Nicholas Matthews Tue, 09/15/2009 - 08:33
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Fast start allows for H323 media connections to be started at the beginning of a call. This is helpful for ringback scenarios, and also reduces the amount of time calls take to establish media. Especially helpful over satellite links. H245 is still negotiated later, but the actual media can be done earlier through H225 messages.

Slow start is the older method, and requires a full h245 exchange before the media is negotiated. H245 is fully responsible for setting this up, and takes more RTT to set up than fast start.

Generally, if you're on a LAN, or in most networks, you probably will never be able to tell a difference. Unless you have high latency networks (satellite, low-speed WAN), or you need to do some type of interoperability or workaround for a bug, you will probably not care if it is fast start or slow start.

Gateways do fast start by default, and CUCM requires an MTP for H323 gateways to do outbound fast start. CUCM does not require MTPs for inbound fast start, but it is not enabled by default.




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