Firstly outlines the origin,working mechanism and types of NAT;then analyzes the problem of NAT traversal in P2PSIP system;and proposes an STUN+TURN scheme based on the research of several NAT traversal methods,while describes it in detail on the foundation of extension of SDP.

By importing the Simple Traversal of UDP through NAT(STUN) protocol, the mapped relation of IP addresses and ports are obtained, and the content in SIP and Session Description Protocol(SDP)messages are changed to ensure the communication connection, and then to realize the NAT traversal.

The idea of hierarchy protocol description is proposed.

However, it is less to model and evaluate the field communication systems by Petri Nets, and there is no example about both realizing field communication and evaluating its system performance by the protocol description of Petri Nets.

The basic concepts of protocol specification and verification are presented briefly, and the basic ideas are given by means of examples with respect to the construction of specifications for implementation and protocol verification.

We propose a top-down design approach which specify desired global behaviors with a conversation protocol,after we analyzed the drawback of the bottom-up approach,and then verify whether the global protocol satisfy the preset system goals.

On the basis of analysis of features of Web service,this paper takes the example of BPEL4WS language to introduce the conversation protocol based on colored Petri net and corresponding method for Web composition service designing.

The notion of conversations,and their associated conversation protocols,as abstract representations to be used to characterize interaction between agents has been discussed in the agent community for several years now.