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Posted by Robert Anderson on February 14, 2005, 12:18 pm
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My small company has ADSL through Pacbell, which we are using for VoIP.
Sometimes you will be talking to someone and they will have trouble hearing
us. The opposite never happens.
We think it is because our upload does not provide us with reliable
bandwidth.
We were thinking that switching to SDSL would help. Any thoughts both on the
problem and whether you think switching to SDSL might help? Is SDSL a
different, more reliable technology? It certainly is priced higher than
ADSL.
thanks.
--
Robert Anderson
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Posted by John Osmon on February 14, 2005, 4:10 pm
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: My small company has ADSL through Pacbell, which we are using for VoIP.
: Sometimes you will be talking to someone and they will have trouble hearing
: us. The opposite never happens.
: We think it is because our upload does not provide us with reliable
: bandwidth.
It certainly sounds like your outgoing link could be congested. Your
ADSL equipment may have counters that you can access that will help you
decide. Look for dropped packets and/or lot of packets being queued to
send.
: We were thinking that switching to SDSL would help. Any thoughts both on the
: problem and whether you think switching to SDSL might help? Is SDSL a
: different, more reliable technology? It certainly is priced higher than
: ADSL.
Reliability for either is probably close to the same, but it sounds like
your problem is related to a *full* pipe rather than an *unreliable* one.
See if your service provider can provide for more upstream bandwidth (as
ADSL or SDSL). That will probably solve your problem.
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Posted by Robert Redelmeier on February 15, 2005, 12:05 am
If you were Registered and logged in, you could reply and use other advanced thread options > My small company has ADSL through Pacbell, which we are using
> for VoIP. Sometimes you will be talking to someone and they
> will have trouble hearing us. The opposite never happens.
> We think it is because our upload does not provide us with
> reliable bandwidth.
Are you sure your uplink isn't saturated? Somebody serving out
pages or P2P? ADSL often underprovides uplink. Sniffer time!
-- Robert
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Posted by Brian LaVallee on February 15, 2005, 9:15 am
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is a temporary fix. More bandwidth fixes everything in the short term.
What you want to implement is QoS, giving your VoIP traffic a higher
priority over all other outbound traffic. A simple TOS bit should be
sufficient, and most VoIP
hard-phones already set the TOS bit to a higher priority.
If the xDSL is your aggregate device, PacBell may not allow you to turn QoS
on in their modem. So you may need another router in front of the xDSL to
use QoS.
Just remember that this will not improve end to end traffic. QoS will be
ignored by any device that is not configured to use it. The priority will
not be used throughout the PacBell network, it will be ignored past the
aggregation point.
> My small company has ADSL through Pacbell, which we are using for VoIP.
> Sometimes you will be talking to someone and they will have trouble
> hearing us. The opposite never happens.
>
> We think it is because our upload does not provide us with reliable
> bandwidth.
>
> We were thinking that switching to SDSL would help. Any thoughts both on
> the problem and whether you think switching to SDSL might help? Is SDSL a
> different, more reliable technology? It certainly is priced higher than
> ADSL.
>
>
> thanks.
>
> --
> Robert Anderson
>
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Posted by Wolfgang S. Rupprecht on February 15, 2005, 6:02 pm
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> If the xDSL is your aggregate device, PacBell may not allow you to turn QoS
> on in their modem. So you may need another router in front of the xDSL to
> use QoS.
Putting a router (or NAT box) in front of the dsl modem won't solve
much. The dsl modem has packet buffers inside it. If your uplink is
saturated, even briefly, this packet buffer is going to be stuffed
with full of other, low-priority traffic. Sure the packets were
ordered when they left the QoS capable router (or nat box), but after
the voip packets got loaded into the dsl modem, the other packets were
stuffed in there until no more fit. The next voip packet that hits
the dsl modem is going to be dropped. If you need QoS on your uplink,
the only place it is going to work is in the last buffer *right*
before your choke-point. That choke point is inside the dsl modem.
Think of it this way, the local router's connection to your dsl modem
is going to be either 10Mbits/sec or 100Mbits/sec. There is always
going to be bandwidth on this link to shove packets at the dsl modem.
The choke point is the dsl uplink which is going to be 128kbits/sec to
600kbits/sec typically. The local router is going to be able to shove
packets in at a much higher rate than they can drain out. The dsl
modem's output buffers for the dsl uplink are going to be packed full.
The only way to do meaningful QoS is to do the final QoS reordering in
the modem itself.
-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/
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