Q.931 is an
ISDN connection control
protocol, roughly comparable to
TCP in the
Internet
protocol stack. Q.931 doesn't provide flow control or perform retransmission,
because the underlying layers are assumed to be reliable and the
circuit-oriented nature of ISDN allocates
bandwidth in fixed increments of 64
kbps. Q.931 does manage connection setup and breakdown. In
H.323 scenario, this
protocol is encapsulated in TCP and sent to
port 1720.
