A test of the internal circuits of two modems and a telephone link between them by which an operator at one modem causes a test pattern to be transmitted to the other modem which, in turn, decodes it, re-encodes it, and retransmits it back to the testing modem.; 两个调制解调器和一个电话链路之间的一种内部电路测试,操作员在其中一个调制解调器 产生测试图型,传送到另一个调制解调器,依次将它解码,然后重新编码,并发回测试调制解调 器。参阅end-to-end test。