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Getting SIP through firewalls and NATs
SIP proxy as firewall controller or NAT ALG
much easier than H.323:
– single protocol vs. H.225.0 + H.245
– SDP
H.245.0
– single-stage negotiation
– no need to maintain TCP connections during call
need to understand INVITE, ACK and BYE
if final SDP in success ACK: ACK only
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