Theo's Blog

SIPit 23 Survery Notes

theo@crazygreek.co.uk (Theo Zourzouvillys) — Fri, 24 Oct 2008 00:59:00 +0000

Robert Sparks has released the results of the survey of implementations taken to the last SIPit.

While not very much comes as a surprise, i'm particularly happy to see this:

"Many teams expressed intent to implement outbound and gruu once something was published as an RFC, and a strong unwillingness to even try until that happens."

Also good to see 2 XCAP servers. I was starting to wonder if anyone would implement it :-)

This is a little worrying, though:

"The only people in the room who had even read the sip-config framework documents are regular IETF participants. Even fewer had read sip-consent or session-policy."

Today's wise words

theo@crazygreek.co.uk (Theo Zourzouvillys) — Sat, 11 Oct 2008 17:24:00 +0000

Julie Meyer's great talk on The Future of Entrepreneurship at FOWA London '08 has this poignant quote in it, that everyone should think about long and hard:

"Our deepest fear is not that we are inadequate. Our deepest fear is that we are powerful beyond measure. It is our light, not our darkness that most frightens us. We ask ourselves, Who am I to be brilliant, gorgeous, talented, fabulous? Actually, who are you not to be? You are a child of God. Your playing small does not serve the world. There is nothing enlightened about shrinking so that other people won't feel insecure around you. We are all meant to shine, as children do. We were born to make manifest the glory of God that is within us. It's not just in some of us; it's in everyone. And as we let our own light shine, we unconsciously give other people permission to do the same. As we are liberated from our own fear, our presence automatically liberates others."

-- Marianne Williamson

The problem with credit ...

theo@crazygreek.co.uk (Theo Zourzouvillys) — Sat, 11 Oct 2008 16:53:00 +0000

... is that it's getting really hard to live life without it.

A few months ago my car broke down. I phoned up the AA, who arranged for it to be towed to the garage, and for a rental car for me for a few days. Shortly after, I got a call from Avis, who told me they needed my credit card details so they could take a deposit for damages, fuel, etc.

I gave them my Maestro card number - and they said that they only take Visa or Mastercard, not Maestro. So, I tried to give them my Visa Debit card. They wouldn't have any of that, either! Only credit, not debit cards accepted here, no sire. On asking why, they said "it's company policy".

Last week, I used my T-Mobile SIM card in my laptop to try to read a message on Facebook. It told me that there were parental controls (!) in place and I would need to remove them before I could access the site. So, I click on "remove content block", and a page later get asked for credit card details.

Guess what? Maestro doesn't work, Visa Debit doesn't work, and neither does my prepaid credit card from virgin.

So there are now 2 reasons i've needed a credit card, despite being lucky enough to have enough cash in my bank to not need one.

While credit cards may provide purchase protection, they're also fostering the deep rooted attitude towards credit so many people in the UK and America have today.

Mortgages, HP, car finance, credit cards, bank loans, pay advances - all instruments of the current "financial crisis" - although I don't think it's a crisis any more than capitalist punishment for being greedy bastards. all of us - not just the bankers.

Avis & T-Mobile are just as much to blame for the economy being the way it is right now as anyone who is in negative equity.

The national average for salary p/a is 23,746 GBP. After paying tax at code 474 and national insurance, that's 1,495.48 per month.

Assuming you could somehow live off half of that, then you could save 8,972 a year. That's 22 years of saving and living off an impossible amount to save 200,000 - the price of a semi-decent house outside of home counties.

Ohh, and hang on - we've just spent 22 years saving - we've not been able to go on holiday, or more importantly pay for a pension. Or pay council tax at perhaps 1000/year!

Houses are too expensive because we've got too many people and not enough land. To reduce house prices, we either need to have less people in the UK, or find more land to build on. We actually have plenty of land that's not built on, but it's mostly being used for farming & agriculture - a noble and important part of our economy, unless we want to dig ourselves into holes for the future by relying on other countries to give us food. Because we joined Europe and had a shoddy immigration policy for so long, we're probably stuck with the population as it is.

So i'd like to propose another solution: we swap some of the Icelandic debt in return for part of their country. We can defrost the land, and then provide it to British people for building houses on. The economy would boom due to all the houses being built, will generate lots of jobs due to all the building and staffing new high streets (which Icelandic companies already have experience in running), house prices in the UK would be in less demand, there would be less people in the UK, and as a result, house prices here would fall.

I should become a politician.

Differences between SIP and HTTP

theo@crazygreek.co.uk (Theo Zourzouvillys) — Sat, 11 Oct 2008 15:22:00 +0000

I was recently asked to justify my smug all-knowing grin when I was recently told that "SIP seems as simple as HTTP".

I can understand how someone who has seen a few SIP messages in a book or in tshark can come to that conclusion, or perhaps even read a summary in a SIP book. But, that's where the similarities end. As soon as you start to deal with SIP at a protocol level, you'll come to realise why it's such a different beast from HTTP.

Similarities

SIP has a similar looking textual representation to SIP.

Caveat emptor: they're actually rather different - a validating SIP header parser will not parse HTTP, and vise versa.

Both have 3 letter response codes in responses.

However a response code in HTTP doesn't mean the same thing in SIP. Both sit in entirely difference namespaces.

Both have normative references to rfc2617.

Except functionality like nonce counts, multiple proxy hops, and Authentication-Info are very confused in SIP.

Differences

SIP initiates sessions. HTTP transfers data.

This is the key one. HTTP was designed as a transfer protocol. SIP was designed for session initialisation.

SIP is for signaling, and isn't designed for transferring the data for the session itself. RTP, MSRP, and XMPP are all examples of the session transport.

HTTP has a strict client/server model. In SIP, the UA is a client and server.

A SIP client is schizophrenic. One second it's a client, then before it knows it, it's a server! This is an important part of SIP - sessions are bi-directional. All agents are both client's and servers.

A transaction in SIP can span multiple messages

Some of which are hop-by-hop (ACK to IxT failure), others are end-to-end (ACK to IxT 2xx).

Infact, SIP has a fairly complex state machine. HTTP doesn't. A Request results in a response. Simple!

SIP has provisional responses

That can go on for an age in SIP. Resources in a large scale SIP platform need to be carefully optimised to handle the very common case of a request waiting a very long period of time for a response - for example while a user's phone rings. Because of this, provisional responses are sent before the final one.

SIP R-URI's can be modified as they traverse "the network"

When a SIP message is sent out from a UA, it only really knows it's next hop (excluding RRiing). Each hop then takes responsibility for passing it on to the next hop - and indeed may even change the real target as it progresses.

HTTP on the other hand doesn't generally change the URL (front end reverse proxies excluded) without doing some nasty hacks like wireless portals, MNOs, and hotels tend to.

SIP messages are processed on a hop by hop basis. HTTP can stream responses back.

A SIP message goes from hop to hop, completing each hope before continuing to the next. Imagine in HTTP downloading the entire file to the proxy before you could start to download it to the web browser!

This all stems from the fact SIP only handles signaling, so it contains only (relatively) small messages. HTTP on the other hand has no real limits on response size.

HTTP provides an entire architecture for caching. SIP doesn't know anything about a caching proxy.

Even a non-caching (pass through) HTTP proxy has very few similarities to a SIP proxy.

SIP doesn't know anything about caching, nor would it be valid to cache a response and provide it to something outside of the transaction.

SIP can (and most commonly does) run over unreliable protocols.

HTTP requires a reliable transport. Congestion control is handled at the transport level.

SIP is broken. HTTP ain't.

SBCs, HERFP, DTMF, identity - it's all rather broken in SIP. HTTP seems to be fairly clean in it's implementation - SIP is far from it.

I'm still waiting for one person to tell me a single part of SIP that isn't broken in one form or another. And yes, I can use the forking card when I see fit :-) answers on a postcard to theo@crazygreek.co.uk please.

Day 3: Niagara Falls - Sodus Point, NY - Sackets Harbour, NY

theo@crazygreek.co.uk (Theo Zourzouvillys) — Wed, 01 Oct 2008 06:06:00 +0000

We awoke to an amazing view of Niagara Falls out of the hotel room window:

After an expensive breakfast at the Marriot ($20 each!), we left the hotel at about 0940, for a quick trip (~5 minutes!) down to the falls to grab the obligatory photos next to the falls...

and we headed back into the USA, after a very rude immigration officer (on the states side). After getting 2 very polite ones, I was starting to wonder what all the fuss people make about them was about - but now I understand!

Leaving Niagara falls we head east along Lake Ontario, and I start to see what I came here for ... endless trees!

After driving for a while through stunning scenery, we arrive in Rochester, NY - which is mostly uninteresting, except a huge Kodak building which was their HQ, now a museum - and continue until we make a stop at an old lighthouse, in Sodus Bay. Inside the lighthouse is a great little collection of local history, and the staff there were very interesting. Sadly, the weather was awful so the view wasn't that great.

We ended up in a quaint little town called Sackets Harbour at about 2000, and stayed in the hotel there for the night.

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Day 2: Shipshewana - Niagara Falls

theo@crazygreek.co.uk (Theo Zourzouvillys) — Sun, 28 Sep 2008 06:00:00 +0000

Awoke to the most beautiful view of Amish countryside and typical American barns.

Went to the Menno-Hoff -an Amish, Mennonite, Hudderite history - such a nice life they lead these days, shame I can never become Amish (i'd need to believe in god, for starters!).

Went to shops, found presents for one of the kids and jordan. After an amazing drive through some Amish communities, we drive into Ohio.

Ohio appears to be the land of absolute nothingness. Toledo was pretty un-interesting, and Cleveland even less so. Just a pretty shoreline onto lake Eire, with a bunch of nice houses.

so, straight out of Ohio and into Pennsylvania.

Then long drive to Niagara Falls.

We pre-booked a room at the Marriott in Niagara Falls, and arrived at about 2200 Local time. The town looked like it was bustling with tourist kitcheyness, so decided to go and explore some. A few drinks in a bar with very good live music, and back to the hotel at 0045 with alarm set for 0930 rise!

Perhaps someone could tell Boris to ask the Canadians for our routemasters back. This photo was taken this evening here in Niagara Falls. Thieving bastards!!

Tomorrow's plan: Head in the general direction on Maine!

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Day 1: Bicester - London - Chicago - Shipshewana

theo@crazygreek.co.uk (Theo Zourzouvillys) — Sat, 27 Sep 2008 04:31:00 +0000

After staying awake all of last night to attend to unfinished business, I was already tired when at 0630 I phoned for a taxi to take me to the train station for the 0710 train. "Sorry love, we're fully booked until seven thirty!". Bollocks.

A brisk walk to the train station later, a 50 minute journey into Marylebone, 2 stops on the Bakerloo to Paddington, then straight on the Heathrow express for 15 minutes. New record from Bicester North to Heathrow T3: 88 minutes including the walk from my house! Who said public transport in the UK sucks?

Despite all the troubles with air traffic control around London today, the Virgin flight left on time at 1115. Almost fell straight asleep, although I woke up about 2 hours into the flight feeling really hot and sweaty, light headed, and feeling like I was going to throw up. Now I fly regularly for periods longer than the 2 hours into the flight i was feeling like this, and most curiously, the only other time i felt like this from travelling was on my last return trip from America over 5 years ago! I put it down to food poisoning that time (never trust the salmon!), but I didn't even eat anything this time!

8 hours and 20 minutes after take off, and a good few hours sleep later and 72 pages through Small is the new Big by Seth Godin, the plane lands in Chicago.

Dreading the normal immigration interrogations, I was pleased to be directed toward a immigration officer who was not only polite and chatty, but also smiled. Yes, can you believe it, she smiled. Shocking! While she was very friendly in her chatting, it was obvious she was asking trying to establish if I was actually a risk to leaving

After meeting up with Ryan, grabbing a Starbucks, and taking a short taxi ride to Alamo, I sign some forms, pay some money (250 GBP) then get told "pick any car you like form that lot. The keys are in the ignition". Hmm!

So, a rather nice looking cream Jeep Liberty later (22 MPG!!), and i'm getting lessons in how to drive again. Well, how to drive an automatic, and what P, R, N, D, 1 & 2. does! A quick few reminds that i need to drlve on the right, and we're all set.

GPS programmed. Destinaiton: Buffallo, NY. Tentative plan: Drive to Niagara Falls, then up to Vermont to see the pretty red leaves.

While stopped at a Burger King for a late lunch, Ryan noticed that there is an Amish community not far away from our tentative plan to get to Niagara Falls. I've always been most curious of the Amish; Their lifestyle seems to very attractive to me, so attached and dependant on technology.

Detour arranged, and we end up in a little town called Middlebury at about 2030 (we're in EST now), and it's dark. Getting out of the car, we notice a whole load of youngsters - all smoking, and chatting away. Oddly, in England, Paris, or Berlin, this sort of crowd would have seemed a little threatening. Yet, here in the middle of Amish paradise, a group of a dozen teenagers just didn't seem in the slightest threatening. At all.

After asking the woman in the gas station (seem, i'm taking the talk already!) for some hints on a nice hotel, she pointed us down a street, and said "that'a'way! Careful of the bogies on the bikes!". Perplexed, we drove off in the direction she pointed us, keeping a close guard for bogies, or even just bikes.

A few minutes later, coming in the other direction is a horse drawn cart, with 2 Amish guys sitting on the back! They have a red flashing light attached to the back. One of them flashes a white light at us, obviously to say we're here!". Travelling just over 3 miles, we must have passed at last a dozen of these going in both directions!

Finally, we find a hotel called Farmstead Inn, by a brand called Trading Place. Only one room left, so I get a double bed, and Ryan gets a "cot", as the amricans call 'em

I've had a total of 4 "wow, you have such a cool accent" comments today.

Sadly, we'll be missing the local attractions: Wednesday for the local weekly hay & livestock, or horse, tack & pony auction on fridays. Damn! There is a whole 3 things listed to do after 6pm here, wow!

All in all, a great first 1/2 day!

I'll uploads the photos tomorrow, I didn't get to grab any this evening, as it's pitch black outside!

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American Road Trip

theo@crazygreek.co.uk (Theo Zourzouvillys) — Tue, 26 Aug 2008 20:00:00 +0000

Ever since a funny set of circumstances left me with a copy of the book Road Trip USA, i've been attracted to the thought of seeing America from the Highway.

The stunning coastlines of the Jersey Shores, the fertile fields of Pennsylvania Dutch country, the thick forests and tiny mountain towns on the old frontier, the Ozarks, the crests of the Appalachians (one day I will hike the trail from Springer Mountain to Katahdin, ohh yes), the Natchez trace, the deep dark Mississippi, the kitsch of Memphis, ohh my, how the list goes on!

Now wonder so few American's leave the country, they don't need to - everything is right at their doorstep!

I'm not particularly interested in big cities - although Chicago and Boston both seem to interest me; Chicago for the architecture, and Boston for Crane, Pool, & Schmidt - i'm far more drawn to the history of the USA, the countryside, the sheer vastness it exudes to a foreigner.

Perhaps the vastness is not really so great, perhaps the roads are just very long and very boring - but without trying, i'll never know!

So, today I booked just under 3 weeks off work for the end of September. I'm flying to New York, where i'm renting a car. The plan - which is really just a guide to get me going, not an itinerary - is to drive west from NY through Dutch Country, meeting US-50 on the West Virginia/Ohio border, and then follow the US-50 all the way through to St Louis.

I've arranged with a friend to meet in St Louis, and he's booked a week of work, so we're going to explore the south central states together - from St Louis (where Ryan lives) the plan currently involves a brief overload of kitsch at Branson, MO; then down through the Ozarks and along the Mississippi until we get to Jackson, MS, then follow the Natchez Trace up to Nashville, TN before heading back to St Louis.

That said, we've got 9 days from when we leave St Louis until we need to be back there as Ryan needs to work. So we'll probably not do the whole loop, and up up skipping some chunks in order to get back on time.

Once back, i'm heading off on my own to Chicago for a day or two, then following Lake Michigan east until I hit Niagara, then (time permitting) up to New Hampshire, before following the coast down through Boston to get back to JFK in time for my flight home.

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Total mileage, according to Google maps is around 4100 miles. Over 21 days, that's around 200 miles per day - probably around 4 hours - the equivalent of driving Oxford to Plymouth each day, or in total a trip from Oxford to Athens and back.

In comparison, last summer from Oxford to Greece and back, I did a total of 4000 miles in 50 hours over 3 days. So at least I know I can do it :-)

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I'm strangely excited about travelling alone. Normally, I travel with friends; i've been told the Americans are very friendly and strike up conversations easily - unlike the British, who look at you like you've just mugged them if you say even hello! these days. I've got a lot of pre-conceptions of Americans (I meet a fair few with work), so it will be interesting to see what the American equivalent of a Devon bumpkin is :-)

America, here I come - Just after a quick game of wif waf!

ps: if anyone fancies joining me for a few days (or lives en-route), let me know!

New blog

theo@crazygreek.co.uk (Theo Zourzouvillys) — Tue, 26 Aug 2008 16:03:00 +0000

Over a year since my last post! No change then - seems to have been a common pattern over the last 10 years.

I've decided that maintaining my own blog software is far to much hassle, so am trying out blogger's own static upload features with my own template. Seems like a far more sensible plan than using some crappy PHP software that needs ot be kept up to date :-)

The old content is still at http://crazygreek.co.uk/content/blog, the new URL is http://crazygreek.co.uk/blogger/ - although i've modified the old feed URL to point to this one.