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It's going to be very hard for anyone to profess that satellite or land
based is faster as a generic statement. There are to many other factors to
consider that impact the throughput of the connection.
Satellite delay is caused by the distance that the signal has to travel from
the VSAT unit to the satellite. This delay of ¼ second is present in all
satellite-based services including the long-distance phone call that we use
today. The throughput performance however, remains unaffected.
A single hop delay is the delay caused by the transmission from a VSAT unit
to another unit. However, certain VSAT topology uses the master hub-station
as the transit gateway to connect between two remote units and that
introduces a two hop delay for each transmission or a 1/2 second delay.
Voice calls are especially sensitive to the delay as are TCP conversation
that haven't been 'tuned' for transmission over a satellite connection.
xDSL and Cable technologies don't suffer from the same delay that a
satellite connection suffers from but there are many other issues that
affect 'speed' that the service providers don't draw attention too.
Cable networks are a shared bandwidth asymetrical technology. You have a
10Mb upstream connection MAX and a 28Mb downstream MAX in most cases. The
upstream is the connection from your PC to the internet and the downstream
is the inverse. What most cable companies do is aggregate multi CMTS hubs,
what you connect into at their site, into a single connection to the
internet. The connection to the internet can range from as slow as 56K to
144Mb. Typically they use multiple T1's (1.544Kb) to the internet. Some do
have the faster connection such as ATM(144Mb) or T3 (45Mb) connections, but
if they do they will only typically have two or four.
Now do the math, on cable they typically try to limit the PC to about
250-500 PC per CMTS Upstream/Downstream, the folks you share the bandwidth
with. If you take 500PC's/28Mb=56K per PC on average worst case. Now the
cable operator usually has many subscribers, say they have 10,000 customer
on a fully max out system. If they have a max of 500 users per CMTS unit
and each unit is capable of delivering 28Mb to the users, that's 560Mb of
data at one time that can be sustained in their system.
(10000Users/500PerCMTS*28Mb=560Mb). Now their connection to the internet
could be the a typical best case 144Mb connection x 2 for 288Mb. There are
faster, but not common. That's almost a 2-1 oversubscription. That is an
excellent ratio and not realistic, more common is a 6-1 to 10-1
oversubscription. So they expect only 1 person out of 6 to 10 to be using
the system as the same time. I like cable because it's truely takes
advantage of the fact that not everyone is transmitting at one time. You
can have as much as 28Mb available to you, if configured so.
xDSL is not a shared connection, as is the case with cable, your limited to
what you paid for. Folks believe this is a benefit for xDSL users, but only
if the service provider doesn't oversubscribe the links. When they do
oversubscribe the links you can have a connection that is slower than a
dialup connection at busy times. How can this be.... Well most xDSL system
are asymetrical, you might have 128Kb upstream and 1.544Mb downstream. Now
this bandwidth isn't shared and you have it all to yourself, to the what's
referred to as the DSLAM. The DSLAM is where your connection terminates.
That's where your 128Kb/1.544Mb connection guarantee stops. The question is
then how do they have there DSLAM connected to the internet. Let's take the
same example as above and say there are 10000 users. In a downstream
configuration that is a MAX of 15G of bandwidth in their network.
(10000Users*1.544Mb=15.44G) Now take the above example of an
oversubscription of 10-1, which would result in the service provider having
1.5Gb of bandwidth to the internet, not likely. So they usually use the
same type of connection as cable, but oversubscribe it a bit more. So lets
say they have four 45Mb connections, that would be an oversubscription of
1-85.
Enough of the figures don't lie, but liars figure examples. I believe the
most important aspect to consider is the stability and consistancy of the
connection. I have both an internet connection feed as well as a satellite
connection. By far the satellite connection provides a much more stable and
consistant connection than does the internet. Both of them do suffer from
delays during fast markets. Then again is the delay our connection or the
data from the exchange?
Not sure if all my ramblings are going to be helpful, but I figure a few of
you might make it to the end of the message. :) The key is not the
quantity (speed), but the quality (reliable). Satellite wins that contest
imho
Brian
----- Original Message -----
From: "cwest" <cwest@xxxxxxxxxxxx>
To: <omega-list@xxxxxxxxxx>
Sent: Wednesday, August 21, 2002 10:23 AM
Subject: RE: Sattelite datafeed faster than landlines ?
> Non-terrestrial is always slower, but the delay may not be relevant as its
> only a few seconds at the most. However, shared bandwidth is another issue
> with satellites and that can cause considerable delays, relatively.
>
> -----Original Message-----
> From: Robert Linders [mailto:Robert@xxxxxxxxxxxxxx]
> Sent: Wednesday, August 21, 2002 6:01 AM
> To: omega-list@xxxxxxxxxx
> Subject: Sattelite datafeed faster than landlines ?
>
> << File: Clear Day Bkgrd.jpg >> Hi List,
> I seem to have a discussion with a friend of mine who claims that a
> sattelite connection (for instance with S&P Comstock) has a faster
> throughput than a landline (internet ADSL or T1).
>
> I believe that due to the propagation delay (signal travels up and down to
> the sattelite) the landline should "always" be faster !
>
> Any ideas?
> Anybody with experience or maybe who has both ?
>
> Thanks
> Robert
>
> =================================
> Robert Linders
> Orlando
> Robert@xxxxxxxxxxxxxx
> =================================
>
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