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We see that almost always the term of "ad-hoc networks" comes with WSN (Wireless Sensor Network). Does it mean an ad-hoc network must be always wireless?

If we define an ad-hoc network as follows:

"An ad hoc network is a network that is composed of individual devices
communicating with each other directly." [1]

Can we imagine a "wired ad hoc" network?

[1] https://www.techopedia.com/definition/5868/ad-hoc-network

Caveat: This question might raise primarily opinion-based answers, and might be put on hold or considered off-topic, for exactly that reason.

Still, I dare to attempt an answer:

Following https://en.wikipedia.org/wiki/Ad_hoc#Networking

The term “ad hoc networking” typically refers to a system of network
elements that combine to form a network requiring little or no
planning.

The linked main wikipedia article subsequently focusses on wireless ad hoc networks only.

However, I don't quite see why a wired ad hoc network should not be thinkable, if a few conditions are met:

• the devices to be connected all have an network interface of matching technology ("Ethernet" springs to mind).


• there is a means to wire them all together, in a fashion that any participating device can talk to any (and to all) other participating device (Star? Bus? Ring? Anyone remeber 10base2?)


• the medium and topology chosen to interconnect the devices must also support multicast (or broadcast) propagation to all participants ("talk to all devices", see above)


• a hub or switch to connect the devices might disqualify the setup as "ad hoc", as this would be an intermediate device (1).


• the participating devices have a means to manage addressing on the emerging common subnet themselves (IPv4: APIPA, IPv6: link-local addresses with DAD), if the given underlying technology does not provide unique identifiers natively


• the participating devices support suitable service announcement/discovery mechanisms and if needed some form of name resolution, so they have a way to find each other and find out what they can do with each other. Multicast based Zeroconf Networking (a.k.a. "Bonjour" or "Avahi") can do this.

... then yes, I would consider such a setup might be called an "ad hoc wired network".

(1) that might be subject of debate because a simple hub or switch fulfills the criterion of "little or no planning" with ease.

As the already present answer point out, ad hoc is a matter of perspective.

From a user's POV an ad-hoc network should be effortless and require no planning. If this precludes bringing along a cable, then yes, it needs to be wireless.

If you admit a cable you can connect two machines with Ethernet. Using obsolete 10BASE2 coax cabling you could even connect a whole lot. I'd call this ad hoc as well.

If you also admit a repeater hub or a simple switch you can connect a larger number of machines. From the user's POV there's little difference between those two. I'd still call this ad hoc since it requires very little effort and next to no planning or preparation.

Technically, the term is used almost exclusively for the WiFi ad-hoc mode. (Coax) Ethernet was actually designed in a similar way but has moved away since, using star or tree topology on the physical layer (L1). Ethernet's data link layer (L2) is still plug & play, so it doesn't disqualify its use for ad-hoc networking.

The network layer (L3) is all the same for wired or wireless networks, so there the differentiation ends.

About the term

The term "Ad Hoc" seems to have completely different meanings in different contexts.

In wireless LAN context "Ad Hoc" means that all devices in the network have the same role. The opposite is an "Infrastructure network" where one device has a special role. The data format (OSI layer 2) is slightly different in both types of networks.

(Note that "WLAN tethering" with a mobile phone uses an "Infrastructure" network, not an "Ad Hoc" one.)

In this context however the term "Ad Hoc" does not say anything about the effort needed for configuring and planning the network:

The effort needed for planning and configuring a "WLAN Ad Hoc" network even seems to be higher than using a "WLAN Infrastructure" network when using modern devices and modern software!

Why do you see the term only in conjunction with wireless LAN?

Of course the operating system does not need to know if the network that you are planning "requires little or no planning" or if it requires a lot of planning.

Therefore you won't find any configuration setting where you will be asked if your network is an "Ad Hoc" network with the meaning of the term "Ad Hoc" described in Marc Luethi's answer.

However because "Ad Hoc" and "Infrastructure" WLAN networks use a slightly different data format, the operating system needs to know which kind of data format shall be used.

Therefore you will definitely find the setting "Ad Hoc" or "Infrastructure" in the WLAN settings.

Is this possible with wired networks, too?

If you want to know if wired network types use the word or term "Ad Hoc":

I don't think so.

Of course there are wired network types having different operating modes that can be selected by configuration. But none of them seems to use the term "Ad Hoc" for a certain selectable operating mode.

If you want to know if there are wired networks which would be "Ad Hoc" when using the WLAN terminology:

"Normal" Ethernet would be the best example.

Ethernet frames are not sent to a device with a certain MAC address which then forwards the frames to the actual receiver. Instead, the "destination MAC address" in the frame sent by the sender will already specify the final destination of the frame (*). In WLAN terminology this would be called "Ad Hoc network".

(*) but not necessarily of the layer-3 packet inside the frame

The term "ad-hoc" is used to distinguish a peer-to-peer wireless network from an access-point based "managed" one.

Wired networks on the other hand always use a symmetric signaling layer, so no such distinction exists, which is why you see the word used rather seldom in wired contexts.

There may be some confusion because Windows 95/98 had a wizard to set up private IP addresses on an interface that was also called "Set up ad-hoc networking".