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.
In comp.dcom.voice-over-ip Robert Anderson wrote: : 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.
Increasing your outgoing bandwidth with SDSL or a speed change of your ADSL 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.
Personally, I've found that using VoIP through a provider that's a company other than the one you also use for access makes for unreliablity. To explain, I have VoIP through Time Warner, who's also my cable and ISP provider. My VoIP connection is flawless and the quality is great.
A person who I work with on projects has a VoIP connection through another provider and his connection is garbage. He cuts out continually and has to call me back on a cell phone.
I realize this is only one example, but I really do think that quality is the reason all the forecasts are saying that cable providers are going to come to dominate VoIP. They have the network and connectivity, along with technical expertise, to make it happen.
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.
No. Putting a router (REAL router, not a nat box) in there WOULD resolve the issue if it was set up properly. a decent router is going to have several megs of cache and the ability to specify the ougoing line rate. So if the dsl line has a 384kbps uplink speed, you set the router to limit outgoing packets to that rate. Then the router only sends 284kb of data per second to the dsl modem. You would likely get some of the lower priority packets dropped, but of cours ethat is exactly what you want to have happen in this case.
What you propose doesn't allow you to send 384kbps out of your
384kbit/sec DSL connection. Using your own numbers you end up only getting 284kb -- if it works.
Like I said, if you want to have your voip packets moved to the head of the queue when the uplink is saturated (eg. 384kbits are being sent up the 384kbit/sec link) then you'd better have the TOS logic right before the choke point.
If you want to keep the modem unsaturated by throwing away 1/4 of your bandwidth then we clearly aren't talking about using the whole link are we? We are talking about some hack that only lets you use 3/4s of it.