What is Network Architecture?

Legal Definition
Network architecture is the design of a communication network. It is a framework for the specification of a network's physical components and their functional organization and configuration, its operational principles and procedures, as well as data formats used. In telecommunication, the specification of a network architecture may also include a detailed description of products and services delivered via a communications network, as well as detailed rate and billing structures under which services are compensated.

The network architecture of the Internet is predominantly expressed by its use of the Internet Protocol Suite, rather than a specific model for interconnecting networks or nodes in the network, or the usage of specific types of hardware links.
-- Wikipedia
Legal Definition
Computer network design. Mapping hardware, software, protocols, and devices. Outcome is successfully allowing different systems and devices to inter-communicate.