[Asterisk-Users] Should I choose DSL @ 1.5 or a full T1?

[Dave Weis]

On Mon, 13 Jun 2005, Damon Estep wrote:
> You guys have me second guessing my training and experience in this
> area, so;
> 1. If I am wrong I apologize to the group.
> 2. I have been trying for a few minutes to find confirmation either way.
>> From what I know about the modulation techniques used by DSL (DMT, CAP,
> QAM) it is impossible for the transceiver in the device to transmit and
> receive at the same time (unless there is discreet "channels" for each
> path and a very good transceiver).

There are three frequency ranges on ADSL, the voice portion (lowest), the 
upstream (middle), and the downstream (highest). They are split into 
different frequencies so filters can pick out the up and down. It's 
capable of full duplex, but as the downstream speed increases, the big 
differential causes the issue below.

> Can anyone provide a more logical explanation of why the outbound
> latency on every DSL modem tested increases with inbound traffic? Even
> at rates well below the maximum data rate, Not the case on a T1. My
> explanation is that the additional latency is due to packet scheduling
> and queuing mechanisms required by the technology.

That is usually due to the TCP acks getting delayed in transit, making the 
other end wait to send the next packets. On a symmetrical circuit you 
don't see it as much, but the asymmetry on ADSL makes it more apparent.

dave


>
> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com
> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Wiley
> Siler
> Sent: Monday, June 13, 2005 6:14 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: RE: [Asterisk-Users] Should I choose DSL @ 1.5 or a full T1?
>
> Are you sure?  Everything I have seen says SDSL = Full Duplex.
> That being achieved by dropping the pair that provided voice and using
> it for signalling.
>
> "Where ADSL utilizes unoccupied frequencies and averts conflict with
> analog voice frequencies, SDSL takes over the whole line. SDSL
> eliminates analog voice capabilities in favor of full-duplex data
> transmission. No splitter, no analog voice-nothing but data. As a decent
> alternative to T1, SDSL has gotten a fair amount of attention from
> Competitive Local Exchange Carriers."
>
> Excerpt from....
> http://www.isp-select.com/SDSL.htm
>
> Cheers,
> Wiley
>
>
>
>
>
>
> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com
> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Damon
> Estep
> Sent: Monday, June 13, 2005 4:55 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: RE: [Asterisk-Users] Should I choose DSL @ 1.5 or a full T1?
>
> You are aware that DSL (even SDSL) is half duplex and a T1 is full
> duplex, right?
>
> 1.5m sdsl can only do 768 sustained duplex, or 1.5 out 0 in, or 0 out
> 1.5 in. a T1 will do 1.5 in and 1.5 out sustained.
>
> This is due to a separate transmit and receive path on a t1 and a shared
> path on sdsl.
>
> The s in sdsl means symmetrical, not duplex, that is that the signaling
> rate is the same in either direction, but still half duplex.
>
> For VoIP a t1 is worth double what a 1.5 sdsl is because of the duplex
> nature of the traffic, unlike most internet that is download-centric.
>
> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com
> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Wiley
> Siler
> Sent: Monday, June 13, 2005 9:43 AM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: RE: [Asterisk-Users] Should I choose DSL @ 1.5 or a full T1?
>
> Speakeasy SDSL Is 1.5 Megs, is business class (so you get an SLA) and
> only costs around $100 per month.
>
> W
>
> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com
> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Robert
> Goodyear
> Sent: Friday, June 10, 2005 7:02 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [Asterisk-Users] Should I choose DSL @ 1.5 or a full T1?
>
>
> On Jun 10, 2005, at 6:38 PM, Michael Welter wrote:
>
>> Barton Fisher wrote:
>>> I'm looking to expand my bandwidth for my Asterisk PBX.  Why should I
>
>>> choose a T1 over DSL for my asterisk server?  I found someone
>>> offering T1's for $290 a month + Loops or 3 Meg for $561 a month +
>>> Loops.  Is this a good deal?
>>>  Thanks
>>>  Bart
>>> ---------------------------------------------------------------------
>>> -
>>> --
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>> Where are you located?  What CLEC gives you a T-1 for $290?
>>
>
> FWIW I provisioned a PRI and a DS-1 for $300 each. Don't know if I'm
> getting a break for having a voice and a data circuit broken out from
> one fiber drop, but that's what I'm paying here in Orange County. Also,
> I had a business cable modem before, which was *allegedly* not shared
> for business customers (suspicious) and the throughput was a roller
> coaster, as was the latency. The DS-1 cleared all that up.
>
> /rg
>
> Robert Goodyear
> Brand Up LLC
> http://www.brand-up.com
>
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-- 
Dave Weis             "I believe there are more instances of the abridgment
djweis at sjdjweis.com   of the freedom of the people by gradual and silent
                       encroachments of those in power than by violent
                       and sudden usurpations."- James Madison