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1.引言包交换的先驱工作起于大约十年前的AR-PA网[见参考文献(21)],英国国家物理实验室网(23),以及商业网(SITA)和Tymnet(20)等。那些早期的工作表明,无论在实验和运行情况下,包交换技术对于分布式数据通信是非常有效的。今天,几十个全国性的或国际性的、公用的或专用的信息包网络在世界各地已经建成或正在研制。由于信息包技术在地面通信中获得成功的发展,人们正在试验把这一技术用于卫星通信(6)和在地面流动的无线电设备之间的通信(10)。另外,国际电信委员会和用户、厂商组织为了制定访问信息包网络和网络互连标准协议所作出的种种努力也表明:信息包网络已经成功地满足了大多数数据通信用户的需要。
1. INTRODUCTION Pioneering work on packet switching started with AR-PA networks [see reference (21)) about 10 years ago, the National Physical Laboratory Network (23) and SITA and Tymnet (20) . Those early efforts showed that packet switching techniques are very effective for distributed data communications both in experimental and operational situations. Today, dozens of nationwide or international, public or private information networks have been or are being developed around the world. Due to the successful development of packet technology in terrestrial communications, one is experimenting with the use of this technology for communications between satellite communications (6) and ground-based radios (10). In addition, the efforts made by the International Telecommunication Commission and user and vendor organizations to establish a standard protocol for accessing packet networks and networks also indicate that packet networks have successfully addressed the needs of most data communication users.