[mythtv-users] Way OT: High-speed Data Service Delivery

[Jason Long]

Apologies to the list for dragging this out..


On 7/11/11 10:52 PM, Jay Ashworth wrote:
> ----- Original Message -----
>> From: "Jason Long"<jlong at jasonlong.com>
>> On 7/11/11 7:35 PM, Jay Ashworth wrote:
>>> Though, these days, it's almost never actually a T-3 bringing you
>>> your DS-3/STS-1. It usually fiber.
>> That's not correct. A DS3 is delivered via copper coax.
> 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.
>
>>            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.
> 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

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.

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".

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.

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
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


Back to mythtv discuss?

Jason


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