The diagram below offers an overall view on the methods use by both the OSI and TCP/IP model.

ISO Approach

- Occasionally called Horizontal Approach

- OSI asserts that distributed applications function over a strict hierarchy of layers and are constructed from a common tool kit of standardized application service elements.

- In OSI each distributed application service selects functions from a large common -toolbox? of application service element (ASEs) and complements these with application service elements that perform functions specific to given end-user service.

TCP/IP Approach

- Occasionally called Vertical Approach

- In TCP/IP every application entity is composed of whatever set of function it needs beyond end to end transport to support a distributed communications service.

- Most of these application processes builds on what it requirements and assumes only that an underlying transport mechanism (datagram or connection) will be provided.