通信知识-1ENG(XMPP)

    
  XMPP(Extensible Messaging and Presence Protocol) is an open Standard Protocol developped by Jabber using XML(Extensible Markup Language). The XMPP protocol is more used in IM Development(Instance Messaging) to encrypte the information sends by the server or the client.
This can explain the reason why the Yahoo client can't be connected to the skype server.
We keep asking ourselves why the xmpp choosed the xml. When we look for the characteristics of xml we find that its design goal emphasizes simplicity, generality and usability over the internet what is needed by the IM tecknology and in the same way by the XMPP.
The IM will then use a XMPP agreement to send and receive text or other information.
Here we need to emphasis on the fact that the xmpp developed the xml and is being more and more developed to assure the security and strongness.

The xmpp use two process to exchange information:
     1. Synchronization process(同步流程): In this process, the client needs to have a verification of the authenticity of the message so that it can move to the next step, 

     2. Asynchronous Process(异步流程): For this case the client and the server need the authentification just in the beggining of the connection, for the rest they will keep exchanging datas.

At the end, let's give an example of message delivery scenario:

   Consider [e-mail] needs to send e-mail to [e-mail], in this case the xxx client will send the message to yahoo.com server, the server will verify if the client really belongs to the server. The next step will be that the yahoo.com server will try to get connected to the gmail.com server, if the connection succeed and don't occure any problem, the gmail.com server will find at the end the client yyy to deliver the msg.
Using a schema it will be:
   xxx(client)---yahoo.com(server)---gmail.com(server)---yyy(client).