H323 slow start and fast start .. With Cisco IOS gateway configuration

Before discussing on this topic we must be aware of how the basic call flow occurs on h323 protocol.
here is the basic call signalling that happens with h323

here the the h225 and h245 signalling uses two different TCP connection.

In case of h323 fast start the h245 steps which is the capability and media negotiation steps occurs in the setup message of h225 step.

In normal scenario as per the above diagram can be considered as slow start as h245 negotiation is occurring with separate TCP connection .

so with fast start few message transaction occurs compare to slow start.

Now lets focus on the configuration for the same in cisco IOS gateway.

we can configure this either globally or dial peer level.

In case of global level.

1. Go to configutaion mode

2. Go to voice service mode. with command " voice service voip"

3 Configure the command "h323 call start slow" to revert to fast start configure "h323 call start fast"


In case of individual dial peer level


1. Go to configutaion mode

2. Create a Voice class using command " voice class h323 tag "

3. under the voice class command configure 'call start slow"

4. use the voice class command under the the voip dial peer  command 



Done...:-)