I'm at a site that has Layer 3 Cisco switches and routers end to end. Cisco IP phones plug directly into Layer 3 switches with various routers in the core.

1) If all connections are Layer 3 do I need to concern myself with trusing COS? I would trust DSCP in this case yes?

2) Cisco phones by default send voice rtp audio with DSCP marked as EF, is that correct? If not, I know how to create policy-maps and reclassify it. My thought was it is already classified as high as possible.

3) I've read that QoS must be end to end or you don't really have a full implementation, as in the one device your traffic passes through that is not performing QoS will likely be running FIFO or WFQ, which do not give precedence to class based traffic. So in theory I need to implement CBWFQ or LLQ on every Layer 3 device end to end that RTP audio will touch. Do I have this correct?

4) If the voice traffic has the potential to travel to most Layer 3 devices in the network as it travels between the Call Manager and phones, I need to apply QoS outbound on each Layer 3 interface that is likely to be in a voice path yes?

Sorry, I'm a newb, I understand it in theory but I still hit the wall on occassion with my light saber while blindfolded.

Thanks, Mike