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Bi-Directional IP Over Satellite? 51

Posted by Cliff from the what-would-you-need-to-do-it dept.
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."
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Bi-Directional IP Over Satellite? More

Bi-Directional IP Over Satellite?

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  • here's the info you need (Score:3, Funny)

    by Anonymous Coward on Tuesday February 18, 2003 @08:47PM (#5331028)

    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!!

    • 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).

    • Re:here's the info you need (Score:4, Funny)

      by aminorex ( 141494 ) on Tuesday February 18, 2003 @11:45PM (#5332201) Homepage Journal
      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 (Score:5, Insightful)

    by grantdh ( 72401 ) on Tuesday February 18, 2003 @08:47PM (#5331030) Homepage Journal
    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...
    • By increasing the buffer size, I presume you mean increasing the TCP window size. Modifying the TCP slow start algorithm can make an improvement too.

      Another common method for reducing the effect of a large latency on TCP is to place special proxies at either end of the satelitte link. These proxies will fake TCP ACKs in order to stop latency problems. The also handle any error recovery by buffering the packets they have received, until they receive the real ACK from the other side of the satelitte link. As far as I remember, there was some jiggery-pokery involved in dealing with all possible combinations of SYN and FIN flags but I cannot remember the details.

      Steve.

  • not worth it... (Score:1, Informative)

    by Anonymous Coward
    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)

  • Latency.... (Score:4, Informative)

    by jsimon12 ( 207119 ) on Tuesday February 18, 2003 @08:54PM (#5331074) Homepage
    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?

  • Latency 2 (Score:3, Informative)

    by jsimon12 ( 207119 ) on Tuesday February 18, 2003 @09:01PM (#5331128) Homepage
    ...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.

    • Re:Latency 2 (Score:2, Informative)

      by crmartin ( 98227 )
      Mild quibble: a geosycnhronous satellite is only about 18,000 miles "up" -- geosynchronous orbit is 22,300 miles from the center of the Earth, and one Earth radius is about 4,000 miles. But I've observed the ping time to be 770 +/- 35 msec in a configuration that I was trying to work with. (There's a lot of other delay in there in things like the signal processing of the very low level signal.) Thus the basic point is correct, even if the arithmetic is wrong.
      • Sorry, I must have been hopped up on goofballs or something.
        • Hey, you can make up a better excuse than that. For example, I'd assumed you'd worked it backwards from 800 ms -- without subjecting myself to long division, it's of the right order of magnitude. Um, er -- yeah, 430 millisec one way, 860 millisec round trip time ... see, that must be what you did. Right? ;-)
          • I think it really was raditaion from orbiting solar debris, I had forgetten my foil hat, or was it statis electrcity from slide rules?

  • Here's research about it (Score:5, Informative)

    by Isomer ( 48061 ) on Tuesday February 18, 2003 @09:26PM (#5331280) Homepage
    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 [waikato.ac.nz] 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.
  • If you are looking to connect sites in remote areas, satelliete untethers you from the phones.

    If you are looking at satellite for any other reason, forget about it. Especially if you are looking to use Direcway as your solution.

    Satellite give you fast transfer rates, but managing a network on the other side will be very difficult.
  • Whatever happened to the ZModem file transfer protocol? It was optimized to work over high latency satellite connections, and did so very robustly.

    I wounder if it would be possible to use it's capabilities to solve the TCP/IP latency problems. Is Chuck Forsberg still living on his houseboat in Seatlle?

    • The zmodem protocol and TCP have similarities in that they allow X bytes of unacked data to be streamed before the transmitter pauses. X has to be large enough to compensate for the bandwidth-delay product on the communications link. With TCP, this is done by setting the receive window in the receiver's TCP stack to an appropriate value.
      • Increasing the receive window helps, but is not a complete solution by itself - when a dodgy packet is received, a large amount of data will have to be retransmitted (remember that this is a satelitte link, not a T1 - the BER is much worse for a satelitte).

        Steve.

        • BER (Score:1)

          by Detritus ( 11846 )
          The raw link BER my be poor, but that may not be what the user sees. I've worked at places that had 56K international data circuits through Intelsat and DOMSAT earth stations and satellites. From what I remember, the earth stations used special satellite modems to provide the digital data link through the analog spacecraft transponder. The only problems we had with the BER on the circuits was when the Sun was in alignment with the satellite, which increased the noise floor and temporarily interrupted the circuit.
          • True about the BER - dunno quite what I was thinking about. Still - when a bad packet is received, or one is dropped somewhere you still have the entire window to retransmit.
      • The nice thing about Zmodem is that it has adaptive block sizes.

  • It would help if you can give us more details on how you intend to use the Internet connection. If it's mostly for hauling "bulk" data, Satellite is okay. But it's danged slow for interactive use.
    • Apologies for not responding earlier, i didn't even notice they posted the thread to be honest. Righteo, the reason by satellite: It's to a remote area in Fiji, connecting to here to provide internet access via our 150Mb fibre backbone. Why us? I don't know, management don't tell techs anything. I would have thought Telstra could provide the setup cheaper seeing they'd already have the infrastructure. We have the modulators, upconverters, dishes, etc. (we're a satellite broadcasting company) but none of the IP data kit for satellite use, just your standard LAN/WAN fitout. I did come accross Unidirectional Link Routing, and noticed it was supported by software from UDCast (http://www.udcast.com/) and also in IOS 12.1 from Cisco. Anyone had any experience with these?
  • One alternative to satellite that I have considered,
    in order to get Internet into a remote location
    (Faya-Largeau, in northern Chad, a Saharan oasis
    town about 300 miles from land lines) is a tethered
    balloon with a repeater. The power for the repeater
    would be solar, and run up the tether. Does anybody
    know of someone who has done anything like this?
    UAVs are pricey, but I have no clue whether the
    operating time of a helium weather balloon, or the
    tether-weight vs. balloon-size tradeoffs would
    make such an approach prohibitively expensive.

  • The main telecom in Australia has a two-way satellite service available Australia wide (mostly for rural areas). They also have a 1-way satellite with modem back channel.

    Perhaps you can check their web-site and e-mail their tech's - perhaps they'll be willing tell you the setup they use.

    Failing that - are there any slashdot readers that have this service? - if so, what is your setup?

    Their two-way satellite web-site is here [bigpond.com]

  • Starband (Score:3, Informative)

    by jaydho ( 98032 ) on Wednesday February 19, 2003 @01:07AM (#5332652) Homepage
    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!
  • My employer is currently looking at the IP3 (they say cubed) product fom Kromos.com We are pleased at what we have seen so far of the product and the engineers' willingness to address concerns we have so far expressed.

  • Hire an expert (Score:3, Insightful)

    by anticypher ( 48312 ) <anticypher@@@gmail...com> on Wednesday February 19, 2003 @06:58AM (#5333671) Homepage
    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 [packeteer.com] 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
    • Yep, all true. I should have said that we are only replacing what's usually referred to as the IDU (Indoor Unit) pieces. We already own hubs, stationary and mobile earth stations. The Kromos gear (among other things) circumvents the TCP congestion algorithm. As I understand it, TCP interprets the propagation delay over the space segment as network congestion and throttles throughput way back.

    • Re:Hire an expert (Score:2, Informative)

      by SirLeNerd ( 21841 )
      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.

  • then don't do that then !

    Seriously, first ensure through the use of traffic shapers if the bad satellite network latencies are no problem for you before you go on thinking more deeply about the real implementation.

    I know of an organisation where someone from management decided that for the new infrastructure they'll go for satellite instead of DSL... 'for reliability reasons'.

    Well it turns out that an (extremely crappy) application they depend on is not able to accept latencies above 1sec, which the satellite turns out to have. And then one day the satellite link failed for some hours (I don't know why).

    Now they still pay for the satellite they don't use plus the DSL lines they wanted to avoid... because DSL turns out to be more reliable and has far lower latencies... D'oh !

    But try convincing such a suit that a satellite would be a bad idea in the first place :-) He didn't believe us and now he has to justify the consequences (= more money spent than necessary)

    • "And then one day the satellite link failed for some hours (I don't know why)."

      Well if on that day the sun appears to be right behind your satellite to your dish, it could make things harder for your receiver.

      And if you use microwave bands - there's always rain.

      Satellite is good for remote locations - no cables, no towers nearby with access to cables, no nothing.

      But use the cables when you can.

      Satellite bandwidth is fine for broadcasting because everyone gets the same info and latency usually doesn't matter. Not good for situations when each user wants different info.

      I don't see it changing unless you can increase bandwidth using spatial means (e.g. multiple satellites working together to send "holographic" signals which are resolved by each receivers differently - they each see a different "picture"). Someone is probably working on that somewhere.

      There will always be latency until someone finds a way of sending info faster than light, or manages to launch and run lots of low orbit satellites cheaply.

  • Simple solution. (Score:3, Funny)

    by cybermace5 ( 446439 ) <g.ryan@macetech.com> on Wednesday February 19, 2003 @09:20AM (#5334087) Homepage Journal
    Head down to the local hobby store and pick up a few model rocket kits. Start with one of the ready-to-go plastic ones, then gradually work up to a multi-stage D engine model. Go to college and get a complement of engineering and science majors, all doctorates. Design and build a liquid-fuel launch vehicle, and place the satellite of your own design into orbit.

    You could skip a few steps, and rubberband enough Estes model rockets to an 802.11 wireless access point, trailing a really long Ethernet cable.
  • 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 :)

  • MS Windows Required? (Score:2, Insightful)

    by Sloppy ( 14984 )
    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.

  • You didn't even say WHY your company needs it.

    If you don't know why you need it, you probably don't. If you don't say why you need it and ask such a question...

    The fact that modem backhaul was an option is also another indicator.

    Advantages:
    1) Good for remote areas - middle of ocean, middle of desert, on some mountains (some have WiFi tho).
    2) Good for broadcast.
    3) Good for mobile stuff (but wireless/cellular networks are good in some areas).

    Disadvantages:
    1) Latency (if geosync).
    2) Expensive (you said bi-directional).
    3) Not that reliable (lightning, bad weather, or sun got up on wrong side of satellite, feeling grumpy etc).

    Why expensive? Most geosync satellite stuff is shared bandwidth over big footprint - unless they figured out how to send and receive holographic sat signals. Good for broadcasting the same 1.5Mbps stream to 200 million people, but bad for different streams per person. Which is why many satellite ISPs died. Copper pair, coax, fibre cheaper for most populated locations - one fibre could carry as much bandwidth as a whole satellite, and doesn't have to be shared by all subscribers.

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