Question: In a Transparent end-to-end Packet-switched Streaming Service (PSS), how does a PSS client in Passive Mode infer the presence of a NAT (Network Address Translation) or Firewall after issuing an SP PLAY request?
Option 1: By receiving an ICMP error message indicating blocked ports.
Option 2: Through direct query to the access system's configuration database.
Option 3: By analyzing TCP handshake failures on alternative ports.
Option 4: If no UDP packets arrive after a short, predefined time interval (e.g., some seconds).
Explanation: In Passive Mode, the client relies on observing network behavior rather than actively probing for NAT presence. The absence of incoming UDP packets following an SP PLAY request within a brief timeframe suggests a NAT or Firewall is blocking packets, leading the client to assume its presence based on empirical evidence from the network's response (or lack thereof).