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Linkstar up and running - terrible uploads

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Dec 10th, 2007 at 11:29am  
Hi, I need some help from the experts on this forum.  I just recently finished installing a linkstar terminal in Iraq (couldn't have done it without the info gleened from this site, thanks all), got everything up and running, but I am experiencing what I think are terrible upload speeds.  The service package I subscribe to is called Star Pro Office 2000 premium, 2000kbps down, 512kbps up (10:1).  Published averages are 512kbps down and 96kbps up during peak hours.  Now on the download side, the speeds I'm seeing are right where I expected them to be(20-120 kBps).  On the upload side, its terrible.  I'll take suggestions how to measure upload, but using www.speedtest.net (no matter which server I pick) the upload speed maxes out at 22kbps (less than 1/4 the published average) during all hours of the day.  Uploading large files to email takes forever.  VoIP is near impossible.  Incoming webcam is great, outgoing is c**p.  I've checked to see if I'm throttled.  Any ideas why this may be (I am simultaneously working this issue with my service provider, will post any updates).  Could it be a hardware issue?  A setting on the RCST?  Please help!!!  Thanks,
Brendan
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Reply #1 - Dec 11th, 2007 at 8:16am  
Hello Brendan,

do you experience this with a single PC connected or with several connected and only one active?
Suggest to connect only one PC and then open the cmd window and type netstat. check what connections you have on your PC, could be you have a virus or an application you are not aware of the is taking all the bandwidth.
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Reply #2 - Dec 11th, 2007 at 11:14am  
Hi Brendan,

That's usual with LinkStar systems. MF-TDMA or other slotted (or diversity) Aloha based uplinks run at effiencies near 40-60%. That means that almost half of your link is wasted just to keep the connection alive, due to collisions with transmission coming from other terminals. So out of your 512 kbit/s I would anticipate something like 200-300 kbit/s to be available for the user payload at maximum.

You also have a shared service and that means you are contending with other terminals for the time slots on the satellite carrier as well. 1:10 could mean anything from that 10 terminals share the single inroute carrier to that your ISP *anticipates* that only 10 terminals will do that while the real number could be much more. Assuming the first case, that leaves us with 20-30 kbit/s per each terminal if all 10 terminals are active during the day at the same time. Since 20-30 kbit/s is practically almost nothing and usually there are multiple PCs per each terminal, all terminals tend to load their uplinks at 100% and this results in the final bottleneck.

The way out would be to migrate to a VSAT technology that uses more efficient uplinking techniques, such as iDirect's D-TDMA (near 98% efficiency) or a dedicated system - SCPC for example (100%). Not all iDirect providers are the same though and there are lots of badly oversubscribed networks, so I'd advise to proceed with caution.
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Reply #3 - Dec 12th, 2007 at 9:27am  
Thanks for the replies.  My initial tests were conducted with only one PC connected straight to the RCST.  I'll try the netstat and see what I get. 

Thats unfortunate news about the Linkstar system.  It brings up another question that you may or may not be able to answer.  In order to "migrate" to a different VSAT technology, will I need to upgrade my dish/lnb/buc?  Lets say, to go to an iDirect 7000, can I only switch out the modem?  I have a channel master 1.2m dish, NJR2184F LNB, the part number for the BUC is VCD-022275-0000, although I'm unsure of the Model Number.  I haven't found any distinguishing markings on the feed asy either.

On the subject of oversubscribing networks, can you recommend a service provider (in the middle east) who does not oversubscribe, who provides reliable service?

Thanks,
Brendan
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Reply #4 - Dec 12th, 2007 at 12:32pm  
The migration plan really depends on the characteristics of the satellite coverage and the carrier size of the particular network operator and not the VSAT platform itself. There are many iDirect services out there that run in different freqency bands like Ku-Band, Extended Ku-Band, C-Band, require various antenna sizes, LNBs and BUCs operating in different frequency ranges, etc. Once you choose the operator, they will provide you with migration plan and will help you to determine what equipment of yours you can reuse.

As I am a CTO of a satellite ISP, I don't think it would be really that polite to recommend the company I work in. Smiley All shared services are actually oversubscribed - that's why the service itself is called "shared." Dedicated services are usually very cost-prohibitive for small groups of users as satellite space segment is very expensive itself. Different ISPs use different bandwidth management techniques that derives the quality of service end users perceive. Much of that is a black box for the end user as QoS/bm stuff is more like a know how of a particular operator. Nobody would want to disclose how they do their own business, so if I would be on a place of an end user, I would be heading to a company that you just feel comfortable yourself with when discussing various technical aspects.
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