Data Rates question for Meraki MR44

[Keith_Li]

Dear All, 

            I have a question would like to ask on MR44, for MR44 2.4Ghz is using 2:2x2 and 5Ghz is using 4:4x4, for instance there are 8 endpoints connecting to 5Ghz at the same time, will the data rates for endpoints will get slower compared to have 4 endpoints connecting to 5Ghz at the same time ?  i have an example below, please correct me if my concept is wrong, Thanks 

case1:

600Mbps for 4: 4 x 4 - if there are 4 endpoints connecting to 5Ghz, the data rates for each endpoint will be 150Mbps

case2:

600Mbps for 4: 4 x 4 - if there are 8 endpoints connecting to 5Ghz, the data rates for each endpoint will be 75Mbps

[GreenMan]

Data rates don't change just with the quantity of connected clients;   rates are determined by the signal quality.   What will change is the amount of time each client gets access to on the selected channel.   Imagine you're in a meeting with two other people - you each speak at a particular rate.   But because there's only three of you, you can all get to speak reasonably often.   Now imagine there are ten of you in the same room.   When you can speak, you still speak at the same rate, but you don't get to speak so often, so your overall contribution to the conversation (your aggregate traffic over time) drops.  This is partly why faster data rates are better - if you can say what you need to say more quickly (at a higher connection rate) there's more time left for others to speak.   It's one reason why it's good to avoid very low minimum connecttion rates in your wifi setup (the old 802.11b rates, for example)

Incidentally - imagine your meeting room is an aircraft hangar and you're each standing in one corner - you all have to speak loudly and slowly in order to be understood   (hence low data rates when your far from your AP - hence your meetings taking a very long time!)

[alemabrahao]

Data Rates are not about number of antennas.

Data rates define the speed of data transmission in wireless communication. The data rate can be referred to as the number of bits transmitted from one device to another or over a network per second. Data rates are usually expressed in bits per second or bytes per second. In most wireless communication networks, along with the useful data bits, additional data is transmitted for signaling, error correction, and addresses. This makes the useful data rate less than the actual data rate.

There are many variables that can affect the client's data rate, the most common being the distance from the antenna. The greater the distance from the antenna, the lower the data rate will be.

[GreenMan]

Good points made by @alemabrahao ...    When an AP has multiple antennas, for modern wifi these are most often used for transmitting more data to the same client device simultaneously (the concept of spatial streams) - it's a bit like connecting multiple wires, for a wired connection - you can send more data at the same time.   As I mentioned before, this helps increase the connected data rate, so you send what you need to send in less time, leaving more airtime for others.   Note that, in order to take advantage of each spatial stream, the client device also needs the corresponding number of antennas.   You'll find that higher end laptops and tablets will likely support more spatial streams than a smartphone, for example - and this is one reason why they can connect at higher data rates.   Bear in mind that, if you 'speed up' the wifi for some users, who are capable of higher data rates, not only do you improve their experience, but there's more airtime left for everyone else - their user experience improves too.

[Keith_Li]

lets use an example of the following, i have a 4:4x4 mumimo wireless router, and i have 2 x devices with 4 x 4 MIMO antennas connecting to the wireless router, does it has a formula on calculating the throughput of each device on this figures ?

[KarstenI]

No exact formula, but a rough estimate:

Use the given condition from https://mcsindex.com and use half of this value. That will provide you with a hint that quite often is accurate enough.

[alemabrahao]

This is not an exact science, there are several factors.

MIMO increases receiver signal-capturing power by enabling antennas to combine data streams arriving from different paths and at different times. Smart antennas use spatial diversity technology, which puts surplus antennas to good use. When antennas outnumber spatial streams, the antennas can add receiver diversity and increase range.

More antennas usually equate to higher speeds. A wireless adapter with three antennas can have a speed of 600 Mbps. An adapter with two antennas has a speed of 300 Mbps. The router needs multiple antennas and must fully support all features of 802.11n to attain the highest speed possible.

Take a look at this:  https://documentation.meraki.com/MR/Wi-Fi_Basics_and_Best_Practices/Meraki_MR_SU-MIMO%2C_MU-MIMO%2C_...

[Keith_Li]

for example a MR76 that has 4 x 4 MIMO, if there are 5 x devices with 3 antennas connecting to it, 5 of the devices will has a speed of 300 Mbps ? will this speed will decrease if more devices connecting at the same time ?  so the bottleneck will be the lan adapter of MR76 ? if the lan switch are using 1 giga ethernet ? 

[alemabrahao]

Have fun.

https://blogs.cisco.com/networking/cisco-will-ride-the-802-11ac-wave2

https://blog.router-switch.com/2014/12/why-you-should-upgrade-with-cisco-802-11ac-solution/

https://blogs.cisco.com/networking/too-fast-too-furious-with-catalyst-wi-fi-6-mu-mimo

[alemabrahao]

One more https://techimike.com/cwna-chapter-10-mimo/

[KarstenI]

The main question is what these devices are doing. If they want to transmit simultaneously, they share the same airtime.

For the LAN adapter, no non-lab AP in the enterprise space will ever cross the 1 Gig rate with a Wi-Fi-6 AP.

[KarstenI]

I am pretty sure @Keith_Li is talking about throughput, not the WLAN term of data rates. And there, the calculation is not correct as the overhead is missing and other factors are not considered. But the conclusion is correct. The more clients want to use the given Airtime, the less Airtime per client is available.

[Keith_Li]

Yes it’s the throughout I want to talk about not the data rate, as we will have a meeting with our customer to propose to use MR36 ratter than MR44, due to budget issue. mr36 support 2.4ghz 2:2x2 and 5Ghz 2:2x2 whereas mr44 support 2.4Ghz 2:2x2 and 5Ghz 4:4x4 Need to explain to customer if they are using mr36 for 2.4ghz. The performance are still ok compared to mr44 on 2.4Ghz, just wonder if you can provide me the overhead of this ? Thanks 

[GreenMan · Accepted solution]

Good point @KarstenI   - terminology is important.   For me 'data rates' implies the kind of value your client device tells you if you look at your active WiFi connection and find details from the driver  (for my laptop, for example, mine is currently showing   Link speed (Receive/Transmit)   574/574 (Mbps)   This is the rate at which 802.11 is putting bits through the radio, when it transmits.
To your point, regarding data transmission overheads and mine regarding access to airtime on a shared channel (let alone access to a shared LAN and an MX with a shared Internet uplink), I certainly won't be seeing those values if I performed (for example) a network speedtest.   (which incidentally actually runs at 276/26 Mbps for me right now)

It's often about understanding where your bottlenecks are.    With networks in a busy office these days it's often about WAN bandwidth, available WiFi airtime or a combination of the two.