CUCM-->H323-->PSTN-- Call Flow Wireshark

[HemanthKannan]

Hi All

I was Trying to Capture Wireshark Logs for an Outbound Call on CUCM 

CUCM-->H323-->PSTN--
CUCM - NO Otubound Fast Start Enabled

Why is connect Message Coming after TCS,MSD and OLC Messages.
Please Help me to understand this.

[Jaime Valencia]

If you want to understand the call flow of messages for an H323 call, then you should refer to the standard, you can find plenty of information on how H323 works on google.

[HemanthKannan]

Hi Jaime

Thanks for your response

I found a basic Call Flow examples But still am not clear why TCS MSD OLC are Exchanged before connect message

[moyo oyegunle]

I believe it's because you have H323 Fast start off. Then H245 Capability exchange will occur later in call flow.

Here's a page on the support forum that explains this:

https://supportforums.cisco.com/discussion/9976441/fast-start-vs-slow-start-h323-voip-gateway

Kindly Vote or Mark question as correct if this helps.

[Shadi Shami]

Correct and with fast start you will OLC messages tigether with the setup message.

[Nadeem Ahmed]

I have uploaded a ITU standard which has every deep down and in detailed information about each aspect of H.323 fast start, slow start what all info need to be sent and what not to be. Br, Nadeem Ahmed