Wifi to hard wired pc speeds good, wifi to wifi... not as good...

[jeffoffline]

So I recently started upgrading my network to AC (on a budget) and i'm running into speeds slower than I expected when transfering between my laptop and desktop wirelessly... if either of them is connected via a network cable the transfer speed is pretty quick. My hardware is a refurb Netgear AC1450 reflashed to R6300v2, intel dual band AC 7260 adapter in my laptop, and a Linksys Wireless-AC Universal Media Connector (WUMC710), both computers have gigabit NIC's.

I have everything connecting on 5ghz and there's no other 5ghz networks near me, the speed is set to 1300 Mbps. My desktop is about 10 feet away from the router with clear line of site to it. My laptop is in my office directly above the router and when checking the signal on my phone it shows -42 dbm.

With my desktop connected via a network cable I see transfer speeds from my laptop around 100 Mbps, if I disable the laptop wifi and hook the WUMC710 up to the laptop I see speeds around 120 Mbps. So clearly both adapters are showing speeds 100+ Mbps for me. Now if I hook the WUMC710 up to my desktop (shows connecting at 1300 Mbps with ~90% signal) and use the 7260 adapter in my laptop my transfer speeds drop down to around 60 Mbps. That's what has me stumped, if both adapters individually are able to transfer at 100+ to a hard wired computer why is the transfer so much slower when they're both wireless. Does this point to some problem the router has with handling wifi to wifi connections?

Any thoughts on what I could do to speed this up or test it further? I was using a mix of NetStress and timing a 1 GB file copy between computers to get the speeds.

Also just for further testing I turned my old router (TPLINK TL-WDR3600 with DD-WRT) into a client bridge and hooked that up to my desktop and with that setup I see about 40 Mbps to my laptop.

Any help or suggestions is much appreciated.

 

[azazel1024]

Um, because if it is Wifi to Wifi, you are halving your maximum possible speeds. Laptops has to pass a packet to the router, then has to stop, router then passes a packet to the desktop and has to stop. Laptop then passes packet, rinse and repeat.

Wireless is a shared medium, the more devices talking on it, the more the bandwidth is reduced.

As you can see, you get around 120Mbps with only one leg being wireless and 60Mbps with both legs being wireless. That is roughly what I would have expected. Granted, 120Mbps with only one being wireless is kind of slow, but then again, no idea what kind of attenuation you are looking at (-42dBm isn't necessarily indicative of other interference, but should be faster with a signal that strong).

 

[jeffoffline]

I wasn't aware that wifi to wifi connections are halved, I assume this is the same principle as to why using a repeater halves your speed? To make sure I understand correctly:

wifi laptop <--> router <--> wifi desktop

will only be half the speed of

wifi laptop <--> router <--> wired desktop

correct?

I agree the speed of the wireless overall seems slow, granted the WUMC710 tested poorly on SmallNetBuilder and perhaps I'm just seeing similar performance with the 7260 adapter. I'm going to return the WUMC710 as it's performance is just incredibly sporadic. I'll probably replace it with another 1750 router to use as a bridge and see what that does for my performance.

 

[azazel1024]

Yes, that is correct. They have to share talk time, which is why.

The more things you have on wireless, the more the airtime is shared.

 

[sfx2000]

Yes, that is correct. They have to share talk time, which is why.

The more things you have on wireless, the more the airtime is shared.

ethernet is full-duplex for the most part - (both parties can talk/listen at the same time).

WiFi is half-duplex - talk or listen...

And as mentioned above, WiFi is like an ethernet hub, not a switch... shared media...

 

[stevech]

Yes, WiFi uses ONE wireless channel/frequency for transmitting and receiving.
whereas
Cell phones use two frequencies ... one for uplink from phone, one for downlink from cell tower.

low cost handheld walkie-talkies - like family radio service radios - are also like WiFi, half-duplex. One at a time. Manual procedure for listen-before-talk (clear channel assessment with these. This is carrier-sense-multiple-access with collision avoidance - aka CSMA/CA.

WiFi automates CSMA/CA and tries to avoid colliding transmissions but it happens. And with WiFi signals spanning +/- 3 WiFi channel numbers, we get adjacent channel collisions! fun, eh? Too bad the IEEE didn't just designate 3 channel numbers since we wound up with 20MHz wide signals. They envisioned 2MHz signals way back then.

 

[sfx2000]

Yep, and that's the risk of CA...

in 802.16, we saw that, and that's why we went with a scheduled MAC... 802.11 couldn't do this due to legacy issues, but there was talk of it...

sfx

 

[jeffoffline]

Thanks for the clarification guys, I had no idea wifi was half duplex.

 

[jegesq]

FYI, there are companies out there that are adapting full duplex techniques and technology to wireless RF. Very interesting stuff. Attempts to deal with the half-duplex spectrum issues, i.e., that current radio can't talk at the same time they are receiving.

http://www.extremetech.com/extreme/...uble-throughput-alleviate-the-spectrum-crunch

 

[L&LD]

FYI, there are companies out there that are adapting full duplex techniques and technology to wireless RF. Very interesting stuff. Attempts to deal with the half-duplex spectrum issues, i.e., that current radio can't talk at the same time they are receiving.

http://www.extremetech.com/extreme/...uble-throughput-alleviate-the-spectrum-crunch

I would love to believe this breakthrough - but it will require me to purchase a working example to test for myself though.