This is a network protocol which enables a client in a NAT (or multiple NATs) to find out its public address, the type of NAT behind it and the internet side port associated by the NAT with a particular local port and this whole process aids to set up UDP communication between two hosts that are both behind NAT routers. STUN stands for Simple Traversal of UDP (User Datagram Protocol) through NATs (Network Address Translators).

Protocol overview

STUN is a client-server protocol. Any VoIP phone or software package includes a STUN client, which sends a request to the STUN server. As a reply the public IP address of the NAT router and the port was opened by the NAT to allow incoming traffic back in to the network is sent to the STUN client. Such a response also helps the STUN client to identify the NAT being used as different types of NATs handle incoming UDP packets vividly. Its compatible with Full Cone, Restricted Cone, and Port Restricted Cone. (Restricted Cone or Port Restricted Cone NATs, allows packets from the endpoint through to the client from the NAT once the client has send a packet to the endpoint). Symmetric NAT (also known as bi-directional NAT) which is frequently found in the networks of large companies does not work with STUN as the IP addresses of the STUN server and the endpoint is different, and therefore the NAT mapping the STUN server is different from the mapping that the endpoint uses to send packets through to the client. Network address translation could give you more information on this.

After the client discovers its external addresses communication with its peers occurs. When the NATs are full cone,either side can initiate communication and if they are restricted cone or restricted port cone both sides must start transmitting together. The techniques described in the STUN RFC does not necessarily require using the STUN protocol; they can be used in the design of any UDP protocol. STUN comes in handy in the cases of Protocols like SIP which use UDP packets for the transfer of sound/video/text signaling traffic across the Internet. As both endpoints are often behind NAT, a connection cannot be set up in the traditional way. The STUN server communicates on UDP port 3478 but the server will hint clients to perform tests on alternate IP and port number too (STUN servers have two IP addresses).

Hyper Transport Technology

The demand for faster processors, memory and I/O is a familiar refrain in market applications ranging from personal computers and servers to networking systems and from video games to office automation equipment. Once information is digitized, the speed at which it is processed becomes the foremost determinate of product success. Faster system speed leads to faster processing. Faster processing leads to faster system performance. Faster system performance results in greater success in the marketplace. This obvious logic has led a generation of processor and memory designers to focus on one overriding objective - squeezing more speed from processors and memory devices. Processor designers have responded with faster clock rates and super pipelined architectures that use level 1 and level 2 caches to feed faster execution units even faster. Memory designers have responded with dual data rate memories that allow data access on both the leading and trailing clock edges doubling data access. I/O developers have responded by designing faster and wider I/O channels and introducing new protocols to meet anticipated I/O needs. Today, processors hit the market with 2+ GHz clock rates, memory devices provide sub5 ns access times and standard I/O buses are 32- and 64-bit wide, with new higher speed protocols on the horizon.Increased processor speeds, faster memories, and wider I/O channels are not always practical answers to the need for speed. The main problem is integration of more and faster system elements. Faster execution units, faster memories and wider, faster I/O buses lead to crowding of more high-speed signal lines onto the physical printed circuit board. One aspect of the integration problem is the physical problems posed by speed.

Hyper Transport technology has been designed to provide system architects with significantly more bandwidth, low-latency responses, lower pin counts, compatibility with legacy PC buses, extensibility to new SNA buses, and transparency to operating system software, with little impact on peripheral drivers.