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the works and vote up the proposals youd like to see incorporated into future releases by

visiting . Some of the discussions there can get prey technical,extending to the depths of the core code that makes the CMS tick. Still, even if you dont

understand everything thats going on, this is the place to go if you want to champion a

beer media gallery, see closer integration with BBPress or propose an obscure language

for an interface translation.

The developers document their progress at , whichshould be considered essential reading for anyone who uses WordPress in daily life.

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MULTIMEDIA EXPERT

Lens filters are a crucial part of a photographers arsenal, performing tricks

that cant be emulated with digital effects. Ben Pitt rounds up the choices

THESE DAYS, THE word filter usually refersto a digital eect, applied by the camera orin soware. Many of these eects wouldpreviously been achieved by placing a glassfilter in front of the cameras lens.In many cases, it makes more sense to apply

these eects digitally. For example, you coulduse a blue filter to remove the yellow colourcast caused by household lighting, but its mucheasier to adjust the white balance manually, orjust let the automatic white balance function doits thing. The same applies to so focus andvarious other special-eect filters, such asstarbursts and diracted multiple images. It canbe fun to see these eects through the lens ofan SLR, but theres no way to adjust or removethem once youve captured a picture.However, some filters cant be emulated

digitally because of the way they interactwith the light. They give the photographera strategic advantage rather than simplyapplying an explicit eect. Its these filtersthat were exploring in this article. But first,lets deal with a few practicalities.

CHOOSING AND FITTING

Virtually all SLR and CSC lenses include a filterthread; some compact cameras do, too. This isa standardised screw-in aachment that meansyou can aach filters from a wide range ofmanufacturers. The thread comes in dierentsizes, though, so its important that you buyfilters that fit your lens. The thread size isstated in millimetres, and is usually wrien onthe lens barrel, accompanied by a symbol.If youve got a collection of lenses with

dierent thread sizes, you shouldnt need tobuy multiple sets of filters. Stepping ringsconvert from one size to another. We useKood stepping rings that cost around 7 each

and work perfectly well. Youll need to buyfilters to fit your biggest lens and then usestepping rings to fit them to your smallerlenses do it the other way around, and thefilters wont cover the larger lens.The filters themselves are widely available

from specialist photography stores andwebsites. The leading brands include Hoya,Cokin, Tien and B+W, but there are manyothers. Prices vary widely, with nominallysimilar products costing anything from 5 to80. More expensive filters come with thepromise of superior optical performance,although in our experience, we havent had anymisgivings about filters around the 20 mark.Each filter includes a filter thread of its

own, which makes it possible to use morethan one at a time. This has some interestingcreative applications, as well see below,although stacking them compounds their

optical imperfections and increases thelikelihood of internal reflections, resulting inlens flares. There will also come a point wherethe corners of the frame will be obscured bythe barrel of the outermost filter, causingheavy vigneing.Cokin filters work slightly dierently. The

filters themselves are square rather thanround and are available in four sizes. Up tothree of these filters sit in a specially designedholder, which aaches to the lens using anadaptor ring. This system makes it quicker toswap filters in and out, and also to position afilter higher or lower; this can be very useful,

as well see later. The design is a lile bulkierthan conventional screw-in filters, though.

ULTRA-VIOLET

The most popular type of filter is ultra-violet(UV), which filters out ultra-violet light. Thisreduces the haziness that can aect distantlandscape subjects, although the dierence isprey subtle. In practice, people tend to useUV filters precisely because they make verylile impact on the photo. Theyre used moreto protect the lens. Aer all, its much beerto scratch a 20 filter than a lens costinghundreds of pounds. This filter can staypermanently aached to the lens withoutany risk of it adversely aecting a photo.

POLARISERS

The other big sellers, according to distributorIntro 2020, are circular polarising filters. These

work using the same principle as the 3Dglasses used in cinemas, whereby light can befiltered based on the polarity of light waves.Most light is randomly polarised, so you cantselectively filter it out with a polarising filter.However, blue skies and certain types ofreflections are partially polarised, and computerscreens are highly polarised, so it is possibleto suppress them with a polarising filter.Two types of polarising filter were once

common: linear and circular. However, linearpolarising filters can cause problems withautofocus systems so youre unlikely tofind them on sale these days.

Making more of yourcamera with lens filters

From le: ultra-violet (UV), circular polariser, neutraldensity (ND), Fader ND and three close-up filters

Certain filters give the photographer a strategicadvantage rather than applying an explicit effect

152 MARCH 2014 | COMPUTER SHOPPER | ISSUE 313

MULTIMEDIA EXPERT

153ISSUE 313 | COMPUTER SHOPPER | MARCH 2014

A circular polarising filter comprises twoelements, and rotating the outer elementdetermines which polarity of light is filteredout. A 90 twist takes the filter from oneextreme to the other, so its quick to adjust bytrial and error youll see the eect throughthe cameras viewfinder or LCD screen. Youcan even try a polariser out by holding it upto your eye, to check whether its worth usingbefore aaching it to the lens.Darkening a blue sky with a polariser helps

the clouds to stand out, and also avoids thecommon problem whereby the sky is toobright compared to the land. However, thistrick works only when the lens and filter arefacing roughly at right angles to the positionof the sun. Thats easy to achieve aroundmidday in summer, but at other times youllfind that the benefit disappears whenshooting away from or into the sun.Polarisers also filter out reflections o

shiny objects such as glass and water and, toa lesser extent, light reflecting o foliageand skin. Theyre perfect for avoidingreflections when taking photos throughglass. Theyre also useful for takingphotos of water, especially if you wantto capture whats below the surface.However, their eectiveness dependson the angle of incidence. Youll needto be looking down on the water ratherthan across it for the eect to work.

In general, polarising filters are great forreducing glare and washed-out skies whenshooting on sunny days. However, they alsotend to suppress contrast, so colours can lookflat. Still, you can always restore contrast laterusing image-editing soware. Shooting Rawand processing in soware such as Lightroomwill give lots of control over the balance ofcolours, while the polarising filter shouldensure that your highlights arent clipped.Bear in mind that polarising filters reduce

the overall strength of the light to around half.This shouldnt be a problem if youre shootingin sunlight, but its worth bearing in mind.

NEUTRAL DENSITY

Sometimes reducing the amount of lightis exactly what you want, and thats whereneutral density (ND) filters come in. Think ofthem as sunglasses for your camera,

darkening the image by a factor of anythingfrom two to 1,000.Their strength can be described in three

ways. The most common is to express theratio as a single number: an ND8 filter willreduce the light to an eighth of its originalstrength, so youll need to multiply the shuerspeed by eight to compensate. Sometimes NDfilters are referred to in stops. A single stopmeans half or double the exposure value, soan ND8 is a three-stop filter because it hashalved the intensity three times (half, quarter,eighth). A few manufacturers refer to NDfilters according to their optical density, whichis the scientific measurement expressed as alogarithmic ratio. Here, 0.3 is equivalent toND2, 0.6 is ND4, 0.9 is ND8, and so on. SearchWikipedia for neutral density to see a tablethat compares the three measurement types.ND filters are typically used in conjunction

with a tripod when a long exposure time isdesired to blur motion. Shuer speeds slowerthan one second are great for turningflowing water into wispy streaks of light.

Waves in the sea or ripples in a lakeare smoothed over to give anethereal sheen, and reflections inrippling water become hazy. A verylong exposure will blur clouds, andtransform a busy high street into aghost town, complete with ghostlystreaks of colour here and there.ND filters arent just for long

exposures. You might want to use aspecific shuer speed, such as 1/100s, to

capture a small amount of motion blur, but

No filters and 1/10s shuer speed at f/8

For more blur, we added our circular polarising filter and set the aperture to f/11,giving a 10-second exposure time. Note the muted colours from the polarising filter

An ND8 filter gives a one-second shuer speed, blurring the water a lile

Adding a graduated ND filter darkens the sky to avoid clipped highlights. Note thevigneing in the top corners, from using so many filters stacked on top of each other

Up to three of Cokins square filters sitin a specially designed holder. This one is agraduated ND filter

MULTIMEDIA EXPERT

154 MARCH 2014 | COMPUTER SHOPPER | ISSUE 313

NEXT MONTH

CREATE AND CUSTOMISE FONTS

Are you sick of trawling through longlists of dreary fonts? We reveal how youcan give them a new lease of life, and howto make your own from scratch.

sensible to include them here. A close-up filter

is essentially a magnifying glass. Its a single-

element lens that makes the image bigger and

also lets the camera focus closer to the subject.

It turns any standard kit lens into a macro lens.

Inevitably, a close-up filter cant deliver the

same optical performance as a dedicated macro

lens. In our experience, focus deteriorates

heavily towards the edges of the frame; for

more powerful filters, focus isnt too hot in

the centre, either. So focus towards the

edges isnt necessarily a terrible affliction. It

can be quite flaering at times, drawing the

eye to the centre of the frame. Heavy colour

fringing doesnt look so good, but we were

impressed with Lightrooms ability to remove

much of this with its Defringe controls,

located in the Lens Corrections module.

Our Hama set of close-up lenses include

three strengths, rated at N1, N2 and N4. They

allowed us to get closer and make subjects

appear bigger in the frame. The N4 lens made

subjects appear over twice as big. However, the

fall-o in focus meant there wasnt much of a

boost in detail. It might be just as eective to

crop and resize the image in soware. Still,

theres something to be said for achieving the

eect in the camera, and the so focus eect

does have a certain dreamy atmosphere that

could be turned to your advantage.

LIFE THROUGH A LENS

This is only a small selection of the filter types

currently available. Head to www.cokin.co.uk

or www.hoyafilter.com and youll find dozens

more, such as sepia tints, starbursts and so

focus diusers. You might be able to achieve

similar results in editing soware, but theres

something to be said for composing shots

with these eects already in place.

also want a wide aperture for a narrow depth

of field. Using an ND filter lets you set the

shuer speed and aperture for creative eect,

and still control the overall exposure level. It

may also come in handy when the cameras

maximum shuer speed isnt fast enough.

The only drawback is that more powerful

ND filters can cause problems for the cameras

autofocus and metering, because theres not

enough light for the camera to measure. There

may be not enough light for you to compose

the shot, either. For the strongest ND filters,

rated at ND1000, theres no hope of composing

the shot with the filter aached. The only option

is meter and focus, aach the filter and adjust

the exposure seings manually.

FADER ND

Rather than buying lots of ND filters at

dierent strengths, you might want to go for

a Fader ND filter. The strength can be varied

from ND2 to ND400 simply by rotating the

outer element. Thats because these filters are

actually two polarising filters. Line up their

polarities and they act like a single polarising

filter, but turn the outer one by 90 and

together they cut out almost all the light.

They start to display rippling eects at very

dark seings, but theres a wide usable range.

Its more cost-eective than buying lots of

conventional ND filters, and having one

adjustable filter is convenient, too. A Fader

ND filter is also useful for video, providing an

easy way to perform smooth manual exposure

adjustments without having to mess around

with the aperture and shuer speed controls.

GRADUATED ND

The graduated ND is another spin on the ND

concept. It varies from one part of the frame

to another, darkening one side of the frame

while leaving the other clear. Theres a

graduated area in the middle to give a smooth

transition from one to the other. The obvious use

for this filter is to darken skies to avoid over-

exposure when compared with the ground.

However, you could use it in any shot, in any

orientation, where a part of a photo is too bright.

Graduated ND filters vary in their strength

and the size of the graduated section. Cokins

square filters are particularly useful, as they

can be slid up and down in the holder to

position the filter precisely. The holder can

also be rotated to vary the angle, which is also

true of screw-in grad ND filters. We tried out

the Cokin ND Grad Kit, which comprises a

holder and three filters rated at ND2, ND4

and ND8. The ND8 uses a gentler graduation

to counterbalance its higher strength. For even

stronger filtering, the Cokin holder makes it

easy to combine multiple grad ND filters. You

could use two in opposite directions to darken

both the top and the boom of the frame

while leaving the middle clear.

If you shoot Raw and process your photos

in Lightroom, youll have the digital equivalent

of grad ND filters at your disposal in the

shape of the aptly named Graduated Filter.

Theres oen more highlight detail in a Raw

file than is shown at default processing seings,

and invariably more than you get from shooting

JPEGs. However, using a grad ND filter in front

of the lens means its far less likely that the

brightest parts of the sky will be clipped. This

means you can boost the exposure seings to

ensure that youve captured plenty of detail in

the darkest parts of the foreground.

CLOSE-UP

Close-up filters are dierent to all the others

described here, as they bend the light rather

than filter it. That technically makes them

lenses rather than filters, but as they aach

to an existing lenss filter thread, it seems

The same scene without (le) and with (right) a circular polarising filter (JPEGs straight from the camera). With the filter, the sky is darker, revealing the cloudtexture and also leing us boost the overall exposure to bring out the colours in the trees. Also, the suns reflection in the railings is greatly reduced. Theres lessdierence between the sunlit and shaded areas of the grass, because the reflections on the grass have been reduced, too

If youve got a collection of lenses with differentthread sizes, you dont need to buy multiple sets of filters.Stepping rings convert from one size to another

http://www.cokin.co.ukhttp://www.hoyafilter.com

BUSINESS EXPERT

155ISSUE 313 | COMPUTER SHOPPER | MARCH 2014

Installing a free serveroperating systemYour budget for a server is probably modest, so why pay Microsoft for your

OS? Simon Handby explains how to install the free Linux alternative

the optical drive to the top of the boot order;this is usually a case of selecting it and thenpressing +. Save the changes and reboot.Unlike the desktop version, the Ubuntu

Server disc isnt a LiveCD that boots into aworking version of the OS. Instead, when youboot from it, youll see a simple languageselection screen before geing to an equallysimple install menu. Most of the installationprocess is self-explanatory, but to get startedchoose Install Ubuntu Server. Aer a fewsimple questions, youll be prompted toprovide a hostname for the server. Itscommon to use a naming theme for servers,such as planets in the solar system orcharacters from The Simpsons, but adescriptive name such as FileServ could bemore practical. Type a name then hit Enter.Continue through the next steps, providingyour name, username and password, thenchoosing whether to encrypt your homedirectory doing so will be more secure.

ACTING THE PARTITION

Aer youve set the time zone, youll beprompted to partition the systems disks. Youcan take a few approaches here. If you wantto configure a server with mirrored drives, seethe box on page 156. For detailed advice, seethe Partitioning for Ubuntu section of theUbuntu Installation Guide, which you can readby clicking the link in the Further Informationbox on page 157. Well assume your server hasa single disk or a RAID array that presents

LONG-TERM RELATIONSHIP

Ubuntu Server has two significant versions:the latest, Ubuntu 13.10, and a more tried-and-tested Long Term Support (LTS) version, forwhich updates are guaranteed to be availablefor five years aer its release. For a serverenvironment, we generally recommend optingfor stability and support over the latestfeatures, unless you specifically require afeature thats available only in the latestversion. Here, well be using the most recentLTS release: Ubuntu 12.04 LTS. Download thisfrom www.ubuntu.com/download/server. Fora business server, we recommend using the64-bit version; just remember that youllneed a 64-bit processor to go with it.Once youve downloaded the ISO file, youll

need to burn it to a CD, which you can dousing Windows integrated disc burner or thethird-party utility of your choice. To install theoperating system, youll need to boot fromthe CD, so enter the servers BIOS and move

NOT EVERY SMALL business needs a server,but for those who do its easy to stick with thefamiliarity of Windows and buy a Micrososerver operating system. This isnt necessarilya bad thing; weve coveredWindows Server2012 Essentials in depth (see Shopper 301 and302), and it has many advantages beyond thefamiliarity of its Windows interface. However,its not necessarily as simple to configure asyoud expect, and it may not be the mostcost-eective choice for a small firm.Fortunately, theres a credible alternative

in the various Linux variants available. Severalof these are free, but cost savings are onlypart of the araction of Linux. It was wrienfrom the outset as a multi-user, multitaskingoperating system. Many of its componentpackages can be updated individually withoutaecting other components or requiring aserver reboot, while many of its proponentsargue that its more secure and is less oenthe target of malware aacks thanWindows.Linux generally has lower system requirementsthan an equivalentWindows system, too,which in turn could enable you to makesavings by buying less-powerful hardware.This month, were looking at installing

and configuring a computer using UbuntuServer, which is a server-specific version ofthe popular Linux distribution. There arealternative distributions worth considering,such as the Community Enterprise OperatingSystem (CentOS), which is compiled from thesame source code as Red Hat EnterpriseLinux, and Novells SUSE distribution, whichhas an excellent reputation for stabilityand ease of use. However, we alreadycover Ubuntu regularly in our Linux Expertsection, and its widespread popularityand refined soware ecosystem make itone of the best choices around if yourerelatively new to Linux.

When it comes to servers, prioritise stability over the latest features

We wouldn't bother with the automatic keyboard detection; it's easy to do it manually

http://www.ubuntu.com/download/server

BUSINESS EXPERT

156 MARCH 2014 | COMPUTER SHOPPER | ISSUE 313

itself as a single volume. We recommendusing logical volume management (LVM). Thisis a way to configure a servers disk space thatsabstracted from the underlying physical diskconfiguration, and should make it easier toadd and reconfigure storage devices in future.Choose Guided - use entire disk and set

up LVM and press Enter. On the next twoscreens, confirm the target disk and agree towrite the changes to it. Opt to use the wholevolume group for guided partitioning: selectContinue on the next screen, hit Enter and,when prompted, write the changes to the disk.The installation will now continue. Unless youknow that you use an HTTP proxy, leave thefield blank when prompted and select Continue.Choose to install security updates automatically.The next screen allows you to choose

additional soware packages to add functions

beyond those of a basic file server. Those youchoose will depend on the role you plan foryour server. Next month, well be configuringa DNS server and Samba file server, so selectthose using the cursor keys and spacebar, andtab over to select Continue. Agree to install theGRUB boot loader and wait for the installationto complete, rebooting when prompted.

COMMAND AND CONQUER

When Ubuntu Server first starts, youll noticethat it doesnt load a graphical user interface(GUI). Instead, youll see a simple text promptfor entering commands, known in Linux as thecommand shell or command line. There are goodreasons for the absence of a GUI; installing oneadds complexity. It places greater demand onthe system resources and introduces moreavenues for anyone trying to hack the server.

Many authorities recommend that you dontinstall a GUI. However, without one, the serverwill be harder to configure. Well be installinga desktop interface, but well show you how tounload it to keep it from hogging resources.Log on to the server by entering the

username created during the install, followedby the password. You should see textinformation summarising the system, with asummary that tells you how many packageshave updates available, and how many ofthese are security-related. Its a good idea toupdate the server immediately. Type sudoapt-get update (without quotes) and pressEnter, and Ubuntus command-line packagemanager will update its list of the latestsoware packages. Next, enter sudo apt-getdist-upgrade and the system will intelligentlyapply updated soware to the system.

Configuring RAID: combining disksinto a volume with redundant storageA RAID array combines two ormorehard disks to create a single volume,oen with redundant storage toensure your data still exists even ifone disk fails. If youre not installingUbuntu Server on a computer with ahardware RAID controller, it may betempting to use two disks and themotherboards onboard RAID 1 optionto create amirrored array. However, ifthe motherboard fails, youmight needto find an identical one to recover thearray data, so well take you throughLinuxs soware RAID capabilities.Follow the installation until youre

prompted to partition the disks, thenchooseManual, select the first harddisk and agree to create the newpartition table on it. Select FREESPACE and choose Automatically partition the free space. Whenthe installer displays the results of partitioning, select the / partition(likely to be #1) and press Enter, scroll down to Bootable flag, pressEnter to switch it on, then select Done seing up the partition.Select the second disk, and repeat the steps above.Scroll up, select Configure soware RAID and agree to write the

changes and configure RAID. Select CreateMD device and choose

RAID 1. If you want to boot from anyother type of RAID array, youll haveto install an alternative boot loader.Next, hit Enter to confirm two

active devices. Press Enter again toconfirm zero spare devices, then usethe space bar to select two activedevices for the array. These should be/dev/sda1 and /dev/sdb1; thismeansthe first partition on the first disk(sda1) and the first partition on thesecond disk (sdb1). Agree to writethe changes, then repeat these stepswith the remaining partitions (/dev/sda5 and /dev/sdb5) and pick Finish.Scroll down to RAID 1 device #0

and select partition #1 underneath it.On the next screen, select Use as andchoose Ext4 journaling file system.

Underneath, selectMount point and choose / (the root file system).Then select Done seing up the partition. In the main partitioningmenu, scroll down to RAID 1 device #1 and select partition #1, thenon the next screen select Use as and choose swap area. Select Doneseing up the partition. Scroll down to Finish partitioning and writechanges to disk, choose not to boot if the RAID becomes degraded,and write the changes to disk. Your installation should now continue.

Its a lile complicated, but when youve finished seing up theRAID array, it should look similar to this

We recommend using Guided partitioning and seing up LVM Choose packages to suit the role this server will play; well use DNS and Samba

BUSINESS EXPERT

157ISSUE 313 | COMPUTER SHOPPER | MARCH 2014

Apt-get is the name of the tool youreusing. Typing sudo means youre using it asthe Root SuperUser, which allows you to runcommands that are usually restricted in orderto help keep your system secure. For reasonsof security, you have to enter your passwordevery time you issue a sudo command.Theres usually no need to reboot the

server aer applying updates in fact, youshould barely ever have to but in this case itis necessary. Once the updates have finished,type sudo shutdown -r 0 to force a restart,or replace 0 with a number of minutes toschedule a delay first. Shutdown is a usefulcommand to know in Linux. Changing -rto -h will make the server halt rather thanrestart. Another useful command is exitfollowed by Enter; this will log out your useraccount without shuing down the server. Analternative way of restarting the system is totype sudo reboot, which does the same thingas the sudo shutdown -r 0 command.

Aer restarting, we can install the Ubuntudesktop. Log back on and type sudo apt-getinstall ubuntu-desktop. Linux package namesare case-sensitive, and in this context Ubuntushould not be capitalised. The desktop packagesamount to roughly 450MB, so theyll take awhile to download, depending on the speed of

your internet connection. Once the installationis complete, restart the server using theshutdown command. Youll now boot into thesame Ubuntu interface used by the desktopversion. Enter your password to log on.

UNITY COMMUNITY

If youre not familiar with the Ubuntu Unitydesktop, its worth taking a minute to have alook around. The top panel contains variousshortcuts, with the power icon at the rightlaunching a menu with links to useful toolssuch as a soware updater and the systemseings menu. Move the mouse to the tople to reveal global navigation options. Whenan open application has the focus, this areawill usually include application-specific menus.At the le-hand side of the screen is the

Launcher, which is similar to the taskbar inWindows. Clicking an icon will start that app,while you can remove an icon from thelauncher by right-clicking it and selecting

Unlock from Launcher. To find any installedprogram, click the Dash home icon at the topand search for it by name, much as you wouldin theWindows 8 Start screen. Try this byclicking the icon, typing terminal and eitherhiing Enter or clicking on the Terminal iconin the results. This should open a command

shell, providing a windowed version of thecommand-line environment we had beforeinstalling the GUI.As we explained, the Ubuntu desktop

makes administering the computer far easierat the cost of additional system overheads. Asa compromise, well change the configurationso that the GUI loads only when we need it.There are a couple of ways to do this, butquickest is to create an override file. Inside theTerminal session, type echo "manual" | sudotee /etc/init/lightdm.override. The wordmanual will be output by the terminal if allsgone well. Tee is the name of the programwere using to create the file, and manual isthe command were puing into it. Type sudoreboot to restart the system. You can alsoreboot by selecting Shut Down from the UnityGUIs power icon menu and choosing Restart.You should find that the system reboots

back into the command shell as it did whenfirst installed. From here, you can start thedesktop interface when you need it withstartx. Dont use sudo for this unless youwant the entire desktop environment to runas root; this is not a good idea. To stop theGUI again, simply choose Log Out from thepower icon menu and click Log Out whenprompted, and you should return to thecommand shell. Youll still be logged on tothe command session; if you plan to leavethe computer unaended, remember to typeexit and hit Enter.You should now have a server with the

latest soware updates, a GUI that you canswitch on and o as needed, and knowledgeof how to shut down, restart or update theserver from the command shell. Next month,well show you how to configure it.

NEXT MONTH

GET SERVING!

We explain how to configure your new

server to provide essential services to

other computers on the network.

Before updating Ubuntu, tell it to discover the most recent soware packages Create an override file to stop the GUI loading by default

Finding an application is as simple as searching for it

Ubuntu Server installation guide

hp://tinyurl.com/UbuntuInstallGuide

Ubuntu Server guide

hp://tinyurl.com/UbuntuServerGuide

Further information

For a server environment, we recommend opting forstability and support over the latest features

http://tinyurl.com/UbuntuInstallGuidehttp://tinyurl.com/UbuntuServerGuide

LINUX EXPERT

158 MARCH 2014 | COMPUTER SHOPPER | ISSUE 313

Making the mostof your broadbandThis month, Nigel Whitfield delves deeper into the configuration of the

Asterisk internet telephony system to help enhance your broadband use

LASTMONTH, WE showed you how theaddition of an alternative firmware can turn aTP Link TL-WDR3600 router from a humblepiece of network kit into a flexible Linux-powered appliance, on which you can installand configure lots of extra applications. Incase you missed it, download last monthsLinux Expert from www.shopperdownload.co.uk/313/linuxexpert312.pdf.This month were going to look a lile

more at how you can use the Asterisk internettelephony system. At its simplest, Asterisklets you set up multiple user accounts usingthe SIP internet telephony protocol. This letsyou use real SIP phones, PC soware andsmartphone clients to make calls internally, aswell as with other people with a SIP telephonysystem. By adding a SIP service, you can alsomake and receive phone calls to real phones,geing a proper incoming phone number.Well even show you how you can answer thisreal number anywhere in the world.While some of the instructions are specific

to the version of Asterisk installed on therouter, the config files will be much the sameon any Linux installation, so you should beable to follow our examples quite easily evenif youre running Linux on, say, a spare PCtucked away in a corner, rather than on arouter. Indeed, you may want to experimenton that first anyway.

BEFOREWE GO ON

If you want to make the most of Asterisk,there are a few things to bear in mind; theyrenot prerequisites, but they can make life a lotsimpler, especially if youre planning on usinga VoIP system as your main phone.

First, although its not absolutelynecessary, try to get a fixed IP address fromyour internet provider, as it may prove to beadvantageous. You dont have to have one touse SIP, which is the standard Voice over IP(VoIP) protocol used by Asterisk, but if youdo, it will be much easier to connect to your

system remotely when youre out and about.That means, for example, that if you can get adata connection abroad, you can make andreceive calls through your home Asterisk PBX.With the data bundles available in Europenow, it can actually be cheaper to make callsthat way than to pay roaming charges.If youre simply elsewhere in the UK, you canbe available on your usual number, so yourmobile can be just for people who really needit. If you dont have a fixed IP address youllneed to set up a dynamic DNS system, whichassigns a web address to your home network.Your router then updates the web addresswith its current IP address. We like www.noip.com, which is supported by most routers.Youll also need SIP phones to make and

receive calls. Real ones, which look like aregular telephone but plug into your homenetwork, cost from 35 upwards. However,you can use a soware client instead. ManyAndroid devices have SIP built in or you canuse apps, like 3CXPhone for Android and iOS.

Seing up a so phone to work with Asterisk

is very simple

Manually edit the sip_peers file if you find you

cant make or receive calls successfully

Like other VoIP services, with Sipgate you can choose a city in which youd like a phone number

http://www.shopperdownload.co.uk/313/linuxexpert312.pdfhttp://www.shopperdownload.co.uk/313/linuxexpert312.pdfhttp://www.noip.comhttp://www.noip.com

LINUX EXPERT

159ISSUE 313 | COMPUTER SHOPPER | MARCH 2014

CONFIGURING ASTERISK

Asterisk is configured using text files; whenyou enter details in the web interface on therouter, youre really just updating these, andthe same is true of the other front-ends thatare available for it. Well look at the text filesin more detail another time (you can do someprey clever things with them), but to startwith, lets walk though the basic setup.If youve not installed the packages on

your router yet, go to the Soware tab,update the list of packages, and install firstasterisk18, then luci-app-pbx, which providesthe OpenWRT configuration interface, whichwill appear on a new Services tab.If you want to see whats being changed,

connect to the router via SSH and look at thefiles in the /etc/asterisk directory. As wementioned before, youll find plenty ofinformation to help understand these atwww.asteriskdocs.org.Start by clicking on the SIP Accounts tab

in the router interface. This will let you add ina SIP provider if you want to have a realtelephone number to make and receive callson. If you dont see a blank account form,click the Add buon. Fill in the username andpassword from your SIP provider VoIP Talk(www.voiptalk.org) and Sipgate (www.sipgate.co.uk) are both good choices and ensure the

options for both incoming and outgoing callsare set to Yes. For some providers, you maybe given additional seings, such as Realm,Proxy and perhaps a port number (the defaultis 5060). If you need to add any of these, clickthe Additional Field drop-down menu, selectthe right one, and click Add.When you have filled in all the information,

click the Save and Apply buon. This data will

be stored in the sip_peers.conf file in theconfig directory. However, if youre using thestandard OpenWRT installation, you may findthat Asterisk is failing to register with the SIPprovider correctly (see Solving registrationproblems, page 160, to find out how to fix it).Next, you can create accounts for

telephones, whether physical or smartphones,which can make and receive internet-only SIPcalls, or allow you to make calls within yourown home between devices. With a bit ofconfiguration, you can also enable theaccounts to make and receive real phonecalls using your SIP service.Go to the User Accounts tab in seings,

and fill in the form for the first extension. TheFull Name will be sent with the call anddisplayed on SIP phones. The username iswhat most people think of as the phonenumber, which other SIP users dial. You canuse a name such as nwMobile as we have or,if you want to dial between the phones onyour system, its more sensible to give themnumeric names, which can be dialled easily ifyou use a phone with a standard keypad.The seings here are on OpenWRT andstored in /etc/asterisk/sip_users.conf.Pick a password, allow the phone to take

incoming and make outgoing calls, leingthem access your SIP service, and youre moreor less ready. Find a SIP client for a phone orPC (in the example were using Blink for OS X)and log in to an account using the details youhave just created, with the server set to yourinternet address or dynamic DNS name.

Picking a SIP accountTo call other people, you need a SIP service. This provides the link between your VoIPdevices and the public telephone network; without it, you can only call other users on yourown or a linked Asterisk system, or a direct SIP address. A provider will allocate you anumber oen with a choice of city which ordinary callers can use to reach you, andwhich will appear as your caller ID when you dial from your VoIP phone to an ordinarynumber. Check the terms, though, as some charge amonthly fee per number, whileothers dont. Some provide special dialling codes to call customers on other VoIPnetworks free, or have beer rates to certain countries. Its even possible to port existingBT numbers to a SIP service, so you could ditch a second phone line, for example, andmove the number to a SIP provider via Asterisk.In our example here, were using Sipgate (www.sipgate.co.uk), and picking a Belfast

number. Weve done this because friends in the Republic of Ireland can call the northcheaper than calling the rest of the UK, by swapping the 028 UK dialling code for the 048Irish one, and avoidingmaking an international call. When you receive your confirmationemail, click on Seings to see the data youll need to link Asterisk to your account.

For Sipgate, you just need to enter your username, password and hostname

Dont forget tomake sure that the appropriate ports are opened on your firewall to allow VoIP

Although its notabsolutely necessary, tryto get a fixed IP addressfrom your internet

provider, as it may proveto be advantageous

http://www.asteriskdocs.orghttp://www.voiptalk.orghttp://www.sipgate.co.ukhttp://www.sipgate.co.ukhttp://www.sipgate.co.uk

LINUX EXPERT

160 MARCH 2014 | COMPUTER SHOPPER | ISSUE 313

NEXT MONTH

RUN A PRINT SERVER

ONYOUR ROUTER

We show you how to use an OpenWRTprint server to share a USB printer withany computer on your network.

The next step is to test everything; mostVoIP services have a test number that you candial to check everything is set up. On Sipgate,its 10000; enter that into your test client and,if alls well, youll hear a message telling youthings are working OK.Now, try dialling the number youve been

allocated from a dierent phone. This is where

things may be a lile more fiddly, as its quitecommon for firewalls and NAT to play havocwith SIP (one reason why Skype becamepopular), so if your Asterisk router is behindanother router, you will need to ensure thatconnections to port 5060 are passed to yourSIP router, and also the UDP ports requiredfor the actual voice calls, which by default are

19850 to 19900 in the OpenWRT package.But if all is well, you should receive incomingcalls on the VoIP phone youve set up.You can now set up more options on the

Call Routing tab, such as specifying that certainnumbers always go via a specific SIP provider,using paerns to match. Thats particularlyimportant if only some of your SIP providershave a 999 service, so you can ensure thatwhichever phone is used, a 999 call will alwaysbe routed to someone who can handle it. Youcan also make dierent extensions ring forcalls on dierent SIP accounts, or use themfor outgoing calls. Just remember that if youchange seings in the web interface, you willprobably need to re-edit the sip_registrationsand sip_peers files, too, so its a good idea tocopy these files aer changing them.

Solving registration problemsA common problem youmay have withAsterisk on OpenWRT is that the systemwont register with your SIP provider, andyou cant receive any incoming calls.Thats usually due to a bug in one of thelibraries in certain versions of the soware,including the current release.Theres a fairly straightforward

workaround for this; do it when you haveadded the local user accounts, to avoidthe seings being overwrien by theLuci configuration tool. Edit the sip_peers.conf file with your favourite text editor.Therell be a section with a name basedon your SIP account, such as:

[peer-1939369_sipgate_co_uk]

For Sipgate, change the line that says:

type = peer

to:

type = friend

Alter the qualify seing to yes and thenadd a line that says:

dtmfmode = rfc2833

Next, edit sip_registrations.conf, which iswhere the info needed for outgoing calls viathe VoIP provider goes. The entry will looksomething like this:

register => 1939369:PASSWORD@peer-

1939369_sipgate_co_uk

where 1939369 is your Sipgate number. Youneed the IP address of the SIP server; in thecase of Sipgate, its 217.10.79.23, but youcant just swap that in, as some providerswont register you if you just use the IPaddress. Change the line to look like this:

register => 1939369@sipgate.

co.uk:PASSWORD@217.10.79.23

replacing the IP address and password withthe correct ones, and your own number. Butremember: do this aer youve set up otheroptions in the Luci interface.

The Seings screen on Sipgate will show whether your PBX has connected

correctly, as well as other essential seings

The PBX tab in OpenWRT will show you the current status of Asterisk

You can stop and restart Asterisk from the System/Startup tab aer

editing the config files

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PARTING SHOTS

162 MARCH 2014 | COMPUTER SHOPPER | ISSUE 313

ZygoteZygote is pulling his hair out over MafiaLeaks and the Swiss cloud network. Still, there

is a cure for baldness on the horizon, although it does seem to require a pound of flesh

used them to simulate fans

playing his rubbish songs 24

hours a day. This generated a

spectacular return of 33 dollars

for every dollar he invested. The

fact that his music aracted a

torrent of abuse and universally

unfavourable reviews seems only

to have helped perpetuate his

ride to the top of the charts a

lesson Sir Cli learned ages ago.

FOGGY LOGIC

The Chinese government is

having a problem keeping tabs

on its population because its

mass surveillance cameras are

playing up. The computer-

controlled spy network works

exactly as designed, but the

cameras oen cant see beyond

10 metres, and now winter is here

they are sometimes down to a

range of three metres. This is not

very useful when trying to watch

over vast areas of urban sprawl.

The reason the system is

failing is down to smuy smog.

Pollutant air particles are

generated by the increasing

levels of coal burned in Chinese

power stations, factories and

homes, and the pollution is so

bad that airborne particles block

visibility. Even infrared images

are next to useless. Two teams of

boffins have been given significant

government funds, not to come

up with a cure for the smog, but

to develop soware that will

filter out all the gunge from the

camera images. The South China

Morning Post reports that aer

recent terrorist alerts, the

engineers need to completely

rewrite algorithms in

mathematical models, do lots

of computer simulation and

extensive field tests.

Zygote reminds them that

even if the cameras fail to spot

terrorists intent on mischief,

chances are the bad guys wont

be able to see their targets, either.

WHOLE NEW BALD GAME

At last, the announcement weve

all been waiting for: researchers

at Durham University have

found a way to cure baldness.

Computer scientists, geneticists

and dermatologists have proved

that cells taken from a specific

area of the body can be grown in

a three-dimensional culture and

used to create a new head of hair.

We show that human dermal

papilla cells, when grown as

spheroids, are capable of

inducing de novo hair follicles in

human cranial skin, they say. If

thats too jargon-heavy for you,

allow Zygote to translate it into

plain English: We can cure

baldness using cells taken from

nipples and foreskins.

Zygote has always been

puzzled by the oensive terms

used for gentlemen with receding

hairlines who resort to comb-

overs, transplants and wigs, but

now understands that calling

them a tit or a dickhead is merely

a statement of scientific fact.

SWISS FORTRESS

Zygote is intrigued to learn

that Switzerland is extending its

long tradition of rigorous data

protection. The government-

owned telecommunications

provider Swisscom announced

it is seing up a national

cloud-hosting system that will

warehouse 250 petabytes of data

and adhere to the strongest

privacy laws in the world.

The Swiss cloud network will

be completely independent from

outside interests and act as a

haven from the prying eyes of

foreign secret services and other

sinister forces, leaving the field

clear for traditional users such

as cuckoo clock manufacturers,

money launderers and the

custodians of mislaid Nazi loot.

AIR APPARENT

Hot on the heels of Apples

announcement that its new

datacentre will be solar-powered,

Microso has bought the total

output of a brand-new wind

farm. The 55 giant turbines at the

Keechi Wind Project in Texas will

generate 110 megawas, and is

already plugged into the electric

grid that feeds Microsos San

Antonio mission control. This

proves that while the sun shines

out of Apples assets,Microso

continues to run on hot air.

BLOW ME DOWN

Whistleblowing websites such as

Wikileaks use anonymous data-

sharing systems with no central

server to be tracked down by

the enemies of free speech.

The obvious reason for this is

to protect the identities of

contributors. This is especially

relevant at a new site dedicated

to blowing the whistle on the

Mafia. MafiaLeaks.orgs moo is

simply, If you know something,

say something. The site features

a section optimistically labelled

We are hiring, which invites

the heroic to join us. However,

Zygote questions the wisdom in

linking this anonymous website

to Facebook, where anyone

hiing the Like buon can be

instantly identified.

Zygote also notes that

theMafiaLeaks.org key image

shows a young brunee looking

surprisingly relaxed, seeing as she

is about to be shot in the head

by a Mafia gangster. Its taking

Facebook unfriending a bit too far.

SOUND AS A POUND

Spotify is an excellent online

showcase where recording artists

get paid a very small royalty every

time someone clicks a buon to

hear one of their music tracks.

The more plays they get, the

higher the royalty payment. With

millions of people using the Spotify

service, some chart-toppers can

do very well. Recently, an unknown

artist by the name of JohnMatrix

shot to virtual stardom. The new

music sensation has now been

revealed as Peter Fillmore, an

Australian soware security

engineer who has never wrien

a song, sung a note or played an

instrument in his life.

Fillmore hacked into the

charts with catchy lile tunes

such as Ive Only Known You Five

Minutes And I Want You Dead,

from his fake album Kim Jong

Christmas, and hoovered up a

million hits in less than a month.

He harnessed three virtual

servers linked to Amazon, and

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