H.323 and SIP are the application control protocols of multimedia communication developed by ITU and IETF, respectively, mainly used in IP phones. H.323 protocol earlier, its main design ideas are based on traditional telephone mode. And SIP The protocol has been submitted later, it draws on the design idea of the HTTP protocol. At present, a large number of H.323 protocols in the IP phone, but in a long time, SIP replaces H.323 is inevitable, so in the current transition period H. The interoperability of the two major agreements between 323 and SIP seems important. Although they come from two different organizations, they have different design ideas, but the content is almost the same, always around the various signaling of the phone, just achieve The way is different. This article introduces a development idea of H.323 and SIP internet access.
Since it is the gateway of H.323 and SIP, it must support both H.323 and SIP agreements. The main task of the gateway is to be responsible for the conversion of H.323 and SIP signaling. So the gateway is mainly composed of 3 parts: H.323 Endpoint, SIP UA, Translator.
For example: H.323 Call SIP phone process (for gateway inside): H.323 EP section receives a call setup message, then handed this setup message to Translator, TRANSLATOR Extracts some important parameters in this setup message, for example:: Source address, destination address, serial number, identifier, etc.
Of course, this is just the simplest mode, and a gateway is designed to support the following four modes:
The following detailed explanation: The following figure is the two SIP terminal call flows that have no proxy servers.
The figure below is two H.323 terminal call flows without registered gatekeepers.
This is initiated by the H.323 terminal.
Let's take a look at the SIP terminal to initiate a call through the gateway.
By observing the above flow chart, it can be easily seen that the GW sends a setup message immediately after receiving the INVITE message, and vice versa. So you can get the following H.323 and SIP message correspondence: H.323 Message SIP Message SETUP INVITECALL Proceeding 100 TryingAlerting 180 RingingConnect 200 Okrelease Complete Bye
It is worth noting that SETUP and INVITE are not one by one in the case of a non-fast call, in fact, the above-mentioned correspondence can only correspond to some moments, for example, after the SIP UA is sent 180 rings, the operator decides to answer the phone. 200 OK corresponds to Connect.
Therefore, in this type, consider the most complex cases to join Proxy and GK, and the call flow is as follows:
