In high-speed serial link design, the Total Channel Requirement is a mandatory hard specification that the entire high-speed link (PCB + cable) must strictly comply with. The system's final insertion loss, return loss, and other parameters must meet this specification to ensure signal integrity and proper communication between chips.

In addition to the Total Channel Requirement, two additional columns of data are typically provided: the PCB Budget and the Cable Assembly Budget. These are recommended reference values derived from engineering experience. It is important to emphasize that these two recommended values are not mandatory absolute targets, regardless of how the loss is actually distributed between the PCB and the cable in practical testing. In actual design, these two portions follow a "trade-off" budget allocation principle.

• If the PCB trace is long and results in higher loss, this can be compensated by selecting a high-quality, low-loss cable;
• Conversely, if the cable loss is relatively high, the PCB design must adopt lower-loss dielectric materials or shorter trace lengths.

As long as the combined loss of the PCB and cable, when summed, still meets the overall budget of the Total Channel Requirement, the design is deemed compliant.

Additionally, in the 98x Channel Specification, due to the higher data rates at which 98x devices operate, there are often scenarios in the design phase where it is difficult for the PCB to meet the recommended PCB targets specified in the Channel Specification. To address this, the 98x Channel Specification provides two alternative reference standards: PCB Focus and Cable Focus. The core distinction lies in how the total budget is flexibly allocated between the board and the cable. In system design, customers need only satisfy one of the two approaches to meet the recommended values of the 98x Channel Specification and comply with TI's design recommendations.