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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."
you'd be better off in the long haul having a T1 trunk line pulled to your building. cheaper, not necessarily faster, but better response times (dont have to worry about the 200ms delay in getting a transmission between the ground and the satellite)
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?
...as well as any tips towards curing the inevitable latency issues...
Really not going to cure the latency issues, since the main problem involves the speed of light being limited to 186,000 miles/second and the satellite being in orbit about 40,000 miles up, meaning 80,000 miles both ways, in turn equaling about half a second of travel time. So sure you can tweak the TCP/IP stack, but the main problem is you will be lucky to ever get a ping better then 600ms, more then likely you will get something on the order or 1000ms or worse.
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.
On the mod to C, he may be kidding, but he's got a point. Some latency issues can't be solved, except by reducing the latency. You call yourself an IT pleb, so I take it you're doing business work. If it's to supply email and web access to your business, the latency really won't hurt much, for most things. If you're planning to provide remote access over the link, find a lower-latency link. Interactive work with significant latency is very nearly impossible. Also, satellite latency is much more than roundtrip time. You're in a huge collision domain, covering what, 45% of the Earth's surface? I don't know how they resolve it, but I know that on my Sprint Broadband Direct (one central tower on a mountaintop, covering much of the northern Colorado Front Range), I get pingtimes as low as 40ms, and as high as 6000ms. Seems there's a lot of "waiting your turn". I can't imagine what it's like over satellite, but unless there's a seperate channel for every single user of the transponder, you face the same problem, only worse. In space service, you may have access to more frequencies than in terrestrial broadcast protocols, but you're still limited.
If you're going to be doing remote access, your users will probably be happier coming in over a 33.6Kbps modem link (if you can keep internal surfers under control).
My family lives way out in the woods (no phone, solar for electricity.) For the past couple years we've had Starband. It is really solid and can get 300kps+ download speeds, uploads won't come close to what you're wanting, probably 20kps max. However, they offer a more expensive (monthly fee) for businesses that need more badnwidth (probably 400kps downloads 100kps uploads), I think instead of the $79 we pay it is about $149 for the higher speed and they may call this "Plus" service. You also get a dedicated IP address... Definitley worth checking out, good luck to you!
You still have the latency issues, but one of the Hughes DIUs actually gratiutiously(sp) acks the tcp packets on both sides... much like the old telebit PEP based modems... they also do http cacheing. Their satellites are LEO, so you've got about 750ms RTT to deal with between your location and their headend... Like other posters have said, it's good for bulk non-attendated data transfer, but to actually be sitting there using it for day to day activites, it's kinda painful. (Try to run a ssh or telnet session over a satellite link some time... you gain a whole new respect for using ed :)
The most costly part of running a satellite operation is the bandwidth. I'm the operations/engineering manager for a satellite provider in Canada and I've experienced this first hand.
Depending on your choice of systems you can get anywhere from approx 590ms to over 1000ms. We operate 3 different flavors of satellite services.
A SCPC (Single channel per carrier --> think dedicated) with a frame relay core. Very reliable and average pings are 650ms. This system even supports voice over frame technology too!
The other system is a dedicated IP based TDM/TDMA system (Time Division Multiplexing/Time Division Multiple Access). The unit does IP spoofing (ie does local 3way TCP handshaking) etc... Ping times with our setup usually come in at about 900ms (based on timeplan and a few other parameters)
Since you are not driving a business with this, your needs will differ. Finding an expert to help you would be very benificial.
Personally I believe you would be best off with an SCPC solution since you have only 2 sites (HO and a remote).
Best of luck.