[asterisk-users] Moving from DSL to T1

[Kevin Keane]

In terms of telephony, a T-1 can make a huge difference over DSL. DSL gives you a lot of raw bandwidth, true, but for voice that really doesn't matter all that much. Voice calls only take a relatively small amount of bandwidth anyway; you can fit dozens of concurrent calls into a DSL or T-1. When used strictly for telephony (non-VoIP), a T-1 is designed for 24 concurrent calls, each one takes up 56kbit. For VoIP use, most providers tell you that a phone call takes up about 80kbit/s.

What really matters is the latency, and T-1 is a huge improvement over DSL in that area. The easiest way to measure latency is the ping time to a server that is "close to you" Internet-wise. A DSL has latencies of between 40ms (if it's extremely good and not too many other people are using it) and 1000ms (if there is a problem somewhere). A good T-1 may have latencies as low as 5 ms or so. Also, with a T-1 the bandwidth is guaranteed and bidirectional. With a DSL line, you may get burstable bandwidth - you don't actually have that bandwidth, you just get to compete for excess bandwidth with your neighbors.

Latency also is the reason VoIP does not work at all over satellite connections even though they tend to have plenty of bandwidth.

To answer the OP's question: assuming that you will be using the T-1 for mixed VoIP and data (the most likely scenario in this case), a T-1 is really not much different from a DSL line. Both provide you with IP connectivity. Just make sure that QoS is set up correctly on your router and firewall to give priority to VoIP calls. If you are using VoIP and DSL concurrently and your router/firewall supports that configuration, you may also need to modify routing tables to make sure calls go in and out over the correct link.

From: asterisk-users-bounces at lists.digium.com [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of jon pounder
Sent: Sunday, September 12, 2010 12:07 PM
To: asterisk-users at lists.digium.com
Subject: Re: [asterisk-users] Moving from DSL to T1

On 09/12/2010 02:34 PM, Kyle Kienapfel wrote:


Really it depends on what the capabilies of dsl were assuming you are just using both dsl and t1 as internet connections.

a dsl that has close to 1mb/sec out and 10mb/sec or so in, is going to be pretty comparable to a t1 actually so not really sure why you would make that switch in the first place.

as long as there is a static ip for the server on either, you wouldn't see much difference. (t1 is actually usually delivered over hdsl which is basically the same thing as adsl except the bandwidth is more symetric.)

if you have a low speed dsl, such as like 128kb/sec up and 512 down you'll see much faster performance, but again not much big diff if both are just internet connections.

This is also assuming your carrier doesn't particularly grossly oversell either service. You need to make sure you are getting transit, not burstable, or quality may suffer depending on how its oversold.




On Sun, Sep 12, 2010 at 10:43 AM, Richard Stuppi <richard at stuppi.com<mailto:richard at stuppi.com>> wrote:
I work in a small office and have fallen into the role of network support based on knowing enough about networking to be dangerous.

Our office is moving from DSL to a T1.  Were using Asterisk as our PBX and I'm looking for hints or resources that might help me make the transition as error free as possible.

Are there well known gotchas that I shoud be aware of?

Thanks in advance,

Richard Stuppi
richard at stuppi.com<mailto:richard at stuppi.com>
626-221-8010


You should be more specific,
A)Are you switching from voip over DSL to voip over T1
B) ... or using the T1 for phones?
C)Are you switching from analog lines + DSL to just a T1 for voice and data?

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