P2P穿透打洞文件传输源码及例子

Internet Engineering Task Force Yunhong Gu Internet Draft University of Illinois at Chicago Intended status: Informational April 12, 2010 Expires: October 12, 2010 UDT: UDP-based Data Transfer Protocol draft-gg-udt-03.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 15, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document describes UDT, or the UDP based Data Transfer protocol. UDT is designed to be an alternative data transfer protocol for the situations when TCP does not work well. One of the most common cases, and also the original motivation of UDT, is to overcome TCP's Yunhong Gu Expires - October 12, 2010 [Page 1]  UDT April 12, 2010 inefficiency in high bandwidth-delay product (BDP) networks. Another important target use scenario is to allow networking researchers, students, and application developers to easily implement and deploy new data transfer algorithms and protocols. Furthermore, UDT can also be used to better support firewall traversing. UDT is completely built on top of UDP. However, UDT is connection oriented, unicast, and duplex. It supports both reliable data streaming and partial reliable messaging. The congestion control module is an open framework that can be used to implement and/or deploy different control algorithms. UDT also has a native/default control algorithm based on AIMD rate control. Yunhong Gu Expires - October 12, 2010 [Page 2]  UDT April 12, 2010 Table of Contents 1. Introduction...................................................4 2. Packet Structures..............................................5 3. UDP Multiplexer................................................8 4. Timers.........................................................8 5. Connection Setup and shutdown..................................9 5.1 Client/Server Connection Setup............................10 5.2 Rendezvous Connection Setup...............................10 5.3 Shutdown..................................................11 6. Data Sending and Receiving....................................11 6.1 The Sender's Algorithm....................................11 6.2 The Receiver's Algorithm..................................12 6.3 Flow Control..............................................15 6.4 Loss Information Compression Scheme.......................15 7. Configurable Congestion Control (CCC).........................15 7.1 CCC Interface.............................................15 7.2 UDT's Native Control Algorithm............................16 Security Considerations..........................................18 Normative References.............................................18 Informative References...........................................18 Author's Addresses...............................................19 Yunhong Gu Expires - October 12, 2010 [Page 3]  UDT April 12, 2010 1. Introduction The Transmission Control Protocol (TCP) [RFC5681] has been very successful and greatly contributes to the popularity of today's Internet. Today TCP still contributes the majority of the traffic on the Internet. However, TCP is not perfect and it is not designed for every specific applications. In the last several years, with the rapid advance of optical networks and rich Internet applications, TCP has been found inefficient as the network bandwidth-delay product (BDP) increases. Its AIMD (additive increase multiplicative decrease) algorithm reduces the TCP congestion window drastically but fails to recover it to the available bandwidth quickly. Theoretical flow level analysis has shown that TCP becomes more vulnerable to packet loss as the BDP increases higher [LM97]. To overcome the TCP's inefficiency problem over high speed wide area networks is the original motivation of UDT. Although there are new TCP variants deployed today (for example, BiC TCP [XHR04] on Linux and Compound TCP [TS06] on Windows), certain problems still exist. For example, none of the new TCP variants address RTT unfairness, the situation that connections with shorter RTT consume more bandwidth. Moreover, as the Internet continues to evolve, new challenges and requirements to the transport protocol will always emerge. Researchers need a platform to rapidly develop and test new algorithms and protocols. Network researchers and students can use UDT to easily implement their ideas on transport protocols, in particular congestion control algorithms, and conduct experiments over real networks. Finally, there are other situations when UDT can be found more helpful than TCP. For example, UDP-based protocol is usually easier for punching NAT firewalls. For another example, TCP's congestion control and reliability control is not desirable in certain applications of VOIP, wireless communication, etc. Application developers can use (with or without modification) UDT to suit their requirements. Due to all those reasons and motivations described above, we believe that it is necessary to design a well defined and developed UDP-based data transfer protocol. As its name suggest, UDT is built solely on the top of UDP [RFC768]. Both data and control packets are transferred using UDP. UDT is connection-oriented in order to easily maintain congestion control, reliability, and security. It is a unicast protocol while multicast is not considered here. Finally, data can be transferred over UDT in Yunhong Gu Expires - October 12, 2010 [Page 4]  UDT April 12, 2010 duplex. UDT supports both reliable data streaming and partial reliable messaging. The data streaming semantics is similar to that of TCP, while the messaging semantics can be regarded as a subset of SCTP [RFC4960]. This document d