本技术报告比较了SONET（同步光网络）和SDH（同步数字体系）之间的技术差异，如与这两种体系相关的适用标准所述。它只涉及T1X1成员提出的问题。2工作组（数字传输网络架构），因此，不能保证它涵盖了两者之间的所有差异。此外，应注意的是，所描述的差异是在起草和批准本技术报告时所理解的。 由于两种数字层次结构的标准都在不断发展，本技术报告中描述的一些差异可能不再存在，而其他差异可能已经出现。

This Technical Report provides a comparison of the technical differences between SONET (Synchronous Optical NETwork) and SDH (Synchronous Digital Hierarchy) as described in the applicable standards pertaining to the two hierarchies. It covers only those issues raised by members of the T1X1.2 working group (Digital Transmission Network Architecture), therefore, no assurance can be given that it covers all differences between the two. Furthermore, it should be noted that the differences described are as understood at the time of this Technical Report was drafted and approved. Since the standards for both digital hierarchies continue to evolve, some differences described in this Technical Report may no longer exist, while others may have arisen.