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Apologies to the list for dragging this out..<br>
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On 7/11/11 10:52 PM, Jay Ashworth wrote:
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cite="mid:20428781.1295.1310449954159.JavaMail.root@benjamin.baylink.com"
type="cite">
<pre wrap="">----- Original Message -----
</pre>
<blockquote type="cite">
<pre wrap="">From: "Jason Long" <a class="moz-txt-link-rfc2396E" href="mailto:jlong@jasonlong.com"><jlong@jasonlong.com></a>
</pre>
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<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">On 7/11/11 7:35 PM, Jay Ashworth wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Though, these days, it's almost never actually a T-3 bringing you
your DS-3/STS-1. It usually fiber.
</pre>
</blockquote>
<pre wrap="">
That's not correct. A DS3 is delivered via copper coax.
</pre>
</blockquote>
<pre wrap="">
Not quite.
A DS-3 is a *bit stream* (equivalent in speed, though not necessarily
in framing, to an STS-1) that has traditionally been delivered over dual
coaxes (a "T-3") to customer facilities, yes.
If you can get a LEC to deliver you a *newly installed* copper T-3
to you these days, my hat is off to you. If they have to do all that
engineering and trenching anyway, I guarantee you they will be putting
fiber in the dirt, and the only thing that will be a physical copper
T-3 will be the 10 or 20 feet from their side of your room to yours...
assuming you cant take delivery on 100BaseT these days for some reason.
</pre>
<blockquote type="cite">
<pre wrap=""> Sure, once your bits hit that fiber they travel close to the
speed of light, but your DS3 signal still only allows you to transmit
bits onto the wire at a line rate 44.54Mbps (after signaling
overhead), so it's a moot that fiber is even involved.
</pre>
</blockquote>
<pre wrap="">
Not if you're the one installing it, it's not. I put in a copper T-3 and
all those repeaters, and that's *all* I can shove down it. If I give
you fiber, even if the handoff from my mux to your gear is coax, my mux can
do a *lot* more stuff. Looking from the carrier side, there, in case I
wasn't clear.
My last job, I took a 10baseT Ethernet handoff from Level3... and their
physical delivery to me came out of a mux with OC-12 SONET on the back of
it -- 622Mbps to the building, to give me 10.
No, no one's installing T-3 *distribution* services anymore, so far as I
know.
Cheers,
-- jra
</pre>
</blockquote>
<br>
Well, you eliminated a chunk of my original message which makes it
look like I said something that I didn't, and prefaced your email
based on that. In context, I said fiber from LEC to prem via OCx,
terminating to a MUX, where services could be provisioned and handed
off to customers.. A DS3 is handed off via copper coax (not fiber).
I never implied pulling copper from LEC to customer.. and if you
have 10baseT, it's not a DS3 anymore. <br>
<br>
My point though is that fiber doesn't magically make a DS3 capable
of serializing bits onto a wire any faster.. Further to my point is
that since fiber propagates bits at ~speed of light, the delay
introduced is negligible when calculating an answer to the question
"How long to transfer CentOS over a DS3". <br>
<br>
To answer the question, based on serialization delay alone, for a
DS3 w/out any L2-L7 protocol overhead, it would take ~17 minutes to
transfer CentOS 5.42G ISOs. After adding in protocol overhead for IP
and TCP it would take another 30 seconds. Then there is TCP slow
start and sliding windows to account for, packet loss,
re-transmissions, and L2 framing overhead, application layer
overhead, queuing delays and current circuit utilization. The fact
that fiber is even involved is *largely* insignificant for
calculating a sufficiently accurate answer to the question.<br>
<br>
<small>5.42G (CentOS) = 5,819,680,686 bytes = 46,557,445,489 bits /
44,540,000 bits/s (DS3) = 1045 sec / 60 sec = 17 minutes<br>
5,819,680,686 bytes (CentOS) / 1500 byte MSS = ~3,879,787 packets
* (20B IP + 20B TCP) = 155,191,480 bytes = 1,241,531,840 bits /
DS3 = 27 seconds<br>
<br>
</small><br>
Back to mythtv discuss?<br>
<br>
Jason<br>
<br>
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