(Cont) a complex task is broken into subtasks: modular design Each subtask is implemented separately as a layer arranged in a vertical stack Each layer performs a related subset of the functions required to communicate with another system It relies on the next lower layer to perform more primitive functions and to conceal the details of those functions -It provides services to the next higher layer. Layers should be defined so that changes in one layer do not require changes in other layers. So, instead of using a single complex protocol, it's more flexible to implement a stack of protocols! Reduce the design and development workload significantly9 (Cont.) • A complex task is broken into subtasks: modular design — Each subtask is implemented separately as a layer, arranged in a vertical stack • Each layer performs a related subset of the functions required to communicate with another system. — It relies on the next lower layer to perform more primitive functions and to conceal the details of those functions. — It provides services to the next higher layer. — Layers should be defined so that changes in one layer do not require changes in other layers. • So, instead of using a single complex protocol, it’s more flexible to implement a stack of protocols! — Reduce the design and development workload significantly!