A system and method are provided for mapping information into Synchronous Payload Envelopes (SPEs). The method provides information bytes at a nominal system clock-based data rate, which is about equal to a system clock, but may be adjusted. An external clock has a rate approximately equal to the system clock rate. The method generates SPEs with identically-positioned information bytes, regardless of differences between the system and external clock rates. The SPEs are combined with Transport Overhead (TOH) and transmitted as a message frame at the external clock rate. SPEs are generated maintaining the positions of the information bytes within each SPE, without pointer adjustments, despite differences between the system and external clock rates. Expressed another way, message frames are generated with payload and TOH sections, and the information bytes are located exclusively in the payload sections. As a result, constant pointer values (e.g., H1/H2 or V1/V2) are maintained for all the SPEs.