Traffic Management for the Available Bit Rate (ABR) Service in ...

4.14 Summary of Switch Congestion Control Schemes
We have observed in our preceding survey that di erent schemes have addressed
di erent subsets of switch scheme goals listed in chapter 3. In this section, we summa-
rize these goals and approaches and identify areas not addressed by these proposals.
If we sort the schemes by time, we nd that early schemes addressed the basic
problem of achieving max-min fairness with minimal complexity. We can see a tran-
sition from using purely bit-based ideas for ER-feedback to using purely ER-based
ideas for the same purpose.
Early schemes used a number of concepts which have been based on the legacy
of bit-based feedback design, which may not be best when explicit-rate feedback
capabilityisavailable. For example, control of queuing delayisdonetypically through
an threshold-based or hysteresis-based approach which is a legacy from bit-based
feedback design. This approach does not work when there is high variance in queue
uctuations due to tra c variation. As discussed in a later chapter, using queue
thresholds alone to detect congestion is a awed technique especially when rate-based
control is used.
Later schemes addressed the speed of convergence and the implementation com-
plexityofthescheme, and faced a tradeo between the two. The issue of measurement
raised in this dissertation has been recognized in several contemporary schemes. Some
of the schemes described in this section have been developed at the same time, or
after the development of the OSU, ERICA and ERICA+ schemes. As a result, they
share several features with the schemes we have described in this dissertation.
91