Grandstream phones, APD-80 and 85638-01 cables

A number of months ago, I deployed a new SIP network using Grandstream GXP-1782 phones. For some of the folks that are always on the phone, we got a couple of Plantronics DECT headsets - which are specificially listed on the compatible headset list published by Grandstream.

The headset plugged into a APD-80 adapter cable. The Plantronics documentation states that a "85638-01 adapter" cable is required - although this is listed as an adapter to extend the APD-80 cable. When you look at the length of the APD-80 cable, this seems nuts - however the 85638-01 cable holds a secret.

Without the special 85638-01 cable, pickup and hangup of the phone was very unreliable. Lots of sites have this documented as a straight through cable - but it is not. The pins on this are actually reversed - ie:

End One End Two
1 4
2 3
3 2
4 1

See example photo:


Using this cable, you should find that the hangup and pickup functions work correctly without spending $15 per cable.

Credits to Michael Schneider for discovering this

Migration from Wordpress to Nikola

A new year, a new blog engine.

While Wordpress is quite useful, its a heavy, hunking bit of software for those who just post occasionally and don't really need any dynamic content at all. This is where Nikola comes into play.

Nikola takes posts in reST, Jupyter Notebook, YAML, TOML, Markdown or HTML and runs them through the theming engine to get plain, static HTML.

The benefit of this is almost zero load on your web server - as there is no dynamic data to process. Especially good for cheap VPS packages from the many online providers.

So far, I'm impressed!

New page - converting PWM hubs to voltage controlled

New guide up - right here.

My Xen servers main board didn't have a second PWM controlled fan header to use with a PWM fan hub for the 3 case fans. Its a 4RU case - which has server grade 140mm fans that can draw up to 0.9A each and get up to around 3600 RPM.

So here's how I used an ATTiny85 to generate a PWM signal from the variable 'Speed Control' voltage on pin 2 of the SYS_FAN header.

Enabling BBR Congestion-Based Congestion Control on kernel-xen

With the release of kernel-xen version 4.9.40, I have enabled CONFIG_TCP_CONG_BBR. This adds support for using BBR to improve the throughput from your servers (mostly web servers) to your clients.

If you run my kernel-xen package on your Xen guests, you can also take advantage of this new feature.

To enable, ensure you are running kernel-xen version 4.9.40 or above, then create a file called /etc/sysctl.d/enable-bbr.conf containing:


You can activate this by typing: $ sysctl -p

The changes will automatically apply at the next system boot.

To read more about BBR and why it makes such a difference, head on over to acmqueue for a far more in-depth analysis than I could provide.

Turnbull handballs encryption problem to tech companies

In a speech in London overnight, Turnbull said companies should not be able to build end-to-end encryption tools that meant nobody - including courts and law enforcement - could access the content of communications.

If you're in the tech industry, and you know your local Liberal party member, point them to this and tell them to go fuck themselves. Regards, The Internet.

If you don't know who your local member is, search here:

Staying safe online - is it even possible?

So every once in a while, you come across something in IT Security that just makes you want to cry.

Usually, these are chained exploits that when executed properly have devastating effects.

Take the latest Pwn2Own competition. One of the successful hacks there was epic. And scary.

In a nutshell, an 'Edge' browser exploit to get into the Windows 10 VMWare guest, then a bug in the VMWare guest to own the VMWare host. Yes, hacking the VMWare host - from a web page.

That's scary.