Hands on: Problems with offline files

How to solve some of the quirks in Windows’ handling of offline files

Following my recent article on offline files, I’ve had a number of emails from readers who have encountered problems when using this Windows networking option over slow-speed virtual private network (VPN )and wireless links.

Readers have reported problems when using XP where the speed of the connection is just sufficient for Windows to try to open the remote server version of a file rather than the locally cached (offline files) copy.

In such circumstances it would be more sensible to carry on working offline, but the Windows software insists on connecting to the remote share regardless.

The good news is that there are a couple of ways around this issue, one of which is to upgrade to Windows Vista, about which more later. For those sticking with XP, however, you’ll need to get your hands dirty with Registry and group policy settings and, even then, may not get the desired results.

Slow links and XP
Here’s what you need to do if you’re running Windows XP.

First, make sure you’re using the latest service pack (SP2), otherwise the options I’m about to mention won’t be available. It’s also a good idea to apply any post-SP2 updates. Next, open up the Group Policy editor, by typing gpedit.msc from a command window or via the Start menu’s Run command.

This will load up the Microsoft Management Console (MMC) with the Group Policy snap-in loaded, from where you can edit what’s called the Local Group Policy Object which, in turn, controls the way Windows behaves.

Note, however, that if you log on to an Active Directory domain, the Group Policy settings configured by the network administrator will take preference over your local settings and you may have to get this option configured for you.

Assuming that isn’t the case, the setting you want to change will be defined in the local administrative templates. It’s called Configure Slow Link Speed and sets the threshold below which Windows will consider a connection to be ‘slow’ and connect to cached offline files rather than the associated network share.

This entry can be found in the Computer Configuration folder, under Administrative Templates/Network/
Offline files.

If the Configure Slow Link Speed setting isn’t enabled, a default threshold of 64,000bits/sec is assumed. The number here is typed as bits/sec divided by 100, so for 32Kbits/sec you should type 320. You’ll also have to reboot to activate the group policy setting, or type the command gpupdate in a command window to activate it.

However, by itself the Group Policy change will have no effect. You also have to edit the Registry and add a new key to tell Windows what you want it to do. The usual warnings about editing the Registry apply (take a backup if you’re worried) but, assuming you’re happy to proceed, start the Registry editor (regedit) and add a new REG_DWORD entry to tell Windows to go offline when a link below the speed threshold is detected.

To do this browse to HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\NetCache from the Edit menu, select New and click DWORD Value. Type GoOffline OnSlowLink to name the entry, then press Enter. Finally, double-click the value you’ve just created and set it to 1 – either hexadecimal or decimal, it doesn’t matter.

Once you’ve enabled this option (and rebooted) Offline Files should recognise any network connection speed slower than the value specified by the Configure Slow Link Speed group policy setting as slow enough to go offline. It should then use the locally cached files rather than those on the remote server.

At least that’s the theory. In practice it’s difficult to test fully, although I did manage to force Windows to go offline on a 100Mbit/sec Lan connection using this technique. However, I’ve also seen lots of posts on support forums indicating that it doesn’t always give the desired results. In particular, the transition from offline to online status is far from seamless.

It’s also an all-or-nothing setting applied to all links and all users of the PC. Plus, if you configure offline files to synchronise the local cache whenever you log on or off, the software will still attempt to do this no matter what the Configure Slow Link Speed setting.

Offline with Vista
Life gets a whole lot easier if you’re a Windows Vista user. Indeed, you don’t really have to do much at all to address the problems with slow links with the latest OS.

That’s because the caching engine has been totally rewritten for Vista, providing more control over the way the software works.

The biggest change is the addition of an Explorer button marked ‘Work offline’ which forces Windows to use the cached versions of offline files regardless of the connection speed. Click this and you in effect disconnect yourself from the network so that all you can see and access will be files that you’ve made available offline.

The button then changes to ‘Work online’ enabling you to reconnect to your remote network shares when a fast link becomes available. You can still synchronise when working offline and access the network to send/receive email.

Other changes in Vista include the way the local cached copy is synchronised with the online copy. To this end Vista keeps track of the blocks that are modified while offline and only transfers changed blocks back to the network share.

This makes synchronisation from the client to the server much faster, although it only applies when transferring changes from client to server – not in the other direction. And since some applications (such as Microsoft Word, for example) create a new temporary file when you modify an existing document, you won’t always see the benefit.

The synchronisation process has also been modified to only synchronise the shares for the user who is logged on. This addresses a problem whereby you could get an ‘access denied’ error for folders belonging to someone else.

Another plug for Powerline networks
So much then for offline files. Another request I’ve had recently is for more information about Powerline or Homeplug networking products, with a lot of confusion as to what they can be used for and whether or not it’s a secure alternative to wireless.

I have to admit that I was initially sceptical about these products, which are designed to use the AC mains wiring in a building for networking, saving the need to install a separate UTP Lan or employ wireless access points, bridges and routers. Having used them in anger, however, I’ve become a convert and, like all converts, something of an evangelist for the technology involved.

The biggest advantage, as far as I’m concerned, is the speed and ease with which these products allow a network to be created.

About the size of a large three-pin plug, all you have to do is plug one into a mains socket in one part of a building and a second into another somewhere else and you’ve got an instant network. No setup is needed, the two devices will just find each other and communicate using frequencies not required for the transmission of power, to create an Ethernet bridge.

Anything connected to one Homeplug adapter will be networked to those attached to the other, with a choice of either single-port adapters or those with built-in Ethernet switches, typically allowing four or more devices to be connected. Plug in additional adapters and the network simply grows in size – it really is that simple.

That said, Homeplug networking does have its limitations, most of which are to do with the fact that it’s not a wireless technology. So, for example, if you want to use Homeplug to connect a notebook PC to a broadband router, you’ll need two adapters.

The router is connected to one, while the notebook will need to be equipped with a wired Ethernet interface to enable it to be connected to the other. Even then you could always plug a wireless access point into the Homeplug network and connect the notebook via Wifi. You can also buy Wifi extenders that have a wireless access point built into a Homeplug adapter.

But then there’s the little matter of security. We all know how easy it is to piggyback onto an unsecured Wifi network, and the worry is that your neighbours could similarly connect to your Homeplug network, simply by plugging an adapter into one of their sockets. After all, both houses are, at some point, connected to the same AC supply.

The reality is that this is unlikely to be the case, primarily because of the distances involved. I’ve tried it for myself, plugging an adapter into one house and another next door, and it didn’t work.

If you are worried, and judging by my inbox a lot of people are, then all Homeplug devices can also be configured to encrypt the data they’re transmitting. Disabled to begin with, a simple Windows utility is provided to turn encryption on to create a secure private Lan, with the option of activating this on all the devices on the network at one go.

I’ve done this on a number of different products and, interestingly, it has been the same software every time, albeit branded with a different vendor logo. As a result, I’ve never had any compatibility issues, at least not with the security option.

I have had problems mixing the latest Homeplug AV (200Mbits/sec) adapters with earlier, 85Mbits/sec implementations. However, that aside, Homeplug works well, is inherently more secure than wireless and can solve a lot of network cabling problems very quickly and easily indeed.