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本文扼要地介绍了公共数据网(PDN)中使用的三层协议即在物理层使用的X.21和X.21bis协议。在数据链路层使用的HDLC协议和在网络层使用的X.25协议。IBM的系统网络结构原来有用的三层协议,二者并不相同。本文提出了三种使SNA可以进入公共数据网的办法,即使用二套协议,在数据链路层进行变换和在会议层进行变换,并且对它们进行了比较。
This article briefly describes the three-layer protocol used in public data networks (PDNs), the X.21 and X.21bis protocols used at the physical layer. The HDLC protocol used at the data link layer and the X.25 protocol used at the network layer. IBM’s original three-tier system network architecture agreement, the two are not the same. This article presents three ways to get SNAs into the public data network, using two sets of protocols, transforming at the data link layer, and translating at the conference layer, and comparing them.