[asterisk-users] Moving from DSL to T1

[Hans Witvliet]

On Sun, 2010-09-12 at 15:32 -0700, Kevin Keane wrote:
> 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.

You consider 40ms extremely good???
Either your isp or youself must have a considerable number of hops to
cross.
At home (cheap abo) i got following transit delays (round trip)
national 15 ms
international 17-35
transatlatic or satelite is above 200ms

At work
national 3-4 ms
international 20-25 ms

 

> Latency also is the reason VoIP does not work at all over satellite
> connections even though they tend to have plenty of bandwidth.
Please define "does not work at all over satellite" ???
Sure, it is not studio HIFI quality, but is th same quality as you get
from official commercial telco providers.
We still have voip over S-band and X-band satelites running NOW between
NL and afghanistan. All the people are more than satisfied.


> 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.


Other big advantage of T1 above (commercial end-user grade) DSL lines, is that you have a higher upload bandwith
Theyoften sell it as 1Mb up, but most of the time you'll have to be
satisfied with the half. But with strong compression that is still more
than enough.