The matching of packets by rules is connection-based, known as Stateful Packet
Inspection (SPI), using the Router’s firewall mechanism. Once a packet matches a
rule, all subsequent packets with the same attributes receive the same QoS param-
eters, both inbound and outbound. Connection-based QoS also allows inheriting
QoS parameters by some of the applications that open subsequent connections.
For instance, QoS rules can be defined on SIP, and the rules will apply to both con-
trol and data ports (even if the data ports are unknown). Applications that support
such inheritance have an ALG in the firewall. They are:
• SIP
• MSN Messenger/Windows Messenger
• TFTP
• FTP
• MGCP
• H.323
• Port triggering applications
• PPTP
• IPSec
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