In the 1980s, when we wrote the first edition of this book, there were many, many more protocols in common use at the data link, network, and transport layers than there are today. Why do you think the number of commonly used protocols at these layers has declined? Do you think this trend will continue? What ❦ ❦ ❦ ❦ Minicases 21 are the implications for those who design and operate networks?

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