New frontiers in communication systems

New research by the universities of Bristol, Keio and industrial partners have unlocked 80 THz of fibre-optic bandwidth that will enable future exascale data centres and transform 5G networks.

The research on optical communication technologies, wavelength division multiplexing and networks form the backbone of every wired network across the whole Internet. Work until now has been focused and limited on utilizing ~11 THz of bandwidth (C and L Band) centred at 193 THz.
Optical networks based on this frequency bands have been able to support up to 230 channels at 50 GHz spacing.

The technology fabricated and tested is based on cascaded arrayed waveguide gratings (AWGs) and is designed to potentially construct a 1600 x 1600 wavelength router that can guide data at the speed of light. Specially designed quantum dot chips are used for light sources.

This single passive optical system can route immense information offering manifold increase from current systems. It can single-handedly interconnect over one million end points while offering at least ten Gb/s per end point. Critically it is also future proof since it's transparent to any communication signal and it can also potentially consume zero power due to its passive nature.

Read the full article at New frontiers in communication systems.

How long does a deprecated IPv6 address remain attached to an interface?

This may be obvious to normal folk but it wasn't to me, hence this post to remind me in the future.

The question posed to mine bad self was:

How long does a deprecated IPv6 address remain attached to an interface?

You may already know the answer. But in case you don't...

I packed a bag full of things I'd need - crab paste sandwiches, weak lemon drink, a compass, silk stockings and a plastic carrot - and set off on my journey through the Googles, a bit of oxygen but mainly laughing gas in my lungs.

My first stop, and first sip of weak lemon drink, was at an Oracle manpage:

An IPv6 deprecated address will eventually be deleted when not used,

Excellent! But when?

My next stop pointed out the bleeding obvious (good, old Wiki):

When an address is assigned to an interface it gets the status "preferred", which it holds during its preferred-lifetime. After that lifetime expires the status becomes "deprecated" and no new connections should be made using this address. The address becomes "invalid" after its valid-lifetime also expires

Er, yeah, that actually makes sense. Indeed:

$ ip addr | fgrep -A 1 temporary
    inet6 fd3c:c307:7f95:0:6957:dcf5:f759:e2e9/64 scope global temporary dynamic
       valid_lft 575828sec preferred_lft 56828sec
    inet6 fd3c:c307:7f95:0:d5b5:b1d0:a807:21a9/64 scope global temporary deprecated dynamic
       valid_lft 490031sec preferred_lft 0sec
    inet6 fd3c:c307:7f95:0:10d:8171:ff7f:777f/64 scope global temporary deprecated dynamic
       valid_lft 404233sec preferred_lft 0sec
    inet6 fd3c:c307:7f95:0:4dc0:7c07:c401:490b/64 scope global temporary deprecated dynamic
       valid_lft 318436sec preferred_lft 0sec

When valid_lft = 0 then it's curtains for that address. The default on my computer seems to be to set a valid_lft = 604800 (7 days) that is seven times the preferred_lft = 86400 (24 hours). Not a massive deal but it does mean that after seven days I'd have six or seven deprecated ULA addresses hanging around per interface, and eventually another six or seven deprecated global unicast addresses per interface too, assuming privacy extensions are enabled. Messy.

I know, I know, I can disable ULA if I want to. But I don't want to. So that's that solved.

There is a max_addresses parameter (default 16). I tried to find out if the system would remove the old deprecated addresses or report a failure when this limit is reached, but the bloody stupid thing gave up long before I got near this limit and removed all deprecated addresses far too early, and refused to create more ULAs.. I may visit this again sometime. Of course with this default of 16 I could easily exceed this limit assuming two routers with two global IPv6 addresses are reachable via one NIC, and ULA is enabled - easily achievable using fibre and LTE on one router, for example.

RFC 4862 talks about how deprecated and invalid addresses should be treated but doesn't mention when the node should simply drop the address altogether. It makes sense for an operating system to simply rid itself of the burden as soon as the address has expired.

You may now enjoy the crab paste and put the plastic carrot to good use.

For reference (at time of writing):

valid_lft and preferred_lft can be set/queried in Linux at /proc/sys/net/ipv6/conf/default/temp_valid_lft and /proc/sys/net/ipv6/conf/default/temp_preferred_lft, respectively:

$ cat /proc/sys/net/ipv6/conf/default/temp_*
86400
604800

References:

• https://home.regit.org/2011/04/ipv6-privacy/
• http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/networking/ip-sysctl.txt?id=HEAD

Why hasn't anyone told me about BT Wifi?

First and foremost I have to admit something quite embarrassing: although I had heard of BT Openzone I had not taken any notice of what it actually was, and I had no idea what BT Fon was either.

I shall assume you are as ignorant as I, and try to explain why I find this fascinating.

This is no less than an Internet revolution.

O2 broadband and BT's 21CN

I noticed recently that BT were messing about inside all of their cabinets. Curious, I decided to have a look on their website to see if it was part of the 21CN roll-out. Indeed it was, and as of June I will be able to increase my broadband connection from a pathetic <3 Mbps to a delicious >60 Mbps. Annoyingly, that would be at twice the price, but it will probably be worth it.

I am, however, a long-term O2 customer and the price they are currently giving me for unlimited broadband is unmatched by far. So I went to their website to see if they offered the same product at a reduced price (O2 broadband runs over BT's local loop network). I was informed by a very helpful O2 Guru that they are currently testing on BT's 21CN network and have had positive results. They don't have a date when this will be ready but will announce it on the website when they are ready to roll it out.

So long as I don't have to wait too long, I'm happy to wait and see what O2's prices are.

As this page explains, there's a chance we'll have to fork out to replace those ancient BT sockets, and no, you cannot replace them yourself by law. Seems... fair?

P.S. The nerd in the BT adverts is an absolute tosser. Which idiot thought he was a good replacement for the yummy mummy?



Actually.

Running DIMES Agent at start-up

The DIMES Agent does not run until logged in on Windows Vista and later due to UAC as the Windows service, although installed, is blocked automatically by the operating system.

There is still a way to make sure the Agent loads at system start, however: by running it as a scheduled task.

Note: The agent is unable to interact with the desktop so you will not be able to view statistics or change settings once running (but you can through the website). It will run in the background only. Also, on Windows 7 at least, you cannot stop the task once it is running unless you kill it.

Once installed, delete the shortcut from the Startup folder as it is no longer needed, and will probably cause problems later on.

Open the DIMES Agent with the Start Menu shortcut if it hasn't loaded already and input your user details.

Close the DIMES Agent.

Then, open Scheduled Tasks in the Control Panel.

Select Action and Create Task...



Once the window is open you can give the task a name that makes sense (such as DIMES).



Change User or Group... should be changed to SYSTEM and Run with highest privileges must be ticked. UAC blocks DIMES from running because it needs higher privileges to create raw sockets in order to ping.

Next select the Triggers tab and click on New...



From the Begin the task drop-down select At startup.

Enabled should already be ticked but make sure it is and click OK.



Next select the Actions tab and click on New...



Select Start a program from the Action drop-down.

Click Browse... and navigate to the DIMES Agent executable.

Click OK.



That should be it! There are other options you can play with if you need to but once you're done click OK.



Now all you need to do is start it by selecting Run from the Actions menu.



You can check that the DIMES Agent is running by looking at the Task Manager (you'll need to click on Show processes for all users as it will be running under the SYSTEM account).



Or by checking your account statistics, although these take a little while to update.

If you're pedantic, like me, you could always use Wireshark to make sure the pings are going out.