Define and discuss hubs

[mlagally]

This is a carry forward for the open tasks from https://github.com/w3c/wot-architecture/pull/603 to be able to merge that PR.

• [ ] update Edge Device section to discuss hubs vs. gateways
• [ ] add explicit definitions for hubs and gateways to terminology
• [ ] make sure use of "Gateway" in "Smart Home Gateway" is consistent with definition of "Gateway" (e.g. if it manages local devices, and is NOT just a proxy... maybe it should be a "Smart Home Hub"?
• [ ] Explicitly allow for star as well as p2p topologies in architectural patterns (addressing https://github.com/w3c/wot-architecture/issues/585)
• [ ] cite use of hubs as a place to locate "digital twins", and along the way clarify the various functions that a digital twin might perform, and which are optional (e.g. protocol conversion, state caching, simulation, prediction, etc). A "simple" digital twin might just do protocol conversion and state caching, for instance, and these simple twins are commonly supported by hubs.

[chachamimm]

"Gateways" is a feature that enables communication between two or more different communication protocols, For example, IP protocol and non IP protocol. "Hubs" is α feature that concentrates lines used to physically connect communication devices such as IoT devices, PC and so on.

"Gateways" is a feature of Network Layer. "Hubs" is a feature of Datalink Layer.

Equipments of "Gateways" have "Gateways" feature and "Hubs" feature. Physical lines should be concentrated. If equipments of "Gateways" have "Hubs" feature, it would be convenient.

I think we should discuss equipments and features separately.

[egekorkan]

I agree with the definitions proposed by @chachamimm . From my experience, gateways and hubs are not as commonly defined as switches, routers and access points. Is there any reputable, non-biased source that we can ideally cite in our specs? If I google for both of them, I only find products of companies or somewhat biased sources

[mlagally]

Arch call on June 23rd: decide to close.