Update overview-wais.md

  - Based on OpenAPI Specification (OAS) 3.0

## AdvantEDGE Integration

- WAIS is implemented as a single sandbox pod within AdvantEDGE, providing service for all applications running as part of that sandbox

WAIS is implemented as a single sandbox pod within AdvantEDGE, providing service for all applications running as part of that sandbox

- 3 components:

WAIS components:

- Northbound Interface (NBI) & Core - (tightly coupled) implements the WAIS API & internal service logic

- Southbound Interface (SBI) - (decoupled from NBI/Core) implements glue logic between AdvantEDGE & the NBI/Core

- Threads:

    - Main thread      - (NBI/Core) Handles requests to the WAIS API (server) from users (i.e. scenario pods)

    - NBI event thread - (NBI/Core) Handles event channel from SBI (for WAIS subscriptions)

    - SBI event thread - (SBI) Handle events from AdvantEDGE (scenario updates, mobility events, etc.) & updates Loc. Service database)

  - _Main thread:_ (NBI/Core) Handles requests to the WAIS API (server) from users (i.e. scenario pods)

  - _NBI event thread:_ (NBI/Core) Handles event channel from SBI (for WAIS subscriptions)

  - _SBI event thread:_ (SBI) Handle events from AdvantEDGE (scenario updates, mobility events, etc.) & updates Loc. Service database)

- Supports hot-restart

  - User / app subscriptions with and without a duration parameter survive WAIS pod restarts

### WebSocket Support

WAIS implements the [ETSI MEC009](https://www.etsi.org/deliver/etsi_gs/MEC/001_099/009/03.01.01_60/gs_MEC009v030101p.pdf) _REST-based subscribe/notify with Websocket

fallback_ pattern.

This pattern requires sending a test notification to the notification endpoint URI in the subscription request to determine

if it is directly reachable or not. On success, standard REST-based notification methods continue; on failure (and upon client request),

WAIS creates a WebSocket subscription endpoint where the client may connect to receive notifications.

_**NOTE:**_ WebSockets are required when client applications subscribing for notifications are behind a NAT/firewall.