Jan 27, 2009

QoS curveball

This is one of those random head scratchers that can frustrate you for a day, and if you are lucky enough to solve the mystery, make you go "What the hell!!??".

We have a hybrid VOIP system, which basically connects existing POTS infrastructure to IP Gateways handling inter-branch communication on IP infrastructure. We installed our first pure IP phones at a new branch last week. Unfortunately we had to connect these phones to a very basic switch. The telecomms company involved with the installation gave our IT Dept a call, saying they cannot access the IP phone's web interface from a PC connected on the same switch. Huh? Ping? Nope. Ok try another workstation on the same switch. Success. Huh? Try first workstation again. Nope. WTF!!! Try from a server on another switch at the same branch. Success. Try from the router connected to that same switch. FAIL. Damn....

com problem

We were baffled. To cut a long story short, I managed to get comms up and running after disabling Layer 2 QoS on the Siemens admin interface. 


I dont know how this will affect voice quality yet. In a low volume environment such as ours I'm sure it should be just fine. The other option is of course to buy a proper QoS switch....
The thing is, I still cant figure out why certain workstations (standard XP Pro) were able to communicate with the IP phone while others couldn't. Maybe someone has can shed some light?

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