I know that we all are now using wireless routers, but why are there no wireless switches? What's the problem we are facing in introducing that technology or are these wireless switches not needed now? Please explain.
117 Answers
Switches are intelligent networking devices that take signals in from a particular port and then rebroadcast it on a specific port that it knows has previously hosted the intended recipient. In the event that the port is not connected or a different device is connected then it rebroadcast on all ports until it learns where the recipient is.
A hub on the other hand always broadcasts on all ports.
Wireless networks do not have an equivalent of wired ports and (theoretically speaking) are equivalent to 10base2 coaxial style network cable where signals are broadcast onto a wire that connects all machines at once. Hence a switch or even a hub is not a relevant comparison. (There is also link encryption but can be ignored for the moment)
Back in the day in order to traverse network segments you needed an intermediate device which watched for signals on one network segment that were meant for the other and rebroadcasted back and forth as necessary. That device was a router. It is still what your current router does, it takes signals from wireless, wired, and WAN networks and moves them as necessary. Routers operated at a higher level that switches and were aware of protocol adresses and gateways and so on. They were smarter.
A "switch" is a specific type of networking equipment. It is better than a hub, but not necessarily as good as a router. Wifi does not use or require it because of the method by which it works.
11With (wired) ethernet, you can have switched because you can have a non-shared medium (individual cables not all hard-wired together like they would be in a hub). With wireless, you inherently have a shared medium...
1The closest concept to a wireless switch is a signal booster or repeater, which are devices that do pretty much exactly what they sound like. Nobody calls them a switch though, because they're technically hubs (which are usually called repeaters when they only join two network segments), not switches. WiFi has a single shared medium, you can't selectively broadcast to only one 'port' because everything is on a single 'port', so it's a hub not a switch. It's pretty rare to see these devices outside of very specific circumstances though, as it's almost always better to extend the network using a wired connection and multiple wireless access points with the same SSID.
Note, however, that the term 'router' isn't always an accurate description of what most people call wireless routers. Most of them are capable of just acting a a bridge instead of a router, and it's not all that unusual to see them used in this way (for example, the guest network where I work is handled through a wireless AP configured as a bridge, with the actual routing being handled by our gateway systems).
1I suspect you are asking about wireless switches, rather than wireless routers which do exist.
In wired networking way back when, all machines on a particular leg were connected to the same wire and had to take it in terns somehow to send packets. Various schemes existed to manage this including token ring and the "just try, and back off for a random time in the case of a collision" where a collision is where two machines try to use the line at the same time.
With a hub you effectively have the same arrangement, the hub is fairly dim just more convenient to connect things to. You still have a single collision domain so at most one machine is sending a packet at a time. Some hubs have small buffers which would allow them to more efficiently handle collisions than the individual machines on the network leg would between them, but you still have a single collision domain because the hub doesn't selectively send packets: every packet sent still goes to all machines on that leg so only one device can talk at once.
With a switch there is more intelligence in the switching device: all machines can be talking to it at once and it has the internal bandwidth and store-and-forward buffers to push the packets between each. A switch will know which machines are connected to which port so can send ethernet packets to just the machine that needs it instead of every one. This essentially means that you have one collision domain per connected device. With a hub, the effective throughput of the network leg degrades massively as more machines try to talk at the same time even if no two machines are talking to the same other machine, with a switch this is not the case.
Switching hubs exist and are a hybrid needed because with a hub each connected machine needs to be talking the same protocol and speed. A 10/100mbps switching hub for instance would effectively (or actually) be two hubs (one at each speed) with a two port switch or router sat between them. Really simple switching hubs actually had different ports for the different speeds, but must had the intelligence required to allow any physical port to connect to either side depending on the speed the machine at the other end tried to connect at. With this you still effectively have a single collision domain.
A router connects two network legs as separate collision domains. This might be two wired networks using the same protocol, network legs using different protocols, or a wired leg and a wireless one, etc. A standard wireless access point is a router by this definition. An AP with multiple ethernet ports is actually two devices in the same box: a switch and the AP. A bridge is similar but it connects the two networks as a single leg - wireless extenders operate like this, bridging to wireless network legs, and a switching hub is effectively a bridge too.
So...
Why there is no wireless switch?
The reason you don't see wireless switches, is that you generally only have one "wire": the small patch of universe between the devices that are taking part in the network - all devices share the same universe so share the same collision domain s oonly one can send a packet at once. You can have multiple "wires" with wireless by using multiple distinct sets of radio frequencies, allowing different devices to talk on at the same time if they do so on different frequency sets. This is why there are several ranges in each wireless standard - you can set your network to use one while your neighbour uses another and your devices won't interferee with each other. Some wireless access points support protocols that allow different devices to use different frequencies on the same network, but unless you have only a small number of devices and there are no local competing networks using the same frequency ranges, you won't get one collision domain per device like you do with a wired switch (just one collision domain per frequency range).
0TL;DR
Modern MU-MIMO (Multi-user MIMO) access points are the closest we have to switched Wi-Fi.
Detail
There are two main features we associate with ethernet switches.
- Non broadcast packets are sent only to the nominated user device.
- The switch fabric overall has a higher bandwidth than any individual link.
Until recently, Wi-Fi access points could do neither of these things, but with modern beamforming techniques they can do both.
An analogy
We normally think of radio as being like standing in the middle of a field shouting. As long as only one person is shouting, everyone else in the field can hear them clearly, but if more than one person is shouting at once it starts to get garbled, so we take it in turns (Time-division multiplexing). It is a shared medium.
Beamforming is more like speaking into a parabolic dish pointed at someone else's ear. Because the signal is directed at a specific location, there is no need to shout, and it is almost inaudible for everyone else. Not only this but many pairs of people in the field can do the same, with none of their conversations interfering with each other.
This, this beamforming technique fulfils both of our criteria for 'wireless switching'.
MIMO
The practical implementation of these techniques in WiFi is MU-MIMO.
In radio, multiple-input and multiple-output, or MIMO (/ˈmaɪmoʊ, ˈmiːmoʊ/), is a method for multiplying the capacity of a radio link using multiple transmission and receiving antennas to exploit multipath propagation.
Effectively, if you have multiple antennae, so each signal takes a slightly different path from access point to user device, MIMO can potentially use much of the the bandwidth of each 'stream' simultaneously (like pointing one parabolic dish at your left ear and another at your right *8').
MU-MIMO is an enhancement to MIMO which allows access points to maintain connections to multiple user devices simultaneously.
Multi-user MIMO (MU-MIMO) can leverage multiple users as spatially distributed transmission resources, at the cost of somewhat more expensive signal processing.
Without MU-MIMO, access points connect to only one user device at a time, so access to different user devices has to be spread out over time. With MU-MIMO that limitation doesn't apply.
Wi-Fi 5 (802.11ac) supported MU-MIMO in the Downlink direction - so multiple user devices could receive packets simultaneously, but would have to wait their turn to acknowledge receipt of those packets. This functionality was only optionally supported on devices with "Wave 2" certification.
Wi-Fi 6 (802.11ax) supports MU-MIMO in both the Downlink and Uplink directions. With multiple bi-directional spacial streams, equivalent to separate Cat5 cables coming from an Ethernet switch, this is the closest Wi-Fi currently gets to switched ethernet.
MU-MIMO in practice
MU-MIMO technology is not very widely supported yet, and all devices (access point and user devices) have to support it for it to be used.
Just one device within rance of the access point which doesn't support MU-MIMO will prevent all MU-MIMO devices from making use of their MU-MIMO capability for the duration of it's transmissions.
Wi-Fi routers are switches. Consider the situation of multiple devices connected to a single access point. That access point defines a single wireless LAN, on which the packets are switched among the devices. The devices are not on different network segments with their own IP subnet; they are all in 192.168.0.1/8 or whatever.
The typical Wi-Fi router can switch packets between the wireless LAN and the wired one; a mixture of wired and wireless clients can be on the same subnet.
Devices that use Linux tend to do achieve this functionality with the help of a kernel feature called "ethernet bridging".
Wi-Fi switching products are integrated as multi-function devices that provide routing so they are called and sold-as Wi-Fi routers.
2A wireless transmitter is like a multiport hub in that everything to be transmitted is duplicated to all receivers except itself (receiver is shut off). A receiver is a 2 port hub. In a wireless access point, these theoretical hubs are essentially connected to a switch via 2 simplex ports and the switch performs 802.11<->802.11 and 802.11<->Ethernet (and presumably Ethernet<->Ethernet if it has multiple ports) interworking. The 2 simplex ports share the same 802.11 MAC address table and are logically combined into one port. Instead of dropping the packet if the destination MAC address of a packet received on this port is on this port like a regular switch does, the packet is processed and sent to the outgoing simplex port regardless, unless it is a lightweight AP, which uses LWAPP / CAPWAP tunnels to a WLC usually connected to an upstream switch or the same switch the AP is connected to, or remote if using H-REAP.
For a lightweight AP:
All the client (802.11) packets are encapsulated in a LWAPP packet by the LAP and sent to the WLC. WLC descapsulates the LWAPP packet and acts based on the destination IP address in the 802.11 packet. If the destination is one of the wireless clients associated to the WLC, it encapsulates the packet again with the LWAPP and sends it to the LAP of the client, where it is decapsulated and sent to the wireless client. If the destination is on the wired side of the network, it removes the 802.11 header, adds the Ethernet header, and forwards the packet to the connected switch, from where it is sent to the wired client. When a packet comes from the wired side, WLC removes the Ethernet header, adds the 802.11 header, encapsulates it with LWAPP, and sends it to the LAP, where it is decapsulated, and the 802.11 packet is delivered to the wireless client.
In short, the reason why a wireless switch doesn't exist is because a wireless medium can only be a hub – it is broadcast to all nodes. It is up to the mobile stations and the L2 circuitry behind the transmitter/receiver, i.e. the functional switch in the wireless access point, to perform CSMA/CA to avoid collisions, like a regular ethernet hub, where the nodes perform CSMA/CD.
