All, Why section 5.1 is an author's impression: Statement: "SONET and SDH were defined as competing standards" Fact: SONET was developed first by ANSI based on the 24 channel PDH hierarchy existing in North America and Japan. The basic rate based on DS3. Some time later ETSI developed SDH based on the 30 channnel PDH deployed in Europe. The basic rate based on E4 (3x DS3). To be able to deploy SONET and SDH worldwide the regional SDO experts came together in ITU-T to define a frame structure and a frame-rate that would allow interconnection of SONET and SDH. A compromise was agreed and approved in an ITU-T meeting in Seoul in 1988. Statement: "Significant confusion resulted from this situation." Fact: The result of the compromise is documented in ITU-T recommendation G.707 which includes the frame definition and frame-rates, and documents how SONET and SDH can interconnect. Statement: "Equipment manufacturers needed to select the market segment they intended to address. The cost of chipsets for a limited market increased. Fact: Most equipment vendors did/do sell their equipment in both regions. I was involved in chip designs for SONET/SDH in several companies, they all support SONET and SDH in a single chip, and the selection is a matter of provisioning, the addition cost to support both was minimal (single chip: higher volume = lower cost) Statement: "Service providers needed to consider the merits of the two standards and their long-term role in the industry when examining their investment options. Fact: Because the regions or applicability of SONET and SDH are well known SPs do not have to make this consideration. Statement: "Only a limited number of equipment manufactures were available for selection." Question: What do you consider a limited number? Statement: "As SONET was considered to be the variant, interworking had to be performed before the SDH-based segment was reached." Fact: SONET is *NOT* a variant it is equivalent to SDH. The reason for placing the interconnection functionality on the SONET side was that in a previous agreement on interconnection the functionality was placed on the European side. Conclusion: There is a single frame structure used by both SONET and SDH. This is documented in ITU-T recommendation G.707 (ANSI and ETSI still have their SONET resp. SDH standard available in their own documentation, but they are aligned with G.707). It depends on the application of the frame structure in an environment with 24 channel legacy PDH to call it SONET and in an evironment with 30 channel legacy PDH to call it SDH. The meeting in Seoul in 1988 shows that SDOs can compromise to find a common frame structure that can be used in different regions/applications. Best regards, Huub. _______________________________________________ Ietf mailing list Ietf@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf