OS pairs the card to the phone by locking it with an automatically generated password and checksum - which means it can recognise the card and be sure the content hasn't changed. Why does Windows Phone 7 do that? "We use the built-in flash memory on the phone and the flash on the microSD as a single file system," Kindel told us: "if the user were to pull it out, it would break that file system." Your music, pictures, apps and everything else will be spread across both areas of storage and the phone has no way of knowing what's on the microSD card so it can't just tell you something is missing - it has to reset the phone to make sure you don't try to use something that's no longer available.Setting the password isn't permanent - but the vast majority of devices don't implement passwords for SD cards so they won't even recognise the card to format it (some Nokia phones support this part of the SD card standard). Windows Phone 7 microSD expansionSuppose you want to replace a low capacity microSD with a larger one and you don't mind resetting your phone? After all you can get your apps back from the marketplace and your media from the Zune software.The problem is, according to Charlie Kindel, "these memory cards have very different speed characteristics and if the user is willy-nilly putting in different memory cards that would hurt the phone experience." Having a slow SD card in your camera will mean it takes slightly longer to save a photo but you might never notice; having apps launching from a slow SD card could make your Windows Phone feel very sluggish. Why can't you just buy a fast microSD card of the right class? "Yes, it's about read write speeds [which is what the SD class number indicates]," senior product manager Greg Sullivan told us. "The IO rate is part of it but actually what's equally important are the bit error rates. That will impact the speed of the checksum rewrite." Microsoft was hoping that the issue wouldn't come up for most users (and we agree that the majority of mainstream users will never open up their phone to change the memory card). "Most of the microSD slots are not user accessible for that very reason," Sullivan told us. When they are, as with the Samsung Focus, "there's a big sticker that asks you to read the Quick Start guide before changing the microSD".Larger Windows Phone 7 microSD cardsThe obvious answer is for Microsoft or the handset manufacturers to test and certify memory cards.But the Windows Phone team told us they didn't have the time or resources to do this before launch, that manufacturers tested only the microSD cards they buy in bulk, which aren't available in retail - and that just going by what the chassis specification for the handset says (or even the class of the microSD card) isn't enough to guarantee good performance and performance varies between vendors and even between different cards from the same manufacturer. The same member of the Windows phone team told us they're now busily buying every microSD card they can get their hands on and testing it in their phones, and when they have a list of which cards perform well enough to recommend they'll be distributing the information.But for now, the <a href="http://support.microsoft.com/kb/2450831">official Microsoft line</A> is still not to swap out your microSD card for a new one.

Explained: Windows Phone 7 microSD card: why you can't change it

Microsoft has been saying all along that even if you can get at the microSD slot in a Windows Phone that the point isn't to be able to...

VoIP Security Threats Explained

In a recent report issued by CompTIA, the Computer Technology Industry Association, 50% of small and medium sized businesses (SMBs) had very little trust in the security offered by VoIP vendors, or for that matter, voice over IP security in general.It is true, having your voice and data running on the same infrastructure leaves your telecommunications particularly vulnerable to all the security threats inherent in an IP network. Viruses, Trojan Horses, and worms can all wreak havoc on a network, and having your voice network go down for even the shortest time is intolerable for most business.That said, security has come a long way, and most attacks can be stopped at the gateway by a good network administrator. While attacks on VoIP networks in particular are by no means widespread, the possibilities are there, if not imminent, and pose a very real threat to the very time sensitive requirements of voice over IP.The following is a compilation of just some of the security threats facing a voice over IP network, as well as some security measures that could be taken to prevent such attacks.SPIT - The new Spam for VoIPMost anybody that receives email is familiar with the term Spam. Who among us has not received dozens of unsolicited emails, clogging up our mailboxes and causing us to waste our valuable time? Laws have been made to reduce the clutter in our mailboxes, and major offenders have been fined heavily, in some cases put in jail.Spam is basically the broadcasting of advertisements, announcements, or other unwanted messages, over a network or networks, ending up in the mail boxes of anyone that has an email address on that network. At worst, spam is frustrating for the recipient, and can also cause network problems utilizing a good majority of bandwidth that is meant for other things. As email applications are connectionless and not sensitive to time delay, eventually the recipient will receive their emails intact, albeit a few minutes later than it would normally take.Spam over Internet telephony, otherwise known as SPIT, can have far greater consequences than email spam. Spitters that target VoIP gateways can use up the available bandwidth, severely disrupting Quality of Service and causing a major degradation in voice quality.The open nature of VoIP phone calls makes it easy for spitters to broadcast audio commercials just as email advertisements are broadcast. On closed networks like Vonage or Skype, or even your companies LAN, it is a little more difficult as the spitter would have to hack into the network in order to implement the broadcast. It can, however, be done.The ability to broadcast audio messages over a VoIP network is not, in itself, necessarily a bad thing. Companies should be able to get out important messages quickly, and on a broader scope, emergency services could easily communicate mandatory evacuations, or warn of impending disasters in the event of catastrophe.While Spit is certainly a technical possibility, to date, we have not seen a lot of it. In 2004, the peer to peer VoIP network Skype got hacked into, and users were inundated with unsolicited audio messages. Shortly thereafter, Skype had found and closed the loophole in the network. One other legal recourse is to get on the national Do Not Call list, to prevent solicitors from bombarding your voice mail boxEavesdroppingProbably one of the scariest vulnerabilities of VoIP is the ability of an outsider to eavesdrop on a private conversation. This concept is nothing new to IP data networks, and generally requires a packet analyzer to intercept IP packets, and in the case of VoIP, saving the data as an audio file. Hackers then have the ability to learn user ids and passwords, or worse, to gain knowledge of confidential business information.While it is true that eavesdropping occurs on traditional telephone lines as well as cellular networks, for someone to tap into your home phone line pretty much requires a physical presence outside your house. In the case of an IP network, a hacker requires only a laptop, some readily available software, and the knowledge of how to hack into your network.Security analysts have long used encryption techniques to protect the confidentiality of data traveling through an IP network, and the same concept holds true for voice packets. The challenge with voice is to encrypt strongly and quickly, to protect confidentiality and as not to slow down the packet flow.Nevertheless, if someone really wants to listen in on your calls, no type of telecommunication is 100% secure.Phishing the Waters of Voice over IPAnother variation of an email attack, Phishing is designed to trick a user into revealing sensitive data such as user names, passwords, bank accounts, credit cards, and even social security numbers. In the case of VoIP, the attack could come as a voice mail message urging you to call a designated number and provide your user information. Even if the call is automated, touch tones can be easily deciphered. Depending on what information they get, hackers can use it to access bank accounts, or to steal identities.While you can program a PBX to restrict call backs to known phishers, as more users become familiar with the pitfalls of the Internet, it becomes common knowledge to never give out sensitive information to automated media, be it via data or voice.SIP Registration HijackingThe Session Initiation Protocol (SIP) is becoming widely accepted as the method for setting up VoIP phone calls. The process involves a Registrar (in some cases the company PBX itself), which maintains a database of all users subscribed to the network, and basically maps their telephone number to an IP address.Registration hijacking occurs when the packet header of either party is intercepted by a hacker, who substitutes his IP address for that of the legitimate one. Attacks can take the form of fraudulent toll free calls, denial of service attacks that can render the user's device useless, or a simple diversion of communication.SpoofingAnother hack that is well known in data networks is spoofing Also known as a man in the middle attack, spoofing requires hacking into a network and intercepting packets being sent between two parties. Once the IP address or phone number of the trusted host is discovered, hackers can use this attack to misdirect communications, modify data, or in the case of Caller ID Spoofing, transfer cash from a stolen credit card number.SIP registration hijacking is a form of spoofing. Both of these spoofs, as well as other hacks such as eavesdropping, can be prevented by employing encryption techniques at the call set up phase. Today, the up and coming mechanism to achieve this is to send SIP messages over an encrypted Transport Layer Security channel. Putting these two protocols together forms the acronym SIPS.There is no doubt that IP networks can be, and are, hacked into. Since a converged network consists of data and voice, VoIP is as vulnerable as any application to these disruptions, but with a downtime tolerance of no more than 5 minutes a year, such interruptions are considered intolerable for voice applications.As of today, most of these security threats are not wide spread, and are presented here as a what could happen in the future scenario. Industry experts agree that as voice over Internet telephony becomes more wide spread, malicious hacking attempts are bound to follow.These and other VoIP security threats can be prevented by a vigilant network staff, using all the known security precautions typical of an IP network. No VoIP solution is secure out of the box, and must be locked down by using common sense approaches, including but not limited to changing default passwords, closing down unused ports and services, utilizing firewalls and VPNs for network communications, and diligent intrusion detection.	 	 		 			 				 					 						Author Michael Talbert is a certified systems engineer and web designer with over 7 years experience in the industry. For more information on <a href="http://voip-facts.net/" target="_new">VoIP Telecommunications</a>, visit the website VoIP-Facts.net, or the <a href="http://voip-facts.net/voip-blog/" target="_new">VoIP Facts Blog</a> for up to date industry news and commentary.

VoIP Security Threats Explained

In a recent report issued by CompTIA, the Computer Technology Industry Association, 50% of small and medium sized businesses (SMBs) had v...