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what is h.245?

  • This topic has 3 replies, 1 voice, and was last updated 22 years ago by ksabc.
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  • #21827

    where can i find info on h.245

    Tom Howard

    You can download the H.245 specification from the I.T.U.

    H.245 is part of the H.323 protocol suite, although it is a protocol in its own right. It is used to negotiate the setup of multimedia channels, allowing two ends to compare their capabilities and open media channels between each other.


    There is a Training CD offered by on H.323 and will be a lot more useful than the ITU site.


    H.245 is used for exchange the codec/function ability each endpoint owned and decide what Codec/application need start in this IP call;

    Audio Codec example : G.723.1, G.729A, G.711, NetCoder, GSM 6.10 or

    Application Example : T.38 Real-Time Fax, T.120 Shared Board etc.

    Most common used is G.723.1 and G.729A in VOIP Call;

    in h.323 V2, there have Fast Start mode, means no H.245 session exist in the call, replaced with a simple and fast message embedded in the H.225 Q.931 SETUP/ALERTING/CallProgress etc. mesages to fast the connection speed, you know in normal h.245 start mode, there have about more than 10 messages exchanged between two h.323 endpoint, if the internet isn’t fast, it will take about 3-10 seconds to establish the voice connection, so currently Fast Start mode is a standard setting in most gateway;


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