Bi-Directional IP Over Satellite?

Kranky asks: "My company is looking at doing bi-directional TCP/IP over satellite, ie. data over satellite with a satellite backhaul as opposed to modem backhaul, and being the solo IT pleb here I was wondering if anyone had any recommendations for gear to use to achieve the goal or if they'd done similar and could give any pointers. Basically we're looking at 512kb/s [in both] directions and I'm wondering what sort of gear we'll need for the link, as well as any tips towards curing the inevitable latency issues. I assume there will be a cache and routers at either end (remote site will use us for internet access) but having never come across doing this whole IP over satellite thing before I have no real idea what we'll need. Any recommendations, pointers, or links would be appreciated."

Comments

here's the info you need

[Anonymous Coward]

what sort of gear we'll need for the link

A satellite dish, and a satellite. Don't forget the satellite, many people forget this essential device.

any tips towards curing the inevitable latency issues

Simply change the speed of light on your immediate area, and latency issues are solved!

I think this is enough to get you started! Hope this helps!!

Re:here's the info you need

[aminorex]

Now most network engineers, when asked to adjust the
speed of light, will just look at you like you are
crazy, but in fact, given that you can adjust the
electrical permittivity and magnetic permeability
of the medium (in this case, free space), it's
actually a no-brainer: Just frob the mu-zero and
epsilon-zero numbers until your ping times through
the bird are optimal.

I have permittivity and permeability modulators
ready to ship. Unfortunately they are locked
up in Nigeria in customs, but if you would care to
send me your bank routing number, I could deduct
the small customs fee, and in return cut you 10%
of the gross on sales when they get to the states!
It's a great opportunity for a smart mover!

Latency can delay link

[grantdh]

Make sure that whatever you're using lets you configure buffer sizes and such for the TCP/IP transmission. A client of mine was using a satellite to link their networks in head office and a mine in the back of nowhere. They used a large number of transponders on the satellite but weren't getting anywhere near the transfer rate they should. It was all due to the TCP/IP stack not sending on packets until it had received ACKs for those it had already sent. Given the small pending buffer size and the high latency of sending packets up & back twice (from HQ to site then the ACK coming back), it could only send a few before it had to stop & wait. Increasing the buffer solved the problem.

They were using NT and Citrix (this was back in 1997) and had to hack the registry on the gateway machines, but once it was done they got the expected bandwidth.

First thing to check, of course, is what bandwidth you'll need between the remote site and your HQ (could be high if you're going to use the link to hook them into the 'net). Next thing is figure out how many transponders you'll need on the bird to give you that bandwidth. Then figure the cost of using that many transponders. Once you recover from the sticker shock, you can determine whether they get a slow email/news only link or a full high-speed surfing link :)

Sorry I can't give you exact details - I wasn't doing the technical aspects of the project and haven't kept up with satellite pricing lately...

Latency....

[jsimon12]

It is ok if you have no other solutions, but be aware that the latency is mind numbing at times, especially for Internet access. The geosync orbit of the satellites adds almost a half a second to the round trip (and that is simply the electromagnetic signal traveling the 80,000 miles it takes to get there and come back), so on average your best ping will be at least 900-1000ms, least that is my experience with bidirectional satellite Internet access. Other then that it is good for transferring large files and stuff, just tweak your TCP/IP stack, just sucks if you have to do lots of small files or shell access, they are doable, but the latency will drive you nuts.

Why do you "have" to go satellite? Is terrestrial wireless an option?

Here's research about it

[Isomer]

The WAND Research group did a lot of research about this several years ago, when NZ's bandwidth was a piece of string and people were investigating using satellite for most of NZ's traffic. Their publications are available on their website. You probably want to look at all the ones that mention a high bandwidth delay product. basically issues you have are not having a large enough tcp window size, and the latency on connection setup/tear down. The tcp window size can be easily tuned on most OS's (including windows), the latency on connection setup issue can be resolved by using proxies at both ends that forward from one to the other and keep their connections open.