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I have a Raspberry Pi 3 B+ board and I am trying to connect it both to a local wireless hotspot and another machine via cable. I am not connected to the Internet on any of the devices and all data transfer is local. My question is that do wireless and wired connections affect each other? is their bandwidths seperated or using one, will slow down the other?

MohammadHossein R
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  • Hi @MohammadHossein R, I fell jealous that your super question has 400 views in a day! :) – tlfong01 Oct 28 '19 at 11:49
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    @tlfong01 LOL :))) I am active on other sites like Stackoverflow but honestly having this much attention and upvotes surprised me too – MohammadHossein R Oct 28 '19 at 11:55
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    You managed to get onto Hot Network Questions, so that will drive views – Baldrickk Oct 28 '19 at 12:04
  • @Baldrickk, I noticed something called Hot Network Questions, but I never know what does that mean. So should be like most viewed hot 100 among all stack exchanges. – tlfong01 Oct 28 '19 at 13:46

3 Answers3

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As noted by other answers, the physical mediums are of course separate and do not affect each other.

However, it is a valid question whether they share a common bus in the Raspberry Pi 3 hardware. Infamously, the wired network chip is on the same USB controller as the USB ports, causing bandwidth to be shared with any USB drives connected.

Raspberry Pi 3B+ hardware block diagram (Image source: shabaz on Element14 forums)

As visible in the block diagram, the 802.11n wireless network chip in the upper left has its own dedicated SDIO bus to the processor. The bandwidth available is thus fully independent of the wired network controller on the right side.

jpa
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  • When I read the first answer, I thought I understood 90% of the story. After the second answer, 90% dropped to 50%. After the third answer, only 10% is left! :) – tlfong01 Oct 28 '19 at 08:19
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    I wasn't quite sure about the architecture but, yes of course, this is a basic thing to look at and is the first thing to check. Also depending what USB devices are used, if only mouse/keyboard, then low impact on bandwidth. – Nick.T Oct 28 '19 at 08:45
  • @jpa, Your picture is very good, almost perfect, except not showing the standard code of Ethernet and GigiBit Ethernet. I always mix up 802.3 with 802.11. Or Rpi4B Gigabit Ethernet is now 802.4 or 802.5? – tlfong01 Oct 28 '19 at 11:47
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    @tlfong01 Ethernet is 802.3, no matter which version of RasPi or network speed. 802.4 and 802.5 were Token bus and ring networks that are no longer in common use. – WooShell Oct 28 '19 at 13:08
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    @WooShell, Oh my goodness. I only made up the numbers 802.4, 803.5 as a joke. Never image that they exists. I do remember I saw the names token bus and ring bus. I also remember my friend, a research guy, placed his bet on something called ATM, which is based on statistics and probability, but I guess ATM is also gone with the wind. Now I am waiting for 5thGen sim card to insert into my SamSung phone! Just thinking aloud. Sorry for the typos. I almost forgot my first modem is called acoustic coupler, placed on a dial phone, and I could almost count the bits, at 300 baud! – tlfong01 Oct 28 '19 at 13:36
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    @tlfong01 Actually you got it backwards. ATM is based on physical switches (like wall light switch, not like Ethernet switch) so bandwidth is guaranteed. Ethernet (and Wifi) on the other hand is statistical. 10GB Ethernet will give you 10GB only if you are the only person on the network using it - otherwise the bandwidth is shared - you get 10GB 90% of the time only if everyone does not use it 90% of the time. If we have 10GB ATM it would give each connection 10GB. – slebetman Oct 28 '19 at 16:06
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    ... A lot of people bet on ATM because of the guaranteed bandwidth thing allowing you to absolutely engineer and design a network. What ended up happening is people don't mind too much if sometimes the network is slow (bandwidth is statistical) therefore Ethernet won being cheaper to implement (10GB ethernet for 100 PCs requires 10GB but 10GB ATM for 100 PCs would require 1000GB or force you to provision fewer simultaneous connections - ethernet does not drop connection but just slows down) – slebetman Oct 28 '19 at 16:10
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Wired and wireless data transmission are completely different. Wired connections for usual ethernet use electrical signals on the wire, wireless connections use radio waves with modulation on different frequencies, resp. channels. You do not have radio waves on the wire so they are completely independent from each other each with its own bandwidth.

Wired connections normally have 100 MBit or 1 GBit raw data with protocol overhead, wireless connections usually have about 100 MBit but with special technology up to 400 MBit.

Ingo
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  • (1) My home WiFi router is dual band 2.4Gbit/s and 5Gbit/s. so raw speed is 5Bbit/s? (2) My smart phone is 4.5thGen. And my service provider says I can upgrade to 5thGen 2020Q2, and that speed would then be 10+ times higher. I am planning to learn new technology for the next couple of years. I sometimes worry that 5thGen smart phone would take over 5Gbit/s WiFi. So my bad dream is that very soon everybody would throw away their WiF router and desktop PC and use dual screen 5thGen mobile phone, one pocket friendly 6", another 25" 4k desktop screen-sharing like Uber? – tlfong01 Oct 28 '19 at 00:44
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    @tlfong01 That's GHz, not Gbps. – chrylis -cautiouslyoptimistic- Oct 28 '19 at 07:58
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    @chrylis -on strike, Oh my goodness, what a silly careless mistake! Many thanks for pointing that out. Cheers. – tlfong01 Oct 28 '19 at 08:02
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    I think that the O.P. was trying to ask is if they share the same (USB) bus or are different buses (USB, PCI, ...). – Ismael Miguel Oct 28 '19 at 09:11
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    @tlfong01: The two are definitely related. WiFi uses channels or frequency bands. These have a center frequency near 2.4Ghz (2400 Mhz) or 5Ghz and a width of 10/20/40 Mhz. It's the band width, not the center frequency, which determines your wireless data speed. You still need to differentiate Mbps and MHz because modern WiFi can send more than one bit per Hz. – MSalters Oct 28 '19 at 10:41
  • @MSalters, Oh my goodness, more than one bit per Hz! I need to google to check out how to do that. I do vaguely remember a guy called Shannon who says you need two Hz to transfer one bit. I guess I mess up things again. Need to wiki again. Thanks for the clarification. – tlfong01 Oct 28 '19 at 11:41
  • @tlfong01: There's also an earlier guy named Hartley. See Shannon-Hartley theorem – MSalters Oct 28 '19 at 12:03
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The wireless and the cable connections are different media and do not interfere with each other. Therefore, basically saying, each have their own bandwidth and characteristics.

From there on, the operating system you use on the device will have a network stack, likely to respect the OSI model (physical, data, network...). At the network/transport layer, the OS will have a routing protocol to decide which link to use (cable or wireless) based on preference. All this to say that, if you run a simple test, you are likely to notice the bandwidth of only one connection

Nick.T
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  • When I learned Ethernet ages ago, I was told that electromagnet wave travels in vacuum. I now know that Ethernet is wired, and only electrical signals (electrons, not waves?) travels along the wire. But now comes the optical fibre wires, and I was told that waves from the ISP travels along the optical cable, and at my home converts (?) to electrical signal (waves becomes electrons?) to a copper CAT5 Ethernet cable then to Windows PC. How confusing! – tlfong01 Oct 28 '19 at 08:30
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    @tlfong01: Electromagnetic waves travel in anything. They travel fastest in vacuum as there are no pesky electrons in the way. But despite the slower speed, we prefer cables as they offer a more controlled travel of the electromagnetic waves. In particular glass fiber is very good at making sure the wave sticks to the inside of the fiber. – MSalters Oct 28 '19 at 10:46
  • @MSalters, Ah thanks a lot for the explanation. Your points are very good. (1) EM waves travels in vacuum (highest speed as light), and lower speed in non vacuum medium (air, water, glass etc, but cannot pass copper, this is a bit confusing :)). (2) We prefer copper wires because we can direct and confine where the signal goes, (less leaking radiation/radio waves) (3) Optical fibre is best because of high speed (almost as fast as light), low "leaking", though they are also EM waves and photons, but not slow electrons. I learnt this basics in mid school physics, but never filly understand! :) – tlfong01 Oct 28 '19 at 11:37