The Test Bed: Networking Archives

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All access points are one to Extricom mobile clients

It is rare for someone in the Wifi industry to talk honestly about the snags as well as the advantages of the technology. They will boast of the range of the latest 11n links but omit to point out that doubling the range quadruples the area of contention (and that is not counting interference between networks in the vertical plane - ie on different floors).

They will tell you that the speed is 300Mbits/sec without pointing out that much of that goes on network overheads, and that the top speed anyway depends on bonding two channels which you are not supposed to do if there are other networks in range. In cities, of course, there are always networks in range so the only way you can get top speed is by playing road hog.

"People don't notice the problems because Wifi, particularly 11n, is so resilient. All they see is a drop in performance," said Phil Belanger, who worked on the 11n spec.

Belanger can talk about these things because his company, Extricom, offers a technology that addresses problems associated with Wifi networks that use multiple access points. There is apparently no standard way of setting these up - the Wifi specs do not cover it. But the usual way is to site access points to give minimal overlap in their coverage and ensure that neighbouring ones use a different channel.

There are some problems with this. The signal strength is erratic and tails off with distance, and 11n performance can be hit badly if the system has to cope with legacy 11a/b/c devices, which will inevitably be present on large public or campus sites. Also there can be an appreciable hiatus when a user crosses from one access-point area to another.

Extricom's approach is to connect all access points to a smart switch and present them to the roaming clients as a single device. The switch can decide, packet by packet, which access point to draw the data from; this can also help it decide which access point to use to send data. There is no channel contention because all access points use the same channel. To use the jargon: Extricom separates the MAC and PHY layers, putting the former into the switch.

There are no boundary problems within the network area because there are no boundaries. Moreover, using a system called Channel Blanketing, the overheads of coping with multiple protocols can be avoided by assigning a different channel to each of the different WiFi flavours: one for 11b/g at 2.4GHz, one for 11n at 2.4GHz, one for 11a at 5GHz and another at 11n at 5GHz (click in image to see larger version).

The latest development, announced at the Wireless and Mobile 09 show in London yesterday, is a cascading switch that allows you to double up two Extricom networks, each with 16 access points. This can be either to double the coverage area, or to provide resilience in places like hospitals where the network cannot be allowed to go down.

If Extricom has to go through all this trouble to avoid problems campus sites where access points can be carefully sited and managed, there must surely be questions about how 11n will scale up in crowded cities and blocks of flats where the siting and use of Wifi equipment is chaotic and people are being encouraged to throw HD video around.

But at least we are finally going to get a firm spec. Belanger tells me the one for 11n will be finalised this September, and that all current Draft 11n products should be compatible with it.

Posted by Clive Akass on May 20, 2009 | Permalink | Comments (0)

Microsoft makes your PC talk in its sleep

Looking a little out of place among some of the more exotic and photogenic exhibits at Microsoft Research's 'Innovation Day' in Cambridge today was a distinctly DIY-looking collection of circuit boards and wires called Somniloquy. Named after the medical term for talking in your sleep, this interesting project could eventually be another important piece of the power management jigsaw.

Microsoft researcher James Scott explained that Somniloquy - which is really an external network adapter with added intelligence - allows your PC to go to sleep while still presenting an 'active' state to networked applications. At the moment, if you put your PC into S3 or hybrid sleep mode, the network card is normally turned off and so your PC can't be reached over the network.

With Somniloquy, a small amount of power (about 4-5 watts in the prototype we saw) is drawn via the USB bus to maintain network connectivity. Traffic is monitored and buffered, and if packets are received - for example, a remote desktop connection - that require the PC to be turned on, it's instantly woken from the sleep state.

It's very much a work in progress. According to Scott, work started in 2007 in collaboration with researchers at the University of California, San Diego, and a technical paper has just been published. The hardware is designed around a commercially-available GumStix ARM-powered computer-on-a-module costing around $200

Somniloquy performs its magic by buffering network traffic and data on an SD card - in effect, it masquerades as the PC when the PC goes tro sleep. Many simple tasks can be achieved by bypassing the PC's processor and using Somniloquy's low-power CPU instead, saving even more energy. For example, it could download files to the SD card and wake up the PC to transfer data when it's full, then put the PC to sleep again until another batch of data is ready.

It will be fascinating to see if this idea makes it out of the research labs: Wake-on-LAN is much less flexible and is a nightmare to implement. Somiloquy could certainly help cure your PC's sleepless nights.

Posted by Kelvyn Taylor on May 6, 2009 | Permalink | Comments (0)

XBMC and HD HomeRun

In the June 2009 issue of PCW, I look at home entertainment networks, and one of the devices that's touched on is the HD HomeRun from Silicon Dust, distributed in the UK by Nectar. The full article will be online later in the month, but for now you can download a diagram here, which shows the real-world network I have set up at home.

One of the key parts of that is my Macbook Pro, which has XBMC installed on it; this allows it to play back just about any of the media on the network, including Freeview recordings stored on the PVR, or on the network, as well as DivX and other video. And, as I mentioned in the article, it can use the HD HomeRun to watch live TV, unfortunately, I didn't have enough space to go into the details of setting it up and the documentation for HD HomeRun is a little opaque, to put it kindly.

Essentially, HomeRun has two Freeview tuners, and makes streams from those available over the network via its Ethernet port; ignore the HD in the name - it won't be compatible with the DVB-T2 standard that's going to be used in the UK.

If you want to use XBMC to watch streams from the HomeRun, here's what you have to do. First, you need a Windows PC to run the setup program (or to put up with lots more hassle, which I'll explain later). You'll also have to install XBMC on that PC, even if you don't intend to use it.

Run the HD HomeRun Setup program, and for at least one of the tuners, select the application as XBMC. I strongly recommend getting the latest version from the Silicon Dust website - it adds support for the 'Logical Channel Numbers' used on Freeview, and will automatically update the HomeRun's firmware.

Tell the setup program to scan for channels, and when it's finished, you will find a folder called 'HDHomeRun XBMC TV' in your Documents and Settings folder. Inside this will be lots of files with the extension .strm, which is what XBMC uses to select a channel on the tuner; the file for Film 4 is called '15 Film4.strm' for instance - the 15 is the Freeview channel number.

Now, in XBMC, you can select Videos, then Add source, browse to the folder containing the strm files, and click OK. Give it a name if you want something other than the folder name, and it'll appear in your video source list. Click that, and you'll see the .strm files, and clicking on one of them will connect to the tuner and stream live TV.

If you want to do this on a Mac, you'll need the very latest version of XBMC, as some recent ones had broken HomeRun support, or Plex which is based on the same code. Either share the folder with the strm files from your PC, or copy them to somewhere on the Mac, and add the folder as a video source as I described in the previous paragraph.

You can also right click on a .strm file and choose to add it to the Library in XMBC, giving it a different name; the first time you'll have to add a genre - Live TV, say. Add your favourite channels this way, and then you can access them in Library mode, via the genre you gave them.

And if you don't have a PC to run the setup program and generate all those .strm files? Well, you can do it manually. If you don't mind a lot of hassle. This is what you'll see if you look in the file for Film4, for my HomeRun unit, on the Crystal Palace transmitter:

hdhomerun://12105ED3/tuner0?channel=t8qam16:538000000&program=27136

The first set of numbers is the id of the HomeRun - on a label on the bottom, or visible in the Mac utility. Tuner0 is the first tuner, t8qam16 is the mode (some muxes use QAM64 mode), and 538000000 is the centre frequency, in Hz, of UHF channel 29, which carries the mux (useful table here) while 27136 is the service ID for the Film4 stream (find other SIDs here). The HD Homerun Config GUI works on the Mac, and you can see most of these parameters using the scan buttons, too, but you'll still need to convert the channel numbers to their correct frequencies.

So, armed with that, you could roll your own .strm files, or create hdhomerun:// references to put straight into XBMC. Personally, I think it's less painful to have a PC create them for you.

It's not exactly plug and play, but it is a great little gadget that can turn almost any laptop into a portable TV for you.

Posted by Nigel Whitfield on May 1, 2009 | Permalink | Comments (2)

HDHomeRun comes to the UK

Fancy a networked dual-tuner Freeview tuner box? Nectar Electronics has just launched the HDHomeRun in the UK. It's apparently been selling in the US for a couple of years, using the ATSC digital TV standard, but this UK model is a DVB-T box.

A cabled connection to your router is required, and it will work on any PC running Vista Media Center, Media Center 2005 or other 3rd party media software such as SageTV, BeyondTV, GBPVR, Media Portal or Total Media.

The HDHomeRun box costs £179 (inc. Vat and delivery), but Nectar is knocking £20 off for orders made before 31st March 2009,

Posted by Kelvyn Taylor on March 17, 2009 | Permalink | Comments (0)

My Dutch Wifi hell

Last week's trip to Amsterdam for Panasonic's European convention was interesting - and not just for the products. As well as online services - Viera Cast is built into just about every Panasonic product short of fridges and washing machines - there were demonstrations of full HD 3D television, plus a whole new range of products for Freesat, including some Blu-ray recorders that I hope we'll be able to review in the coming months.

The other interesting thing came from some experimenting with Wfi and VoIP. Since it was a business trip, I took my laptop and naturally my mobile phone. And since it would have been rude to visit Amsterdam just for the one night of the Panasonic press trip, I went a couple of days earlier and stayed in a small hotel in the city centre.

Free Wifi in hotel rooms has various advantages; besides the obvious one of being able to do your work, you can also tune in to the BBC's radio streams of course. But something I was keen to try out was avoiding roaming charges; even after the EU caps, they're still frankly pretty expensive.

Some time ago, regular readers of PCW may remember, I wrote about using a Nokia N95 with the Asterisk PBX software (you can find the article here). Quite a few of the Nokia phones have support for the open SIP standard, which means that as well as using them with software like Asterisk, you can use them with a calling service such as VOIPtalk, so if there's free Wifi in your hotel, or conference centre, then in theory you can make and receive calls much more cheaply.

And it worked a treat - mostly. I'll come to the caveat later. But with calls to UK or Netherlands landlines at 1.4 pence per minute, and to UK mobiles at 11.9p, it beats 38 pence per minute to call home. There's no setup fee, so you can just top up with £5, and get an 056 number for people to call you on - it'll cost them the same as a UK local call, and you'll also avoid the 19 pence per minute for incoming calls.

On a Nokia phone that supports SIP, it's incredibly easy. Once you've set the phone up, you can sign in to the SIP service when you're connected to a Wifi network, then find a number in your phone book and instead of pressing the green button, just call up the menu and choose 'Internet call' instead. Quality was, largely, excellent, with none of the annoying echo that I've sometimes had when roaming, or on poor VoIP networks. Over the course of my stay, I tried three different hotel Wifi networks, and none blocked SIP calls - so for the sake of a £5 topup, it's worth investigating, if you have a compatible phone.

What of the Wifi hell mentioned in the headline? Well, all the places I stayed or visited had Wifi, and advertised it as free. But in the first hotel, there were times I felt like throwing the laptop at the wall. It was impossible to maintain a connection for long, and to make a Wifi call I had to walk down two flights of impossibly steep Dutch stairs to the lounge, as that was the only place to get a good signal. The laptop would keep reporting that it was no longer connected to the internet, unless I left it in the corner of my room by the bathroom door - hardly convenient for work.

The hotel assured me their wireless network was set up by a professional, four years ago. And the four years is probably the important part. Back then, wireless wasn't quite as widespread as it is now. Today, it's very different - as I found out when I fired up iStumbler, the Mac equivalent of Netstumbler. While the network was indeed working fine down in the lounge, in my hotel room it was an entirely different matter. I could certainly see both the hotel's basestations - amongst the 22 wireless networks visible in my hotel room.

Of those, a dozen were overlapping either completely or partly with the wireless channel used by my hotel; even if the hotel changed the channel of their network, the smallest number of overlapping networks they could have achieved would have been eight, so it's likely performance would still have been pretty dismal.

At the hotel where I stayed for the Panasonic convention, there was free Wifi too - though they recommended you used the wired connection, which they charged you for. It turned out the wired one simply wouldn't work, redirecting everything to a random holding page that never showed up.

But the Wifi wasn't always much better, at least in the rooms, probably down to the modern steel construction of the building. And, as all the assembled hacks from the UK and elsewhere checked into their rooms and signed on, speed plummeted.

Making VoIP calls worked - but only if I went to the lobby or stood in the corridor outside my room - neither of which would be ideal for a late night call to the loved ones.

So, I can say that VoIP on a Nokia phone is a geat idea for avoiding roaming charges, as long as you can get a decent Wifi connection. But perhaps hotel Wifi has had its day, especially in densely populated cities like Amsterdam.

Posted by Nigel Whitfield on March 3, 2009 | Permalink | Comments (1)

Cebit08’s new Homeplug devices

There are dozens of companies showing off Ethernet-over-mains devices at Cebit08, but here are the best bits:

Intellon’s prototype "homeplug in a wall socket" is an extremely neat design which can be used instead of regular wall sockets to network a house.

An Intellon spokesperson, who didn’t want to be named, said that Wifi dead-spots and poor Wifi performance for video meant there was a demand for new homes to use Homeplug. The company is already in talks with an unnamed house builder in the UK to get them into new builds.

Sadly, you can’t retrofit your house with these cool wall sockets unless you’re a certified electrician - otherwise you’ll invalidate your home insurance.

The Intellon spokesperson rubbished the idea that powerline technology transmits wirelessly from floor to floor. Due to the strict power emissions the EU puts on all consumer electronics, Homeplugs can only talk to each other wirelessly if they are up to 3cm apart, but no more.

Convergence is the Homeplug buzzword of choice this year, since a raft of audio and video streamers, as well as set top boxes, are getting Homeplug built into them. More exciting than that was Gigafast’s Homeplug that hosts a USB port. It lets a computer in another room use the USB port as if it were built into the machine. Here it is plugged into a USB rocket launcher:

Gigafast’s Homeplug-enabled security camera could really kick Wifi cameras into touch, especially when combined with its video decoding box the other end, plugged directly into a PC.

For now, however, none of Gigafast's products will be on sale in the UK.

Nearly every manufacturer is showing off a “Y-cable”, which combines a power supply and Homeplug into one box. An Ethernet and a power cable comes out of the transformer, so a wide range of existing devices don’t have to be modified to use Homeplug. The only downside to this technology is the high cost of a Y-cable and that they can only provide up to 30W power output, since if you go higher the signal-to-noise ratio becomes too low for Homeplug to operate.

Posted by Emil Larsen on March 6, 2008 | Permalink | Comments (1)

One powerline to rule them all

Devolo, the largest Homeplug seller with 2.5million out of the total 12million sold, will give the Homeplug Alliance a big boost in the coming months by using Intellon chips only and dropping Intellon's competitor, DS2, altogether.

Netgear has also backtracked from using DS2-only chips in its high end consumer range by releasing a 200mbit/sec Homeplug AV device called the XAV101.

Intellon's dominance could make buying powerline brands that use Panasonic or DS2 chips a gamble, since each is incompatible with the next.

Devolo is demonstrating the next speed hike, 400mbit/sec Homeplug prototypes, at Cebit08. In reality, file transfer rates (TCP) of 180mbit/sec are achieved in good conditions. The plugs use a low frequency for the first 100mbit/sec (this frequency is compatible with older AV Homeplugs) and add a new, higher frequency for the remaining 80mbit/sec.

Backwards-compatibility is a move in the right direction because Homeplug AV (200mbit/sec) devices are not compatible with older 14 and 85mbit/sec plugs, which was a blow for early adopters.

Devolo says 400mbit/sec products will arrive in a year's time at the earliest.

Posted by Emil Larsen on March 6, 2008 | Permalink | Comments (0)

Free IP switchboard for Windows

A new Windows-based software switchboard is easier to use than competing Linux-based PBXs, owner 3CX says.

The change to software PBXs reduces cost and improves functionality by integrating Voip services side-by-side with the regular BT phone line. A free package called Asterisk has taken pole position, but it's primarily Linux only whereas 3CX's Sip-compatible software can be installed on all major Windows operating systems, including Windows XP.

3CX says being Windows based is a big benefit because the setup is a breeze compared with Asterisk, its graphical interface is a doddle to use and it integrates well with Windows networks and applications.

Posted by Emil Larsen on December 4, 2007 | Permalink | Comments (0)

Continue reading Free IP switchboard for Windows.

Divx Connected comes late to the party

Divx is to license software to media streamers that plug into your TV, which will let you access videos, photos and music files stored on your PC.

The software, called Divx Connected, will also give TVs access to the internet. Numerous plug-ins will allow utilities like Google Earth and internet radio stations to be accessed, although there will be no browser for the foreseeable future.

Divx founder, Jerome Rota, said: "There're just two chips inside, one to decode and one to do networking, so the cost of the box has the ability to go very low."

Posted by Emil Larsen on October 17, 2007 | Permalink | Comments (1)

Continue reading Divx Connected comes late to the party.

Wannabe mobile WUSB competes with next-generation Bluetooth

Plans for a version 1.1 of the Wireless USB specification are almost an admission that the current version is not yet ready for mobile use. This is far from saying that it is pointless: the dongle adapters and WUSB hubs currently available are basically cable replacements for fixed devices such as PCs and peripherals such as printers in which power consumption is not an issue.

Sales in the US, where they have been available for months, indicate that people have quickly realised the potential of a technology that can get rid of the mass of wires around desktops and offer more choice in where peripherals can be placed in a room.

Posted by Clive Akass on October 2, 2007 | Permalink | Comments (1)

Continue reading Wannabe mobile WUSB competes with next-generation Bluetooth.

All access points are one to Extricom mobile clients

Microsoft makes your PC talk in its sleep

XBMC and HD HomeRun

HDHomeRun comes to the UK

My Dutch Wifi hell

Cebit08’s new Homeplug devices

One powerline to rule them all

Free IP switchboard for Windows

Divx Connected comes late to the party

Wannabe mobile WUSB competes with next-generation Bluetooth

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