It is however true for aviation weather charts. And textual data like tafs and metars can be sent wholly in a single packet, so you throw a few of them in just to make sure.
What value does half a weather chart have? Broadcasting packets multiple times is more for single direction communications where there is no feedback channel. I have not observed any significant packet loss over Thuraya, it is simply a very slow ultra high latency connection. However, it is fast enough to live with the TCP overhead but not fast enough to use standard web sites. With my custom weather site, it is fast enough for real ife use. I was merely commenting on the fact that Thuraya GmPRS needs about 2-3 minutes to establish after you turn it on. That is 2-3 minutes until the first request passes, from then on it works as it should.
…it transfers data at around 50kbit but with an extremely long latency. I don’t think it is useable with standard web pages. You need specific applications tailored towards sat phone use.
Just for my understanding, am I correct that in fact you see two separate issues?
1) The latency which makes it difficult to use interactive AJAX stye webpages. You need services which take one click an then deliver the data you want without much “ping-ping” style data transfers.
2) The data rate of 50kbit is fast enough to transfer quite a bit of compressed data but modern websites are so big that you can not realistically use them.
What value does half a weather chart have?
What I was getting at is that e.g. this
delivered in 30 seconds is better than this
delivered in 3 minutes, with massive amounts of protocol delays caused by the necessary error correction. A bird in the hand etc
1) The latency which makes it difficult to use interactive AJAX stye webpages. You need services which take one click an then deliver the data you want without much “ping-ping” style data transfers.
I am no protocol specialist but I think that if you have say a 1 second latency it breaks the TCP/IP protocol, for websites that involve significant up/down traffic i.e. a large number of small objects being requested – a common feature of virtually all websites. It is common for a web page to contain 100 little objects, each of which has to be fetched separately. With a 1 second latency (e.g.) such a page would take 200 seconds, and it’s very possible that the browser will show absolutely nothing until the last bit arrives (don’t ask me why). The data should “always” arrive “eventually” but the timeout values typically present often result in a total data loss at the client browser which just bombs out. For example I know of one site which presents an image, updated every 1 minute, which fails totally if the image takes more than a minute to download. I have no idea why, but that’s what happens.
Long delays are unavoidable with a geostationary satellite like Thuraya. That is the main reason why international telephone traffic went to undersea fibre the instant that was technically possible. It used to be like speaking to somebody on the moon. There was a way to route a call over an undersea (copper) cable instead, by dialing a prefix, and paying extra… Thuraya don’t care because they have gone after the low-end Middle East / Africa / India market, with extremely cheap Thuraya-to-Thuraya rates of (2010) €0.22/minute which is astonishing for a satphone.
2) The data rate of 50kbit is fast enough to transfer quite a bit of compressed data but modern websites are so big that you can not realistically use them.
The Thuraya GMPRS 50kbits/sec rate is very usable provided you are careful. I recall this from my tests. Sure you can’t go to some crazy “$100k/week web maintenance budget” outfit like sony.com, and you need to be very careful picking up emails (almost daily somebody sends me a 10MB email with jpegs which MIME-encoded is 20MB and would cost $100 to download – practically you need a means of just getting the headers and then downloading the “safe” bodies) but it is OK for any website which a pilot might use for a real reason when airborne. In my original satcomms writeup is a link to a (not anymore really very) private URL which delivers wx data with the adverts stripped off. It is no longer fully functional (the guy who did it is now flat out pushing out an online shop for my business) but most of it is ok. At 56k, that site goes like greased **** 
It runs on an ADSL server which is why I don’t want too much traffic on it.
Unfortunately back in 2010 the reliability was crap, and their customer service was nonexistent. Today, they communicate much better, but I have not been able to test the latest XT phone (GMPRS) because my Lenovo tablet is on win8 and Thuraya don’t do a win8 driver. I tried winXP (under a VM) but it doesn’t work at all. I am sure it would work with a winXP laptop but I can’t use a laptop in the cockpit. So I am still on the old 7100 phone and the 9.6kbit/sec dial-up.
Thuraya don’t do a win8 driver
Why do you need a specific driver for the XT?
It’s bog standard AT command set over usbserial; the only thing you might need to do manually is to set the APN name (“get”).
At least with Fedora I just plugged it in, said “Mobile Data connection”, and set the APN name; that was all.
It doesn’t appear as a serial port – or anything whatsoever that’s visible in Control Panel.
When the cable is connected, one gets a beep from the T2, so it detected “something” allright, but no COM port appears, and no new modem appears. The USB port in the XT is neither Prolific nor FTDI (the two main USB-serial chip players).
At least with Fedora I just plugged it in, said “Mobile Data connection”, and set the APN name; that was all.
That sounds like the phone presents more than just a COM port, but presents a Hayes modem which your O/S auto detected (by sending AT to it) and assumed it is a GPRS/3G modem…
I have an email from Thuraya saying they don’t support win8, but that could just be a script monkey reply.
1) The latency which makes it difficult to use interactive AJAX stye webpages. You need services which take one click an then deliver the data you want without much “ping-ping” style data transfers.
Yes.
2) The data rate of 50kbit is fast enough to transfer quite a bit of compressed data but modern websites are so big that you can not realistically use them.
Yes.
This means you need a server end that just sends the data in one go. Most web pages don’t do that and have a lot of traffic going back and forth. TCP is fine for that, Peter’s example of sending a picture is what Thuraya can do well with reasonable burst data throughput but bad latency. TCP has no issue with long delays. My custom sat briefing page works great in the cockpit with Thuraya.
I wonder how well it will work in a low wing plastic Cirrus … maybe better
Reading through the past post I think my personal executive summary is:
+ The one big advantage of the Thuraya solution is the low annual fee to keep the SIM card running
- The big disadvantage is the antenna. As long as one needs an external antenna to make it work properly this will not be a good solution. The external antenna is expensive as a part and paperwork plus installation are even more expensive.
All other aspects like bandwidth usage, firewalls etc. seem as if they could be solved with enough development effort.
As a result the most interesting question for further testing would be, as Alexis suggests, how the antenna situation will be with different antennas in different airframes. From practical experience with Iridium I can say that the only really acceptable solution is one permanent antenna location. If the antenna needs to be moved around in relation to the aircraft heading, this will not work out when downloading the latest weather in a difficult situation.
Has anybody seen this post?
The big disadvantage is the antenna. As long as one needs an external antenna to make it work properly this will not be a good solution. The external antenna is expensive as a part and paperwork plus installation are even more expensive.
It is definitely not needed on the old 7100 phone, although if you are flying on a heading of about 330 (directly away from the satellite) then you may have a problem.
All other aspects like bandwidth usage, firewalls etc. seem as if they could be solved with enough development effort.
I disagree, the bandwidth is equally important and so is its use to do limited internet browsing, email and messaging. You can’t transfer a satellite image over Iridium SBD really. Also you need to carefully assemble raw data for radar and other things whereas I can just slap an additional image onto my page in case I find a new source of radar data. Thuraya is great for ad-hoc internet connectivity.
