I am in the process of deploying VOIP at a number of office locations. My initial efforts have been somewhat disappointing, due to voice quality problems.
I am trying to get a better understanding of how SIP works, so I can figure out where the network bottlenecks are that are causing my voice problems.
Does anyone know any good links to a detailed technical explanation of how calls are handled by typical VOIP providers (Vonage, Broadvoice, etc...)? I am particularly interested in the question of how SIP proxies work (i.e. does all the voice traffic flow thru the proxies, or do they just initiate sessions and the two VOIP endpoints communicate directly). Also, how do SIP terminal adapters work when they are located behind NAT routers?