How does VoIP work on non-QoS DSL?
Posted on 2009-12-28
Please help out...
After completing a CCNA VoIP class I'm still confused about a "VoIP over DSL" topic:
1. Why? All throughout my Cisco VoIP class there was a HUGE emphasis on having a QoS - on your WAN side and to have ISP manage the QoS for VoIP and Data. It was to the point where it almost was a LAW that (nobody should ever set-up a VoIP system without having VoIP QoS implemented by their ISP) And god forbid you set-up a VoIP phone system on anything but a dedicated QoS managed T1 circuit because you can't have VoIP calls go through the "Public Internet" which would ruin any VoIP quality...
After truly believing these concepts which I learned in the classroom, I go out to the real world and see a bunch of very CHEAP VoIP providers such as Access Line etc. who claim to provide VoIP service on an ADSL home-grade connection from ANY ISP, without ANY QoS. AND their pre-sales engineer telling me that QoS is not necessary on a WAN line and that they have 100k customers using it fine on DSL lines (Especially if a second DSL line only used for VoIP, and not both Voice and Data). And that QoS is NOT needed because of something related to 'Windowing', and that TCP/IP can figure it all by itself by adjusting the window size...
Was I mislead in Cisco VoIP curriculum or these "CHEAP PBX" guys are just getting lucky with good quality ADSL lines?
2. Why is that in Cisco VoIP class it's SO emphasized to have VLANs on your LAN unconditionally, but the "CHEAP PBX" guys laugh at it and say that VoIP traffic is so small that unless you're using a HUB or your LAN is overloaded, the VOIP traffic will be just fine and doesn't need to be prioritized, nor any QoS on LAN is needed!?
Again, I feel that I was mislead by Cisco's VoIP curriculum and makes me look stupid in front of $9.99 / month / line "Cheap PBX guys".
Please share your knowledge on this topic. It's been bothering me for a while now :)