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

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...

Hire an expert

[anticypher]

Basically we're looking at 512kb/s [in both] directions

For the prices you will pay for 512kb/s, you can afford to hire an engineer who has done this before for less than your first month's bill. If you have so little clue "being the solo IT pleb here" you have to ask /., then your company is going to be in for some very nasty surprises. A company with only one IT guy doesn't have the budget for what the satcomms companies will propose, 512k with both/several ground stations, maintenance contracts, SLAs, installation, training, commisioning, licensing, etc.

Others have pointed out the technical problems you will face, TCP slow start vs. transaction mode, TCP windows, TCP/UDP/ICMP timeouts. Those technical problems are small compared to the administrative, billing, negotiation and regulatory problems you must deal with. Find an expert, pay them what they are worth, and avoid being screwed by the satcomms companies. It will be worth it, even in the short term.

Packeteer was working on specialised satellite gear, but I don't see anything on their web page. Ask them, their boxes work great for tweaking long latency and high congestion links. Somehow you will have to tweak the machines on both sides of the link, either at the router level or each machine's TCP stack. Consider not allowing "interactive" traffic, especially not web browsing, or putting some severe restrictions on which web sites the lusers can view.

the AC

MS Windows Required?

[Sloppy]

I was looking at some stuff related to this a few weeks ago, and I noticed they all seemed to have one thing in common: they don't have "normal" interfaces.

Instead of giving you an ethernet interface like you get with DSL or a cable modem, these things (at least the ones I looked at) all required you to use a weird USB box, that had to be plugged into a machine running Microsoft Windows and some proprietary drivers.